Scale-Up of Fluidized Beds and the Similarity Rule for Solid Mixing Processes

Abstract

To establish a rational scale-up method for fluidized beds the mixing characteristics of fluidized solids and those of floating bodies in the bed are examined experimentally. For experiments in mixing of bed particles magnetically separable tracer particles were developed. Floating bodies were simulated by polypropylene tablets. For four geometrically similar equipment units of 50, 150, 300 and 600mm inside diameters, the sizes of bed particles and floating bodies and the gas velocity were adjusted so that the scaling law of Horio et al. (AIChE J., 32, 1466 (1986)) was satisfied. From the measured lateral diffusivity of solids and the segregation pattern of floating bodies it was confirmed that the scaling law of Horio et al. can be extended to the mixing behavior of both the bed particles and the floating bodies. Based on the present data as well as those in the literature the following new correlation for E_r, the lateral diffusivity of solids in non-tapered gas-solid fluidized beds was developed :
(u₀-u_mf) D_e/E_r=1.07 [(u₀-u_mf) u_mf/gL_mf] ^0.25 (B/L_mf) ^0.75
where D_e is the equivalent bed diameter and B is the two-dimensional bed thickness.