Hydrogen, for the operation of a polymer electrolyte fuel cell, can be produced by means of autothermal reforming of liquid hydrocarbons. Experiments, especially with ATR 4, which produces a molar hydrogen stream equivalent to an electrical power in the fuel cell of 3 kW, showed that the process should be preferably run in the temperature range between 700 ° and 850 °. This ensures complete hydrocarbon conversion and avoids the formation of considerable amounts of methane and organic compounds in the product water. Experiments with commercial diesel showed promising results but insufficient long‐term stability. Experiments concerning the ignition of the catalytic reaction inside the reformer proved that within 60 s after the addition of water and hydrocarbons the reformer reached 95% of its maximum molar hydrogen flow. Measurements, with respect to reformer start‐up, showed that it takes approximately 7 min. to heat up the monolith to a temperature of 340 ° using an external heating device. Modelling is performed, aimed at the modification of the mixing chamber of ATR Type 5, which will help to amend the homogeneous blending of diesel fuel with air and water in the mixing chamber.
Mixture formation plays an important role in the diesel reforming process. It is important to maintain proper O2/C and H2O/C ratios to avoid hot spots and coking. Fuel must be completely evaporated before entering the reaction zone in order to prevent catalyst damage by coking. Computational fluid dynamics (CFD) is used to optimise the mixing process. Turbulent mixing, diesel spray injections and evaporation and simplified chemical reactions have been calculated. This revealed critical parts of the existing construction. However, experimental verification is necessary. To identify thermodynamic conditions for a possible carbon formation process, experiments with idealised model fuels as well as with real diesel fuel were carried out. Flow visualisation experiments serve for the verification of the CFD simulations. Quartz glass reactors as models of the reformers were operated under real mixing temperatures (400 °C) to observe the effect of the flow profile on fuel sprays. Experiments with coloured fuels were used to visualise the flow and concentration profiles in the mixing chamber. Results were compared with CFD models. Two patented reformers were designed as a result of the CFD optimisation. These were operated for 500 h and 1,000 h respectively with a commercially available diesel, showing very promising results.
This paper deals with general aspects and experimental results of autothermal reforming of Jet A-1 and Diesel fuel. With that respect, at first a process analysis based on the so called pinch-point methodology compares three different reforming routes, i.e. steam reforming, partial oxidation and autothermal reforming. The analysis is based on the application of a high temperature polymer electrolyte fuel cell (HT-PEFC). Then, specifications of different possible fuels for reforming are given. Their constraints with respect to their suitability for autothermal reforming are discussed. Finally, experiments with respect to the long-term stability of two reforming reactors revealed that it is decisive to posses a highly sophisticated educt and fuel evaporation technology in combination with a homogeneous mixing of the educts. Thereby, very promising long-term stabilities for autothermal reforming of Jet A-1 and Diesel fuel were achieved. E.g., there was 99 % conversion of Jet A-1 at the end of the long-term experiment after 2,000 h on stream.
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