Question

The gas turbine cycle of a gas-steam combined cycle power plant has a pressure ratio of 12. The air enters the compressor at 310 K and 100 kPa (1) and the turbine at 1400 K (3). The combustion gases leaving the gas turbine (4) are used to heat the steam to 12.5 MPa up to 500 °C (6) in a heat exchanger. The flue gas exits the heat exchanger (5) at 247 °C. The steam is expanded in a high pressure turbine to a pressure of 2.5 MPa, and is reheated in the combustion chamber to 550 °C before it expands in the low pressure turbine to 10 kPa. The steam mass flow is 12 kg/s. Establish the appropriate working conditions and assumptions. Assuming isentropic pump efficiencies 75%, compressor 85% and both turbines 90%,
a) Draw a diagram of the installation (0.5)   
b) Complete the table of states indicated for each state considered, p, T, h, s, exergy and steam title when necessary and draw the T-s diagram of the combined cycle. Include the water saturation curve in the drawing and represent all the states of the cycle in the diagram (1)

b) Calculate the air flow rate in the system. (0.5)  

c) Calculate the thermal power supplied by the combustor. (0.5)  

d) Heat dissipated in the condenser (0.5)  

(e) Net power supplied by the system (1)  

(f) Combined cycle thermal performance (1 )  

(g) Exergy destroyed in the intermediate exchanger (1 )  

(h) Exergetic performance of the combined cycle (1)  

(i) Classify the elements of the installation according to the exergy destroyed in each of them by reference to the total exergy destroyed in the combined cycle (%) (1 ). You can represent the result graphically in whatever way you think is most appropriate.
(g) Analyse the effect of the isentropic efficiency of the steam turbine on the exergy and thermal efficiency of the combined cycle using a parametric table. Represent the results in a single graph including both yields (2)