Coating of particles with finer particles using a draft-tube spouted-bed

Fluidized bed coaters or granulators with spray nozzles are used to produce coating particles, granules and agglomerates in various industrial fields. When the binder liquid containing fine particles is sprayed into a hot flu idized bed, the fluidizing particles grow in size by agglomeration due to t he particles colliding with the spray droplets that first form liquid and t hen solid bridges between particles. This phenomenon causes unstable coatin g or granulating and ill-balanced products. The question then arises about mono-core coating with finer particles. We investigated the characteristics of the mono-core coating using a draft-tube spouted-bed coater, applying t he separation force due to the high-speed gas from the inlet nozzle. As a r esult, it is found that mono-core coating could be achieved due to the shea r force and the external solid circulating system. It is shown that the coa ting ratio can be controlled by selecting the coating operation time and th e concentration of binder liquid. Also, it is found that choking of the dra ft-tube can be delayed by increasing the inlet gas velocity and the bed tem perature.