SOLIDS MIXING IN THE BOTTOM ZONE OF FLUIDIZED BEDS

摘要

In the literature, the values of lateral solids dispersion coefficient (D_(sr)) in dense fluidized beds determined by different authors are scattered, ranging from 0.0001 to 0.1m~2/s. The present work is aimed to investigate the reasons for the divergence through CFD-DEM simulations. Results indicate that the particle trajectory shows multi-scale characteristics: macro-scale movement following the gross circulation of emulsion phase, and local-scale movement induced by bubbles closing to it. The effects of fluidizing velocity and bed width on D_(sr) are examined. It is deduced that D_(sr) embodies multi-scale mixing mechanisms, which makes D_(sr) difficult to predict or scale up.