DESIGN AND EXPERIMENTAL EVALUATION OF STABILIZING FEEDBACK CONTROLLERS FOR CONTINUOUS CRYSTALLIZERS

The development and experimental evaluation of stabilizing control schemes for a continuous isothermal evaporative pilot crystallizer, equipped with on-line crystal size distribution (CSD) sensors and a system for fines removal, are discussed. A first-principles modeling procedure is followed to derive models for the crystallizer and the CSD sensors. An output error optimization procedure is applied to estimate unknown empirical parameters of the process model with experimental process data. The experimental results reveal a strong influence of the fines removal rate on CSD dynamics. Two stabilizing control schemes are presented. The first is a simple proportional output feedback scheme which uses information on the number of fines to manipulate the fines removal rate. Experimental results indicate that sufficient stability and dampening can be achieved with this controller. The second scheme is an observer-based control scheme in which information on the actual process state is used to stabilize the CSD by manipulating the fines removal rate. Simulation results demonstrate that this state feedback approach exposes better performance compared to the output feedback approach.