Final Boiler

8/3/2019 Final Boiler

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Steam Generator (Boiler)

1Prepared by M. Ola & R. Bhaskar


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` A steam generator or boiler is usually a closed vessel

made of metal/alloy. Its function is to transfer the heat

to waterand ultimately to generate steam.

` Open vessels, generating steam at atmospheric pressure

are not considered to be boiler

` The steam produced may be supplied to

` Power Generation

` Heating

o Space heating

o Hot watersupply` Industrial Processes

o Sugar mills

o Chemical industries2Prepared by M. Ola & R. Bhaskar


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Classification of Boilers

Tube Content (Relative position of hot gas and water):

Fire tube boiler

Hot gasses pass through the tubes that are surrounded by

water. Horizontal return tubular, vertical tubular, Lancashire,

Cochran, Cornish, locomotive fire box,scotch marine etc.

Water tube boiler

The tubes contain water and the hot gases flow outside

Babcock and Wilcox, Stirling boiler, La-mont boiler, Benson

boiler and Loeffler boiler



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` Method of firing(Furnace Position):

` Internally fired boiler

Lancashire, Locomotive, and Scotch

` Externally fired boiler

Babcock and Wilcox

` Pressure of steam:

` High pressure (>80 kg/cm2)

Babcock and Wilcox, Lamont etc

` Low pressure (


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According to the tube shape & position:

(i) Form: Straight or bent orsinuous

(ii) Inclination: Horizontal or inclined or vertical

Method of circulation of water:

Forced circulation: Lamont, Velox, Benson boiler

Natural circulation: Lancashire, Babcock Wilcox



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` Combustion ofsolid, liquid, or gas

` Electrical or nuclear energy

` Hot waste gases of other chemical reactions

According to use:

Land boilersPortable boiler

Mobile boilers

Prepared by M. Ola & R. Bhaskar


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` Should be absolutely reliable, capable of producing

maximum steam at required pressure with minimum of

fuel consumption, minimum attention and minimum

initial cost and operating cost.

` Simple constructions

` Quickstarting from cold

` Strong enough against temperature stress

` Well design combustion chamber

` Less floor area,space & light weight` Best gauges,safety valves and other mountings

` Easily accessible for inspection, cleaning and repairs



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Fire Tube Boilers

A fire tube boileris a type ofboilerin which hot gases / flue

gases (products ofcombustion)from a fire (heat source) passthrough one or more tubes running through a sealed

container of water. The heat energy from the gases passes

through the sides of the tubes by thermal conduction, heating

the water and ultimately creating steam.A fire-tube boileris

sometimes called a "smoke-tube boiler" or"shell boiler" orsometimes just "fire pipe".

Types of Fire Tube Boiler

Cochran boiler

Lancashire boiler Scotch marine boiler Locomotive boiler etc.



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Vertical TubularVertical Tubular Boiler:Boiler:

` Used in small factories, small water supply

plants, winch engines in mines and on sites of

temporary nature such as construction work etc.

` Required minimum floor space, not requiredelaborate foundations, and is portable.

` Cheap, easy to start but inefficient due to large

wastage of fuel and less heating surface.

` Vertical Boilers are: Simple (having one to three

cross tubes), fire tubes and water tubes types.



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Simple Cross tube vertical boiler:Simple Cross tube vertical boiler:

` consists of acylindrical shellsurrounding acylindrical fire

box.` heating surface

is about 8-10times the grate

area.` 50% efficiency



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Cochran Boiler:Cochran Boiler:` It is a Vertical multitubular fire tube boiler

` Improvement over the simple vertical boiler asit provides greater heating surface.

` Total heating surface area is about 10-25 timesof the grate area

` Efficiency 70-75%` Ranges from 1m dia. X 2m height, evaporation

20kg/hr to 3m dia. X6m height, evaporation3000kg/hr.

` Internally fired` Coal or oil burnt



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Cochran Boiler:

Consists of an external cylindrical shell and a fire box

fuel is fed into the grate through the fuel door and lighted fuel is burnt on the grate and hot gases go to the

combustion chamber through a short flue tube

hot gases pass through fire tubes and heat the

surrounding water and convert it into steam

Since the steam is lighter, it goes up the steam space

waste gases enter the smoke box and are released through

the chimney

During shut down, the boiler attendant can enter the

boiler through the man hole



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` It is horizontal fire tube boiler size range from

a shell 2m diaX6m long to 3m diaX10m long

` Working pressure range are up to 20kg/cm2

` Ratio of heating surface to grate area is 24-30

` Efficiency is about 56% without economizer

and 75% with economizer.` In Lancashire Boiler two flue tubes.



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Water Tube Boiler

A water tube boiler is a type of boiler in which water circulates in

tubes heated externally by the hot gases / flue gases. Water tube

boilers are used for high- pressure boilers. Fuel is burned inside thefurnace, creating hot gas which heats up water in the steam generating

tubes.

Types of watertube boiler

Babcock & Wilcox boiler

Sterling boiler etc.



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Water Tube Boiler

The drums are used forstorage of water and steam. As they are not required to

contain tubular heating surface, they can be much smaller in diameter than the fire

tube shell and can, therefore, be built to resist high pressure. Generation ofsteam is

quicker as water is subdivided into small volume. The initial cost, operational costand maintenance costs of water tube boiler is higher than that of an equivalent fire

tube boiler



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` Water tube boiler having lager

pressure ranges and larger sizes.

` Three main parts, steam & waterdrum, water tubes and furnace.



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` Babcock & Wilcox boiler



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` Fire tubes boilers has a large volume of water, therefore more

flexible and can meet the sudden demand ofsteam without muchdrop of pressure.

` Fire tubes boiler is rigid and ofsimple mechanical construction,so greater reliability and low in first cost.

`

Fire tube boilers can be made in smallest sizes therefore simpleto fabricate and transport, occupies less floor space but moreheight.

` Due to mostly externally fired water tubes boilerso furnace canbe altered considerably to meet the fuel requirements.

` Water tubes boilers are more readily accessible for cleaning,inspection and repairs, compared to the fire tube boilers.

` Modern trend is in the favors of water tube boiler due tocontinuous increase in capacities and steam pressures.



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Boiler Mountings:

Mountings are required for proper and safe

functioning of the boilerwhich are generallymounted over the boiler shell.

Water Level Indicator

Pressure gauge Safety valves

Steam stop valve

Blow off cock

Feed Check valve



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Water Level Indicator

The water level indicator

is needed to ascertain the

water level ofa boiler.

Two water level indicators

should be fitted for each

boilerin such a place thatthe water level can be

constantly seen.



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Pressure Gage

A pressure gauge is aninstrument by means ofwhich

the pressure exerted inside a vessel can be measured.

There are two types ofpressure gauges, one is Bourdon

tube pressure gauge and the otheris diaphragm type

gauge.

Fig.:A Bourdon Tube Pressure Gage 32Prepared by M. Ola & R. Bhaskar


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Safety Valve

The safety valve (pressure relief valve)is

used in a boiler to relieve the

pressure ofsteam when it is above the

working pressure.

Its function is to discharge a portion of

the steam from the boiler automatically

when the steam pressure exceeds the

normal limit. It is mounted on the top of

the shell.

As per boiler regulation two safety

valves are required to be fitted in each

boiler.



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Steam Stop Valve

The function of the stop valve or junction valve is to regulate the

flow ofsteam from the boiler to the main steam pipe.

To shut offthe steam completely when required.



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Boiler Accessories

Accessories are used for efficient running ofthe boiler

Superheater

Economiser

Air preheater



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AirPreheater:



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Used to recover heat from the exhaust flue gases

Installed in between the economizer and chimney.

The required airforcombustion is passed

through the air preheaterwhere its temperature is

raised.

Then hot air passed to the furnace.

ADVANTAGES

Gives higherfurnace temperature which results

more heat transfer thus increase evaporative

capacity.

Approximately boiler efficiency increases about 2%

for each 30-35oC

rise in air temperature.



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BoilerPerformance

As the function of a boiler is to generate steam, so the amount of water

evaporated may be considered as a performance ofthe boiler.

The quantity of steam which is actually produced in boiler at obser ved

conditions is known as an actual evaporation.

The observed conditions are the pressure, quality of steam and temperature

of feed water.

As the steam is usually generated in a boiler at constant pressure, so heat

supplied by the fuel is equal to the enthalpy absorbed by the steam.

If ma be the mass of steam formed actually in a given time in kg

(or sometimes per kg of fuel), then

Q=ma (h2h1)

where Q denotes the amount ofheat utilized and h2h1, denotes the amount of

enthalpy absorbed per kg ofsteam.



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BoilerPerformance

Superheated steam: when the dry steam is further

heated at constant pressure, thus raising its temperature,

it is said to be superheated steam

Dryness fraction or Quality of steam: It is the ratio ofdry

steam per kg ofwet steam

x = ms/ (ms + mw)

ms = mass ofdry steam

mw = mass ofwaterin suspension



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Boiler Capacity

Evaporation or equivalent evaporation per hour

may be taken as a measure of boilercapacity. It is

generally measured in tons or kg per hour.



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Selection of Boiler

The selection of type and size ofa boiler

depends on the following factors

The power required and working pressure

The geographical position of the power house

Quality of the fuel and water available

Steam generation rate.

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