In: Chemistry
Consider a combined gas-steam power cycle. The topping cycle is a simple Brayton cycle that has a pressure ratio of 7. Air enters the compressor at 15 ºC at a rate of 10 kg/s and the gas turbine at 950 ºC. The bottoming cycle is a reheat Rankine cycle between the pressure limits of 6 MPa and 10 kPa. Steam is heated in a heat exchanger at a rate of 1.15 kg/s by the exhaust gases leaving the gas turbine, and the exhaust gases leave the same exchanger at 200 ºC. Steam leaves the high-pressure turbine at 1 MPa and is reheated to 400 ºC in the heat exchanger before it expands in the low-pressure turbine. Assuming 80 percent isentropic efficiency for all pumps and turbines,
1) determine the enthalpy of air at the compressor outlet.
2) determine the enthalpy of air at the turbine outlet
3) determine the enthalpy of steam-water mixture at the low pressure turbine outlet
4) determine the moisture content at the exist of the low-pressure turbine
5) determine the steam temperature at the inlet of the high-pressure (hint: trial and error)
6) determine the net power output of the combined plant
7) determine the thermal efficiency of the combined plant