A spray drying apparatus is a method of producing a dry powder from a liquid or slurry by rapid drying with a hot gas. This is the preferred method of drying many heat sensitive materials such as foods and pharmaceuticals. A consistent particle size distribution is the reason for drying some industrial products such as catalysts. Air is a hot drying medium; however, if the liquid is a flammable solvent such as ethanol or the product is oxygen sensitive, then nitrogen is used.

Chinese medicine extract spray dryer

All spray drying equipment uses a type of atomizer or nozzle to disperse in a liquid or slurry to a controlled droplet size spray. The most common are rotating disks and single-fluid high-pressure vortex nozzles. Nebulizer wheels are known to provide a broad particle size distribution, but both methods allow particle size distribution to be consistent. Alternatively, for some applications two-fluid or ultrasonic nozzles are used. The droplet size from 10 to 500 microns can be achieved by appropriate selection, depending on the needs of the process. The most common application is in the diameter range of 100 to 200 microns. Dry powders are usually free flowing.

The most common spray drying equipment is called single effect because there is only one dry air at the top of the drying chamber. In most cases, air is blown into the liquid that is injected downstream. The powder obtained by this type of dryer is fine with a lot of dust and poor fluidity. In order to reduce dust and increase the fluidity of the powder, drying equipment manufacturers have a new generation of spray drying equipment called multi-effect spray drying equipment for more than 20 years. One at the top (according to the single effect) and one for the integrated static bed at the bottom of the chamber: instead of drying the liquid in one stage, the drying is carried out in two steps. The integration of this fluidized bed allows granules to be obtained by agglomerating fine particles in a humidified atmosphere inside the fluidized powder and having a medium particle diameter of 300 micrometers in a usual range of 100. Due to this large particle size, these powders are free flowing.

The spray drying apparatus is dried in such a way that the fines produced by the first stage of drying can be recovered in a continuous stream or at the top of the chamber (around the spray liquor) or at the bottom of the integrated fluidized bed. Drying of the powder can be accomplished by externally vibrating the fluidized bed. The hot dry gas can be passed in a direction that flows downstream or countercurrent to the atomizer. The co-flow causes the particles to have a system and a particle separator (usually a cyclone device) that works more efficiently within the lower residence time. The countercurrent method is capable of a larger residence time of the particles in the chamber and is usually associated with a fluidized bed system.