There are many drying methods, among them, freeze drying, vacuum drying and spray drying are the hot topics. This because of they have very similar applications field, but each of them have its advantages and disadvantages, we will list the differences between from some aspects.
Vacuum Drying Schematic Diagram
Spray Drying Schematic Diagram
Freeze Drying Schematic Diagram
Difference 1: Temperature.
The biggest difference between the 3 drying method is the temperature applied:
- Product temperatures in freeze drying are generally below 0C in primary drying and 30C during secondary drying stage.
- Vacuum drying temperature typically higher than 40C.
- Spray drying temperature have to be 80C or higher.
Difference 2: Raw Material Form
- Any form product can use freeze drying or vacuum drying, like liquid, paste, powder, irregular etc.
- Spray drying mostly use for turn liquid material to powder or granular.
Difference 3: Working Theory
- Freeze drying theory is sublimation. Works by freezing the product, then reduce the drying chamber pressure, enable ice direct sublimate to vapor. Water in product is removed from solid to vapor, no liquid phase involve.
- Vacuum drying method, raw product no need freezing. It works by reduce drying chamber pressure to enable the water boiling point reduce, when pressure drop to a certain level, the water start boiling and escape. Water is removed from liquid to vapor.
- Spray drying works by use hot gas impact raw material cause water quick vaporize.
Difference 4: Drying Time
- Freeze drying is batch production, drying cycle several hours to several days.
- Vacuum drying and spray drying is continuous.
Difference 5: Drying Cost
Freeze drying > Vacuum drying > Spray drying
Different 6: Drying Capacity
Freeze drying is batch production, so its capacity is small, vacuum drying and spray drying can continuously work, capacity is large.
Different 7: Dried Quality
Freeze drying has the highest dried quality, because most of its drying processes are finished below 0 degree.
Freeze dried product keep original shape and nutrition, vacuum drying a bit out of shape and nutrition loose.