THERMAL POWER PLANT
Thermal Power Stations
• Coal Fired
– Turbo alternators driven by steam turbine
• Oil Fired
– Crude oil OR Residual oil
• Gas Fired
– Fastest growing primary fuel, worldwide
– Combined cycle
• First stage - Gas turbine & Second stage - Steam Turbine
• Diesel Fired
– IC Engine as prime mover
– Standby power plants
Selection of site
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Nearness to load center
Supply of water
Availability of coal
Land requirement
Type of land
Labour supplies
Ash disposal
Distance from populated area
thermodynamic cycle
• a type of steam engine involving a continuous
cycle of vaporization of liquid and
condensation back to liquid in a sealed system
merits & demerits
• Merits:
• Fuel used is cheaper
• Cheaper installation cost comparatively
• Cheaper production cost in comparison with diesel power
plant
• Can be installed at ay place irrespective of the existence of
fuels unlike HEPP
• Can be located near to load center unlike HEPP
• Able to respond rapidly changing loads without difficulty
• Steam engines and turbine can work under under 25% of
over load continuously
• Portion of steam raised can be used as process steam in
various industries (paper mills, textile mills etc)
Merits & Demerits
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Demerits:
High maintenance and operating cost
Pollution
Requirement of water in huge quantity
Handling of coal and ash is quite difficult
The plant cost increases with the increases in the
operating temperature and pressure
• Require long time for erection and put into action
• Efficiency fall rapidly below 75% of full load
Schematic diagram of Coal Fired Power Plant
Components
1. Cooling tower
2. Cooling water pump
3. Transmission line
4. Transformer
5. Generator
6. L.P turbine
11. H.P turbine
7. Condensate pump 12. De-aerator
8. Surface condenser 13. Feed water heater
9. I.P turbine
14. Coal conveyor
10. steam control valve 15. Coal hopper
16. Coal pulverizer
17. Boiler steam drum
18. Bottom ash
19. Super-heater
20. Forced draught
21. Re-heater
22. Combustion
23. Economizer
24. Air pre-heater
25. Precipitator
26. Induced draught
27. Flue gas stack
Fuel & Ash Handling
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Coal delivery: by trucks, wagons etc
Coal storage: Dead & Live storage
Crusher: coal is crushed to increase the area
Magnetic separator: removes impurities
Pulverizer: device to transform coal into fine powder
Ash pit: when fuel gets burnt, ash is collected in ash pit
Ash quenching: Ash is hot & dusty, hence needs to be quenched
Ash delivery: Quenched ash is taken using conveyors to the site
Furnace
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A place where fuel is burnt
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Encloses burning equipments
Types
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Grate fired: uses stationary or movable grates, suited for solid fuels.
1. Hand fired – uses stationary grate, small size plants, discontinuous process
2. Stoker fired – uses movable grate, medium & large size plants, continuous process
. Over feed stoker: the fuel & air move are not in the same direction
. Under feed stoker: the fuel & air move in the same direction
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Chamber fired: suited for pulverized coal, liquid or gaseous fuels.
Boiler
• Water tube boiler: DM water circulates through tubes & hot flue gases flow
over them.
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Less liable to explosion, produce high pressure steam, high efficiency, heating surface is large
• Fire tube boiler: hot flue gases pass through the tubes which are surrounded
by water.
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Low cost, compact in size, heating surface is small, cannot produce high pressure steam, liable to explode, low efficiency
Water tube boiler
Fire tube boiler
Methods to improve thermal efficiency
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Air pre-heater :
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hot flue gases are used to pre-heat the air
pre-heats the air to be supplied to the furnace
Accelerates combustion
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Economizer :
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hot flue gases are used to heat the feed water
Improves efficiency
Reduces heat losses of flue gas
Reduces fuel consumption
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Super heater :
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Increases temperature of generated steam
High thermal efficiency
Avoids corrosion of turbine blades
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Re-heaters :
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Exhaust Steam from hp turbine is expanded
High turbine efficiency as the stages increase
CONDENSER
Types
 Surface condenser
 No direct contact between steam & cooling
water
 Impure water can be used for cooling
 Low running cost , high vacuum is obtained
 Increased efficiency
 Requires large space
 High initial cost
 Jet Condenser
 Direct contact between steam & cooling
water
 Low initial cost
 Compact
 Low efficiency
Impulse -H.P turbine And
Reaction - L.P & I.P turbine
TYPES OF TURBINE
Cooling towers
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To reduce thermal pollution which occurs in open system
To cool water coming out of the condenser in a closed system
Water cooled, Air cooled cooling towers
Uses either natural draft or mechanical draft
Natural draft – utilizes buoyancy large space, high cost, less efficient
Mechanical draft uses fan, requires less space, improves efficiency
Forced draft tower: blower type fan is located at the base of the tower & forces air into the tower
Induced draft tower: fan is located at the top of the tower & pulls air through the tower. The
fan induces hot moist air out the
Contd..
• Different types of cooling towers
Induced draft
Draught
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Draught : difference between absolute gas pressure & the ambient atmosphere pressure.
If Patm< Pg as draught is positive & Patm>Pgas draught is negative
Types of Draught: Natural & Mechanical
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Natural draft is subjected to outside air conditions and temperature of flue gases leaving the furnace, as
well as the chimney height. All these factors make proper draft hard to attain and therefore make
mechanical draft equipment much more economical.
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Mechanical draft: reduces chimney height, independent of weather condition, easy control
Induced draft: This is obtained by simply using an induced draft fan (ID fan) which removes flue gases from
the furnace and forces the exhaust gas up the stack. Almost all induced draft furnaces operate with a
slightly negative pressure.
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Forced draft: Draft is obtained by forcing air into the furnace by means of a fan (FD fan) and ductwork.
Forced draft furnaces usually have a positive pressure & use under fed stoker firing.
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Balanced draft: Balanced draft is obtained through use of both induced and forced draft. This is more
common with larger boilers . The induced draft fan works in conjunction with the forced draft fan allowing
the furnace pressure to be maintained slightly below atmospheric.
ELECTROSTATIC PRECIPITATOR
Fuel and ash handling
Governing system
Functions:
• To maintain constant shaft speed at all loads
• To maintain constant steam flow through turbine
• To maintain constant pass out and inlet/outlet steam
pressures at all flows
Methods of governing:
• Throttle governing
• Nozzle control governing
• By-pass governing
• Fly ball speed governing etc
Governing system