FLUIDIZED-BED SPRAY GRANULATION - INVESTIGATION OF THE COATING PROCESS ON A SINGLE SPHERE

The coating and granulation of solid particles in a fluidized bed is a process which converts pumpable and atomizable liquids (solutions, sl urries, melts) into granular solids in one step by means of drying. Th e solution to be processed is sprayed onto a fluidized bed. Particle g rowth can take place either via surface layering or agglomeration. In the case of surface layering the atomized droplets deposit a thin laye r of liquid onto the seed particles. The solvent is then evaporated by the hot fluidizing, leaving behind the dissolved material on the surf ace. Although fluidized bed spray granulation and film coating have be en applied in industry for several years, there is still a lack of und erstanding of the physical fundamentals and the mechanisms by which sp herical granules are formed. Hence a new method was developed which al lows the direct observation of the subsequent particle-forming mechani sms such as droplet deposition, spreading, wetting and drying. The aut hors present a laboratory scale apparatus in which a single freely sus pended particle can be coated under well defined and constant coating and drying conditions. With this device, particle-growth-rate and the development of particle morphology were measured and investigated unde r various experimental conditions. (C) 1997 Elsevier Science S.A.