Energy Cycle for a Simple-Cycle Gas Turbine
shows an energy-flow diagram for a simple-cycle gas turbine, the description of which is given below:
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| Energy flow diagram for gas-turbine unit |
— The air brings in minute amount of energy (measured above 0°C).
— Compressor adds considerable amount of energy.
— Fuel carries major input to cycle.
— Sum of fuel and compressed-air energy leaves combustor to enter turbine.
— In turbine smallest part of entering energy goes to useful output, largest part leaves in exhaust.
Shaft energy to drive compressor is about twice as much as the useful shaft output.
Actually the shaft energy keeps circulating in the cycle as long as the turbine runs. The important comparison is the size of the output with the fuel input. For the simple-cycle gas turbine the output may run about 20% of the fuel input for certain pressure and temperature conditions at turbine inlet. This means 80% of the fuel energy is wasted. While the 20% thermal efficiency is not too bad, it can be improved by including additional heat recovery apparatus.
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