ENTRAINMENT OF FINES FROM FLUIDIZED BEDS WITH AN EXPANDED FREEBOARD

Abstract

Apart from accomodating cyclones, expanded freeboards are very effective at reducing the particle carryover from fluidized beds by reducing the superficial gas velocity. However, few experimental studies have been done on this aspect of entrainment. Batch experiments on entrainment have been carried out at velocities of 0.2m/s to 0.8 m/s using Group A FCC powders in 76 mm and 152 mm diameter columns and also in a column constructed from a 76 mm diameter section 1.1m high at the bottom having a 152 mm diameter section with a height of 1.3 m above it. This is referred to as the expanded column. Results show that by doubling the diameter of the top section the total entrainment fluxes, Ez , are reduced to about 1% of the original values. The elutriation rate constants, K* i∞ , of fines entrained from fluidized beds with an expanded freeboard are best calculated using as the equilibrium concentrations those in the dense bed, Xbi , but the gas velocities and the cross sectional area used are those based on the larger expanded section of the column.