Quantification of the Improvement of Performance of Solid Oxide Fuel Cell Using Chiller-Based Fuel Recirculation

Solid oxide fuel cells operate at high temperature, typically in the range 650-850 degrees C, utilizing between 50% and 75% of fuel. The remaining fuel can be either burned in a post-combustor located downstream of the solid oxide fuel cells (SOFC) stack or partially recycled. Several of the SOFC-based power systems include recirculation which is used to supply the steam to the fuel processing unit based on steam reforming. In such a system, the recycled stream makes it possible to eliminate the supply of water from the external source. In the same time, recirculation aids in increasing the overall fuel utilization in the power system. As a result the efficiency increases by 5-12% points. The electrochemical reaction in SOFC generates a substantial amount of water by combining the hydrogen molecules with oxygen extracted from the air entering the cathodic compartments. The recycled stream contains water vapor which is circulated in the recycled loop. In the current analysis, the system for recirculation of the anodic off-gas with complete removal of water was proposed and studied. Performance of a planar cell operated with different rates of recycling was studied using the experimental setup with chiller-based recirculation. Quantification of the improvement of the efficiency was based on the analysis of the increase of voltage of cell operated at a given current density. The experimental study demonstrated that the performance of a stand-alone SOFC can be increased by 18-31%. Additionally, the numerical model was proposed to determine the performance in other operating conditions.