Fast and exergy efficient start-up of micro-solid oxide fuel cell systems by using the reformer or the post-combustor for start-up heating

The start-up process of a micro-solid oxide fuel cell system strongly influences its overall efficiency, especially for portable applications where a frequent switch-on and switch-off is required. We present herein a novel start-up process for such systems that exploits existing units, such as the post-combustor or the reformer, as a heat source to reach the operation temperature of the cell at 600 °C. Our experimental results show that the employment of platinum catalysts in the post-combustor or rhodium catalysts in the reformer for total oxidation of butane by air combined with an electrically heated wire led to a faster and more efficient start-up than conventional start-up methods using only electrical energy. By using the post-combustor as heat source, the start-up time could be reduced by 79% and the exergy cost by 86%. The latter includes the cost of the stand-alone fuel cell system to produce electrical energy for the joule heating of the wire (i.e. the system efficiency is accounted for). There are several advantages to use the reformer as heat source during start-up, such as prevention of coking of the fuel cell or improved heat transfer by internal heating of the other components. The start-up performance, however, was lower than that of the post-combustor: the start-up time could be reduced by 65% and the exergy cost by 68% compared to a conventional start-up.