Gasification of wood chip particles: Experimental and numerical study of char-H2O, char-CO2, and char-O2 reactions

In wood gasification, oxidation of charparticles by H2O, CO2 or O-2 plays a major role in the performance and efficiency of air gasifiers. These reactions are generally analyzed under carefully design and controlled laboratory conditions, using either micro-samples to focus on the reaction kinetics or large spherical particles, but rarely using the real shape encountered in industrial processes. The objective of this work was to conduct a complete parametric study on char gasification kinetics at particle scale in operating conditions like those of industrial applications. Experimental results from a macro-Thermo Gravimetric reactor are compared to those from a char particle model, which analyzes reactivity versus conversion through the surface function F(X). We first show that particle thickness is a representative dimension of a char particle with respect to its apparent kinetics. Second, considering the three reactions independently, we compared the influence of temperature (800-1050 degrees C) and reacting gas partial pressure (0.03-0.4 atm) and determined the intrinsic kinetic parameters and surface function F(X). Simulations provided profiles of temperature and gas concentrations within the particle, mainly revealing internal mass diffusion limitation. The experimental data base proposed and the model results improve our understanding of the gasification reaction and support the elaboration of process models. (C) 2011 Elsevier Ltd. All rights reserved.