Gas turbine power plant :
A gas turbine power plant consists of a rotary multistage compressor, generally of axial flow type, in which air or working substance is compressed. Compressed air flows to the combustion chamber where fuel is burnt, thereby raising the temperature of the working substance. The high pressure, high temperature working substance expands in a turbine producing mechanical power. Turbine in turn drives a generator for producing electrical energy. A gas turbine works on Brayton cycle.
Simple Gas Turbine Cycle:
(Gas Turbine cycle modified for higher efficiency)
Improving efficiency of simple Brayton cycle
The efficiency of simple Brayton cycle can be improved by
(i) Use of heat exchanger between compressor delivery and combustion chamber, utilizing heat of exhaust gases;
(ii) Use of two stage expansion with re-heating;
(iii) Use of multistage compression with inter-cooling.
A gas turbine using atmospheric air as working medium is known as open cycle gas turbine. In closed cycle gas turbine the working substance is recirculated and it does not come into direct contact with atmospheric air. A fluid with better thermodynamic properties can be used as working substance in such turbines.
Gas turbines can run on gaseous, liquid as well as solid fuels. As compared to a steam turbine, it does not require condenser and associated bulky cooling arrangements. Gas turbines operate on lower pressures as compared to steam turbines hence stress on various parts is less.
For starting a gas turbine enough power is required to drive the compressor which is nearly 30 to 40% of the normal output.
Sometimes gas turbines are used in combination with steam cycle where exhaust heat of the gas turbine is used in boiler for steam cycle.
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