In wood gasification, oxidation of char particles by H 2 O, CO 2 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 1C) 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.

Two-stage fixed bed gasification is one of the most promising technologies for low and medium energy production from biomass. In industrial processes, control and optimisation is often based on constructor know-how rather than on an understanding of the mechanisms involved. We present a new original tool, the Continuous Fixed Bed Reactor (CFiBR), which was specifically designed and built to enable a fine understanding of the limiting stage of a gasifier: the char bed gasification zone. The reactor, the instrumentation, the operating procedure and set-up tests are described in detail. The potential of the reactor is demonstrated through the characterisation of the gasification of a continuous wood char bed. Temperature profiles and gas concentrations along the 65 cm bed were established and showed that the most reactive zone was the first 10 cm of the char bed. Accurate energy and mass balances provided relevant information regarding the contributions of the main reactions involved in the fixed char bed gasification process. (Résumé d'auteur

In gasification processes, char-H 2 O and char-CO 2 are the main heterogenous reactions that are responsible for carbon conversion into H 2 and CO. These two reactions are generally looked at independently without considering interactions between them. The objective of this work was to compare kinetics of each reaction alone to kinetics of each reaction in a mixed atmosphere of H 2 O and CO 2. A char particle was gasified in a macro thermo gravimetry reactor at 900 ı C successively in H 2 O/N 2 , CO 2 /N 2 , and H 2 O/CO 2 /N 2 atmospheres.

RéSUMéL'utilisation du bois et du gaz naturel pour couvrir les besoins énergétiques dans les procédés de transformation des noix de cajou a un impact négatif sur l'environnement. Les coques issues du décorticage des noix sont imbibées de CNSL et nécessitent un traitement intermédiaire avant leur valorisation énergétique. Les petites unités de transformations au Burkina-Faso font face à cette problématique liée au déficit de réponse technique dans leur contexte. L'objectif de cette étude vise donc à caractériser les coques d'anacarde et proposer des voies de valorisation possibles. Après une caractérisa-tion initiale des coques, une étude thermochimique comparée a été réalisée dans des conditions de torréfaction (250°C) et de pyrolyse (450°C). Les résultats des tests réalisés montrent que le traitement thermochimique permet d'obtenir trois types de produits : solide (char), liquide (huile ou fraction condensable des gaz) et gazeux (gaz incondensable), dans des proportions et qualité relativement différentes selon la température opératoire. A 250°C (resp. 450°C), on produit 48,5% (resp. 17,0%) de char à 25,6 MJ/kg (resp. 27,2 MJ/kg) de PCI et 13,8% (resp. 47,5%) d'huile. Les PCI des huiles produites sont presque similaires et se situent au-dessus de 36 MJ/kg, avoisinant ainsi ceux des produits pétroliers. Sous réserve de l'analyse des fumées émises lors de la combustion de ces produits, le traitement thermochimique en conditions anoxiques semble donc être une option intéressante pour valoriser les coques d'anacarde.