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Vacuum Freeze Drying

General Information
The Principles of Freeze-Drying
At atmospheric pressure (approx. 1,000 mbar) water can have three physical states
• Solid;
• Liquid;
• Gaseous.

Below the triple-point (for pure water: 6.1 mbar at 0°C),  only the solid and the gaseous states exist.

The principle of freeze/sublimation-drying is based on this physical fact. The ice in the product is directly converted into water vapor (without passing through the “fluid state”) if the ambient partial water vapor pressure is lower than the partial pressure of the ice at its relevant temperature. The freeze-drying process is divided into two different physical process steps. Step one is the freezing of the material below its solidification temperature and step two removes the ice or solvent crystals at very low temperatures.

Installation of an ALD industrial freeze-drying unit,

Continuous freeze-drying system with up
to 60 tons of fresh product per day per unit

The Freezing Process
The freezing process has a great influence on the quality of the finished product and the time that will be required to dry the material. For continuously operating freeze-drying installations with high throughputs the most familar freezing systems will be continuous blast air freezing belts. In addition, fluidised bed systems, freezing channels or chambers will be used.