The present work deals with a study coupling experiments and modeling of charcoal gasification by steam at large particle scale. A reliable set of experiments was first established using a specially developed "macro-TG" apparatus where a particle was suspended and continuously weighed during its gasification. The main control parameters of a fixed-bed process were modified separately: steam gasification of beech charcoal spheres of different diameters (10 to 30 mm) was studied at different temperatures (830 to 1030 • C), different steam partial pressures (0.1 to 0.4 atm H 2 O), and different gas velocities around the particle (0.09 to 0.30 m/s). Simulations with the particle model were performed for each case. Confrontations with experimental data indicate that the model predictions are both qualitatively and quantitatively satisfactory, with an accuracy of 7%, until 60% of conversion, despite the fact that the phenomena of reactive surface evolution and particle fracturing are not well understood. Anisotropy and peripheral fragmentation make the end of the process difficult to simulate. Finally, an analysis of the thermochemical situation is proposed: it is demonstrated that the usual homogeneous or shrinking core particle models are not satisfying and that only the assumption of thermal equilibrium between the particle and the surrounding gas is valid for a model at bed scale.

In the field of biomass torrefaction, lots of product properties have been widely investigated at the lab scale but some uncertainties remain about the gains in terms of grindability and hygroscopicity of torrefied products. In this study, beech wood chips (with an initial moisture content of 10-12 %) have been torrefied in a pilot-scale rotary kiln. The torrefaction severity was controlled by adjusting the temperature, the treatment duration and the solid holdup in the kiln. Mass losses ranging between 1.7 % and 25 % have been obtained. Properties of torrefied wood chips were then analyzed in terms of composition, heat content, hygroscopicity and grinding energy requirement. Dynamic vapor sorption measurements show that a minimum of hygroscopicity is reached for a mass loss (ML) between 1.7 and 7.8 %. The moisture uptakes for mass losses above this optimum remain stable at values twice lower than that of raw biomass. Finally, a new method is proposed to estimate the grindability of wood chips. This method takes into account the grinding energy consumption and the particle size distribution of ground samples. A reduction by a factor of 6.3 of the apparent specific surface grinding energy is observed between a moisture content of 41 % and the dryness. This energy measurement is in turn reduced by a further factor of 8.1 after torrefaction with a 25 % mass loss.

In this paper, we present new thermogravimetic analysis on cardboard material performed at different heating rates. Several reaction schemes are proposed to serve as an interpretation basis. Considering the experiments independently, it is found that the best fitted parameters are highly sensitive upon the heating rate. In order to avoid complicated and hazardous interpolation schemes, a simplest interpretation is proposed that does not involve a heating rate dependency on the kinetic parameters.