Spray-drying is a technique based on the transformation of a fluid into a dry powder by atomization in a hot drying gas stream that is generally air 1.
The spray-drying process consists of four fundamental steps: (i) atomization of the liquid feed, (ii) drying of spray into drying gas, (iii) formation of dry particles and (iv) separation and collection of the dry product from the drying gas 2, 3, 4. Fig. 1 shows a scheme of the conventional spray-drying process. First, the fluid is fed into the drying chamber by a peristaltic pump through an atomizer or nozzle that can be a rotary atomizer, a pressure nozzle or a two-fluid nozzle and the atomization occurs by centrifugal, pressure or kinetic energy, respectively 5. The small droplets generated (micrometer scale) are subjected to fast solvent evaporation 6, 7 leading to the formation of dry particles that are separated from the drying gas by means of a cyclone that deposes them in a glass collector situated in the bottom of the device 8, 9.
Heng et al. described in detail the major phases involved in spray-drying process 10. In addition, a description of the emergence and evolution of this technology and the hardware used in the process is available in the literature 11.