Basics of coal based thermal power plant.

1. BASICS OF COAL
BASED THERMAL
POWER PLANT
Presented by
Shubham Kumar Gupta
Roll no. 13/ME/143
Department of Mechanical Engineering

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Introduction
Major parts of power plants
Mechanism

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A Thermal Power Plant converts the heat energy of
coal into electrical energy. It works on basic Rankine
cycle. 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. After this steam is condensed in the
condenser and again sent to the boiler by pump.
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

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 Vindhyachal Thermal Power Station, Madhya
Pradesh with an installed capacity of 4,760MW
owned and operated by NTPC.
 The 4,620MW Mundra Thermal Power Station
located in the Kutch district of Gujarat is currently
the second biggest operating thermal power plant in
India owned and operated by Adani Power.
 The 4,000MW Mundra Ultra Mega Power Plant
(UMPP), also located in the Kutch district of Gujarat,
ranks as the third largest thermal power plant in
India owned and operated by Coastal Gujarat Power
Limited (CGPL), a subsidiary of Tata Power.
 Talcher Super Thermal Power Station or NTPC
Talcher Kaniha, located in the Angul district of
Odisha, is a 3,000MW coal-fired power plant owned
and operated by NTPC.

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1.Boiler
• A boiler or steam generator is a closed vessel in
which water under pressure, is converted into
steam.
• Always designed to absorb maximum amount
of heat released in the process of combustion.
Boilers are of two types-
a. Fire tube boiler
b. Water tube boiler

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2. STEAM TURBINE
A steam turbine converts heat energy of steam into
mechanical energy and drives the generator. This
energy conversion basically occurs in two steps:
a. The high pressure, high temperature steam first
expands in nozzles and comes out at a high velocity.
b. The high velocity jets of steam coming out of the
nozzles, impinge on the blades mounted on a wheel,
gets deflected by an angle and suffer a loss of
momentum which is absorbed by the rotating wheel
in producing torque.
These are of two types :-
Impulse turbine
Reaction turbine

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3. Condenser
Condenser refers to the shell and tube heat exchanger
(or surface condenser) installed at the outlet of every
steam turbine. 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.

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4. Pump
Condensate Extraction Pumps (CEP) extract the
condensate water from the condenser and increase
its pressure to the original. Extraction pump is usually
a vertical shaft, two stage, centrifugal pump, which is
used in applications involving high pressure and high
volume. Centrifugal pumps are of the type, which due
to their high capacity, require a specific minimum
suction head to operate. The condensate water is
drawn from the condenser by the extraction pump and
send to the low pressure feed water heater.

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5. Feed Water Heater (FWH):
A feedwater heater is used in a
conventional power plant to preheat
boiler feed water. The source of heat
is steam bled from the turbines.There
are basically two types of FWH:
a. Open type FWH (Deaerator):
In this type of FWH , the extracted
steam is allowed to mix with FW.
A deaerator is a device that is widely
used for the removal of oxygen and
other dissolved gases from the
feedwater to steam-generating boilers.
At least one open type FWH i.e.
deaerator is needed in every power
plant.

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b. Closed type FWH:
These are typically shell and tube type heat
exchanger where the feed-water passes throughout
the tubes and is heated by turbine extraction steam.
These do not require separate pumps before and
after the heater to boost the feed-water to the
pressure of the extracted steam as with an open
heater. They are further divided into high pressure
FWH and low pressure FWH.
Low pressure FWH: It is situated between
condensate pump and deaerator. It normally
extract the steam from low pressure turbine.
High pressure FWH: It is located after the boiler
feed pump and extract the steam from high
pressure turbine.

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Figure: Closed type FWH
Figure: Deaerator

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6. Economiser:
Flue gases coming out of the boiler carry lot of heat.
An economiser extracts a part of this heat from flue
gases and uses it for heating feed water. This use of
economiser result in saving coal consumption and
higher boiler efficiency.
7. Superheater:
Super heater is used to remove the moisture
content from the steam. It raises the temperature of
steam above 540 degree C.
8. Boiler Drum:
The main function of boiler drum is
to store water and steam sufficiently
to meet varying load requirement
and to separate vapour or steam
from water-steam mixture.

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10. Air preheater:
After flue gases leave economizer, some further heat can be
extracted from them and used to heat incoming air. Preheated air
increases the combustion rate and since the air is heated by the
exhaust gases, fuel consumption is reduced. Due to higher
temperature of air, furnace temperature increases, so low grade coal
can be burnt efficiently.
9. 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.

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11. Electrostatic Precipitator (ESP):
It is particulate collection device that removes
particles from a flowing gas using the force of an
induced electrostatic charge. Boilers burning
pulverised coal produce 20% bottom ash and 80% fly
ash. Bottom ash are collected under the furnace in a
water filled ash hooper. For flyash an ESP is needed.

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12. Cooling Tower:
Cooling tower is a steel or concrete hyperbolic
structure having a reservoir at the base for storage of
cooled water. A condenser needs huge quantity of
water to condense the steam. The cooling tower can
be either mechanical draught or natural draught.

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13. Draught/Draft system:
The function of the draft system is basically:
a. To supply to the furnace the required quantity of air for
complete combustion of fuel.
b. To remove the gaseous products of combustion from
the furnace and throw these through chimney to
atmosphere.
For this purpose two types of fan are used:
i. Force Draught (FD) fan: FD fans are installed at inlet
to the air preheater. They handle cold air. It supplies
combustion air to the steam generator.
ii. Induced Draught (ID) fan: Id fans are basically
located at the foot level of stack/chimney. They
handle hot combustion gases and remove the flue
gas from the furnace and exhaust them through the
chimney into the atmosphere.
Another fan is used in coal handling plant called Primary Air (PA) fan.
It supplies air to dry and transport pulverised coal to the furnace.

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D i a g r a m o f a t y p i c a l c o a l -
f i r e d t h e r m a l p o w e r s t a t i o n
1. Cooling tower 10. Steam Control valve 19. Superheater
2. Cooling water pump 11. High pressure steam turbine 20. Forced draught (draft) fan
3. transmission line (3-phase) 12. Deaerator 21. Reheater
4. Step-up transformer (3-phase) 13. Feed water heater 22. Combustion air intake
5. Electrical generator (3-phase)14. Coal conveyor 23. Economiser
6. Low pressure steam turbine 15. Coal hopper 24. Air preheater
7. Condensate pump 16. Coal pulveriser 25. Precipitator
8. Surface condenser 17. Boiler steam drum 26. Induced draught (draft) fan
9. Intermediate pressure steam
turbine
18. Bottom ash hopper 27. Flue gas stack

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Figure: Modern Pulverised coal fuelled electricity generating unit