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Beko discusses the process of producing oil-free compressed air using continuous monitoring.

In daily use, there is usually considerable insecurity about the constant, reliable quality of process oil-free compressed air.

Even oil-free compressors are not a 100 per cent guarantee.

In addition, the treatment downstream of the compressor is not always able to reduce the residual oil content in the system to the required degree.

Finally, continuous monitoring is extremely difficult.

Most companies using oil-free compressed air do not know how contaminant free it really is; in terms of process safety, they ’fly blind’.

This applies, above all, to highly sensitive applications where compressed air with a far lower residual oil content than specified for ISO 8573 (Class 1) for technically oil-free compressed air is required, for example in medical technology, pharmaceutics, surface technology and food processing.

A general difficulty can develop into a real problem: the continuous monitoring and measurement of the (hopefully) extremely low residual oil content in the compressed air.

After all, this involves values in the order of 0.003mg oil introduction or less in 1m3 of compressed air.

The ISO 8573-1 (Class 1) standard defines the oil content, including the oil vapour, of a maximum of 0.01mg/m compressed air.

This corresponds to approximately four hundredths of what is contained in atmospheric air.

This amount is already so small that it can only be guaranteed with multi-stage downstream treatment.

In German production and processing plants alone, damage running into millions of Euros occurs annually as a result of contaminated compressed air.

Subsequent to expansion of the compressed air during the application, the oil fractions in it settle on surfaces, for example, and cause an oil film that affects the adhesion of paints or complicated bonds.

In most cases, the problem is focused on residual aerosols and oil vapours.

These may, among others, impair sensitive tool parts at the point of consumption, wash out basic lubrications on components or contaminate end products.

In many cases, oil mists also contain harmful nitrosamines.

A fraction of 0.3mg of oil per metre in breathing air is perceived as an odour.

As such, oil free does not necessarily mean oil free.

Even downstream of dry-running screw and piston compressors, in which the real compression process takes place without oil as a lubricant, sealant and coolant, clean compressed air in the sense of absolutely oil-free compressed air cannot be expected.

The danger lies in the raw material: the induced air.

With the intake air, hydrocarbons enter the compression process, in particular when the air is taken directly from the environment and not from an especially protected compressor room.

Solvents such as acetone, aromatic hydrocarbons such as benzene, toluene or xylene and polycyclic aromatic hydrocarbons such as naphthalene contaminate the compressed air.

In addition, there are fuel residues in the ambient air, namely hydrocarbons such as gas oils, petrol or kerosene.

It also contains all components of normal ambient air in a compressed form: dusts, dirt particles, particulate matter, moisture and germs.

To aggravate the situation, some contaminants even affect each other, thus forming further risk factors.

For example, water forms an emulsion when combined with oil, and dust can aggregate with oil or water and form larger dirt particles.

In this respect, it should be noted that compression to an operating pressure of 8bar(g), for example, means nine times the concentration of the ambient air components.

Even when placing an oil-free compressor in an area that has been carefully shielded against environmental effects and provided with filtered ambient air, the user is not necessarily safe.

Oil vapours can also reach the outside through the compressor-internal gearbox-casing ventilation.

In large compressors, this is an almost continuously occurring effect.

This means that even the best oil-free compressor in the ideal location needs support.

In most plants, this is implemented by means of drying equipment with simultaneous oil separation and by oil separation filters – often employed as a combination.

However, such components downstream of a compressor are not always in a position to limit the residual oil content in the system to the range required for demanding applications because the factors exerting an influence on filtration and adsorption in a compressed-air plant are too extensive.

This starts with the hydrocarbon molecules, which are modified by shearing and heat input in the compressor.

The aerosol state downstream of a screw compressor is smaller than downstream of a piston compressor.

Other influential factors are the operation mode of the plant, the frequency control, the cooling and the design of the oil separators.

A continuous up and down during the compressor operation leads to huge stress on the oil separator, while frequency-controlled compressors cause a varying oil introduction that is higher in the lower-speed range than during full-load operation.

High-quality activated carbon filters are ideal for compressed-air processing, but they also require the plant operator’s attention.

For these filters, regular maintenance and replacement in time are vital requirements for safe and reliable operation.

This is not always easy because the influences affecting the filters often escape the plant operator’s control.

The flow rate, the temperature and the moisture, for example, affect the adsorption capacity of the filters.

In the event that an increased oil introduction into the compressed air takes place, the operator rarely has the time to react to the oil penetration with the disconnection of the plant.

Even after a pre-alarm, he or she only has a few minutes to prevent the worst case: the emergence of oil-containing compressed air at the points of consumption.

According to example calculations from Beko Technologies, this occurs in less than five minutes in a compressed-air plant that is operated with a flow rate of 7m/s and that has a pipework length of 2,000m.

The cost-intensive consequences include contaminated products, machine and process failures, production stoppages and even health problems for the employees.

Until recently, no particularly reliable technical solution was available for the processing of constantly oil-free compressed air, not to mention the possibility of continuous residual oil content monitoring via measurement and control.

This has changed thanks to the introduction of a solution for compressed-air processing: the catalysis method.

Bekokat, a catalytic converter developed by Beko Technologies, offers compressed-air purity that, with a residual oil content of 0.003mg/m3 of compressed air, exceeds the requirements of ISO 8573-1 for the technically oil-free compressed air of Class 1.

Combined with the Metpoint OCV measuring system for the detection of hydrocarbon vapours, Bekokat represents a dual strategy for high process safety during the processing of oil-free compressed air.

The Bekokat method enables oil-free compressed air via a different technological approach than previous solutions: via catalysis.

This method realises the total oxidation of hydrocarbons – in a concentrated, comprehensive process step subsequent to compression.

The complete removal of oil from compressed air thus takes place in one single plant component.

This component functions independently of the ambient conditions, the oil input concentration and the relative humidity of the compressed air.

Bekokat tackles the lubricants and oils in the compressed air supplied by the compressor.

Subsequent to the compression stage, these exist in the form of gas, vapour or aerosol.

Through the employment of the Bekokat, such air components are fully converted into CO2 and water.

Even the condensate accumulating during the cooling down of the compressed air is oil free thanks to the catalysis method and can also flow directly into the sewerage system without being processed.

In the Bekokat, granular material serves as the catalytic converter, which is heated up to an operating temperature of approximately 150C by means of heating elements.

In the catalytic converter, the oil molecules are broken down until only one carbon atom remains.

In the final catalysis phase, the oil molecules are oxidised down to water and CO2.

It is essential that the hydrocarbon chains (the oil molecules) can be ’cracked’ at any point.

They are continuously broken down until only CO2 and hydrogen remain.

Therefore, the Bekokat system can deal with hydrocarbon chains from oil-free and oil-lubricated compressors varying in length.

It is not always well known that activated carbon filters are not able to adsorb polar compounds such as alkenes, alcohols, glycols or ketones.

In contrast, the Bekokat system also does a good job as far as these substances are concerned and completely removes them from the compressed air.

This is generally independent of the inlet conditions.

Further on in the process, the purified compressed air is cooled down in a heat exchanger to approximately 10-15C above the inlet temperature and is available for the respective application.

The long service life of the special granular material of the Bekokat is also beneficial as far as profitability is concerned; it only needs to be replaced after 20,000 operating hours.

In contrast, the life of an activated carbon filter is already depleted after approximately 500 operating hours, even under ideal operating conditions.

With the Bekokat method, it is possible to constantly achieve oil-free compressed air with a residual oil content of 0.003mg/m3 of compressed air, delivering the level of quality required in the demanding fields of medicine and pharmaceutics, food processing and packaging and surface technology.

In these fields, there has been a lack of safe processing as well as a lack of uninterrupted, continuous measurement and monitoring of the oil-free compressed air.

It is possible to determine the residual oil content in compressed air via multiple regular laboratory investigations, but in most cases the respective results are only available after several days or weeks.

This is too late to react quickly and in an effective manner to any quality problems caused by oil-contaminated compressed air – as is substantiated by the previous calculation example by Beko: less than five minutes for an emergency shutdown subsequent to an ’oil accident’ in the system.

Here, the operator should not follow the ostrich (head-in-the-sand) method for lack of monitoring possibilities.

In highly sensitive applications, this is intolerable and, with the establishment of stricter international quality assurance methods, this also becomes riskier with regards to legal aspects.

Therefore, a technology allowing the stationary online measurement and monitoring of the vaporous residual oil content of the compressed air – without requiring any time-consuming laboratory investigations – has been needed.

Beko’s Metpoint OCV monitors the residual oil amount in the compressed-air flow online down to the range of a thousandth of a milligram per cubic metre.

Even extreme limit values of 0.001mg/m residual oil content can be continuously monitored online during running operation.

This system has been certified by TUV Nord in accordance with the requirements of ISO 8573-1 (Classes 1-4).

As the Metpoint OCV is able to continuously monitor the residual oil content of the compressed air, complicated samplings and time-consuming laboratory evaluations are no longer required.

The partial volume flow taken from the flowing compressed air is supplied via a rising main to a separate sensor unit, in which the hydrocarbon vapour content is measured by means of a photo-ionisation detector (PID).

The dimensioning of this sampling and the measuring section correspond to the stipulations of ISO 8573.

The electrical signal resulting from the PID measurement is amplified and electronically evaluated.

Subsequently, the results are indicated on a touch-screen display and simultaneously stored in the internal memory.

With a capacity of 2Gb, the memory is able to record up to 10 years of detected values.

The acquired data can be used for both the documentation of the compressed-air quality and the identification of contamination sources.

In the event that the recorded oil-vapour values in the monitored compressed air exceed the tolerance limits, the system will automatically trigger an alarm.

In this way, inadmissible concentrations of residual oil are detected and indicated in time to prevent a large number of possible problems, such as the contamination of pipe work and products, damage to machines and plants and high costs for rejects or repair.

The new measurement technology is said to be future proof thanks to its networking ability.

It allows a smooth and effective IT connection of the devices and thus integration into the existing IT infrastructure of the plant operator.

If a bypass is available, the Metpoint OCV can be serviced and calibrated on location without requiring the pressure in the system to be reduced or the plant to be completely closed down.

Documentation in the event of maintenance or calibration measures is via an electric signature of the person in charge.

With the catalytic total oxidation of hydrocarbons according to the Bekokat method and with the continuous online oil vapour monitoring with the Metpoint OCV measuring system, the quality in compressed-air processing reaches a high level.

When combined, these two systems become a dual strategy implementing excellent process safety and quality assurance.

Beko Technologies

Beko develops, manufactures and sells components and systems worldwide for an optimised compressed air quality.

Beko develops, manufactures and sells components and systems worldwide for an optimised compressed air quality.

Beko stands for compressed air technology at its best. For more than two decades, Beko has developed, manufactured and sold high-quality, reliable and efficient components and systems for compressed air processing and condensate technology. Now, Beko offers a complete program for all tasks related to the transport and processing of compressed air. Expert advice and a qualified service are a trademark of the company.

Only a complete understanding of the business leads to success. Therefore, Beko always focuses on the customer and on their unique demands. The Beko consultants and development engineers are trained in the latest developments in order to implement futureproof solutions for our clients. Operational reliability, energy conservation, environmental friendliness and a contribution to decent working conditions constitute important focal points of the Beko philosophy.

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