Gas Turbines are one of the most efficient equipment for
converting fuel energy to mechanical energy.
The three main
sections of a Gas Turbine are the Compressor, Combustor and Turbine. The gas turbine power plant has to work
continuously for long period of time without output and
performance decline. Apart from the main sections there are
other important Auxiliaries systems which are required for
operating a Gas Turbine Power Plant on a long term basis
Gas turbine engines derive their power from burning fuel in
a combustion chamber and using the fast flowing
combustion gases to drive a turbine in much the same way
as the high pressure steam drives a steam turbine.
One major difference however is that the gas turbine has a
second turbine acting as an air compressor mounted on the
same shaft. The air turbine (compressor) draws in air,
compresses it and feeds it at high pressure into the
combustion chamber increasing the intensity of the burning flame.
It is a positive feedback mechanism
As the gas turbine speeds up, it also causes the compressor
to speed up forcing more air through the combustion
chamber which in turn increases the burn rate of the fuel
sending more high pressure hot gases into the gas turbine
increasing its speed even more. Uncontrolled runaway is
prevented by controls on the fuel supply line which limit the
amount of fuel fed to the turbine thus limiting its speed.
simple diagram of gas power plant cycle.
CLASSIFICATION OF GAS TURBINE:-
1- Constant pressure combustion gas turbine
(a) Open cycle constant pressure gas turbine.
(b) closed cycle constant pressure gas turbine
2-Constant volume combustion gas turbine.
Operation of gas turbine.
2- Shut Down.
1- Starting of gas turbine.
Starting of gas turbine power plant require an auxiliary
power source , till the plant own compressor inducts air and
compresses it to a pressure such that expansion from
resosnalbale temperature will develop enough power to
sustain operation . the stater may be
1 - Internal combustion engine.
2- A steam turbine.
3- An Auxiliary electric motor
4- Another gas turbine.
It Must be coupled to the turbo - compressor shaft with a
disengaging or over - running clutch.
A main generator or its direct connected exciter may be
pressed into temporary service as a motor.
1 Run the unit and induct the air,
2- Actuate the combustion ignition system and inject the
The fuel is controlled to obtain the necessary warm up
3- Adjust the speed and voltage and synchronize the alternator.
4- Build up the load on the alternately governed gear control;
SHUNT DOWN F OF GAS TURBINE:-
Shunt down of gas turbine occur very quickly after the fuel is
cuts of from the combustor. A Rapid shunt down is desirable
since it minimizes the "chilling" effect resulting from passing
cold air through the hot turbine. Turning gears are usually
employed , or alternating the starting device may be operated
at reduced speed to ensure symmetrical of rotor.
This avoids thermal " kinking of the shaft.
Gas turbine fuel used:-
various types of fuel are used in gas power turbine.
1- Gaseous Fuels.( Natural gas)
2- Liquid Fuels. ( Liquid fuels of petroleum.)
3- Solid Fuels.(such as coal)
Advantage of gas turbine power plant over thermal power plants:-
- No ash handling problem.
- Low capital cost
- the gas turbine plants can be installed at selected load center as space requirement is less where steam power plants can not accommodated.
- fewer auxiliaries used
- gas turbine can built quickly.
- economical as thermal power plant in components.
- storage of fuel is much smaller and handling is easy
APPLICATION OF GAS TURBINE POWER PLANTS.
- To Drive generators and supply peak load in steam , diesel or hydro plants.
- To work as combination plants with conventional steam boilers.
- To supply mechanical drive fr auxiliaries.