Compatible compressor lubricants
Food-grade compressor lubricants are one method of addressing an oil contamination problem. These compressor lubricants are available in two varieties:
* full (or direct) contact lubricants, which can be ingested without harm, and
* incidental (or indirect) contact lubricant, which can be ingested in very small amounts without harm. These lubricants have a chemical additive package and are not intended to come into direct contact with the food or beverage product. They tend to be more durable than full contact lubricants and offer a longer oil life cycle than their direct contact counterparts. However, they are not as durable as semi-synthetic or full-synthetic compressor oils.
The advantages of using food-grade lubricants include meeting FDA regulations and U. S. Public Health Service guidelines, as well as reducing the risks of severely contaminating the product. Using food-grade lubricants also enables a plant to use oil-flooded rotary compressors, or lubricated reciprocating compressors. Both cost less initially and require less maintenance than oil-free compressors. The disadvantages of using food-grade lubricants include more frequent compressor oil replacement, higher lubricant cost, lower temperature resistance, and, in some areas, limited availability.
The oil-free alternative
Oil-free air compressors are another option. These compressors are available in three varieties:, reciprocating, rotary screw, and centrifugal (a dynamic compressor as opposed to a positive displacement machine).
Although large oil-free reciprocating compressors seem to be disappearing from the modern industrial environment, many older machines are still in use today and can be found throughout industry. Today, most oil-free reciprocating compressors are rated less than 30 hp, with some packaged, multi-unit systems rated to 60 hp.
The most common modern designs of oil-free compressors are the rotary screw and the centrifugal varieties. These machines are available in a broad horsepower range from several manufacturers.
The advantages of oil-free compressors for the food and beverage industry are fairly obvious. The risk of compressed air contamination inherent with the use of these machines is almost non-existent. This alone may convince many food and beverage processors that oil-free compressors are their total solution. However, the need for adequate compressed air filtration certainly is not eliminated simply by installing an oil-free compressor. In-line compressed air filters are still needed to ensure that only clean, dry, contaminate-free air makes contact with the product or product container.
The disadvantages to oil free compressors are that they usually carry a higher price tag, and, in many cases, have higher annual maintenance costs than their lubricated counterparts. Some oil-free compressors also have a higher rate of energy consumption, and, therefore may cost more to operate. Because nearly 60% to 70% of a compressor’s total cost over its life span is the cost of electricity, operating cost should not be ignored.
Clean air, no matter what
Whether a food processing plant uses lubricated or oil free compressors, proper filtration is still required to ensure that clean air is supplied to the process equipment. Specialized filters — such as activated carbon filters or PTFE-impregnated depth or membrane surface filters — are also required as part of the in-line filtration package. PTFE filters use non-shedding, hydrophobic filter elements to eliminate bacterial contamination in the compressed air stream. These filters, Figure 3, must be cleaned with steam to ensure their continued effectiveness. PTFE filters meet FDA requirements of CFR Title 21 if clean, dry compressed air is supplied to them. Therefore, pre-filtration for these filters is essential in meeting FDA requirements, Figure 4.
It is essential that the compressed air be clean prior to reaching the PTFE filters. But clean, dry air is beneficial for most applications, not just food and beverage processing plants. Clean, dry compressed air can maximize the life and reliability of cylinders, valves, and seals, leading to lower maintenance costs and higher productivity through reduced downtime.
An ideal compressor, filter, and dryer arrangement for providing clean dry air is shown in Figure 5. Unfortunately, pneumatic systems designed and installed with this or comparable arrangements are rare in the most industrial facilities, including the food and beverage industry.
FDA vs. USDA supervision
In every food and beverage processing facility we have visited, we have found at least one USDA representative on site. Each facility also had a testing laboratory. The USDA regularly tests for bacterial contamination of the product, taking random samples of the packaged food or beverage. Not only are detailed records of the test results maintained on file, but the actual item sampled is also stored on site. However, the USDA may not identify chemical contamination of the product unless that contaminant has contributed to bacterial infestation.
Our experience concerning the FDA has been very different. Although the FDA has clearly defined regulations regarding compressed air standards, we have not, in the last two years, seen a single FDA representative in any of the food or beverage facilities we have audited. We cannot claim that they do not visit the plants we have audited — they very well may — but we have never actually encountered an inspector while performing our work. We know that the FDA monitors pharmaceutical manufacturers very closely in regard to compressed air standards. However, our observations seem to suggest that the food and beverage industry seldom comes under close scrutiny by the FDA.