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

提出了一种利用化石燃料的高性能二氧化碳液化回收联合发电系统。系统采用纯氧作为氧化气体，固体氧化物燃料电池（SOFC）作为顶顶循环。SOFC的废气用其氧化气体纯氧进行补燃，燃烧气体的热量在闭式循环MHD/燃气轮机循环的底循环中得到利用。由于SOFC在1300 K左右的高温条件下运行，其本身热效率非常高，可达55%左右，并且其排出的燃料气体在联合循环中具有很高的利用价值。这就是为什么采用SOFC作为封顶周期的原因。纯氧加燃后的废气最高温度可达2300 K左右。该温度超出了燃气轮机的适用极限，而与闭式循环MHD发电机的合适入口温度一致。这就是为什么选择MHD/燃气轮机循环作为底部循环的原因。为了确定该系统的实际组成和计算总热效率，在SOFC的电池电压为0.77 V和燃料利用率为85%，MHD发电机的焓提取率和绝热效率分别为35%和80%，稀有燃气轮机和压气机的绝热效率分别为88%的条件下，对热平衡进行了详细的研究。结果表明，该系统的总热效率达到63.24% （HHV）和70.18% （LHV）。对于有二氧化碳回收的系统来说，这个效率是非常高的。因此，该系统具有良好的性能，值得进一步研究和开发。

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.