Thermodynamic Analysis of Integrated Molten Carbon Fuel Cell–Gas Turbine Cycles for Sub-MW and Multi-MW Scale Power Generation

This paper investigates the thermodynamic potential of the integration of molten carbon fuel cell (MCFC) technology with gas turbine systems for small-scale (sub-megawatt or sub-MW) as well as large-scale (multi-MW) hybrid cycles. Following the proposals of two important MCFC manufacturers, two plant layouts are discussed, the first based on a pressurized, externally reformed MCFC and a recuperated gas turbine cycle and the second based on an atmospheric MCFC, with internal reforming integrated within an externally fired gas turbine cycle. Different levels of components quality are considered, with an analysis of the effects of variable pressure ratios, different fuel mixture compositions (variable steam-to-carbon ratio) and turbine inlet temperature levels, together with potential advantages brought about by an intercooled compression process. The analysis shows interesting effects due to the peculiarity of the mutual interactions between gas turbine cycle and fuel cells, evidencing the importance of a careful thermodynamic optimization of such cycles. Results show the possibility to achieve a net electrical efficiency of about 57–58% for a small plant size (with a difference of 1.5–2 percentage points between the two layouts), with the potential to reach a 65% net electrical efficiency when integrated in advanced cycles featuring high-efficiency, large-scale equipment (multi-MW scale cycles).