Formulation of Highly Concentrated Suspensions for Spray Drying in a Fluidized Bed

Abstract

Spray drying of suspensions leads most often to free-flowing powder products of good quality. However, this process is energy-consuming, especially because of the high amounts of liquid to be evaporated from the sprayed suspension. Indeed, in order to ensure a good quality and stability of spraying, the amount of solvent must be determined so as to avoid excessive suspension viscosities. For a given amount of solvent, it is also possible to improve the viscosity of concentrated suspensions by deflocculation using appropriate dispersants.Through the use of an adequate dispersant, we showed that it is possible to obtain fully dispersed suspensions and to optimize their dryness in order to reduce the moisture content to be evaporated. The effect of different salts and the molecular weight of polyacrylic acid is investigated to improve the formulation of concentrated calcite suspensions with the focus on spray drying.A new continuous process, developed to enable the drying of highly concentrated slurries at low temperature, is also described. This process is based on the coupling of coating/attrition of a suspension in a fluidized bed of inert particles, and it strongly increases the surface area available for heat and mass transfers.Further analysis of this process has been carried out addressing the drying kinetics in a drying pipe. It shows a strong influence of the support wettability as well as the surface tension of suspension on the drying kinetics of suspension films. The surface tension of the suspension and humidity were found to be crucial parameters to optimize the powder recovery.

Keywords

• spray drying
• inert particles
• suspension
• drying kinetics
• attrition