Numerical analysis of hydrodynamics and crystal motion in a batch crystallizer

In this work, we investigate numerically the hydrodynamics and crystal motion in a draft tube batch crystallizer using Computational Fluid Dynamics (CFD) coupled with the Discrete Phase Model (DPM). The flow generated by the rotating impeller interacts with baffles and generates a complex, unsteady, three-dimensional turbulent flow with large-scale recirculations. To investigate this flow, a Multiple Reference Frame approach is first used as initial condition for a more accurate Sliding Mesh Model. Turbulence is modeled with the k-epsilon model considering the Unsteady Reynolds-Averaged Navier-Stokes formulation. The computational model is first used to analyze the impact of the liquid volume in the vessel on hydrodynamics. Coupling CFD with DPM, crystal motion is then investigated. For this purpose, crystals are introduced in the flow at eight different positions. Crystal motion has been investigated in a Lagrangian manner through one-way coupling considering drag and buoyancy forces. Deposition probabilities have been calculated for different crystal types and interpreted as an indicator for unfavorable crystallization conditions, allowing identifying suitable liquid volumes and seeding positions. (C) 2013 Elsevier B.V. All rights reserved.