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In: Mechanical Engineering

A combined cycle power system uses a simple gas-turbine Brayton cycle in conjunction with a simple...

A combined cycle power system uses a simple gas-turbine Brayton cycle in conjunction with a simple Rankine cycle to produce a total power of 100 MW. In such configuration, the exhaust stream from the gas turbine is used as the heat source for the steam power cycle in a heat exchanger as shown in the figure. The following data are known for the gas-turbine cycle. Atmospheric air enters the compressor at 100 kPa and 20oC, the compressor pressure ratio is 8, the compressor isentropic efficiency is 85%, the maximum gas cycle temperature is 1100oC, and the gas turbine isentropic efficiency is 90%. Additionally, it is known that the gas stream leaves the heat exchanger at the saturation temperature of the steam flowing through it. The following data are known for the steam-turbine cycle. Steam flows through the heat exchanger with a pressure of 6000 kPa, leaving at 320oC, the steam-cycle condenser operates at 20 kPa, and the isentropic efficiency of the steam turbine is 90%.

(a) Schematically draw the complete system including all the equipment required for the analysis. Additionally, sketch the corresponding thermodynamic diagrams for the Brayton and Rankine cycles involved. Assign a different number to each stream and use such number in the diagrams.

(b) Find the power generation efficiency of the gas-turbine.

(c) Find the power generation efficiency of the Rankine cycle.

(d) Find the steam-turbine power, the gas-turbine power, and the total efficiency of the combined cycle.

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