Engineering Homework Help

I’m working on a mechanical engineering question and need an explanation and answer to help me learn.

Combined cycle power plants are some of the cleanest and most efficient fossil fuel power plants in operation today. Watch the following videos for background on combined cycles. The first video shows a good overview of a typical plant and the second shows actual photo/video of a plant.

Siemens’ Flex-Plants™ – Flexible Combined Cycle Power Generation (Links to an external site.)

Duke Energy Power Plant Tour (Links to an external site.)

In the Sacramento region, we have several combined cycle plants providing hundreds of megawatts of power to SMUD, including:

Cosumnes Power Plant (at Rancho Seco)

Carson Ice Cogeneration

Sacramento Power Authority 47th Ave

A combined cycle power plant has a net power output of 264 MW. Air enters the compressor of the Brayton cycle at 100 kPa and 17^oC. The pressure ratio is 20, the turbine inlet temperature is 1620 K and the gases leaving the turbine are used to heat the steam of the Rankine cycle to 600^oC and 6 MPa. The combustion gas leaves the heat exchanger (HRSG) at 400 K and the condenser pressure is 10 kPa. The isentropic efficiency of the compressor is 87%, the gas turbine isentropic efficiency is 90%, the steam turbine isentropic efficiency is 92% and the pump efficiency is 65%. The condenser sub-cools the water by 10^oC (10^oC less than the saturation temperature). Using variable specific heat analysis, determine:

1. Rate of heat input in the combustion chamber, Qin in kW.
2. Rate of heat transfer in the HRSG, in kW.
3. Power input to the pump, in kW.
4. Power input to the compressor, in kW.
5. Net power output from the Brayton cycle, in kW.
6. Net power output from the Rankine cycle, in kW.
7. Overall efficiency.

Note: Submit your work and calculations, no formal write-up necessary. Individual assignment.