Food and drink processing: why take the risk?

Published:  08 July, 2011


Are food and drink manufacturers familiar with their industry’s Code of Practice and the ISO 8573-1 Standard? If so, why is it that some manufacturers are still risking oil contamination of their manufacturing processes by not using oil-free compressor technology?” Paul O’Neill, manager of Atlas Copco Compressors Oil-free Air division asks the question.


Compressed air users in the food and drinks industry are subject to the Code of Practice developed jointly by the British Retail Consortium and BCAS. The Code places the burden of responsibility for the provision of uncontaminated air in process operations fairly and squarely on the shoulders of the user who must ensure that their entire process, including compressed air, is free from contamination by dirt, water and oil.

The recent BSDA 2010 UK Soft Drinks Report indicates that the bottle and canned drinks industry is about to experience a boom in the UK and an important finding in the report indicates that there is an increasing demand from consumers to ensure that product claims are scientifically proven, honest, true and trustworthy. Obviously, that trust impinges fully on end-product quality. So, if food and drink manufacturers are familiar with their industry’s Code of Practice and the latest ISO 8573-1 Standard, why is it that some in the supply chain are still risking oil contamination of their manufacturing processes by not using oil-free compressor technology − equipment proven to meet the most stringent quality standards of process air?

Why are they taking the risk? Is it lack of knowledge? Lack of funds? Or lack of care and attention? Let us examine the facts about air supply contaminants and the factors that should be influencing the manufacturers’ choice of equipment.

Firstly, there is the need to recognise the problem of oil contaminants in pipelines where it can appear in three forms in the air stream, aerosols, vapours and wall flow. Coalescing filters will only partially remove aerosols and have no affect on vapours while wall flow, oil in liquid form that creeps along the pipe wall, either appears in the condensate or, more problematically, travels to the application process. It is important to note that oil can transform between these forms under different flow conditions so they all have to be eliminated at source to achieve 100% oil-free air.

There is also what I consider to be an erroneous and biased viewpoint, especially held by filtration specialists, that moisture in the system poses a greater contamination threat to air quality than residual oil. Not only is that a spurious argument but reputable compressor manufacturers include high efficiency dryers to eliminate that risk as an essential component of their systems. What’s more, problems with corrosion contaminants in pipework can be overcome by replacing iron or steel networks with anodised aluminium/polymer systems.

A word about air purity standards: The ISO 8573-1 (1991) edition of the standard established five air purity classes, 1-5, with Class 1 being the purest. But only aerosols and liquids were considered. Below 35°C vapours could be ignored. Higher levels of air purity are vital to critical applications such as pharmaceuticals, electronics and, above all, food processing. Consequently, the second edition of the standard, released in 2001,  included measurements of all three forms of contamination - aerosols, vapour and liquids and a higher class of air purity, Class 0. ISO 8573-1 Ed. 2 (2001) was revised in 2010 to reflect a changed dust content and gave rise to the current standard, ISO-8573-1 Ed. 3 (2010).

Some filter facts of life: Within industry there may be a lack of knowledge on the properties of coalescing and active carbon filters. A basic prefilter acting as a general purpose coalescing filter, will achieve particle removal down to 1 micron and removal of liquid water and maximum remaining aerosol oil content of 0.1mg/m³ (0.1 ppm) at 21°C (70ºF). Importantly, there is no vapour removal.

A high efficiency coalescing filter will achieve particle removal down to 0.01 micron and maximum remaining aerosol oil content of 0.01mg/m³ (approximated to 0.01 ppm) at 21°C (70ºF) but, once again, there is no vapour removal.

As with all filtration systems, there is always the possibility of by-pass contamination (where filters are removed from the system to defeat pressure drop) and subsequent risk to product quality. One important 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 and performance is often specified at 20°C. If the ambient temperature in a compressor room increases to 30°C, the compressor outlet temperature could easily be ten degrees greater, increasing the liquid oil carryover by a factor of 20 times the expected value.

High temperatures also shorten the lifetime of activated carbon filters – they are simply not usable at process temperatures above 40°C and remember, they work in a similar way to that of a sponge and water. An activated carbon filter in its non-saturated state absorbs the oil vapour like a sponge, but in just the same way, a fully saturated active carbon filter no longer absorbs oil vapour. So, how do you find out whether the active carbon is saturated?

There is another important area where urban or rather industrial myth and reality needs to be examined and that’s oil in the atmosphere. First the myth: there is a large amount of oil in atmospheric air, as much as 20mg/m3, especially where machining activity exists in the vicinity, and an oil-free compressor will aspirate this air and pass it on to the downstream process.

The reality? This is a claim that certain sales companies trying to push oil-injected solutions will present. There are several graphs in circulation that try to confuse potential oil-free compressor users. Make no mistake, these claims are absolutely baseless.

Tests carried out by the TÜV, the highly respected third party accreditation organisation, in the vicinity of heavy machining activity, vehicular traffic and a refuse incinerator, showed that the atmospheric oil content to be negligible: 0.003mg/m3. Further tests carried out in the same environment on the outlet oil content of a Z-series oil-free compressor showed zero oil.

Getting down to brass tacks, is the reluctance to adopt oil-free compressed air systems likely to be through lack of funds? Is oil-free air expensive?

Once again we have a wide divergence between myth and the well-established facts of the real situation. The myth implies that oil-free compressors are expensive. The reality is that the capital cost of an oil-free compressor may be greater than that of an oil-injected compressor and filters but the initial price differential is narrowed considerably when you consider the whole life cost.


But, the most important cost consideration of all, and this is why for critical applications oil-free is the only solution, is the possibility of production downtime, contaminated end product and the irrevocable damage to a company’s brand image and reputation.

The bottom line is simply – only totally oil-free compressors can deliver guaranteed 100% oil-free air. I can make this statement from a position of total impartiality as Atlas Copco Compressors offers both oil-free and oil-injected machines and filters. However, we want our customers to use the right equipment for the right applications and given the above evidence in the food and drink industry, depending on application, that equipment is oil-free.


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