UNIT 1 COAL BASED THERMAL POWER PLANT

1. COAL BASED THERMAL POWER
PLANT
Prepared by,
SELVAN P,
ASSISTANT PROFESSOR
KAMARAJ COLLEGE OF ENGINEERING AND TECHNOLOGY,
VIRUDHUNAGAR

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
 Super heater and Reheater
 Air pre heater
 Alternator with Exciter
 Protection and control equipment
 Instrumentation

5. COAL BASED THERMAL POWER PLANT

7.  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.
Main circuits in thermal Power Plant

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.  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
SITE SELECCTION FOR THERMAL
POWER STATIONS

10. COAL HANDLING

11. Preparation of coal

12. Ash handling system

13. Ash handling system design

14.  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

15. Mechanical sys

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

18. Pneumatic system

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

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

21. CRUSHING PLANT

22. IMPACT CRUSHER

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

24.  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
Draught System

25. 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.

26. 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.

27.  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.

28. Balanced Draught system

29. 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
Cooling Towers and Spray Ponds

30. 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
Wet type

31.  Natural draft spray filled
tower
 Hyperbolic cooling tower

32.  Forced draught  Induced draught
MECHANICAL DRAUGHT SYSTEM:

33. Dry type cooling tower
 Direct type  Indirect type with surface
condenser

34.  Indirect with spray
condenser
 Indirect with ammonia

35. 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
 For super critical boilers – 2,20,000 kJ/m2 hr. C
 Higher thermal efficiency 40-42%
 Presently 246 bar and 538 ͦC are used for unit sizes above 500 MW.

36. Supercritical boiler

38. Types of super critical boilers

39. Cont..

40. Water tube boilers

41. Benson Boiler

42. LOEFFLER BOILER

44. 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.

45. Surface condenser(non contact)

46. Low level jet condenser (contact type)

48. 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 unmixed forms

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

50. 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)

51. 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.

52. 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

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

54. 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

55. Binary cycle Power Plant

56. Cogeneration systems

58. Steam turbine cogen system