The industrial process for converting a liquid solution or slurry into a dry powder is known as spray drying. A typical spray dryer operates by dispersing liquid feed in the form of a mist into a cylindrical chamber, where a stream of hot gas can dry the droplets in a split second. Although the vast majority of spray dryers are for pilot and process-scale production, the technique is also available for lab-scale applications.

The first stage of the spray drying process is called atomization. Atomization occurs when the liquid is fed into and sprayed through an atomization device, forming a vertical liquid jet due to gravity and other turbulent forces. When the liquid jet falls through space, the loss in surface tension causes it to lose its cylindrical shape and become a stream of droplets. To atomize the feed, lab-scale spray dryers generally use a pressure nozzle that forces the liquid through an orifice. However, two-fluid atomizers are sometimes used to mix the feed with a compressed gas, helping to produce very fine particles.

During the second stage of spray drying, the atomized droplets are brought into contact with a hot gas inside the chamber. There are different methods that can be used for this interaction, depending on the material and desired product. In co-current flow the material is sprayed in the same direction as the hot air, while in counter-current flow the material is sprayed in the opposite direction. The latter technique produces a very hot product and is therefore only suitable for thermally stable powders.

The third stage occurs as the droplets are exposed to the high-temperature gas, enabling the rapid evaporation of moisture at the particle’s surface. As the moisture vaporizes, the concentration of the solute inside the particle increases past its saturation point, resulting in the formation of a thin shell that encapsulates the surface. The evaporation also allows the size of the particles to diminish and their surfaces to cool. In the final stage, the product is separated from the drying medium at the base of the chamber using centrifugal force.

Spray drying is commonly used in the food industry, particularly to encapsulate ingredients such as flavors, oils, lipids and vitamins. In the pharmaceutical industry, it is an ideal technique for satisfying quality standards regarding particle-size distribution, morphology and density. The technology is also prevalent in chemicals, coatings, fragrances and cosmetics.

Lab spray dryers are generally made for R&D labs where they help guide method development for larger-scale applications. They have a sizable market in academia as well. One of the most commonly used suppliers of the technology is BÜCHI. Other suppliers include LabPlant, Yamato Scientific and European SprayDry Technologies. In 2015, the total market was less than $10 million, with the pharmaceutical and food industries providing a source of steady growth.

Laboratory Spray Dryers at a Glance:

Leading Suppliers

• BÜCHI Labortechnik
• Yamato Scientific
• LabPlant

Largest Markets

• Food Ingredients
• Pharmaceuticals
• Chemicals

Instrument Cost

• $6,000–$70,000