Quantifying drying performance of a filter dryer: Experiments and simulations

Drying is one of the most commonly used unit operations in the preparation of dry granules by thermally removing volatile solvent from the wet solid. The study focuses on the quantitative investigation of heat transfer in a filter dryer in the quest to determine the optimum drying conditions. Consequently, contact drying kinetics of glassbeads-ethanol and lactose-ethanol system is investigated using an agitated filter dryer (Charles Thompson). Discrete element method is employed to simulate granular flow, mixing and heat transport in the vessel. Typical system with glass beads is numerically simulated using appropriate material properties and validated by the experimental findings. A parametric study for both simulations and experiments is performed to assess the effect of various conditions of wall temperature, fill level and impeller speed on the drying performance in the filter dryer. A high wall temperature showed an increase in the drying rate and a sharp rise in the average bed temperature, thereby decreasing the total time for drying operation. An increase in fill volume (bed depth) at constant wall temperature and speed resulted in a decline in the drying rate. The rotational speed had a nominal impact on drying of glass beads. Hence low rotational speeds seemed optimal for contact drying. (C) 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.