Thermodynamic and exergoeconomic analysis of biogas fed solid oxide fuel cell power plants emphasizing on anode and cathode recycling: A comparative study

•Four biogas-fed solid oxide fuel cell power plants are proposed.•Performance of systems is compared with each other economically.•Efficiency of biogas fed fuel cell with anode–cathode recycling is the highest.•For current density of 6000A/m2 the optimum anode recycle ratio is around 0.25.•Unit product cost of biogas fed fuel cell with anode–cathode recycling is 19.07$/GJ. Four different configurations of natural gas and biogas fed solid oxide fuel cell are proposed and analyzed thermoeconomically, focusing on the influence of anode and/or cathode gas recycling. It is observed that the net output power is maximized at an optimum current density the value of which is lowered as the methane concentration in the biogas is decreased. Results indicate that when the current density is low, there is an optimum anode recycling ratio at which the thermal efficiency is maximized. In addition, an increase in the anode recycling ratio increases the unit product cost of the system while an increase in the cathode recycling ratio has a revers effect. For the same working conditions, the solid oxide fuel cell with anode and cathode recycling is superior to the other configurations and its thermal efficiency is calculated as 46.09% being 6.81% higher than that of the simple solid oxide fuel cell fed by natural gas. The unit product cost of the solid oxide fuel cell-anode and cathode recycling system is calculated as 19.07$/GJ which is about 35% lower than the corresponding value for the simple natural gas fed solid oxide fuel cell system.