The process involving conversion of fluid into fine droplets and exposing them to a hot drying media, so as to achieve defined dry particulate matter is spray drying. It is a widely used continuous industrial process which involves particle formation from feed fluid which may be in the form of solution, emulsion or pumpable suspension into either dry powder or granules. Spray drying involves following steps.

Conversion of the feed into fine droplets is achieved by either pumping the feed under high pressure through an orifice or by spraying through a high speed rotating perforated disc. The former is known as Nozzle Atomization and is popularly used to produce coarse droplets resulting in large granular particles of dried products. The latter is known as Rotary Disc Atomization and produces fine droplets resulting in fine powder particles of dried products.

Air, which is, normally the drying media used, is heated to a predefined temperature depending upon the characteristics of the feed fluid and dried product either an indirect hot air generator or a direct hot air generator. This hot air is brought in contact with the spray droplets in one of the following ways through the air distributor.

Co-current-Air and particles move in the same direction.

Counter-current-air and particles move in the opposite direction.

Mixed flow - particles are subjected to co-current and counter-current phase.

The thermal energy of the hot air is used for evaporation and the cooled air pneumatically conveys the dried particles in the system. The contact time of the hot air and the spray droplets is only a few seconds, during which drying is achieved and the air temperature drops instantaneously. The dried particle never reaches the drying air temperature. This enables efficient drying of heat sensitive materials without thermal decomposition.