Coupled Computational Fluid Dynamics–Discrete Element Method Simulations of a Pilot-Scale Batch Crystallizer

Computational fluid dynamics (CFD) coupled with the discrete element method (DEM) has been used to investigate numerically crystal dynamics in an existing pilot-scale batch crystallizer. The CFD-DEM combination provides a detailed description of crystal dynamics considering a four-way coupling. In a previous analysis, CFD had been coupled with a discrete phase model (DPM) using a simple one-way coupling. The corresponding predictions are then compared with those obtained through four-way coupling considering KH2PO4 crystals in water. From the CFD-DEM simulation, it is possible to investigate quantitatively the driving force controlling crystal growth and the interaction of crystals with reactor walls, baffles, and impellers. This delivers essential data for process improvement. Different seeding procedures were also compared. The seed crystals have been injected either within the complete liquid volume or, as in the experiments, through a funnel. By varying the most important crystallization process parameters, we found optimal conditions for a liquid phase volume in the crystallizer of 24 L, for injection through a funnel above the baffle, and for an initial seed crystal size of 0.5 mm.