Gas turbine exhaust enters the heat-recovery steam generator (HRSG) of a GTCC plant at 550 C, 1.15 bar and leaves at 150 C, 1.05 bar. Liquid water enters the HRSG at 90 C, 200 bar, and leaves as super

a. The stream availability of the gas turbine exhaust at entry to the HRSG can be determined using the thermodynamic property tables. At 550C and 1.15 bar, the specific entropy of the gas turbine exhaust is 6.518 kj/kgK. The stream availability can be calculated as the difference between the specific entropy of the gas turbine exhaust and the specific entropy of the surroundings, which we assume to be at 25C and 1 bar. Therefore, the stream availability of the gas turbine exhaust at entry to the HRSG is: Stream availability = Specific entropy of gas turbine exhaust – Specific entropy of surroundings = 6.518 – 0.189 = 6.329 kj/kgK b. The stream availability of the water at exit from the HRSG can also be determined using the thermodynamic property tables. At 500C and 200 bar, the specific entropy of the superheated steam is 5.063 kj/kgK. The stream availability can be calculated as the difference between the specific entropy of the superheated steam and the specific entropy of the surroundings (25C and 1 bar). Therefore, the stream availability of the water at exit from the HRSG is: Stream availability = Specific entropy of superheated steam – Specific entropy of surroundings = 5.063 – 0.189 = 4.874 kj/kgK c. The ratio of gas mass flow rate to water mass flow rate can be determined using the mass balance equation. Assuming steady-state and no accumulation, the mass flow rate of gas turbine exhaust at entry to the HRSG is equal to the mass flow rate of water at exit from the HRSG. Therefore, the ratio of gas mass flow rate to water mass flow rate is 1:1. d. To calculate the stream availability of superheated steam at a pressure of 10 bar and a temperature of 250C, we first need to find the specific entropy of the steam at these conditions using the thermodynamic property tables. At 10 bar and 250C, the specific entropy of the superheated steam is 6.222 kj/kgK. The stream availability can be calculated as the difference between the specific entropy of the superheated steam and the specific entropy of the surroundings (25C and 1 bar). Therefore, the stream availability of superheated steam at 10 bar and 250C is: Stream availability = Specific entropy of superheated steam – Specific entropy of surroundings = 6.222 – 0.189 = 6.033 kj/kgK