Thermodynamic and exergetic analysis of a novel multi-generation system based on SOFC, micro-gas turbine, s-CO2 and lithium bromide absorption refrigerator

Abstract

To improve the utilization of waste heat from a solid oxide fuel cell (SOFC), a novel multi-generation energy system is proposed and analyzed from the viewpoints of energy and exergy. It consists of a SOFC, a micro-gas turbine (MGT), a supercritical carbon dioxide (S-CO2) Brayton cycle and a lithium bromide absorption refrigerator. The main part of the SOFC-MGT waste heat is recovered by a S-CO2 Brayton cycle to generate excessive electric power. The residual exhaust heat of MGT is respectively recovered by a domestic heating device and a lithium bromide absorption refrigerator to produce heating and cooling. In this study, a mathematical model of the proposed system is developed to evaluate the system thermodynamic characteristics and determine the influences of input parameters like ambient temperature, fuel flow rate, current density and air flow rate. The results reveal that the multi-generation energy system obtains the electric power of 696.9 kW, heating capacity of 24.98 kW and cooling capacity of 88.81 kW under design condition, and the energetic round trip efficiency and electrical efficiency of the system are 70.49% and 60.59%, respectively. According to sensitivity analysis, the current density has the greatest influence on the system round trip efficiency and electrical efficiency and the reformer intake fuel flow rate shows the most influential effect on SOFC voltage. The burner accounts for the maximum exergy destruction among all components. Overall, the multi-generation energy system based on SOFC is superior to the standalone SOFC power system in the respect of energy and exergy.