(267a) Agitated Drying of Active Pharmaceutical Ingredients: Effect of Intermittent Mixing on Heat Transfer
AIChE Annual Meeting
Thursday, November 18, 2021 - 10:15am to 10:30am
The discrete element method (DEM) has been used previously to examine heat transfer for particle-particle and particle-wall conduction for a dry bed of particles. The rate of heat transfer can be described by a heating time, which is the time required to heat the bulk material to a fraction of the wall temperature. In this study, we simplified the problem and focused specifically on how to maximize heat transfer while minimizing particle breakage during the drying process. We performed DEM simulations using intermittent mixing, defined as alternate stirring and non-stirring periods of the impeller, as an approach for minimizing particle breakage by decreasing the number of impeller revolutions. We found that the heating time initially decreased with increasing impeller revolutions and then reached a plateau. For a single cycle of intermittent mixing, the starting time of the stirring period influenced the heating time. Moreover, for multiple cycles of intermittent mixing with similar number of impeller revolutions, the heating time of the material bed decreased with increasing intermittent mixing cycles to a certain point and then reached a plateau. When we calculated the relative stirring time (RST), the ratio of stirring time per cycle, we found that intermittent mixing beds with similar RST and number of impeller revolutions gave similar heating time within a certain range of number of impeller revolutions. This work provides insight into how intermittent mixing can be optimized during the drying process in order to maintain effective heat transfer while diminishing particle breakage. This work was partially supported by Takeda Pharmaceuticals International Co.