Have you ever wondered how you could get powders of food items such as milk, fruit juices, etc? You can get almost anything, from mimosa extracts to penicillin to egg yolk to fertilizers in the powdery form. Spray drying technology is the answer.
Spray drying is the process of transforming fluid into dry matter (or particulate) by spraying the fluid into a hot dry medium such as hot gas. The process involves three basic steps:
- An atomizer breaks the fluid into droplets of the right size (neither too large, nor too small) and disperses them into the drying medium. You could have either rotary atomizers, pressure nozzle atomizers, or two-fluid nozzle atomizers.
- The dispersed droplets mix with the hot dry gas. An air disperser disperses hot gas in the drying chamber. Within seconds the droplets become dry.
- The Powder is Separated and Collected. The drying chambers have cone bottoms to separate the powder. The air goes through a side outlet. Finer separation is achieved through high efficiency cyclones and fabric filters.
The spray-drying systems are divided based on :
- On the Basis of Air Flow
- Co-current. The droplet spray and the dry air both pass through drying chamber in same direction.
- Counter current. Spray and air are introduced at opposite ends of the chamber.
- Mixed. Both current flows are combined.
- From Where Air/Gas is taken.
- Open cycle. Which takes atmospheric air
- Closed cycle. Which uses air or nitrogen and recycle it
- Semi Closed. The air required for combustion is taken from outside. The products of combustion are recycled.
- On the number of Stages
- Single Stage. The drying is done in one stage.
- Two Stage. Drying is done in two stages.
- On Basis of Position
- Vertical dryer
- Horizontal Dryer
The main benefits include:
- The flexibility it allows with respect to the end product; the size, from minute particles to bigger particles suitable for oral intake; and the form, crystalline or amorphous.
- Can be designed to different capacities.
You could take pharmaceutical industry, food industry, fertilizer and pesticide industry; the applications of spray drying are countless.
While the bulk of spray drying systems is a disadvantage, the advantages are many more than the cons; which is why spray drying is so widely used.