Introduction to Mukand

Mukand Ltd needs no introduction to people who have been one of the leaders in this field

Mukand has grown over a period of 68 years from 1937 to a company which has a turn

over of more than 3000 crores and employees nearly 700 workers and more than 500

qualified engineers

Company Profile

Name MS Mukand Ltd

Location MS Mukand Ltd Thane-Belapur Road Kalwe Dist-Thane

Tel- 9122-7635820 79201381

Facsimile - 9122-7630978

Established Year- 1937

Product Range- Heat Exchanger Pressure Vessels Cranes Storage Tanks Agitators

Collumns

Employee Nos - 7000

Yearly Turnover- 3000 Crores

ldquoMukand is Steel The Quality Steelrdquo this motto has been proved by Mukandrsquos 76

years of performance in the steel sector that has lead Mukand to be the leader of high

technical Steel makers in the private sector It makes products out of which thousands of

other products are made Besides this its biggest strength lies in the ability to manage

projects however big they might be With its vast resources of men machines capital and

materials Mukand Ltd is growing and helping others to grow It has the largest foundry in

the Non-Government sector a well equipped machine building division and an efficient

engineering and construction division that provides best of the service to many vital sectors

of national economy like steel oil refineries fertilizers plants and even equipments for the

space research program Mukand has also diversified in the contracts and engineering

service activity The company has comprehensive facilities required for making and

shaping high quality steels Mukand started its machine building activity by making

Electric Overhead Travel Cranes (EOT) for its own use but now it has grown into highly

diversified industrial machinery making division It offers a comprehensive range of

machinery required for material handling in workshop [ mills mines and ports for

processing of metals chemicals and fertilizers With years of experience in the engineering

field it was but logical to diversify into the field of engineering consultancy Reason of

Mukandrsquos growth is the technological lead that it has maintained over others Over the

years Mukand has taken pioneering steps to change the phase of steel making In India

Whether itrsquos innovating a new process or products they have been at the fore-front

Plants and Collaboration

Under taking the governtmentrsquos policy of attracting foreign investors Mukand started itrsquos

foreign collaboration with technical collaborators like Nippon Steel (Japan) The British

Steel Corporation ( UK) Amsted and National Tor-Integ Corp (Luxemberg ) Hitachi

Ltd (Japan ) Mecon ( India ) and Fertilizer corp of India to name a few

Some of the main customers of Mukandrsquos are

Bajaj Ltd

Kalyani Forgs Ltd

Bhusan Power and Steels Ltd

TELCO

Bharat Gears

Welspun Ltd

Kinetic Honda Motors Ltd

Hero Honda

Ashok Leyland

Ford

SKF Bearing

Indian Railway

ISRO

Some of the major competitors of Mukand are

Bihar Alloys

Punjab Concasts

Mahindra Ugine Steel Corp ( Musco )

Factor ASP Durgapur

Kalyani Steels

Punchmahal Steels

Rathi Alloys

Krishna Steels

Malvika Steel Ltd

Madhya Pradesh Iron and Steel Corp

Introduction to various division of Mukand

The company is divided into following main division

Kalwe Steel Plant (KSP )

Machine Building Division ( MBD )

Engineering and Construction division ( ECD )

Research and Development dept ( R amp D )

Kalwe Steel Plant

The Kalwe Steel Plant produce 3 lacs tone of steel per annum and is continuously on it by

using continuous casting sequence The sales value of Rolled Steel products was 41420

crores last giving a rise of 20 on annual basis

Products-

Blooms Billets Wire Rods and Bright Bars in various sizes The different categories of

steel manufactured by Mukand are alloy construction steel ball bearing steal carbon

construction steel cold heading quantity steel high carbon steel electrode quality steel

leaded and sulpharised free cutting steel Semi free cutting steel spring steel and stainless

steel The Kalwe steel plant is further divided into various departments for better

administration and smooth functioning

WIRE ROLLING MILL

During the training program we were placed in the ldquoWire Rolling Millrdquo (WRM)

department of Mukand Ltd Our main assignment was to study the reheating furnace and

reduce its oil consumption Basically the scrap Iron and Steel are melted in the High Power

Induction Furnace percentage of Carbon and Alloying elements are adjusted in the liquid

melt and finally liquid steel is formed Billet and blooms of steel are cast in the continuous

caster unit These billets are hot rolled in the rolling mill to form various shape members

such as bars wires plates etc as shown in the figure

The Wire Rolling Mill Department is the most important department in the factory Here in

this department mainly wires are manufactured from steel billets In the manufacturing of

the steel wires the hot billets of different grades of steels are received from steel melting

shop or from steel plant Hospet Billets are in size of 100mm X 100mm 125mm X 125mm

165mm X 165mm The steel billets are heated in the Billet Reheating Furnace and the Hot

Rolled in different Roll Stands to the required finished size of wire The prepared wire is

coiled in the coiling unit and then it is sent for dispatch

Introduction

Furnace is a device used for heating The name derives from Latinfornax ovenIn American English and Canadian English the term furnace on its own is generally

used to describe household heating systems based on a central furnace (known either as a boiler or a heater in British English) and sometimes as a synonym for kiln a device used in the production of ceramics In British English the term furnace is used exclusively to mean industrial furnaces which are used for many things such as the extraction of metal from ore (smelting) or in oil refineries and other chemical plants for example as the heat source for fractional distillation columns

The term furnace can also refer to a direct fired heater used in boiler applications in chemical industries or for providing heat to chemical reactions for processes like cracking and are part of the standard english names for many metallurgical furnaces worldwide

Types of Reheating Furnaces

Reheating furnaces are divided into two general classes Batch Type Continuous Type

Continuous Type furnaces

1) Pusher-Type FurnacesThe furnace at the Bloom Mill at KSP is a Pusher-type Furnace Continuous pusher-

type furnaces were designed initially for heating billets and small bloom sections The hearths were relatively short in length and were sloped downward longitudinally towards the discharge end to permit an easy movement of billets through the furnace Pushers were used to push forward the charge of cold billetsLonger furnaces generally are constructed now Some have hearths about 245 to 32 meters (80 to 105 feet) long with top and bottom firing and contain preheating heating and soaking zones Recuperators are utilized to provide waste-heat recovery Multiple-zone furnaces (eg five-zone slab heating furnace) have been evolved from one-zone furnace in the early designs to the modern five-zone slab heating furnace The steel to be heated in a continuous furnace can be charged either from the end or through a side door In either case the steel is moved through the furnace by pushing the last piece charged with a pusher at the charging end As each cold piece is pushed into the furnace against the continuous line of material a heated piece is removed The heated piece is discharged by several methods such as through an end door by gravity upon a roller table which feeds the mill or pushed through a side door to the mill table by suitable manual or mechanical means or withdrawn through the end door by a mechanical extractor

2) Walking-Hearth Furnaces

The reheating furnace at the WRM department is a Walking-Hearth Furnace In a walking-earth furnace travel of the work through the heating chamber follows the same general path as in the walking-beam furnace The main difference in method of conveyance in these two furnace types is that in the walking-hearth furnace the work rests on fixed refractory piers These piers extend through openings in the hearth and their tops are above the hearth surface during the time when the work is stationary in the furnace The furnace gases can thus circulate between most of the bottom surface of the work and the hearth To advance the work toward the discharge end of the furnace the hearths is raised vertically to first contact the work and then raise it a short distance above the piers The hearth then moves forward a preset distance stops lowers the work onto its new position on the piers continues to descend to its lowest position and then moves backward to its starting position toward the charging end of the furnace to await the next stroke In general the same advantages and disadvantages of the walking-beam furnace apply to walking-hearth furnaces

Billet Reheating Furnace

In the Billet Reheating Furnaces the charge is fed in the form of billets or ingots It is a precision engineered product which is widely used across different industries for various applications It is used mostly in steel rolling mills The best feature of these billet reheating furnaces is its minimum fuel consumption amp minimum burning losses

This is the heart of any hot rolling mill where in the charge is heated to rolling temperature The charge could be in the form of billets blooms slabs or ingots The type of furnace could be pusher walking hearth or walking beam ndash either top fired or top and bottom fired The fuel used could be either oil or gas The burners are located in a manner so as to achieve uniform heat distribution The radiation heat energy is efficiently transferred through the useful heat transfer area created by the charge bed The furnace is basically divided into three zones namely preheating heating and soaking zones The actual heating takes place in the heating zone The temperature uniformity up to desired limits between the core and the surface is achieved in the soaking zone The flue gases move in a direction opposite to that of the charge thereby ensuring considerable amount of waste heat recovery by convection in the preheating zone which is also termed as the recuperative zone For charge with higher thickness as in case of blooms and slabs burners are provided below and above the skids as against conventional furnaces where burners are provided only on the top This is known as top and bottom fired Reheating Furnace Our furnaces are highly fuel efficient due to proper roof profile zonal distribution optimum preheating recuperative zone lengths proper burner flue port locations and good instrumentation including furnace chamber pressure control eliminating atmosphere air ingress which also reduces the scale loss and de-carbides of the charge The furnaces could be side charged through water cooled driven rollers or front charged by hydraulic pusher Discharge can be at the side through driven water cooled rollers or discharge ejector with pinch-cum-pullout roll mechanism or end discharge through discharge ramp or slabbloom extractor

Single-zone firing comes with higher scale losses Single-zone firing furnaces have greater tendency to cause decarburization of high-carbon steel than the top-and bottom fired furnaces since the steel is in the furnace longer and is exposed to furnace gases with hydrogen and water vapor combinations The scaling of steel is practiced sometimes deliberately to remove the decarburized surface layer Those furnaces provided only with top firing require longer hearths for equal production than those with top and bottom firing but in the case of pusher-type furnaces do not require a special soaking zone to eliminate cold spots on the work caused by contact with water-cooled skids Side-discharge furnaces have less air infiltration at the hot end than end-door discharge furnaces End-door discharge of the usual gravity type induces cold air into the furnace by the stack effect at the discharge section of the furnace End-door discharge however is mechanically simpler for removing the heated stock particularly slabs and heavy blooms A level hearth eliminates the stack effect of hearths sloping upwards towards the charging end This stack effect draws cold air into the furnaces at the hot end and therefore causes higher fuel consumption and scale losses For a batch-type furnace it is preferred to preheat certain grades of alloy and high-carbon steels in a supplementary furnace before the stock is transferred into the hotter furnaces The preheating zone of a continuous furnace makes this unnecessary Finally regenerators or recuperators act as a reservoir of heat supply which is especially valuable for efficient soaking of steel

Modern furnace components

The furnace components can be divided into three categories

1 The burners heat exchanger draft inducer and venting2 The controls and safety devices3 The blower and air movement

The flame originates at the burners and is drawn into the heat exchanger by the negative pressure produced by the draft inducer The hot gases produced by the combustion

of the flame pass through the chambers of the heat exchanger and heat the metal walls of the heat exchanger The gases cool as they transfer the heat to the heat exchanger and are at about 120 degF (50 degC) as they exit on a high efficiency furnace The cooled gases then enter the draft inducer blower and are pushed into the venting pipes The exhaust gases then are directed out of the house through the vent pipes The controls include the gas valve ignition control igniter flame sensor transformer limit control blower control board and flame roll out switch The transformer provides 24 volts of electricity to power the controls 24 volts is applied to the thermostat that is installed in the living space The thermostat is basically an automatic switch that closes and completes the electrical circuit when the room temperature drops below the heat setting This then allows 24 volts to the circuit board which initiates the heat sequence The circuit board has a relay that closes to power up the motor on the draft inducer blower Then the circuit board igniter relay is energized which sends 120 volts to the hot surface igniter and makes it glow bright and get extremely hot Next the gas valve relay in the circuit board is energized This allows voltage to the gas valve and energizes a solenoid coil in the gas valve which opens the valve to allow gas to flow to the burners The gas flows into the burners and is ignited by the hot surface igniter The ignition control circuit board applies an AC voltage to the flame sensor which is just a stainless steel rod An interesting thing occurs inside a burning flame which is called ionization That is free electrons are produced which can conduct electricity through the flame itself The electrons will normally flow from the flame sensor through the flame when present and back to ground through the grounded burners

The ignition system must prove that a flame is present to continue the gas flow or if theres no flame then shut off the gas flow through the gas valve to prevent a possible explosion It also must not be fooled into thinking there is a flame present by a flame sensor that is touching the ground from being broken or bent This produces a half-wave of electrical current from each full wave The ignition control circuit detects the half-wave to determine if the sensor is merely touching ground If the ignition control receives this half wave signal from the flame sensor then combustion will continue Now the circuit board timer counts a determined amount of time and energizes the blower relay This relay powers up the blower motor and air is then pushed over the heat exchanger where it removes the heat from the hot metal and enters the ductwork to go to the various rooms in the house The limit control is a safety device that will open the electrical circuit to the ignition control and stop the gas flow if the furnace overheats The flame roll-out switch does the same thing if the flame was rolling out of the heat exchanger instead of being completely induced into it by the draft inducer

The blower creates a negative pressure on the intake side which draws air into the ductwork return air system and blows the air out through the heat exchanger and then into supply air ductwork to distribute throughout the home

Walking Hearth Mec h anism

An alternate method of transporting the ingots billets from the charging end of the furnace

to the discharging door point is by using a walking hearth furnace The furnace hearth has

alternately fixed and moving beams The fixed beams are part of the hearth at either

sidewall ends of the furnace and the moving beams are in between two fixed beams

Walking beam hearth furnaces have three fixed and two moving hearths or walking

beams A hydraulic system is provided to operate the walking beams through hydraulic

cylinders In the older designs there used to be a lifting and lowering cylinder which lifted

the beam through bell crank levers Once the beam reaches the top position all the ingots

billets that were resting on the fixed beams of the hearth get lifted up and now rest on the

moving beams when another hydraulic cylinder moves the beam forward by one stroke

which is normally around 700 - 1000mm all the ingots billets move forward by a

distance equal to one stroke of the forward backward cylinder The lifting lowering

cylinder now lowers the moving beam by a preset height through limit switches proximity

switches In the downward movement when the levels of the fixed and moving beam

tops are equal the ingots billets now rest on the fixed beams or the hearth at a new

point which is one cylinder stroke ahead of its previous position The moving beams

continue its downward movement ensuring that its top surface is well and truly

below the fixed beams It comes to rest at this position Now the forward backward

cylinder retracts the moving beams to their original position This completes one full cycle

of transportation In modern walking hearth furnaces the moving hearths are mounted on

rollers which ride up amp down a ramp actuated by hydraulic cylinders One hydraulic

cylinder performs the pulling up of the beam on the ramp and subsequently lowering it and

the other pulls pushes the beam forward backward as above The advantage of the ramp

system is that there are no linkages bell crank levers mounted on pivot bearings

which require extensive maintenance Each moving beam has a water seal at the

bottom to prevent the escape of flue gases into the cellar from in between the fixed amp

moving beams The Inside view of a typical WBWH Furnace is shown in Figure

Figure Inside ( c ellar) view of a Walk i ng Hearth Furnace

Since each of the billets is exposed on all four sides except the narrow strip resting on the

beams the heating is uniform and fast There is no danger of the ingots billets sticking to

each other the rate of heating can be high to reduce the residence time of the charge

inside the furnace thus reducing the burning scaling losses considerably For the same

length of the furnace the productivity of the hearth is much higher than for the

corresponding length of the pusher hearth furnace

Refractories The furnace also uses refractories for insulation purposes Any material can be

described as a lsquoRefractoryrsquo if it can withstand the action of abrasive or corrosive solids liquids or gases at high temperature The various combination of operating conditions in which refractories are used makes it necessary to manufacture a range of refractory materials with different properties Refractory materials are made in varying combinations and shapes depending on their application General requirement of refractory material are

They should withstand high temperature They should withstand sudden change of temperature They should withstand action of molten metal slag glass hot gases etc They should withstand load and abrasive forces at service condition They should conserve heat They should have low coefficient of thermal expansion They should not contaminate the material with which it comes into contact

Fire-clay refractories such as Fire bricks Siliceous-fireclays and aluminous clay refractories consists of aluminum silicates with varying Silica (SiO2) content up to 78 and Al2O3 content up to 44

High Alumina RefractoriesAlumina-silicate refractories containing more than 45 alumina are generally termed as high alumina materials The alumina concentration ranges from 45-100 The refractoriness of high alumina refractories increases with increase in alumina percentage The application of high alumina refractories include the hearth and shaft of blast furnaces ceramic kilns cement kilns glass tanks and crucibles for melting a wide range of materials

Insulating MaterialsInsulating materials greatly reduce the heat losses through wallsInsulation is achieved by providing a layer of materials with low heat conductivity between the internal hot surface and external surface thus keeping the temperature of the external surface low

Insulating materials can be classified into following groups- Insulating Bricks Insulating castables Ceramic fibers Calcium silicate Ceramic coatingThe characteristics of Ceramic fibers are remarkable combination of the properties of

refractories and traditional insulation material Lower thermal conductivity Light weight Lower heat storage Thermal shock resistance Chemical Resistance

Mechanical resilience Low Insulation cost Ease of maintenance Ease of handling Thermal Efficiency

High Emissivity coatingEmissivity (ie the measure of materialrsquos ability to both absorb and radiate heat) is often considered as an inherent physical property that does not normally change (Other examples are density specific heat and thermal conductivity) However the development of high emissivity coatings allows the surface emissivity of the material to be increased High emissivity coatings are applied on the interior surface of furnaces

Benefits of high emissivity coatings in furnace chambers are uniform heating and extended life of refractotries and metallic components such as radiant tubes and heating elements For intermittent furnaces or where rapid heating is required use of such coatings was found to reduce fuel or power by 25-45

Water cooling system in Walking Hearth FurnaceThe early design of WB Furnace used alloy steel Walking Beams that were exposed directly to the heat of the Furnace and were subjected to heat Corrosion so it operated at Maximum Temperature of about 1050 C compared with Re-heating Furnaces that must heat steel toTemperatures up to 1315 C Hence WB-Reheating Furnaces consist of water-cooled Steel members topped with refractors in such a manner that only the refractories are exposed directly to the heat of Furnace Alternatively the beams and supports may be constructed of water ndashcooled Tubular sections (with ldquobuttonsrdquo on the top surfaces to keep the Hot steel from direct ndashcontract with the water cooled tubes)

Heat recovery System

Recuperators(i) Recuperators (Waste Heat Recovery System) are placed in the path of the Flue Gasses of the Furnace between Furnace outlet and the chimney The combustion airgas is preheated in the recuperator through heat of the Flue gas and supplied to the Furance Burners in Pre-Heating Zone at about 400-5000C This results in savings of Heat Energy hence fuel(ii) Based on the material of Construction recuperators are two types

Metallic (Made of SS) Ceramic

(iii) Metallic recuperators have distinct advantages over Ceramic recuperators in terms of lower initial investment easier maintenance amp repair etc and are more popular in SRRM industryOn the other hand Ceramic recuperators have a longer life and can withstand much higher temperatures as compared to Metallic recuperators of about15000C vis-agrave-vis 11000C for metalrecuperators(iv) Based on the Design and method of Heat transfer the Recuperators are of two types

Tubular Convection Double Shell Radiation

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

processing of metals chemicals and fertilizers With years of experience in the engineering

field it was but logical to diversify into the field of engineering consultancy Reason of

Mukandrsquos growth is the technological lead that it has maintained over others Over the

years Mukand has taken pioneering steps to change the phase of steel making In India

Whether itrsquos innovating a new process or products they have been at the fore-front

Plants and Collaboration

Under taking the governtmentrsquos policy of attracting foreign investors Mukand started itrsquos

foreign collaboration with technical collaborators like Nippon Steel (Japan) The British

Steel Corporation ( UK) Amsted and National Tor-Integ Corp (Luxemberg ) Hitachi

Ltd (Japan ) Mecon ( India ) and Fertilizer corp of India to name a few

Some of the main customers of Mukandrsquos are

Bajaj Ltd

Kalyani Forgs Ltd

Bhusan Power and Steels Ltd

TELCO

Bharat Gears

Welspun Ltd

Kinetic Honda Motors Ltd

Hero Honda

Ashok Leyland

Ford

SKF Bearing

Indian Railway

ISRO

Some of the major competitors of Mukand are

Bihar Alloys

Punjab Concasts

Mahindra Ugine Steel Corp ( Musco )

Factor ASP Durgapur

Kalyani Steels

Punchmahal Steels

Rathi Alloys

Krishna Steels

Malvika Steel Ltd

Madhya Pradesh Iron and Steel Corp

Introduction to various division of Mukand

The company is divided into following main division

Kalwe Steel Plant (KSP )

Machine Building Division ( MBD )

Engineering and Construction division ( ECD )

Research and Development dept ( R amp D )

Kalwe Steel Plant

The Kalwe Steel Plant produce 3 lacs tone of steel per annum and is continuously on it by

using continuous casting sequence The sales value of Rolled Steel products was 41420

crores last giving a rise of 20 on annual basis

Products-

Blooms Billets Wire Rods and Bright Bars in various sizes The different categories of

steel manufactured by Mukand are alloy construction steel ball bearing steal carbon

construction steel cold heading quantity steel high carbon steel electrode quality steel

leaded and sulpharised free cutting steel Semi free cutting steel spring steel and stainless

steel The Kalwe steel plant is further divided into various departments for better

administration and smooth functioning

WIRE ROLLING MILL

During the training program we were placed in the ldquoWire Rolling Millrdquo (WRM)

department of Mukand Ltd Our main assignment was to study the reheating furnace and

reduce its oil consumption Basically the scrap Iron and Steel are melted in the High Power

Induction Furnace percentage of Carbon and Alloying elements are adjusted in the liquid

melt and finally liquid steel is formed Billet and blooms of steel are cast in the continuous

caster unit These billets are hot rolled in the rolling mill to form various shape members

such as bars wires plates etc as shown in the figure

The Wire Rolling Mill Department is the most important department in the factory Here in

this department mainly wires are manufactured from steel billets In the manufacturing of

the steel wires the hot billets of different grades of steels are received from steel melting

shop or from steel plant Hospet Billets are in size of 100mm X 100mm 125mm X 125mm

165mm X 165mm The steel billets are heated in the Billet Reheating Furnace and the Hot

Rolled in different Roll Stands to the required finished size of wire The prepared wire is

coiled in the coiling unit and then it is sent for dispatch

Introduction

Furnace is a device used for heating The name derives from Latinfornax ovenIn American English and Canadian English the term furnace on its own is generally

used to describe household heating systems based on a central furnace (known either as a boiler or a heater in British English) and sometimes as a synonym for kiln a device used in the production of ceramics In British English the term furnace is used exclusively to mean industrial furnaces which are used for many things such as the extraction of metal from ore (smelting) or in oil refineries and other chemical plants for example as the heat source for fractional distillation columns

The term furnace can also refer to a direct fired heater used in boiler applications in chemical industries or for providing heat to chemical reactions for processes like cracking and are part of the standard english names for many metallurgical furnaces worldwide

Types of Reheating Furnaces

Reheating furnaces are divided into two general classes Batch Type Continuous Type

Continuous Type furnaces

1) Pusher-Type FurnacesThe furnace at the Bloom Mill at KSP is a Pusher-type Furnace Continuous pusher-

type furnaces were designed initially for heating billets and small bloom sections The hearths were relatively short in length and were sloped downward longitudinally towards the discharge end to permit an easy movement of billets through the furnace Pushers were used to push forward the charge of cold billetsLonger furnaces generally are constructed now Some have hearths about 245 to 32 meters (80 to 105 feet) long with top and bottom firing and contain preheating heating and soaking zones Recuperators are utilized to provide waste-heat recovery Multiple-zone furnaces (eg five-zone slab heating furnace) have been evolved from one-zone furnace in the early designs to the modern five-zone slab heating furnace The steel to be heated in a continuous furnace can be charged either from the end or through a side door In either case the steel is moved through the furnace by pushing the last piece charged with a pusher at the charging end As each cold piece is pushed into the furnace against the continuous line of material a heated piece is removed The heated piece is discharged by several methods such as through an end door by gravity upon a roller table which feeds the mill or pushed through a side door to the mill table by suitable manual or mechanical means or withdrawn through the end door by a mechanical extractor

2) Walking-Hearth Furnaces

The reheating furnace at the WRM department is a Walking-Hearth Furnace In a walking-earth furnace travel of the work through the heating chamber follows the same general path as in the walking-beam furnace The main difference in method of conveyance in these two furnace types is that in the walking-hearth furnace the work rests on fixed refractory piers These piers extend through openings in the hearth and their tops are above the hearth surface during the time when the work is stationary in the furnace The furnace gases can thus circulate between most of the bottom surface of the work and the hearth To advance the work toward the discharge end of the furnace the hearths is raised vertically to first contact the work and then raise it a short distance above the piers The hearth then moves forward a preset distance stops lowers the work onto its new position on the piers continues to descend to its lowest position and then moves backward to its starting position toward the charging end of the furnace to await the next stroke In general the same advantages and disadvantages of the walking-beam furnace apply to walking-hearth furnaces

Billet Reheating Furnace

In the Billet Reheating Furnaces the charge is fed in the form of billets or ingots It is a precision engineered product which is widely used across different industries for various applications It is used mostly in steel rolling mills The best feature of these billet reheating furnaces is its minimum fuel consumption amp minimum burning losses

This is the heart of any hot rolling mill where in the charge is heated to rolling temperature The charge could be in the form of billets blooms slabs or ingots The type of furnace could be pusher walking hearth or walking beam ndash either top fired or top and bottom fired The fuel used could be either oil or gas The burners are located in a manner so as to achieve uniform heat distribution The radiation heat energy is efficiently transferred through the useful heat transfer area created by the charge bed The furnace is basically divided into three zones namely preheating heating and soaking zones The actual heating takes place in the heating zone The temperature uniformity up to desired limits between the core and the surface is achieved in the soaking zone The flue gases move in a direction opposite to that of the charge thereby ensuring considerable amount of waste heat recovery by convection in the preheating zone which is also termed as the recuperative zone For charge with higher thickness as in case of blooms and slabs burners are provided below and above the skids as against conventional furnaces where burners are provided only on the top This is known as top and bottom fired Reheating Furnace Our furnaces are highly fuel efficient due to proper roof profile zonal distribution optimum preheating recuperative zone lengths proper burner flue port locations and good instrumentation including furnace chamber pressure control eliminating atmosphere air ingress which also reduces the scale loss and de-carbides of the charge The furnaces could be side charged through water cooled driven rollers or front charged by hydraulic pusher Discharge can be at the side through driven water cooled rollers or discharge ejector with pinch-cum-pullout roll mechanism or end discharge through discharge ramp or slabbloom extractor

Single-zone firing comes with higher scale losses Single-zone firing furnaces have greater tendency to cause decarburization of high-carbon steel than the top-and bottom fired furnaces since the steel is in the furnace longer and is exposed to furnace gases with hydrogen and water vapor combinations The scaling of steel is practiced sometimes deliberately to remove the decarburized surface layer Those furnaces provided only with top firing require longer hearths for equal production than those with top and bottom firing but in the case of pusher-type furnaces do not require a special soaking zone to eliminate cold spots on the work caused by contact with water-cooled skids Side-discharge furnaces have less air infiltration at the hot end than end-door discharge furnaces End-door discharge of the usual gravity type induces cold air into the furnace by the stack effect at the discharge section of the furnace End-door discharge however is mechanically simpler for removing the heated stock particularly slabs and heavy blooms A level hearth eliminates the stack effect of hearths sloping upwards towards the charging end This stack effect draws cold air into the furnaces at the hot end and therefore causes higher fuel consumption and scale losses For a batch-type furnace it is preferred to preheat certain grades of alloy and high-carbon steels in a supplementary furnace before the stock is transferred into the hotter furnaces The preheating zone of a continuous furnace makes this unnecessary Finally regenerators or recuperators act as a reservoir of heat supply which is especially valuable for efficient soaking of steel

Modern furnace components

The furnace components can be divided into three categories

1 The burners heat exchanger draft inducer and venting2 The controls and safety devices3 The blower and air movement

The flame originates at the burners and is drawn into the heat exchanger by the negative pressure produced by the draft inducer The hot gases produced by the combustion

of the flame pass through the chambers of the heat exchanger and heat the metal walls of the heat exchanger The gases cool as they transfer the heat to the heat exchanger and are at about 120 degF (50 degC) as they exit on a high efficiency furnace The cooled gases then enter the draft inducer blower and are pushed into the venting pipes The exhaust gases then are directed out of the house through the vent pipes The controls include the gas valve ignition control igniter flame sensor transformer limit control blower control board and flame roll out switch The transformer provides 24 volts of electricity to power the controls 24 volts is applied to the thermostat that is installed in the living space The thermostat is basically an automatic switch that closes and completes the electrical circuit when the room temperature drops below the heat setting This then allows 24 volts to the circuit board which initiates the heat sequence The circuit board has a relay that closes to power up the motor on the draft inducer blower Then the circuit board igniter relay is energized which sends 120 volts to the hot surface igniter and makes it glow bright and get extremely hot Next the gas valve relay in the circuit board is energized This allows voltage to the gas valve and energizes a solenoid coil in the gas valve which opens the valve to allow gas to flow to the burners The gas flows into the burners and is ignited by the hot surface igniter The ignition control circuit board applies an AC voltage to the flame sensor which is just a stainless steel rod An interesting thing occurs inside a burning flame which is called ionization That is free electrons are produced which can conduct electricity through the flame itself The electrons will normally flow from the flame sensor through the flame when present and back to ground through the grounded burners

The ignition system must prove that a flame is present to continue the gas flow or if theres no flame then shut off the gas flow through the gas valve to prevent a possible explosion It also must not be fooled into thinking there is a flame present by a flame sensor that is touching the ground from being broken or bent This produces a half-wave of electrical current from each full wave The ignition control circuit detects the half-wave to determine if the sensor is merely touching ground If the ignition control receives this half wave signal from the flame sensor then combustion will continue Now the circuit board timer counts a determined amount of time and energizes the blower relay This relay powers up the blower motor and air is then pushed over the heat exchanger where it removes the heat from the hot metal and enters the ductwork to go to the various rooms in the house The limit control is a safety device that will open the electrical circuit to the ignition control and stop the gas flow if the furnace overheats The flame roll-out switch does the same thing if the flame was rolling out of the heat exchanger instead of being completely induced into it by the draft inducer

The blower creates a negative pressure on the intake side which draws air into the ductwork return air system and blows the air out through the heat exchanger and then into supply air ductwork to distribute throughout the home

Walking Hearth Mec h anism

An alternate method of transporting the ingots billets from the charging end of the furnace

to the discharging door point is by using a walking hearth furnace The furnace hearth has

alternately fixed and moving beams The fixed beams are part of the hearth at either

sidewall ends of the furnace and the moving beams are in between two fixed beams

Walking beam hearth furnaces have three fixed and two moving hearths or walking

beams A hydraulic system is provided to operate the walking beams through hydraulic

cylinders In the older designs there used to be a lifting and lowering cylinder which lifted

the beam through bell crank levers Once the beam reaches the top position all the ingots

billets that were resting on the fixed beams of the hearth get lifted up and now rest on the

moving beams when another hydraulic cylinder moves the beam forward by one stroke

which is normally around 700 - 1000mm all the ingots billets move forward by a

distance equal to one stroke of the forward backward cylinder The lifting lowering

cylinder now lowers the moving beam by a preset height through limit switches proximity

switches In the downward movement when the levels of the fixed and moving beam

tops are equal the ingots billets now rest on the fixed beams or the hearth at a new

point which is one cylinder stroke ahead of its previous position The moving beams

continue its downward movement ensuring that its top surface is well and truly

below the fixed beams It comes to rest at this position Now the forward backward

cylinder retracts the moving beams to their original position This completes one full cycle

of transportation In modern walking hearth furnaces the moving hearths are mounted on

rollers which ride up amp down a ramp actuated by hydraulic cylinders One hydraulic

cylinder performs the pulling up of the beam on the ramp and subsequently lowering it and

the other pulls pushes the beam forward backward as above The advantage of the ramp

system is that there are no linkages bell crank levers mounted on pivot bearings

which require extensive maintenance Each moving beam has a water seal at the

bottom to prevent the escape of flue gases into the cellar from in between the fixed amp

moving beams The Inside view of a typical WBWH Furnace is shown in Figure

Figure Inside ( c ellar) view of a Walk i ng Hearth Furnace

Since each of the billets is exposed on all four sides except the narrow strip resting on the

beams the heating is uniform and fast There is no danger of the ingots billets sticking to

each other the rate of heating can be high to reduce the residence time of the charge

inside the furnace thus reducing the burning scaling losses considerably For the same

length of the furnace the productivity of the hearth is much higher than for the

corresponding length of the pusher hearth furnace

Refractories The furnace also uses refractories for insulation purposes Any material can be

described as a lsquoRefractoryrsquo if it can withstand the action of abrasive or corrosive solids liquids or gases at high temperature The various combination of operating conditions in which refractories are used makes it necessary to manufacture a range of refractory materials with different properties Refractory materials are made in varying combinations and shapes depending on their application General requirement of refractory material are

They should withstand high temperature They should withstand sudden change of temperature They should withstand action of molten metal slag glass hot gases etc They should withstand load and abrasive forces at service condition They should conserve heat They should have low coefficient of thermal expansion They should not contaminate the material with which it comes into contact

Fire-clay refractories such as Fire bricks Siliceous-fireclays and aluminous clay refractories consists of aluminum silicates with varying Silica (SiO2) content up to 78 and Al2O3 content up to 44

High Alumina RefractoriesAlumina-silicate refractories containing more than 45 alumina are generally termed as high alumina materials The alumina concentration ranges from 45-100 The refractoriness of high alumina refractories increases with increase in alumina percentage The application of high alumina refractories include the hearth and shaft of blast furnaces ceramic kilns cement kilns glass tanks and crucibles for melting a wide range of materials

Insulating MaterialsInsulating materials greatly reduce the heat losses through wallsInsulation is achieved by providing a layer of materials with low heat conductivity between the internal hot surface and external surface thus keeping the temperature of the external surface low

Insulating materials can be classified into following groups- Insulating Bricks Insulating castables Ceramic fibers Calcium silicate Ceramic coatingThe characteristics of Ceramic fibers are remarkable combination of the properties of

refractories and traditional insulation material Lower thermal conductivity Light weight Lower heat storage Thermal shock resistance Chemical Resistance

Mechanical resilience Low Insulation cost Ease of maintenance Ease of handling Thermal Efficiency

High Emissivity coatingEmissivity (ie the measure of materialrsquos ability to both absorb and radiate heat) is often considered as an inherent physical property that does not normally change (Other examples are density specific heat and thermal conductivity) However the development of high emissivity coatings allows the surface emissivity of the material to be increased High emissivity coatings are applied on the interior surface of furnaces

Benefits of high emissivity coatings in furnace chambers are uniform heating and extended life of refractotries and metallic components such as radiant tubes and heating elements For intermittent furnaces or where rapid heating is required use of such coatings was found to reduce fuel or power by 25-45

Water cooling system in Walking Hearth FurnaceThe early design of WB Furnace used alloy steel Walking Beams that were exposed directly to the heat of the Furnace and were subjected to heat Corrosion so it operated at Maximum Temperature of about 1050 C compared with Re-heating Furnaces that must heat steel toTemperatures up to 1315 C Hence WB-Reheating Furnaces consist of water-cooled Steel members topped with refractors in such a manner that only the refractories are exposed directly to the heat of Furnace Alternatively the beams and supports may be constructed of water ndashcooled Tubular sections (with ldquobuttonsrdquo on the top surfaces to keep the Hot steel from direct ndashcontract with the water cooled tubes)

Heat recovery System

Recuperators(i) Recuperators (Waste Heat Recovery System) are placed in the path of the Flue Gasses of the Furnace between Furnace outlet and the chimney The combustion airgas is preheated in the recuperator through heat of the Flue gas and supplied to the Furance Burners in Pre-Heating Zone at about 400-5000C This results in savings of Heat Energy hence fuel(ii) Based on the material of Construction recuperators are two types

Metallic (Made of SS) Ceramic

(iii) Metallic recuperators have distinct advantages over Ceramic recuperators in terms of lower initial investment easier maintenance amp repair etc and are more popular in SRRM industryOn the other hand Ceramic recuperators have a longer life and can withstand much higher temperatures as compared to Metallic recuperators of about15000C vis-agrave-vis 11000C for metalrecuperators(iv) Based on the Design and method of Heat transfer the Recuperators are of two types

Tubular Convection Double Shell Radiation

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

Malvika Steel Ltd

Madhya Pradesh Iron and Steel Corp

Introduction to various division of Mukand

The company is divided into following main division

Kalwe Steel Plant (KSP )

Machine Building Division ( MBD )

Engineering and Construction division ( ECD )

Research and Development dept ( R amp D )

Kalwe Steel Plant

The Kalwe Steel Plant produce 3 lacs tone of steel per annum and is continuously on it by

using continuous casting sequence The sales value of Rolled Steel products was 41420

crores last giving a rise of 20 on annual basis

Products-

Blooms Billets Wire Rods and Bright Bars in various sizes The different categories of

steel manufactured by Mukand are alloy construction steel ball bearing steal carbon

construction steel cold heading quantity steel high carbon steel electrode quality steel

leaded and sulpharised free cutting steel Semi free cutting steel spring steel and stainless

steel The Kalwe steel plant is further divided into various departments for better

administration and smooth functioning

WIRE ROLLING MILL

During the training program we were placed in the ldquoWire Rolling Millrdquo (WRM)

department of Mukand Ltd Our main assignment was to study the reheating furnace and

reduce its oil consumption Basically the scrap Iron and Steel are melted in the High Power

Induction Furnace percentage of Carbon and Alloying elements are adjusted in the liquid

melt and finally liquid steel is formed Billet and blooms of steel are cast in the continuous

caster unit These billets are hot rolled in the rolling mill to form various shape members

such as bars wires plates etc as shown in the figure

The Wire Rolling Mill Department is the most important department in the factory Here in

this department mainly wires are manufactured from steel billets In the manufacturing of

the steel wires the hot billets of different grades of steels are received from steel melting

shop or from steel plant Hospet Billets are in size of 100mm X 100mm 125mm X 125mm

165mm X 165mm The steel billets are heated in the Billet Reheating Furnace and the Hot

Rolled in different Roll Stands to the required finished size of wire The prepared wire is

coiled in the coiling unit and then it is sent for dispatch

Introduction

Furnace is a device used for heating The name derives from Latinfornax ovenIn American English and Canadian English the term furnace on its own is generally

used to describe household heating systems based on a central furnace (known either as a boiler or a heater in British English) and sometimes as a synonym for kiln a device used in the production of ceramics In British English the term furnace is used exclusively to mean industrial furnaces which are used for many things such as the extraction of metal from ore (smelting) or in oil refineries and other chemical plants for example as the heat source for fractional distillation columns

The term furnace can also refer to a direct fired heater used in boiler applications in chemical industries or for providing heat to chemical reactions for processes like cracking and are part of the standard english names for many metallurgical furnaces worldwide

Types of Reheating Furnaces

Reheating furnaces are divided into two general classes Batch Type Continuous Type

Continuous Type furnaces

1) Pusher-Type FurnacesThe furnace at the Bloom Mill at KSP is a Pusher-type Furnace Continuous pusher-

type furnaces were designed initially for heating billets and small bloom sections The hearths were relatively short in length and were sloped downward longitudinally towards the discharge end to permit an easy movement of billets through the furnace Pushers were used to push forward the charge of cold billetsLonger furnaces generally are constructed now Some have hearths about 245 to 32 meters (80 to 105 feet) long with top and bottom firing and contain preheating heating and soaking zones Recuperators are utilized to provide waste-heat recovery Multiple-zone furnaces (eg five-zone slab heating furnace) have been evolved from one-zone furnace in the early designs to the modern five-zone slab heating furnace The steel to be heated in a continuous furnace can be charged either from the end or through a side door In either case the steel is moved through the furnace by pushing the last piece charged with a pusher at the charging end As each cold piece is pushed into the furnace against the continuous line of material a heated piece is removed The heated piece is discharged by several methods such as through an end door by gravity upon a roller table which feeds the mill or pushed through a side door to the mill table by suitable manual or mechanical means or withdrawn through the end door by a mechanical extractor

2) Walking-Hearth Furnaces

The reheating furnace at the WRM department is a Walking-Hearth Furnace In a walking-earth furnace travel of the work through the heating chamber follows the same general path as in the walking-beam furnace The main difference in method of conveyance in these two furnace types is that in the walking-hearth furnace the work rests on fixed refractory piers These piers extend through openings in the hearth and their tops are above the hearth surface during the time when the work is stationary in the furnace The furnace gases can thus circulate between most of the bottom surface of the work and the hearth To advance the work toward the discharge end of the furnace the hearths is raised vertically to first contact the work and then raise it a short distance above the piers The hearth then moves forward a preset distance stops lowers the work onto its new position on the piers continues to descend to its lowest position and then moves backward to its starting position toward the charging end of the furnace to await the next stroke In general the same advantages and disadvantages of the walking-beam furnace apply to walking-hearth furnaces

Billet Reheating Furnace

In the Billet Reheating Furnaces the charge is fed in the form of billets or ingots It is a precision engineered product which is widely used across different industries for various applications It is used mostly in steel rolling mills The best feature of these billet reheating furnaces is its minimum fuel consumption amp minimum burning losses

This is the heart of any hot rolling mill where in the charge is heated to rolling temperature The charge could be in the form of billets blooms slabs or ingots The type of furnace could be pusher walking hearth or walking beam ndash either top fired or top and bottom fired The fuel used could be either oil or gas The burners are located in a manner so as to achieve uniform heat distribution The radiation heat energy is efficiently transferred through the useful heat transfer area created by the charge bed The furnace is basically divided into three zones namely preheating heating and soaking zones The actual heating takes place in the heating zone The temperature uniformity up to desired limits between the core and the surface is achieved in the soaking zone The flue gases move in a direction opposite to that of the charge thereby ensuring considerable amount of waste heat recovery by convection in the preheating zone which is also termed as the recuperative zone For charge with higher thickness as in case of blooms and slabs burners are provided below and above the skids as against conventional furnaces where burners are provided only on the top This is known as top and bottom fired Reheating Furnace Our furnaces are highly fuel efficient due to proper roof profile zonal distribution optimum preheating recuperative zone lengths proper burner flue port locations and good instrumentation including furnace chamber pressure control eliminating atmosphere air ingress which also reduces the scale loss and de-carbides of the charge The furnaces could be side charged through water cooled driven rollers or front charged by hydraulic pusher Discharge can be at the side through driven water cooled rollers or discharge ejector with pinch-cum-pullout roll mechanism or end discharge through discharge ramp or slabbloom extractor

Single-zone firing comes with higher scale losses Single-zone firing furnaces have greater tendency to cause decarburization of high-carbon steel than the top-and bottom fired furnaces since the steel is in the furnace longer and is exposed to furnace gases with hydrogen and water vapor combinations The scaling of steel is practiced sometimes deliberately to remove the decarburized surface layer Those furnaces provided only with top firing require longer hearths for equal production than those with top and bottom firing but in the case of pusher-type furnaces do not require a special soaking zone to eliminate cold spots on the work caused by contact with water-cooled skids Side-discharge furnaces have less air infiltration at the hot end than end-door discharge furnaces End-door discharge of the usual gravity type induces cold air into the furnace by the stack effect at the discharge section of the furnace End-door discharge however is mechanically simpler for removing the heated stock particularly slabs and heavy blooms A level hearth eliminates the stack effect of hearths sloping upwards towards the charging end This stack effect draws cold air into the furnaces at the hot end and therefore causes higher fuel consumption and scale losses For a batch-type furnace it is preferred to preheat certain grades of alloy and high-carbon steels in a supplementary furnace before the stock is transferred into the hotter furnaces The preheating zone of a continuous furnace makes this unnecessary Finally regenerators or recuperators act as a reservoir of heat supply which is especially valuable for efficient soaking of steel

Modern furnace components

The furnace components can be divided into three categories

1 The burners heat exchanger draft inducer and venting2 The controls and safety devices3 The blower and air movement

The flame originates at the burners and is drawn into the heat exchanger by the negative pressure produced by the draft inducer The hot gases produced by the combustion

of the flame pass through the chambers of the heat exchanger and heat the metal walls of the heat exchanger The gases cool as they transfer the heat to the heat exchanger and are at about 120 degF (50 degC) as they exit on a high efficiency furnace The cooled gases then enter the draft inducer blower and are pushed into the venting pipes The exhaust gases then are directed out of the house through the vent pipes The controls include the gas valve ignition control igniter flame sensor transformer limit control blower control board and flame roll out switch The transformer provides 24 volts of electricity to power the controls 24 volts is applied to the thermostat that is installed in the living space The thermostat is basically an automatic switch that closes and completes the electrical circuit when the room temperature drops below the heat setting This then allows 24 volts to the circuit board which initiates the heat sequence The circuit board has a relay that closes to power up the motor on the draft inducer blower Then the circuit board igniter relay is energized which sends 120 volts to the hot surface igniter and makes it glow bright and get extremely hot Next the gas valve relay in the circuit board is energized This allows voltage to the gas valve and energizes a solenoid coil in the gas valve which opens the valve to allow gas to flow to the burners The gas flows into the burners and is ignited by the hot surface igniter The ignition control circuit board applies an AC voltage to the flame sensor which is just a stainless steel rod An interesting thing occurs inside a burning flame which is called ionization That is free electrons are produced which can conduct electricity through the flame itself The electrons will normally flow from the flame sensor through the flame when present and back to ground through the grounded burners

The ignition system must prove that a flame is present to continue the gas flow or if theres no flame then shut off the gas flow through the gas valve to prevent a possible explosion It also must not be fooled into thinking there is a flame present by a flame sensor that is touching the ground from being broken or bent This produces a half-wave of electrical current from each full wave The ignition control circuit detects the half-wave to determine if the sensor is merely touching ground If the ignition control receives this half wave signal from the flame sensor then combustion will continue Now the circuit board timer counts a determined amount of time and energizes the blower relay This relay powers up the blower motor and air is then pushed over the heat exchanger where it removes the heat from the hot metal and enters the ductwork to go to the various rooms in the house The limit control is a safety device that will open the electrical circuit to the ignition control and stop the gas flow if the furnace overheats The flame roll-out switch does the same thing if the flame was rolling out of the heat exchanger instead of being completely induced into it by the draft inducer

The blower creates a negative pressure on the intake side which draws air into the ductwork return air system and blows the air out through the heat exchanger and then into supply air ductwork to distribute throughout the home

Walking Hearth Mec h anism

An alternate method of transporting the ingots billets from the charging end of the furnace

to the discharging door point is by using a walking hearth furnace The furnace hearth has

alternately fixed and moving beams The fixed beams are part of the hearth at either

sidewall ends of the furnace and the moving beams are in between two fixed beams

Walking beam hearth furnaces have three fixed and two moving hearths or walking

beams A hydraulic system is provided to operate the walking beams through hydraulic

cylinders In the older designs there used to be a lifting and lowering cylinder which lifted

the beam through bell crank levers Once the beam reaches the top position all the ingots

billets that were resting on the fixed beams of the hearth get lifted up and now rest on the

moving beams when another hydraulic cylinder moves the beam forward by one stroke

which is normally around 700 - 1000mm all the ingots billets move forward by a

distance equal to one stroke of the forward backward cylinder The lifting lowering

cylinder now lowers the moving beam by a preset height through limit switches proximity

switches In the downward movement when the levels of the fixed and moving beam

tops are equal the ingots billets now rest on the fixed beams or the hearth at a new

point which is one cylinder stroke ahead of its previous position The moving beams

continue its downward movement ensuring that its top surface is well and truly

below the fixed beams It comes to rest at this position Now the forward backward

cylinder retracts the moving beams to their original position This completes one full cycle

of transportation In modern walking hearth furnaces the moving hearths are mounted on

rollers which ride up amp down a ramp actuated by hydraulic cylinders One hydraulic

cylinder performs the pulling up of the beam on the ramp and subsequently lowering it and

the other pulls pushes the beam forward backward as above The advantage of the ramp

system is that there are no linkages bell crank levers mounted on pivot bearings

which require extensive maintenance Each moving beam has a water seal at the

bottom to prevent the escape of flue gases into the cellar from in between the fixed amp

moving beams The Inside view of a typical WBWH Furnace is shown in Figure

Figure Inside ( c ellar) view of a Walk i ng Hearth Furnace

Since each of the billets is exposed on all four sides except the narrow strip resting on the

beams the heating is uniform and fast There is no danger of the ingots billets sticking to

each other the rate of heating can be high to reduce the residence time of the charge

inside the furnace thus reducing the burning scaling losses considerably For the same

length of the furnace the productivity of the hearth is much higher than for the

corresponding length of the pusher hearth furnace

Refractories The furnace also uses refractories for insulation purposes Any material can be

described as a lsquoRefractoryrsquo if it can withstand the action of abrasive or corrosive solids liquids or gases at high temperature The various combination of operating conditions in which refractories are used makes it necessary to manufacture a range of refractory materials with different properties Refractory materials are made in varying combinations and shapes depending on their application General requirement of refractory material are

They should withstand high temperature They should withstand sudden change of temperature They should withstand action of molten metal slag glass hot gases etc They should withstand load and abrasive forces at service condition They should conserve heat They should have low coefficient of thermal expansion They should not contaminate the material with which it comes into contact

Fire-clay refractories such as Fire bricks Siliceous-fireclays and aluminous clay refractories consists of aluminum silicates with varying Silica (SiO2) content up to 78 and Al2O3 content up to 44

High Alumina RefractoriesAlumina-silicate refractories containing more than 45 alumina are generally termed as high alumina materials The alumina concentration ranges from 45-100 The refractoriness of high alumina refractories increases with increase in alumina percentage The application of high alumina refractories include the hearth and shaft of blast furnaces ceramic kilns cement kilns glass tanks and crucibles for melting a wide range of materials

Insulating MaterialsInsulating materials greatly reduce the heat losses through wallsInsulation is achieved by providing a layer of materials with low heat conductivity between the internal hot surface and external surface thus keeping the temperature of the external surface low

Insulating materials can be classified into following groups- Insulating Bricks Insulating castables Ceramic fibers Calcium silicate Ceramic coatingThe characteristics of Ceramic fibers are remarkable combination of the properties of

refractories and traditional insulation material Lower thermal conductivity Light weight Lower heat storage Thermal shock resistance Chemical Resistance

Mechanical resilience Low Insulation cost Ease of maintenance Ease of handling Thermal Efficiency

High Emissivity coatingEmissivity (ie the measure of materialrsquos ability to both absorb and radiate heat) is often considered as an inherent physical property that does not normally change (Other examples are density specific heat and thermal conductivity) However the development of high emissivity coatings allows the surface emissivity of the material to be increased High emissivity coatings are applied on the interior surface of furnaces

Benefits of high emissivity coatings in furnace chambers are uniform heating and extended life of refractotries and metallic components such as radiant tubes and heating elements For intermittent furnaces or where rapid heating is required use of such coatings was found to reduce fuel or power by 25-45

Water cooling system in Walking Hearth FurnaceThe early design of WB Furnace used alloy steel Walking Beams that were exposed directly to the heat of the Furnace and were subjected to heat Corrosion so it operated at Maximum Temperature of about 1050 C compared with Re-heating Furnaces that must heat steel toTemperatures up to 1315 C Hence WB-Reheating Furnaces consist of water-cooled Steel members topped with refractors in such a manner that only the refractories are exposed directly to the heat of Furnace Alternatively the beams and supports may be constructed of water ndashcooled Tubular sections (with ldquobuttonsrdquo on the top surfaces to keep the Hot steel from direct ndashcontract with the water cooled tubes)

Heat recovery System

Recuperators(i) Recuperators (Waste Heat Recovery System) are placed in the path of the Flue Gasses of the Furnace between Furnace outlet and the chimney The combustion airgas is preheated in the recuperator through heat of the Flue gas and supplied to the Furance Burners in Pre-Heating Zone at about 400-5000C This results in savings of Heat Energy hence fuel(ii) Based on the material of Construction recuperators are two types

Metallic (Made of SS) Ceramic

(iii) Metallic recuperators have distinct advantages over Ceramic recuperators in terms of lower initial investment easier maintenance amp repair etc and are more popular in SRRM industryOn the other hand Ceramic recuperators have a longer life and can withstand much higher temperatures as compared to Metallic recuperators of about15000C vis-agrave-vis 11000C for metalrecuperators(iv) Based on the Design and method of Heat transfer the Recuperators are of two types

Tubular Convection Double Shell Radiation

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

The Wire Rolling Mill Department is the most important department in the factory Here in

this department mainly wires are manufactured from steel billets In the manufacturing of

the steel wires the hot billets of different grades of steels are received from steel melting

shop or from steel plant Hospet Billets are in size of 100mm X 100mm 125mm X 125mm

165mm X 165mm The steel billets are heated in the Billet Reheating Furnace and the Hot

Rolled in different Roll Stands to the required finished size of wire The prepared wire is

coiled in the coiling unit and then it is sent for dispatch

Introduction

Furnace is a device used for heating The name derives from Latinfornax ovenIn American English and Canadian English the term furnace on its own is generally

used to describe household heating systems based on a central furnace (known either as a boiler or a heater in British English) and sometimes as a synonym for kiln a device used in the production of ceramics In British English the term furnace is used exclusively to mean industrial furnaces which are used for many things such as the extraction of metal from ore (smelting) or in oil refineries and other chemical plants for example as the heat source for fractional distillation columns

The term furnace can also refer to a direct fired heater used in boiler applications in chemical industries or for providing heat to chemical reactions for processes like cracking and are part of the standard english names for many metallurgical furnaces worldwide

Types of Reheating Furnaces

Reheating furnaces are divided into two general classes Batch Type Continuous Type

Continuous Type furnaces

1) Pusher-Type FurnacesThe furnace at the Bloom Mill at KSP is a Pusher-type Furnace Continuous pusher-

type furnaces were designed initially for heating billets and small bloom sections The hearths were relatively short in length and were sloped downward longitudinally towards the discharge end to permit an easy movement of billets through the furnace Pushers were used to push forward the charge of cold billetsLonger furnaces generally are constructed now Some have hearths about 245 to 32 meters (80 to 105 feet) long with top and bottom firing and contain preheating heating and soaking zones Recuperators are utilized to provide waste-heat recovery Multiple-zone furnaces (eg five-zone slab heating furnace) have been evolved from one-zone furnace in the early designs to the modern five-zone slab heating furnace The steel to be heated in a continuous furnace can be charged either from the end or through a side door In either case the steel is moved through the furnace by pushing the last piece charged with a pusher at the charging end As each cold piece is pushed into the furnace against the continuous line of material a heated piece is removed The heated piece is discharged by several methods such as through an end door by gravity upon a roller table which feeds the mill or pushed through a side door to the mill table by suitable manual or mechanical means or withdrawn through the end door by a mechanical extractor

2) Walking-Hearth Furnaces

The reheating furnace at the WRM department is a Walking-Hearth Furnace In a walking-earth furnace travel of the work through the heating chamber follows the same general path as in the walking-beam furnace The main difference in method of conveyance in these two furnace types is that in the walking-hearth furnace the work rests on fixed refractory piers These piers extend through openings in the hearth and their tops are above the hearth surface during the time when the work is stationary in the furnace The furnace gases can thus circulate between most of the bottom surface of the work and the hearth To advance the work toward the discharge end of the furnace the hearths is raised vertically to first contact the work and then raise it a short distance above the piers The hearth then moves forward a preset distance stops lowers the work onto its new position on the piers continues to descend to its lowest position and then moves backward to its starting position toward the charging end of the furnace to await the next stroke In general the same advantages and disadvantages of the walking-beam furnace apply to walking-hearth furnaces

Billet Reheating Furnace

In the Billet Reheating Furnaces the charge is fed in the form of billets or ingots It is a precision engineered product which is widely used across different industries for various applications It is used mostly in steel rolling mills The best feature of these billet reheating furnaces is its minimum fuel consumption amp minimum burning losses

This is the heart of any hot rolling mill where in the charge is heated to rolling temperature The charge could be in the form of billets blooms slabs or ingots The type of furnace could be pusher walking hearth or walking beam ndash either top fired or top and bottom fired The fuel used could be either oil or gas The burners are located in a manner so as to achieve uniform heat distribution The radiation heat energy is efficiently transferred through the useful heat transfer area created by the charge bed The furnace is basically divided into three zones namely preheating heating and soaking zones The actual heating takes place in the heating zone The temperature uniformity up to desired limits between the core and the surface is achieved in the soaking zone The flue gases move in a direction opposite to that of the charge thereby ensuring considerable amount of waste heat recovery by convection in the preheating zone which is also termed as the recuperative zone For charge with higher thickness as in case of blooms and slabs burners are provided below and above the skids as against conventional furnaces where burners are provided only on the top This is known as top and bottom fired Reheating Furnace Our furnaces are highly fuel efficient due to proper roof profile zonal distribution optimum preheating recuperative zone lengths proper burner flue port locations and good instrumentation including furnace chamber pressure control eliminating atmosphere air ingress which also reduces the scale loss and de-carbides of the charge The furnaces could be side charged through water cooled driven rollers or front charged by hydraulic pusher Discharge can be at the side through driven water cooled rollers or discharge ejector with pinch-cum-pullout roll mechanism or end discharge through discharge ramp or slabbloom extractor

Single-zone firing comes with higher scale losses Single-zone firing furnaces have greater tendency to cause decarburization of high-carbon steel than the top-and bottom fired furnaces since the steel is in the furnace longer and is exposed to furnace gases with hydrogen and water vapor combinations The scaling of steel is practiced sometimes deliberately to remove the decarburized surface layer Those furnaces provided only with top firing require longer hearths for equal production than those with top and bottom firing but in the case of pusher-type furnaces do not require a special soaking zone to eliminate cold spots on the work caused by contact with water-cooled skids Side-discharge furnaces have less air infiltration at the hot end than end-door discharge furnaces End-door discharge of the usual gravity type induces cold air into the furnace by the stack effect at the discharge section of the furnace End-door discharge however is mechanically simpler for removing the heated stock particularly slabs and heavy blooms A level hearth eliminates the stack effect of hearths sloping upwards towards the charging end This stack effect draws cold air into the furnaces at the hot end and therefore causes higher fuel consumption and scale losses For a batch-type furnace it is preferred to preheat certain grades of alloy and high-carbon steels in a supplementary furnace before the stock is transferred into the hotter furnaces The preheating zone of a continuous furnace makes this unnecessary Finally regenerators or recuperators act as a reservoir of heat supply which is especially valuable for efficient soaking of steel

Modern furnace components

The furnace components can be divided into three categories

1 The burners heat exchanger draft inducer and venting2 The controls and safety devices3 The blower and air movement

The flame originates at the burners and is drawn into the heat exchanger by the negative pressure produced by the draft inducer The hot gases produced by the combustion

of the flame pass through the chambers of the heat exchanger and heat the metal walls of the heat exchanger The gases cool as they transfer the heat to the heat exchanger and are at about 120 degF (50 degC) as they exit on a high efficiency furnace The cooled gases then enter the draft inducer blower and are pushed into the venting pipes The exhaust gases then are directed out of the house through the vent pipes The controls include the gas valve ignition control igniter flame sensor transformer limit control blower control board and flame roll out switch The transformer provides 24 volts of electricity to power the controls 24 volts is applied to the thermostat that is installed in the living space The thermostat is basically an automatic switch that closes and completes the electrical circuit when the room temperature drops below the heat setting This then allows 24 volts to the circuit board which initiates the heat sequence The circuit board has a relay that closes to power up the motor on the draft inducer blower Then the circuit board igniter relay is energized which sends 120 volts to the hot surface igniter and makes it glow bright and get extremely hot Next the gas valve relay in the circuit board is energized This allows voltage to the gas valve and energizes a solenoid coil in the gas valve which opens the valve to allow gas to flow to the burners The gas flows into the burners and is ignited by the hot surface igniter The ignition control circuit board applies an AC voltage to the flame sensor which is just a stainless steel rod An interesting thing occurs inside a burning flame which is called ionization That is free electrons are produced which can conduct electricity through the flame itself The electrons will normally flow from the flame sensor through the flame when present and back to ground through the grounded burners

The ignition system must prove that a flame is present to continue the gas flow or if theres no flame then shut off the gas flow through the gas valve to prevent a possible explosion It also must not be fooled into thinking there is a flame present by a flame sensor that is touching the ground from being broken or bent This produces a half-wave of electrical current from each full wave The ignition control circuit detects the half-wave to determine if the sensor is merely touching ground If the ignition control receives this half wave signal from the flame sensor then combustion will continue Now the circuit board timer counts a determined amount of time and energizes the blower relay This relay powers up the blower motor and air is then pushed over the heat exchanger where it removes the heat from the hot metal and enters the ductwork to go to the various rooms in the house The limit control is a safety device that will open the electrical circuit to the ignition control and stop the gas flow if the furnace overheats The flame roll-out switch does the same thing if the flame was rolling out of the heat exchanger instead of being completely induced into it by the draft inducer

The blower creates a negative pressure on the intake side which draws air into the ductwork return air system and blows the air out through the heat exchanger and then into supply air ductwork to distribute throughout the home

Walking Hearth Mec h anism

An alternate method of transporting the ingots billets from the charging end of the furnace

to the discharging door point is by using a walking hearth furnace The furnace hearth has

alternately fixed and moving beams The fixed beams are part of the hearth at either

sidewall ends of the furnace and the moving beams are in between two fixed beams

Walking beam hearth furnaces have three fixed and two moving hearths or walking

beams A hydraulic system is provided to operate the walking beams through hydraulic

cylinders In the older designs there used to be a lifting and lowering cylinder which lifted

the beam through bell crank levers Once the beam reaches the top position all the ingots

billets that were resting on the fixed beams of the hearth get lifted up and now rest on the

moving beams when another hydraulic cylinder moves the beam forward by one stroke

which is normally around 700 - 1000mm all the ingots billets move forward by a

distance equal to one stroke of the forward backward cylinder The lifting lowering

cylinder now lowers the moving beam by a preset height through limit switches proximity

switches In the downward movement when the levels of the fixed and moving beam

tops are equal the ingots billets now rest on the fixed beams or the hearth at a new

point which is one cylinder stroke ahead of its previous position The moving beams

continue its downward movement ensuring that its top surface is well and truly

below the fixed beams It comes to rest at this position Now the forward backward

cylinder retracts the moving beams to their original position This completes one full cycle

of transportation In modern walking hearth furnaces the moving hearths are mounted on

rollers which ride up amp down a ramp actuated by hydraulic cylinders One hydraulic

cylinder performs the pulling up of the beam on the ramp and subsequently lowering it and

the other pulls pushes the beam forward backward as above The advantage of the ramp

system is that there are no linkages bell crank levers mounted on pivot bearings

which require extensive maintenance Each moving beam has a water seal at the

bottom to prevent the escape of flue gases into the cellar from in between the fixed amp

moving beams The Inside view of a typical WBWH Furnace is shown in Figure

Figure Inside ( c ellar) view of a Walk i ng Hearth Furnace

Since each of the billets is exposed on all four sides except the narrow strip resting on the

beams the heating is uniform and fast There is no danger of the ingots billets sticking to

each other the rate of heating can be high to reduce the residence time of the charge

inside the furnace thus reducing the burning scaling losses considerably For the same

length of the furnace the productivity of the hearth is much higher than for the

corresponding length of the pusher hearth furnace

Refractories The furnace also uses refractories for insulation purposes Any material can be

described as a lsquoRefractoryrsquo if it can withstand the action of abrasive or corrosive solids liquids or gases at high temperature The various combination of operating conditions in which refractories are used makes it necessary to manufacture a range of refractory materials with different properties Refractory materials are made in varying combinations and shapes depending on their application General requirement of refractory material are

They should withstand high temperature They should withstand sudden change of temperature They should withstand action of molten metal slag glass hot gases etc They should withstand load and abrasive forces at service condition They should conserve heat They should have low coefficient of thermal expansion They should not contaminate the material with which it comes into contact

Fire-clay refractories such as Fire bricks Siliceous-fireclays and aluminous clay refractories consists of aluminum silicates with varying Silica (SiO2) content up to 78 and Al2O3 content up to 44

High Alumina RefractoriesAlumina-silicate refractories containing more than 45 alumina are generally termed as high alumina materials The alumina concentration ranges from 45-100 The refractoriness of high alumina refractories increases with increase in alumina percentage The application of high alumina refractories include the hearth and shaft of blast furnaces ceramic kilns cement kilns glass tanks and crucibles for melting a wide range of materials

Insulating MaterialsInsulating materials greatly reduce the heat losses through wallsInsulation is achieved by providing a layer of materials with low heat conductivity between the internal hot surface and external surface thus keeping the temperature of the external surface low

Insulating materials can be classified into following groups- Insulating Bricks Insulating castables Ceramic fibers Calcium silicate Ceramic coatingThe characteristics of Ceramic fibers are remarkable combination of the properties of

refractories and traditional insulation material Lower thermal conductivity Light weight Lower heat storage Thermal shock resistance Chemical Resistance

Mechanical resilience Low Insulation cost Ease of maintenance Ease of handling Thermal Efficiency

High Emissivity coatingEmissivity (ie the measure of materialrsquos ability to both absorb and radiate heat) is often considered as an inherent physical property that does not normally change (Other examples are density specific heat and thermal conductivity) However the development of high emissivity coatings allows the surface emissivity of the material to be increased High emissivity coatings are applied on the interior surface of furnaces

Benefits of high emissivity coatings in furnace chambers are uniform heating and extended life of refractotries and metallic components such as radiant tubes and heating elements For intermittent furnaces or where rapid heating is required use of such coatings was found to reduce fuel or power by 25-45

Water cooling system in Walking Hearth FurnaceThe early design of WB Furnace used alloy steel Walking Beams that were exposed directly to the heat of the Furnace and were subjected to heat Corrosion so it operated at Maximum Temperature of about 1050 C compared with Re-heating Furnaces that must heat steel toTemperatures up to 1315 C Hence WB-Reheating Furnaces consist of water-cooled Steel members topped with refractors in such a manner that only the refractories are exposed directly to the heat of Furnace Alternatively the beams and supports may be constructed of water ndashcooled Tubular sections (with ldquobuttonsrdquo on the top surfaces to keep the Hot steel from direct ndashcontract with the water cooled tubes)

Heat recovery System

Recuperators(i) Recuperators (Waste Heat Recovery System) are placed in the path of the Flue Gasses of the Furnace between Furnace outlet and the chimney The combustion airgas is preheated in the recuperator through heat of the Flue gas and supplied to the Furance Burners in Pre-Heating Zone at about 400-5000C This results in savings of Heat Energy hence fuel(ii) Based on the material of Construction recuperators are two types

Metallic (Made of SS) Ceramic

(iii) Metallic recuperators have distinct advantages over Ceramic recuperators in terms of lower initial investment easier maintenance amp repair etc and are more popular in SRRM industryOn the other hand Ceramic recuperators have a longer life and can withstand much higher temperatures as compared to Metallic recuperators of about15000C vis-agrave-vis 11000C for metalrecuperators(iv) Based on the Design and method of Heat transfer the Recuperators are of two types

Tubular Convection Double Shell Radiation

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

Introduction

Furnace is a device used for heating The name derives from Latinfornax ovenIn American English and Canadian English the term furnace on its own is generally

used to describe household heating systems based on a central furnace (known either as a boiler or a heater in British English) and sometimes as a synonym for kiln a device used in the production of ceramics In British English the term furnace is used exclusively to mean industrial furnaces which are used for many things such as the extraction of metal from ore (smelting) or in oil refineries and other chemical plants for example as the heat source for fractional distillation columns

The term furnace can also refer to a direct fired heater used in boiler applications in chemical industries or for providing heat to chemical reactions for processes like cracking and are part of the standard english names for many metallurgical furnaces worldwide

Types of Reheating Furnaces

Reheating furnaces are divided into two general classes Batch Type Continuous Type

Continuous Type furnaces

1) Pusher-Type FurnacesThe furnace at the Bloom Mill at KSP is a Pusher-type Furnace Continuous pusher-

type furnaces were designed initially for heating billets and small bloom sections The hearths were relatively short in length and were sloped downward longitudinally towards the discharge end to permit an easy movement of billets through the furnace Pushers were used to push forward the charge of cold billetsLonger furnaces generally are constructed now Some have hearths about 245 to 32 meters (80 to 105 feet) long with top and bottom firing and contain preheating heating and soaking zones Recuperators are utilized to provide waste-heat recovery Multiple-zone furnaces (eg five-zone slab heating furnace) have been evolved from one-zone furnace in the early designs to the modern five-zone slab heating furnace The steel to be heated in a continuous furnace can be charged either from the end or through a side door In either case the steel is moved through the furnace by pushing the last piece charged with a pusher at the charging end As each cold piece is pushed into the furnace against the continuous line of material a heated piece is removed The heated piece is discharged by several methods such as through an end door by gravity upon a roller table which feeds the mill or pushed through a side door to the mill table by suitable manual or mechanical means or withdrawn through the end door by a mechanical extractor

2) Walking-Hearth Furnaces

The reheating furnace at the WRM department is a Walking-Hearth Furnace In a walking-earth furnace travel of the work through the heating chamber follows the same general path as in the walking-beam furnace The main difference in method of conveyance in these two furnace types is that in the walking-hearth furnace the work rests on fixed refractory piers These piers extend through openings in the hearth and their tops are above the hearth surface during the time when the work is stationary in the furnace The furnace gases can thus circulate between most of the bottom surface of the work and the hearth To advance the work toward the discharge end of the furnace the hearths is raised vertically to first contact the work and then raise it a short distance above the piers The hearth then moves forward a preset distance stops lowers the work onto its new position on the piers continues to descend to its lowest position and then moves backward to its starting position toward the charging end of the furnace to await the next stroke In general the same advantages and disadvantages of the walking-beam furnace apply to walking-hearth furnaces

Billet Reheating Furnace

In the Billet Reheating Furnaces the charge is fed in the form of billets or ingots It is a precision engineered product which is widely used across different industries for various applications It is used mostly in steel rolling mills The best feature of these billet reheating furnaces is its minimum fuel consumption amp minimum burning losses

This is the heart of any hot rolling mill where in the charge is heated to rolling temperature The charge could be in the form of billets blooms slabs or ingots The type of furnace could be pusher walking hearth or walking beam ndash either top fired or top and bottom fired The fuel used could be either oil or gas The burners are located in a manner so as to achieve uniform heat distribution The radiation heat energy is efficiently transferred through the useful heat transfer area created by the charge bed The furnace is basically divided into three zones namely preheating heating and soaking zones The actual heating takes place in the heating zone The temperature uniformity up to desired limits between the core and the surface is achieved in the soaking zone The flue gases move in a direction opposite to that of the charge thereby ensuring considerable amount of waste heat recovery by convection in the preheating zone which is also termed as the recuperative zone For charge with higher thickness as in case of blooms and slabs burners are provided below and above the skids as against conventional furnaces where burners are provided only on the top This is known as top and bottom fired Reheating Furnace Our furnaces are highly fuel efficient due to proper roof profile zonal distribution optimum preheating recuperative zone lengths proper burner flue port locations and good instrumentation including furnace chamber pressure control eliminating atmosphere air ingress which also reduces the scale loss and de-carbides of the charge The furnaces could be side charged through water cooled driven rollers or front charged by hydraulic pusher Discharge can be at the side through driven water cooled rollers or discharge ejector with pinch-cum-pullout roll mechanism or end discharge through discharge ramp or slabbloom extractor

Single-zone firing comes with higher scale losses Single-zone firing furnaces have greater tendency to cause decarburization of high-carbon steel than the top-and bottom fired furnaces since the steel is in the furnace longer and is exposed to furnace gases with hydrogen and water vapor combinations The scaling of steel is practiced sometimes deliberately to remove the decarburized surface layer Those furnaces provided only with top firing require longer hearths for equal production than those with top and bottom firing but in the case of pusher-type furnaces do not require a special soaking zone to eliminate cold spots on the work caused by contact with water-cooled skids Side-discharge furnaces have less air infiltration at the hot end than end-door discharge furnaces End-door discharge of the usual gravity type induces cold air into the furnace by the stack effect at the discharge section of the furnace End-door discharge however is mechanically simpler for removing the heated stock particularly slabs and heavy blooms A level hearth eliminates the stack effect of hearths sloping upwards towards the charging end This stack effect draws cold air into the furnaces at the hot end and therefore causes higher fuel consumption and scale losses For a batch-type furnace it is preferred to preheat certain grades of alloy and high-carbon steels in a supplementary furnace before the stock is transferred into the hotter furnaces The preheating zone of a continuous furnace makes this unnecessary Finally regenerators or recuperators act as a reservoir of heat supply which is especially valuable for efficient soaking of steel

Modern furnace components

The furnace components can be divided into three categories

1 The burners heat exchanger draft inducer and venting2 The controls and safety devices3 The blower and air movement

The flame originates at the burners and is drawn into the heat exchanger by the negative pressure produced by the draft inducer The hot gases produced by the combustion

of the flame pass through the chambers of the heat exchanger and heat the metal walls of the heat exchanger The gases cool as they transfer the heat to the heat exchanger and are at about 120 degF (50 degC) as they exit on a high efficiency furnace The cooled gases then enter the draft inducer blower and are pushed into the venting pipes The exhaust gases then are directed out of the house through the vent pipes The controls include the gas valve ignition control igniter flame sensor transformer limit control blower control board and flame roll out switch The transformer provides 24 volts of electricity to power the controls 24 volts is applied to the thermostat that is installed in the living space The thermostat is basically an automatic switch that closes and completes the electrical circuit when the room temperature drops below the heat setting This then allows 24 volts to the circuit board which initiates the heat sequence The circuit board has a relay that closes to power up the motor on the draft inducer blower Then the circuit board igniter relay is energized which sends 120 volts to the hot surface igniter and makes it glow bright and get extremely hot Next the gas valve relay in the circuit board is energized This allows voltage to the gas valve and energizes a solenoid coil in the gas valve which opens the valve to allow gas to flow to the burners The gas flows into the burners and is ignited by the hot surface igniter The ignition control circuit board applies an AC voltage to the flame sensor which is just a stainless steel rod An interesting thing occurs inside a burning flame which is called ionization That is free electrons are produced which can conduct electricity through the flame itself The electrons will normally flow from the flame sensor through the flame when present and back to ground through the grounded burners

The ignition system must prove that a flame is present to continue the gas flow or if theres no flame then shut off the gas flow through the gas valve to prevent a possible explosion It also must not be fooled into thinking there is a flame present by a flame sensor that is touching the ground from being broken or bent This produces a half-wave of electrical current from each full wave The ignition control circuit detects the half-wave to determine if the sensor is merely touching ground If the ignition control receives this half wave signal from the flame sensor then combustion will continue Now the circuit board timer counts a determined amount of time and energizes the blower relay This relay powers up the blower motor and air is then pushed over the heat exchanger where it removes the heat from the hot metal and enters the ductwork to go to the various rooms in the house The limit control is a safety device that will open the electrical circuit to the ignition control and stop the gas flow if the furnace overheats The flame roll-out switch does the same thing if the flame was rolling out of the heat exchanger instead of being completely induced into it by the draft inducer

The blower creates a negative pressure on the intake side which draws air into the ductwork return air system and blows the air out through the heat exchanger and then into supply air ductwork to distribute throughout the home

Walking Hearth Mec h anism

An alternate method of transporting the ingots billets from the charging end of the furnace

to the discharging door point is by using a walking hearth furnace The furnace hearth has

alternately fixed and moving beams The fixed beams are part of the hearth at either

sidewall ends of the furnace and the moving beams are in between two fixed beams

Walking beam hearth furnaces have three fixed and two moving hearths or walking

beams A hydraulic system is provided to operate the walking beams through hydraulic

cylinders In the older designs there used to be a lifting and lowering cylinder which lifted

the beam through bell crank levers Once the beam reaches the top position all the ingots

billets that were resting on the fixed beams of the hearth get lifted up and now rest on the

moving beams when another hydraulic cylinder moves the beam forward by one stroke

which is normally around 700 - 1000mm all the ingots billets move forward by a

distance equal to one stroke of the forward backward cylinder The lifting lowering

cylinder now lowers the moving beam by a preset height through limit switches proximity

switches In the downward movement when the levels of the fixed and moving beam

tops are equal the ingots billets now rest on the fixed beams or the hearth at a new

point which is one cylinder stroke ahead of its previous position The moving beams

continue its downward movement ensuring that its top surface is well and truly

below the fixed beams It comes to rest at this position Now the forward backward

cylinder retracts the moving beams to their original position This completes one full cycle

of transportation In modern walking hearth furnaces the moving hearths are mounted on

rollers which ride up amp down a ramp actuated by hydraulic cylinders One hydraulic

cylinder performs the pulling up of the beam on the ramp and subsequently lowering it and

the other pulls pushes the beam forward backward as above The advantage of the ramp

system is that there are no linkages bell crank levers mounted on pivot bearings

which require extensive maintenance Each moving beam has a water seal at the

bottom to prevent the escape of flue gases into the cellar from in between the fixed amp

moving beams The Inside view of a typical WBWH Furnace is shown in Figure

Figure Inside ( c ellar) view of a Walk i ng Hearth Furnace

Since each of the billets is exposed on all four sides except the narrow strip resting on the

beams the heating is uniform and fast There is no danger of the ingots billets sticking to

each other the rate of heating can be high to reduce the residence time of the charge

inside the furnace thus reducing the burning scaling losses considerably For the same

length of the furnace the productivity of the hearth is much higher than for the

corresponding length of the pusher hearth furnace

Refractories The furnace also uses refractories for insulation purposes Any material can be

described as a lsquoRefractoryrsquo if it can withstand the action of abrasive or corrosive solids liquids or gases at high temperature The various combination of operating conditions in which refractories are used makes it necessary to manufacture a range of refractory materials with different properties Refractory materials are made in varying combinations and shapes depending on their application General requirement of refractory material are

They should withstand high temperature They should withstand sudden change of temperature They should withstand action of molten metal slag glass hot gases etc They should withstand load and abrasive forces at service condition They should conserve heat They should have low coefficient of thermal expansion They should not contaminate the material with which it comes into contact

Fire-clay refractories such as Fire bricks Siliceous-fireclays and aluminous clay refractories consists of aluminum silicates with varying Silica (SiO2) content up to 78 and Al2O3 content up to 44

High Alumina RefractoriesAlumina-silicate refractories containing more than 45 alumina are generally termed as high alumina materials The alumina concentration ranges from 45-100 The refractoriness of high alumina refractories increases with increase in alumina percentage The application of high alumina refractories include the hearth and shaft of blast furnaces ceramic kilns cement kilns glass tanks and crucibles for melting a wide range of materials

Insulating MaterialsInsulating materials greatly reduce the heat losses through wallsInsulation is achieved by providing a layer of materials with low heat conductivity between the internal hot surface and external surface thus keeping the temperature of the external surface low

Insulating materials can be classified into following groups- Insulating Bricks Insulating castables Ceramic fibers Calcium silicate Ceramic coatingThe characteristics of Ceramic fibers are remarkable combination of the properties of

refractories and traditional insulation material Lower thermal conductivity Light weight Lower heat storage Thermal shock resistance Chemical Resistance

Mechanical resilience Low Insulation cost Ease of maintenance Ease of handling Thermal Efficiency

High Emissivity coatingEmissivity (ie the measure of materialrsquos ability to both absorb and radiate heat) is often considered as an inherent physical property that does not normally change (Other examples are density specific heat and thermal conductivity) However the development of high emissivity coatings allows the surface emissivity of the material to be increased High emissivity coatings are applied on the interior surface of furnaces

Benefits of high emissivity coatings in furnace chambers are uniform heating and extended life of refractotries and metallic components such as radiant tubes and heating elements For intermittent furnaces or where rapid heating is required use of such coatings was found to reduce fuel or power by 25-45

Water cooling system in Walking Hearth FurnaceThe early design of WB Furnace used alloy steel Walking Beams that were exposed directly to the heat of the Furnace and were subjected to heat Corrosion so it operated at Maximum Temperature of about 1050 C compared with Re-heating Furnaces that must heat steel toTemperatures up to 1315 C Hence WB-Reheating Furnaces consist of water-cooled Steel members topped with refractors in such a manner that only the refractories are exposed directly to the heat of Furnace Alternatively the beams and supports may be constructed of water ndashcooled Tubular sections (with ldquobuttonsrdquo on the top surfaces to keep the Hot steel from direct ndashcontract with the water cooled tubes)

Heat recovery System

Recuperators(i) Recuperators (Waste Heat Recovery System) are placed in the path of the Flue Gasses of the Furnace between Furnace outlet and the chimney The combustion airgas is preheated in the recuperator through heat of the Flue gas and supplied to the Furance Burners in Pre-Heating Zone at about 400-5000C This results in savings of Heat Energy hence fuel(ii) Based on the material of Construction recuperators are two types

Metallic (Made of SS) Ceramic

(iii) Metallic recuperators have distinct advantages over Ceramic recuperators in terms of lower initial investment easier maintenance amp repair etc and are more popular in SRRM industryOn the other hand Ceramic recuperators have a longer life and can withstand much higher temperatures as compared to Metallic recuperators of about15000C vis-agrave-vis 11000C for metalrecuperators(iv) Based on the Design and method of Heat transfer the Recuperators are of two types

Tubular Convection Double Shell Radiation

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

The reheating furnace at the WRM department is a Walking-Hearth Furnace In a walking-earth furnace travel of the work through the heating chamber follows the same general path as in the walking-beam furnace The main difference in method of conveyance in these two furnace types is that in the walking-hearth furnace the work rests on fixed refractory piers These piers extend through openings in the hearth and their tops are above the hearth surface during the time when the work is stationary in the furnace The furnace gases can thus circulate between most of the bottom surface of the work and the hearth To advance the work toward the discharge end of the furnace the hearths is raised vertically to first contact the work and then raise it a short distance above the piers The hearth then moves forward a preset distance stops lowers the work onto its new position on the piers continues to descend to its lowest position and then moves backward to its starting position toward the charging end of the furnace to await the next stroke In general the same advantages and disadvantages of the walking-beam furnace apply to walking-hearth furnaces

Billet Reheating Furnace

In the Billet Reheating Furnaces the charge is fed in the form of billets or ingots It is a precision engineered product which is widely used across different industries for various applications It is used mostly in steel rolling mills The best feature of these billet reheating furnaces is its minimum fuel consumption amp minimum burning losses

This is the heart of any hot rolling mill where in the charge is heated to rolling temperature The charge could be in the form of billets blooms slabs or ingots The type of furnace could be pusher walking hearth or walking beam ndash either top fired or top and bottom fired The fuel used could be either oil or gas The burners are located in a manner so as to achieve uniform heat distribution The radiation heat energy is efficiently transferred through the useful heat transfer area created by the charge bed The furnace is basically divided into three zones namely preheating heating and soaking zones The actual heating takes place in the heating zone The temperature uniformity up to desired limits between the core and the surface is achieved in the soaking zone The flue gases move in a direction opposite to that of the charge thereby ensuring considerable amount of waste heat recovery by convection in the preheating zone which is also termed as the recuperative zone For charge with higher thickness as in case of blooms and slabs burners are provided below and above the skids as against conventional furnaces where burners are provided only on the top This is known as top and bottom fired Reheating Furnace Our furnaces are highly fuel efficient due to proper roof profile zonal distribution optimum preheating recuperative zone lengths proper burner flue port locations and good instrumentation including furnace chamber pressure control eliminating atmosphere air ingress which also reduces the scale loss and de-carbides of the charge The furnaces could be side charged through water cooled driven rollers or front charged by hydraulic pusher Discharge can be at the side through driven water cooled rollers or discharge ejector with pinch-cum-pullout roll mechanism or end discharge through discharge ramp or slabbloom extractor

Single-zone firing comes with higher scale losses Single-zone firing furnaces have greater tendency to cause decarburization of high-carbon steel than the top-and bottom fired furnaces since the steel is in the furnace longer and is exposed to furnace gases with hydrogen and water vapor combinations The scaling of steel is practiced sometimes deliberately to remove the decarburized surface layer Those furnaces provided only with top firing require longer hearths for equal production than those with top and bottom firing but in the case of pusher-type furnaces do not require a special soaking zone to eliminate cold spots on the work caused by contact with water-cooled skids Side-discharge furnaces have less air infiltration at the hot end than end-door discharge furnaces End-door discharge of the usual gravity type induces cold air into the furnace by the stack effect at the discharge section of the furnace End-door discharge however is mechanically simpler for removing the heated stock particularly slabs and heavy blooms A level hearth eliminates the stack effect of hearths sloping upwards towards the charging end This stack effect draws cold air into the furnaces at the hot end and therefore causes higher fuel consumption and scale losses For a batch-type furnace it is preferred to preheat certain grades of alloy and high-carbon steels in a supplementary furnace before the stock is transferred into the hotter furnaces The preheating zone of a continuous furnace makes this unnecessary Finally regenerators or recuperators act as a reservoir of heat supply which is especially valuable for efficient soaking of steel

Modern furnace components

The furnace components can be divided into three categories

1 The burners heat exchanger draft inducer and venting2 The controls and safety devices3 The blower and air movement

The flame originates at the burners and is drawn into the heat exchanger by the negative pressure produced by the draft inducer The hot gases produced by the combustion

of the flame pass through the chambers of the heat exchanger and heat the metal walls of the heat exchanger The gases cool as they transfer the heat to the heat exchanger and are at about 120 degF (50 degC) as they exit on a high efficiency furnace The cooled gases then enter the draft inducer blower and are pushed into the venting pipes The exhaust gases then are directed out of the house through the vent pipes The controls include the gas valve ignition control igniter flame sensor transformer limit control blower control board and flame roll out switch The transformer provides 24 volts of electricity to power the controls 24 volts is applied to the thermostat that is installed in the living space The thermostat is basically an automatic switch that closes and completes the electrical circuit when the room temperature drops below the heat setting This then allows 24 volts to the circuit board which initiates the heat sequence The circuit board has a relay that closes to power up the motor on the draft inducer blower Then the circuit board igniter relay is energized which sends 120 volts to the hot surface igniter and makes it glow bright and get extremely hot Next the gas valve relay in the circuit board is energized This allows voltage to the gas valve and energizes a solenoid coil in the gas valve which opens the valve to allow gas to flow to the burners The gas flows into the burners and is ignited by the hot surface igniter The ignition control circuit board applies an AC voltage to the flame sensor which is just a stainless steel rod An interesting thing occurs inside a burning flame which is called ionization That is free electrons are produced which can conduct electricity through the flame itself The electrons will normally flow from the flame sensor through the flame when present and back to ground through the grounded burners

The ignition system must prove that a flame is present to continue the gas flow or if theres no flame then shut off the gas flow through the gas valve to prevent a possible explosion It also must not be fooled into thinking there is a flame present by a flame sensor that is touching the ground from being broken or bent This produces a half-wave of electrical current from each full wave The ignition control circuit detects the half-wave to determine if the sensor is merely touching ground If the ignition control receives this half wave signal from the flame sensor then combustion will continue Now the circuit board timer counts a determined amount of time and energizes the blower relay This relay powers up the blower motor and air is then pushed over the heat exchanger where it removes the heat from the hot metal and enters the ductwork to go to the various rooms in the house The limit control is a safety device that will open the electrical circuit to the ignition control and stop the gas flow if the furnace overheats The flame roll-out switch does the same thing if the flame was rolling out of the heat exchanger instead of being completely induced into it by the draft inducer

The blower creates a negative pressure on the intake side which draws air into the ductwork return air system and blows the air out through the heat exchanger and then into supply air ductwork to distribute throughout the home

Walking Hearth Mec h anism

An alternate method of transporting the ingots billets from the charging end of the furnace

to the discharging door point is by using a walking hearth furnace The furnace hearth has

alternately fixed and moving beams The fixed beams are part of the hearth at either

sidewall ends of the furnace and the moving beams are in between two fixed beams

Walking beam hearth furnaces have three fixed and two moving hearths or walking

beams A hydraulic system is provided to operate the walking beams through hydraulic

cylinders In the older designs there used to be a lifting and lowering cylinder which lifted

the beam through bell crank levers Once the beam reaches the top position all the ingots

billets that were resting on the fixed beams of the hearth get lifted up and now rest on the

moving beams when another hydraulic cylinder moves the beam forward by one stroke

which is normally around 700 - 1000mm all the ingots billets move forward by a

distance equal to one stroke of the forward backward cylinder The lifting lowering

cylinder now lowers the moving beam by a preset height through limit switches proximity

switches In the downward movement when the levels of the fixed and moving beam

tops are equal the ingots billets now rest on the fixed beams or the hearth at a new

point which is one cylinder stroke ahead of its previous position The moving beams

continue its downward movement ensuring that its top surface is well and truly

below the fixed beams It comes to rest at this position Now the forward backward

cylinder retracts the moving beams to their original position This completes one full cycle

of transportation In modern walking hearth furnaces the moving hearths are mounted on

rollers which ride up amp down a ramp actuated by hydraulic cylinders One hydraulic

cylinder performs the pulling up of the beam on the ramp and subsequently lowering it and

the other pulls pushes the beam forward backward as above The advantage of the ramp

system is that there are no linkages bell crank levers mounted on pivot bearings

which require extensive maintenance Each moving beam has a water seal at the

bottom to prevent the escape of flue gases into the cellar from in between the fixed amp

moving beams The Inside view of a typical WBWH Furnace is shown in Figure

Figure Inside ( c ellar) view of a Walk i ng Hearth Furnace

Since each of the billets is exposed on all four sides except the narrow strip resting on the

beams the heating is uniform and fast There is no danger of the ingots billets sticking to

each other the rate of heating can be high to reduce the residence time of the charge

inside the furnace thus reducing the burning scaling losses considerably For the same

length of the furnace the productivity of the hearth is much higher than for the

corresponding length of the pusher hearth furnace

Refractories The furnace also uses refractories for insulation purposes Any material can be

described as a lsquoRefractoryrsquo if it can withstand the action of abrasive or corrosive solids liquids or gases at high temperature The various combination of operating conditions in which refractories are used makes it necessary to manufacture a range of refractory materials with different properties Refractory materials are made in varying combinations and shapes depending on their application General requirement of refractory material are

They should withstand high temperature They should withstand sudden change of temperature They should withstand action of molten metal slag glass hot gases etc They should withstand load and abrasive forces at service condition They should conserve heat They should have low coefficient of thermal expansion They should not contaminate the material with which it comes into contact

Fire-clay refractories such as Fire bricks Siliceous-fireclays and aluminous clay refractories consists of aluminum silicates with varying Silica (SiO2) content up to 78 and Al2O3 content up to 44

High Alumina RefractoriesAlumina-silicate refractories containing more than 45 alumina are generally termed as high alumina materials The alumina concentration ranges from 45-100 The refractoriness of high alumina refractories increases with increase in alumina percentage The application of high alumina refractories include the hearth and shaft of blast furnaces ceramic kilns cement kilns glass tanks and crucibles for melting a wide range of materials

Insulating MaterialsInsulating materials greatly reduce the heat losses through wallsInsulation is achieved by providing a layer of materials with low heat conductivity between the internal hot surface and external surface thus keeping the temperature of the external surface low

Insulating materials can be classified into following groups- Insulating Bricks Insulating castables Ceramic fibers Calcium silicate Ceramic coatingThe characteristics of Ceramic fibers are remarkable combination of the properties of

refractories and traditional insulation material Lower thermal conductivity Light weight Lower heat storage Thermal shock resistance Chemical Resistance

Mechanical resilience Low Insulation cost Ease of maintenance Ease of handling Thermal Efficiency

High Emissivity coatingEmissivity (ie the measure of materialrsquos ability to both absorb and radiate heat) is often considered as an inherent physical property that does not normally change (Other examples are density specific heat and thermal conductivity) However the development of high emissivity coatings allows the surface emissivity of the material to be increased High emissivity coatings are applied on the interior surface of furnaces

Benefits of high emissivity coatings in furnace chambers are uniform heating and extended life of refractotries and metallic components such as radiant tubes and heating elements For intermittent furnaces or where rapid heating is required use of such coatings was found to reduce fuel or power by 25-45

Water cooling system in Walking Hearth FurnaceThe early design of WB Furnace used alloy steel Walking Beams that were exposed directly to the heat of the Furnace and were subjected to heat Corrosion so it operated at Maximum Temperature of about 1050 C compared with Re-heating Furnaces that must heat steel toTemperatures up to 1315 C Hence WB-Reheating Furnaces consist of water-cooled Steel members topped with refractors in such a manner that only the refractories are exposed directly to the heat of Furnace Alternatively the beams and supports may be constructed of water ndashcooled Tubular sections (with ldquobuttonsrdquo on the top surfaces to keep the Hot steel from direct ndashcontract with the water cooled tubes)

Heat recovery System

Recuperators(i) Recuperators (Waste Heat Recovery System) are placed in the path of the Flue Gasses of the Furnace between Furnace outlet and the chimney The combustion airgas is preheated in the recuperator through heat of the Flue gas and supplied to the Furance Burners in Pre-Heating Zone at about 400-5000C This results in savings of Heat Energy hence fuel(ii) Based on the material of Construction recuperators are two types

Metallic (Made of SS) Ceramic

(iii) Metallic recuperators have distinct advantages over Ceramic recuperators in terms of lower initial investment easier maintenance amp repair etc and are more popular in SRRM industryOn the other hand Ceramic recuperators have a longer life and can withstand much higher temperatures as compared to Metallic recuperators of about15000C vis-agrave-vis 11000C for metalrecuperators(iv) Based on the Design and method of Heat transfer the Recuperators are of two types

Tubular Convection Double Shell Radiation

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

This is the heart of any hot rolling mill where in the charge is heated to rolling temperature The charge could be in the form of billets blooms slabs or ingots The type of furnace could be pusher walking hearth or walking beam ndash either top fired or top and bottom fired The fuel used could be either oil or gas The burners are located in a manner so as to achieve uniform heat distribution The radiation heat energy is efficiently transferred through the useful heat transfer area created by the charge bed The furnace is basically divided into three zones namely preheating heating and soaking zones The actual heating takes place in the heating zone The temperature uniformity up to desired limits between the core and the surface is achieved in the soaking zone The flue gases move in a direction opposite to that of the charge thereby ensuring considerable amount of waste heat recovery by convection in the preheating zone which is also termed as the recuperative zone For charge with higher thickness as in case of blooms and slabs burners are provided below and above the skids as against conventional furnaces where burners are provided only on the top This is known as top and bottom fired Reheating Furnace Our furnaces are highly fuel efficient due to proper roof profile zonal distribution optimum preheating recuperative zone lengths proper burner flue port locations and good instrumentation including furnace chamber pressure control eliminating atmosphere air ingress which also reduces the scale loss and de-carbides of the charge The furnaces could be side charged through water cooled driven rollers or front charged by hydraulic pusher Discharge can be at the side through driven water cooled rollers or discharge ejector with pinch-cum-pullout roll mechanism or end discharge through discharge ramp or slabbloom extractor

Single-zone firing comes with higher scale losses Single-zone firing furnaces have greater tendency to cause decarburization of high-carbon steel than the top-and bottom fired furnaces since the steel is in the furnace longer and is exposed to furnace gases with hydrogen and water vapor combinations The scaling of steel is practiced sometimes deliberately to remove the decarburized surface layer Those furnaces provided only with top firing require longer hearths for equal production than those with top and bottom firing but in the case of pusher-type furnaces do not require a special soaking zone to eliminate cold spots on the work caused by contact with water-cooled skids Side-discharge furnaces have less air infiltration at the hot end than end-door discharge furnaces End-door discharge of the usual gravity type induces cold air into the furnace by the stack effect at the discharge section of the furnace End-door discharge however is mechanically simpler for removing the heated stock particularly slabs and heavy blooms A level hearth eliminates the stack effect of hearths sloping upwards towards the charging end This stack effect draws cold air into the furnaces at the hot end and therefore causes higher fuel consumption and scale losses For a batch-type furnace it is preferred to preheat certain grades of alloy and high-carbon steels in a supplementary furnace before the stock is transferred into the hotter furnaces The preheating zone of a continuous furnace makes this unnecessary Finally regenerators or recuperators act as a reservoir of heat supply which is especially valuable for efficient soaking of steel

Modern furnace components

The furnace components can be divided into three categories

1 The burners heat exchanger draft inducer and venting2 The controls and safety devices3 The blower and air movement

The flame originates at the burners and is drawn into the heat exchanger by the negative pressure produced by the draft inducer The hot gases produced by the combustion

of the flame pass through the chambers of the heat exchanger and heat the metal walls of the heat exchanger The gases cool as they transfer the heat to the heat exchanger and are at about 120 degF (50 degC) as they exit on a high efficiency furnace The cooled gases then enter the draft inducer blower and are pushed into the venting pipes The exhaust gases then are directed out of the house through the vent pipes The controls include the gas valve ignition control igniter flame sensor transformer limit control blower control board and flame roll out switch The transformer provides 24 volts of electricity to power the controls 24 volts is applied to the thermostat that is installed in the living space The thermostat is basically an automatic switch that closes and completes the electrical circuit when the room temperature drops below the heat setting This then allows 24 volts to the circuit board which initiates the heat sequence The circuit board has a relay that closes to power up the motor on the draft inducer blower Then the circuit board igniter relay is energized which sends 120 volts to the hot surface igniter and makes it glow bright and get extremely hot Next the gas valve relay in the circuit board is energized This allows voltage to the gas valve and energizes a solenoid coil in the gas valve which opens the valve to allow gas to flow to the burners The gas flows into the burners and is ignited by the hot surface igniter The ignition control circuit board applies an AC voltage to the flame sensor which is just a stainless steel rod An interesting thing occurs inside a burning flame which is called ionization That is free electrons are produced which can conduct electricity through the flame itself The electrons will normally flow from the flame sensor through the flame when present and back to ground through the grounded burners

The ignition system must prove that a flame is present to continue the gas flow or if theres no flame then shut off the gas flow through the gas valve to prevent a possible explosion It also must not be fooled into thinking there is a flame present by a flame sensor that is touching the ground from being broken or bent This produces a half-wave of electrical current from each full wave The ignition control circuit detects the half-wave to determine if the sensor is merely touching ground If the ignition control receives this half wave signal from the flame sensor then combustion will continue Now the circuit board timer counts a determined amount of time and energizes the blower relay This relay powers up the blower motor and air is then pushed over the heat exchanger where it removes the heat from the hot metal and enters the ductwork to go to the various rooms in the house The limit control is a safety device that will open the electrical circuit to the ignition control and stop the gas flow if the furnace overheats The flame roll-out switch does the same thing if the flame was rolling out of the heat exchanger instead of being completely induced into it by the draft inducer

The blower creates a negative pressure on the intake side which draws air into the ductwork return air system and blows the air out through the heat exchanger and then into supply air ductwork to distribute throughout the home

Walking Hearth Mec h anism

An alternate method of transporting the ingots billets from the charging end of the furnace

to the discharging door point is by using a walking hearth furnace The furnace hearth has

alternately fixed and moving beams The fixed beams are part of the hearth at either

sidewall ends of the furnace and the moving beams are in between two fixed beams

Walking beam hearth furnaces have three fixed and two moving hearths or walking

beams A hydraulic system is provided to operate the walking beams through hydraulic

cylinders In the older designs there used to be a lifting and lowering cylinder which lifted

the beam through bell crank levers Once the beam reaches the top position all the ingots

billets that were resting on the fixed beams of the hearth get lifted up and now rest on the

moving beams when another hydraulic cylinder moves the beam forward by one stroke

which is normally around 700 - 1000mm all the ingots billets move forward by a

distance equal to one stroke of the forward backward cylinder The lifting lowering

cylinder now lowers the moving beam by a preset height through limit switches proximity

switches In the downward movement when the levels of the fixed and moving beam

tops are equal the ingots billets now rest on the fixed beams or the hearth at a new

point which is one cylinder stroke ahead of its previous position The moving beams

continue its downward movement ensuring that its top surface is well and truly

below the fixed beams It comes to rest at this position Now the forward backward

cylinder retracts the moving beams to their original position This completes one full cycle

of transportation In modern walking hearth furnaces the moving hearths are mounted on

rollers which ride up amp down a ramp actuated by hydraulic cylinders One hydraulic

cylinder performs the pulling up of the beam on the ramp and subsequently lowering it and

the other pulls pushes the beam forward backward as above The advantage of the ramp

system is that there are no linkages bell crank levers mounted on pivot bearings

which require extensive maintenance Each moving beam has a water seal at the

bottom to prevent the escape of flue gases into the cellar from in between the fixed amp

moving beams The Inside view of a typical WBWH Furnace is shown in Figure

Figure Inside ( c ellar) view of a Walk i ng Hearth Furnace

Since each of the billets is exposed on all four sides except the narrow strip resting on the

beams the heating is uniform and fast There is no danger of the ingots billets sticking to

each other the rate of heating can be high to reduce the residence time of the charge

inside the furnace thus reducing the burning scaling losses considerably For the same

length of the furnace the productivity of the hearth is much higher than for the

corresponding length of the pusher hearth furnace

Refractories The furnace also uses refractories for insulation purposes Any material can be

described as a lsquoRefractoryrsquo if it can withstand the action of abrasive or corrosive solids liquids or gases at high temperature The various combination of operating conditions in which refractories are used makes it necessary to manufacture a range of refractory materials with different properties Refractory materials are made in varying combinations and shapes depending on their application General requirement of refractory material are

They should withstand high temperature They should withstand sudden change of temperature They should withstand action of molten metal slag glass hot gases etc They should withstand load and abrasive forces at service condition They should conserve heat They should have low coefficient of thermal expansion They should not contaminate the material with which it comes into contact

Fire-clay refractories such as Fire bricks Siliceous-fireclays and aluminous clay refractories consists of aluminum silicates with varying Silica (SiO2) content up to 78 and Al2O3 content up to 44

High Alumina RefractoriesAlumina-silicate refractories containing more than 45 alumina are generally termed as high alumina materials The alumina concentration ranges from 45-100 The refractoriness of high alumina refractories increases with increase in alumina percentage The application of high alumina refractories include the hearth and shaft of blast furnaces ceramic kilns cement kilns glass tanks and crucibles for melting a wide range of materials

Insulating MaterialsInsulating materials greatly reduce the heat losses through wallsInsulation is achieved by providing a layer of materials with low heat conductivity between the internal hot surface and external surface thus keeping the temperature of the external surface low

Insulating materials can be classified into following groups- Insulating Bricks Insulating castables Ceramic fibers Calcium silicate Ceramic coatingThe characteristics of Ceramic fibers are remarkable combination of the properties of

refractories and traditional insulation material Lower thermal conductivity Light weight Lower heat storage Thermal shock resistance Chemical Resistance

Mechanical resilience Low Insulation cost Ease of maintenance Ease of handling Thermal Efficiency

High Emissivity coatingEmissivity (ie the measure of materialrsquos ability to both absorb and radiate heat) is often considered as an inherent physical property that does not normally change (Other examples are density specific heat and thermal conductivity) However the development of high emissivity coatings allows the surface emissivity of the material to be increased High emissivity coatings are applied on the interior surface of furnaces

Benefits of high emissivity coatings in furnace chambers are uniform heating and extended life of refractotries and metallic components such as radiant tubes and heating elements For intermittent furnaces or where rapid heating is required use of such coatings was found to reduce fuel or power by 25-45

Water cooling system in Walking Hearth FurnaceThe early design of WB Furnace used alloy steel Walking Beams that were exposed directly to the heat of the Furnace and were subjected to heat Corrosion so it operated at Maximum Temperature of about 1050 C compared with Re-heating Furnaces that must heat steel toTemperatures up to 1315 C Hence WB-Reheating Furnaces consist of water-cooled Steel members topped with refractors in such a manner that only the refractories are exposed directly to the heat of Furnace Alternatively the beams and supports may be constructed of water ndashcooled Tubular sections (with ldquobuttonsrdquo on the top surfaces to keep the Hot steel from direct ndashcontract with the water cooled tubes)

Heat recovery System

Recuperators(i) Recuperators (Waste Heat Recovery System) are placed in the path of the Flue Gasses of the Furnace between Furnace outlet and the chimney The combustion airgas is preheated in the recuperator through heat of the Flue gas and supplied to the Furance Burners in Pre-Heating Zone at about 400-5000C This results in savings of Heat Energy hence fuel(ii) Based on the material of Construction recuperators are two types

Metallic (Made of SS) Ceramic

(iii) Metallic recuperators have distinct advantages over Ceramic recuperators in terms of lower initial investment easier maintenance amp repair etc and are more popular in SRRM industryOn the other hand Ceramic recuperators have a longer life and can withstand much higher temperatures as compared to Metallic recuperators of about15000C vis-agrave-vis 11000C for metalrecuperators(iv) Based on the Design and method of Heat transfer the Recuperators are of two types

Tubular Convection Double Shell Radiation

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

of the flame pass through the chambers of the heat exchanger and heat the metal walls of the heat exchanger The gases cool as they transfer the heat to the heat exchanger and are at about 120 degF (50 degC) as they exit on a high efficiency furnace The cooled gases then enter the draft inducer blower and are pushed into the venting pipes The exhaust gases then are directed out of the house through the vent pipes The controls include the gas valve ignition control igniter flame sensor transformer limit control blower control board and flame roll out switch The transformer provides 24 volts of electricity to power the controls 24 volts is applied to the thermostat that is installed in the living space The thermostat is basically an automatic switch that closes and completes the electrical circuit when the room temperature drops below the heat setting This then allows 24 volts to the circuit board which initiates the heat sequence The circuit board has a relay that closes to power up the motor on the draft inducer blower Then the circuit board igniter relay is energized which sends 120 volts to the hot surface igniter and makes it glow bright and get extremely hot Next the gas valve relay in the circuit board is energized This allows voltage to the gas valve and energizes a solenoid coil in the gas valve which opens the valve to allow gas to flow to the burners The gas flows into the burners and is ignited by the hot surface igniter The ignition control circuit board applies an AC voltage to the flame sensor which is just a stainless steel rod An interesting thing occurs inside a burning flame which is called ionization That is free electrons are produced which can conduct electricity through the flame itself The electrons will normally flow from the flame sensor through the flame when present and back to ground through the grounded burners

The ignition system must prove that a flame is present to continue the gas flow or if theres no flame then shut off the gas flow through the gas valve to prevent a possible explosion It also must not be fooled into thinking there is a flame present by a flame sensor that is touching the ground from being broken or bent This produces a half-wave of electrical current from each full wave The ignition control circuit detects the half-wave to determine if the sensor is merely touching ground If the ignition control receives this half wave signal from the flame sensor then combustion will continue Now the circuit board timer counts a determined amount of time and energizes the blower relay This relay powers up the blower motor and air is then pushed over the heat exchanger where it removes the heat from the hot metal and enters the ductwork to go to the various rooms in the house The limit control is a safety device that will open the electrical circuit to the ignition control and stop the gas flow if the furnace overheats The flame roll-out switch does the same thing if the flame was rolling out of the heat exchanger instead of being completely induced into it by the draft inducer

The blower creates a negative pressure on the intake side which draws air into the ductwork return air system and blows the air out through the heat exchanger and then into supply air ductwork to distribute throughout the home

Walking Hearth Mec h anism

An alternate method of transporting the ingots billets from the charging end of the furnace

to the discharging door point is by using a walking hearth furnace The furnace hearth has

alternately fixed and moving beams The fixed beams are part of the hearth at either

sidewall ends of the furnace and the moving beams are in between two fixed beams

Walking beam hearth furnaces have three fixed and two moving hearths or walking

beams A hydraulic system is provided to operate the walking beams through hydraulic

cylinders In the older designs there used to be a lifting and lowering cylinder which lifted

the beam through bell crank levers Once the beam reaches the top position all the ingots

billets that were resting on the fixed beams of the hearth get lifted up and now rest on the

moving beams when another hydraulic cylinder moves the beam forward by one stroke

which is normally around 700 - 1000mm all the ingots billets move forward by a

distance equal to one stroke of the forward backward cylinder The lifting lowering

cylinder now lowers the moving beam by a preset height through limit switches proximity

switches In the downward movement when the levels of the fixed and moving beam

tops are equal the ingots billets now rest on the fixed beams or the hearth at a new

point which is one cylinder stroke ahead of its previous position The moving beams

continue its downward movement ensuring that its top surface is well and truly

below the fixed beams It comes to rest at this position Now the forward backward

cylinder retracts the moving beams to their original position This completes one full cycle

of transportation In modern walking hearth furnaces the moving hearths are mounted on

rollers which ride up amp down a ramp actuated by hydraulic cylinders One hydraulic

cylinder performs the pulling up of the beam on the ramp and subsequently lowering it and

the other pulls pushes the beam forward backward as above The advantage of the ramp

system is that there are no linkages bell crank levers mounted on pivot bearings

which require extensive maintenance Each moving beam has a water seal at the

bottom to prevent the escape of flue gases into the cellar from in between the fixed amp

moving beams The Inside view of a typical WBWH Furnace is shown in Figure

Figure Inside ( c ellar) view of a Walk i ng Hearth Furnace

Since each of the billets is exposed on all four sides except the narrow strip resting on the

beams the heating is uniform and fast There is no danger of the ingots billets sticking to

each other the rate of heating can be high to reduce the residence time of the charge

inside the furnace thus reducing the burning scaling losses considerably For the same

length of the furnace the productivity of the hearth is much higher than for the

corresponding length of the pusher hearth furnace

Refractories The furnace also uses refractories for insulation purposes Any material can be

described as a lsquoRefractoryrsquo if it can withstand the action of abrasive or corrosive solids liquids or gases at high temperature The various combination of operating conditions in which refractories are used makes it necessary to manufacture a range of refractory materials with different properties Refractory materials are made in varying combinations and shapes depending on their application General requirement of refractory material are

They should withstand high temperature They should withstand sudden change of temperature They should withstand action of molten metal slag glass hot gases etc They should withstand load and abrasive forces at service condition They should conserve heat They should have low coefficient of thermal expansion They should not contaminate the material with which it comes into contact

Fire-clay refractories such as Fire bricks Siliceous-fireclays and aluminous clay refractories consists of aluminum silicates with varying Silica (SiO2) content up to 78 and Al2O3 content up to 44

High Alumina RefractoriesAlumina-silicate refractories containing more than 45 alumina are generally termed as high alumina materials The alumina concentration ranges from 45-100 The refractoriness of high alumina refractories increases with increase in alumina percentage The application of high alumina refractories include the hearth and shaft of blast furnaces ceramic kilns cement kilns glass tanks and crucibles for melting a wide range of materials

Insulating MaterialsInsulating materials greatly reduce the heat losses through wallsInsulation is achieved by providing a layer of materials with low heat conductivity between the internal hot surface and external surface thus keeping the temperature of the external surface low

Insulating materials can be classified into following groups- Insulating Bricks Insulating castables Ceramic fibers Calcium silicate Ceramic coatingThe characteristics of Ceramic fibers are remarkable combination of the properties of

refractories and traditional insulation material Lower thermal conductivity Light weight Lower heat storage Thermal shock resistance Chemical Resistance

Mechanical resilience Low Insulation cost Ease of maintenance Ease of handling Thermal Efficiency

High Emissivity coatingEmissivity (ie the measure of materialrsquos ability to both absorb and radiate heat) is often considered as an inherent physical property that does not normally change (Other examples are density specific heat and thermal conductivity) However the development of high emissivity coatings allows the surface emissivity of the material to be increased High emissivity coatings are applied on the interior surface of furnaces

Benefits of high emissivity coatings in furnace chambers are uniform heating and extended life of refractotries and metallic components such as radiant tubes and heating elements For intermittent furnaces or where rapid heating is required use of such coatings was found to reduce fuel or power by 25-45

Water cooling system in Walking Hearth FurnaceThe early design of WB Furnace used alloy steel Walking Beams that were exposed directly to the heat of the Furnace and were subjected to heat Corrosion so it operated at Maximum Temperature of about 1050 C compared with Re-heating Furnaces that must heat steel toTemperatures up to 1315 C Hence WB-Reheating Furnaces consist of water-cooled Steel members topped with refractors in such a manner that only the refractories are exposed directly to the heat of Furnace Alternatively the beams and supports may be constructed of water ndashcooled Tubular sections (with ldquobuttonsrdquo on the top surfaces to keep the Hot steel from direct ndashcontract with the water cooled tubes)

Heat recovery System

Recuperators(i) Recuperators (Waste Heat Recovery System) are placed in the path of the Flue Gasses of the Furnace between Furnace outlet and the chimney The combustion airgas is preheated in the recuperator through heat of the Flue gas and supplied to the Furance Burners in Pre-Heating Zone at about 400-5000C This results in savings of Heat Energy hence fuel(ii) Based on the material of Construction recuperators are two types

Metallic (Made of SS) Ceramic

(iii) Metallic recuperators have distinct advantages over Ceramic recuperators in terms of lower initial investment easier maintenance amp repair etc and are more popular in SRRM industryOn the other hand Ceramic recuperators have a longer life and can withstand much higher temperatures as compared to Metallic recuperators of about15000C vis-agrave-vis 11000C for metalrecuperators(iv) Based on the Design and method of Heat transfer the Recuperators are of two types

Tubular Convection Double Shell Radiation

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

the beam through bell crank levers Once the beam reaches the top position all the ingots

billets that were resting on the fixed beams of the hearth get lifted up and now rest on the

moving beams when another hydraulic cylinder moves the beam forward by one stroke

which is normally around 700 - 1000mm all the ingots billets move forward by a

distance equal to one stroke of the forward backward cylinder The lifting lowering

cylinder now lowers the moving beam by a preset height through limit switches proximity

switches In the downward movement when the levels of the fixed and moving beam

tops are equal the ingots billets now rest on the fixed beams or the hearth at a new

point which is one cylinder stroke ahead of its previous position The moving beams

continue its downward movement ensuring that its top surface is well and truly

below the fixed beams It comes to rest at this position Now the forward backward

cylinder retracts the moving beams to their original position This completes one full cycle

of transportation In modern walking hearth furnaces the moving hearths are mounted on

rollers which ride up amp down a ramp actuated by hydraulic cylinders One hydraulic

cylinder performs the pulling up of the beam on the ramp and subsequently lowering it and

the other pulls pushes the beam forward backward as above The advantage of the ramp

system is that there are no linkages bell crank levers mounted on pivot bearings

which require extensive maintenance Each moving beam has a water seal at the

bottom to prevent the escape of flue gases into the cellar from in between the fixed amp

moving beams The Inside view of a typical WBWH Furnace is shown in Figure

Figure Inside ( c ellar) view of a Walk i ng Hearth Furnace

Since each of the billets is exposed on all four sides except the narrow strip resting on the

beams the heating is uniform and fast There is no danger of the ingots billets sticking to

each other the rate of heating can be high to reduce the residence time of the charge

inside the furnace thus reducing the burning scaling losses considerably For the same

length of the furnace the productivity of the hearth is much higher than for the

corresponding length of the pusher hearth furnace

Refractories The furnace also uses refractories for insulation purposes Any material can be

described as a lsquoRefractoryrsquo if it can withstand the action of abrasive or corrosive solids liquids or gases at high temperature The various combination of operating conditions in which refractories are used makes it necessary to manufacture a range of refractory materials with different properties Refractory materials are made in varying combinations and shapes depending on their application General requirement of refractory material are

They should withstand high temperature They should withstand sudden change of temperature They should withstand action of molten metal slag glass hot gases etc They should withstand load and abrasive forces at service condition They should conserve heat They should have low coefficient of thermal expansion They should not contaminate the material with which it comes into contact

Fire-clay refractories such as Fire bricks Siliceous-fireclays and aluminous clay refractories consists of aluminum silicates with varying Silica (SiO2) content up to 78 and Al2O3 content up to 44

High Alumina RefractoriesAlumina-silicate refractories containing more than 45 alumina are generally termed as high alumina materials The alumina concentration ranges from 45-100 The refractoriness of high alumina refractories increases with increase in alumina percentage The application of high alumina refractories include the hearth and shaft of blast furnaces ceramic kilns cement kilns glass tanks and crucibles for melting a wide range of materials

Insulating MaterialsInsulating materials greatly reduce the heat losses through wallsInsulation is achieved by providing a layer of materials with low heat conductivity between the internal hot surface and external surface thus keeping the temperature of the external surface low

Insulating materials can be classified into following groups- Insulating Bricks Insulating castables Ceramic fibers Calcium silicate Ceramic coatingThe characteristics of Ceramic fibers are remarkable combination of the properties of

refractories and traditional insulation material Lower thermal conductivity Light weight Lower heat storage Thermal shock resistance Chemical Resistance

Mechanical resilience Low Insulation cost Ease of maintenance Ease of handling Thermal Efficiency

High Emissivity coatingEmissivity (ie the measure of materialrsquos ability to both absorb and radiate heat) is often considered as an inherent physical property that does not normally change (Other examples are density specific heat and thermal conductivity) However the development of high emissivity coatings allows the surface emissivity of the material to be increased High emissivity coatings are applied on the interior surface of furnaces

Benefits of high emissivity coatings in furnace chambers are uniform heating and extended life of refractotries and metallic components such as radiant tubes and heating elements For intermittent furnaces or where rapid heating is required use of such coatings was found to reduce fuel or power by 25-45

Water cooling system in Walking Hearth FurnaceThe early design of WB Furnace used alloy steel Walking Beams that were exposed directly to the heat of the Furnace and were subjected to heat Corrosion so it operated at Maximum Temperature of about 1050 C compared with Re-heating Furnaces that must heat steel toTemperatures up to 1315 C Hence WB-Reheating Furnaces consist of water-cooled Steel members topped with refractors in such a manner that only the refractories are exposed directly to the heat of Furnace Alternatively the beams and supports may be constructed of water ndashcooled Tubular sections (with ldquobuttonsrdquo on the top surfaces to keep the Hot steel from direct ndashcontract with the water cooled tubes)

Heat recovery System

Recuperators(i) Recuperators (Waste Heat Recovery System) are placed in the path of the Flue Gasses of the Furnace between Furnace outlet and the chimney The combustion airgas is preheated in the recuperator through heat of the Flue gas and supplied to the Furance Burners in Pre-Heating Zone at about 400-5000C This results in savings of Heat Energy hence fuel(ii) Based on the material of Construction recuperators are two types

Metallic (Made of SS) Ceramic

(iii) Metallic recuperators have distinct advantages over Ceramic recuperators in terms of lower initial investment easier maintenance amp repair etc and are more popular in SRRM industryOn the other hand Ceramic recuperators have a longer life and can withstand much higher temperatures as compared to Metallic recuperators of about15000C vis-agrave-vis 11000C for metalrecuperators(iv) Based on the Design and method of Heat transfer the Recuperators are of two types

Tubular Convection Double Shell Radiation

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

beams the heating is uniform and fast There is no danger of the ingots billets sticking to

each other the rate of heating can be high to reduce the residence time of the charge

inside the furnace thus reducing the burning scaling losses considerably For the same

length of the furnace the productivity of the hearth is much higher than for the

corresponding length of the pusher hearth furnace

Refractories The furnace also uses refractories for insulation purposes Any material can be

described as a lsquoRefractoryrsquo if it can withstand the action of abrasive or corrosive solids liquids or gases at high temperature The various combination of operating conditions in which refractories are used makes it necessary to manufacture a range of refractory materials with different properties Refractory materials are made in varying combinations and shapes depending on their application General requirement of refractory material are

They should withstand high temperature They should withstand sudden change of temperature They should withstand action of molten metal slag glass hot gases etc They should withstand load and abrasive forces at service condition They should conserve heat They should have low coefficient of thermal expansion They should not contaminate the material with which it comes into contact

Fire-clay refractories such as Fire bricks Siliceous-fireclays and aluminous clay refractories consists of aluminum silicates with varying Silica (SiO2) content up to 78 and Al2O3 content up to 44

High Alumina RefractoriesAlumina-silicate refractories containing more than 45 alumina are generally termed as high alumina materials The alumina concentration ranges from 45-100 The refractoriness of high alumina refractories increases with increase in alumina percentage The application of high alumina refractories include the hearth and shaft of blast furnaces ceramic kilns cement kilns glass tanks and crucibles for melting a wide range of materials

Insulating MaterialsInsulating materials greatly reduce the heat losses through wallsInsulation is achieved by providing a layer of materials with low heat conductivity between the internal hot surface and external surface thus keeping the temperature of the external surface low

Insulating materials can be classified into following groups- Insulating Bricks Insulating castables Ceramic fibers Calcium silicate Ceramic coatingThe characteristics of Ceramic fibers are remarkable combination of the properties of

refractories and traditional insulation material Lower thermal conductivity Light weight Lower heat storage Thermal shock resistance Chemical Resistance

Mechanical resilience Low Insulation cost Ease of maintenance Ease of handling Thermal Efficiency

High Emissivity coatingEmissivity (ie the measure of materialrsquos ability to both absorb and radiate heat) is often considered as an inherent physical property that does not normally change (Other examples are density specific heat and thermal conductivity) However the development of high emissivity coatings allows the surface emissivity of the material to be increased High emissivity coatings are applied on the interior surface of furnaces

Benefits of high emissivity coatings in furnace chambers are uniform heating and extended life of refractotries and metallic components such as radiant tubes and heating elements For intermittent furnaces or where rapid heating is required use of such coatings was found to reduce fuel or power by 25-45

Water cooling system in Walking Hearth FurnaceThe early design of WB Furnace used alloy steel Walking Beams that were exposed directly to the heat of the Furnace and were subjected to heat Corrosion so it operated at Maximum Temperature of about 1050 C compared with Re-heating Furnaces that must heat steel toTemperatures up to 1315 C Hence WB-Reheating Furnaces consist of water-cooled Steel members topped with refractors in such a manner that only the refractories are exposed directly to the heat of Furnace Alternatively the beams and supports may be constructed of water ndashcooled Tubular sections (with ldquobuttonsrdquo on the top surfaces to keep the Hot steel from direct ndashcontract with the water cooled tubes)

Heat recovery System

Recuperators(i) Recuperators (Waste Heat Recovery System) are placed in the path of the Flue Gasses of the Furnace between Furnace outlet and the chimney The combustion airgas is preheated in the recuperator through heat of the Flue gas and supplied to the Furance Burners in Pre-Heating Zone at about 400-5000C This results in savings of Heat Energy hence fuel(ii) Based on the material of Construction recuperators are two types

Metallic (Made of SS) Ceramic

(iii) Metallic recuperators have distinct advantages over Ceramic recuperators in terms of lower initial investment easier maintenance amp repair etc and are more popular in SRRM industryOn the other hand Ceramic recuperators have a longer life and can withstand much higher temperatures as compared to Metallic recuperators of about15000C vis-agrave-vis 11000C for metalrecuperators(iv) Based on the Design and method of Heat transfer the Recuperators are of two types

Tubular Convection Double Shell Radiation

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

Refractories The furnace also uses refractories for insulation purposes Any material can be

described as a lsquoRefractoryrsquo if it can withstand the action of abrasive or corrosive solids liquids or gases at high temperature The various combination of operating conditions in which refractories are used makes it necessary to manufacture a range of refractory materials with different properties Refractory materials are made in varying combinations and shapes depending on their application General requirement of refractory material are

They should withstand high temperature They should withstand sudden change of temperature They should withstand action of molten metal slag glass hot gases etc They should withstand load and abrasive forces at service condition They should conserve heat They should have low coefficient of thermal expansion They should not contaminate the material with which it comes into contact

Fire-clay refractories such as Fire bricks Siliceous-fireclays and aluminous clay refractories consists of aluminum silicates with varying Silica (SiO2) content up to 78 and Al2O3 content up to 44

High Alumina RefractoriesAlumina-silicate refractories containing more than 45 alumina are generally termed as high alumina materials The alumina concentration ranges from 45-100 The refractoriness of high alumina refractories increases with increase in alumina percentage The application of high alumina refractories include the hearth and shaft of blast furnaces ceramic kilns cement kilns glass tanks and crucibles for melting a wide range of materials

Insulating MaterialsInsulating materials greatly reduce the heat losses through wallsInsulation is achieved by providing a layer of materials with low heat conductivity between the internal hot surface and external surface thus keeping the temperature of the external surface low

Insulating materials can be classified into following groups- Insulating Bricks Insulating castables Ceramic fibers Calcium silicate Ceramic coatingThe characteristics of Ceramic fibers are remarkable combination of the properties of

refractories and traditional insulation material Lower thermal conductivity Light weight Lower heat storage Thermal shock resistance Chemical Resistance

Mechanical resilience Low Insulation cost Ease of maintenance Ease of handling Thermal Efficiency

High Emissivity coatingEmissivity (ie the measure of materialrsquos ability to both absorb and radiate heat) is often considered as an inherent physical property that does not normally change (Other examples are density specific heat and thermal conductivity) However the development of high emissivity coatings allows the surface emissivity of the material to be increased High emissivity coatings are applied on the interior surface of furnaces

Benefits of high emissivity coatings in furnace chambers are uniform heating and extended life of refractotries and metallic components such as radiant tubes and heating elements For intermittent furnaces or where rapid heating is required use of such coatings was found to reduce fuel or power by 25-45

Water cooling system in Walking Hearth FurnaceThe early design of WB Furnace used alloy steel Walking Beams that were exposed directly to the heat of the Furnace and were subjected to heat Corrosion so it operated at Maximum Temperature of about 1050 C compared with Re-heating Furnaces that must heat steel toTemperatures up to 1315 C Hence WB-Reheating Furnaces consist of water-cooled Steel members topped with refractors in such a manner that only the refractories are exposed directly to the heat of Furnace Alternatively the beams and supports may be constructed of water ndashcooled Tubular sections (with ldquobuttonsrdquo on the top surfaces to keep the Hot steel from direct ndashcontract with the water cooled tubes)

Heat recovery System

Recuperators(i) Recuperators (Waste Heat Recovery System) are placed in the path of the Flue Gasses of the Furnace between Furnace outlet and the chimney The combustion airgas is preheated in the recuperator through heat of the Flue gas and supplied to the Furance Burners in Pre-Heating Zone at about 400-5000C This results in savings of Heat Energy hence fuel(ii) Based on the material of Construction recuperators are two types

Metallic (Made of SS) Ceramic

(iii) Metallic recuperators have distinct advantages over Ceramic recuperators in terms of lower initial investment easier maintenance amp repair etc and are more popular in SRRM industryOn the other hand Ceramic recuperators have a longer life and can withstand much higher temperatures as compared to Metallic recuperators of about15000C vis-agrave-vis 11000C for metalrecuperators(iv) Based on the Design and method of Heat transfer the Recuperators are of two types

Tubular Convection Double Shell Radiation

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

Mechanical resilience Low Insulation cost Ease of maintenance Ease of handling Thermal Efficiency

High Emissivity coatingEmissivity (ie the measure of materialrsquos ability to both absorb and radiate heat) is often considered as an inherent physical property that does not normally change (Other examples are density specific heat and thermal conductivity) However the development of high emissivity coatings allows the surface emissivity of the material to be increased High emissivity coatings are applied on the interior surface of furnaces

Benefits of high emissivity coatings in furnace chambers are uniform heating and extended life of refractotries and metallic components such as radiant tubes and heating elements For intermittent furnaces or where rapid heating is required use of such coatings was found to reduce fuel or power by 25-45

Water cooling system in Walking Hearth FurnaceThe early design of WB Furnace used alloy steel Walking Beams that were exposed directly to the heat of the Furnace and were subjected to heat Corrosion so it operated at Maximum Temperature of about 1050 C compared with Re-heating Furnaces that must heat steel toTemperatures up to 1315 C Hence WB-Reheating Furnaces consist of water-cooled Steel members topped with refractors in such a manner that only the refractories are exposed directly to the heat of Furnace Alternatively the beams and supports may be constructed of water ndashcooled Tubular sections (with ldquobuttonsrdquo on the top surfaces to keep the Hot steel from direct ndashcontract with the water cooled tubes)

Heat recovery System

Recuperators(i) Recuperators (Waste Heat Recovery System) are placed in the path of the Flue Gasses of the Furnace between Furnace outlet and the chimney The combustion airgas is preheated in the recuperator through heat of the Flue gas and supplied to the Furance Burners in Pre-Heating Zone at about 400-5000C This results in savings of Heat Energy hence fuel(ii) Based on the material of Construction recuperators are two types

Metallic (Made of SS) Ceramic

(iii) Metallic recuperators have distinct advantages over Ceramic recuperators in terms of lower initial investment easier maintenance amp repair etc and are more popular in SRRM industryOn the other hand Ceramic recuperators have a longer life and can withstand much higher temperatures as compared to Metallic recuperators of about15000C vis-agrave-vis 11000C for metalrecuperators(iv) Based on the Design and method of Heat transfer the Recuperators are of two types

Tubular Convection Double Shell Radiation

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

(v) In the SRRM industry Tubular Convection type Metallic recuperator (Shell amp Tube Type) is more prevalent and described below a) The hot Flue gases are carried through a number of parallel small diameter tubes while the incoming air to be heated enters a shell surrounding the tubes and passes over the hottubes one or more times in a direction normal to their axis

b) If the tubes are baffled to allow the gas to pass over them twice the heat exchanger is termed a two-pass recuperator if two baffles are used a three-pass recuperator etc

c) Although baffling increases both the cost of the exchanger and the pressure drop in the combustion air path it increases the effectiveness of heat exchanged) Shell and tube type recuperators are generally more compact and have a higher effectiveness than radiation recuperators because of the larger heat transfer area made possible throughthe use of multiple tubes and multiple passes of the gases e) The tubes on the inlet side of the flue gases are made of either stainless steel or heat resistant Ni cast steel to withstand the prevailing high temperatures A typical Double Stage Cross Flow type Recuperator is illustrated as below

Furnace Oil

A dark viscous residual fuel obtained by blending mainly heavier components from crude distillation unit short residue and clarified oil from fluidized catalytic cracker unit os called as Furnace Oil

Furnace Oil is one of the cheapest fuels available for industrial use It is a by-product of petroleum refineries While processing the CRUD Oil FO (Furnace Oil) is one of the products along with other petroleum fuels like HSD Petrol etc In India it is sold under BIS specification IS 1593-1982

Technical Specification Table Requirements for fuel oils

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

S No

Characteristic Requirement For Method of Test

Grade

LV Grade MVI

Grade MV2

Grade HV

Ref to [P ] ofIS 1448

1 2 3 4 5 6 7

Acidity inorganic Nil P 2

Ash percent by mass Max

01P 4

(Method A)

Gross calorific value Not limited but to be reportedP 6

(for reference)P (for routine)

Relative density at 1515oC

Not limited but to be reported

Flash point [Pensky martens (closed)] Min

66oC P 21

Kinematic viscosity in centistokes at 50oC Max

80 125 180 370 P 25

Sediment percent by mass Max

025 P 30

Sulphur total percent

by mass Max35 4 4 45

P 33(for reference)

and P 35(for routine)

Water content percent by volume Max

1 P 40

Typically it has a calorific value as 10000 calgm The furnaces which are used mainly for heating or pre-heating a large quantity of metal are the main users of FO This can be stored in vertical as well as horizontal tanks above ground or even underground in some cases The dimensions and capacities of these tanks are predefined in India by CCOE which is the regulating body for fuel storages

For direct burning FO is viscous as well as not suitable for complete combustion It is pre-heated to 55 degrees Celsius onwards depending upon application The flow increases with temperature and it improves the combustion also A water based scrubber is used in the exhaust chimney of furnace which arrests considerable amount of carbon suite and improves the emissions

The entire FO yard as per IS standards pre-heating in storage tanks as well as pipesamp Pumps etc pumping station level controls control-panels and entire distribution pipeline is designed taking into consideration the application required capacity of storage logistics available space and government norms

Properties Of Furnace Oil

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

1) ViscosityViscosity is the most important characteristic in the furnace oil specification It

influences the degree of pre-heat required for handling storage and satisfactory atomization If the oil is too viscous it may become difficult to pump burner may be hard to light and operation may be erratic Poor atomization may result in the carbon deposits on the burner tips or on the walls

2) Flash PointAs per the Controller of Explosives classification Furnace oil falls in the class C category with minimum flash point standard of 66 deg C Since Penskey Martens Closed Cup method is used it is apparent that a small quantity of low boiling point hydrocarbons is sufficient to lower the flash point drastically

3) Pour PointIt is a very rough indication of the lowest temperature at which Furnace Oil is

readily pumpable In the specification the pour point of Furnace oil is not stipulated However for Furnace oil manufactured indigenously and for imported parcels the pour point is such that current supplies normally can be handled without heating the fuel oil handling installation

4) WaterWater may be present in free or emulsified form and can on combustion cause

damage to the inside furnace surfaces especially if it contains dissolved salts It can also cause sputtering of the flame at the burner tip Water content of furnace oil when supplied is normally very low as the product at refinery site is handled hot and maximum limit of 1 is specified in the standard

5) SedimentFurnace oil being a blend of residues contains some quantity of sediments These

have adverse effect on the burners and cause blockage of filters etc However the typical values are normally much lower than the stipulated value of maximum 025 percent by mass

6) AshAsh is incombustible component of the furnace oil and is expressed as a percentage

mass of the furnace oil sample Ash consists of extraneous solids residues of organometallic compounds in solution and salts dissolved in water present in the fuel These salts may be compounds of sodium vanadium calcium magnesium silicon iron etcAsh has erosive effect on the burner tips causes damage to the refractories at high temperatures and gives rise to high temperature corrosion and fouling of equipment

7) SulphurSulphur determination includes burning of known quantity of oil treating the

sulphur oxidation products formed during combustion and weighing of sulphur in the form of sulphateThe sulphur di-oxide may come in direct contact with the product during the combustion process and may create adverse quality effects in the product

8) Calorific Value

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

Calorific value of a fuel is the quantity of heat generated in kilocalories by complete burning of one

kilogram weight of fuel Gross calorific value is higher than net calorific value to the extent of heat

required to change water formed by combustion into water vapours

Billet Furnace Reheating

Once the billets are charged into the furnace they are gradually heated to the range of 1050 oC to

1150 oC while passing slowly from different zones of the furnace There are mainly three zones of

the furnace viz-a viz

Pre-heating Zone- Temperature range 0-300 oC

Heating Zone- Temperature range 300-900 oC

Soaking Zone- Temperature range 900-1150 oC

Time required for heating the billet to desired temperature was around 2 Hours at averageWhile

heating the billets are progressively pushed in the downwards direction Due to the inclined base of

the furnace they move slowly downwards

Temperature Regime

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

a)Pre-heating Zone

For every 22 0C preheating of combustion air there is 1 saving in fuel consumption By

preheating the air for combustion inside the furnace to 450- 5000C it is not necessary to utilize

the fuel to heat firstly the huge quantity of air from ambient to 450- 5000 C before

raising the temperature of the furnace to the desired set temperature in the heating soaking

zone This hot air also reduces the quenching effect of injecting cold air into the hot furnace

and betters the combustion efficiency and finally it helps to achieve a higher flame temperature

which increases the rate of transfer of heat to the furnace atmosphere and subsequent transfer of

this heat to the ingotbillet The net effect of higher hot air temperature is a

huge reduction in specific fuel consumption by 5- 20 (depending on the

temperature of hot air at the burners) results in longer life of refractories quicker heating of the

ingot billet With the reduction in the residence time of the ingot billet inside the furnace the

losses due to scale formation is also greatly reduced The same advantages cannot be obtained

by having longer furnaces and allowing the flue gases to preheat the ingots billets at the

charging or preheating zone The apparent heat losses due to flue gases exiting at the

high temperature of 750 -8500 C will be totally offset by installation of high efficiency

recuperator to allow an exit temperature to the chimney at the same or less temperature

earlier being sent ie 180- 2200 C

b) Heating Zo ne amp Soaki ng Zone

The temperature at the heating zone is maintained at 1050- 11000C and the soaking zone

temperature or temperature of the ingotbillet at discharge is maintained at 10-200C below

the heating zone temperature A properly soaked ingotbillet at 10500C is easier to roll

than an ingot billet heated to 11500C without soaking The sign of improper soaking is the

bow shape of the bar exiting the 1st roll pass in the roughing mill This is because of the

non-uniformity in temperature between top and bottom of the ingotbillet If the temperature at

the top of the ingot is higher than the bottom then the top is more plastic than the bottom and

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

deforms greater than the bottom causing increase in length at top more than at bottom

resulting in a bow shape If the bow is high then there would be difficulty in entry of the bar

into the succeeding pass In wall tilters such a bar could get stuck between two walls

Approximately 70 of the heating is completed at the heating zone The general practice

in most SRRM is to use the furnace as a single long heating zone from charging to discharge

with a single temperature gradient This is a wrong practice For smooth trouble free rolling it

is necessary to properly soak the ingots billets to achieve a temperature differential of

not more than 200 C from top to bottom of the ingot billet It takes 13 minutes for

the temperature at the centre to attain the temperature at the top of the billet ingot for

100mm cross-section Higher cross-sections will take longer So if the travel from the heating

zone to the discharge end takes less than 15 minutes then the temperature to be maintained

at the heating zone should be correspondingly higher than 100C mentioned earlier

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

What temperature should the billet is reheated up to

Hot rolling is a metalworking process that occurs above the recrystallization temperature

of the material After the grains deform during processing they recrystallize which maintains

an equiaxed microstructure and prevents the metal from work hardening The starting material is

usually large pieces of metal like semi-finished casting products such as slabs blooms and

billets If these products came from a continuous casting operation the products are usually fed

directly into the rolling mills at the proper temperature In smaller operations the material starts

at room temperature and must be heated This is done in a gas- or oil-fired soaking pit for larger

workpieces and for smaller workpieces induction heating is used As the material is worked the

temperature must be monitored to make sure it remains above the recrystallization temperature

To maintain a safety factor a finishing temperature is defined above the recrystallization

temperature this is usually 50 to 100 degC (122 to 212 degF) above the recrystallization temperature

If the temperature does drop below this temperature the material must be re-heated before more

hot rolling

Hot rolled metals generally have little directionality in their mechanical properties and

deformation induced residual stresses However in certain instances non-metallic inclusions will

impart some directionality and workpieces less than 20 mm (079 in) thick often have some

directional properties Also non-uniformed cooling will induce a lot of residual stresses which

usually occurs in shapes that have a non-uniform cross-section such as I-beams and H-beams

While the finished product is of good quality the surface is covered in mill scale which is

an oxide that forms at high-temperatures It is usually removed via pickling or the smooth clean

surface process which reveals a smooth surface Dimensional tolerances are usually 2 to 5 of

the overall dimension

How is billet temperature measured

Billet temperatures are measured by using a data collection device mounted on a billet as

shown in Fig 1 Total of 20 points are selected for measurement by using TC (thermocouples) as

shown in Fig 2 The data collection device is put into a water jacket filled with water This water

jacket is covered with heatprotective material to minimize exposure to heat radiation When the

test billet is discharged from the furnace the data collection device is removed and the stored

data are transferred to a PC using a serial cable This measurement is carried out for the

following two extremely different furnace operation patterns

1 CCR (Cold Charge Rolling) pattern An operation pattern when the billet with a normal

temperatureis charged

2 WCR (Warm Charge Rolling) pattern An operation pattern when the billet with high

initialtemperature is charged

(a) Measurement positions for CCR pattern

(b) Measurement positions for CCR pattern

In general the furnace temperature set value of soaking zones is fixed to satisfy the required rollingtemperature of the billet Therefore the billet temperature can be controlled by controlling thetemperature set value of preheating zone and heating zone Since the discharging billet temperature is Sensitive to the variation of furnace temperature set value of heating zone

the variation range of the furnace temperature of heating zone is smaller than that of the preheating zone In practice the billet temperature pattern is controlled by controlling the furnace temperature of preheating zone The different furnace temperature set value of preheating zone is the main difference of the above CCR and WCR pattern It is observed that the measured temperatures have several characteristics as follows1 The ambient temperature of the billet top side along the track is not uniform at the same zone

(TC11) 2 The ambient temperature of the billet at a furnace center side is higher than the ambient

temperature at furnace wall sides (TC131118 and 20 ) 3 The ambient temperature of the billet right side (TC16 ) is higher than the temperature of the

billet left side (TC19 ) The temperature difference between them decreases as the billet is transported through the furnace Finally TC1116 and 19 have similar values at the soaking zones

4 Also the billet core temperature (ieTC246813 15 and 17 ) at the furnace center side is higher than that of the the core temperature at the furnace wall side

For example (TC2 minusTC17 ) is about 601048644C when the billet is discharged Since the part of the billet which is on the skid buttonis called the skid part measurement points within the billet can be classified into skid and non skid partsThe temperatures of the skid and non-skid parts are measured by using TC installed in holes that

goes into 10 50 and 90 along the billet thickness direction as shown in Fig 2 (ie TC78

and 9 for nonskid part and TC1213 and 14 for skid part) Since the billet temperature of skid

part is lower than that of the non-skid part the billet temperature of skid part should be greater

than the required target temperature Therefore only the temperature profiles of skid part will be

used for billet heat transfer modeling in the Next section

Standard Operating Practices for major Mechanical equipment of RHF

IngotBillet charging or collection bed

1 The counted and weighed ingots billets (using weighing Balance) are received by the Furnace Operator and loaded on to the charging table by MobileEOT Crane

2 If ingots are charged the taper end is alternately placed so that two consecutive ingots form a rectangle This is to prevent the ingots from sloping to one side during pushing in the furnace

3 The ingots are brought in front of the pusher head either manually or through the roller table in groups of 7-10nos and the pusher mechanism is operated to push these ingots billets into the furnace

4 The collection bed is made of rails of 60mm square billets laid length wise at 200mm spacing between rails

5 If it is mechanized check the chain drives and lubricate as required using grease6 Tools used Endless chain slings tongs

Pusher Mechanism

1 Thestrokeofthepusherissetatapproximately700-1000mmor7to 10 ingotbillet thicknesses This is approximately 700 -1000 kgs for single row charging and 1400 -2000 kgs for double row charging

2 The stroke is adjusted by means of two limit switches which are set for extreme forward position and extreme backward position of the pusher head by the operator

3 The ingots are placed in front of the pusher in the form of a rectangle by alternating the taper by the operator

4 For best operating practice in charging the ingots billets are chargedleavingagapof150mmbetweeningotbillet and side walls in case of single row charging and additionally a gap of 150mm between the left side rows and right side rows of ingots billets in case of two row charging

5 In order to ensure sweeping of ashsolid deposits on the hearth it is advisable to stagger the ingots billets to cover as much width of the hearth as possible over five to six lines of ingotsbillets at a time

6 Prior to the running of the pusher for operational purpose It is necessary that the following actions are taken by the operator

7 For Screw amp Nut Type Pusher

bull Clean the screw of all foreign particles scale etcbull Apply grease with a brush grade EP-3 lithium base mixed with 1 molybdenum di-

sulphide on Screw thread and nut for lubrication at high temperaturesbull Check oil leveling ear box using the dipstick gauge provided and top up if necessary

For Hydraulic Cylinder with Hydraulic Power Packbull Check oil level in tank clean filters once a weekbull Arrange the alternate ingots with its taper opposite to the previous ingot This is to

prevent piling up of ingots inside the furnacebull Wait for the ejector operatorrsquos signal before pushing any ingot into the furnacebull Check that the correct Heat No ingots billets are charged into the furnacebull Keep a count on the ingots billets charged

Ejector

1 The ejector is operated by an operator who is seated either on a seat mounted on the ejector trolley or by the side of it with a good view of the hot ingots on the furnace hearth He not only operates the ejector but also signals through a bell to the pusher operator to push the ingots by one stroke into the emptied space

2 Ifthepusherisoperatedhydraulicallythesamehydraulicsystemisconnected to the pinch roll and trolley movement drives instead of electric motors The valves for operating the drives are mounted on the operator desk Other operations remain the same as before

3 Ejector positioned by operator in line with the last ingot on the furnace hearth4 Eject or operates the pinch roll gear box to move the ejector in and out of the furnace

pushing out a single ingot into the extractor rotating table5 Operator checks sufficiency of cooling water6 Operator wears blue goggles to protect his eyes from the heat glare7 Operator signals to pusher operator to push ingots

8 Operator gets the signal to push from the Mill operator through a blinking light or bell9 Operator checks oil level in the trolley and pinch roll gearboxes at beginning of shift or if

drives are through hydraulic motors he checks the oil level in the hydraulic tank if this duty is assigned to him instead of the pusher operator

Extraction of Hot-IngotsBillets amp loading on Roller Table

1 In many furnaces a motorized extractor is provided where only billets are charged This is just a pair of pinch rolls which is driven either through gear box or hydraulic motor arrangement similar to the ejector pinch rolls But in most furnaces the ejector pushes the ingot on to a rotating table

2 In single row charged furnaces the extraction is mostly done manually by the workmen at the discharge door by using a long steel hook In this case there is no ejector

3 The work men at this location clean the hearth of scale and ash regularly throughout the shift to prevent the ingot from getting stuck or gets piled The cleaning is done using long scrapers

Door Operating Mechanism

Two doors viz ejector door and discharge door are operated from the ejector operatorrsquos desk for pneumatically operated doors and by the workmen who are at the discharge door end by operating the hand winchcounter weighted levers for manual operation Each time the ejector has to be operated first the above two doors are opened The ingotbillet is ejected from the furnace The doors are then closed This is repeated after each ejection of ingot billet Since the operation is very frequent it is advisable to automate the opening and closing by providing pneumatic cylinders The Door Operating Hand-winch is illustrated at Figure

Fig2 Door operating hand-winch

Heat losses affecting furnace performance

Ideally all heat added to the furnace should be used to heat the load or the stock In practice

however a lot of heat is lost in several ways as shown in figure

Heat losses in a Furnace

Flue gas losses

Loss from moisture in fuel fuel usually consist some moisture and some heat is utilized to

evaporate this moisture inside the furnace

Loss due to hydrogen in fuel which results in formation of water

Loss through openings in furnace radiation loss occurs when there are openings in the furnace

and theses losses can be significant especially for those furnaces which are operating above the

temperature of 540 oC A second loss is through air infiltration because the drat of stackchimney

causes negative pressure inside the furnace drawing in air trough leaks or cracks or whenever

the furnace doors are opened

Furnace skinsurface losses also called wall losses while temperature inside the furnace are

high heat is conducted through the roof floor and walls and emitted to the ambient air once it

reaches the furnace skin or surface

Other losses there are several other ways in which heat is lost from a furnace Although

quantifying all of them is difficult Some of them can be included

Stored heat losses when When the furnace is started the furnace structure and insulation also

heat up and this heat only leaves when the furnace are shut down again Thus these type of losses

increase with the number of times the furnace is turned off and on

Material Handling Losses The equipment used to move the stock through the furnace such as

conveyor belts walking beams bogies etc also absorb heat Every time equipment leave the

furnace they lose their heat Therefore this loss increases with the number of equipments and the

frequency by which they enter and exit the furnace

Cooling media losses water is used to cool down rolls bearings and other equipments But this

water also absorbs heat away with it

Incomplete combustion losses Heat is lost if combustion is incomplete because unburnt fuel or

particles have absorbed heat but this heat has not been brought to use

Loss due to formation of scales

• Modern furnace components

the variation range of the furnace temperature of heating zone is smaller than that of the preheating zone In practice the billet temperature pattern is controlled by controlling the furnace temperature of preheating zone The different furnace temperature set value of preheating zone is the main difference of the above CCR and WCR pattern It is observed that the measured temperatures have several characteristics as follows1 The ambient temperature of the billet top side along the track is not uniform at the same zone

(TC11) 2 The ambient temperature of the billet at a furnace center side is higher than the ambient

temperature at furnace wall sides (TC131118 and 20 ) 3 The ambient temperature of the billet right side (TC16 ) is higher than the temperature of the

billet left side (TC19 ) The temperature difference between them decreases as the billet is transported through the furnace Finally TC1116 and 19 have similar values at the soaking zones

4 Also the billet core temperature (ieTC246813 15 and 17 ) at the furnace center side is higher than that of the the core temperature at the furnace wall side

For example (TC2 minusTC17 ) is about 601048644C when the billet is discharged Since the part of the billet which is on the skid buttonis called the skid part measurement points within the billet can be classified into skid and non skid partsThe temperatures of the skid and non-skid parts are measured by using TC installed in holes that

goes into 10 50 and 90 along the billet thickness direction as shown in Fig 2 (ie TC78

and 9 for nonskid part and TC1213 and 14 for skid part) Since the billet temperature of skid

part is lower than that of the non-skid part the billet temperature of skid part should be greater

than the required target temperature Therefore only the temperature profiles of skid part will be

used for billet heat transfer modeling in the Next section

Standard Operating Practices for major Mechanical equipment of RHF

IngotBillet charging or collection bed

1 The counted and weighed ingots billets (using weighing Balance) are received by the Furnace Operator and loaded on to the charging table by MobileEOT Crane

2 If ingots are charged the taper end is alternately placed so that two consecutive ingots form a rectangle This is to prevent the ingots from sloping to one side during pushing in the furnace

3 The ingots are brought in front of the pusher head either manually or through the roller table in groups of 7-10nos and the pusher mechanism is operated to push these ingots billets into the furnace

4 The collection bed is made of rails of 60mm square billets laid length wise at 200mm spacing between rails

5 If it is mechanized check the chain drives and lubricate as required using grease6 Tools used Endless chain slings tongs

Pusher Mechanism

1 Thestrokeofthepusherissetatapproximately700-1000mmor7to 10 ingotbillet thicknesses This is approximately 700 -1000 kgs for single row charging and 1400 -2000 kgs for double row charging

2 The stroke is adjusted by means of two limit switches which are set for extreme forward position and extreme backward position of the pusher head by the operator

3 The ingots are placed in front of the pusher in the form of a rectangle by alternating the taper by the operator

4 For best operating practice in charging the ingots billets are chargedleavingagapof150mmbetweeningotbillet and side walls in case of single row charging and additionally a gap of 150mm between the left side rows and right side rows of ingots billets in case of two row charging

5 In order to ensure sweeping of ashsolid deposits on the hearth it is advisable to stagger the ingots billets to cover as much width of the hearth as possible over five to six lines of ingotsbillets at a time

6 Prior to the running of the pusher for operational purpose It is necessary that the following actions are taken by the operator

7 For Screw amp Nut Type Pusher

bull Clean the screw of all foreign particles scale etcbull Apply grease with a brush grade EP-3 lithium base mixed with 1 molybdenum di-

sulphide on Screw thread and nut for lubrication at high temperaturesbull Check oil leveling ear box using the dipstick gauge provided and top up if necessary

For Hydraulic Cylinder with Hydraulic Power Packbull Check oil level in tank clean filters once a weekbull Arrange the alternate ingots with its taper opposite to the previous ingot This is to

prevent piling up of ingots inside the furnacebull Wait for the ejector operatorrsquos signal before pushing any ingot into the furnacebull Check that the correct Heat No ingots billets are charged into the furnacebull Keep a count on the ingots billets charged

Ejector

1 The ejector is operated by an operator who is seated either on a seat mounted on the ejector trolley or by the side of it with a good view of the hot ingots on the furnace hearth He not only operates the ejector but also signals through a bell to the pusher operator to push the ingots by one stroke into the emptied space

2 Ifthepusherisoperatedhydraulicallythesamehydraulicsystemisconnected to the pinch roll and trolley movement drives instead of electric motors The valves for operating the drives are mounted on the operator desk Other operations remain the same as before

3 Ejector positioned by operator in line with the last ingot on the furnace hearth4 Eject or operates the pinch roll gear box to move the ejector in and out of the furnace

pushing out a single ingot into the extractor rotating table5 Operator checks sufficiency of cooling water6 Operator wears blue goggles to protect his eyes from the heat glare7 Operator signals to pusher operator to push ingots

8 Operator gets the signal to push from the Mill operator through a blinking light or bell9 Operator checks oil level in the trolley and pinch roll gearboxes at beginning of shift or if

drives are through hydraulic motors he checks the oil level in the hydraulic tank if this duty is assigned to him instead of the pusher operator

Extraction of Hot-IngotsBillets amp loading on Roller Table

1 In many furnaces a motorized extractor is provided where only billets are charged This is just a pair of pinch rolls which is driven either through gear box or hydraulic motor arrangement similar to the ejector pinch rolls But in most furnaces the ejector pushes the ingot on to a rotating table

2 In single row charged furnaces the extraction is mostly done manually by the workmen at the discharge door by using a long steel hook In this case there is no ejector

3 The work men at this location clean the hearth of scale and ash regularly throughout the shift to prevent the ingot from getting stuck or gets piled The cleaning is done using long scrapers

Door Operating Mechanism

Two doors viz ejector door and discharge door are operated from the ejector operatorrsquos desk for pneumatically operated doors and by the workmen who are at the discharge door end by operating the hand winchcounter weighted levers for manual operation Each time the ejector has to be operated first the above two doors are opened The ingotbillet is ejected from the furnace The doors are then closed This is repeated after each ejection of ingot billet Since the operation is very frequent it is advisable to automate the opening and closing by providing pneumatic cylinders The Door Operating Hand-winch is illustrated at Figure

Fig2 Door operating hand-winch

Heat losses affecting furnace performance

Ideally all heat added to the furnace should be used to heat the load or the stock In practice

however a lot of heat is lost in several ways as shown in figure

Heat losses in a Furnace

Flue gas losses

Loss from moisture in fuel fuel usually consist some moisture and some heat is utilized to

evaporate this moisture inside the furnace

Loss due to hydrogen in fuel which results in formation of water

Loss through openings in furnace radiation loss occurs when there are openings in the furnace

and theses losses can be significant especially for those furnaces which are operating above the

temperature of 540 oC A second loss is through air infiltration because the drat of stackchimney

causes negative pressure inside the furnace drawing in air trough leaks or cracks or whenever

the furnace doors are opened

Furnace skinsurface losses also called wall losses while temperature inside the furnace are

high heat is conducted through the roof floor and walls and emitted to the ambient air once it

reaches the furnace skin or surface

Other losses there are several other ways in which heat is lost from a furnace Although

quantifying all of them is difficult Some of them can be included

Stored heat losses when When the furnace is started the furnace structure and insulation also

heat up and this heat only leaves when the furnace are shut down again Thus these type of losses

increase with the number of times the furnace is turned off and on

Material Handling Losses The equipment used to move the stock through the furnace such as

conveyor belts walking beams bogies etc also absorb heat Every time equipment leave the

furnace they lose their heat Therefore this loss increases with the number of equipments and the

frequency by which they enter and exit the furnace

Cooling media losses water is used to cool down rolls bearings and other equipments But this

water also absorbs heat away with it

Incomplete combustion losses Heat is lost if combustion is incomplete because unburnt fuel or

particles have absorbed heat but this heat has not been brought to use

Loss due to formation of scales

• Modern furnace components

Pusher Mechanism

1 Thestrokeofthepusherissetatapproximately700-1000mmor7to 10 ingotbillet thicknesses This is approximately 700 -1000 kgs for single row charging and 1400 -2000 kgs for double row charging

2 The stroke is adjusted by means of two limit switches which are set for extreme forward position and extreme backward position of the pusher head by the operator

3 The ingots are placed in front of the pusher in the form of a rectangle by alternating the taper by the operator

4 For best operating practice in charging the ingots billets are chargedleavingagapof150mmbetweeningotbillet and side walls in case of single row charging and additionally a gap of 150mm between the left side rows and right side rows of ingots billets in case of two row charging

5 In order to ensure sweeping of ashsolid deposits on the hearth it is advisable to stagger the ingots billets to cover as much width of the hearth as possible over five to six lines of ingotsbillets at a time

6 Prior to the running of the pusher for operational purpose It is necessary that the following actions are taken by the operator

7 For Screw amp Nut Type Pusher

bull Clean the screw of all foreign particles scale etcbull Apply grease with a brush grade EP-3 lithium base mixed with 1 molybdenum di-

sulphide on Screw thread and nut for lubrication at high temperaturesbull Check oil leveling ear box using the dipstick gauge provided and top up if necessary

For Hydraulic Cylinder with Hydraulic Power Packbull Check oil level in tank clean filters once a weekbull Arrange the alternate ingots with its taper opposite to the previous ingot This is to

prevent piling up of ingots inside the furnacebull Wait for the ejector operatorrsquos signal before pushing any ingot into the furnacebull Check that the correct Heat No ingots billets are charged into the furnacebull Keep a count on the ingots billets charged

Ejector

1 The ejector is operated by an operator who is seated either on a seat mounted on the ejector trolley or by the side of it with a good view of the hot ingots on the furnace hearth He not only operates the ejector but also signals through a bell to the pusher operator to push the ingots by one stroke into the emptied space

2 Ifthepusherisoperatedhydraulicallythesamehydraulicsystemisconnected to the pinch roll and trolley movement drives instead of electric motors The valves for operating the drives are mounted on the operator desk Other operations remain the same as before

3 Ejector positioned by operator in line with the last ingot on the furnace hearth4 Eject or operates the pinch roll gear box to move the ejector in and out of the furnace

pushing out a single ingot into the extractor rotating table5 Operator checks sufficiency of cooling water6 Operator wears blue goggles to protect his eyes from the heat glare7 Operator signals to pusher operator to push ingots

8 Operator gets the signal to push from the Mill operator through a blinking light or bell9 Operator checks oil level in the trolley and pinch roll gearboxes at beginning of shift or if

drives are through hydraulic motors he checks the oil level in the hydraulic tank if this duty is assigned to him instead of the pusher operator

Extraction of Hot-IngotsBillets amp loading on Roller Table

1 In many furnaces a motorized extractor is provided where only billets are charged This is just a pair of pinch rolls which is driven either through gear box or hydraulic motor arrangement similar to the ejector pinch rolls But in most furnaces the ejector pushes the ingot on to a rotating table

2 In single row charged furnaces the extraction is mostly done manually by the workmen at the discharge door by using a long steel hook In this case there is no ejector

3 The work men at this location clean the hearth of scale and ash regularly throughout the shift to prevent the ingot from getting stuck or gets piled The cleaning is done using long scrapers

Door Operating Mechanism

Two doors viz ejector door and discharge door are operated from the ejector operatorrsquos desk for pneumatically operated doors and by the workmen who are at the discharge door end by operating the hand winchcounter weighted levers for manual operation Each time the ejector has to be operated first the above two doors are opened The ingotbillet is ejected from the furnace The doors are then closed This is repeated after each ejection of ingot billet Since the operation is very frequent it is advisable to automate the opening and closing by providing pneumatic cylinders The Door Operating Hand-winch is illustrated at Figure

Fig2 Door operating hand-winch

Heat losses affecting furnace performance

Ideally all heat added to the furnace should be used to heat the load or the stock In practice

however a lot of heat is lost in several ways as shown in figure

Heat losses in a Furnace

Flue gas losses

Loss from moisture in fuel fuel usually consist some moisture and some heat is utilized to

evaporate this moisture inside the furnace

Loss due to hydrogen in fuel which results in formation of water

Loss through openings in furnace radiation loss occurs when there are openings in the furnace

and theses losses can be significant especially for those furnaces which are operating above the

temperature of 540 oC A second loss is through air infiltration because the drat of stackchimney

causes negative pressure inside the furnace drawing in air trough leaks or cracks or whenever

the furnace doors are opened

Furnace skinsurface losses also called wall losses while temperature inside the furnace are

high heat is conducted through the roof floor and walls and emitted to the ambient air once it

reaches the furnace skin or surface

Other losses there are several other ways in which heat is lost from a furnace Although

quantifying all of them is difficult Some of them can be included

Stored heat losses when When the furnace is started the furnace structure and insulation also

heat up and this heat only leaves when the furnace are shut down again Thus these type of losses

increase with the number of times the furnace is turned off and on

Material Handling Losses The equipment used to move the stock through the furnace such as

conveyor belts walking beams bogies etc also absorb heat Every time equipment leave the

furnace they lose their heat Therefore this loss increases with the number of equipments and the

frequency by which they enter and exit the furnace

Cooling media losses water is used to cool down rolls bearings and other equipments But this

water also absorbs heat away with it

Incomplete combustion losses Heat is lost if combustion is incomplete because unburnt fuel or

particles have absorbed heat but this heat has not been brought to use

Loss due to formation of scales

• Modern furnace components

8 Operator gets the signal to push from the Mill operator through a blinking light or bell9 Operator checks oil level in the trolley and pinch roll gearboxes at beginning of shift or if

drives are through hydraulic motors he checks the oil level in the hydraulic tank if this duty is assigned to him instead of the pusher operator

Extraction of Hot-IngotsBillets amp loading on Roller Table

1 In many furnaces a motorized extractor is provided where only billets are charged This is just a pair of pinch rolls which is driven either through gear box or hydraulic motor arrangement similar to the ejector pinch rolls But in most furnaces the ejector pushes the ingot on to a rotating table

2 In single row charged furnaces the extraction is mostly done manually by the workmen at the discharge door by using a long steel hook In this case there is no ejector

3 The work men at this location clean the hearth of scale and ash regularly throughout the shift to prevent the ingot from getting stuck or gets piled The cleaning is done using long scrapers

Door Operating Mechanism

Two doors viz ejector door and discharge door are operated from the ejector operatorrsquos desk for pneumatically operated doors and by the workmen who are at the discharge door end by operating the hand winchcounter weighted levers for manual operation Each time the ejector has to be operated first the above two doors are opened The ingotbillet is ejected from the furnace The doors are then closed This is repeated after each ejection of ingot billet Since the operation is very frequent it is advisable to automate the opening and closing by providing pneumatic cylinders The Door Operating Hand-winch is illustrated at Figure

Fig2 Door operating hand-winch

Heat losses affecting furnace performance

Ideally all heat added to the furnace should be used to heat the load or the stock In practice

however a lot of heat is lost in several ways as shown in figure

Heat losses in a Furnace

Flue gas losses

Loss from moisture in fuel fuel usually consist some moisture and some heat is utilized to

evaporate this moisture inside the furnace

Loss due to hydrogen in fuel which results in formation of water

Loss through openings in furnace radiation loss occurs when there are openings in the furnace

and theses losses can be significant especially for those furnaces which are operating above the

temperature of 540 oC A second loss is through air infiltration because the drat of stackchimney

causes negative pressure inside the furnace drawing in air trough leaks or cracks or whenever

the furnace doors are opened

Furnace skinsurface losses also called wall losses while temperature inside the furnace are

high heat is conducted through the roof floor and walls and emitted to the ambient air once it

reaches the furnace skin or surface

Other losses there are several other ways in which heat is lost from a furnace Although

quantifying all of them is difficult Some of them can be included

Stored heat losses when When the furnace is started the furnace structure and insulation also

heat up and this heat only leaves when the furnace are shut down again Thus these type of losses

increase with the number of times the furnace is turned off and on

Material Handling Losses The equipment used to move the stock through the furnace such as

conveyor belts walking beams bogies etc also absorb heat Every time equipment leave the

furnace they lose their heat Therefore this loss increases with the number of equipments and the

frequency by which they enter and exit the furnace

Cooling media losses water is used to cool down rolls bearings and other equipments But this

water also absorbs heat away with it

Incomplete combustion losses Heat is lost if combustion is incomplete because unburnt fuel or

particles have absorbed heat but this heat has not been brought to use

Loss due to formation of scales

• Modern furnace components

Heat losses affecting furnace performance

Ideally all heat added to the furnace should be used to heat the load or the stock In practice

however a lot of heat is lost in several ways as shown in figure

Heat losses in a Furnace

Flue gas losses

Loss from moisture in fuel fuel usually consist some moisture and some heat is utilized to

evaporate this moisture inside the furnace

Loss due to hydrogen in fuel which results in formation of water

Loss through openings in furnace radiation loss occurs when there are openings in the furnace

and theses losses can be significant especially for those furnaces which are operating above the

temperature of 540 oC A second loss is through air infiltration because the drat of stackchimney

causes negative pressure inside the furnace drawing in air trough leaks or cracks or whenever

the furnace doors are opened

Furnace skinsurface losses also called wall losses while temperature inside the furnace are

high heat is conducted through the roof floor and walls and emitted to the ambient air once it

reaches the furnace skin or surface

Other losses there are several other ways in which heat is lost from a furnace Although

quantifying all of them is difficult Some of them can be included

Stored heat losses when When the furnace is started the furnace structure and insulation also

heat up and this heat only leaves when the furnace are shut down again Thus these type of losses

increase with the number of times the furnace is turned off and on

Material Handling Losses The equipment used to move the stock through the furnace such as

conveyor belts walking beams bogies etc also absorb heat Every time equipment leave the

furnace they lose their heat Therefore this loss increases with the number of equipments and the

frequency by which they enter and exit the furnace

Cooling media losses water is used to cool down rolls bearings and other equipments But this

water also absorbs heat away with it

Incomplete combustion losses Heat is lost if combustion is incomplete because unburnt fuel or

particles have absorbed heat but this heat has not been brought to use

Loss due to formation of scales

• Modern furnace components

causes negative pressure inside the furnace drawing in air trough leaks or cracks or whenever

the furnace doors are opened

Furnace skinsurface losses also called wall losses while temperature inside the furnace are

high heat is conducted through the roof floor and walls and emitted to the ambient air once it

reaches the furnace skin or surface

Other losses there are several other ways in which heat is lost from a furnace Although

quantifying all of them is difficult Some of them can be included

Stored heat losses when When the furnace is started the furnace structure and insulation also

heat up and this heat only leaves when the furnace are shut down again Thus these type of losses

increase with the number of times the furnace is turned off and on

Material Handling Losses The equipment used to move the stock through the furnace such as

conveyor belts walking beams bogies etc also absorb heat Every time equipment leave the

furnace they lose their heat Therefore this loss increases with the number of equipments and the

frequency by which they enter and exit the furnace

Cooling media losses water is used to cool down rolls bearings and other equipments But this

water also absorbs heat away with it

Incomplete combustion losses Heat is lost if combustion is incomplete because unburnt fuel or

particles have absorbed heat but this heat has not been brought to use

Loss due to formation of scales

• Modern furnace components