This document provides an overview of the major components and processes involved in a coal-based thermal power plant. It discusses the key circuits in the plant including coal/ash handling, air/gas, feedwater/steam, and cooling water. It also describes site selection factors and the functions of major equipment like boilers, turbines, condensers, and cooling towers. Key coal preparation and ash removal processes are explained. Finally, it covers supercritical boilers and defines important thermal power plant concepts like steam rate and heat rate.

1. COAL BASED THERMAL POWER
PLANT
T.SURESH
P.SELVAN
ASSISTANT PROFESSORS
KAMARAJ COLLEGE OF ENGG AND TECH
MADUARAI
UNIT - I

2. Major Components of a Thermal Power Plant
– Coal Handling Plant
– Pulverizing Plant
– Draft or Draught fan
– Boiler
– Ash Handling Plant
– Turbine and Generator
– Condenser
– Cooling Tower And Ponds
– Feed Water Heater
– Economiser
– Evaporator
– Super heater and Reheater
– Air pre heater
– Alternator with Exciter
– Protection and control equipment
– Instrumentation

5. COAL BASED THERMAL POWER PLANT

7. Main circuits in thermal Power Plant
• Coal and Ash Circuit
Coal from the storage is fed into the boiler through coal
handling equipment for the generation of steam. Ash
produced due to the combustion of coal is removed to ash
storage through ash handling system.
• Air and Gas Circuit
Air is supplied to the combustion chamber through FD fan or
ID fan. The dust from the air is removed before supplying to
the combustion chamber.
The exhaust gases carrying sufficient quantity of heat and
ash are passed through the dust collectors where most of
the dust is removed before exhausting the gases to the atm.
through chimney.

8. • Feed water and steam flow Circuit
The steam generated in the boiler is fed to the steam prime
mover to develop the power. The steam coming out of the
prime mover is condensed in the condenser and then fed to
the boiler with the help of the pump.
• Cooling water circuit
The quantity of cooling water required to condense
the steam is considerably large and it is taken either from
lake, river or sea.
if adequate cooling water is available throughout the
year then we can use the river- open system
if not, we can use cooling pond or cooling tower –
closed system.
Due to the evaporative loss 2-5% of cooling water lost
in the system. For that we need to use make up water.

9. SITE SELECTION FOR THERMAL POWER
STATIONS
• Availability of coal-400MW coal 5000-6000tons/day
• Ash disposal facilities -1500-2000tons/day(20-40% ash in coal)
• Space requirements
• Nature of land – bearing capacity of the land should be 10 bar
• Availability of water-60MW plant (20-30 thousand tons/hr)
(for cooling towers make up water 500-600tons/hr.)
(for 1000MW – 3.78million litres of fresh water/day)
• Transport facilities
• Availability of labour
• Public problem
• Size of the plant

11. COAL HANDLING

12. Preparation of coal

13. Ash handling system

14. Ash handling system design

15. • The modern ash handling system usually used
in large steam power plants are …….
•Belt conveyor system(Mechanical)
•Pneumatic system
•Hydraulic system
•Steam jet system
For bottom ash disposal

16. Mechanical sys

17. Hydraulic system
Low velocity High velocity
50 tons/hr. 120 tons/hr
500 m 1000 m
3-5m/s above 5 m/s

19. Pneumatic system

20. Removal of ash from Hot flue gas
There are two methods adopted for removing the
ash.
Cyclone separator Electrostatic Precipitator

21. Crushing Process
There are four basic process to reduce the size
• Impact
• attrition
• Shear
• compression

22. CRUSHING PLANT

23. IMPACT CRUSHER

24. Screening Process:
There are three basic type of screening process
• Scalping
• Fine removals
• Grading

25. Draught System
• The draught is to supple required quantity of air
for combustion and remove the burnt products
from the system.
• Difference of pressure required to maintain the
constant flow of air and to discharge the gases
through the chimney to atmoshpere is known as
draught.
A draught may be
• 1. Natural Draught
• 2. Mechanical Draught

26. Natural Draught
A natural Draught is provided by the chimney
or stack.
Natural draught has its limitation . Modern
plants has high rate of heat transfer and
Draught losses are very high. In view of this
Natural draught is used only for small boilers.

27. Mechanical Draught
Modern large size plants use very large size of boilers of capacity
above 1000,000 kg per hour. such boiler needs tremendous volume
of air (around 200000 m3) Per minute. A chimney provide this.
Therefore mechanical draught is used.
Forced draught
In forced draught system the fan is installed near the boiler .The fan
force the air through the furnace , economizer, air preheater and
chimney. The pressure of air, throughout the system, is above
atmospheric and air is forced to flow through the system.

28. • Induced draught
In an induced draught system , the fan is installed near the base
of the chimney . The burnt gases are sucked out from the boiler ,
thus reducing the pressure inside the boiler to less than
atmosphere. This induces fresh air to enter the furnace.

29. Balanced Draught system

30. Cooling Towers and Spray Ponds
Condensers need huge quantity of water to condense the
steam. Water is led into the plants by means of circulating water
pumps and after passing through the condenser is discharged
back into the river.
If such a source is not available closed cooling water
circuit is used where the warm water coming out of the
condenser is cooled and reused.
Types
Wet type
Dry type

31. Wet type
Types
Natural draught cooling tower
Mechanical draught cooling tower
Natural draught cooling tower
Natural draft spray filled tower
Natural draft packed type tower
Hyperbolic cooling tower

32. • Natural draft spray
filled tower
• Hyperbolic cooling
tower

33. • Forced draught • Induced draught
MECHANICAL DRAUGHT SYSTEM:

34. Dry type cooling tower
• Direct type • Indirect type with
surface condenser

35. • Indirect with spray
condenser
• Indirect with ammonia

36. SUPERCRITICAL BOILERS
• Pressure from 125 bar, T = 510 ̊C to 300 bar & 660 ̊C
• The power plant which is operated above the critical
pressure and temperature condition is called supercritical
power plant.
• Sub critical Boiler Super critical Boiler
Economiser Economiser
Evaporator Superheater
Superheater
• The super critical boilers are above 300 MW capacity units
available.
• Water reaches to this state at a critical pressure above
22.1 MPa and 374 oC
• Heat transfer coefficient for sub critical boiler is 165000
kJ/m2 hr. C

37. Supercritical boiler

39. Types of super critical boilers

40. Cont..

41. Water tube boilers

42. Benson Boiler

43. LOEFFLER BOILER

45. Condensers
The function of the condenser is to condense the
steam exiting the turbine. The condenser helps
maintain low pressure at the exhaust.
• Two types of condensers are used.

46. Surface condenser(non contact)

47. Low level jet condenser (contact type)

49. Feed water treatment
• River water contains dissolved minerals
Cl-, SO4
2-, HCO3
- of
Na+, Mg2+, Ca2+ and Fe2+
• These are the materials in the water. These unwanted
materials can be removed by the following processes,
Mechanical method
Thermal method
chemical method
Purpose of feed water treatment is to remove the unwanted
materials
Undissolved and suspended solid materials
dissolved salts and minerals
dissolved gases
other materials (as oil, acid) either in mixed or

50. Undissolved and suspended solid materials
• Turbidity and sediment
• Sodium and potassium salts
• Chlorides
• Iron
• Manganese
• Silica
• Microbiological growths
• colour

51. Undissolved and suspended solid
materials
Usually the turbidity in muddy and turbulent river
will be 60,000 ppm.
The turbidity of feed water should not exceed 5
ppm.
These materials can be removed by settling,
coagulation and filtration.
Heating and evaporation produces hard stony scale
deposits
Standard measurement – CaCO3 in water (ppm)

52. Dissolved salts and minerals
• It contains Calcium and Magnesium salts. Its in the form
of carbonates, bicarbonatees, sulphates and chlorides.
– It recognised by hardness of the water
• Temporary hardness
caused by bicarbonates of calcium and magnesium
that can be removed by boiling
• Permanent hardness
caused by chlorides, sulphates and nitrates of
calcium and magnesium. Can’t removed by boiling.
Because they form a hard scale on heating surfaces.

53. Steam Rate and Heat Rate
• Steam Rate
• It is defined as the rate
of steam flow required
to produce unit shaft
output.
• Steam Rate=1/Wnet
kg/kWs
• Heat Rate
• It is defined as the rate
of heat input required
to produce unit shaft
output.
• Heat Rate = Q1/(Wt-
Wp)=kJ/kWs

54. TYPES OF TURBINE
• Impulse:
Pelton wheel
(tangential)
High H, Low D
• Reaction
Francis , Kaplan
Radial Axial
Medium H, Low H,
Medium D
Medium D

55. Governing of turbines
• Throttle governing
controlling of steam
pressure inlet
• Nozzle control
governing
high pressure steam
• By-pass governing
suitable for reaction
turbines via by-pass valve

56. For more details go through your text

57. Cogeneration systems

58. Steam turbine cogen system

59. Reheat Rankine Cycle Problems
A steam power station uses the following cycle:
Steam at boiler outlet 150 bar, 550 ͦ C
Reheat at 40 bar to 550 ͦ C
Condenser at 0.1 bar
Using the Mollier chart and assuming ideal
processes, find the (a) Quality at turbine
exhaust, (b) cycle effieciency, (c) steam rate.

60. Answers
• h1= 3465 kJ/kg
• h2= 3065 kJ/kg
• h3= 3565 kJ/kg
• h4= 2300 kJ/kg
• X4= 0.88
• Wp= 15 kJ/kg
• Qs= 3758.17 kJ/kg
• Wt= 1665 kJ/kg
• Wnet= 1650 kJ/kg
• ηcycle= 43.9%
• Steam Rate =
3600/1650= 2.18
kg/kWhr