Over the past sixty years, Atlas Copco has pioneered the development of oil-free air technology, resulting in a range of oil-free air compressors to suit applications that refuse to compromise when it comes to 100% oil-free clean air.
After being involved with compressors for the better part of a century, in 1967 Atlas Copco introduced oil-free compressors, and has recently achieved a new milestone, setting the standard for air purity as the first manufacturer to be awarded ISO 8573-1 CLASS 0 certification.
In 2001 the ISO 8573-1 compressed air standard was revised in order to address the needs of critical applications where pure air was essential. Industries such as pharmaceuticals, food and beverages, electronics and textiles had to exclude any risk of contamination and the severe consequences that could follow, such as spoiled or unsafe products, production downtime and damage to brand and reputation.
The revision established a more comprehensive measuring methodology. And to the existing purity classes a new and more stringent class was added: ISO 8573-1 CLASS 0.
Using rigorous testing methodologies and having all possible forms of oil carry over measured across a wide range of temperatures and pressures, the respected German testing authority TÜV found no traces of oil in the output air stream of Atlas Copco’s Z range of oil-free compressors. Atlas Copco thereby became the first compressor manufacturer to receive certification for a new industry standard of air purity.
According to Atlas Copco Compressors’ Luka Popovac, “Atlas Copco felt it was important to independently verify that our oil-free compressors are actually 100% oil-free so that customers who have these demanding applications could be sure.”
Temperature effect
One aspect influencing the performance of compressed air systems is temperature. When using oil-injected compressors with oil removal filters, oil carryover through filter media increases exponentially according to the temperature at the filtration interface. Filtration performance is usually specified at 25°C.
If the ambient temperature in the compressor room increases to 30°C, the compressor outlet temperature could be 40°C with the oil carryover 20 times the specified value. Such temperatures are not unusual even in colder countries, where the compressor room temperature is substantially higher than that outside.
Temperatures also cause an increase in the vapour content of the air, some of which can carry through to the end product. Moreover, high temperatures shorten the lifetime of activated carbon filters. An increase in temperature from 20°C to 40°C can cut filter lifetime by up to 90%. Even worse, the activated carbon filter does not warn the user when it is saturated. It will simply allow oil to pass on to processes.
For Atlas Copco’s oil-free compressors, air quality is independent of temperature.
Compressed Air in food
Compressed air is used in two ways within the food manufacturing process. The first is Energy Compressed Air, where the air acts as a medium for storing and transmitting energy to drive the pneumatics in the factory, including conveyor belts and packing machines.
The other way is so called Process Compressed Air, in which it is an active ingredient in the production process. Examples include using compressed air for moulding of tablets, pasta formation and fermentation.
Compressed air is also used to control the valves and actuators in automated lines for filling, packaging and bottling. Oil in the air builds up and will find its way to these components, causing jamming and production stoppage. In addition, the components continuously vent out the air, which can come into contact with the end product.
Compressed air is also used in pneumatic conveying where it pushes foodstuffs, such as powdered milk or cocoa powder, along pipes. Here oil contaminant will mix with the powder and spoil the product. It is also used to clean bottles, packages and moulds prior to filling. Besides being a health hazard, oil in the compressed air will contaminate the food containers and alter the flavour of the end product.
Many food and beverage production facilities also generate Nitrogen which is then used to prevent the oxidisation of foods, i.e. to stop food going stale. Typically compressed air is used to generate the nitrogen. If there is oil in the compressed air, the membrane used to separate the nitrogen quickly breaks down.
“Oil is the enemy of the nitrogen membrane, therefore oil contamination can lead to an expensive replacement bill,” explains Popovac.
Another use for compressed air is to cool down baked goods after they emerge from the oven. Contamination of the air spoils these end products leading to rejections and production losses.
A breath of fresh air
“Globally it has been well accepted that the best practice is to use an oil-free compressor in the food industry,” says Popovac. “Many of the major brewers and food producers have now changed over to oil-free.”
There are, however, still manufacturers who believe that oil-injected compressors with oil removal filters can deliver oil-free air. This solution is often referred to as “technically oil-free air”. However, even under optimum conditions and with several stages of oil removal, the air quality with regard to oil is suspect.
To achieve even barely acceptable air quality with oil-injected compressors, it is necessary to have air cooling devices and several stages of oil removal with multiple components. A failure of any of these components or inadequate maintenance can result in oil contamination.
“Another perception that exists among some food and beverage producers is that you can get away with using an oil-injected compressor by filling it with food-grade oil,” explains Popovac.
“The thinking is that it’s much cheaper to do it this way, so what’s the problem?
“We think it is important that people are aware of the real risks associated with that oil, which is continuously in contact with metal parts and transferring minute metal shavings. That oil then goes down the line and potentially touches the products somewhere along the line.”
With oil-injected compressors there will always be a risk of contamination and the possibility of severe consequences for the business.
Upgrading to oil-free
Although many major manufacturers throughout the world have upgraded their machinery to oil-free, Australia is still behind the mark. The real issue, according to Popovac, has been people putting the initial capital costs ahead of the risk and maintenance costs that build up over time.
“What is happening overseas, in countries such as the UK, is that the food retailers are placing more stringent requirements on their suppliers. This is in turn forcing the food industry to evaluate how they produce their products.”
Atlas Copco Compressors Australia Technical Support Engineer, Nashaat Bakhit says that “whether it’s food-grade oil, mineral oil, any sort of oil, after a period of time the oil will become oxidised and its properties will degrade quickly. Even if it’s a food-grade oil, once it starts losing its properties, it’s not going to be a healthy choice in compressors.
“If we compare to oil used for frying hot chips, in time it degrades and then the taste of the chips will change. Because of various factors, including heat, the oil properties start to change.”
While many major companies have already looked at converting to oil-free, the small-to-medium businesses in food production are reluctant to consider it.
However, as Popovac points out, “anybody that has a risk-minimisation or a food safety strategy in place should really examine their processes and see where the risks lie. Not every application has compressed air coming in contact with the food, but if after doing a risk assessment you find several areas where that’s possible, then you need to examine what the consequences of contamination will be.”
With food-grade oil there may only be a tiny amount coming in contact with the food, but in terms of product quality, the flavour and colouring can still be affected.
Although an oil-free compressor is initially more expensive to purchase than an oil-injected compressor, there are significant savings in maintenance costs to be realised.
A final consideration that may not be immediately obvious is the environmental impact of using oil. According to Popovac, “a standard oil-injected machine will need its oil changed regularly, resulting in hundreds of litres of oil being disposed into the environment. An oil-free compressor will at most use a modest amount of gearbox oil.
“Especially if you are running a number of compressors over a lot of hours, you are consuming a significant amount of oil which needs to be disposed of – hopefully in an environmentally friendly way. By using oil-free compressors you will dramatically reduce your company’s impact on the environment.”