Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas.
This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals. A consistent particle size distribution is a reason for spray drying some industrial products such as catalysts.
Air is the heated drying medium; however, if the liquid is a flammable solvent such as ethanol or the product is oxygen-sensitive then nitrogen is used.
All spray dryers use some type of atomizer or spray nozzle to disperse the liquid or slurry into a controlled drop size spray.
The most common of these are rotary disk and single-fluid high pressure swirl nozzles. Atomizer wheels are known to provide broader particle size distribution, but both methods allow for consistent distribution of particle size.