Compressed air is energy in the form of compressed ambient air. Compressed air is permanently trying to expand back to atmospheric pressure and thus performs work during the expansion process. Besides electrical energy compressed air is one of the most important forms of power for industrial production processes and is widely used thanks to numerous advantages:
► Can be produced locally and on demand
► Can be stored easily and without losses
► Can be transported easily
► High amount of energy per volume
► Can be easily converted to other forms of energy in a space-saving way, e.g.
• blast air (compressed air gun or nozzle)
• fast linear movement with increased force (compressed air cylinder)
• rotary movement with increased torque (compressed air motor)
• etc.
► Versatile applications
The compressed air contains contaminations and moisture from the ambient air which are concentrated depending on the operating pressure. Oil-lubricated compressors add amounts of oil to the compressed air (residual oil). When the compressed and hot air is cooled down to an appropriate operating temperature, larger amounts of water condense (condensate). Untreated contamination in the compressed air would contaminate and damage the compressed air system, the compressed air consumers and the products that come into contact with the compressed air.
Compressed air treatment removes the unwanted contamination and provides the purity of the compressed air required for the application, e.g. standard instrument air, technically oil-free compressed air, sterile ultra-pure air or medical breathing air. Many industries have a specific air quality requirement governed by best practice or legislation.
The aim of compressed air treatment is to ensure a continuous and trouble-free operation of applications that use compressed air, to minimize downtimes, unscheduled maintenance and repair work, and to remove specific contamination that may be harmful to the product.
And, most of all, compressed air treatment actively contributes to environmental protection as well as occupational health and safety. Liquid oil droplets, finest oil mist, oil contaminated solid particles and gaseous, foul-smelling oil vapor, i.e. contamination which occurs on site during compressed air production, can be eliminated completely and thus do not contaminate the local environment.
The compressed air treatment system comprises several consecutive treatment components, referred to as treatment chain, which treat the compressed air in stages in order to achieve the required purity.
Compressed air cooling occurs in every compressed air system. Mostly, an after-cooler is already integrated in the compressor unit as discharge temperatures without after-cooling can range from approx. 70°C up to 120°C. Cooling creates large amounts of condensate, which must be discharged from the compressed air system directly after the compressed air cooler. However, where there is no compressed air after-cooler on the compressor or the existing cooling is insufficient for downstream treatment processes requiring lower compressed air temperatures, an additional compressed air cooler is required to produce a suitable application temperature (approx. 25°C to 35°C).
For further information see Cooling
Compressed air drying is the most elementary key component of compressed air treatment. The important task of compressed air drying is to reduce the amount of moisture contained in the compressed air down to a defined residual value. At the outlet of the compressor there is, compared to the sum of all other contaminants, 1000-times more moisture – 100% saturated – which means even the slightest temperature reduction of the compressed air on its way to the application causes a condensation of liquid water, forming condensate within the compressed air.
Compressed air dryers eliminate the moisture and thus produce dry, non-saturated compressed air where no further condensation can occur – either within the compressed air system or at the point of use.
Note
Both, cooler and dryer reduce the amount of moisture within the compressed air. While coolers deliver compressed air, which is still 100% saturated with moisture, dryers produce non-saturated compressed air. Coolers are therefore used for pure temperature reduction, while dryers are used for a real compressed air drying process by bringing down the moisture to a defined pressure dew-point and thus ensure that no further condensation can occur.
Note
Non-saturated, dry compressed air is able to pick up moisture again. Therefore, "wet" sections of a compressed air system can be dried subsequently with dry compressed air. It takes a while – but it works!
For further information see Drying
Compressed air filtration is an elementary component for compressed air treatment and is present more than once in the treatment chain.
Compressed air filters remove all types of solid and liquid contaminants from the compressed air in stages, i.e. large amounts of condensate and coarse contamination particles such as rust, abrasion particles, oil droplets and dust are filtered in the first stages and then fine oil mist and fine dust particles are filtered in subsequent stages. Compressed air filters containing activated carbon also remove foul-smelling odors and oil vapor. Specific compressed air filters even remove viruses and germs and thus produce sterile compressed air.
For further information see Filtration
Condensate technology is applied to almost every component of the compressed air treatment chain.
It is divided in condensate discharge and condensate treatment. During the condensate discharge process large amounts of liquid, generated by means of condensation or specific separation, are being removed from the compressed air system. As a result, a carryover of liquid contaminations throughout the compressed air system can be avoided. The condensate treatment process is used to clean the condensate from dirt, oil and hydrocarbon.
The condensate may then enter the sewage system or a river, lake or similar waters in an ecologically compatible way.
For further information see Condensate technology