2017 Volume 43 Issue 1 Pages 50-56
In our previous studies, CO2 gasification characteristics of char produced by rapid pyrolysis were evaluated for various biomass samples of softwoods and hardwoods, which were pyrolyzed at 1000°C in a small-scale fluidized bed with porous alumina as bed material under N2 flow (regular gasification). The characteristic curve of conversion rate dX/dt versus conversion obtained from the gas evolution rate revealed a sharp peak the gasification at conversion of around X=0.05 in the case of softwoods, which was suggested to be affected by the bed material. In the present study, the effects of the type of bed material on the gasification characteristics were examined using bed materials of alumina, silica sand and pulverized brick for the gasification of cypress. It was found that the characteristic peak in gasification was observed only with alumina as bed materials. To elucidate the cause of this phenomenon, the char and bed materials were together cooled to room temperature under a nitrogen flow, separated by sieving, and then independently gasified. The char produced in the alumina bed was found to have a low conversion rate, while the alumina bed material was gasified more rapidly and showed the characteristic peak in gasification. While the ratios of hydrogen production to carbon monoxide production in the gasification of separated char and bed materials were always lower than those of regular gasification, the decrease in the case of char gasification was much greater than in the case of bed materials. The decrease in the ratio in the gasification of char was the biggest for alumina followed by brick, while the decrease in the gasification of bed materials was the smallest for alumina and the largest for silica sand. The present results indicate that the reactive carbonaceous material with high hydrogen content was easily moved to alumina and hold, which showed rapid gasification at the first stage of gasification.
