Question 5.2: A gas turbine-based combined-cycle operates without suppleme......
A gas turbine-based combined-cycle operates without supplementary firing (refer to Figures 5.2 and 5.4). The rate of heat input to the gas turbine unit is Q_{in} = 600 MW. The thermal efficiencies of the topping gas turbine \eta_{GT} is 0.33 and that of the bottoming steam turbine \eta_{ST} is 0.29. Calculate the power outputs of the simple cycle and combined-cycle gas turbine-based power plants.
1. Power output of the simple-cycle gas turbine power plant
P_{GT}=\eta_{GT}Q_{i n}=0.4\times600=240~{\mathrm{MW}}
2. Overall thermal efficiency of the combined-cycle
\eta_{C C}=\eta_{GT}+\eta_{ST}\left(1-\eta_{GT}\right)=0.4+0.33\times(1-0.4)=0.598
3. Overall power output of the combined-cycle power plant
P_{\mathrm{CC}}=\eta_{\mathrm{CC}}Q_{\mathrm{in}}=0.598\times600~{\mathrm{MW}}=358.8~{\mathrm{MW}}
4. Power output of the bottoming steam power plant
P_{\mathrm{ST}}=P_{\mathrm{CC}}-P_{\mathrm{GT}}=358.8-240=118.8~\mathrm{MW}