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Question 13.7: A combined-cycle power plant comprising an MHD generator, st......

A combined-cycle power plant comprising an MHD generator, steam generator, and a steam turbine plant (see Figure 13.10) is operating as follows:

• Power output of the combined-cycle plant is P_{CC} = 120 MW
• MHD generator efficiency is \eta_{MHD} = 0.4
• Steam turbine plant efficiency is \eta_{ST} = 0.32

Calculate (i) the combined-cycle overall efficiency, (ii) the MHD generator exhaust heat rate, and (iii) the MHD generator and steam turbine power outputs.

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1. Overall efficiency of combined-cycle power plant

\mathbf{h}_{\mathrm{CC}}\,=\,\mathbf{h}_{\mathrm{MHD}}\,+\,\mathbf{h}_{\mathrm{ST}}\,-\,\mathbf{h}_{\mathrm{MHD}}\mathbf{h}_{\mathrm{ST}}\,=\,0.4\,+\,0.32-\,0.4\times0.32\,=\,0.592

2. Thermal energy input to the MHD generator

Q_{\mathrm{in}}=P_{\mathrm{CC}}/\eta_{\mathrm{CC}}=120/0.592=202.7\mathrm{~MW}

3. Power output of the MHD generator

P_{\mathrm{MHD}}=Q_{i n}\ \eta_{\mathrm{MHD}}=202.7\times0.4=81.08\ \mathrm{MW}

4. Exhaust heat rate of the MHD generator

Q_{\mathrm{exh}}=Q_{\mathrm{in}}-P_{\mathrm{MHD}}=202.7-81.08=121.6~M W

5. Power output of the steam turbine power plant (without supplementary firing)

P_{ST}=Q_{\mathrm{{exh}}}\,\eta_{S\Gamma}=121.6\times0.32=38.92\ \mathrm{MW}

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