Optimization and part-load performance analysis of MCFC/ST hybrid power system

Based on a benchmark hybrid power system of molten carbonate fuel cell(MCFC) integrated with the steam turbine(ST) bottom cycle system, a new MCFC/ST hybrid power system is proposed in this paper. The detailed thermodynamic models of the overall system are established. The effects of the key parameters on the new system performance are deeply studied. The exergy analysis method is used to reveal the theoretical root of performance advantage of new system. The off-design performance of the new system is analyzed. In order to improve the off-design performance of the new system, two control modes are proposed to make the fuel cell operate at 650 °C. The results indicate that the total exergy loss of the new system is obviously reduced compared with the benchmark system. The net efficiency of the new system reaches the highest when the carbon-to-steam ratio is 2.5, CO2 utilization rate is 75%, fuel utilization rate is 85% and the current density is 1500 A/m2. The fuel cell is more efficient at part load than at the design point and the net hybrid power system efficiency increases in the first control mode and almost remains unchanged in the second control mode with the decrease of the load.