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Glossary Compressed Air Treatment

Adsorption dryer

In adsorption dryers, the compressed air flows through a vessel filled with porous granulated material which acts as a desiccant. This absorbs moisture from the air and dries the compressed air.  Adsorption dryers dehumidify the air and absorb moisture from the compressed air in the form of water vapour.
BOGE heatless adsorption dryers are suitable for applications requiring compressed air with a pressure dew point of less than +3 °C.  They are able to achieve dew points of up to -70 °C, which prevents condensation even in outdoor pipework. Pressure dew points of up to -40 °C can be achieved with the standard model. Adsorption dryers are CFC-free and  therefore environmentally-friendly.



Catalytic converter

Converters are integrated directly after the compression stage in oil lubricated standard compressors, to generate oil-free compressed air. Directly after the compressor, the oil-laden compressed air is passed through the converter, where long-chain hydrocarbons are broken down until only carbon dioxide and water remain.  The catalyst itself is not chemically consumed in the process. The result is oil-free compressed air as well as the complete elimination of oil from the condensate. Expensive condensate treatment and disposal can be dispensed with. Condensate which forms after the converter is now oil-free.



Compressed air filter

Basic pre-filters filter solid impurities to a particle size of approx.3 μm out of the compressed air but filter out very little oil and moisture.  Compressed air filters used as pre-filters take the load off high performance filters and dryers when the air is very dusty. Finer filters can be dispensed with if the demands on the quality of the compressed air are low.

Compressed air pre-filters operate according to the principle of superficial filtration. They have a purely sifting effect. The pore size indicates the size of particle that can just about be filtered out. The impurities remain only on the outer surface of the filter elements. Other types of compressed air filters are microfilters, activated carbon filters, activated carbon adsorbers and sterile filters, each with their specific way of working, which can be used depending on the requirements placed on the compressed air quality.



Compressed air receiver

Compressed air receivers are an important part of every compressed air system. Compressed air receivers of an adequate size act as a buffer between compressed air generators and consumers, and ensure that compressor stations operate efficiently at a consistent working pressure. The size of the compressed air receiver is determined by the free air delivery of the compressor, the control system, and compressed air consumption.

Compressed air receivers are coated with anti-corrosive paint or are galvanised.  They are available in horizontal or vertical versions in sizes of 50 to 10,000 litres. BOGE compressed air receivers meet strict design and manufacturing standards, and intervals between inspections can be maximised as a result.

Compressed air receivers are subject to the German Pressure Vessel Regulations (DruckbehV) for pressure vessels, pressurised gas containers and filling systems, the Technical Rules for Pressure Vessels (TRB) and DIN EN standards. The accident prevention regulations (UVV) are mandatory and must always be complied with. Operators of compressed air receivers are legally obliged to keep themselves informed about the latest accident prevention regulations at all times.



Compressed air treatment

Modern production equipment needs reliable compressed air treatment. Applications differ widely and range from untreated blowing air to absolutely dry, oil-free and sterile compressed air.

Impurities in our atmosphere are usually invisible to the naked eye. But they can seriously impede the reliable operation of a compressed air network and consumer devices, and have an adverse effect on the quality of products.

Impurities include particles of dirt, moisture, mineral oil aerosols, unburned hydrocarbons and traces of heavy metals such as lead, cadmium, mercury and iron. Compressors draw in ambient air, including the impurities contained in the air, and concentrate them many times. Lubrication oil and wear debris also pass from the compressor into the compressed air.


The correct treatment of compressed air in several steps, through pre-filters, microfilters and activated carbon, brings benefits:


  • increased service life of downstream compressed air consumer devices
  • improved and consistent product quality
  • compressed air lines free of condensate and rust
  • fewer malfunctions
  • pipelines without condensate collectors
  • lower servicing outlay
  • lower pressure loss from leakage and flow resistance
  • lower energy consumption due to lower pressure loss




Condensate disposal for compressors

Condensate consists primarily of the water in the compressor intake air, which precipitates during compression.  Condensate to be disposed of may contain the following impurities:

  • mineral oil aerosols and unburned hydrocarbons from the intake air
  • particles of dust and dirt of the most varied kinds from the intake air
  • cooling and lubricating oil from the  compressor
  • rust, wear debris, pieces of sealing material and weld from the pipeline


Condensate is highly contaminated because of its high content of harmful substances, and for this reason it must be disposed of responsibly. Condensate disposal must take into account that the mineral oils in the condensate are hard to biodegrade. The consistency of the condensates also changes with the marginal conditions. Most condensates are as fluid as water. But pasteous condensates can occur in exceptional cases.

Distinctions must be made between condensate from different compressed air systems. The properties of the condensate to be disposed of can vary.


  • oil lubricated compressor systems: In compressors of this type, the oil  in the compression chamber flushes part of the aggressive and solid matter out of the compressed air. The result of this is that oil lubricated systems normally produce condensate that has a pH-value in the neutral range.
  • oil-free compressor systems: Most of the harmful substances in oil-free systems are discharged with the condensate. This is why the condensate has an acidic pH-value. pH-values between 4 and 5 are not uncommon.



Condensate technology

Compression causes the moisture in the air to form droplets of water, or condensate. This water is usually drawn into the compressed air receiver with the volume flow.  This is where the compressed air is stored.  Heat is given off to the cooler surroundings by the large surface of the receiver, and the compressed air cools down.  This causes a large part of the condensate to precipitate on the walls of the receiver. The condensate collects on the floor of the receiver and is removed by a suitable condensate separator.

Compressed air receivers that are only emptied at irregular intervals can be corroded by the condensate. One way of protecting receivers against corrosion is to galvanise the receiver in a dip-tank. It is not absolutely essential to galvanise the receiver if the condensate is drained regularly. Galvanising is also a useful option if the condensate contains a high concentration of aggressive components.



Refrigerant compressed air dryer

Compressed air dryers are devices for removing moisture from compressed air generated by a compressor. The air taken in by the compressor is a mixture of gases which generally contains water vapour. The capacity of the air to absorb water varies and depends mainly on the temperature. If the temperature of the air rises, as is the case when air is compacted in the compressor, its capacity to absorb water vapour also increases. This makes it necessary to remove the water from the compressed air.

Compressed air dryers often work on the heat exchange principle. Every refrigerant compressed air dryer has an air-to-air and an air-to-refrigerant heat exchanger. The hot compressed air from the compressor initially flows into the air-to-air heat exchanger. There, it is cooled down by the already treated cold compressed air according to the counter flow principle. At the same time, it heats up the already treated compressed air.

The compressed air then flows into the air-to-refrigerant heat exchanger. This consists of two separate pipelines designed on the counter flow principle. Hot compressed air flows in one pipeline, and in the other a gaseous refrigerant which absorbs the thermal energy from the compressed air. The compressed air is cooled down in this way and loses its ability to absorb water. The resulting condensate is separated from the compressed air in a water separator. It is then discharged from the system in a condensate separator.