Comparison and optimization of different fuel processing options for biogas-fed solid-oxide fuel cell plants

The biogas needs to be reformed before electro-chemical conversion in the solid-oxide fuel cell, which can be promoted efficiently with wise thermal management and reforming conditions. To ensure the system safety and catalysts durability, additional mineral-bearing water and carbon deposition should be avoided. This paper conducted a detailed biogas-SOFC CHP system analysis considering four layouts, featuring hot and cold recirculation of the anode off-gas, partial oxidation and complete internal reforming. The process optimization and sensitivity analysis are performed with the design variables including the recirculation ratio, and external reformer temperature. The anode supported SOFC operates at 800 °C and 0.4 A/cm2 current density. The results show that pre-reforming with hot recirculation and cold recirculation schemes achieve the highest system efficiency between 56% and 63%. The pre-reforming with hot recirculation scheme has a broader self-sufficient water range eliminating the carbon deposition risk at the recirculation ratio of 42–78% and reforming temperature of 400–650 °C. The no pre-reforming with hot recirculation scheme achieves maximum system efficiency of 58% due to the fuel dilution. Moreover, the partial oxidation with hot recirculation scheme maximum efficiency is limited to 58.9%, given that the partial oxidation reaction is less efficient than steam and dry reforming reactions. The proposed system layout could demonstrate the feasibility of biogas-SOFC with different reforming options especially on small scale with high efficiency and optimal thermal integration opportunities.