Effect of fuel cell operating parameters on the performance of a multi-MW solid oxide fuel cell/gas turbine hybrid system

The principal planar solid oxide fuel cell operating parameters are pressure, stack temperature and temperature gradient, cell voltage, fuel utilization, leakage rate and percentage of internal reforming. This paper shows the effects of these parameters on overall fuel cell/gas turbine hybrid system performance. The baseline conceptual system used to investigate these parameters is a 500MW hybrid system. The system performance was simulated using ASPEN Plus and GateCycle (TM) commercial software platforms and a GE developed FORTRAN code to simulate the fuel cell performance. Parameter choices for the baseline case are: 15atm pressure, 725C average cell temperature, 150C stack temperature rise, 0.75V average cell voltage, 80% fuel utilization, 1% leakagTe rate and 70% internal reforming. At these conditions, the system efficiency is predicted at approximately 65.8%. The addition of a steam turbine bottoming cycle, increases the hybrid system efficiency by 4% to 70%. Increasing the average cell voltage to 0.8V or the percentage of internal reforming to 90% also increases the hybrid system efficiency to nearly 70%. The optimum pressure for maximum efficiency is 8 atm for the hybrid system; the optimum pressure for the hybrid with a steam turbine bottoming cycle is 9 atm. While increasing the SOFC temperature rise, cell voltage, and percentage of internal reforming improve system efficiency, they may adversely affect stack cost and reliability; these competing effects must be traded when designing a practical system.