Control of segregation by non-uniform aeration in a fluidized bed spray granulator

Abstract

Controlling and influencing the rate of particle growth in spray granulators is key for consistent product quality and size, while reducing energy consumption and product re-circulation. To this end, we have implemented a new control device to actively change the fluidization topology of fluidized spray granulators and to influence the local particle segregation in the areas affected by the granulation, selectively growing fine particle fractions at will. Simulations using computational fluid dynamics coupled with the discrete element method (CFD-DEM) demonstrate how the different operational modes can be switched in a short period of time, resulting in full local segregation in less than 40 s, without changing the fluidization air or inlet temperature. It is shown how a central spout preferentially drags big particles to the top of the bed, while a side aeration system, where two smaller spouts are opened at the outermost sides of the bed, creates a concentration of fines in the spraying region. This process can be repeated as long as the fluidization velocity of all particle sizes in the bed can be attained and full fluidization is underway. The spout regime could be used to clean the distributor plate of undesired big or overgrown particles, and side aeration to preferentially grow finer particles, while homogeneous aeration should be the default operation mode when no anomalies are detected.