Performance evaluation of micro gas turbine-solid oxide fuel cell hybrid system under part-load conditions

Design-point and part-load characteristics of a gas turbine-solid oxide fuel cell hybrid micro generation system, of which total power output is 30 kW, are investigated for its prospective use in the small distributed energy systems. A cycle analysis of the hybrid system has been performed to obtain general strategies of highly efficient operation and control. The method of analysis has been verified by comparison with previous results, of which power output was assumed in the range from 259 to 519 kW. Then, the part-load performance of the 30 kW system has been evaluated. Two typical operation modes, i.e., constant and variable rotation speed gas turbine operation, are considered. It is found that the variable speed mode is more advantageous to avoid performance degradation under part-load conditions. Operating under this mode, despite 10% adiabatic efficiency drop in the gas turbine components, the generation efficiency can be maintained over 60% (LHV) in the power output range from 40 to 100%. The turbine exhaust temperature, however, is increased with decreasing the power output under the variable speed mode with the constant SOFC operating temperature, so that the thermal durability of recuperator material becomes a critical issue. Finally, the effect of compressor/turbine operating lines on the system performance is evaluated.