Effects of volatile–char interactions on the volatilisation of alkali and alkaline earth metallic species during the pyrolysis of biomass

Abstract

An important feature of a fluidised-bed gasifier is the continuous contact between volatiles and char. The aim of this study is to experimentally investigate the effects of volatile–char interactions on the volatilisation of AAEM species during pyrolysis of two sugarcane industry wastes, bagasse and cane trash. A two-stage quartz fluidised-bed/fixed-bed reactor was used for this fundamental study. Our results indicate that the volatile–char interactions could lead to the additional volatilisation of alkali and alkaline earth metallic (AAEM) species, particularly if the volatile–char interactions have resulted in additional char weight losses. The monovalent Na and K behaved differently from the divalent Mg and Ca in biomass. Our results provide circumstantial but clear evidence that the AAEM species in biomass could behave distinctly differently from those in brown coal, largely due to the differences in the structure and composition between biomass and coal. The development of biomass gasification technologies must consider the special thermochemical characteristics of biomass. Furthermore, even the bagasse and cane trash grown in the same area behave drastically differently, at least partly due to the different microstructures of bagasse and cane trash.