Miniature Fuel Processors for Portable Fuel Cell Power Supplies
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Miniature Fuel Processors for Portable Fuel Cell Power Supplies Jamie Holladay, Evan Jones, Daniel R. Palo, Max Phelps, Ya-Huei Chin, Robert Dagle, Jianli Hu, Yong Wang, and Ed Baker Battelle Pacific Northwest Division, PO Box 999, K8-93, Richland WA 99352, U.S.A. ABSTRACT Miniature and microscale fuel processors that incorporate novel catalysts and microtechnology-based designs are discussed. The novel catalyst allows for methanol reforming at high gas hourly space velocities of 50,000 hr-1 or higher while maintaining a carbon monoxide levels at 1% or less. The microtechnology-based designs extremely compact and lightweight devices. The miniature fuel processors, with a volume less than 25 cm3, a mass less than 200 grams, and thermal efficiencies of up to 83%, nominally provide 25 to 50 watts equivalent of hydrogen, which is ample for the portable power supplies described here. With reasonable assumptions on fuel cell efficiencies, anode gas and water management, parasitic power loss, the energy density was estimated at 1700 Whr/kg. These processors have been demonstrated with a CO cleanup method and a fuel cell stack. The microscale fuel processors, with a volume of less than 0.25 cm3 and a mass of less than 1 gram, are designed to provide up to 0.3 watt equivalent of power with efficiencies over 20%. INTRODUCTION Portable electronic technologies such as PDA’s, notebook computers, and microelectrochemical systems (MEMS) have fueled a need for new, high-energy, small-volume power supplies for both military and commercial markets. Wireless electronic devices are currently limited to battery technologies, which, despite recent advances, are insufficient to provide the long-term power these new microelectronic systems require. A solution to this problem would be hybrid systems composed of a microscale fuel processor, proton exchange membrane fuel cells, and secondary batteries. Hybrid systems combine high-energy liquid hydrocarbon fuels (e.g., up to 12.4 kWhr/kg for diesel) with clean fuel cell power, and battery convenience. This paper summarizes work on hydrocarbon selection, fuel reforming catalyst development, and the progress of two fuel processing systems (25 to 100 watts for soldier and personal portable power and 0.025 to 0.500 watts for sub-watt power ranges). In addition to the fuel processor, these systems integrate two fuel vaporizers (one for the fuel processor and one for the catalytic fuel combustor); a catalytic combustor; and two heat exchangers, which preheat reactants and recuperate heat from product streams. This paper reports progress in these projects that has been made since the previous publications [1,2].
FUEL REFORMING A wide range of hydrocarbon fuels such as methanol, ethanol, propane, butane, gasoline, and diesel are being reformed into hydrogen-rich streams for fuel cells. Diesel has the highest raw energy density; however, the raw energy density of the fuel does not necessarily translate to
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the ultimate energy density of the device. For example, even though diesel ha
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