(267b) Computational Modeling of Drying of Pharmaceutical Wet Granules in a Fluidized Bed Dryer Using Coupled CFD-DEM Approach

Fluidized bed drying is a topic of interest for scientists and engineers because of its complicated physics and its presence in a wide range of industrial processes e.g. pharmaceutical product manufacturing, food processing, wood processing, reduction of iron ore, flue gas cleaning, the roasting of sulfide ores, drying of coal, catalyst industry and many more. Here, we propose a model based on coupled Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) approach to simulate the drying of granular particles in fluidized bed dryer associated to the drug manufacturing process. The drying process of wet granular particles in a fluidized bed dryer involves momentum, heat and mass transfer between the particles and the drying medium which is inherently a multiphase-multicomponent flow problem.

Methods:

The model was implemented using an opensource software CFDEM® coupling where the fluid phase was solved by OpenFOAM® codes and the motion of particles were calculated by LIGGGHTS® codes. The information between the fluid phase and particles were exchanged at certain time intervals. A reaction engineering based approach was used to model the evaporation of water from the wet granules and the existing CFDEM® code was modified to incorporate the model for the evaporation. The cohesion force acting between the wet granules due to the formation of liquid bridge between the wet granules was considered in the model.

Results:

Our model was capable of capturing the heat, momentum and mass transfer between the particles and the drying medium. The model was used to predict the drying of lactose monohydrate particles. Numerical simulations were performed to predict the change of particle moisture content and temperature with time during the fluidization process. The variation of average particle temperature and average moisture content with time agreed well with the experimental results obtained from the literature. Agglomeration of wet particles was observed during the drying process due to the cohesion force generated by the liquid bridge between the wet particles. The agglomeration of particles was not present after the particles became dry as expected. It was also observed that the temperature of the dry particles increased at a much higher than the wet particles since the latent heat of evaporation for the water in the wet particles was supplied by the particle itself. This was also observed in the experiments.

Conclusions:

A validated coupled CFD-DEM model was developed to simulate the drying of pharmaceutical wet granules. The effect of particle-particle cohesion due to the formation of liquid bridge between the wet particles was considered in the model. The results obtained from the simulations indicate that the motion and rate of increase of temperature of wet particle are significantly different from those of dry particles. This model can further help set up reliable scale up, troubleshooting or optimization schemes by greatly replacing the burden of the cost of design of experiments.