In a single pressure combined cycle power plant with supplementary firing, the compressor intake air condition is 15 C and 1 bar, the compressor pressure ratio is 15, and its isentropic efficiency is 0.88. The 200 MW gas turbine burns natural gas with an HV of 49.5 MJ/kg and an excess air ratio of 3.8. The gas turbine inlet temperature is 1270 C and the isentropic efficiency of the turbine is 0.92. Supplementary firing uses coal with an HV of 34 MJ/kg to raise the gas temperature up to 900 C at the HRSG inlet. HRSG generates superheated steam at 9 MPa and 540 C from feedwater at 110 C. The pinch point in the HRSG is 13 K. The temperature of stack gas leaving the HRSG is 250 C. Assume an isentropic exponent of 1.4, the isobaric specific heat of 1.05 kJ/kg K for gas, and of 4.187 kJ/kg-K for water.

Find the following:

a) the heat added in supplementary firing per kg of the gas turbine exhaust gas, 

b) the net specific work of the gas turbine plant, 

c) the air mass flow rate, 

d) the thermal efficiency of the gas turbine plant, 

e) the rate of steam generation in the HRSG, 

f) the ratio of steam flow rate to airflow rate.

Answer rating: 100% (QA)

a Q m Cp T2T1 Q 1 105 9001270 Q 273 kJkg b Wnet m Cp T2T1 1eta Wnet 1 ... View the full answer