INTRODUCTION

1.1 History: The history of the modern steel making really started from 1760, when Huntsman

invented in England the crucible process for making the steel. The process was gradually

upgraded to produce alloy and tool steel. But the quantity produced by the crucible process was

small. Large scale steel production became possible only after Henry Bessemer developed the

Bessemer converter process of steel making in 1856.

At the time of Indian independence, total production was near about 2.5 million tons per annum

(MTPA).Electric arc furnaces made only very minor contribution to the total output. From the

second five year plan period and onwards, public sector integrated steel plants were set up in

different parts of India. The establishment of these steel plants with foreign technical assistance

not only boosted up Indian steel production, but also contributed to the training of a new breed of

steel technologists. The availability of technical manpower and the demand for steel subsequently

attracted large scale private investment in the steel sector. As a result, large number of electric arc

furnace based mini steel plants also came up in the country. But relatively cost high cost of

electricity in the country, the EAF based steel industries face periodic slowdown.

Steel is an alloy of iron and carbon. Although theoretically the carbon content in steel may range

up to 1.7%, in practice most of the steels produced are of hypereutectoid composition. Eutectoid

(0.8% C) and hypereutectoid (>0.8% C upto 1.1% C) steels are produced only for special

purposes.

Electric arc furnace steel making has emerged as a major steel making process in recent years. In

India electric furnace based plants are usually classified as mini steel plants because they

generally produce less than one million ton of steel per year. Although steel scrap is still the

preferred metallic charge material in electric arc furnace, sponge iron is also being used regularly

in most plants partly because of short supply of steel scrap and because of the need to dilute

tramp elements.

The growth of the arc furnace based steel industry has been encouraged by the development of

modern large capacity ultra-high power arc furnace. Some improvements are also provided like

oxygen lancing.

Steel production necessarily involves production of millions of tons of slag as well as waste gases

containing harmful constituents like carbon dioxide, dioxin, furans, etc.

1.2 Constructional Features: The furnace consists of a steel shell, lined with suitable refractory

materials and is mounted on a tilting mechanism, in which hydraulic system is used to tilt the

furnace. Three electrodes enter through roof. These are rigidly supported by electrode holders.

The electrode movement is usually controlled automatically. The hood may be swung away for

charging. In this type of furnace the heat is generated by the area formed between the electrodes

and the charge.

1.2.1 Hearth: The hearth acts as a receptacle of slag and metal. The hearth lining is divided into

two sections – backing lining and working lining. A firebrick lining is provided, against the shell

for thermal insulation. Next a backing lining is constructed with few layers of high fired

magnesite bricks. The working lining is made to provide a monolithic, joint free surface.

The hearth should be able to withstand high temperature, slag and metal corrosion as well as

mechanical and thermal stresses. Recent developments include introduction of gas stirring

through the bottom and eccentric bottom taping (EBT) system for draining out the furnace.

Permeable blocks or porous refractory elements are introduced thorough the bottom for admitting

inert gas for stirring the bath. Oxygen and natural gas may also be injected through the bottom to

reduce electric energy consumption. One or more such porous elements can be fixed at the

bottom.

In the eccentric bottom tapping system, a tap hole is provided at the bottom eccentrically. This is

made with special designed blocks, which can be opened and closed through a lever, and lever

can be operated hydraulically or pneumatically. With the introduction of this system, the need to

tilt the furnace for tapping out metal has been eliminated. This has minimized thermal stresses,

which used to cause spalling of refractories during operation.

1.2.2 Side Walls: The side walls of electric arc furnace are subjected to severe thermal shocks,

corrosive slag action-and mechanical abuse during charging etc. Hot spots formed on the side

wall are subjected to the most severe condition. The main factors influencing not spot formation

are:

a. Radiation from arc flames,

b. Arc position and blowout,

c. Reflected heat from the bath surface,

d. Duration of power input,

e. Absence of protective cover from radiation by charged scrap etc.

The side wall lining is expected to erode uniformly over the entire area. The general tendency,

however is to line the side walls with magnetic bricks up to the slag line. However, magnesia-

carbon bricks are also used at the slag line. The balance of the side walls is most commonly lined

with magnesia-chrome brick. Direct bonded basic bricks with or without tar impregnation,

magnesia-carbon bricks, high purity magnesite and fusion cast bricks have been seen on the

construction of side walls. Attempts have been made to contain the hot spot by suitably altering

the process parameters, e.g.

a. Balancing arc power of central electrode by adding reactance,

b. Operating the furnace under positive pressure and shielding the arc fume and smoke,

c. Operating shorter arc length,

d. Directing the flame away from the wall.

However, the most effective way is use a highly conducting refractory lining with additional

water cooling. Thus lining with magnesia carbon black 10-15% carbon and water-cooling

arrangement are now considered the most suitable mode of lining for side walls.

1.2.3 Roof: The roof of an arc furnace is usually made from silica bricks which are supported

circumferentially by a ring of the same external diameter as that of the shell. High alumina brick

(70% alumina) is also popular in many countries. Basic bricks have also been occasionally used.

However, basic bricks are heavy and may be used for making suspended roof of patented designs.

The circumferential ring is usually water-cooled. Three circular openings are provided for

introduction of the electrodes. These holes are placed at the corners of an equilateral triangle. In

modern furnace almost the entire roof is constructed with water-cooled panels. The roof is

subjected to thermal, mechanical and chemical stresses. The problem has been tackled by:

a) Improving the quality of refractories,

b) Changes in the design of laying.

Graphite electrodes are generally used in electric arc furnace. The diameter of the electrodes

depend upon the magnitude of power transmitted and may be upto 100cm. Since the graphite

electrodes are very costly proper precaution needs to be taken not only during storage and

handling but also during actual furnace operation. When an electrode is mostly used up, a new

electrode is fitted onto remaining portion by means of threaded nipple. There are three type of

electrode erosion mechanism, namely erosion at the electrode tip due to the action of the electric

arc, oxidation of the electrode sides by the furnace atmosphere and mechanical breakage due to

scrap fall, mechanical fracture of the electrode joints and thermal shocks.

STEEL MAKING

2.1 Process: The process steps involved in basic electric arc furnace operation are:

a) Charging

b) Melting down

c) Refining

d) Finishing

Refining is usually carried out under the influence of an oxidizing slag. This is necessary for

good dephosphorization. When desulphurization is also desired, a second reducing slag is made

after draining out the oxidizing slag completely.

2.1.1 Charging: The electrodes are raised and then the roof swung away. A drop bottom type

basket carrying the metallic charge is then lowered into the furnace through the open top. The

metallic charge drops into the furnace when the basket bottom open up. The charge consists of

steel scrap, lime/limestone and coke. Door charging is also practised is case of small furnace.

For smooth melting, the proportion of heavy and light melting scrap is usually adjusted carefully

for heavy and light melting scrap is usually adjusted carefully for each furnace. Generally light

scrap is charged first. Heavy melting scrap is placed above the layer of light scrap and below the

electrodes. Remaining light scrap is charged on the top lime/limestone scrap interferes with

arcing and hence should be charged either at the bottom or in the banks. A part of the iron ore

required for oxidation may be charged into the furnace along with the first batch of scrap is

charge. Remaining iron ore is shovelled into the bath from time to time.

Alloying elements like nickel or copper may be charged with scrap. Alloying elements prone to

oxidation are usually added after melting. The relatively refractory alloying elements are

shovelled directly into the crater region.

2.1.2 Melting Down: As soon as the arc is struck, melting starts below the electrodes. The

electrodes bore through the metallic charge and a pool of molten metal forms at the bottom. The

electrodes ‘hunt’ and the current fluctuates widely as the electrodes bore through the metallic

charge. The arc stabilizes when the charge below the electrodes melts completely. The furnace

noise also subsides. The mode of heat transfer from the electric arc to the environment is

important with regard to the economic operation of the furnace. Further melting takes place by

radiation of heat from this molten pool as well as from the arc and also by the electrical resistance

offered by the scrap charge. The melting may be hastened by forcing the unmelted stock from the

banks into the molten pool either by mechanical rabbling or by rotating the hearth by a few

degrees. Of course, the electrodes must be raised before attempting this. The power consumption

is maximum during the melting down period. Successive scrap charges may be placed into the

furnace as the existing charge subsides and room becomes available. During melting silicon,

manganese, carbon, phosphorus, etc. are oxidized in varying degrees and form the first slag. As

lime gradually dissolves in the slag, its basicity increases. During the early stages of melting a

charge, the furnace transformer capacity is not fully utilised fully owing to instabilities in the

electric arc reducing the furnace power input. Attempts have been made to stabilize the arc by

various techniques such as hollow electrodes, cored electrodes and arc seeding but so significant

improvement has yet been made in production furnaces.

2.1.3 Refining and Finishing: At the end of the melting down period, a basic slag is formed. The

slag contains various oxides like FeO, CaO, SiO2, MnO, and Al2O3 etc. The refining takes place

under the influence of this basic oxidizing slag. Fluorspar (CaF2) is added to maintain adequate

fluidity in the slag. Silicon is oxidized to silca which passes into the slag. Evolution of {CO} gas

stirs the bath and the phenomenon is known as carbon boil. In order to ensure adequate carbon

boil the opening carbon content of the bath should be 0.25 to 0.3% higher than the final carbon

content desired. A carburiser is, therefore, added with the steel scrap charge if necessary. The

carbon boil facilitates purging of dissolved gases and flotation of inclusions. Dephosphorization

is favoured by a basic oxidizing slag. The dephosphorization is favoured by a basic oxidizing

slag. The dephosphorization reaction may be written as follows:

2[P] + 5(FeO) = (P2O5) + 5Fe

(P2O5) + 4(CaO) = (4CaO. P2O5)

It is necessary to maintain the basicity of slag by periodic addition of lime. A flush slag practice

is usually practised in electric furnace operation. In this practice, the furnace is inclined and a part

below. A large part of the phosphorus oxidized during melting us removed with the first slag.

Fresh lime and iron ore are charged to continue the refining reactions. As the carbon-oxygen

reaction rate picks up the intensity of the carbon boil also increased. The slag may froth. As the

slag level rises, a part of the slag will automatically overflow out through the door sill. The

overflow slag carries away dissolved (P2O5). This helps in continuing the dephosphorization

reaction. The phosphorus level drops to 0.015-0.02%. The metal temperature also rises. Periodic

addition of iron ore assists in continuing the oxidation reaction.

At the end of the oxidizing period the slag is drained out. The last part of the slag may have to be

raked out manually. The bath is deoxidized first by the addition of ferrosilicon and

ferromanganese, and finally by addition of aluminium. Desulphurization is favoured by high

manganese content in the metal, high temperature of the bath and a basic reducing slag. Most of

the steel grades are generally prepared under a single oxidizing slag. However, those grades of

steel which have a more restrictive sulphur specification and where loss of expensive alloying

elements is likely, a second reducing slag is usually made after the first oxidizing slag. In order to

form the reducing slag, the flux materials usually consist of burnt time, sand and fluorspar.

Pulverized coke is added to this slag. Under the influence if the arc, the following reaction takes

place:

(CaO) + 3C = (CaC2) + {CO}

A typical carbidic slag is gray in colour and it disintegrates into powder upon cooling. The major

constituents of the slag are CaO—60-65%, SiO2—18-22%, MgO—7-9%, CaC2—1-2%, +FeO,

CaO, Al2O3, MnO.

The formation of carbide in the slag may be verified by quenching a slag sample in water, the

presence of carbide may be detected by the typical smell of acetylene. The carbide helps to

maintain a lo oxygen potential in the slag by a process known as diffusion deoxidation. It is well

known that the iron oxide partition coefficient kFeO = (FeO)/[FeO] is a constant at a constant

temperature. (CaC2) reacts with (FeO) in the slag according to the reaction.

(CaC2) + 2(FeO) = (CaO) + Fe + 2{CO}

Thus, the oxygen potential of the slag is depleted. As a result further amount of iron oxide

diffuses from metal to slag to keep kFeO constant. Continued reduction in the (FeO) content of the

slag by carbide reaction also automatically reduces the [FeO] content in the metal, i.e. the bath is

deoxidized. In diffusion deoxidization the product is {CO} gas which escapes from the system.

The reducing slag favours desulphurization according to the reaction

(CaO) + [FeS] = (CaS) + (FeO)

(FeO) + (CaC2) = (CaO) + Fe + 2[CO]

Where carbon pick up has to be avoided in low carbon steels (usually less than 0.15% C) a

reducing slag may be made by appropriate additions of finely ground ferrosilicon to the slag.

Silicon deoxidizes the bath forming silica which passes off into the slag. Silicon deoxidizes the

bath forming silica which passes off into the slag and is fluxed off by the lime. A lime-alumina

slag may also be made for low carbon steels from lime and aluminium shots or granules. Calcium

aluminate slag desulpurizes the bath and also absorbs metallic oxides including iron oxide. The

oxygen content in the slag is kept low by periodic additions of aluminium.

In single slag practice the bath is deoxidized with ferromanganese and ferrosilicon after draining

out the slag. Final deoxidation with aluminium shots is usually carried out in the ladle during

tapping the steel.

2.1.4 Induction Stirring: Molten steel in the electric arc furnace may be stirred by an induction

stirrer installed underneath the bottom of the furnace shell. The bottom segment of the furnace

shell is fabricated from austenitic stainless steel plates on order to avoid induction heating effect.

The inductor generates a moving magnetic flux during operation. The moving magnetic flux

reacts with the induced field in the bath which promotes low intensity stirring of the bath. Several

designs of the induction stirrer are available. The stirring promotes a better homogeneity of the

bath in alloy steels and encourages faster slag metal reactions.

2.2 Development in EAF Technology: In recent years, remarkable progress in steel making

technology through EAF route has been made. Ultrahigh power (UHP) furnaces are a new

development. Improved operating techniques such as operation under high power factor,

formation of foamy slag and use of oxyfuel burners have resulted in reduction of power and

electrode consumption. The capacity of a mini steel plant with EAF can be increased significantly

by implementing these innovative measures. Some of are as follows:

2.2.1 Ultrahigh Power (UHP) transformers: The first factor when considering UHP

transformers is the capacity. Transformer rating per ton of steel melted is continually increasing.

With each new shop designed, the previous limitations such as electrode current handling

capability, electrode holder design and refractory wear are re-evaluated and incremental increases

in specific power input are made. It is reasonable to expect the KVA/ton rating to continue to

gradually increase until the absolute increase until the absolute limits of materials are reached.

The latest development in transformer design is 3-legged transformer which permits adjustment

of the voltage of each phase independently. This provides the ability to control hot spots in the

furnace while maintaining maximum power input.

An additional item is associated with the UHP transformer is controlling flicker on the incoming

power lines. It is more common that the power lines ate shared with other consumers where the

control of flicker becomes mandatory. Therefore, most new UHP melt shops are equipped with

static VAR generators to obtain flicker control.

2.2.2 Design of cooling system for side wall and roof: An important development in furnace

shell design is the application of water-cooling of those portions of the upper side wall lining

which suffer maximum wear rate. Cooling helps realization of the full usable life from all of the

lining without mid-campaign patching. The areas to which this water cooling concept is

principally applied are the “hot spots” where the side is closest to the electrodes and which are

subject not only to the most intense thermal radiation, but also to direct impingement of the arc

flare and bombardment by iron oxide particles which tend to penetrate and flux the refractory

lining material. Other areas subject to excessive wear due to factors such as oxygen lancing,

addictive injection practices are suitable for water-cooling considerations. Tap to lap time may be

reduced by 5-10 min by installing water cooled side wall and roof panels. The possibility if heat

recovery from the cooling water may be examined. Some heat recovery is more easily obtained

under those conditions.

2.2.3 New design of electrodes: Water-cooled electrodes are the common terminology for

another new technology. This technology consists of employing water cooled electrode sections

between the furnace electrode holder and the conventional graphite electrode. The advantage is

that the electrodes run cooler and graphite losses by oxidation at high temperature are reduced.

Argon injection through hollow electrodes as used in electrodes arc furnace promises operational

and metallurgical benefits. Argon injection through hollow electrodes results in quicker and more

stable furnace arc with higher levels of heat release, especially during the scrap melt down

period. Thus, furnace production rate is increased and electrode consumption is decreased. A

metallurgical benefit is gained since hydrogen and nitrogen pick-up by the steel is reduced with

the argon hollow-electrode practice.

2.2.4 Furnace shell design: The constant search for ways to increase productivity has led to

several developments in shell design. One such development is the split shell design, in which the

shell design, in which the shell structure is considered in two separable sections- lower section

containing the hearth plus a free board allowance for board allowance for slag, and an upper

section containing the balance of the shell side wall. The two section containing are coupled

together in such a way that the upper section with the used side wall lining can be removed and

replaced with a newly-lined upper section, Thus, the furnace downtime for a side wall

replacement is greatly reduced. This also allows improved working conditions for the actual

relining work, and thus, provides additional safety and efficiency benefits. The split shell feature

is used mostly on larger size continuously operated furnace, for which side wall relining time has

a significant effect on furnace availability. The detrimental effect of high power operation on side

wall lining life has increased the attractiveness of the split shell feature.

Effective use of split shell feature requires that auxiliary equipment mounted on the upper shell

section, such as door lifting mechanisms, injection pipes, auxiliary burners, etc. be designed for

easy removal or rapid disconnection from supply feeders. The furnace service charge must be

adequate for the weight of the newly lined shell section.

In the removable shell design the entire shell is made easily removable from the furnace structure.

This development was motivated by a need avoid contamination in the production of different

grades of alloy steel. The weight of a complete full lined shell has limited the application of this

feature to relatively few smaller ones.

Still another innovation designed to improve efficiency and productivity is the tapered shell, in

which the diameter of the hearth and lower side sections of the shell are of larger diameter than

the top of opening. The top section is tapered (or cone-shaped) to effect the change in diameter.

Several advantages are attributed to this shell design. Some of the important ones are:

a. Longer side wall lining life due to the larger shell diameter at the spot areas, and thus , a

longer distance from the arcs to these areas, refractory erosion being inversely proportional to the

square of this distance,

b. Improved thermal efficiency because of reduced heat loss and increased reverberatory heating

of the charge, and

c. Greater shell volume to accommodate larger charges and more efficient operation with low

density scrap.

A larger EAF charging volume with bigger furnace diameter has been tried successfully for

single bucket charging of scrap allows much higher electrical power input than to bucket

charging in a standard furnace. Chemical yield improves when furnace volume is increased. For

rapid furnace operation, reducing power off time is important. A reduction in the number of

buckets charged also means lower radiation losses, short furnace cycle time, increased

productivity and overall improvement in energy balance.

2.3 Furnace Heat Balance:

UHP FURNACELow to Medium Power

Furnace

Electrical Energy 50 - 60 % 75 - 85 %

INPUTS Burners 5 - 10 %

Chemical Reactions 30 - 40 % 15 - 25 %

TOTAL INPUT 100% 100%

OUTPUTS

Steel 55 - 60 % 50 - 55 %

Slag 8 - 10 % 8 - 12 %

Cooling Water 8 - 10 % 5 - 6 %

Miscellaneous 1 - 3 % 17 - 30 %

Off gas 17 - 28 % 7 - 10 %

To melt steel scrap, it takes a theoretical minimum of 300 kWh/ton. To provide superheat above

the melting point of 2768 F requires additional energy and for typical tap temperature

requirements, the total theoretical energy required usually lies in the range of 350 to 370

kWh/ton. However, EAF steelmaking is only 55 to 65 % efficient and as a result the total

equivalent energy input is usually in the range of 560 to 680 kWh/ton for most modern

operations. This energy can be supplied from a variety of sources as shown in the table below.

The energy distribution is highly dependent on local material and consumable costs and is unique

to the specific meltshop operation. The above figures are highly dependent on the individual

operation and vary considerably from one facility to another. Factors such as raw material

composition, power input rates and operating practices (e.g. post-combustion, scrap preheating)

can greatly alter the above balance. In operations utilizing a large amount of charge carbon or

high carbon feed materials, up to 60 % of the energy contained in the off gas may be calorific due

to large quantities of un-combusted carbon monoxide. Recovery of this energy in the EAF could

increase energy input by 8 to 10 %. Thus it is important to consider such factors when evaluating

the energy balance for a given furnace operation.

2.4 Various systems used in EAF:

2.4.1 Mechanical Systems: Mechanical systems are integral to the operation of the EAF and

many are inter-related. To gain a better perspective of the importance of various systems in the

furnace operation, it is good to step back and evaluate the function of the electric arc furnace

itself. The EAF has several primary functions:

1. Containment of steel scrap

2. Heating and melting of steel scrap

3. Transfer of molten steel to the next processing stage

It is easy to see that the first function, scrap containment can only be properly carried out if the

furnace shell is properly maintained. The furnace shell consists of a refractory lined bottom that

helps contain the liquid steel and typically, a water-cooled upper section that only comes into

contact with scrap and slag. Heating and melting of the scrap are accomplished by supplying

electrical energy through the electrodes and chemical energy through the use of burners and

oxygen lances. Transfer of the liquid steel to the ladle is accomplished by tilting the furnace and

opening either a tapping spout or a bottom tap-hole to allow the steel to flow from the furnace. It

is apparent that many sub-systems come into play throughout the tap-to-tap cycle. Many of these

systems are dependent of the following systems in order to be able to function properly:

Hydraulic system

Cooling water system

Lubrication System

2.4.2 Hydraulic system: The hydraulic system provides motive power for almost all EAF

movements including roof lower/raise, roof swing, electrode arms up/down/regulation/swing,

furnace tilt forward/backward, slag door raise/lower and movement of any auxiliary systems such

as the burner lance. The hydraulic system consists of a central reservoir, filters, an accumulator,

hydraulic valves and hydraulic piping. As hydraulic fluid passes through valves in one of two

directions within a given circuit, hydraulic cylinders are extended or contracted to provide

movement of various mechanical components. Without sufficient fluid flow and pressure within a

circuit, movement is impossible. Thus issues such as low fluid level, low accumulator pressure,

system leaks, fluid degradation due to over-heating, solids build-up in valves or in hydraulic lines

and wear in mechanical components can lead to poor system performance and in some cases,

system failure.

2.4.3 Electrodes: One of the most important elements in the electric circuit and consumable cost

in electric furnace steelmaking are the electrodes The electrodes deliver the power to the furnace

in the form of an electric arc between the electrode and the furnace charge. The arc itself is a

plasma of hot, ionic gasses in excess of 6,000°F. Electrodes come in two forms: amorphous and

graphitic carbon, or graphite. Since only graphite electrodes are used in steelmaking only they

will be discussed here.

Graphite electrodes are composed of a mixture of finely divided, calcined petroleum coke mixed

with about 30% coal tar pitch as a binder, plus proprietary additives unique to each manufacturer.

This mixture is extruded at approximately 220°F, the softening temperature of pitch, to form a

cylindrical rod known as a "green electrode". The green electrode is now given a controlled bake

in a reducing atmosphere at temperatures as high 1800°F and again impregnated with pitch to

increase its strength and density and lower the electrical resistivity. The electrodes are now ready

to be graphitized, i.e. converting the amorphous carbon into crystalline graphite. This is

accomplished by passing an electric current through them and heating them to as much as

5000°F. The graphitizing consumes as much as 3000-5000kWH/ton of electrode. The final

product is strong, dense, and has a low electrical resistivity. Lastly the electrode is machined to

its final shape. Into each end of the electrode is a recess in which threads are machined. These are

used to accept a threaded nipple manufactured in the same way so that the electrode column can

be lengthened as it is consumed.

Historically, electrode consumption has been as high as 12-14 pounds per tons of steel, but

through continuous improvement in electrode manufacturing and steelmaking operations, this has

been reduced to the neighbourhood 3.5 to 4.5 pounds per ton. Most electrode consumption is

through oxidation and tip sublimation, with some small pieces lost around the connecting joint. A

considerable portion is also lost to mechanical breakage caused by scrap cave-ins in the furnace

or crushing the electrode into the charge.

Electrodes are commonly available in sizes from 15 - 30 inches in diameter varying lengths to 10

feet. They come in three grades: regular and premium and the newer DC grade.

2.4.4 Cooling water system: Another system that is integral to EAF operation is the cooling water

system. Typically, there are several cooling systems. Some operations require extremely clean,

high quality cooling water. Transformer cooling, delta closure cooling, bus tube cooling and

electrode holder cooling are all such applications. Typically, these systems will consist of a

closed loop circuit, which conducts water through these sensitive pieces of equipment. The water

in the closed loop circuit passes through a heat exchanger to remove heat. The circuit on the open

loop side of the heat exchanger typically flows to a cooling tower for energy dissipation. Other

water cooled elements such as furnace side panels, roof panels, offgas system ducting, furnace

cage etc. will typically receive cooling water from a cooling tower.

The cooling circuit typically consists of supply pumps, return pumps, filters, a cooling tower cell

or cells and flow monitoring instrumentation. Sensitive pieces of equipment normally have

instrumentation installed to monitor the cooling water flow rate and temperature. For most water-

cooled equipment, interruption of the flow or inadequate water quantities can lead to severe

thermal over loading and in some cases catastrophic failure.

2.4.5 Lubrication System: Many modern furnaces have an automatic system that provides

lubrication to various moving parts based on various "events" occurring during the tap-to-tap

cycle. For example, some parts are lubricated every three roof swings, following tapping, etc.

Some components such as roller bearings are critical to furnace operation and are lubricated

periodically by hand. Some hard to reach locations are serviced using tubing and remote blocks.

2.4.6 Auxiliary Systems: In addition to the major mechanical systems associated with the EAF,

there are also many auxiliary systems that are integral to furnace operation and performance.

Oxygen lance system. Over the past 20 years, the use of oxygen in EAF steelmaking has grown

considerably. In the past when oxygen consumption of less than 300 cubic feet per ton of steel

were common, lancing operations were carried out manually using a consumable pipe lance.

Most modern operations now use automatic lances and most facilities now use a non-consumable,

water-cooled lance for injecting oxygen into the steel. Many of these lances also have the

capability to inject carbon as well.

Carbon injection system: Carbon injection is critical to slag foaming operations, which are

necessary for high power furnace operations. Carbon reacts with FeO to form CO and "foam" the

slag.

2.4.7 Oxy-fuel burner system: Oxy-fuel burners are now almost standard equipment on large

high-powered furnaces. In operations with short tap-to-tap times, they provide an important

function by ensuring rapid melting of the scrap in the cold spots. This ensures that scrap cave-ins

are kept to a minimum and as a result, electrode breakage is minimized. In large diameter

furnaces, burners are essential to ensure a uniform meltdown. Non-uniform scrap meltdowns may

result in operating delays and lost productivity. The biggest maintenance issue for burners is to

ensure that they do not get plugged with metal or slag. The closer burners are mounted to the

bath, the greater the risk of them becoming plugged while in a low-fire mode. Some burners are

mounted directly in the water-cooled panel while others are mounted in a copper block. If burners

are fired at high rates against large pieces of scrap, the flame can blow back on the furnace shell

damaging the water-cooled panel. Thus the panel area should be inspected for wear around the

burner port. If a copper block is used, it will be more resistant to flame blow back but should still

be inspected regularly for wear and cracks.

2.4.8 Electrode spray cooling system: It is common for electrodes to have a spray cooling system

in order to reduce electrode oxidation. Spray rings direct water sprays at the electrode below the

electrode clamp and the water runs down the electrode thus cooling it. Sprays rings can reduce

overall electrode consumption by as much as 10-20%. In addition, spray cooling usually results in

improved electrode holder life and surrounding insulation. Due to the reduction in radiation from

the electrode, power cable, air hose and hydraulic hose life is also greatly improved.

2.4.9 Temperature Sampling System: The modern disposable thermocouple was introduced to

steelmaking almost 40 years ago and temperature measurement had become an integral part of

tracking progress throughout the tap-to-tap cycle in steelmaking. Expendable probes are also used

for tracking bath carbon content and dissolved oxygen levels in the steel. These tools have

enabled the tap-to-tap cycle to be accelerated by eliminating long waiting periods for lab results,

thus increasing productivity. Disposable probes are typically mounted in cardboard sleeves that

slide on to a steel probe(pole) which has internal electrical contacts. The disposable probe

transmits an electrical signal to the steel pole, which in turn transmits the signal to an electronic

unit for interpretation. Almost all probes rely on an accurate temperature measurement to

precisely calculate carbon or oxygen levels. Most facilities keep several spare poles on hand so

that they can be quickly replaced if they have reading problems.

2.4.10 Off gas Direct Evacuation System: Early offgas evacuation systems were installed so that

the furnace operators could better see what was happening in and around the furnace. Since the

early days of EAF steelmaking, the offgas system has evolved considerably and most modern

EAF shops now use a "fourth hole" direct furnace shell evacuation system (DES). The term

fourth hole refers to an additional hole other than those for the electrodes, which is provided for

off gas extraction. On DC furnaces with only one electrode, the fume extraction port is

sometimes referred to as the "second hole". It is important to maintain sufficient draft on the

furnace for the following reasons:

1. To provide adequate pollution control.

2. Excessive shop emissions make it difficult for the crane operator to charge the furnace.

3. Excessive emissions around the electrode ports can result in damage of hoses, cables, the

electrode holder, the furnace delta, roof refractory, accelerated electrode wear, damage to

the electrode spray cooler etc.

4. Emissions at the roof ring can result in warping of the roof ring structure.

5. Excessive emissions of carbon monoxide to the secondary canopy system may result in

explosions in the ductwork downstream.

6. Excessive dust build-up may cause arcing between electrode phases.

Most DES systems consist of water-cooled duct, spray cooling, dry duct and may or may not

have a dedicated DES booster fan.

2.5 Environmental issues: Although the modern electric arc furnace is a highly efficient recycler

of steel scrap, operation of an arc furnace shop can have adverse environmental effects. Much of

the capital cost of a new installation will be devoted to systems intended to reduce these effects,

which include:

enclosures to reduce high sound levels

Dust collector for furnace off-gas

Slag production

Cooling water demand

Heavy truck traffic for scrap, materials handling, and products

Environmental effects of electricity generation

Because of the very dynamic quality of the arc furnace load, power systems may require technical

measures to maintain the quality of power for other customers; flicker and harmonic distortion

are common side-effects of arc furnace operation on a power system.

REFERENCE

1. Steel Making, A. K. Chakrabarti

2. http://en.wikipedia.org/wiki/Electric_arc_furnace

3. http://www.scribd.com/doc/15508209/Electric-Arc-Furnace-Steel-Making