Model-based control of a granulation system

Granulation, the process by which granules are made from powdered, slurried, solution or molten feed material, is an important process in many industries. The main objective in the granulation process is to produce granules with consistent product quality, as indicated by various industry standard variables which can be related to two fundamental process quantities: particle size distribution and bulk density. While it is customary to specify a desired setpoint value for bulk density, the specifications on particle size distribution typically take the form of an upper limit (dU) and a lower limit (dL) determined by the screen sizes used in product classification. The paper discusses the peculiar control problems arising from such a combination of product quality specifications and then develops a model-based control scheme which systematically addresses the problems. Simulation studies illustrate the control system implementation and performance for various situations of practical significance.