Local solid mixing in gas-solid fluidized beds

Diffusivity of the solid particles in a 152-mm ID gas-solid fluidized bed w as determined at different regimes of fluidization. The gas was air at room temperature and atmospheric pressure and the solids were 385 mum sand or 7 0 mum FCC particles. The experiments were done at superficial gas velocitie s from 0.5 to 2.8 m/s for sand and 0.44 to 0.9 m/s for FCC tin both bubblin g and turbulent regimes). Movement of a tracer was monitored by radioactive particle tracking (RPT) technique. Once the time-position data became avai lable, local axial and radial diffusivity of solids were calculated from th ese data. Calculated diffusivities are in the range of 3.3 x 10(-3) to 5.6 x 10(-2) m(2)/s for axial and 2.6 x 10(-4) to 1.5 x 10(-3) m(2)/s for radia l direction. The results show that the diffusivities, both axial and radial , increase with superficial gas velocity and are linearly correlated to the axial solid velocity gradient. Solid diffusivity in a bed of FCC was found to be higher than that of a bed of sand at the same excess superficial gas velocity. (C) 2001 Elsevier Science S.A. All rights reserved.