Thermodynamic Evaluation Of Solid Oxide Fuel Cells Converting Biogas Into Hydrogen And Electricity

Although biogas has many qualities as a source of renewable and distributed energy, most full-scale applications are large facilities due to the lack of efficient small-scale systems. In this context, solid oxide fuel cells (SOFC) have been promoted as an alternative to convert biogas into electricity and heat with high efficiency. However, few studies have considered the use of the anode exhaust gas to co-produce green hydrogen together with electricity and heat, which could increase the performance and profitability of these systems. Thus, since there is a lack of studies focusing on these systems, this research proposes a new approach to model SOFC with direct internal reforming to produce power, hydrogen and heat. The results indicate that the proposed system is capable of reaching exergy efficiencies between 57% and 69% depending on the methane content of biogas. Hydrogen separation reduces the amount of fuel that has to be burned, which leads to less destruction of exergy in multiple processes (e.g., mixers, burners and heat exchangers). However, this design change also diminishes the amount of heat delivered by the system (-82% compared with conventional cogeneration), which may negatively affect the energy integration with anaerobic digestion. In addition, major performance improvements can be achieved by optimizing the hydrogen recovery of the pressure swing adsorption and the SOFC operating temperature.