Role of seed particles in the prediction and control of product particle size in fluidized-bed dryers

Particle size distribution in a fluidized-bed dryer (where a solution is converted to a solid granular particle) depends on several different rate processes taking place. These include particle growth, particle attrition, product rate, feed deposition rate, elutriation rate, and seed attrition rate. While these rate processes are basic, depending on the material being dried, some become more important than others. Few new seed particles are generated within the bed when the physical properties of many materials being dried are such that little particle attrition takes place. Under these conditions, the particle size distribution in the bed continually increases unless some measure is taken to introduce into, or generate within the bed, new seed particles. This paper briefly describes the mathematical model which predicts the particle size distribution expected when drying solutions in a fluidized bed. The important role that seed particles play in determining the steady-state particle size distribution of the bed is stressed. An experiment is described in which information was obtained that helped determine what seed particles are, and what size particles became seeds