Fuel Processing in Ceramic Microchannel Reactors for SOFC Applications

摘要

Effective operation of practical solid-oxide fuel cell (SOFC) systems relies upon heat exchangers and chemical reactors. System efficiency can be improved and cost reduced by combining unit processes into single components. This work describes a ceramic microchannel reactor that achieves process intensification by combining heat-exchanger and catalytic-reactor functions to provide high-quality syngas to the SOFC stack. Microchannel heat exchangers and reactors can deliver very high performance in small packages. Such heat exchangers are typically fabricated from stainless-steel metal sheet using diffusion-bonding processes. Ceramic microchannel reactors offer some significant advantages over their metallic counterparts, including very-high-temperature operation, corrosion resistance in harsh chemical environments, low cost of materials and manufacture, and compatibility with ceramic-supported catalysts. In this work, reactor design is based on the results of three-dimensional computation fluid dynamics (CFD) simulations using ANSYS/FLUENT. Models include the conjugate heat transfer between fluid- and solid-phase materials, and are used to create a design that achieves high reactor performance while meeting the unique requirements of the reactor- fabrication process. This CFD model has been coupled with CHEMKIN, a powerful chemical- kinetics modelling tool, to include simulation of chemically reacting flow. The current reactor design utilizes four layers of microchannels. Inert heat exchange in two of the layers provides thermal energy to drive methane steam-reforming reactions on the other two catalyst-coated layers. The reactor body is fabricated by CoorsTek, Inc. (Golden, CO, USA) using 94% alumina and high-volume-manufacturing methods. High-temperature co- sintering of the four layers results in a single hermetically sealed polycrystalline ceramic body. Catalytic activity is enabled by washcoating a rhodium catalyst over an alumina- ceria oxide support structure deposited within the reactor. Heat-exchanger effectiveness of up to 88% has been demonstrated. Reactive heat- exchanger testing has been completed on steam reforming of methane with 90% methane conversion and high selectivity to syngas. Experimental results are validated and interpreted using the ANSYS/FLUENT model.