Unit 2 -Gas And Diesel Power Plants Gas turbine types Open and closed cycle gas turbine Advantage and disadvantages Diesel engine power plant Component and layout Components

Gas turbine power plant

A Gas Turbine consists of three main segments    Compressor    Combustor    Turbine.

Principle Of Operation Ambient air is compressed to 11-30 bar pressure and as a consequence its temperature rises. Most of this warm air is used in the combustor to burn the fuel (natural gas or a liquid e.g. oil etc.). The resulting hot gas expands through the turbine, doing work, and exits at nearly atmospheric pressure but a temperature of up to 500-640 °C.

Principle Of Operation Work extracted during the expansion is used to turn the turbine which drives the generator that produces electricity. The hot exit gas from the turbine still has significant amounts of energy which is used to raise steam to drive a steam-turbine and another generator. This combination of gas and steam cycle gives rise to the term ‘combined cycle gas turbine’ (CCGT) plant

Open cycle-gas turbine

combined cycle – gas turbine

Advantages Of Gas Turbine Plants They are more compact, since fuel is burnt directly in the small combustion Chamber in the gas turbine rather than in a bulky boiler Gas Turbine has no condenser They can be started and take more load quickly (i.e.30 seconds to 30 min) They are simpler in design and easy to maintain They consume less metal and other materials for the same capacity They cost less Unlike steam turbines , they require very less water for cooling Gas Turbine is more suitable for power generation, where water scarcity exists or the water is more precious

Disadvantages Of Gas Turbine Plants They have a lower specific power They have lower efficiency at the modern state of progress They have a shorter service life They are more sensitive to fuel quality

Diesel Engine Power Plant A Diesel power station(also known as Stand-by power station) uses a diesel engine as prime mover for the generation of electrical energy. This power sattion is generally compact and thus can be located where it is actually required. This kind of power station can be used to produce limited amounts of electrical energy. In most countries these power stations are used as emergency supply stations

Operation The diesel burns inside the engine and the combustion process causes rotational mechanical energy that turns the engine shaft and drives the alternator. The alternator inturn, converts mechanical energy into electrical energy. This type of electricity generating power station will probably be used a long time into the future, due to a need for reliable stand-by electrical source for emergency situations.

Essential components of diesel power plant Diesel engine Air intake system Exhaust system Fuel supply system Engine starting system Lubricating system Engine cooling system Governing system

Advantages Higher thermal efficiency than thermal plant Wide range of fuels can be used Easy fuel handling Simple layout, easy to install Quick to respond to load variations Initial investment is less than other plants

Disadvantages Diesel cost is high Does not work satisfactorily under continuous overload conditions Noise pollution Maintenance cost is high Capacity limited to 50 MW Life less than steam power plant