Analysis of reaction mechanism and kinetics of biomass in pyrolysis and gasification

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Biomass gasification is a promising technology because of the high thermal efficiency. However, a large amount of condensable organic compounds (tar) which causes blockages and corrosion of pipes are evolved in biomass gasification.In this study, the inhibition of the gasification rate of biomass char by H_2 and tar was investigated. At first, the reaction rate of char in steam gasification was measured using a thermobalance reactor by varying partial pressure of H_2 (P_<H2>=0, 3, 10, 25kPa). The rate of steam gasification was decelerated by the presence of H_2 and the inhibition was significant when the partial pressure of H_2 was high (P_<H2>=25kPa). It was found that reverse oxygen exchange occurred at first period and dissociative adsorption of H_2 on char occurred at second period. The effect of levoglucosan, which is major component of pyrolysis product from cellulose, on the reaction rate of char was also measured with a newly developed drop-tube/fixed bed thermobalance reactor. It was found that not only H_2 but also other hydrocarbons evolved by pyrolysis of levoglucosan substantially inhibit char gasification when the feed rate of levoglucosan was high (250mg/min).In addition, the effects of alkali and alkaline earth metals (AAEM), which can act as an excellent catalyst for the gasification and combustion reactions, on the interactions between the three major components of biomass (cellulose, xylan and lignin) were investigated. It is found that AAEM decreased the generation of water-soluble tar derived from cellulose. AAEM do not have significant influence on the interaction between cellulose and xylan.