Modeling and scaling up of industrial spray dryers: A review

Abstract

The paper presents a review of research works, experiments and simulations on spray drying in the industrial scale. The research area in the industrial spray drying process covers control of powder properties (bulk density, morphology), particles agglomeration (final PSD), residence time, wall deposition and safety of the process and the product. Limited number of literature references on spray drying in the industrial scale is due to high costs of running experiments and validation of theoretical models. Recent works on hydrodynamics in spray towers showed transient, oscillating, 3D flow of dispersed and gas phase which results from construction of inlet and exhaust ducts and swirl decay due to wall roughness (deposits). Applications of the most advanced and accurate empirical methods to calculate spray drying kinetics in industrial scale; the Characteristic Drying Curves (CDC) and the Reaction Engineering Approach (REA) were presented. The main obstacles denying confident scaling up of the spray drying process; lack of dynamic similarity between small and large units, gas turbulence modelling, determination of drying kinetics and neglecting of agglomeration process are highlighted. Methods of modelling of the agglomeration process in spray drying (transition functions, full scale agglomeration) are described. Examples of modelling and measurements of hydrodynamics, wall deposition, agglomeration process and drying kinetics in the industrial towers are presented and discussed.