Dynamics of heat-sensitive pharmaceutical granules dried in a horizontal fluidized bed combined with a screw conveyor

Abstract

Continuous manufacturing can greatly benefit the pharmaceutical industry for improving production yields, size flexibility, and transferability among sites.This study investigated the dynamics of pharmaceutical granules dried in a continuous horizontal fluidized bed dryer (FBD) equipped with a screw conveyor to evaluate the feasibility of the process.Pharmaceutical granules are often irregularly shaped and feature a large particle size distribution, thus complicating the operation of traditional continuous FBDs with smooth fluidization regimes. The presence of screw conveyor enhanced plug flow, decreased agglomeration, and improved fluidization stability and homogeneity.The residence time distribution (RTD) of solid flow was evaluated by the pulse-tracer injection method. The dispersion model and the tanks-in-series model were both suitable for describing the particle flow through the dryer. The corresponding Peclet numbers vary between 9.8 and 13.3 while the tank number better fitting the model are between 5.4 and 7.2.The influences of different parameters were studied. The internal screw conveyor rotation was the most critical parameter affecting the solid RTD, followed by air velocity. The air temperature also had a moderate impact. The solid throughput rate had a negligible effect on the solid RTD, but it did have a direct impact on the overall drying rate.