Analysis and optimization of hybrid MCFC gas turbines plants

High temperature fuel cells are electricity producers that guarantee relevant energetic and environmental performances. They feature high electricity to input chemical energy ratios and availability of high temperature heat. Notwithstanding, the search for a further increase in electric efficiency, especially when applying a CHP solution is not feasible, has brought to plant integration with gas turbines (GTs) in several studies and some pilot installations. While for pressurized fuel cells the choice of internal combustion gas turbines seem to be the only one feasible, in ambient pressure fuel cells it seems useful to analyze the combination with indirect heated GT. This choice allows to optimize turbine pressure ratio and cell size. In this work, a parametric performance evaluation of a hybrid molten carbonate fuel cell (MCFC) indirect heated gas turbine has been performed by varying the fuel cell section size and the fuel utilization coefficient. The analysis of performance variation with the latter parameter shows how a cell that is optimized for stand alone operation is not necessarily optimized for the integration in a hybrid cycle. Working with reduced utilization factors, in fact can reduce irreversible losses and does not necessarily yield to less electricity production since the heat produced in the post combustor is recovered by the gas turbine section. This aspect has not been taken into sufficient consideration in literature. The analysis illustrates the methodology to define new operating conditions so to allow global output and global efficiency maximization.