Mixing of particles in apparatuses with a circulating fluidized bed

Abstract

A phenomenological model of mixing of particles in a circulating fluidized bed has been formulated; a distinctive feature of the model is allowance for convective particle fluxes in the radial direction that ensure a substantial decrease observed in practice in the concentration of the particles over the riser's height. As a result of a comparison of experimental and calculated mixing curves it has been established that the value of the coefficient of radial dispersion of the particles lies in the interval 0.0006-0.006 m 2 /sec.It is common knowledge that the mixing of particles in a circulating fluidized bed (CFB) is a multifactor process occurring against a background of a complex internal hydrodynamics [1]. To model the phenomenon one has used different schemes, which reflect, to an extent, the regularities of the actual process of mixing of particles in CFB apparatuses. The models proposed can arbitrarily be subdivided into two large groups. The first group includes the models of axial (longitudinal) mixing, in which the determining quantities and concentrations are considered as being dependent only on the longitudinal component. In [2], a critical analysis of such models has been made and a fairly simple two-zone model of longitudinal mixing has been proposed on the basis of such analysis; the model includes the following equations:for the bed's core ∂Aρ 1 c _