Page 910 - Basic Electrical Engineering

these may form undesirable deposits in the water flow system. A water
treatment plant is, therefore, required in a thermal power plant.
To increase the efficiency of the conversion of heat into mechanical

energy, steam is generated at very high temperature and pressure. Further,
large capacity turbines and generators of the range of hundreds of megawatts

are installed to reduce the capital cost per kilowatt of energy produced.
It may be noticed that in a thermal power station, steam and hot water are

produced along with electricity. The waste heat in the form of hot air and
steam can be used in certain process industries like paper mills, textile mills,

food-processing industry, chemical industries, etc. When the otherwise waste
heat is used, the overall plant efficiency is increased.
The system where electricity, steam, and hot water are simultaneously

made available, is called cogeneration. The efficiency of a thermal power
plant is around 40 to 50 per cent. Cogeneration increases the overall

efficiency.

13.4.2 Gas-fired Thermal Power Stations

Natural gas is used as the source of energy to generate electricity. A gas

turbine is the prime mover which will drive the generator. The hot gases
exhausted from the turbines can be passed through a heat exchanger to

produce steam. This steam can be used to run a steam turbine which would
drive another generator. This way, the total thermal efficiency of the plant
can be increased. This method is called the combined-cycle method of

generation of electricity. If it is decided not to use the hot gases exhausted
from the gas turbine for further generation of electricity, the hot gases can be

used to produce steam for use in various industrial processes. Gas-fired
stations are more environment friendly as compared to coal-fired power

stations, as the flue gases emitted contain almost zero sulfur dioxide. As can
be imagined, the installation cost of gas-fired stations would be less than the

coal-fired ones. However, the operational cost of gas-fired stations will be
high due to the higher cost of fuel, i.e., the gas used. In the state of Rajasthan