Cold start simulations of a gasoline based fuel processor for mobile fuel cell applications

Abstract

The cold start behaviour of the gas processing unit is one crucial issue for the use of gasoline based fuel reformers for mobile fuel cell systems. In this contribution different cold start strategies for a mobile fuel reformer based on gasoline are presented and discussed. The simulation studies are based on 1-d, dynamic multiphase models for both an autothermal gasoline reformer (ATR) and a thermally integrated reforming unit consisting of an ATR, a heat exchanger and a high-temperature-shift-reactor (HTS). Setup and geometric parameters for both models correspond to pilot stage systems considered by DaimlerChrysler. Results on the reactive heat-up of the ATR by partial and total oxidation of gasoline show the impact of the air/fuel-ratio and the thermal load on the cold start duration. The use of the reformat during the rapid start-up of the ATR is mainly limited by the availability of steam for autothermal operation. Due to the high thermal capacities of the system, the whole reforming unit requires much longer time for the cold start. Especially the slow convective heat-up of the HTS restricts the conversion of CO and the subsequent use of the reformat in the fuel cell. Several options for the acceleration of the cold start were investigated. Both a simple λ-control strategy and the reactive heat-up of the HTS by (partial) oxidation of the reformat with injected air reduce the cold start time significantly. With these measures a hydrogen-rich reformat with acceptable CO-concentration is available within two minutes. Moreover, the cold start time can be further reduced, if the HTS is heated up electrically to their ignition temperature at the beginning of the cold start. Thereby the CO-conversion in the HTS already starts in the first minute and, depending on the availability of steam for the feed stream, a cold start of the reforming unit below one minute seems to be possible.