Segregation and dispersion of a binary system of particles in a fluidized bed

Abstract The steady‐state segregation and dispersion of a binary system of particles in a liquid‐fluidized bed was investigated. One of the species had a density of 1,600 kg/m 3 and the other 1,900 kg/m 3 , and both exhibited a narrow size range of 1.00 to 1.18 mm. A generalized model for describing the dispersion coefficient, D, was proposed. That is, D = αdU f /ϕ, where d is the particle diameter, U f the local interstitial fluid velocity, and ϕ the local volume fraction of solids. The model had one adjustable parameter α, which was fixed at 0.7 for both particle species and for the six different superficial fluidization velocities used. The particle segregation was described with reference to the monocomponent fluidization parameters of the two species, based on the Richardson and Zaki equation. Good descriptions of the concentration profiles of the two species were produced for all superficial velocities examined. Additional experiments involving other binary systems were also conducted in order to test the generality of the model. These systems involved particles of closer settling velocities, and, hence, displayed more mixing. Very small adjustments in the terminal velocities of the species, typically 2%, were needed to achieve satisfactory agreement between the theoretical and experimental concentration profiles, with the model parameter, α, equal to 0.7. This adjustment was justified because of apparent changes in the average particle sizes of the two species due to particle‐size segregation. © 2006 American Institute of Chemical Engineers AIChE J, 2006