PARTICLE MIXING AND SEPARATION IN A BINARY SOLIDS FLOATING FLUIDIZED-BED

The floating gas-solid fluidized bed (FGSFB) is a large-particle fluid ized bed confined in a tapered column with inserted grids. By applicat ion of two types of particles in an FGSFB, a wide variety of operation s can be carried out. The visual appearance and the hydrodynamic behav iour of such binary FGSFBs is reported in this paper. Two extreme type s of behaviour were observed in the experimental set-up: (1) almost co mplete separation occurs in beds of two types of particle with the sam e diameter but a particle density ratio rho(p, 2) /rho(p, 1) of ca. 2 (+/-1400 vs+/-700 kg/m(3)); (2) a relatively well-mixed situation is f ound in beds with two types of particle having the same density but a particle diameter ratio d(p, 2) d(p, 1) of ca. 2 (3.0 vs 1.7 mm). Expe rimentally determined pressure gradient values were always within the range of those measured for FGSFBs of the single-particle type. A meas ure for the separating force, the so-called separation tendency W, is derived and shown to be quantified by single-particle properties. Its value can be used to predict whether complete or intermediate mixing o ccurs, or if the binary FGSFB will be completely separated.