460038 Parametric Analysis of Fluidized Bed Drying of Pharmaceutical Materials
Hao Chen, Xue Liu, Cody Bishop, Benjamin J. Glasser
Department of Chemical and Biochemical Engineering, Rutgers University, Piscataway, NJ, 08854
Fluidized beds are extensively used in the pharmaceutical and other chemical industries either as a batch or continuous process for drying moist powders and granular solids because of good mixing of solids and intensive heat and mass transfer between the solid and hot gas phases in the system. It has been reported that an average of 12% of all energy consumed is used on drying, and the cost of drying could reach up to 60%-70% of total cost of investments . Therefore, optimal operation of the drying process is sought to meet the requirements for cost-effective manufacturing.
In this work, parametric analysis of four fluidized bed dryer operating parameters – initial moisture content, material loading, heating air temperature and air flux – and their effect on drying were studied using two factorial experimental designs. Two different dryer scales, the Glatt GPCG-1 and MiniGlatt, were used to dry Dibasic Calcium Phosphate powders. According to a Pareto analysis, initial moisture content and air flux are the most significant variables. For the larger GPCG-1, the four variables used in the factorial tests were found to be independent. For the smaller MiniGlatt, the interaction of the initial moisture content and the air flow rate was also significant. From the parametric analysis, it was observed that drying is dominated by the constant drying stage, and zero-order kinetics, for the mild drying conditions (appropriate for many pharmaceutical products) we considered in this work. A comparison of the two dryers and an evaluation of energy efficiency were also carried out. It was found that drying should be carried out with relatively low temperatures and high air fluxes for both the large and small scale dryers in order to maximize the energy efficiency.
In the second part of this work, the effect of particle size on drying was investigated. It is commonly believed that during the constant drying stage, where convective drying dominates, small particles dry faster than larger particles because the former have larger surface-area-to-volume ratio. However, it was observed for the DCPA that large (150-212 micron) and small (53 – 106 micron) particles have the same drying rate during the constant-rate drying stage. Similar phenomena were also found for the MCC (microcrystalline cellulose) PH101 and the wet granules mainly consisting of lactose and MCC. This indicates that surface area may not be a key variable controlling the drying rate during the constant-rate stage. A comparison of fluid bed drying and oven drying is also carried out in this work.
Our work serves to characterize performance of fluidized bed dryer systems and provide physical insight into the fundamentals of drying of porous materials.
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