Thermal power plants operate using the Rankine cycle. Water is heated into steam in a boiler using heat from burning fuel. The high-pressure steam drives turbines which are coupled to generators, producing electricity. The low-pressure exhaust steam from the turbines is condensed into water in a condenser, where it is pumped back into the boiler to repeat the cycle. Thermal power plants contribute the majority of electricity generation in India due to their ability to efficiently convert fuel into power on a large scale.

2. Thermal Power Plants in India

3. A typical Thermal Power Station Operates on a Cycle which is shown in Picture.
The working fluid is water and steam. This is called feed water and steam cycle.
The ideal Thermodynamic Cycle to which the operation of a Thermal Power
Station closely resembles is the RANKINE CYCLE. In steam boiler the water is
heated up by burning the fuel in air in the furnace & the function of the boiler is
to give dry super heated steam at required temperature. The steam so produced is
used in driving the steam Turbines. This turbine is coupled to synchronous
generator (usually three phase synchronous alternator), which generates electrical
energy.

4. The exhaust steam from the turbine is allowed to condense into water in
steam condenser of turbine, which creates suction at very low pressure
and allows the expansion of the steam in the turbine to a very low
pressure. The principle advantages of condensing operation are the
increased amount of energy extracted per kg of steam and thereby
increasing efficiency and the condensate which is fed into the boiler again
reduces the amount of fresh feed water.
The condensate along with some fresh make up feed water is again fed
into the boiler by pump (called the boiler feed pump). In condenser the
steam is condensed by cooling water. Cooling water recycles through
cooling tower. This constitutes cooling water circuit. The ambient air is
allowed to enter in the boiler after dust filtration. Also the flue gas comes
out of the boiler and exhausted into atmosphere through stacks. These
constitute air and flue gas circuit. The flow of air and also the static
pressure inside the steam boiler (called draught) is maintained by two
fans called Forced Draught (FD) fan and Induced Draught (ID) fan.

6. Inside the boiler there are various heat exchangers, viz. Economiser,
Evaporator (not shown in the fig above, it is basically the water tubes, i.e.
down comer riser circuit), Super Heater (sometimes Reheater, air
preheater are also present).
In Economiser the feed water is heated to considerable amount by the
remaining heat of flue gas.
The Boiler Drum actually maintains a head for natural circulation of two
phase mixture (steam + water) through the water tubes.
There is also Super Heater which also takes heat from flue gas and raises
the temperature of steam as per requirement.

7. INTRODUCTION
 A Thermal Power Plant converts the heat energy of coal
into electrical energy. Coal is burnt in a boiler which
converts water into steam. The expansion of steam in
turbine produces mechanical power which drives the
alternator coupled to the turbine. Thermal Power Plants
contribute maximum to the generation of Power for any
country.
 Thermal Power Plants constitute 75.43% of the total
installed captive and non-captive power generation in
India.
 In thermal generating stations coal, oil, natural gas etc.
are employed as primary sources of energy.

8. Selection of site for a Thermal Station
Obviously the location of thermal power station is best at the center
of gravity of the load, but many times it is not possible to establish a
thermal power plant at the CG of the load. Since normally CG point
of the load may be at the heart of the city. So other points are to be
considered to decide the best optimized location of the power
plant.
The electric power generation plant must be constructed at
such a place where the cost of land is quite reasonable.
The land should be such that the acquisition of private property
must be minimum.
A large quantity of cooling water is required for the condensers etc
of thermal power generation plant, hence the plant should
preferably situated beside big source of natural water source such as
big river.

9. Availability of huge amount of fuel at reasonable cost is one of
the major criterion for choosing plant location.
The plant should be established on plane land.
The soil should be such that it should provide good and firm
foundation of plant and buildings.
The thermal power plant location should not be very nearer
to dense locality as there are smoke, noise steam, water vapors
etc.
There must be ample scope of development of future demand.
Place for ash handling plant for thermal power station should
also be available very near by.
Very tall chimney of power station should not obstruct the
traffics of air ships.

10. GENERAL LAYOUT OF
THERMAL POWER PLANT

11. Boiler
Turbine
Economizer
Air preheater
Super heater
Reheater
Condenser
Feed heater
Cooling power
FD and ID Fan

12. A boiler or steam generator is a
closed vessel in which water
under pressure, is converted
into steam. it is one of the major
components of a thermal power
plant. Always designed to
absorb maximum amount of
heat released in the process of
combustion.
Boilers are of two types-
1. Fire tube boiler
2. Water tube boiler

13. In thermal power plants generally 3 turbines are used to
increases the efficiency.
• High pressure turbine
• Intermediate pressure turbine
• Low pressure turbine

14. Economizer
Flue gases coming out of the boiler carry lot of heat. An economizer
extracts a part of this heat from flue gases and uses it for heating
feed water. This use of economizer results in saving coal
consumption and higher boiler efficiency

15. Air Pre Heater
The function of air pre heaters is to preheat the air before
entering to the furnace by utilizing some of the energy left in
the flue gases before exhausting them to the atmosphere.
After flue gases leave economizer, some further heat can be
extracted from them and used to heat incoming heat. Cooling
of flue gases by 20 degree centigrade increases the plant
efficiency by 1%.

16. Superheater:
Superheater is a component of a steam-generating unit in
which steam, after it has left the boiler drum, is heated
above its saturation temperature. The amount of
superheat added to the steam is influenced by the
location, arrangement, and amount of super heater
surface installed, as well as the rating of the boiler. The
super heater may consist of one or more stages of tube
banks arranged to effectively transfer heat from the
products of combustion. Super heaters are classified as
convection , radiant or combination of these.

17. Reheater: Some of the heat of superheated steam is used to
rotate the turbine where it loses some of its energy. Reheater is also steam
boiler component in which heat is added to this intermediate-pressure
steam, which has given up some of its energy in expansion through the
high-pressure turbine. The steam after reheating is used to rotate the
second steam turbine where the heat is converted to mechanical energy.
This mechanical energy is used to run the alternator, which is coupled to
turbine , there by generating electrical energy.

18. Condenser
Steam after rotating steam turbine comes to condenser. Condenser refers
here to the shell and tube heat exchanger (or surface condenser) installed
at the outlet of every steam turbine in Thermal power stations of utility
companies generally.
These condensers are heat exchangers which convert steam from its
gaseous to its liquid state, also known as phase transition.
In so doing, the latent heat of steam is given out inside the condenser.
Where water is in short supply an air cooled condenser is often used.
An air cooled condenser is however significantly more expensive and
cannot achieve as low a steam turbine backpressure (and therefore less
efficient) as a surface condenser.
The purpose is to condense the outlet (or exhaust) steam from steam
turbine to obtain maximum efficiency and also to get the condensed steam
in the form of pure water, otherwise known as condensate, back to steam
generator or (boiler) as boiler feed water.

19. CONDENSER

20. Feed Water heater
oFeed water heating improves overall plant
efficiency.
o Thermal stresses due to cold water entering the
boiler drum are avoided.
oQuality of steam produced by the boiler is
increased.

21. A condenser needs huge quantity of water to condense the
steam .
Typically a 2000MW plant needs about 1500MGallon of
water.
Most plants use a closed cooling system where warm water
coming from condenser is cooled and reused
Small plants use spray ponds and medium and large plants
use cooling towers.
Cooling tower is a steel or concrete hyperbolic structure
having a reservoir at the base for storage of cooled water
Height of the cooling tower may be 150 m or so and
diameter at the base is 150 m

22. Air
Heater
Force Draft Fan (FD Fan):
The function of FD FAN is to supply sufficient quantity of air required for
complete combustion.
The air flow is as shown below FD Fan Air Heater Furnace
FD Fan Furnace
Induced Draft Fan (ID Fan):
The function of Induced Draft fan is to suck the gases out of furnaces and
throw them into the stack.
Boiler is provided with two no. of Induced Draft Fans.

23.  1. Boiler is an apparatus to produce steam.
 2.Thermal energy released by combustion of fuel issued to make
steam at the desired temperature and pressure.
 CLASSIFICATION OF BOILERS
 The boiler may be classified as :
 1.Horizontal, vertical or inclined
 2. Fire tube & water tube
 3. Externally fired & internally fired
 4. Forced circulation & internally fired
 5.High pressure & low pressure
 6. Forced circulation & natural circulation
 7. Stationary & portable
 8. Single tube & multi tube boilers

24. In the fire tube boiler the hot gases are inside the tubes & the water
surrounds in the tube.
ex. Cochran, locomotive etc.

25.  In the water tube boiler the water is inside the tube
& the hot gases are surround them.
 ex. Stirling

26.  Horizontal , vertical or inclined
 If the axis of boiler is horizontal, the boiler is called horizontal.
 If the axis is vertical then it is called vertical.
 If the axis is inclined then it is called inclined.
 Advantage of horizontal boiler:
 a. it should be repaired easily.
 b. occupies less floor area.
Externally & internally fired
 The boiler is known as externally fired if the fire is outside the shell.
 ex. Babcock & wilcox
 In case of internally fired boilers, the furnace is located inside the boiler shell.
 ex: cochran, lancashire etc.
 High pressure & low pressure boilers
 The boilers which produce steam at pressure of 80 bar and above are called high pressure
boiler.
 ex. Velox
 The boiler which produce steam at pressure below 80 bar are called low pressure boiler.
 ex. Cochran
 Single tube multi-tube boilers
 The fire tube boilers are classified as single tube & multi tube boilers, depending upon the fire
 tube is one more than one.
 Ex: cornish boiler

27. STEAM TURBINE
A steam turbine is a device that extracts thermal energy from
pressurised steam and uses it to do mechanical work.

Principle of steam turbine:
1.The steam energy is converted mechanical work by expansion
through the turbine.
2.Expansion takes place through a series of fixe blades(nozzles)
and moving blades.
3. In each row fixed blade and moving blade are
called stage.
Steam turbine:
• Widely used in CHP(combined heat and power) applications.
• Oldest prime mover technology
• Capacities: 50 kW to hundreds of MWs
• Thermodynamic cycle is the “Rankin cycle” that uses a
boiler

28. Types of steam turbine:
1) Impulse steam turbine:
 The basic idea of an impulse turbine is that a jet of steam
from a fixed nozzle pushes against the rotor blades and
impels them forward.
 The velocity of steam is twice as fast as the velocity of
blade.
 Pressure drops take place in the fixed blade (nozzle).
2) Reaction steam turbine:
 A reaction turbine utilizes a jet of steam that flows from a
nozzle on the rotor.
 Actually, the steam is directed into the moving blades by
fixed blades designed to expand the steam.
 The result is a small increase in velocity over that of the
moving blades.

29. THANK
YOU
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