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 media; however, if the liquid is a flammable solvent, such as ethanol, or the product is oxygen sensitive 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 nozzles and single-fluid pressure swirl nozzles. Alternatively, for some applications two-fluid or Ultrasonic Nozzle are used. Depending on the process needs drop sizes from 10 to 500 micron can be achieve with the appropriate choices. The most common applications are in the 100 to 200 micron diameter range

A spray dryer is a drying equipment used in spray drying. It takes a liquid stream and separates the solute or suspension as a solid and the solvent into a vapor. The solid is usually collected in a drum or cyclone. The liquid input stream is sprayed through a nozzle into a hot vapor stream and vaporised. Solids form as moisture quickly leaves the droplets. A nozzle is usually used to make the droplets as small as possible, maximising heat transfer and the rate of water vaporisation. Droplet sizes can range from 20 μm to 180 μm depending on the nozzle.

Spray dryers can dry a product very quickly compared to other methods of drying. They also turn a solution, or slurry into a dried powder in a single step, which can be advantageous for profit maximization and process simplification.