Review of gasification fundamentals and new findings: Reactors, feedstock, and kinetic studies

The purpose of this work is to comprehensively review recent findings on gasification kinetics related to the reaction mechanism, the effects of the experimental procedure on the overall reaction, and methods to evaluate kinetic models. Understanding the recent findings in gasification requires the presentation of selected publications that cover several potentially ambiguous concepts. Firstly, conventional reactor definitions are not sufficient given that three reactions (combustion, pyrolysis and gasification) occur in an industrial gasifier. Secondly, variables affecting char reactivity during gasification show that the char surface area is the most complex variable to analyze. Also, single-step kinetic models provide better descriptions of the reaction mechanism assuming kinetic control of the overall reaction. The new findings are related to the gasification reaction mechanism and the interpretation of kinetic results: (a) the maximum gasification rate observed is a consequence of the gas concentration development upon changing the inert gas for the gasifying agent, and not due to changes in the char surface during gasification, as proposed by Bhatia and Perlmutter in 1980; (b) increasing the time of holding the char at the reaction temperature in an inert gas decreases the gasification rate; (c) char micropore surface area and alkali content are the two most important variables affecting the gasification rate; and, (d) laboratory studies may not represent the real gasification mechanism under kinetically controlled conditions due to the presence of mass transfer limitations from interparticle diffusion. Therefore, the acceptance of intrinsic kinetics reported in the literature should be revalidated. (C) 2016 Elsevier Ltd. All rights reserved.