Effect of foam spray drying process parameters on powder morphology

Abstract

The paper presents analysis of the effect of feed foaming on quality of sprayed dried powders. A series of extensive experiments of co-current spray drying of foamed maltodextrin solution for different solid concentrations, initial temperatures of drying air and foaming gas/liquid ratio (GLR) were carried out. Significant effect of feed foaming on powder properties was found; bulk density decreases, porosity, angle of repose, Hausner (HR) ratio and sphericity grow with increasing of foaming gas flow rate. Properties of the powder changes from flowable (HR around 1.1) to cohesive (HR above 1.3). Non-foamed particles (GLR = 0) are subjected to stronger deformation than foamed particles as pressure of the internal bubble reduce drying shrinkage and supports shell structure which increase average sphericity of foamed product to above 0.8. Additionally, methodology for determination of the particle wall thickness on the basis of microscopic observation of the contour of the bubble detained in the particle was elaborated. Analysis of the results show that for high GLR, thickness of particles walls decreases as a result of detaining of excessive amount of foaming gas in relation to liquid phase in the droplet. Results presented in the paper allow to select optimal foam spray drying process parameters to obtain admissible level of product degradation.