Forming of powders. Fundamental principles of drying by atomisation

Obtaining solid products from a spray-drying process has been known since the 19th century. Initially used to dry eggs and concentrate juices, the process developed significantly in the 1920s in the dairy and detergent industries. Thanks to its great flexibility, it is now applied to a wide range of products in the agro-industrial, pharmaceutical and cosmetics sectors, as well as for the preparation of pigments and mineral fillers.

Spray-drying consists in obtaining a divided solid by bringing a hot gas into contact with a fluid dispersed in the form of fine droplets. By adjusting the operating parameters, it is possible to control various properties of the finished product, such as the size and shape of the solid particles, or its solubility via the presence of porosity.

In this first dossier [J 2 256], we present the fundamental principles on which spray drying is based. These concern spray formation and characterization, followed by the thermodynamic aspect with mass and heat balances and, finally, the kinetic aspect with droplet drying and the concepts associated with sizing spray-drying devices.

In a second dossier [J 2 257] , we look at the technological aspects of the spray-drying process, reviewing the spraying, gas dispersion and solid recovery stages, as well as the safety aspects of the process. We also give concrete examples of the use of this process in real-life applications.

Readers are also referred to [J 2 251] and [J 2 252] , where the basic concepts associated with powder rheology are presented.