Thermoeconomic analysis and multi objective optimization of a molten carbonate fuel cell – Supercritical carbon dioxide – Organic Rankin cycle integrated power system using liquefied natural gas as heat sink

Abstract

Thermoeconomic analysis is performed for a combined molten carbonate fuel cell – supercritical CO2 – organic Rankine cycle cogeneration system producing power and heat. Having defined some parameters as decision variables and using a genetic algorithm, multi objective optimization is performed for the proposed system to minimize the product unit cost and maximize the exergy efficiency. Three cases are identified from the optimization: in the first one the efficiency is maximized, ε=65.3% (exergy optimization case) in the second one the product unit cost is minimized, cp=0.039cents(US)kWh, (economic optimization case) and in the third case both of the objectives are considered for optimization, ε=64.7% and cp=0.045centskWh, (multi objective optimization case). For each of these cases a parametric study is performed to investigate the effects on the exergy efficiency and product unit cost of such decision parameters as: the fuel cell temperature, the current density, the carbon dioxide turbine pressure ratio and the pinch point temperature difference in the evaporator and heat exchanger combining the molten carbonate fuel cell and SCO2 gas turbine. The first three of the five mentioned parameters are observed to be more important for the balance between the efficiency and product unit cost for optimization. For all the cases, it is concluded that the highest and second highest exergy destruction rates occur in the catalytic burner and fuel cell, respectively.