Vacuum drying

The process of vacuum drying consists of removing the moisture contained in a substance using vacuum. Vacuum drying normally takes place in an enclosed vessel. The chamber must be heated to prevent a drop in temperature caused by evaporation.
A vacuum pump with a volume capable of removing evaporated moisture is used for the drying process. This enables uniform drying of porous or powdery products - both on the inside and on the outer surface.

Vacuum drying can be used, for example, to remove excess moisture from metals after an industrial cleaning process. And to thus prevent corrosion. It can also be used before transporting fresh fruit or vegetables. So that they arrive at their destination as fresh as possible.

A vacuum dryer is composed of a heating chamber containing the product to be dried, and a vacuum system. Optionally, condensers can help recover solvents. Filters protect the vacuum pumps and keep the products inside the chamber.

In the beginning of the drying process, the product is loaded into the chamber. Then, vacuum and heat are applied to reach the boiling point of the solvent. Once the required moisture content is achieved, the chamber is brought back to atmospheric pressure using either ambient air or nitrogen, in case the product to be dried is sensitive.

Vacuum is used to lower the evaporation point of the water or liquid to be removed during the drying process. Consequently, the required sensible heat is reduced and the product to be dried does not have to be heated as much as in conventional heat drying.
Moreover, the contact of the substance being dried with oxygen from the ambient air can be minimized applying vacuum. Therefore, the substance is not damaged during the drying process.

Vacuum drying is faster and gentler than heat drying. Applying vacuum means the boiling point of the water or liquid contained in the product can be reached at a lower temperature. The product to be dried can thus be better preserved. In vacuum drying, the evaporation enthalpy is nearly the same as in conventional drying, but vacuum might reduce the risk of explosion.

For example, when it comes to drying of hazardous powders or other sensitive substances. Moreover, vacuum drying is more energy-efficient as less sensible heat is required during the drying process.

Depending on the required operating pressure, several vacuum technologies can be used for drying purposes. In liquid ring vacuum pumps, vapors are condensed after being extracted from the chamber.

Dry screw vacuum pumps are also well suited for drying. Their ability to handle heavy vapor loads while recovering non-contaminated solvents at the exhaust is a real advantage.

Oil-lubricated rotary vane vacuum pumps can be used when solvents to be removed do not accumulate in the oil. In this case, they are a cost-effective and reliable solution.

Two-stage claw vacuum pumps might also be an option for vacuum drying processes.

When it comes to lighter applications, two-stage rotary vane vacuum pumps and scroll vacuum pumps can be the vacuum generators of choice.

DOLPHIN liquid ring vacuum pumps are the ideal choice for drying. R5 oil-lubricated rotary vane vacuum pumps can be used if the solvent to be removed accumulates in the oil. COBRA dry screw vacuum pumps are a viable solution for handling heavy vapor loads. For lighter applications, the oil-lubricated ZEBRA is well proven. FOSSA offers an excellent dry alternative.

FOSSA scroll vacuum pumps are, for example, used to dry the isolating gas SF6 in transformers.

COBRA dry screw vacuum pumps play a role in drying the transformers themselves.

Wood is dried using DOPHIN liquid ring vacuum pumps.

R5 and COBRA vacuum pumps are perfectly suited for drying drugs.

COMBI CMM, the combination of two MINK dry claw vacuum pumps, are used in industrial cleaning machines to dry the parts after cleaning.

The key aspects to consider when buying a vacuum drying solution are evacuation and drying time. But also, condenser efficiency, volume to be pumped and risk of solid carryover. The composition of the vapors to be extracted is important as it influences the operating pressure.

Vacuum can be used to dry foodstuffs in a particularly gentle way. By lowering the pressure, the boiling point of the water is reduced. This means that the foodstuffs do not have to be heated to high temperatures during the drying process. The products’ consistency, aroma, and nutritional value are therefore unaffected. In addition, the energy consumption is significantly lower compared to conventional heat drying.

Vacuum is used, for example, when drying lettuce or other vegetables after washing. It also plays a role in the processing of fruit slices sold as snacks.

Drying is one of the most common and important processes in the chemical and pharmaceutical industries. It consists of removing a solvent from a solution or a suspension to form a dry solid.

The water or liquid is removed by vaporization which normally requires heat.

Vacuum, however, allows to lower the evaporation point of the liquid. And to reduce the contact of the substance to be dried with oxygen from the ambient air. Therefore, the substances are not damaged during the drying process. Moreover, vacuum drying lowers the risk of explosion and allows for significant energy savings.

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Vacuum drying is commonly used in the plastics industry to remove moisture from plastic material. And thus preparing it for molding or extrusion.

Vacuum dryers allow to gently dry plastics at low temperatures,as the boiling point of water can be lowered by means of vacuum. This means that the material does not need to be heated up to high temperatures. Drying times can therefore be shortened which reduces the risk of material degradation. This would otherwise result from the materials being exposed to elevated temperatures over a long period of time.

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Vacuum drying is increasingly replacing the conventional drying of wood. Under vacuum, the boiling point of water is reduced which enables the drying of wood at lower temperatures.

This brings considerable advantages. The energy consumption can be significantly reduced. Drying times are shorter. And drying defects caused by heat can be avoided. The lack of oxygen during the drying process is another important benefit. It ensures that the wood retains its original color.

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