Modeling, simulation and stabilizing H∞-control of an oscillating continuous crystallizer with fines dissolution

In this contribution, a detailed model for a continuous crystallizer with fines dissolution is derived. The main focus of this article is the identification of physical reasons responsible for oscillations occurring in these crystallization plants. In contrast to many other crystallization models used in literature for the investigation of such limit cycles, detailed kinetic expressions for crystal growth and attrition, as well as for the separation of fines in the annular zone, are incorporated. By dynamic simulations of the model and by comparison with measured data, an undesired dissolution of larger crystals can be identified as a possible reason for the appearance of sustained oscillations. Finally, a stabilizing feedback controller is designed using H∞-theory. It is demonstrated in simulations that this controller enables stable operation of the crystallizer even at a high fines dissolution rate.

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