Fluidized-solids reactors with continuous solids feed—I: Residence time of particles in fluidized beds

Abstract

The distribution of residence times of solid particles is examined in fluidized beds at steady state with continuous feed and discharge of solids, both for beds consisting of a single particle size and for beds consisting of a wide spectrum of particle sizes. The mean age (residence time in bed) of particles of a given size in the overflow and carryover streams is found in all cases to be given by ▪ where F 1 is the mass flow rate of overflow stream, W is the weight of solids in the bed, ψ is the ratio of the size distribution function of overflow particles to that within the bed and ϰ is the elutriation velocity constant of particles whose mean age is being considered. The constant ψ is a measure of the degree of vertical segregation of particles within the bed. In most practical situation the bed may be considered to be not segregated, in which case ψ can be taken to be unity. For significant carryover of solids the elutriation velocity constant κ controls in determining the average length of stay of particles in the fluidized bed. In all cases the mean age of particles of a given size is the same in both the overflow and carryover streams.