Effects of volatile–char interactions on the volatilisation of alkali and alkaline earth metallic species during the pyrolysis of biomass Daniel M. Keown a , Jun-ichiro Hayashi b , Chun-Zhu Li a, * a Department of Chemical Engineering, P.O. Box 36, Monash University, Victoria 3800, Australia b Center for Advanced Research of Energy Conversion Materials, Hokkaido University, N13-W8, Kita-ku, Sappopro 060 8628, Japan Received 26 February 2007; received in revised form 31 May 2007; accepted 31 May 2007 Available online 16 July 2007 Abstract An important feature of a fluidised-bed gasifier is the continuous contact between volatiles and char. The aim of this study is to exper- imentally 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 character- istics 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. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Biomass; Pyrolysis; Volatile–char interactions; Volatilisation of alkali 1. Introduction The use of biomass through gasification represents a potentially attractive and efficient alternative to fossil fuel combustion/gasification. If coupled with CO 2 sequestra- tion, gasification/reforming-based power generation using biomass could lead to a net reduction of CO 2 in the atmo- sphere. However, most of the biomass gasification pro- cesses proposed or demonstrated so far are largely based on experiences from coal gasification. The special thermo- chemical properties of biomass are often not fully consid- ered in the development of these gasification processes. Compared with most bituminous coals, one of the important features of biomass materials is the presence of significant amounts of alkali and alkaline earth metallic (AAEM) species (mainly K, Na, Mg and Ca) in biomass. These AAEM species tend to volatilise during pyrolysis (and gasification/combustion) and are an important con- sideration in all aspects of biomass thermochemical conver- sion such as gasification. While the volatilisation of AAEM species may create slagging and/or fouling problems for the operation of gas turbine blades in the gasification-based power generation cycles [1], the AAEM species retained in char during pyrolysis are important catalysts for the gas- ification/combustion of char [2,3], helping to reduce the gasification temperature and thus increasing the overall gasification process efficiency and process economy. The volatilised AAEM species may also act as catalysts for the steam reforming of volatiles in the gas phase [4]. Therefore, the understanding of the behaviour of AAEM species during pyrolysis (and gasification) is important for the development of advanced biomass gasification technologies. 0016-2361/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2007.05.056 * Corresponding author. Fax: +61 3 9905 5686. E-mail address: chun-zhu.li@eng.monash.edu.au (C.-Z. Li). www.fuelfirst.com Available online at www.sciencedirect.com Fuel 87 (2008) 1187–1194