FLOW STRUCTURE OF THE SOLIDS IN A 3-D GAS-LIQUID-SOLID FLUIDIZED-BED

Local and macroscopic solids flow structure and kinematics in a 3-D ga s-liquid-solid fluidized bed were studied using a noninvasive radioact ive-particle tracking (RPT) technique. Based on the multisite detectio n of gamma radiations emitted from a single radiolabeled tracer partic le freely moving in the fluidized bed, RPT permitted to obtain fast sa mpling of 3-D trajectories of the tracer, whose physical properties we re similar to those of the solids inventory. These trajectories showed the detailed motion sequences of the solid particles as entrained in the bubble wakes, fluctuating randomly or sinking deterministically in the liquid-solid emulsion. Based on measurements done in the vortical -spiral flow regime, the dynamic solids flow structure inside a three- phase fluidized bed can be viewed as a three-zone core-annulus-annulus structure: (I) a central fast-bubble flow region with the particles s wirling upward; (2) a vortical flow region around the velocity inversi on point with the particles momentarily captured in emulsion vortices; and (3) a relatively bubble-free descending flow region where the par ticles spiral down between the velocity inversion point and vessel wal ls. Our solids flow structure of dense fluidized beds are similar to t he flow structure of liquid and/or solid in lean fluidized beds (obser ved through laser sheeting imaging). Measured distributions of local e nsemble-averaged particle velocities and turbulence intensities were c onsistent with the existence of a toroidal recirculatory solids flow p attern in the bed. Measured mean circumferential ensemble-averaged rad ial velocity was essentially zero throughout most of the bed, The soli ds flow turbulence field was nonisotropic, as radial turbulence intens ities were generally lower than longitudinal turbulence intensities.