• Biogas
• Dry reforming
• SOFC modeling
• Solid oxide fuel cell
• Thermodynamic analysis

In the present work, a comparative study of internal and external dry reforming of biogas fuelling solid oxide fuel cells (SOFCs) was carried out to determine which one exhibits better performance. A systems models design of a 5kW biogas-SOFC plant was developed using a flowsheet simulator to perform a thermodynamic analysis of the systems. Both models consist of a solid oxide fuel cell, a combustor, heat exchangers, blowers, a water pump, sources and sinks. Besides, a reformer is integrated into the external reforming system. Waste heat from SOFCs was employed to biogas and air pre-heating and to produce hot water for heating digester. To evaluate the influence of the key operating parameters on the systems performance, a sensitivity analysis was conducted under different operating conditions. Fuel utilization, operating voltage, recirculation ratio and biogas methane content were the chosen key parameter in this study. For the external reforming, the energy calculations for the baseline case shows an auxiliaries consumption three times the one of the internal reforming system, due to a higher airflow rate demand for cooling the SOFC. Hence, the internal reforming model showed a better system electrical efficiency than that of the external reforming model. The exergy assessment revealed that the major exergy destructions for both models can be imputed to SOFC, combustor and the water heat exchanger. The increase in operating voltage improves the systems electrical efficiency and thus the system exergy efficiency but requires a greater cell active area. Increasing the fuel utilization and the recirculation ratio leads to a rise in the system electrical efficiency but the overall system energy efficiency decreased due to a drop in the thermal efficiency. Nevertheless, the system exergy efficiency augments but also the required cell area. A reduction of the cell area is achieved using biogas with high methane concentration with a minimal system efficiency drop.