Vacuum drying technology is used for processes which require low temperatures and/or low oxygen environment for moisture/solvent removal. The drying process takes place in a reduced pressure environment. The process can be either batch or continuous depending on the processing requirements and budget.
The principle behind this technology is based on a property of liquids. The boiling temperature of a liquid reduces in relation to pressure exerted on the liquid. For example, water boils at 100oC at 101.13 kPa, equivalent to sea level conditions. At a barometric pressure of 85 kPa, water will boil at approximately 95oC, therein the principle of vacuum drying. By reducing the pressure exerted on a product the temperature at which the moisture will evaporate is reduced. The introduction of a low-temperature input will aid in the moisture removal without exposing the final product to excessive heat. Vacuum drying processes can range from 0.1 mbar absolute to slightly below atmospheric conditions, however, the value in vacuum drying is realised in the use of low absolute pressures, typically between 0.1 mbar to 25 mbar absolute.
Various types of vacuum pumps can be used such as steam jet ejectors or liquid ring pumps. Energy can be added to the process through thermic oil, steam or electrical heating systems.
Condensers are used to extract the moisture/solvent from the exhaust stream of the drying process. Various configurations are possible.