ENTRAINMENT OF FINES FROM FLUIDIZED-BEDS WITH AN EXPANDED FREEBOARD

Apart from accomodating cyclones, expanded freeboards are very effecti ve at reducing the particle carryover from fluidized beds by reducing the superficial gas velocity. However, few experimental studies have b een done on this aspect of entrainment. Batch experiments on entrainme nt have been carried out at velocities of 0.2 m/s to 0.8 m/s using Gro up A FCC powders in 76 mm and 152 mm diameter columns and also in a co lumn constructed from a 76 mm diameter section 1.1 m high at the botto m having a 152 mm diameter section with a height of 1.3 m above it. Th is is referred to as the expanded column. Results show that by doublin g the diameter of the top section the total entrainment fluxes, E-z, a re reduced to about 1% of the original values. The elutriation rate co nstants, K-ico, of fines entrained from fluidized beds with an expand ed freeboard are best calculated using as the equilibrium concentratio ns those in the dense bed, X-bi but the gas velocities and the cross s ectional area used are those based on the larger expanded section of t he column.