Oil-free compressors find a warm welcome in industries where hygiene in general is a priority or where possible mineral oil contamination poses a particular problem.
Food, drink and pharmaceuticals are all process industries that fall under this umbrella, but other sectors are also important users, such as electronics and the spray paint operations of automotive manufacturers.
“For production sites where the compressed air comes into direct contact with goods, the amounts of oil present and type of oil allowed is subject to strict controls,” says Richard Hilton, product director at Gardner Denver.
“Oil-lubricated compressors have been used in applications in the food and beverage, pharmaceuticals and electronics industries in previous years. However, this is fast becoming a thing of the past. Due to the risks associated with solely relying on filtration to protect products or equipment, most organisations are now switching to oil-free.
“Oil-free compressors are primarily used in applications where air purity is a critical factor. For many industries, such as food and beverage, pharmaceuticals and electronics, even the smallest risk of oil contamination can have very serious consequences that often require significant expense to resolve.”
Due to the risks associated with solely relying on filtration to protect products or equipment, most organisations are now switching to oil-free
Richard Hilton, product director, Gardner Denver
Applications where there is direct contact between compressed air and sensitive products are the most obvious candidates for switching to oil-free. Yet even those where there is no direct contact can benefit from a situation, in which the exhaust from oil-free compressed air systems cannot potentially increase the ambient levels of mineral oil contamination in the local environment.
“While there are no specific regulations specifically relating to oil-free compressors, there are extremely stringent standards in place that regulate the quality and performance of compressed air applications,” says Hilton.
He highlights ISO8573 standards as the most widely-applied guidelines: “Consisting of nine separate parts, part one highlights the amount of contamination allowed in each cubic metre of compressed air and the remaining eight specify the methods of testing for a range of contaminants. This ranges from oil aerosol content and humidity, to solid particle and oil vapour content.”
With an especially high potential for reputational damage to consider in addition to product quality implications, it’s no surprise that the food industry in particular is keen to promote the use of best practice in compressed air.
In the UK, the British Compressed Air Society (BCAS) has responded to this with the publication of the Food and Beverage Grade Compressed Air Best Practice Guideline 102.
Mark Ranger is business line manager for the Oil-Free Air division at Atlas Copco Compressors UK. He also co-chaired the BCAS committee responsible for producing the best practice guideline. “It doesn’t say in that document that you should use an oil-free compressor, but what it does do is say that the air quality that is recommended for compressed air that comes into contact with a food product should be of a certain standard,” he explains. “You could arguably only guarantee that standard using an oil-free compressor.”
For direct contact, the guideline recommends adhering to Compressed Air Purity Designation ISO 8573.1 (2010) class 2:2:1. This means that the amount of dust must be <1 micron, the pressure dewpoint should be -40°C and the oil content <0.01 mg/m3.
The suggestion for indirect contact is ISO 8573.1 (2010) class 2:4:1; where levels of dust should be <1 micron, the pressure dewpoint should be +3°C and the oil content <0.1 mg/m3.
For many users in sensitive industries, even using an oil-free compressor is not a sufficient guarantee of compressed air purity.
That’s because the compressor may not be adding to the contaminant load, but it will deliver air complete with whatever level of ambient mineral oil contamination is present.
It also does nothing to mitigate other forms of contamination. With this in mind, effective monitoring will typically be a key element in compressed air systems where contamination could pose a risk.
If you measured what the unit cost you in a 15-year life cycle, the chances are that an oil-lubricated compressor would have cost you more
Mark Ranger, business line manager, Oil-Free Air division, Atlas Copco
BEKO Technologies specialises in solutions to optimise the quality of compressed air. Marketing specialist Ruth Goodison says: “BEKO Technologies recommends online measurement procedures to ensure that compressed air is monitored at all Critical Control Points, whether it be contact and non-contact with food stuffs [or other sensitive products].
“Periodic or even sporadic sampling and subsequent laboratory analysis would only provide a snapshot of the situation at the time of the sampling and not continual, uninterrupted analysis of compressed air. In order to be in a position to deliver this conclusive and continual quality assurance, BEKO has developed an online measurement procedure to determine the residual oil content in compressed air down to Class 1 and below.
“Given the standard of quality required here, the BEKOKAT system was certified by TÜV Nord in accordance with the ISO 8573-1 standard and validated by the Federal Institute for Drugs and Medical Devices.”
So sensitive industries and applications are the chief targets of oil-free compressor technologies. However, suppliers suggest that there may be good reasons for compressed air users across the board to invest in oil-free machines.
“A compressor is a heavy piece of industrial technology designed for longevity. And if you measured what the unit cost you in a 15-year life cycle, the chances are that an oil-lubricated compressor would have cost you more,” says Ranger.
He suggests that maintenance costs are generally higher with oil-lubricated models, thanks to the need for oil changes and the cost of the lubricant itself.
In addition, any downstream filters will need replacing regularly and will lead to a bigger downstream pressure drop and thus higher energy costs. Hilton confirms some of the chief advantages of opting for oil-free: “Oil-free technology eliminates the need to collect and dispose of oil-contaminated condensate and improves the number of oil change intervals required throughout a machine’s lifetime. Furthermore, an oil-free model does not require an oil separator element or replacement downstream filters. Owners of oil-free compressors also avoid the problems and environmental impact associated with oil disposal.
“Additionally, oil-free units do not experience the downstream pressure drop that can occur in oil-lubricated units, so further energy is not required to increase force and compensate, meaning energy costs are also reduced.”
Furthermore, Gardner Denver has recently been pushing at the boundaries of energy efficiency with the introduction of its new Ultima drive technology for oil-free compressors, as Hilton explains: “While regular units are driven by a single motor using a gearbox that drives both the low- and high-pressure airends, Ultima avoids this set-up entirely.
“Instead, Ultima uses ultra-high efficiency motors which optimise performance throughout the complete volume range, as the airends can be driven at different speeds dependent on demand. This ensures maximum efficiency and pressure ratios at all times.”
So if the picture is so rosy for oil-free, why doesn’t everybody adopt oil-free compressors, whatever their application? The reason is that, whatever the long-term advantages, oil-free compressors typically cost more to buy upfront than their oil-lubricated equivalents. This is enough to put them out of the running with some potential users.
“The initial capital cost is the major drawback,” says Ranger. “An oil-free compressor is by its nature a little bit more complex and there’s a little bit more metal involved in an oil-free compressor, so there are raw material costs and technological advancements in oil-free technology that push up the initial capital cost.”