Kinetics of fluidized bed spray agglomeration for compact and porous particles

Abstract

The effect of the primary particle porosity during the formation of agglomerates in spray fluidized beds is presented in this study. The method is based on the single micro-interactions occurring within the fluidized bed such as inter-particle collisions, droplet spread on the particle surface, aging of the deposited droplets and particle coalescence. The porous character of the particles is expected to directly affect the aging process of the deposited binder layer by penetration into the pores of the substrate. The droplet penetration process is experimentally analyzed by single droplet deposition on spherical, porous alumina particles. The results indicate that the penetration process is mainly governed by the viscosity of the liquid and that at relatively low viscosities, droplet penetration is fast. For highly viscous liquids, the penetration velocity slows down and an additional mechanism, namely drying becomes important. A combined imbibition–drying model is developed and included into a comprehensive stochastic agglomeration model that allows the simulation of agglomerate formation in a batch process. Lab-scale agglomeration experiments with porous and non-porous particles are carried out in an attempt to validate the general tendencies predicted by the main agglomeration model. The results show that the agglomeration rate for porous particles is significantly reduced due to the losses of deposited droplets into the pores of the primary particles; this tendency is much more pronounced at low binder viscosities.