Feedback Control for the Size and Shape Evolution of Needle-like Crystals in Suspension. I. Concepts and Simulation Studies

Two feedback control approaches for influencing the evolution of the average particle dimensions of populations of needle-like crystals in growth-dominated batch cooling crystallization processes are proposed. The first strategy is a path following control (PFC) approach which does not need access to kinetic models for crystal growth. The second approach consists of a considerably more complex nonlinear model predictive controller (NMPC) that requires the availability of multidimensional crystal growth rate models. The main focus lies in analyzing the effectiveness of these two controllers with respect to successfully operating the considered process, bearing in mind the differing requirements regarding the availability of kinetic models. To this end, both control strategies were coupled with a process simulation framework that features a detailed measurement model emulating the behavior of an existing monitoring device for the evolution of the particle size and shape distribution. It is demonstrated how both controllers can identify the attainable region for the average particle dimensions of a given seed population, and also reach an arbitrary target size and shape within the interior of this region. A performance benefit from operating the more complex NMPC was not observed, which renders the PFC approach suitable and sufficient for the considered application.