K. Suresh SenanayakeScientific OfficerNCNDT - AEA

BOILER MAINTENANCE

& OPERATION

Boiler is a closed vessel in which the water under pressure is transferred into steam by the application of heat.

BOILERWHAT IS A BOILER?

The function of boiler is to transfer the heat to the water in the efficient manner.

FUNCTION :-

The chemical energy convert into heat energy by the combustion process which is absorbed by the boiler .

WORKING :-

A boiler must be designed to absorb the maximum amount of heat release in the process of combustion.

QUALITY :-

BOILER

BOILERThe steam produced is used for:

I. Producing mechanical work by expanding it in steam engine or steam turbine.

II. Heating the residential and industrial buildings.

III. Performing certain processes in the sugar mills, chemical and textile industries.

Simple Boiler

Boiler properties:

Safety: The boiler should be safe under operating conditions.

Accessibility: The various parts of the boiler should be accessible for repair and maintenance.

Capacity: Should be capable of supplying steam according to the requirements.

Efficiency: Should be able to absorb a maximum amount of heat produced due to burning of fuel in the furnace.

It should be simple in construction .

Its initial cost and maintenance cost should be low.

The boiler should have no joints exposed to flames.

Should be capable of quick starting and loading.

TYPES OF BOILER

FIRE TUBE BOILE

R

BOILER

OTHER

PACKAGE

BOILER

WATER TUBE BOILE

R

Classification of Boilers•According to what flows in the tube

(i) Water tube (ii) Fire tube•According to position of furnace

(i) Internally fired (ii) Externally fired•According to position of principle axis

(i) Vertical (ii) Horizontal (iii) Inclined•According to application

(i) Stationary (ii) Mobile (Marine, Locomotive)

•According to circulating water(i) Natural circulation (ii) Forced circulation

•According to steam pressure(i) Low (ii) Medium (iii) High

Fire in tube or hot gas send through the tubes and boiler feed water in shell side.

Fire tubes submerged in water.

FIRE TUBE BOILER

It is used for small steam capacities

(up to 25 T/hr and 17.5 Kg/cm2)

Low capital cost and fuel efficient (82%)

Applications

Merits

Water flows through the tubes.Water tubes surrounded by hot gas.

WATER TUBE BOILER

For steam range 5.5 to 130 T/hr Used for power plant

Used as high capacity steam boilers.

Applications

Merits

Demerits Efficient control system need. Capital cost is high.

It comes as a complete package that’s why it is called package boiler. It is generally shell type with fire tube design,

Large number of small diameter tubes leading to good heat transfer.

It has high thermal efficiency compared to other types boilers.

PACKAGE BOILER

•Shell ▫ It consists of one or more steel plates made into

cylindrical shape and welded or riveted together. The ends of the shell are closed by flat or curved plates called “boiler heads”. Curved or hemispherical shaped ends are also called ‘dished ends’

•Foundation and Wall ▫ It is constructed of bricks. The wall of the boiler and

combustion chamber may also be made of bricks. This wall restricts heat to the boiler and forms flue gas passage. Also walls provide supports to drums and tubes.

•Tubes ▫ These are narrow pipes that connect boiler heads. Tubes

act as passages for flue gas in FT Boilers and, Water or steam in WT Boilers where evaporation or steam generation takes place in these tubes.

BASIC COMPONENTS OF A STEAM BOILER

•Baffle plates ▫ These are steel plates that blocks off direct exit of flue

gases to the chimney. Baffles make flue gas path longer and zigzag around heating surfaces and make boiler more efficient. This also support tube banks.

BASIC COMPONENTS OF A STEAM BOILER

Baffle plates

•Grate ▫ A grate consists of cast iron bars on which solid fuel such as

coal or wood is burnt. The air passes through the gaps between the bars and sustains combustion process of fuel. Ashes fall down through the grate.

•Steam space ▫ Entire upper space of boiler and tubes which is not occupied

by water.

•Heating surface ▫ A surface of boiler tubes or plates, that is exposed to flue

gases on one side and water on the other side. Heat energy transfer into water takes place through the heating surfaces

•Feed pump ▫ A pump used to pump feedwater into a steam boiler

BASIC COMPONENTS OF A STEAM BOILER

•Super heater ▫ A super heater is a device used to convert saturated

steam or wet steam into dry steam. Reduction of moisture increases internal energy of the steam and then the thermal efficiency.

•Economizer ▫ This use waste heat pass to the chimney to pre-heat feed

water. This also increases efficiency of steam generating system of the boiler.

BASIC COMPONENTS OF A STEAM BOILER

Super heater

Economizer

Furnace or “Fire Box” is a primary part of the boiler where the chemical energy available in the fuel converted into the thermal energy by combustion process.

A furnace is designed for efficient and complete combustion.

Furnace

Major factors of efficient combustion Time of fuel inside the furnace, Temperature inside the furnace, Mixing of coal and air,

The another important feature of the construction of furnace is to reduce the air infiltration.

Dry bottom furnace

Slag type or wet bottom type furnace

Oil fired furnace

Types of Furnace

Boiler drum is the secondary part of the boiler where the water absorb the heat and converted into the steam, that steam send to the turbine after reheating by the super-heater.

Boiler Drum

Main parts ……• Pressure Gauge• This indicates the pressure of the steam in the

boiler• Water Level Indicator• This indicates the water level in the boiler

• Safety Valve• The function of the safety valve is to prevent the

increase of steam pressure boiler above its design pressure

• Fusible Plug• If the water level in the boiler falls below the

predetermined level, the boiler shell and tubes will be overheated.

• Blow-off Cock• The water supplied to the boiler always contains

impurities like mud, sand, and salt due to heating, these are deposited at the bottom of the boiler, they have to be removed using blow-off cock.

• Steam Stop Valve• It regulates the flow of steam supply outside.

The steam from the boiler first enters into an ant-priming pipe where most of the water particles associated with steam are removed

• Feed Check Valve• The high pressure feed water is supplied to the

boiler through this valve. This valve opens towards the boiler only and feeds the water to the boiler

Multi-pass FT Package Boiler

1. Heat loss due to un-burnt Carbon. This loss can be reduced by using of

proper grinded fuel2. Heat loss due to dry flue gases.

This heat can be minimized by completely utilize of heat of flue gases

3. Heat loss due to moisture in the fuel. For minimizing this loss we must use of

dry fuel as possible as4. Heat loss due to surface radiation.

This heat loss can be minimized by proper maintenance of the furnace

Heat loss in boiler

• Combustion is a chemical reaction between fuel and oxygen which results is release of heat.

• Oxygen is required to burn the fuel that is provided from the atmospheric air.

COMBUSTION AND EXCESS AIR IN BOILER

REACTIONS:-

Carbon (C) + Oxygen (O2) Carbon-Dioxide (CO2) + Heat

Hydrogen (2H2) + Oxygen (O2) Water (H2O) + Heat

The efficiency of boiler may be defined by:-

A. Combustion Efficiency“This efficiency is related to the combustion of fuel and air inside the furnace”

B. Thermal Efficiency“This efficiency is related to the heat transfer to the water inside the boiler drum”

C. Fuel and Fluid Efficiency“It indicates the overall efficiency of the boiler inclusive thermal efficiency of the heat exchanger, Radiation and Convection losses output divided by input”

EFFICIENCY OF BOILER

• The ends of the furnace are protected by refractory materials.

• The boiler is subjected to the pressures developed by the heating process and must be protected from over-pressurization to prevent failure or explosion. Boilers contain safety valves and relief valves as the primary means of preventing over-pressurization.

• Boiler pressure vessel design and construction is done in accordance with the American Society of Mechanical Engineers (ASME) Pressure Vessel Construction Code.

• Installation, repair, and alteration are specified by the National Board Inspection Code (NBIC). The National Fire Protection Association (NFPA) codes are also used in part for specification of electrical and piping installation as well as combustion safety.

Boiler design Safety

Boiler Burners and Burner Controls

Boiler Controls are designed to control the activity within a boiler while ensuring safe and efficient operation.

• Waterside Controlso Pressure determinationo Temperature controlo Water level

• Fireside Controlso Burner controlo Flame detectiono Fuel temperatureo Fuel pressure

•Boiler Operator▫The boiler operator is responsible for

operating and maintaining the boiler in a safe and efficient manner.

•Chief Engineer▫Chief engineer of a boiler plant holds the

responsibility for directing boiler operations, procedures and maintenance.

•Log Sheets▫Log sheets are a paper record of boiler

operation and maintenance, and should be used in all boiler rooms to help ensure safe operation.

Maintenance Basics

This includes;• Startup • Cold iron start up and new plant start up. Most

furnace explosions occur during start up and when switching fuels, so always follow the manufacture's guidelines

• Operation & General Maintenance• Requires proper training, equipment familiarity

and routine maintenance procedures• Shutdown • Whether for a short time or long time, different

procedures exist. If the boiler is to be placed out of service for an extended period of time, proper lay-up procedures are required and must be followed.

General Boiler Operations

Thank you!