Wood-char gasification: experiments and analysis on single particles and packed beds

Abstract

This paper discusses the results from experiments and analysis on the conversion of wood char with reactants of composition typical of gasification. Experimental studies on the steam-char reaction with particles of 4-15 mm diameter (d_o) have led to the evaluation of conversion time variation at different ambient temperatures and steam mass fractions. These are interpreted using a mathematical model validated earlier for carbon dioxide and oxygen/nitrogen mixtures but presently including the C-H₂O heterogeneous chemistry and changes in average gas-phase thermal conductivity. A comparative study on the conversion process for different reactants indicates d_o² dependence for the air/oxygen environment, whereas d_o¹ and d_o^1.2-1.3 indicate dependence in the CO₂ and H₂O atmospheres, respectively. The variation of temperature and reactant mass fractions through the reacting sphere are used to argue the role of diffusion and reaction in the conversion process. Based on the foregoing, the process in a characoal reactor gasifier operation is modeled. The gasification process is modeled with char reacting with different reactants as of a typical gasifier. The propagation of reaction front into the packed char bed against the airstream is modeled. The results are compared with experimental data on a model quartz charcoal reactor based gasifier with regard to propagation of the reaction front through the packed bed along with the experiments of Groeneveld's characoal gasifier.