A client has asked you to perform a conceptual design and initial analysis of a power plant. They
have asked for a combined cycle plant with a gas turbine/Brayton topping cycle and a steam/Rankine
bottoming cycle. The maximum gas turbine inlet temperature is 1300◦C and the maximum steam turbine
inlet temperature is 625◦C.
In order to control the total cost of the plant, the client has indicated that they don’t want any feed-water
heaters, reheaters, or regenerators, i.e., using unmodified cycles.
The efficiencies/effectiveness of each device is given in Table 1.
Table 1: Device parameters
Device Efficiency Effectiveness
Gas compressor 0.93 –
Gas turbine 0.91 –
Gas exhaust/boiler heat exchanger – 0.85
Water pump 0.92 –
Steam turbine 0.95 –
The plant operates under the following conditions: The heat addition to the gas turbine combustor
(Q˙
in) is 500 MW and the air inlet temperature to the gas compressor (TIn,Gas) 25◦C. The minimum heat
rejection temperature (TLow,Steam) is 35◦C and the minimum quality at steam turbine exit (χMin) is 0.9.
These parameters are summarized in Table 2.
Table 2: System parameters
Parameter Q˙
Some of the design parameters that you will have to pick :
• Gas turbine pressure ratio
• Rankine cycle boiler pressure (gas to steam heat exchanger)
1
• Rankine cycle condenser pressure
In your calculations you will have to find and subsiquently discuss in your report:
a) Mass flow rates of air and water
b) Work out of each turbine
c) Combined cycle efficiency
d) Extra credit: perform sweep of your parameters that control % work through each cycle and find
maximum
Sample Solution