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Key points

  • Oil contamination poses a substantial risk to food and drink manufacturers
  • Because it can appear in three forms, oil must be eliminated at the source
  • Only compressors that are completely oil free can ensure pure air

Oil contamination poses a huge risk to compressed-air users but there is a solution, according to Paul O’Neill, manager of Atlas Copco Oil-Free air division.

Compressed air users in the food and drink industry are subject to the Code of Practice developed jointly by the British Retail Consortium and BCAS. The code places responsibility for the provision of uncontaminated air in process operations 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 and true.

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 processes by not using oil-free compressor technology?

First, 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 effect 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, meaning they all have to be eliminated at source to achieve 100 per cent oil-free air. There is also what I consider to be an erroneous and biased viewpoint 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.

Coalescing filters will only partially remove aerosols and have no effect on vapours or wall flow

Next, a word about air purity standards. The ISO 8573-1 (1991) edition of the standard established five air purity classes, 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. That’s why the latest ISO 8573-1 (2001) edition now includes measurements of all three forms of contamination aerosols, vapour and liquids and a higher class of air purity, Class 0.

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 pre-filter 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 (70°F). 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 0.01ppm) at 21°C (70ºF) but, once again, there is no vapour removal.

As with all filtration systems, there is always the possibility of bypass contamination (where filters are removed from the system to defeat pressure drop) and subsequent risk to product quality. Oil carryover through filter media increases exponentially according to the temperature at the filtration interface and if the ambient temperature in a compressor room increases to 30°C, the compressor outlet temperature could easily be 10° 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 work in a similar way to that of a sponge, so won’t absorb oil vapour when they are fully saturated.

There is another important area where 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 baseless.

Tests carried out by the TüV the Dutch third party accreditation organisation in the vicinity of heavy machining activity, vehicular traffic and a refuse incinerator, showed that the atmospheric oil content was 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.

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 divergence between the myth and the facts. 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 risk of production downtime, contaminated end product and the irrevocable damage to a company’s brand image and reputation.

The bottom line is that only totally oil-free compressors can deliver guaranteed 100 per cent oil-free air.

Dealing with the risk of oil contamination in the food and drink industry

Key points

  • Oil contamination poses a substantial risk to food and drink manufacturers
  • Because it can appear in three forms, oil must be eliminated at the source
  • Only compressors that are completely oil free can ensure pure air

Oil contamination poses a huge risk to compressed-air users but there is a solution, according to Paul O’Neill, manager of Atlas Copco Oil-Free air division.

Compressed air users in the food and drink industry are subject to the Code of Practice developed jointly by the British Retail Consortium and BCAS. The code places responsibility for the provision of uncontaminated air in process operations 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 and true.

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 processes by not using oil-free compressor technology?

First, 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 effect 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, meaning they all have to be eliminated at source to achieve 100 per cent oil-free air. There is also what I consider to be an erroneous and biased viewpoint 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.

Coalescing filters will only partially remove aerosols and have no effect on vapours or wall flow

Next, a word about air purity standards. The ISO 8573-1 (1991) edition of the standard established five air purity classes, 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. That’s why the latest ISO 8573-1 (2001) edition now includes measurements of all three forms of contamination aerosols, vapour and liquids and a higher class of air purity, Class 0.

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 pre-filter 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 (70°F). 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 0.01ppm) at 21°C (70ºF) but, once again, there is no vapour removal.

As with all filtration systems, there is always the possibility of bypass contamination (where filters are removed from the system to defeat pressure drop) and subsequent risk to product quality. Oil carryover through filter media increases exponentially according to the temperature at the filtration interface and if the ambient temperature in a compressor room increases to 30°C, the compressor outlet temperature could easily be 10° 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 work in a similar way to that of a sponge, so won’t absorb oil vapour when they are fully saturated.

There is another important area where 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 baseless.

Tests carried out by the TüV the Dutch third party accreditation organisation in the vicinity of heavy machining activity, vehicular traffic and a refuse incinerator, showed that the atmospheric oil content was 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.

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 divergence between the myth and the facts. 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 risk of production downtime, contaminated end product and the irrevocable damage to a company’s brand image and reputation.

The bottom line is that only totally oil-free compressors can deliver guaranteed 100 per cent oil-free air.

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