Oil-free Air Compressors – the facts and fiction

Oil-free compressed air is a necessity in many industrial, food and medical applications. This is because even the slightest trace of oil could have a serious impact on the products and consequently, the health and safety of the end users.

With this in mind, oil-free compressors or activated carbon filtration solutions have been used to ensure that oil is eradiacated from the process. The up side is oil-free compressed air, but the down-side can be low efficiencies and high costs. However, there are other ways to get high quality, oil-free compressed air.

Let’s take a moment to look at the facts and the fiction surrounding oil-free compressed air and oil-free compressors:

Fiction: Oil-free compressors provide contaminant-free air
Although oil-free compressors do reduce the amount of oil that would need to traditionally be removed from compressed air, there are generally 10 contaminants found in a typical compressed air system. These contiminants have to be removed from the system after compression and include: oil vapour and dirt from the atmosphere, other oil vapour from the lubricated compressor, water vapour and condensed liquid water, microorganisms, oil and water aerosols, rust and pipescale.

Fiction: Oil-free compressors don’t need purification equipment
Compressed-air systems typically have purification equipment that uses a dual filter purification solution. These coalescing filters remove six of the ten contaminants (water and oil aerosols, microorganisms, atmospheric dirt, rust and pipescale). The first filter removes larger ‘bulk’, protecting the second higher-efficiency filter. Oil-free compressor installations tend to omit one of the coalescing filters but this can lead to poor air quality and higher operational costs as a result.

Fiction: Oil-free compressors don’t use oil
Oil-free compressors don’t use oil in the compression chamber, so that no oil comes into contact with the air being compressed there. However, oil is often used in the lubrication of the rest of the moving parts and cooling functions of the machine and complex sealings systems are used to ensure that oil does not enter the compression chamber from these other areas. If a failure in these systems occurs, or if the the compressor intake is located too near to the crank case breather, then oil aerosols and vapour can still be ingested into the compressed air system of an oil-free compressor.

Fiction: Oil-free compressors deliver compressed air to Class 0 specification
The International Standard for Compressed Air purity (ISO 8573-1) rates Class 0 as the most stringent air purity classification. Although many oil-free compressor manufacturers claim that their equipment delivers Class 0 air, the process of Class 0 compliance is more complex. To achieve Class 0 the equipment manufacturer and the user must agree contamination levels as part of a written specification and the air tested in-situ, as the level of contamination is dependent on what is drawn into the compressor intake from the surrounding atmosphere.

Fiction: Lower cost of ownership with an oil-free compressor
There is the argument that oil-free compressors reduce overall cost of ownership, as costly filters can be avoided and system pressure losses are lower, delivering a reduction in costs. However, no matter what compressed air system is chosen, the same level of purification equipment will be required to ensure that contaminants are removed. The cost savings achieved by a reduction in system pressure losses need to be weighed carefully against the initial higher purchase price of an oil-free compressor and its higher air end maintenance needs.

Fact: It is possible to have cost-effective oil-free compressed air without oil-free compressors
In the past, if oil-free air was required without the use of an oil-free compressor, then multi-stage filtration treatment of the compressed air from traditional compressors was needed. However, this resulted in additional energy and maintenance costs and the absence of a 100 percent safety guarantee. Now, thanks to BOGE’s bluekat screw compressor range, a significantly more efficient, cost-effective option is available for applications that want oil-free compressed air that can be Class 0 approved.

BOGE’s bluekat compressors:

  • The compressors are based on the highly efficient screw compressors of the S series and include traditional oil injection.
  • A converter is integrated directly after the compression stage. This serves to oxidise the oil contained in the compressed air, turning it into carbon dioxide and water.
  • The resultant purified air has no residual oil, or silica (important in paint spraying applications) and it is also bacteria free.
  • Even oil loaded intake air can be turned into oil-free compressed air, with a content of less than 0.01 mg/m3.
  • The BOGE bluekat series covers the 30 and 37 kW performance classes and produces 3.71 – 5.01 m3/min oil-free compressed air at 8, 10 or 13 bar. A variant with a frequency-controlled drive is also available.
  • An external range of converters is also available which can be fitted to any existing Oil Flooded Screw Compressor, with flow rates up to 32.4m3/min, providing the same benefits as the integrated version.

If you need oil-free compressed air, why not take a look at the facts and see the cost and performance benefits that BOGE’s BLUEKAT can offer, compared to oil-free compressors?

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