The boiler system comprises a feed-water system, steam system, and fuel system. The feed-water system supplies treated water to the boiler and regulate it automatically to meet the steam demand. Various valves and controls are provided to access for maintenance and monitoring.
1. ME 6701 POWER PLANT
ENGINEERING
Faculty
A.R.PALANIVELRAJAN
Assistant Professor
Department of Mechanical Engineering
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2. Layout of Steam Power PLant
The Layout consists of four circuits namely
Coal and ash circuit.
Air and gas circuit.
Feed water and steam flow circuit.
Cooling water circuit.
4. CLASSIFICATION OF
BOILERS
HORIZONTAL, VERTICAL OR INCLINED BOILER
If the axis of the boiler is horizontal, the boiler is called horizontal, if
the axis is vertical, it is called vertical boiler and if the axis is
inclined it is called as inclined boiler. The parts of horizontal
boiler is can be inspected and repaired easily but it occupies
more space. The vertical boiler occupies less floor area.
5. FIRE TUBE AND WATER TUBE
In the fire boilers, the hot gases are inside the tubes and the
water surrounds the tubes.
Examples: Cochran, Lancashire and Locomotive boilers.
In the water tube boilers, the water is inside the tubes and hot
gases surround them.
Examples: Babcock and Wilcox,
Stirling, Yarrow boiler etc.
6. EXTERNALLY FIRED AND INTERNALLY FIRED
The boiler is known as externally fired if the fire is outside the
shell.
Examples: Babcock and Wilcox boiler, Stirling boiler etc.
In case of internally fired boilers, the furnace is located inside
the shell.
Examples: Cochran, Lancashire boiler etc.
7. FORCED CIRCULATION AND NATURAL CIRCULATION
In forced circulation type of boilers, the circulation of
water is done by a forced pump.
Examples: Velox, Lamont, Benson Boiler etc.
In natural circulation type of boilers, circulation of
water in the boiler takes place due to natural
convention currents produced by the application of
heat.
Examples: Lancashire, Babcock and Wilcox boiler etc.
8. HIGHER PRESSURE AND LOW PRESSURE BOILERS
The boiler which produce steam at pressures of 80 bar and
above are called high pressure boilers.
Examples: Babcock and Wilcox, Velox, Lamont, Benson Boiler
etc.
The boilers which produce steam at pressure below 80 bar are
called low pressure boilers.
Examples: Cochran, Cornish, Lancashire and Locomotive boiler
etc.
9. SINGLE TUBE AND MULTI TUBE BOILER
The fire tube boilers are classified as single tube and multi-
tube boilers, depending upon whether the fire tube is one or
more than one.
Examples: Cornish ,simple vertical boiler are the single tube boiler
and rest of the boilers are multi-tube boiler.
10. BOILER MOUNTINGS
Boiler mountings are the machine components
that are mounted over the body of the boiler
itself for the safety of the boiler and for complete
control of the process of steam generation.
11. Various boiler mountings are as under:
1) Pressure gauge
2) Water Level Indicator
3) Fusible plug
4)Safety Valve
5) Steam stop valve
6) Feed check valve
7) Blow off cock
12. PRESSURE GAUGE
To record the steam pressure at which the steam
is generated in the boiler.
13. WATER LEVEL INDICATOR
The function of water level indicator is to indicate
the level of water in the boiler constantly
14. FUSIBLE PLUG
To extinguish fire in the event of water level in the
boiler shell falling below certain specified limit. It
protects fire tubes from burning when the level of
the water in the water shell falls abnormally low. It
is installed below boiler's water level. When the
water level in the shell falls below the top of the
plug, the steam cannot keep it cool and the
fusible metal melts due to over heating.
15. SAFETY VALVE
The function of safety valve is to release the
excess steam when the pressure of steam inside
the boiler exceeds the rated pressure.
16. STEAM STOP VALVE
A valve is a device that regulates the flow of a
fluid (gases, fluidized solids, slurries, or liquids) by
opening, closing, or partially obstructing various
passageways. Its function is to shut off or regulate
the flow of steam from the boiler to the steam
pipe or steam from the steam.
17. FEED CHECK VALVE
The function of a feed check valve is to control
the supply of water to the boiler and to prevent
the escaping of water from the boiler when the
pump pressure is less or pump is stopped.
18. BLOW OFF COCK
To drain out the water from the boiler for internal
cleaning, inspection, repair or other purposes.
28. MODERN HIGH PRESSURE
BOILERS
A boiler which generates steam at pressure
greater than 80 bar, a temperature of about 500
degree, producing steam more than 250 tons per
hour called high pressure boilers.
35. FLUIDIZED BED BOILERS
• Fluidized bed boilers produce steam from
fossil and waste fuels by using a technique
called fluidized bed combustion.
• These can be divided into two types:
1. Bubbling fluidized bed (BFB) boilers
2. Circulating fluidized bed (CFB) boilers
Fluidized bed : defined as the bed of solid
particles behaving as a fluid.
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36. Fluidized Bed Combustion (FBC)
• When an evenly
distributed air or
gas is passed
upward through a
finely divided bed
of solid particles
supported on a fine
mesh, the particles
are undisturbed at
low velocity. (air or
gas experiences a
pressure drop
across the bed)
• As air/gas velocity
is gradually
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37. Fluidized Bed Combustion (FBC)
• With further
increase in
air/gas velocity,
there is bubble
formation,
vigorous
turbulence, rapid
mixing and
formation of
dense defined
bed surface.
• The bed of solid
particles exhibits
the properties of
a boiling liquid
and assumes the
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38. Fluidized Bed Combustion (FBC)
• If solid particles in a fluidized state is
heated to the ignition temperatures of
coal, and coal is injected continuously
into the bed, the coal will burn rapidly
and bed attains a uniform temperature.
• The fluidized bed combustion (FBC)
takes place at about 840°C to 950°C.
• Since this temperature is much below the
ash fusion temperature, melting of ash
and associated problems are avoided.
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39. Bubbling Fluidized bed (BFB) Boiler
Crushed coal (6-20 mm) is injected into the fluidized bed
of limestone just above an air-distribution grid at the
bottom of the bed .
The air flows upwards through the grid from the air
plenum into the bed where combustion of coal occurs.
The products of combustion leaving the bed contain a
large proportion of unburnt carbon particles which are
collected in cyclone separator and fed back to the bed.
The boiler water tubes are located in the furnace.
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41. Bubbling Fluidized bed (BFB) Boiler
As a result of low combustion temperatures (800 – 900°C ),
inferior grades of coal can be used without slagging
problems and there is less formation of Nox.
The volumetric heat release rates are 10 to 15 times
higher and the surface heat transfer rates are 2 to 3 times
higher than a conventional boiler.
This makes the boiler more compact.
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42. Advantages of Fluidized Bed Boilers
Fluidized bed combustion (FBC) has emerged as a viable
alternative and has significant advantages over
conventional firing system and offers multiple benefits –
compact boiler design, fuel flexibility, higher combustion
efficiency and reduced emission such as SOx and NOx.
The fuels burnt in these boilers include coal, rice husk,
bagasse & other agricultural wastes.
The fluidized bed boilers have a wide capacity range- 0.5
T/hr to over 100 T/hr.
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46. Condensers
It is closed vessel in which steam is condensed by
abstracting the heat and where the pressure is
maintained below atmospheric pressure by
continuously condensing the steam by means of
circulating cold water at atmospheric
temperature.
Types:
1.Down flow condenser 2.Central
flow condenser
3.Evaporation condenser
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