How to Remove Contaminants in Compressed Air

Today, virtually all industrial chemical processes use or interact with compressed air systems. Air compression is required in most processes, whether to add texture to products, dry sterilized equipment, divert items and ingredients along the assembly line, or perform a whole range of other tasks.

Throughout all these processes that use compressed air systems, contamination is possible. When this happens, the quality of the products will be compromised. At worst, the contamination can lead to health hazards, especially in food manufacturing. This article discusses common contamination and how to address them in an industrial setting.

Compressed Air Contamination Regulations

Since industrial processes rely heavily on compressed air systems, the International Organization for Standardization established standards for clean, dry air. These standards are detailed in ISO 8573-1.

The purity standards cover the contamination of particles, water, oil, and even microbes in the compressed air, regardless of where the sample was taken in the system.

Medical Compressed Air Requirements

In the medical sphere, there are more regulations to consider. Compressed air needs to be compliant with the National Fire Protection Association Health Code 99 (or simply NFPA 99) to be fit for medical use.

According to the Code, odor, water, carbon monoxide, carbon dioxide, gaseous hydrocarbons, halogenated hydrocarbons, oil and particulates are potential contaminants.

Several agencies, like the Centers for Medicare and Medicaid Services, The Joint Commission, and local authorities having jurisdiction, require facilities to use compressed air systems compliant with the Health Code.

Food Manufacturing Compressed Air Requirements

The food manufacturing industry has similar additional requirements. The Safe Quality Food Institute or SQFI recently introduced the annual testing of food processors to keep track of levels of contamination in particulates, water, oil, microbiological organisms, and relevant gases.

According to Food Engineering, compressed air in food manufacturing may include the following contaminants:

• Hydrocarbons
• Viruses
• Bacteria
• Moisture
• Oil
• Solid particles

The compressed air comes in contact directly with food items or ingredients during the following processes:

• Bagging
• Sparging/Mixing
• Drying
• Air Knives
• Pneumatic Exhaust

Because of all these interactions, it is important to ensure the purity of compressed air. The same is true in various degrees in the processes of other industrial sectors.

What Contaminants Are Present in Compressed Air?

There can be any number of contaminants in compressed air, depending on their application, the environment, equipment used, materials, and several other factors. That said, these contaminants generally fall under the following four main categories:

• Particles – This category includes rust, filings, wear particles, and even atmospheric dirt. These contaminants are also sometimes referred to as solid or dry particles or contaminants.
• Water – This category includes water in its different forms like water vapor, liquid, or aerosolized. Aside from posing potential health issues, moisture in compressed air systems can also affect the longevity of the equipment.
• Oil – Whether from equipment or materials, compressed air systems are constantly exposed to oil and may carry them. The amount of oil in the system depends on certain factors, such as the tools and materials used and the age and efficiency of the system.
• Microorganisms – A mixture of moisture and oil in the compressed air system can be a breeding ground for microorganisms like bacteria or bacteriophages. In ideal conditions, these organisms can freely multiply and cause a wide range of hazards down the road.

The international standard ISO 8573-1 includes more details about each category and the contaminants under them.

Methods for Removing Contaminants in Compressed Air Systems

The following are the two main methods for minimizing contamination in compressed air systems:

Filtration

Fiber filters are used to separate the contaminants from the air. Several factors, including the permeability of the filter medium, the temperature during the process, and oil concentration, affect the success rate of the filtration process, especially when it comes to smaller contaminants.

Aftercooling

The compression process of air generally increases its temperature. This means air straight from the compressor is likely to have a temperature of between 70 and 200°C. Because of this, water, oil, and other similar contaminants will be more difficult to separate.

Using aftercoolers makes it easier to route liquid from condensation to containers, preventing them from circulating in the system.

General Pointers for Removing Contaminants

Even with filters and aftercoolers in the system, contamination may continue to be an issue if they’re not used properly. Here are a few important pointers to help reduce contamination in compressed air systems, and to take full advantage of the filters and aftercoolers present:

• Micron Rating – It can be tempting to assume that filters with smaller micron ratings are more effective and cover more contaminants, but they also pose issues. Filter materials advertising to be effective against particles as small as 0.01 µm, for example, are misleading for the following reasons:
  • It can be easier to separate particles as small as that compared to larger contaminants like 0.1µm.
  • Contaminants as small as 0.01 µm, or about 5000 times smaller than human hair, can have no discernible impact in industrial processes.
  • The most common contaminants like aerosolized oil are between 0.1 to 1.0 µm in size.

When choosing the micron rating of filter materials, it is better to first evaluate the types of contaminants present in the system and select one that is best used against them.

• Filter Material – Micron rating is not the only important quality of a filter. Its composition also plays a role in how effective it is going to be against contaminants.

It is important to select filter materials that are restrictive enough to successfully separate the contaminants while also being permeable enough to not restrict airflow to a degree where the additional pressure and energy costs outweigh the benefits.

• Replacement Interval – When it comes to evaluating the viability of filters in the system, it is important to remember that visual inspections may not be reliable. The challenge is to replace filters at the right time, so as not to risk contamination or waste resources.

Adhering to a schedule, guided by the factory specifications of the filter, is the best course of action here.

Conclusion

Compressed air systems are prone to contamination, whether from moisture, oil, or microorganisms. Since all industrial chemical processes involve compressed air, it is important to minimize contamination to avoid costly and dangerous consequences down the road.

Understanding the regulations surrounding compressed air purity, the potential contaminants, and the most effective methods for reducing contamination will go a long way in preserving air purity.

To learn more about minimizing contamination of compressed air systems, get in touch with us. JHFOSTER has been handling industrial automation and compressed air systems since 1938.