The myths around food-grade compressed air

A common misconception in the food industry is that to have oil-free compressed air you need an oil-free compressor.

“Not so,” according to Martin Curd, sales manager at Southern Cross Compressors Australia. Contaminants in compressed air (dirt, water and oil) come from many sources including ambient air, compressor lubricants and contaminants in the air reticulation system. A common misconception is that by installing an oil-free compressor there is no need for downstream filtration.

In an oil-free compressor, the term ‘oil-free’ refers to the fact that there is no oil in the compression process and therefore does not come into contact with the air being compressed. However, even with an oil-free compressor, filtration is still required to remove dirt, condensate and oil vapour drawn into the compressor intake as well as contaminants in the reticulation system.

Oil is always the biggest concern, explained Martin; and the international minimum quality standard for compressed air used in contact with food, ISO 8573 (2010), allows for a maximum residual oil content of 0.01 mg/m³ and a maximum particulate size of 0.1 micron (reference conditions 1 bar.a and temperature 20°C).

To put that into perspective, normal atmospheric air contains between 0.05 to 0.5 mg /m³. Therefore, regardless of what type of compressor is used, filtration is always required to get to the required air quality.

Oil is injected into the compression space for three reasons:

• To seal the clearances between the rotors and casing.
• To lubricate the bearings.
• Principally to remove the heat of compression.

Without this positive cooling, temperatures reached in non-lubricated compressors are extremely high and can significantly impact compressor life.

When an oil-lubricated compressor is used with coalescing and carbon filtration, maximum oil content requirements drop to 0.003 mg /m³ (three times lower than class 1 or classified as class 0).

Using high-quality coalescing and carbon filtration backed up by the use of a residual oil sensor to monitor compressed air and log (record) the hydrocarbon levels, this level of air quality can be achieved and sustained; however, at significantly lower capital and running costs compared to a non-lubricated compressor.

Combine this with the use of STELLA Food Grade Synthetic PAO Compressor Lubricant which is food-safe, non-toxic and developed for rotary compressors used in the food, drink and pharmaceutical processing and packaging industries and all of the NSF H1\Food Grade\Food Safe requirements for the use in HACCP Certified Food and Packaging Manufacturing Plants are met.

  

Southern Cross KHE rotary screw compressors.

Southern Cross Compressors can offer effectively ‘oil-free’ compressed air at a much lower investment cost, with a much longer life span and a significant reduction in power consumption and service costs.