Steam gasification of wood char: from isolated particle to continuous fixed bed

From the last decades, the continuous increase of the world energy demand and the problem of the increase in the greenhouse effect made the renewable energies more attractive. In this context, the biomass presents an interesting potential, and the emergence of efficient technologies, such as gasification, encourages the development of this route. An experimental study on the steam gasification of an isolated wood char particle was performed on a 'macro- TG' apparatus. The evolution of the particle mass during gasification under precisely controlled operating conditions was recorded. Typically, at a temperature of 930 deg. C and under a steam partial pressure of 0,2 atm, the time for complete gasification of a 7 mm diameter wood char particle was 32 min. The parametric study enabled to identify the temperature and the heating rate during pyrolysis as strongly influent parameters on the gasification rate. Moreover, the investigation of a good indicator for the char reactive surface was carried out. A numerical model of the gasification of a wood char particle was developed. The confrontation with the experimental results from the parametric study enabled to determine the kinetics constants of the steam gasification reaction. The results showed that in industrial conditions, the gasification process of a charcoal particle follows neither a shrinking core, nor a homogeneous model. The model enabled to better understand the coupling between reaction kinetics and heat/mass transfers inside the particle. Finally, an experimental reactor for the gasification of a fixed bed of char particles was especially designed and built; it precisely replicates the operating conditions of an industrial reactor. The first tests in steady state exhibited very satisfactory mass balance closures. (author)