For some applications, high-quality compressed air is of critical importance. The food industry is one of them. Especially the air that comes into contact with the actual food products must be free of harmful contaminants. That makes compressed air filters a key component of a food production air system. It also makes 'compressed air filtration food industry' (and its variations) a much-researched topic.

Compressed air in the food industry

In any industry that makes use of compressed air, there are four types of air to consider:

Process air: air that comes into direct contact with the final product;

Non-contact air: compressed air that is not meant to come into contact with the product;

Instrument air: air that is used for process instruments and control;

Plant air: compressed air for cleaning machinery and operating tools.

When it comes to compressed air quality in the food industry, process air is the main focus.  Packaging systems often rely on compressed air. You will also find it in the mixing, cutting and drying of ingredients. And it is used in the transportation and propulsion of food. All these operations that bring compressed air into contact with the product either directly or indirectly must adhere to strict quality standards.

Sources of contamination

Contaminants are bound to creep in and develop in any compressed air system. Air contamination can come in from or develop in:

The atmosphere: The ambient air that is pulled in by the compressor contains particulate matter, water vapor, oil vapor, and micro-organisms.

Air compressor: The compression process can add its own contaminants, notably oil vapor, oil aerosols, and liquid oil.

Air receiver and piping: The accumulated contaminants from the earlier stages inevitably end up in the receiver as well as the distribution piping. This can lead to the growth of micro-organisms; the resulting chemical reactions can cause pipe scale and rust.

The compressed air quality standard

ISO 8573-1:2010 is the international standard for compressed air quality. It specifies different purity classes, with 0 being the most stringent. For each class, there is an allowed presence of particles, water and oil.

Unsurprisingly, stringent standards apply for the food production sector. The BCAS (British Compressed Air Society) Food and Beverage Grade Compressed Air Best Practice 102 is an excellent reference for the food industry:

Pilot air (to control valves, cylinders, grippers, …): Class 7.4.4

Non-contact compressed air (no contact with ingredients, finished food, packaging material, storage vessels or the manufacturing machinery): Class 1.4.1

Non-contact high risk (possible unintended contact with ingredients, finished food, packaging material, storage vessels or the manufacturing machinery): Class 1.2.1

Contact compressed air (direct contact with ingredients, finished food, packaging material, storage vessels or the manufacturing machinery): Class 1.2.1

Fortunately, filters are available to ensure the quality of compressed air used in food production:

Coalescing filters screen out oil aerosols and wet particulate;

Dust removal filters remove dry particulate;

Adsorption dryers remove water vapor;

Adsorption activated carbon filters remove oil vapor.

These solutions alone are not sufficient. As described above, there are many areas in the compressor system that encourage microbial growth. The main way to limit microbial growth is to put in place sterile air filtration at specific points of contact. These trap the microbes and prevent them from coming in contact with the food product.

Point-of-use filters in general are installed right before any specific piece of equipment or application; they are generally much more effective than after filters. Activated carbon filters remove particles too small to be eliminated by the coalescing filters. Dust filters may also be installed at points of use.

Best practices

Regular monitoring (with dew point meters for instance) and testing the purity of compressed air is the best way to limit air contamination. That’s because the composition of contaminants in the air varies from moment to moment. The same goes for the build-up of contamination within the compressed air systems.

In addition, leading safety guidelines concur on the need to remove moisture wherever possible. This typically means maintaining a pressure dew point of at least -26° C/-15°F (to limit microbial growth). Filtration with a minimum DOP efficiency of 99.999% should be set up at every point where the air might affect the product.

Maintenance

It must be noted that these point-of-use filters must be maintained regularly. In 3-stage filters, the stage 1 and 2 elements must be changed at least once or twice a year. The replacement frequency needs to be doubled for the filter elements in stage 3. Dryers, filters, piping and drain taps must be serviced as well. The change of the sterile filter elements depends on the application and the number of sterilization cycles.

Article Source：Pneumatech