Control of a two-stage mixed suspension mixed product removal crystallizer^⁎

In this work, we consider the problem of controlling a two-stage cooling mixed suspension mixed product removal (MSMPR) crystallizer. For this process, the temperature in the first crystallizer is manipulated for controlling the average crystal dimension (d₄₃), while it is desired to maintain the temperature of the second crystallizer at the minimum allowed value to guarantee maximum yield. Due to system nonlinearities and process delays, the performance of traditional PID controllers are poor. A control scheme is proposed to improve the closed loop performance and achieve desired control objectives. The control scheme is based on the coupling of a PI controller and a model-based nonlinear prediction block that serves as delay and disturbance compensator. The proposed scheme has been tested on the system in case of disturbances in the feed concentration, with and without measurement errors. It is observed that the proposed scheme outperforms the PI controller by reducing the output response settling time and overshoot.