Components and Accessories of Gas Turbine Power Plant

The main components of a gas turbine power plant are compressor, combustor, gas turbine with auxiliary components as intercoolers and regenerators. Some of these are described below.

1. Carryout complete combustion of fuel.
2. High rate of combustion with minimum pressure losses.
3. Carbon deposits must not be formed under any expected conditions of operation.
4. Ease of ignition and starting. Ignition must be reliable under various operating conditions. It is more important in case of aircraft application since they operate under variable conditions of pressure and temperature which vary with altitude.
5. It should have minimum heat losses.
6. Keep the temperature of gases as per the requirements of blade materials used.
7. It should have desired temperature and velocity distribution at inlet to turbine.
8. Volume and weight must be kept within reasonable limits depending on its application.
9. Reliability and serviceability with reasonable life.
10. Thorough mixing of cold and hot air.
11. Flame should be self sustaining and stable. All the above criteria must be satisfied to some degree; however their importance is decided based on its application.

• A swirl vane types of combustion chamber is shown in Figure A.
• The air from compressor is supplied to the combustion chamber, 15% to 20% of air enters into the primary zone to provide A.F. ratio of about 15 : 1 and remainder air is passed through the casing.
• The high velocity of air from compressor is reduced in the diffuser section. Fuel is sprayed through fuel nozzle into the air stream.

• To give a self piloting flame in the air stream, some of the burning mixture in the primary zone is re-circulated back on to the incoming air and fuel.
• It is done by introducing the primary air through twisted radial vanes called swirl vanes. It results into a vortex motion and will induce a region of low pressure along the axis of combustion chamber.
• There are other methods of flame stabilization which shall be discussed later. At a distance away, the free vortex created by swirl vanes dies down and the pressure becomes almost uniform.
• The flame travels in the forward direction and it mixes with the secondary air passed through the perforations in the tube at a velocity of about 30 to 60 m/s. It helps in completing the combustion efficiently.
• Finally, the gases are diluted by the remainder air called tertiary air. It helps in limiting the maximum temperature of gases suitable for blade materials of gas turbine.
• In order to reduce heat losses, the combustion chamber is provided with lining of refractory materials. It has an ignition system to provide a spark across the electrodes of a spark plug for burning of fuel and air. Flame tube is provided with liner of nickel alloys or cobalt alloys to sustain high temperatures of the flame tube.

• Multistage compressors with intercooler in between the stages are used to reduce the work of compression and increase the volumetric efficiency in case of gas turbine power plants using high pressure ratio.
• A cross-flow type of intercooler is shown in Figure B.

• A regenerator is used to heat the compressed air by exhaust hot gases from the turbine before discharged to the surroundings as shown in Figure C.
• It reduces the fuel consumption and improves the thermal efficiency of the plant.
• A regenerator is shown in Figure D.

• Combustion chambers using liquid fuels needs to be injected in metered quantity under pressure as to form conical spray of very fine particles of the size 50 to 100 microns.
• It helps in rapid evaporation of fuel and mixing of fuel vapour with air.
• Thus, the basic requirements of a fuel injection system are:

1. To supply the metered quantity of fuel flow.
2. To atomize the fuel.

• The requirement of injectors for combustion chambers of a gas turbine are to have wide spread spray over a large area to provide additional surface for oxidation. The penetration is not an important consideration for these injectors as in the case of diesel engine applications.
• The type of injectors generally used are centrifugal or swirl type atomizer as shown in Figure E.
• In this the fuel is fed to a conical vortex swirl chamber via the tangential feed ports which imparts a swirling action to the flow.
• The swirl chamber does not run full but has a vapour/air core. The combination of axial and tangential components of velocity causes a hollow conical sheet of fuel to issue from the discharge orifice.
• The cone angle of spray depends on the ratio of axial and tangential components of velocity.
• This conical sheet of fuel then breaks up into the air stream into a spray of fine droplets.
• The breakup of fuel droplets and its distance from orifice is the function of injection pressure.
• There will be a certain minimum fuel pressure at which a fully developed spray will be issued by the orifice, however the actual needed pressures are slightly above this.

Figure D

Accessories of Gas Turbine Power Plant :

Following accessories are usually fitted in a gas turbine power plant :

1. Tachometer : To measure the speed of turbine. It is driven from gas turbine shaft through gears.
2. Lubricating oil pump : It is used to supply the lubricating oil under pressure for lubrication of bearings of the plant.
3. Filters at inlet to the compressor to remove dust and other impurities of surrounding air.
4. Starting motor for starting the plant as discussed earlier in Section.
5. Governor mechanism to control the fuel supply according to the load on the plant so that the speed of the turbine is maintained within prescribed limits.
6. Mufflers at inlet and exhaust for noise control.
7. Oil coolers.