Study on solid oxide fuel cell/closed-Cycle MHD combined power generation system

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We propose a new fossil-fuel-utilized high-performance combined power generation system with liquefaction recovery of carbon dioxide. In the system, pure oxygen is used as the oxidant gas and the solid oxide fuel cell (SOFC) is selected as the topping cycle. The exhaust fuel gas of the SOFC is afterburned with its oxidant gas of pure oxygen and the heat of the combustion gas is utilized in the bottoming cycle of the closed-cycle MHD/gas turbine cycle. Since the SOFC is operated under the high temperature condition of about 1300 K, its thermal efficiency is very high by itself up to about 55 % and, in addition, its exhaust fuel gas has high utility value in the combined cycle. This is the reason why the SOFC is adopted as the topping cycle. The maximum temperature of the afterburned exhaust fuel gas by pure oxygen reaches about 2300 K. This temperature exceeds the applicable limit of gas turbine, whereas coincides with the suitable inlet temperature of the closed-cycle MHD generator. This is the reason why the MHD/gas turbine cycle is selected as the bottoming cycle. To determine the actual make-up of the proposed system and to calculate the total thermal efficiency, detailed heat balance is examined under the condition that the cell voltage and fuel utilization rate of the SOFC are 0.77 V and 85 %, the enthalpy extraction ratio and adiabatic efficiency of the MHD generator 35 % and 80 %, the adiabatic efficiency of the noble gas turbine and compressor 88 %, respectively. It is made clear that the total thermal efficiency of the system reaches 63.24 % (HHV) or 70.18 % (LHV). This efficiency is very high as for the system with carbon dioxide recovery. The proposed system, therefore, has excellent performance and is worth carrying out further research and development.