dust deposition

In many industrial processes, air is used as the working fluid and is
varied in composition and absorbs impurities, eg in the pneumatic
conveying of bulk material.

Many dusts are harmful, toxic or explosive and harm people and the
environment. If the air be conducted later in the process back into
the atmosphere, the dust impurities must be removed from the air.
Often used as working medium, another gas such as nitrogen. Even then,
the foreign substances are filtered to either the purified gas can be
traced back to the process or to gain valuable products back.