Spray drying is transformation of feed from a fluid state into dried particulate form by spraying the feed into a hot drying medium. It is a continuous particle-processing drying operation. The feed can be a solution, suspension, dispersion, emulsion or slip. The dried product can be in the form of powders, granules, or agglomerates.
Feed is finely atomized and is introduced in the drying chamber along with hot air. The mixture of atomized feed and hot air moves towards the air exhaust of drying chamber. The time taken by this mixture to travel upto air exhaust is called as residence time of drying. During this residence time, the feed droplets loose its moisture to the hot air and are converted into dry powder particles. The dry powder falling on to the conical portion of drying chamber slides down to bottom of drying chamber with the assistance of vibrators/knockers and is collected in collection bag/bottle through the rotary valve located at the bottom of drying chamber.
The air leaving the drying chamber entrains some of the dry powder which is recovered in the cyclone separator and collected through rotary airlock. The air leaving the cyclone separator still has traces of dry powder, which is further recovered by scrubbing in wet scrubber or passing it through bag filter. Air from cyclone or bag house is sucked by induced draft fan