Waste heat recovery of a combined solid oxide fuel cell-gas turbine system for multi-generation purposes

In an attempt to recover waste heat from a system composed of a solid oxide fuel cell and gas turbine, a novel multi-generation system is proposed utilizing five different subsystems and investigated from energy, exergoeconomic, and environmental standpoints. The waste heat of the solid oxide fuel cell - gas turbine is recovered by a recompression supercritical CO2 Brayton cycle and a thermoelectric generator, and the total electrical power generated by the supercritical CO2 Brayton cycle and thermoelectric generator is used as the input electricity in a proton exchange membrane electrolyzer to produce hydrogen. The residual heat of the exhaust gases and the waste heat of the supercritical CO2 Brayton cycle in the heat rejection stage are respectively recovered in a domestic hot water heat exchanger and an LiCl-H2O absorption refrigeration system which are responsible for the production of heating and cooling. The evaluations in a base case demonstrate that the five utilized subsystems bring about a 2.49 and 14.4% points enhancement in the exergy and energy efficiencies of the system, respectively, compared to the combined solid oxide fuel cell - gas turbine system. However, they contribute to a 23.57% and 17.7% of the total cost rate and total exergy destruction of the system, respectively. The outcomes also reveal that employing the subsystems conduces to a decline in the environmental index and payback period of the whole system. The sensitivity analysis indicates that the system has a proper thermoeconomic performance within the range of solid oxide fuel cell outlet temperature between 745 and 765 degrees C. The lowest unit cost and the highest exergy efficiency of multi-generation occur at the highest possible pressure ratio of the air compressor. Also, the best economic and environmental performances and the highest exergy efficiency take place at the lowest current density and highest fuel utilization factor equal to 4800 A/m2 and 0.85, respectively.