Energy and exergoeconomic evaluation of a new power/cooling cogeneration system based on a solid oxide fuel cell

A new cogeneration system consisting of a hydrogen-fed SOFC (solid oxide fuel cell), a GT (gas turbine) and a GAX (generator-absorber-heat exchange) absorption refrigeration cycle is proposed and analyzed in detail. The electrochemical equations for the fuel cell and thermodynamic and exergoeconomic relations for the system components are solved simultaneously with EES (Engineering Equation Solver) software. Through a parametric study, the influences of such decision parameters as current density, fuel utilization factor, pressure ratio and air utilization factor on the performance of the system are studied. In addition, using a genetic algorithm, the system performance is optimized for maximum exergy efficiency or minimum SUCP (sum of the unit costs of products). The results show that, the exergy efficiency of the proposed system is 6.5% higher than that of the stand-alone SOFC. It is also observed that the fuel cell stack contributes most to the total irreversibility. The exergoeconomic factor, the capital cost rate and the exergy destruction cost rate for the overall system are observed to be 27.3%, 10.63 $/h and 28.3 $/h, respectively. It is observed that for each 6 $/GJ increase in the hydrogen unit cost, the optimum sum of the unit costs of products is increased by around 62.5 $/GJ.