Plenary Talk: Scale-up of Fluidized Bed Drying: Hydrodynamics, Mixing and Heat and Mass Transfer
Fluidization
2019
Fluidization XVI
General Paper Pool
Plenary Session #3
Thursday, May 30, 2019 - 9:50am to 10:30am
In this talk, we will first present results for scale-up of batch fluidized bed drying for a pharmaceutical application. Parametric analysis of four fluidized bed dryer operating parametersâ initial moisture content, material loading, heating air temperature and air flux â and their effect on drying was studied. Two different dryer scales were used to dry a pharmaceutical excipient powder. Based on these results we are able to introduce a practical scaling rule which can predict the drying behavior in the large scale unit based on results from a bench scale unit. We then discuss using knowledge gained from the batch fluidized bed dryers to predict the behavior of a continuous fluidized bed dryer, where solids continuously flow into and out of the drying chamber. Several pharmaceutical manufacturers are moving towards continuous manufacturing due to its potential to improve agility, flexibility, and robustness. The fluidized bed unit operation can be readily implemented as a continuous process for drying. A model for predicting the effluent moisture content for the continuous dryer was developed by combining the drying kinetics and residence time distribution (RTD) of powder in the dryer. The drying kinetics were obtained from the batch fluidized bed drying process. The RTD was characterized by carrying out a tracer response test in the continuous fluidized bed. A tank-in-series model was used to describe the RTD curves. A maximum mixedness model (MMM) was adopted for characterizing the micromixing in the continuous fluidized bed. The results of the model were compared to experimental results and we discuss how the operating conditions affect the resulting effluent moisture content. Finally, we will discuss the application of these results to improving the operation of pharmaceutical fluidized bed drying.