(419b) DEM Simulation of Particle Granulation in a Twin Screw Wet Granulator

Granulation is a method of particle size enlargement via agglomeration of primary particles to form larger granules. In a Twin Screw Wet Granulator (TSWG), a binder liquid is sprayed onto the surfaces of active pharmaceutical ingredient particles to promote the formation of larger granules with specific morphology, flowability, compressibility and other properties. The morphology of granules formed from a TSWG process depends on the material properties of the primary particles and operating conditions applied but mechanistic understanding of the granulation process remains incomplete even today. A large number of experiments are typically performed to determine the operating parameters required for a specific type of primary particles. The Discrete Element Method (DEM) has been applied extensively by researchers for simulations of various types of particulate processes. However, good agreements between DEM simulations of the TSWG and experimental measurements have not been demonstrated in the literature to date. In this study, the DEM was coupled with a capillary liquid bridge model to simulate the granulation process in a TSWG. Different liquid content (30%, 45% and 60%), screw speed (450 rpm, 675 rpm and 900 rpm) and solid throughput (5 kg/h, 12.5 kg/h and 25 kg/h) were applied to investigate the effects of these parameters on the residence time distribution of particles in the TSWG and size distribution of the granules formed. It was observed that agglomeration of particles occurred in the conveying elements of the TSWG and large granules were kneaded in the kneading elements to generate new granules. Granules were generated with different shapes and sizes at the outlet of the TSWG. The magnitudes of various forces, such as collision forces and capillary liquid bridge forces, were extracted for analyses and size distributions of granules formed at the outlet of the granulator were compared with experimental data reported in a previous study.