Thermal Power Plant *Boiler plant

*Turbine plant
*Condensing plant
*Feed water plant
*Furnace gas circuit
*Steam circuit
*Condenser cooling water circuit (1 kg steam = 60 kg water)
*Cooling air circuit
 Boiler – Steam Generator
• Made of steel
• 14,00,000 kg/hr steam at 350 bar pressure
Cochran Boiler • 1-3 m dia
• 2-6 m high
• 20-3000 kg/hr
• 20 bar
• 70 – 75 %
efficient
1. Shell: It has a vertical axis cylindrical drum with hemispherical dome type shell at
the top.
2. Grate: It is the platform on which the solid fuel is burnt.
3. Combustion Chamber: The burning of fuel takes place in the combustion chamber.
4. Fire Tubes: Cochran boiler has multi tubular fire tubes. The hot flue gases from the
combustion chamber travels to the smoke box through these fire tubes. The fire
tubes helps in the exchange of heat from the hot flue gases to the water.
5. Fire Hole: It is the hole provided to fire the fuel inside the furnace.
6. Furnace: It lies at the bottom of the boiler. Furnace is the place where all the fuel
is burnt. Without furnace the working of this boiler is not possible.
7. Chimney: The chimney is attached to the smoke box. It transfer smoke to the
environment. The size of chimney is small as compared with other boiler.
8. Fire Brick Lining. The fire brick lining is present in the combustion chamber and
helps in the combustion of the fuel.
9. Manhole: A manhole is provided for the cleaning and inspecting of the boiler from
inside.
10. Flue Pipe: It is a small passage connecting the fire box and combustion chamber.
The hot gases enters into combustion chamber through the flue pipe.
Other Boiler mountings and accessories attached to the this boiler are:
1. Pressure Gauge: It measures the pressure of steam inside the boiler.
2. Safety Valve: It blows off the extra steam when the steam pressure
inside the boiler reaches above safety level.
3. Water level Indicator: The position of the water level in the Cochran
boiler is indicated by the water level indicator.
4. Stop Valve: Stop valve is used to transfer steam to the desired
location when it is required. Otherwise it stops the steam in the boiler.
5. Blow off Cock: It is used to blow off the settle down impurities, mud
and sediments present in the boiler water.
Working
In Cochran boiler first the fuel is inserted into the fire box and placed on the grate. The fuel
is ignited through the fire hole provided at the right bottom of the boiler.
The fuel is burnt in the fire box and due to the burning of the fuel, smoke and hot flue gases
emerges out. The hot flue gases enter into the combustion chamber through flue pipes.
From the combustion chamber hot gases enters into the fire tubes. The fire tubes are
surrounded by water. The hot flue gases inside the tubes exchange the heat from the hot
gases to the water. Due to the exchange of heat, the temperature of the water start
increasing and it gets converted into steam. The steam produced rises upward and collected
at top of the boiler in the hemispherical dome. An anti-priming pipe is installed at top of the
boiler which separates the water from the steam and makes it dry steam. This dry steam is
then transfer to the turbines through the steam stop valve.
The hot flue gases and smoke after exchanging heat moves to the smoke box. From the
smoke box the burnt gases and smoke is discharge to the atmosphere through the chimney.
Burnt fuel is transferred to the ash pit. Blow off cock is preset at left bottom of the boiler
and is used to blow of the impurities, mud and sediment from the boiler water.
A fusible plug is also provided at top of the combustion chamber. When the temperature of
the combustion chamber crosses the permissible level, the fusible plug melts and the water
through the combustion chamber enter into the furnace of the boiler and stop the fire. In
this way a big fire accident can be prevented to take place and also protects the boiler from
damage.
Various boiler mounting and accessories are attached to the boiler for its efficient working.
Advantages and Disadvantages

Advantages
(i) Low initial installation cost.
(ii) It requires less floor area.
(iii) Easy to operate and handle.
(iv) Transportation of Cochran boiler is easy.
(V) It can use all types of fuel.

Disadvantages
(i) Low rate of steam generation.
(ii) Inspection and maintenance is difficult.
(iii) High room head is required for its installation due to the
vertical design.
(iv) It has limited pressure range.
Babcock and Wilcox
The various main parts of Babcock and Wilcox Boiler are as follows
1. Drum: It is horizontal axis drum which contains water and steam.
2. Down Take Header: It is present at rear end of the boiler and connects the water
tubes to the rear end of the drum. It receives water from the drum.
3. Up Take Header: it is present at front end of the boiler and connected to the front
end of the drum. It transports the steam from the water tubes to the drum.
4. Water Tubes: They are the tubes in which water flows and gets converted into
steam. It exchanges the heat from the hot flue gases to the water. It is inclined at angle
of 10-15 degree with the horizontal direction. Due to its inclination the water tubes do
not completely filled with water and the water and steam separated out easily.
5. Baffle Plates: Baffle plates are present in between water tubes and it allows the
zigzag motion of hot flue gases from the furnace.
6. Fire Door: It is used to ignite the solid fuel in the furnace.
7. Grate: It is a base on which the burning of the solid fuel takes place.
8. Mud Collector: It is present at the bottom of down take header and used to collect
the mud present in the water.
9. Feed Check Valve: it is used to fill water into the drum.
10. Damper: It regulates the flow of air in the boiler.
The various boiler mounting and accessories used in this type of
boiler are:

1. Superheater: It increases the temperature of saturated steam

to the required temperature before discharging it from steam
stop valve.

2. Pressure Gauge: It is used to check the pressure of steam

within the boiler drum.

3. Water Level Indicator: It shows the level of water within the

drum.

4. Safety Valve: It is a valve which acts when the pressure of

steam within the boiler drum increase above the safety level. It
opens and releases the extra steam in the environment to
maintain the desired pressure within the
boiler.
Working
Now let’s discuss the working of Babcock and Wilcox boiler step by step.
First the water starts to come in the water tubes from drum through down take
header.
The water present in the inclined water tubes gets heated up by the hot flue gases.
The coal burning on the grate produces hot flue gases and it is forced to move in
zigzag way with the help of baffle plates.
As the hot flue gases come in contact with water tubes, it exchanges the heat with
water and converts it into steam.
The steam generated is moved upward and through up take header it gets
collected at upper side in the boiler drum.
An anti-priming pipe is provided in the drum. This anti-priming pipe filters the
water content from the steam and allows only dry steam to enter into superheater.
The superheater receives the water free steam from the anti-priming pipe. It
increases the temperature of steam to desired level and transfers it to the steam
stop valve.
The superheated steam from the steam stop valve is either collected in a steam
drum or made to strike on the steam turbine for electricity generation.
Advantages and Disadvantages

Advantages
Steam generation capacity is high. It is about 2000 to 40000 kg/hr.
It occupies less space.
Replacement of defective tubes is easy.
It is the only boiler that is used to generate large quantity of heat in power stations.
The draught loss is minimum.
Inspection of this types of boiler can be done anytime during its working.

Disadvantages
High maintenance cost.
It is not much suitable for impure and sedimentary water. In case of impure and
sedimentary water, scale may deposit in the tubes and this leads to overheating and
bursting of tubes. That’s why water treatment is must before feeding into the boiler.
Continuously supply of feed water is required for the working. In the case if feed
water is not continuously supplied even for a short period of time, the boiler gets
overheated. Water level must be carefully watched during the operation of the
Babcock and Wilcox boiler.