Vacuum

The term ‘vacuum’ comes from Latin and means “empty” or ‘free of content’. The phenomenon of vacuum is of great importance in process engineering. Different vacuum classes are required depending on the application. The rough vacuum ranges from 900 mbar to 1 mbar absolute, the fine vacuum from 1 mbar to 10⁻³ mbar and the high or ultra-high vacuum from less than 10⁻³ mbar. The fine vacuum ranges from 1 mbar to 10⁻³ mbar. High or ultra-high vacuum refers to absolute pressures of less than 10⁻³ mbar.

In powder mixing technology, a rough vacuum is usually sufficient. Higher vacuum classes are technically more complex and more expensive to produce.

Vacuum technology enables gentle drying of powders. It offers major advantages, particularly for pharmaceutical agents and foodstuffs. Vacuum lowers the boiling point. This allows a large amount of liquid to be evaporated at low temperatures. Low process temperatures are desirable when powdery agents are temperature-sensitive. The vacuum mixing dryers from amixon® are operated at absolute pressures between 10 and 100 mbar.

Vacuum also plays a role in inerting. In the amixon® mixer, the ambient air is first extracted. A protective gas mixture, for example nitrogen and carbon dioxide, is then fed in. This prevents oxidative ageing. The products thus remain stable for longer. The powder is then packaged under a protective atmosphere.

Many vacuum conveying systems operate at pressures between 300 and 600 mbar absolute. The negative pressure generated is sufficient for short to medium conveying distances.

Such a system can also be used as a vacuum cleaner, for example to clean a mixer manually.

However, generating vacuum with vacuum pumps incurs energy and investment costs. The deeper the vacuum, the higher the cost. In practice, various vacuum pumps are used, such as rotary vane pumps, reciprocating piston pumps, screw pumps or liquid ring pumps. The choice of pump depends on the desired final pressure, the gas load and the process duration.