(354d) A Micro-Structured 5 Kw Complete Fuel Processor for Iso-Octane as Hydrogen Supply System for Mobile Auxiliary Power Units

For mobile and portable applications of fuel cell technology there is a need for compact hydrogen supply systems . Fuel processors are a viable option for energy supply of fuel cells owing to the high energy density of liquid fuels such as alcohols and hydrocarbon mixtures. A fuel processor is composed of the reformer reactor itself and devices dedicated to remove the carbon monoxide out of the fuel, which is frequently performed by catalytic reactions such as water-gas shift and preferential oxidation . At IMM, a complete fuel processor was developed and put into operation, which was designed to supply a 5 kW fuel cell with purified reformate applying iso-octane as fuel. Iso-octane had been chosen as a model substance for gasoline. Micro-structured plates coated with noble-metal based catalysts were used to build the reactors either as monoliths or as cross-flow plate heat-exchangers. The fuel processor is composed of an autothermal reformer (ATR) for hydrogen production, a high temperature water-gas shift reactor, which has cross-flow cooling capabilities (HT-WGS), a low temperature water-gas shift reactor (LT-WGS) and a reactor for the preferential oxidation of carbon monoxide, which has cross-flow cooling capabilities (PrOx). The latter three reactors are switched in series after the ATR to perform the catalytic carbon monoxide clean-up. Additionally, a micro-structured heat-exchanger was incorporated between the ATR an the HT-WGS reactor to cool down the reformate from the exit temperature of the ATR to the desired feed temperature of the HT-WGS. The flow scheme of the fuel processor, which was installed on a bread-board level will be discussed. Prior to the incorporation of the reactors into the test-rig, they had been tested individually for their performance applying octane/steam/air feed for the ATR and simulated off-gas of the reactor upstream for each of the CO clean-up reactors. Fast on-line (Micro-)GC analysis was applied for chemical analysis of the reformate. Samples could be taken after each of the four reactors. The gas composition of the reformate changed from reactor to reactor during the operation of the fuel processor until a CO concentration of 120 ppm (d.b.) was achieved after the PrOx reactor, which would be low enough for a CO-tolerant low temperature PEM fuel cell system. A second stage PrOx reactor, which had been built, did reduce the CO-concentration of the reformate below 50 ppm, which had been demonstrated separately for the single reactor. This value is generally regarded as acceptable for reformate tolerant membranes of PEM fuel cells. About 150 Ndm³/min reformate were processed in the micro-structured reactors.