Gas turbine power plants are installed where liquid or gaseous fuel is available in large quantities. The cost of plant is low and they can be put into commission quickly. It requires less space only. The capacity of plant varies from 5 MW to 60 MW based on the availability of fuel. The thermal efficiency of gas turbine plant is about 25%.
Gas Turbine Power Plant in India
- Namrup in Assam – 70 MW.
- Uran in Maharashtra -4 units of 60 MW each.
- Auraiya Gas plant (NTPC) in UP combined cycle power plant having 652 MW capacities.
Different gaseous fuels used in Gas turbine Power plants are
- Natural Gas
- Blast Furnace Gas
- Producer Gas
- Coal Gas
Different oils used for combustion are
- Distillable oils
- Residual oils
- Various paraffin’s used are
- (a) Methane,
- (b) Ethane,
- (c) Propane,
- (d) Octane (gasoline) and
- (e) dodecane (kerosene oil).
Elements of a Simple Gas Turbine Plant
A simple gas turbine plant is shown in Fig. It consists of a compressor, combustion chamber and a gas turbine. The compressor and gas turbine are mounted on the same shaft.
Working of a Gas Turbine
When the unit-runs, the atmospheric air is drawn into the compressor, compressed to several times than that of atmosphere. The compressed air then flows to the combustion chamber, where the fuel is injected. The combustion takes place in the combustion chamber.
The products of combustion, flue gas with high pressure and high temperature are passed through the gas turbine. In the gas turbine, the hot flue gases expand and develop motive force to drive the turbine. Since generator is coupled with the turbine, power is generated whenever turbine rotates. This type of gas turbine is called open cycle gas turbine. The main disadvantage of this type of turbine is that the major portion of the work developed in the turbine is used to drive the compressor and the remainder is used for producing power.
Refinement of open cycle Gas Turbine power plant
Refinement of open cycle is done by providing regenerator, intercooler, reheating in combustion chambers and using two stages of compressor and 2 stages of turbine, as shown in Fig.
These additions raise the efficiency of gas turbine plant to over 30%.
LPC Low Pressure Compressor
HPC High Pressure Compressor
LPT Low Pressure Turbine
HPT=High Pressure Turbine
CC Combustion Chamber
Purpose of each additional equipment in the refinement cycle
- Reheating – Reheat the exhaust gases o f HPT to upper temperature limit, increase enthalpy of exhaust gases and pressure of gases.
- Regenerator – The heat contained in the exhaust gases of LPT is utilized in the regenerator for transferring heat to the cold air coming out of HPC.
- Intercooler – This reduces the work of compressor, hence the power spent by compressor is less when the air is cooled.
Advantages of Gas Turbine Plants
- The capital cost of plant is low.
- This can be quickly commissioned.
- It requires less space.
- Uses minimum water compared to steam power plants.
- Erection and commissioning time is less.
- High reliability and flexibility in operation.
- Capacity to use wide variety of fuels.
- Smaller in size and weight compared to steam power plant.
Disadvantages of Gas Turbine Plants
- Major part of the work developed in the turbine is used to drive the compressor. So net output of the plant is low.
- Since the temperature of the products of combustion is high, service conditions become complicated.
Application of Gas Turbines
- Gas turbine plants are used as standby plants for the hydro electric power plants.
- Gas turbine power plants may be used as peak loads plant and standby plants for smaller power units.
- Gas turbines are used in jet aircrafts and ships.
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