(543d) Experimental Study On Fluidization Behavior of Geldart B and D Particle Systems in Deep Tapered Beds

For large Geldart B and Geldart D particles, the working height attainable in cylindrical bubbling fluidized beds is typically limited by growth of bubbles.  Bubbles coalesce rapidly in these systems, and as a consequence, violent motion associated with bubble breakage at the freeboard can lead to uneven fluctuating forces on the vessel. For Geldart D particles, spouted beds are typically employed to avoid large bubbles, but in a reacting system, use of a spouted bed does not allow uniform solids contact with the reagent gases.  While baffles can be used to reduce the size of bubbles in Geldart B systems, for the intended application, erosive wear could not be tolerated for the scale-up opportunity.  Likewise, reductions in average particle size or superficial velocity or decreases in bed height to accommodate larger bed cross-section were all undesirable for the intended operating targets.  For the latter, the available external surface area for heating from the wall is also compromised when compared with the heat duty needed for scale-up.

An exploratory investigation of bubbling fluidization with tapered geometries was conducted for Geldart D and large Geldart B silicon particles.  Two separate, tapered fluidized bed systems, one 8-in. × 18-in. diameter and a second 17.5-in. × 40-in. diameter, were constructed from plexiglass and used for experimental studies of bubble growth, bubble size, bed density, and aggregate fluidization behavior of these particles.  Acoustical monitoring of pressure fluctuations and accelerometer-based vibration measurements were employed in addition to optical bubble probes and high speed cameras to characterize the bed hydrodynamics over distinct conditions of gas superficial velocity and bed height.  Transition conditions for slugging behavior were identified for two distinct particle size distributions.  Modifications to overall fluidization behavior were demonstrated with design changes to gas delivery, thus allowing enhancement of the overall bed inventory while avoiding the slugging regime.  Comparisons of the experimental data with calculations of fluidization behavior with commercially available simulation software are also presented.