(255f) Development of DEM Model to Study the Impact of Process Parameters and Material Attributes on Twin Screw Wet Granulation Process

Granulation, a widely used process in pharmaceutical, agriculture, food, and paper industry, is the technique of agglomerating particles together into semi-permanent granules (aggregates) made up of easily distinguishable original particles. In wet granulation, the binder liquid is sprayed onto the surface of a mixed granular bed, resulting in the formation of aggregates, to improve powder properties such as flowability and compactability. Despite its importance and widespread use, the process is poorly understood. In this study, a Discrete Element Method (DEM) model has been developed to evaluate the impact of different process parameters (screw speed and powder feed rate) and material attributes (powder cohesion) on continuous twin screw wet granulation process.

Methods:

In this study, we have used the dimensions of ConsiGma TSG to build the DEM model. The geometry was designed using SolidWorks (Fig. 1) and the simulations were carried out using commercial software Altair EDEM. Johnson-Kendall-Roberts (JKR) and Edinburgh-Elasto-Plastic-Adhesive (EEPA) were evaluated as the contact models for particle-particle interactions and Hertz-Mindlin model was used for particle-equipment contacts. For the process parameters, different screw speeds (100 rpm, 200rpm and 300 rpm) and feed rate (5 kg/h, 10 kg/h and 15 kg/h) were evaluated. The level of cohesion representing different L/S ratio was introduced using varying surface energy values. After completion of the simulation, the particle coordination number and particle residence time were quantified. The developed model was validated using previously published experimental data.

Results:

It was observed that the mean residence increases with decrease in screw speed and increase in cohesion. Moreover, coordination number was calculated at different conditions, and it was observed that increase in cohesion increases the coordination number indicating formation of agglomerates. Using the mean residence time distribution for the twin screw granulation, the mean residence time was observed to be approximately 2 seconds in accordance with the previously published data for low cohesion material at 500 rpm. Increase in mean residence time was observed at lower screw speeds and higher levels of cohesion.

Conclusion:

DEM simulations were performed to study twin screw wet granulation to evaluate the impact of process parameters and material attributes. According to the study screw speed, level of cohesion and feed rate significantly influence the twin screw wet granulation process. DEM modeling could be a really useful tool to develop mechanistic understanding of the overall process.