A steam power plant works on the Rankine cycle to convert heat from burning coal into mechanical work. Coal is pulverized and burned in a boiler to produce high pressure steam. This steam powers a turbine, which spins an alternator to generate electricity. The steam is then condensed in a condenser and pumped back to the boiler to repeat the cycle. Thermal efficiency is around 35-40% due to heat lost in the condenser. Proper site selection considers factors like fuel transportation, water availability, and environmental impact.

1. Steam Power Plant

2. Introduction
• Thermal power plant is also referred as coal thermal
power plant and steam turbine power plant.
• A steam power plant using steam as working substance
works basically on Rankine cycle.
• Rankine cycle is a thermodynamic cycle of heat engine
that converts heat into mechanical work.
• Steam is generated in a boiler, expanded in the prime
mover and condensed in the condenser and fed into the
boiler again.
• Thermal efficiency is between 35-40% because of
maximum energy is wasted in condenser.

4. Working diagram Thermal power
station.

5. Working of Steam Power Plant
• The working can be studied conveniently with
the help of various cycles.
• The entire arrangement of steam power plant
can be divided into 4 main circuits namely,
1. Fuel & ash circuit
2. Air & fuel gas circuit
3. Feed water & steam circuit
4. Cooling water circuit

6. Components of Steam Power Plants
• Coal
• Boiler
• Super heater
• Economizer
• Air pre-heater
• Steam Turbine
• Condenser
• Alternator
• Feed water pump
• Cooling Tower

7. Coal
• Coal is transported from coal mines to the generating station. Generally, bituminous coal
or brown coal is used as fuel.
• The coal is stored in either 'dead storage' or in 'live storage'.
• Dead storage is generally 40 days backup coal storage which is used when coal supply is
unavailable. Live storage is a raw coal bunker in boiler house.
• The coal is cleaned in a magnetic cleaner to filter out if any iron particles are present
which may cause wear and tear in the equipment.

8. • The coal from live storage is first crushed in small particles and then taken
into pulverizer to make it in powdered form. Fine powdered coal undergoes
complete combustion, and thus pulverized coal improves efficiency of the
boiler.
• The ash produced after the combustion of coal is taken out of the boiler
furnace and then properly disposed. Periodic removal of ash from the boiler
furnace is necessary for the proper combustion.

9. Boiler
• The mixture of pulverized coal and air (usually preheated air) is taken into boiler and
then burnt in the combustion zone.
• On ignition of fuel a large fireball is formed at the center of the boiler and large amount
of heat energy is radiated from it.
• The heat energy is utilized to convert the water into steam at high temperature and
pressure.
• Steel tubes run along the boiler walls in which water is converted in steam.
• The flue gases from the boiler make their way through super-heater, economizer, air pre-
heater and finally get exhausted to the atmosphere from the chimney.

10. Super-heater
• The super-heater tubes are hanged at the hottest part of the boiler.
• The saturated steam produced in the boiler tubes is superheated to
about 540 °C in the super-heater.
• The superheated high pressure steam is then fed to the steam
turbine.

11. Economizer
• An economizer is
essentially a feed water
heater which heats the
water before supplying to
the boiler.
• It absorbs remaining heat
from the flue gases so
that the temperature of
water is increased &
hence thermal efficiency
is increased.

12. Air pre-heater
• The primary air (PA) fan
takes air from the
atmosphere and it is then
warmed in the air pre-
heater.
• Pre-heated air is injected
with coal in the boiler.
• The advantage of pre-
heating the air is that it
improves the coal
combustion.

13. Steam turbine
• High pressure super heated steam is fed to the steam turbine which
causes turbine blades to rotate.
• Energy in the steam is converted into mechanical energy in the
steam turbine which acts as the prime mover.
• The pressure and temperature of the steam falls to a lower value and
it expands in volume as it passes through the turbine.
• The expanded low pressure steam is exhausted in the condenser.

14. Alternator
• The steam turbine is coupled to an alternator.
• When the turbine rotates the alternator, electrical energy is
generated.
• This generated electrical voltage is then stepped up with the help of
a transformer and then transmitted where it is to be utilized.

15. Condenser
• The exhausted steam is condensed in the condenser
by means of cold water circulation.
• Here, the steam loses it's pressure as well as
temperature and it is converted back into water.

16. Feed water pump
• The condensed water is again fed to the boiler by
a feed water pump.
• Some water may be lost during the cycle, which is
suitably supplied from an external water source.

17. Cooling Tower
• It is used to reduce the temperature of
circulating water after condensation of steam
into water.

18. • PA (Primary air) Fan: Primary air fans supply
high volumes of pre-heated, primary
combustion air to move pulverized coal into
the boiler and drive off excess moisture.
• FD (Forced draught) Fan : It is used to supply
oxygen for proper combustion of coal.
• ID Fan (Induced draught) : It extracts the flue
gas from the boiler & releases to the
atmosphere.

19. ESP (Electrostatic precipitator)
It works on the electric field principle used for
collecting the ash particle from the flue gas.

20. Advantages
• Economical for low initial cost other than any
generating plant.
• Land required less than hydro power plant.
• Since coal is main fuel and its cost is quite cheap than
petrol/diesel so generation cost is economical.
• Maintenance is easier.
• Thermal power plant can be installed in any location
where transportation & bulk of water are available.

21. Disadvantages
• The running cost for a thermal power station is
comparatively high due to fuel, maintenance etc.
• Large amount of smoke causes air pollution. The
thermal power station is responsible for Global
warming.
• The heated water that comes from thermal power plant
has an adverse effect on the aquatic lives in the water
and disturbs the ecology.
• Overall efficiency of thermal power plant is low like
less 30%.

22. Choice of Site
Factors considered for selection of site for thermal
power station:
1. Availability of raw material
2. Nature of land & its cost
3. Availability of water
4. Load centre
5. Transport facilities
6. Availability of labor
7. Ash disposal facilities
8. Future expansion
9. Pollution
10. Distance from populated area

23. 1. Availability of raw material
• Roughly, a steam power plant of 300 MW
capacity requires about 3000 tonnes of coal per
day.
• Therefore, it is necessary to locate plant near
the coal fields to reduce transportation cost.

24. 2. Nature of Land & its Cost
• Total space required is 1500-2500 m2 per MW
capacity of plant including the space required for
coal storage & ash handling system.
• Therefore, land cost must be reasonable to reduce
its capital cost.
• To reduce civil engineering cost, the land
selected should not need much levelling of site.
• Also, the site selected should not have any
mineral deposits.

25. 3. Availability of water
• Roughly, it requires litres of water per day
for 300 MW capacity plant & litres of
water as make up water.
• Thus, it is necessary to locate thermal power plant
near a place where water is available throughout.
e.g. river, sea or lake.
8
18 10
8
36 10

26. 4. Load Centre
• Power plant must be locate near load to which it is supplied.
• However, it is not possible to locate power plant near all loads.
As such, the centre of gravity (C.G.) of all loads is determined
with reference to reference axis where plant is usually located.
• The location of power plant at C.G. of loads reduces the cost
of transmission lines & losses occurring in it.
• Future developments should be taken into account while
selecting the load centre.

27. 5. Transport Facilities
• Power plant should be located where the adequate
transport facilities are available for transportation of
fuel & heavy machinery for transportation.
6. Availability of Labor
• Large men power is needed during the construction of
plant.
• Therefore, labor should be available near the
construction site at cheap cost.

28. 7. Ash Disposal Facilities
• Huge amount of hot ash comes out of coal.
Therefore, there must be sufficient space &
facilities available to dispose large quantities of
ash.
• The scope for use of ash: In concrete, brick
making, filling of low-lying areas etc.
8. Future Expansion
• The site selected should be such that it allows
economic extensions of the plant with the
estimated growth of load.

29. 9. Pollution
• The thermal power plants should be located away
so as to avoid any nuisance from smoke, fly, ash,
noise & heat discharged from plant.
10. Distance from Populated Areas
• Since it employ pulverized fuel-residues & fumes
from them are quite unhealthy, therefore the power
plant should be located away from the densely
populated area.

30. Introduction to Prime Mover (Steam
Turbines)
• A steam turbine is a rotary machine which is designed to
convert the energy of high pressure & high temperature steam
into mechanical power.
• The operation of steam turbine is based upon the principle that
the steam issuing from a small opening attains a high velocity.
• The velocity attained during the expansion of the steam
depends on the initial & final heat contents of the steam.
• The difference of the two represents the heat energy converted
into kinetic energy.

31. • The nozzles are fixed to the casing. If the resultant high velocity
steam is passed over the curved blades, the steam changes its
direction & it would leave in the direction shown in fig.
• Due to this there is change in momentum & it will exert a resultant
force on the blades. If these blades are attached to a disc on rotor or
shaft which is free to rotate, the resultant force would cause the
rotor to rotate. Thus motive power is developed.

32. Classification of Steam Turbines
• There are different ways of classifying steam
turbines.
• According to the Action of steam on moving
blades - Impulse & Reaction type turbine.
• According to Type of flow of steam - Axial
flow & Radial flow turbine.

33. Acc. to Action of Steam on Moving
Blades
1. Impulse Turbine
• In this, steam impinges
against the blades fixed on
rotor periphery.
• This results in impulsive
force on the moving blades
which sets the rotor
rotating.
• The blades have
symmetrical profile.

34. • Impulse turbine has high speed.
• It also gives optimum utilization of steam with a simple clear design.
• The pressure of steam while passing over the moving blades remain
constant & its K.E is converted into mechanical energy.
• Owing to it simple & sturdy construction of all steam carrying parts, it has
long life.

35. 2. Reaction Turbine
• The steam does not expand in nozzles but expands as flows over the
rotor blades, the blades will, therefore, acts also as nozzles.
• Such turbines are characterized by relatively low rpm.
• These turbines are basically the impulse-reaction turbine but in practice
these are called reaction turbines.

37. Acc. to Type of flow of steam
1. Axial flow - In axial flow turbines the steam flows over the
blades in a direction parallel to the axis of wheel.
2. Radial flow - In radial flow turbines the blades are arranged
radially so that the steam enters at the blade tip nearest the axis
of wheel & flows towards the circumference.
• Majority of steam turbines are of ‘axial flow’ type.
RADIAL

38. Steam Nozzles
• The function of steam nozzle is to convert the heat energy of
steam into kinetic energy.
• The chief use of steam nozzle is to develop a high velocity jet
of steam for driving a steam turbine.
• This is achieved by allowing the steam to expand from a
region of high pressure at the inlet to a region of low pressure
at the outlet.
• With expansion of steam through the nozzles, its velocity &
specific volume both increases.
• The nozzle is designed for discharge of maximum weight of
steam for a given pressure drop.

39. • Depending upon the shape, the nozzles are of two types:
1. Convergent-Divergent nozzle
2. Convergent nozzle
• In convergent-divergent nozzles, the X-section first decreases until it reaches
the minimum at a section called the nozzle throat & then it increases as
shown in fig., the largest X-section being at the exit end.
• In convergent type nozzles, the nozzle exit in the throat itself.

40. Governing of Steam Turbine
• The function of governor is to control the fluctuation of
speed of a prime mover within the prescribed limits
with the variation of loads on it.
• It is used to vary the turbine output according to the
load on the alternator with very small fluctuations in
speed.
• The method used for governing of steam turbines are:
1. Throttle governing
2. Nozzles governing
3. By-pass governing
4. Combined throttle & nozzle governing
5. Combined throttle & by-pass governing

41. 1. Throttle governing
• In this type of governing the steam is throttled
down to a lower pressure according to the load
on the turbine before it is supplied to turbine.
• Such method is used for small capacity power
plants since the mechanism is simple with
initial low cost.

42. Throttle governing of steam turbine

43. Working
• Consider the case when the load on turbine shaft is equal to the power
developed by the turbine, the speed is constant & system is equilibrium.
• Assume that the load on turbine is reduced suddenly. At this stage since the
power developed is more than the load, the turbine & governor speeds will
increase due to excess energy developed by turbine.
• The governor balls will fly out & it will raise the sleave of governor,
consequently the differential level will cause the pilot piston to be raised.
• The oil which is supplied under a pressure of 3-4 bar will flow through the pipe
A to cylinder of relay piston & it would force the relay piston to move
downwards while the oil from relay piston cylinder is drained out through pipe
B.
• The downward movement of relay piston operates the throttle valve which in
turn closes the steam ports partially. It throttles the steam & steam pressure at
inlet to the turbine is reduced. When the power developed by the turbine equals
to the load on the turbine, the oil ports C-D are covered & relay piston is
locked.
• This method of governing is simple but it reduces the efficiency of power
plants at parts loads because a part of available energy is lost in irreversible
throttling process.

44. 2. Nozzle Governing
• This method of governing is more efficient than the throttle governing since in this
method only the mass flow rate of steam supplied to the turbine is controlled.
• Total no. of nozzles required are divided into number of sets like N1, N2, N3.
• Each set consists of the no. of nozzles required to affect the required control on the
mass flow rate corresponding to the required power control.

45. • Due to this, different sets of nozzles will have
different number of nozzles.
• The supply of steam to the nozzles is controlled by
opening & closing of valves V1, V2, V3.
• At full load all the valves will supply the steam to all
the nozzle & a part loads one or more number of
valves are closed.

46. 3. By-pass Governing
• At maximum loads the additional amount of
steam cannot be passed through the first-stage
since the reqd. additional no. of nozzles are not
available.
• The difficulty of steam regulation is achieved
by employing by-pass governing.

47. By-pass Governing
Block Diagram

48. Efficiency of Steam Power Station
• The overall efficiency of a steam power station
is quite low (about 29%) due mainly to two
reasons.
• Firstly, a huge amount of heat is lost in the
condenser and secondly heat losses occur at
various stages of the plant.

49. Thermal efficiency
• The ratio of heat equivalent of mechanical
energy transmitted to the turbine shaft to the
heat of combustion of coal is known as
thermal efficiency of steam power station.
Thermal efficiency,
• Heat equivalent of mechanical energy
η = transmitted to turbine shaft_______
Heat of coal combustion

50. • The thermal efficiency of a modern steam
power station is about 30%.
• It means that if 100 calories of heat is supplied
by coal combustion, then mechanical energy
equivalent of 30 calories will be available at
the turbine shaft and rest is lost.

51. Overall efficiency
• The ratio of heat equivalent of electrical output to
the heat of combustion of coal is known as overall
efficiency of steam power station i.e.
Overall efficiency = Heat equivalent of electrical
output________
Heat of coal combustion
• The overall efficiency of a steam power station is
about 29%. It may be seen that overall efficiency
is less than the thermal efficiency.

52. The Simple Ideal Rankine Cycle

53. Environmental Aspects for Selection &
Location of Thermal Power Stations
• Various pollutants released by thermal power plants are:
1. Sulphur dioxide (SO2) & Hydrogen sulphide (H2S)
2. Oxides of nitrogen (NOx), e.g. Nitric oxide, Nitrous oxide,
Nitrogen dioxide , Nitrogen trioxide etc.
3. Suspended particulate matter
4. Thermal pollution
5. Carbon dioxide (CO2)

54. Effects of pollutants
• SO2 and H2S
 Causes suffocation, irritation of throat, asthma, lung cancer.
 Both cause destruction of crops.
• NOx emission irritates eye, nose & throat causing coughing,
headache & damage to lungs.
• SPMs
 Causes respiratory problems like cough, cold, sneezing etc.
 It causes bronchitis & cardiac diseases.
 These also cause corrosion of metal parts of power system.
• CO2 causes global warming of atmosphere.

55. • Acid Rains: SO2 & NOx combine with water to form
H2SO4 & HNO3 respectively which fall in the form of
acid rains in rainy season. It decreases PH value of
rivers, lakes & well water etc. It affects aquatic life,
fertility of soil, damages buildings.
• Thermal Pollution- Hot water cooling is discharged
from power plants into rivers. It causes thermal
pollution. Water is also contaminated due to chemicals
released in water due to their feed water treatment. The
chlorine residue in hot water are harmful to aquatic life
& marine life.

56. Control of Pollutants
• Control of SO2
– By desulphurization of fuels either by chemical process or both
floatation process.
– Removal of SO2 from flue gases by electrostatic precipitators or by
catalytic oxidation.
• Control of SPM
– By using fabric filters,
– Hydraulic & pneumatic ash handling systems
– Electrostatic scrubbers for dust collection.
• Control of NOx
– By reducing the temperature of combustion below 1000 degree Celsius
since formation of NOx below this temp. is very low.
• Control of thermal pollution
– By construction of separate lakes or construction of cooling towers &
cooling ponds to reject the heat of cooling tower to atmosphere before
it is discharged into lakes & rivers.