Dry particle coating and granulation in rotating fluidized beds

The practicability of using rotating fluidized bed as dry particle coater and granulator is investigated in this study. Dry particle coating, in which fine guest particles are coated onto bigger host particles in the absence of binders or solvents, is studied for various systems of host and guest particles. Coating results are explained by considering the collisions between the host and guest particles and among themselves. Balance between collisional energy and adhesion energy is suggested to be the limiting condition for the adhesion and hence the coating of guest particles onto host particles. It is observed that the experimental and theoretical pressure drops across the fluidized bed differ about 35% on an average. This is assumed to be because of the theoretical approximations and loss of particles during fluidization. Guest particles SiC and alumina, which are fine and cohesive, are seen to agglomerate and form spherical granules during fluidization because of the collisions among the guest particles. Dry granulation of cohesive powders in rotating fluidized bed is investigated with the aid of pressure swing. In pressure swing granulation, the powder bed is fluidized in one cycle and compacted in the other cycle. This facilitates the formation of spherical granules without any binders. It is observed that denser granules with narrow size distribution are formed as the granulation time is increased. The mechanism and forces involved in making and shaping these granules is investigated. Mathematical modeling of dry granulation in rotating fluidized beds with the aid of population balances is initiated