Design and analysis of distributed feed solid oxide fuel cell stacks

Conventional solid oxide fuel cell (SOFC) stack designs suffer from severe spatial non-uniformity in both temperature and current density. Such variations are known to create damaging thermal stresses within the stack and thus impact overall lifespan. These variations are even more extreme in the case of internal reforming SOFCs as a result of allowing the exothermic electrochemical reaction and the endothermic reforming reaction to take place side-by-side in the stack. The rate of reforming is much faster than the electrochemical reaction rate, which leads the reforming reaction to reach completion first causing a cold spot and a sudden build-up of hydrogen. Subsequently, a dramatic increase of the electrochemical reaction rate causes the formation of a hot spot. Moreover, this mismatch in reactions rate causes an incomplete integration of the reforming and electrochemical processes.; In this work, a novel stack design aimed at reducing spatial variations at the source and significantly improving heat and mass integration is proposed for both external and internal reforming SOFCs. The proposed design consists of a mechanism of distributed fuel feed in which the heat generation profile and species concentrations can be influenced directly. Simulation results are presented to illustrate the potential benefits of the proposed scheme. Furthermore, overall system efficiency improvements are shown for the internal reforming stack as a result of reducing the amount of steam fed to the stack.; A two-dimensional stack design for fuel delivery and distribution is presented, which addresses the delivery of specific amounts of fuel to the specified locations along stack length. Moreover, the stack design includes static mixers that ensure proper mixing to meet the specifications set by the one dimensional analyses. Finally, a design algorithm that describes the general steps necessary to design a distributed feed SOFC stack is summarized.