(736d) Modeling an Industrial-Scale Fluidized Bed Wurster Coating Process Using CFD-DEM

Industrial fluid-bed coating operations involve the flow of several hundred million beads in a large-scale Wurster-coating device. Experimental measurements available from such large scale operations are limitedâ??very few beads per sample (10-100) can be analyzed for coating thickness uniformity. In such scenarios, computational fluid dynamics (CFD) based modeling models become important for developing a better understanding of the process and identifying the key parameters that influence coating-thickness uniformity. With recent advances in computational hardware and software, including graphics card (GPU) based processing, simulations of larger industrial-scale systems can be performed.

Previous results have shown that the CFD-DEM (discrete element method) approach is better-suited to obtain particle trajectories compared to the CFD-TFM (two-fluid model) approach. With GPU-enabled codes, ~20 million beads can be realistically simulated. Therefore, exploiting the azimuthal symmetry of the geometry to simulate a smaller 3-D sector (pie-slice) of the full unit, the flow results are shown to be reasonable with this idealization. Single-phase CFD simulations were performed to determine the air flow distribution through the distributor plate, which is subsequently used as the inlet boundary conditions for the CFD-DEM models. The bead-size dispersity is also incorporated in the model.

The influence of controllable process parameters, such as air-flow rates, and material properties can be virtually investigated using these CFD-DEM simulations. The residence time distributions of the beads in the active coating region (inside the Wurster column) and the non-coating regions are compared for the different conditions explored. These residence time distributions, especially inside the Wurster column, provide qualitative and quantitative measures of the bead-coating uniformity at present. In future, these residence time measurements can be extrapolated to predict long-term coating uniformity using compartment-based and/or population-balance models.