Hydrodynamics of gas–solid fluidization in tapered beds

Abstract

Gas-solid fluidization has a wide range of industrial applications like catalytic reactions, combustion, gasification, etc. In a number of these applications, there is particle size reduction during the operation leading to severe entrainment and limitation of operating velocity. The various problems associated with particles of different sizes or changing particles sizes could be overcome by adopting tapered beds in fluidization operation.In the present investigation, the fluidization phenomenon in tapered beds has been critically assessed through experimental investigations using particles of different sizes and materials and wide range of apex angles of the vessels. The effect of particle size and apex angle on the fluidization behaviour is clearly brought out which has not been reported so far in literature. The importance of compressive force existing in tapered beds is highlighted.In addition, correlations for all hydrodynamic characteristics, viz. critical fluidization velocity, minimum velocity for full fluidization, maximum velocity for defluidization, peak pressure drop, fluctuation ratio, compressive force, and hysteresis have been developed some of which are proposed for the first time.La fluidisation gaz-solide revêt un vasteéventail d'applications industrielles comme les réactions catalytiques, la combustion, la gazéification, etc. Pour un certain nombre deces applications, il y a une réduction granulométrique durant l'activité menantà un entraînement età une limitation intenses de la vitesse de fonctionnement. Les divers problèmes liés aux particules de dimensions différentes ou aux dimensions de particules changeantes pourraientêtre surmontésen adoptant les lits coniques dans les activités de fluidisation. Dans le cadre de la présenté etude, lephénomène de fluidisation dans les lits coniques aétéévalué de façon critique au moyen devérifications expérimentales employant des particules de dimensions et de matières différentes et d'un vasteéventail d'angles de sommet de fluidiseurs. L'effet de la dimension des particules et del'angle des sommets sur le comportement de la fluidisation est nettement mis enévidence, ce quin'a pasété soulevéà venir jusqu'ici dans la documentation. L'importance de la force decompression qui existe dans les lits coniques est mise enévidence. De plus, les corrélations relativement a l'ensemble des caractéristiques hydrodynamiques, c.-à-d. la vitesse de fluidisation critique, la vitesse minimale de fluidisation complète, la vitesse maximale de défluidisation, la chute des pics de pression, le taux de fluctuation, la force de compression et l'hystérésis, ontétéélaborées, certaines d'entre ellesétant avancées pour la première fois.

Fluid bed film coating of fine ibuprofen particles

“…It is noted that the conical configuration is essential to fluidize these fine powders having such a wide size distributions to ensure that the larger particles can be fluidized without elutriating the finer particles. A complete description of the hydrodynamics of a conical fluidized bed is outside the scope of this study can be found in the literature [43,44] The bed was heated to 28 o C after which a spraying suspension was pushed with a peristaltic pump through a concentric nozzle at the top of the bed with an inner nozzle (300 m) at a spray rate of 1.00 -1.26 mL/min. Several spraying suspension formulations were considered in this study, which are listed in Table 2.…”