Gas Turbine Power Plant | The plant which employs gas turbine as the prime mover for the generation of electrical energy is known as a gas turbine power plant. Air is used as the working fluid in a gas turbine power plant.
The air compressor is used to compress air and is led to the combustion furnace where heat is added to the air, thus raising its temperature. In the compressed air, heat also added by burning fuel in the chamber or by the use of air heaters.
The high-pressure air from the combustion furnace is then passed to the turbine where it expands and does the mechanical work. The turbine drives the alternator. It converts mechanical energy into electrical energy.
It may be mentioned here that compressor, gas turbine and the alternator are mounted on the same shaft so that a part of the mechanical power of the turbine can be used for the operation of the compressor. The gas turbine plants are being used as standby plants for hydro power plants, as a starting plant for driving auxiliaries in power plants.
Gas Turbine Power Plant Layout Arrangements
The important components of the power plant are
- Combustion chamber
- Gas turbine
- Starting motor
In power plant generally, rotator type of compressor is used. The air at atmospheric pressure is drawn by the compressor through the filter which removes the dust from the air. The rotatory blades of the compressor push the air between stationary blades to raise its pressure. Thus air at extreme pressure is produced at the outlet of the compressor.
A re-generator is a device which recovers heat from the exhaust gases of the turbine. The exhaust is passed through the re-generator before wasting to atmosphere. A re-generator consists of a nest of tubes contained in a shell. The compressed air passes through the tubes on its way to the combustion furnace. In this way, compressed air is heated by the hot exhaust gases.
The high pressure air from the compressor is led to the combustion chamber via the re-generator. In the combustion furnace, heat is added to the air by burning oil. The oil is injected through the burner into the chamber at high pressure to ensure customization of oil and its thorough mixing with air. The result is that the furnace attains an extreme temperature about 3000 Fahrenheit. The combustion gases are probably cooled to 1300 F to 1500 F and then delivered to the turbine.
The combustion consisting of a mixture of gases at high temperature and pressure is passed to the turbine. These gases in passing over the turbine blades expand and thus do the mechanical work. The temperature of the exhaust gases from the gas turbine is about 900 Fahrenheit.
The alternator is coupled with the gas turbine. The alternator converts the mechanical energy of the gas turbine into electrical energy. The output from the alternator is given to the bus-bars through the transformer and circuit breakers.
First, the compressor has to be started, before starting the gas turbine. For this purpose, an electric motor is mounted on the same shaft as that of the gas turbine. The motor is energized by the batteries. Once they start, a part of the mechanical power of the gas turbine drives the compressor and there is no need of motor now.
Advantages of Gas turbine Power Plant
- Gas turbine plant is simple in design than others.
- The power station is much smaller in size as compared to the thermal power plant of the same capacity.
- The initial and operating costs are much lower than those of the equivalent steam power plant.
- It requires relatively less water as no condenser is used.
- The maintenance charges are quite small in this power station.
- These gas turbines are much simpler in construction and operation than steam turbines.
- The Gas turbine can be started quickly form cold conditions.
Disadvantages of Gas Turbine Power Plant
- There is a problem for starting the unit. It is because before starting the gas turbine, the compressor has to be operated for which power is required from some external source.
- For driving compressor greater part of the power required by the gas turbine is used, the net output is low.
- The overall efficiency of the gas turbine plant is low because the exhaust gases from the gas turbine contain sufficient heat.
- The temperature of the combustion chamber is quite high 3000 Fahrenheit so that its life is comparatively reduced.
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