Thermal Power Exercise - Application 3 We have a combined cycle power plant designed with four 150 MW gas turbines and one- 350 MW steam turbine. The exhaust gases from each gas turbine pass through a supplementary firing chamber. Then the exhaust gases pass through a waste heat boiler to generate a superheated steam. The generated superheated steam from the four waste heat boilers is supplied to the steam turbine. a 25C Fuel (calorific value=44000 kJ/kg) Nec = 0.96 b C p.c = p.t=8 7c = 0.85 Fuel (calorific value-44000 kJ/kg) 1 bar 850C (Inlet & reference point) "WHB =0.85 The feed water to the other typical three waste heat boilers www 1100 C PGT.net = 4 150 MW GT G t = 0.9 MSF = 0.96 d 7 6 DAH 2 ST For the states of the steam cycle, use the following properties: The generated steam from the other typical three waste heat boilers PST = 350 MW G State Pressure (bar) Temperature (C) Enthalpy (kJ/kg) 1 80 550 3522 2 20 3133 3 0.07 2275 4 0.07 163.4 5 20 163.4 6 20 908.5 7 80 908.5 For the gas turbine plants and the steam plant, mechanical and generator efficiencies of 0.99 and 0.98, respectively. Assume for air and Cp,a=1.003 kJ/kg.K and ya=1.44 and for gases and Cp,g=1.15 kJ/kg.K and yg=1.33. Calculate: 1) The air mass flow rate to each gas turbine plant. 2) The fuel mass flow rate required in each gas-turbine cycle and in each of the supplementary firing. 3) The generated steam mass flow rate by the heat recovery boiler. 4) The gas stack temperature after the waste heat boiler. 5) The efficiencies of gas, steam and combined cycles.