Why Class O matters
11 May 2009
Contamination by even trace quantities of oil within a purity-sensitive process air application can result in damaged batches of end-product, high rejection rates and returns, and production downtime and-clean up operations
Companies that risk contaminating their products in this way are likely to expose their businesses to product recalls, possible legal action and the negative consequences on their commercial reputation. Even food grade oil, which isn’t harmful if ingested in small quantities, can, if there is an oil separator failure, lead to product spoilage and unpleasant discolouration.
The ISO 8573-1 compressed air standard of 1991 was revised in 2001 to address the needs of applications where air purity is essential. The revision established a more comprehensive measuring methodology, including all three forms of oil contamination by air compressors – aerosols, vapour and liquid – to provide a true picture of air quality. To the existing purity classifications of 1-5, a new, more stringent class was added: ISO 8573-1 CLASS 0.
But despite compressed air users’ evident concern with safeguarding their processes, products or environmental standards, there remains divided opinion within the compressed air industry on the necessity for such stringent standards.
On one hand, food manufacturers are subject to a Code of Practice, developed jointly by the British Retail Consortium and the British Compressed Air Society. The Code places the burden of responsibility for the provision of uncontaminated air squarely on the shoulders of the manufacturer who must ensure air is free from contamination by dirt, water and oil.
The introduction of the Code of Practice has raised the debate of whether manufacturers can be confident that their choice of compressor system assures compliance with the Code – and whether that choice will guarantee freedom from contamination of their products.
But, in contrast, are the opinions of the compressor and filter manufacturers who only offer Class 1 rated units according to ISO 8573:1991. They state that Class 0 is no more stringent than Class 1 because it covers all values below 0.01 mg/m3, including zero and that focusing on air quality may disregard operational cost and therefore a balance must be struck when it comes to purity standards.
Because Atlas Copco Compressors offers both solutions − oil-free and oil-injected – it says it is positioned to provide the compressor solutions best suited for specific needs. It has always maintained oil-free compressors are the only solution for oil-free applications.
Compressor oil accounts for the majority of contamination in oil-injected compressor systems. When relying solely on filters and dryers to remove oil, there is exposure to contamination risks.
There are three key failure risks associated with oil-injected compressor systems: Temperature rise will increase oil carry over through the filters; higher temperatures also severely reduce the lifetime of activated carbon filters; and if filters become blocked because they’re not changed in a timely manner, the filter will be bypassed and oil will enter the process.
The dominant factor influencing the purity of filtration systems is ambient temperature. Oil carryover through filter media increases exponentially according to the temperature at the filtration interface.
Filter performance is often specified at 20ºC. If the ambient temperature in the compressor room increases to 30ºC, the compressor outlet temperature could easily be 10 degrees greater than that, increasing the oil carryover by a factor of 20 times the specified value.
A combination of oil removal systems – oil separator, oil removal filters and refrigeration dryer − are the stages responsible for meeting the air quality specifications. A failure of any of these elements would result in contamination of the outlet air and the operator’s process.
One oft-repeated claim against oil free compressors is usually to label them as expensive. However, Atlas Copco’s oil-free technology reduces expenditure in five ways: by avoiding filter replacements, eliminating the costs of lubricants, cutting maintenance costs and that of treating oil-laden condensate, and importantly, avoiding the costs of extra energy needed to combat filter-induced pressure drop.
These costs may not be apparent at the time of purchase but ultimately contribute substantially to the total cost of ownership. What’s more, they eliminate the risk of contaminated end product, production downtime and, above all, a damaged reputation.
John Forman is communications manager, Atlas Copco Compressors
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