Influence of off gas recirculation on the intermediate temperature SOFC with POX reformer

Abstract

Solid oxide fuel cell(SOFC) is a clean and efficient energy utilization technology. Partial oxidation reforming(POX) can be used to simplify SOFC system structure, but its lower hydrogen production rate deteriorates system performance. A wise method may be combining anode off gas recirculation(AOGR) and cathode off gas recirculation(COGR) with POX. Thus, their influence on the coupled system of intermediate temperature SOFC and POX is researched in detail in this paper. Results show that the reforming process gradually changes from exothermic to endothermic as AOGR rate increases. Meanwhile, its oxygen demand declines sharply and the process can even be self-sustained without external air input at the AOGR rate of 0.5 and 0.6. The application of AOGR can improve electrical efficiency up to 51%, but at the expense of thermal efficiency. Excessive AOGR rates will result in decreased cell voltage and insufficient energy supply to the after-burner, so it should be restricted within a reasonable range and the best recommended value is 0.5. The application of COGR has little effect on fuel line parameters, so it cause little deterioration in electrical efficiency while improving thermal efficiency. Besides, cell voltage is also insensitive to it. The combination of AOGR and COGR can obtain better fuel economy and larger cogeneration scale simultaneously at the cost of a tiny electrical output power, while an optimal balance between three efficiencies is also achieved.