Desulfurization of Jet Fuel for Fuel Cell Systems in Aircraft Applications

摘要

To prevent the catalysts in fuel cell systems from being poisoned by sulfur-containing substances the fuel to be used must be desulfurized to a maximum of 10 ppm of sulfur. In this way, damage to the catalysts in the fuel cell and the reformer can be avoided. Diesel fuel for road vehicles within the EU is already desulfurized at the refinery. However, jet fuel is permitted to have up to 3000 ppm of sulfur. Since the conventional hydrodesulfurization process employed in the refinery industry is not suitable for mobile fuel cell applications the present study aims at developing alternative processes and determining their technical feasibility. To this end, a large number of processes were assessed with respect to their application in fuel-cell-based auxiliary power units (APUs). The results revealed that a two-step process combining pervaporation and adsorption as well as hydrodesulfurization with pre-saturation is suitable for the on-board desulfurization of jet fuel. Therefore, a pervaporation process with subsequent adsorption was selected for detailed investigation. Six different membrane materials and ten sorbent materials were screened to choose the most suitable candidates. Further laboratory experiments were conducted to optimize the operating conditions and to collect data for a pilot plant design. Different jet fuel qualities with up to 1675 ppmw of sulfur can be desulfurized to a level of 10 ppmw. Laboratory tests with respect to hydrodesulfurization revealed that also syngas operation is possible without any performance loss in comparison to operation with hydrogen. Pure hydrogen is not available in a fuel cell system based on the reforming of jet fuel. The effects of reaction temperature, operating pressure and liquid hourly space velocity (LHSV) were investigated. Different jet fuel qualities with up to 3000 ppm of sulfur were desulfurized to a level of 15 to 22 ppm. Finally, the technical applicability of hydrodesulfurization with pre-saturation was demonstrated in a pilot plant with an electric power of 5 kW, going beyond the laboratory scale. In a 200-h experiment, a commercial jet fuel with 712 ppm of sulfur was desulfurized to a maximum sulfur content of 10 ppm. In addition, H2S separation by stripping with air turned out to be a suitable method for APU applications. The aim of developing suitable processes for the desulfurization of jet fuel in fuel cell APUs has thus been achieved.