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Any vessel in which solids are transported upward by a gas stream and then recycled to the bottom may be classified as a Circulating Fluidized Bed (CFB). We describe possible CFB operating regimes in the context of this broad classification and highlight commercial processes that employ CFB technology and potential applications. Process design and development require a fundamental understanding of gas and solids hydrodynamicssolids hold-up, mixing and velocity distribution. We discuss techniques used to measure solids mass flux, which is a critical parameter for both design and control. In the last decade, significant research efforts have been devoted to new experimental techniques to measure both gas and solids spatial and temporal distribution. We list these techniques and detail the different modelling approaches that have emerged based on the new data. Characterization of the data is still incomplete and the available models require further refinement to reliably predict the effect of scale, operating conditions and particle characteristics on hydrodynamics. N'importe quel contenant dans lequel des particules sont emportks dans la direction ascendante par un courant gazeux puis recyclkes par le bas peut Stre class6 c o m e un Lit Fluidisk Circulant (LFC). Nous dkrivons les rkgimes possibles des op6rations dans ces LFC en tenant compte de cette dkfinition ktendue et les prockddcs industriels existants et potentiels qui utilisent cette technologie des LFC. La conception et le dkveloppement des proctklks exigent une comprkhension fondamentale des hydrodynamics du gaz et des particulesrktention de solides, degrk de mklange et distribution des vitesses. Nous discutons les diffkrentes techniques utiliskes pour mesurer le taux de circulation de solide qui est un paramttre critique pour aussi bien le design que le contr6le. Durant le dernitres mks, un effort significatif'de recherche a kt6 consenti au dkveloppement de nouvelles techniques exp6rimentales pour mesurer les distributions temporelle et spatiale des diffkrentes caractkristiques du gaz et du solide. Nous reportons ces techniques et nous dktaillons le diffkrentes approches de modklisation qui ont kt6 introduites en se basant sur ces nouvelles donnks.La caradrisation de ces donnks est encore incompltte et les modkles existants doivent Stre encore raflids afin de pddire ad6quatement les effets d'khelle, des conditions @ratoires et des mactkristiques des particules sur I'hydrodynamique.

The transformation of biomass into fuel and chemicals is becoming increasingly popular as a way to mitigate global warming and diversify energy sources. Biomass is a renewable, carbon-neutral resource, and fuels derived from biomass usually burn more cleanly than fossil fuels. It has been estimated that biomass could provide about 25% of global energy requirements. In addition, biomass can also be a source of valuable chemicals, pharmaceuticals and food additives. Several kinds of biomass can be converted to fuel and chemicals. Examples are wood and wood waste, agricultural crops, agricultural waste, litter from animal feedlots, waste from food processing operations and sludge from water treatment plants.Various processes can be used to convert biomass to energy. The biomass can be burned, transformed into a fuel gas through partial combustion, into a biogas through fermentation, into bioalcohol through biochemical processes, into biodiesel, into a bio-oil or into a syngas from which chemicals and fuels can be synthesized. Wood combustion, bioethanol production from either sugarcane or corn, and biodiesel production from oilseeds are currently the most economically significant processes but still need significant improvements. A detailed review of the many processes that can convert biomass into fuels and chemicals shows that no individual process is without drawbacks. As a result, it is recommended that a biorefinery is the best solution to combine and integrate various processes to maximize economic and environmental benefits, while minimizing waste and pollution.