Spray dryers are industrial drying systems that combine the processes of atomization and heating to dry a material. Atomization is the process by which a material is dispersed into extremely fine droplets. In spray drying, a material that is intended to be dried is mixed with a liquid and forced at high speeds into a chamber by a nozzle. Heat is then forced into the chamber, causing the liquid to evaporate and leaving behind fine solid particles.
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Applications of Spray Dryers
Food processing operations like milk drying make extensive use of spray drying procedures. Cereals, many kinds of coffee, teas, spices, egg-based foods, and flavorings are often subject to spray heating processes in advance of packaging and consumption. Spray drying is also used in the development of a wide variety of healthcare and pharmaceuticals-related products. Antibiotics production, for example, often involves spray drying processes. Many ingredients in industrial processes also must be spray dried. Ceramic materials, paint pigments, detergents, catalysts, salts, and a wide variety of other materials can be prepared by spray dryers.
Spray Dryer Design
The evaporation rate and the necessary size distribution of a product determine how much air is needed, which then affects the size and cost of most system components. As a result, these are the most important factors when designing a spray dryer.
Spray Drying Process
The spray drying process begins with collections of materials to be dried and a solvent, which is often water. When the solute and solvent are mixed, the sludge or slurry created by this mixing is spun centrifugally and then forced through an atomizing nozzle at high speeds. While suspended in the drying chamber into which the material has been injected, it is exposed to a heated gas. The solvent falls to the bottom of the chambers as the liquid solvent vaporizes. The dried materials are collected and prepared for the next phase of processing. Depending on the material being dried, spray dryers can use heated air or heated inert gasses. When combustible materials must be dried, gasses like nitrogen are used to minimize reaction risks.
Benefits of Using Spray Dryers
Spray drying is often used when the product must meet exact requirements in terms of particle size distribution, particle shape, bulk density, and residual moisture content. Advantages of spray drying over other industrial drying processes include particle size control, enhancing flow properties of dry solids, evaporative cooling, corrosion reduction, and short residence.