What Is a Spray Dryer?
A spray dryer is a device that enables drying by spraying a solution. The solution is atomized by spraying. The atomization of the solution into particles increases the surface area exposed to hot air compared to the solution as it is, leading to shorter drying times.
The short drying time reduces the effects of heat-induced denaturation. Another advantage of this process is that it requires fewer steps than conventional drying.
The particles produced are used in a wide range of fields, including foods, medical products, alloys, and fine ceramics.
Uses of Spray Dryers
Spray driers are used for a wide range of applications, but some of the most common are listed below.
- Food Products
Instant coffee is one of the most common uses. Instant coffee is dried so that it can be stored for a long time. Powdered coffee is produced by spraying coffee liquid in a spray dryer. It is characterized by its ability to dissolve quickly in cold water.
- Pharmaceuticals
In some cases, compounds that are candidates for new drugs are not developed because they do not dissolve well in water. Although they are soluble in organic solvents, most organic solvents are flammable, limiting their ability to be dried by heat. By using a spray dryer, even compounds that are insoluble in water can be made into drugs.
Principle of Spray Dryers
A spray dryer is roughly composed of a material tank, a blower, a drying chamber, and a filter.
The solution flows from the material tank and is supplied to the drying chamber. The solution in the drying chamber is turned into particles by hot air from the blower and spraying in the drying chamber. The particles produced are captured by the filter.
There are two methods of spraying in the drying chamber:
- Rotary Atomizer Method
Disks with holes are rotated, and the solution is scattered by centrifugal force to dry. Particle size can be adjusted by the shape of the disk and the number of revolutions.
- Nozzle Method
The solution is sprayed through a nozzle under pressure and dried by hot air. There are two types of nozzles: one fluid nozzles and two-fluid nozzles. One-fluid nozzles are used when the installation area of the equipment is not large enough to produce relatively large particles of 150 microns or more. The two-fluid nozzle can produce smaller particles than the rotary atomizer method. It can produce particles at lower pressures than one-fluid nozzles.