BUBBLE FORMATION AT A SINGLE ORIFICE IN GAS-FLUIDIZED BEDS

An earlier developed hydrodynamic model describing dense gas-solid two phase flow has been used to study the bubble formation process at a s ingle orifice. A systematic experimental and theoretical study has bee n conducted to investigate the effect of particle properties (i.e. par ticle diameter and density) on the bubble growth process for Geldart t ype B powders. Theoretical results, obtained for both two-dimensional and three-dimensional geometries, have been compared with experimental data and with predictions from approximate models reported in literat ure. A comparison of the theoretical results and experimental data sho ws that the advanced hydrodynamic model gives a satisfactory good desc ription of the bubble growth process for several particle types which makes this model a useful tool to study the bubble formation process i n fluidised beds. It appears that the influence of particle size and p article density on bubble formation can be related to the effect of th e minimum fluidisation velocity on this process. At a constant gas inj ection rate through the orifice higher minimum fluidisation velocities result in larger bubbles and decreased leakage. Further, it has been found that coarse particles give rise to the formation of relatively e longated bubbles. The detachment times, on the other hand, seem to be independent of the particle size used. Copyright (C) 1996 Elsevier Sci ence Ltd