INTRODUCTION

OF

BOILER

Engr. Omar Sadath, Maritme Lecturer & Trainer, Bangladesh

What is a boiler?

• A boiler is a closed vessel in which water or

other fluid is heated. The heated or vaporized

fluid exits the boiler for use in various

processes or heating applications.

Construction of boiler

• Material- plain low carbon steel. U TS – 430 to 540 mn/m2.

• All flanged plating must be heated after flanging to 600

degree and then allowed to cool slowly in order to stress

relieve.

• Furnace are corrugated for strength, this arrangement also

gives more heating area as compared to plain furnace of

similar dimension.

• Manholes cut into the shell and or end plating must be

compensated by means of compensating ring,these being

riveted or welded in place.

USE OF STEAM ON SHIP

• Heating duties, M.E fuel oil heater,Purifier heater, oil tank heating, Cargo heating, Air conditioning and heating plant, Calorifier, Gelley supply, Sea chests, tracing line for pipe line heating.

• Run turbine Generator

• Run Cargo pump turbines in tanker

• Drive steam driven deck machinery like Winches etc.

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USE OF STEAM ON SHIP

• Operate bilge, Stripping and other steam

driven pump.

• Drive boiler feed water turbine.

• Evaporator/ Fresh water generator heating

media.

• Tank washing in tanker ship and general

cleaning.

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USE OF STEAM ON SHIP

• For boiler soot blowing and for the steam atomized burners.

• Fire fighting as used in steam smothering system.

• Main Engine jacket F.W preheater and Lub oil sump and drain tanks.

• Use in waste oil, Incinerator,slop tanks.

• Use as steam ejector media for ejector pump and vacuum devices.

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Principle of heat transfer in boilers

• Radiation

• Conduction

• Convection

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Schematic Overview of a Boiler Open Feed System

Boiler •Carbonic acid •Oxygen •Scale

Condensate system •Carbonic acid •Oxygen

Feed system •Carbonic acid •Oxygen

Shore make up water •Calcium •Magnesium •Silica

Blow down •TDS •Surface •Bottom

Types of boilers

• Main Boiler- Propulsion of the vessel

• Auxiliary Boiler-Heating of heavy fuel oil using a steam heater, necessary for propulsion would qualify the supplying boiler to be referred to as an auxiliary boiler.

• Tank Boiler-A boiler with large water carrying capacity where the shell is being used as the pressure vessel. Most low pressure auxiliary boilers will come into this category.

• Exhaust Gas Boiler- Boiler operated by hot gas from engine or other exhaust gas sources.

• Drum Type Boiler-Water tube boilers employing steam and water drums. They are also known as bent tube type boilers.

• Package Boiler -Fully automatic, low capacity boilers packaged inside a box type casing, capable of quick steam production and flexible in being positioned anywhere; could be coil type or fire tube type.

C/E HANIF DEWAN 9

Classification of Boilers

Boilers can be classified as follows:

According to geometric orientation of boiler:

According to relative position of water and hot gases:

According to location of furnace:

According to method of water circulation:

According to working pressure:

According to mobility of boiler:

According to number of tubes in the boiler:

According to geometric orientation

of boiler

a) If the axis of boiler is horizontal then it is

called horizontal boiler. Example:- Lancashire

boiler, Locomotive boiler.

b) If the axis of boiler is vertical then it is called

vertical boiler. Example:- Cochran boiler.

c) If the axis of boiler is inclined then it is called

inclined boiler.

According to relative position of water and hot gases

a) Fire tube boilers:- If the hot gases of combustion from the furnace pass through the tubes and water is surrounding the tubes is called fire tube boilers. Example:- Cochran, Lancashire, Locomotive.

b) Water tube boiler:- If the water passes through the tubes and hot gases surrounding the tubes is called water tube boiler. Example:- Babcock and Wilcox boiler.

According to location of furnace

a) Externally fired boilers:- In this boiler the

furnace is placed outside the boiler shell.

Generally water tube boilers are externally

fired. Example:- Babcock and Wilcox boiler.

b) Internally fired boilers:- In this boiler the

furnace is placed inside the boiler shell.

Generally fire tube boilers are internally fired.

Example:- Lancashire, Cochran boiler.

According to method of water circulation

a) Natural circulation boilers:- In this boiler, water

flow take place naturally, by density difference of

water. The flow of water and steam are set up

due to density difference resulting from

difference in temperature. Example:- Lancashire,

Babcock and Wilcox boiler.

b) Forced circulation boilers:- In this boiler, water

flow takes place by a pump. Example:- Benson

boiler, La- mont boiler, Velox boiler.

According to working pressure

a) High pressure boiler:- The working pressure of this boiler is higher than 25 bar. Example:- Babcock and Wilcox boiler.

b) Medium pressure boiler:- The range of working pressure of this boiler is between 10 bar to 25 bar. Example:- Lancashire boiler, Locomotive boiler.

c) Low pressure boiler:- The range of working pressure is between 3.5 to 10 bar. Example:- Cochran and Cornish boiler.

According to mobility of boiler

a) Stationary boiler:- This boiler cannot be moved easily from one place to another place. This are used in power generation or process heating in industries. Example:- Lancashire, Babcock and Wilcox boiler.

b) Mobile boiler:- It is portable boiler and can be easily moved. This is used in marine and locomotive. Example:- Locomotive boiler.

According to numbers of tubes in

the boiler

a) Single tube boiler:- This boiler having only

one fire or water tube for circulation of hot

gases or water. Example:- Cornish boiler.

b) Multi-tube boiler:- This boiler having two or

more fire or water tubes for the circulation of

hot gases or water. Example:- Locomotive,

Cochran, Lancashire, Babcock and Wilcox

boiler.

Smoke tube & Water tube boilers

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Fire tube concept Shell with fire tubes inside Tank type boiler

Water tube concept Drum with fire tubes

Water tube Boiler

• In a water tube boiler, boiler feed water flows through the tubes and enters the

boiler drum. The circulated water is heated by the combustion gases and

converted into steam at the vapour space in the drum. These boilers are selected

when the steam demand as well as steam pressure requirements are high .

• Most modern water tube boiler designs are within the capacity range 4,500 –

120,000 kg/hour of steam, at very high pressures. Many water tube boilers are of

pa kaged onstru tion if oil and /or gas are to e used as fuel. “olid fuel fired water tube designs are available but packaged designs are less common.

• The features of water tube boilers are:

• Forced, induced and balanced draft provisions help to improve combustion

efficiency.

• Less totolerance for water quality, calls for water treatment plant.

• Higher thermal efficiency levels are possible

Comparison between Fire tube boiler

and Water tube boiler

Fire Tube Boiler

1) Hot gases are inside the tube and

water is outside.

2) Operating Pressure limited to 25 bar.

3) Rate of steam generation is lower.

4) Not suitable for large power plant.

5) Chance of explosion is less due to low

pressure.

6) Floor space requirement is more.

7) Cost is less.

8) Required less skill for efficient and

economic working.

9) For producing process steam.

10) There is no problem of scale

deposition and less problem of

overheating and bursting.

Water Tube Boiler

1) Water is inside the tube and hot gases

outside.

2) Can work under as high pressure as

more than 25 bar.

3) Rate of steam generation is higher.

4) Suitable for large power plant.

5) Chance of explosion is higher due to

high pressure.

6) Floor space requirement is less.

7) Cost is more.

8) Required more skill and careful

attention for efficient and economic

working.

9) For producing steam for power

generation as well as process heating.

10) Small deposition of scale will cause

overheating and bursting of the tubes.

COCHRAN BOILER

Cochran boiler is modification of simple

vertical boiler.

Advantages of Cochran Boiler

• It is compact and portable boiler therefore

minimum floor area is required.

• Initial cost of boiler is less.

• It can be moved and set up readily in different

locations.

• Quick and easy installation.

• Any type of fuel can be used.(coal or oil)

Disadvantages of Cochran

Boiler • Steam raising capacity is less due to vertical

design.

• Water along with steam may enter the steam

pipe under heavy loads due to small steam

space.

• Efficiency is poor in smaller size.

Tank type & Drum type boilers

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Fire tube concept Shell with fire tubes inside Tank type boiler

Water tube concept Drum with fire tubes

Type of Boilers

(BIB Cochran, 2003)

3. Packaged Boiler

Oil

Burner

To

Chimney

• Comes in complete

package

• Features

• High heat transfer

• Faster evaporation

• Good convective

heat transfer

• Good combustion

efficiency

• High thermal

efficiency

• Classified based on

number of passes

PACKAGED BOILER • The packaged boiler is so called because it comes as a complete

package. Once delivered to a site, it requires only the steam, water pipe work, fuel supply and electrical connections to be made to become operational.

• Package boilers are generally of a shell type with a fire tube design so as to achieve high heat transfer rates by both radiation and convection.

• The features of packaged boilers are:

• Small combustion space and high heat release rate resulting in faster evaporation.

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

• Forced or induced draft systems resulting in good combustion efficiency.

• Number of passes resulting in better overall heat transfer.

• Higher thermal efficiency levels compared with other boilers.

• This is a packaged boiler. More specifically, it is a typical 3 pass, oil fired packaged boiler.

COMPOSITE FIRE TUBE BOILER

Thanks You!