Spray Drying

Spray drying is a method of forming a dry powder from a liquid or slurry by rapidly drying it with a hot gas, and is the preferred drying method for many thermally sensitive materials such as foods and pharmaceuticals or for materials that require an extremely consistent, fine particle size. Air is the most common heated drying medium, though nitrogen is used instead when the liquid is flammable, such as ethanol, or when the product is oxygen sensitive. A spray dryer disperses the liquid into a controlled droplet size using an atomizer or spray nozzle, most commonly a rotary disk or a single fluid high pressure swirl nozzle, producing drop sizes typically between ten and five hundred micrometers depending on the equipment and process requirements. Alternatives to spray drying include freeze drying, a more expensive batch process, drum drying, a less expensive continuous process for lower value products, and pulse combustion drying, a less expensive continuous process that can handle higher viscosities and solids loading.