Investigation of steam reformation of natural gas for the very small scale production of hydrogen fuel for light duty vehicles in appliance-type refueling systems
Fuel cell propulsion systems fueled directly with hydrogen are being seriously considered as a means of powering future light-duty vehicles. One of the greatest impediments to the introduction of such vehicles is the perception that transitional infrastructure to supply hydrogen will be an insurmountable obstacle. This transitional infrastructure requirement might be met through the introduction of very small scale refueling appliances which provide compressed hydrogen for either one vehicle or a small fleet of vehicles. These small appliances must be efficient, non-polluting and low in cost.
The report investigates the feasibility of one type of refueling appliance based upon chemical reformation of natural gas in a steam reformation process. A natural gas steam reformer employing a palladium-alloy membrane hydrogen separator operated at high pressure and temperature (15+ bar and about 1200 K), should attain a net system efficiency between 60% and 80% (LHV).
Initial kinetic modeling of the reformer suggested that for mono-tubular reactor geometries the reactor was heat transfer limited. Thus, parallel micro-tubular or plate-frame geometries might yield the highest space velocity. Critical issues which must be resolved include required degree of hydrogen recycle for catalyst stability as well as the catalyst-specific kinetics.
Reforming of natural gas to hydrogen appears to be a viable option for very small scale hydrogen refueling appliances. A good deal of experimental and analytical design work is required to develop such systems, but they should meet the important requirements for this application.