Demonstration of Energy Efficient Steam Reforming in Microchannels for Automotive Fuel Processing

A compact, energy-efficient microchannel steam reforming system has been demonstrated. The overall volume of the reactor is 4.9 liters while that of the supporting network of heat exchangers is 1.7 liters1. The reactor contains alternating reaction and combustion gas channels, arranged in crossflow, to provide heat to the reaction. Use of a microchannel configuration in the steam reforming reactor produces rapid heat and mass transport which enables fast kinetics for the highly endothermic reaction. The microchannel architecture also enables very compact and highly effective heat exchangers to be constructed. A network of microchannel heat exchangers allows recovery of heat in the reformate product and combustion exhaust streams for use in vaporizing water and fuel, preheating reactants to reactor temperature and preheating combustion air. As a result of the heat exchange network, the system exhaust temperatures are typically ∼50°C for the combustion gas and ∼130°C for the reformate product while the reactor is operated at 750°C. While reforming isooctane at a rate sufficient to supply a 13.7 kWe fuel cell, the system achieved 98.6% conversion with an estimated overall system efficiency after integration with WGS and PEM fuel cell of 44% (electrical output / LHV fuel). The efficiency estimate assumes integration with a WGS reactor (90% conversion CO to CO2 with 100% selectivity) and a PEM fuel cell (64% power conversion effectiveness with 85% H2 utilization for an overall 54% efficiency) and does not include parasitic losses for compression of combustion air.