Question 13.4: A hydrogen-fired combined-cycle power plant consists of a hy......
A hydrogen-fired combined-cycle power plant consists of a hydrogen combustor and gas and steam turbine power block. It is operating as follows:
• Plant electric power output is P_{el} = 30 MW
• Fuel: hydrogen with lower heating value, LHV = 120 MJ/kg
• Lower heating value of the fuel is LHV = 120 MJ/kg
• Combustor efficiency is \eta_{comb} = 0.985
• Efficiencies of gas and steam turbine trains are \eta_{GT} = 0.4 and \eta_{ST} = 0.33
• Efficiency of electric generator is \eta_{g} = 0.98
• Plant capacity factor CF = 0.9
Calculate (i) the combined-cycle efficiency and the plant overall efficiency, (ii) the fuel energy input rate of the plant, (iii) the fuel consumption rate, (iv) the power outputs of gas and steam turbines, and (v) the annual power generation.
1. Combined-cycle efficiency
\eta_{C C}=\eta_{GT}+\eta_{ST}\left(1-\eta_{GT}\right)=0.4+0.33\ \left(1-0.4\right)=0.5982. Plant overall (electrical) efficiency
\eta_{\mathrm{el}}=\eta_{\mathrm{comb}}\ \eta_{\mathrm{CC}}\ \eta_{\mathrm{g}}=0.985\times0.598\times0.98=0.5773. Plant fuel energy input rate
Q_\mathrm{f}=P_{\mathrm{el}}/\eta_{\mathrm{el}}=30/0.577=52\ \mathrm{MJ/s}4. Plant fuel consumption rate
m_\mathrm{f}=Q_\mathrm{f}/ \mathrm{LHV}=52/120=0.4335~\mathrm{kg/s}=1.56\ t/\mathrm{h}5. Power outputs of gas and steam turbines
P_{GT}=Q_{\mathrm{f}}\;\eta_{\mathrm{comb}}\;\eta_{GT}=52\times0.985\times0.4=20.5\;\mathrm{MW }P_{\mathrm{ST}}=P_{\mathrm{el}}-P_{GT}=30-20.5=9.5~~\mathrm{M W}
6. Annual electric power generation
E_{y r}=8760\ {\mathrm{CF}}\,P_{e l}=8760\times0.9\times30=2365020\ \mathrm{MWh/a}\approx236.5\ \mathrm{GW}\mathrm{h}\mathrm{}\mathrm{~}\mathrm{/}\mathrm{a}.