Carbon deposition and alkali poisoning at each point of the reforming catalysts in DIR-MCFC

Abstract

The extent of local carbon deposition and alkali poisoning of the reforming catalysts in a unit cell (5 × 5 cm) of a direct internal reforming molten carbonate fuel cell was examined. The catalysts in the catalyst bed were sampled from 25 points individually after the unit cell had been operated for both 24 and 100 h, and the amount of carbon, alkali poisoning were then analyzed. There was little difference in the amount of carbon deposition and alkali poisoning with respect to the direction of the cathode gas. They were only dependent on the direction of the anode gas. After 24 h, the amount of carbon deposited on the catalysts loaded in the front region, and the extent of alkali poisoning in the catalysts loaded in the rear region were relatively higher than those of any other regions. After 100 h, the amount of carbon deposition in the catalysts loaded in the front region was still the highest and the amount of alkali poisoning increased rapidly. Meanwhile, relatively low carbon deposition rate and the small increase in alkali poisoning were observed in the catalysts loaded in the rear region. Therefore, the rate of alkali poisoning of the catalyst in the rear region was much slower than those in any other region. These results for catalyst poisoning were explained by a simulation of the unit cell, which was performed to determine the temperature profiles and the extent of the reaction at each point of the unit cell. The simulation showed that the catalysts in the front region treated 90 mol of the initial methane flow, and the temperature was the lowest at this region. Therefore, the catalysts in this region had the highest level of carbon deposition and the rate of alkali poisoning was faster than that of the catalysts in the other regions. This simulation also explained the reasons for the relatively low level of carbon deposition in the rear region, as well as the relatively high rate of alkali poisoning from the start and the low rate of alkali poisoning in the rear region.