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.
In thermal generating stations coal, oil,
natural gas, etc are employed as primary
sources of energy.
11 kV BUS
hopper Gases Stack
Pre-heated Furnace Cooling
Pre-heated Furnace Tower
Feed Water Pump
Feed Water Pump
1. Energy Source: Coal, Natural Gas, Diesel, Oil are the
major sources of primary energy.
Coal fired thermal plants form 55.23% of total
They formed almost 83% of installed thermal power
The prices of the fuel determines the economics
of thermal power plants.
2. Boiler and Furnace: The fuel is burnt in the
furnace to produce steam in the boiler.
Pulverized coal is burnt to produce steam.
Water from the feed pump, after pre-heating
enters the boiler. This water may be obtained
from a nearby river or lake. The condensed
water from the cooling tower is re-used.
To increase the efficiency of the plant
steam is generated at highest possible
temperature and pressure.
To further increase the efficiency steam is
re-heated after it is partially expanded by
an external heater.
3. Prime Movers: These depend on the fuel
Coal fired plants use Steam Turbines.
Gas fired use Gas Turbine Engines, which
are similar to Turbo-Prop engines used in
Diesel fired use IC engines.
In case of coal fired plants steam produced in the
boiler is passed through an axial flow turbine.
The turbine is coupled to the generator and
thus energy conversion is achieved.
Gas fired are usually operated in combined cycle
mode to attain maximum efficiency.
In these types in the 1st stage gas turbine
engines are coupled to the generators.
In 2nd stage the hot gases exhausted
from the gas turbines are passed through
heat exchangers to generate steam which
drives the conventional steam turbine.
Alternatively heat from the exchanger
can be used for industrial purposes.
4. Generators: The prime movers are
coupled to the generators to convert
mechanical energy into electrical energy.
Modern practice is to design and build
generating units having large MW
generating capacity since their capital cost
per kW decreases as the MW capacity is
Increasing the unit capacity from 100MW to
250MW results in saving of about 15% in
their capital cost per kW.
Moreover units of this magnitude result in
fuel saving of almost 8% per kWh.
The cost of installation is also low for such
Presently the max capacity of turbo-generator
sets being produced is nearly 1200 MW.
In India, super thermal power units of capacity
500 MW are being commissioned by BHEL.
Also many Ultra-Mega Power Plants are being
sanctioned to achieve the government s goal of
energy for all.
5. Condenser and Cooling Tower: The
steam after passed through the turbines is
condensed in a condenser.
The water is then supplied to the cooling
tower where it is cooled.
The water is then fed to the feeder pump
from where it is given to the boilers.
6. Precipitators and Chimneys: The waste
gases from the boiler are first passed
through precipitators to separate the solid
dust particles. The fly ash is collected at
The gases are then thrown out with the use
7. Control Room and Switchyard :
The control room monitors the overall
operation of the plant. It is provided with
controls for real and reactive power flow.
It is provided with safety relays and
Switchyard is the place where voltage
levels are stepped up using a step-up
The supply from the generators is
connected to the grid at the switchyard bus.
The switchyard also has energy meters,
SF6 gas breakers, protective relays and
Coal fired units form the majority of thermal power
However, for the same amount of power
generated a combined-cycle gas fired station is
The flue gases emitted by these stations contain
almost zero SO2, 50% CO2 and 25% NOX as
compared to those produced in coal fired.
Also the installation cost of gas fired is
lower than coal fired.
Gas fired units can be started quickly.
The operating costs of Gas fired plants are
high due to high fuel costs. As such these
are used to supply peak load demand and
for short periods.
The waste gases from thermal plants
contain particles and gases like oxides of
sulphur and NOX.
This results in pollution of air.
Thermal pollution also results in due to
large amount of heat released via the
condenser to the cooling water.
It is possible to increase the overall
efficiency of a thermal power plant to 65%
using the techniques of co-generation.
In co-generation, electricity and steam or
hot water is simultaneously made available
for industrial use or space heating.
Power System Analysis, T.K. Nagsarkar
and M.S. Sukhija.
The figures are obtained from Central
Electricity Authority s General Review 2005
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