Fluidization of Mixtures of Two Solids Differing in Density or Size

The complex mechanism by which homogeneous mixtures of two solids achieve fluidization is subjected to theoretical analysis, to elaborate relationships capable to provide their "initial" and "final fluidization velocity" u(if) and u(ff), i.e., the limits that encompass the suspension process. The article shows how the equation that describes the force equilibrium of fluidization can be rewritten in forms that account for the distribution of the components of density- or size segregating mixtures during the transition to the fluidized state. This approach leads to the theoretical expression of u(if) and uff of either type of system, whose differences of behavior are correctly reproduced by accounting for the voidage reduction typical of beds of particles of different size. The comparison with experimental results at varying mixture composition demonstrates that the equations give a coherent interpretation of the dependence of the fluidization velocity interval of two-solid mixtures on the principal variables of interest. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 2325-2333, 2011