Numerical Modelling of Wood Pyrolysis

Abstract: In this project, a numerical model describing the reaction mechanism and the mass and energy transport in wood pyrolysis is studied. The applicability of the model in predicting actual biomass pyrolysis assessed by comparing the model to TGA experimental measurements. The comparison to experiments is done in relation to the mass loss characteristics of chips of varying sizes. The mass loss is of interest as it is a variable necessary in the coupling of reactor and particle models. Three reaction models were simulated and results compared to experimental data, namely, the reaction model developed by Park et al. [Combustion and Flame 157 (2010) 481-494], a simple multicomponent parallel reaction model, and a competitive reaction model. The model of Park et al. did not fit with the experimental data as it underestimates the char yield. The parallel reaction model, which is based on hemicellulose and cellulose decomposition to char and volatiles, also did not agree with the experiments even when fitting the parameters to the data. The downward trend of char yield with increasing temperature suggests there exists competition between the volatiles and char in wood pyrolysis. The proposed competitive reaction model which consists of a hemicellulose reaction to volatiles and a cellulose reaction to volatiles and char is in good agreement with the experimental data. The mass loss characteristics in the experimental temperature range is fairly predicted within reasonable accuracy.