What type of air filter does your compressed air system need?

There’s no doubt for manufacturers in the Middle East that regular maintenance of your air compressor system will keep it running smoothly and more efficiently. Because compressed air filtration is an important part of meeting your production requirements, they require special attention. This article will give you an insight into the types of compressed air inline filters that are available and their suitability for your applications. The most important thing for improving your compressor’s air filter is to both understand the needs of your compression system and the right equipment to meet those needs. That way, you can have a high quality air compressor system that is cost efficient and easy to maintain.

The application and use of your compressed air will decide which filters you need. Not all applications that use compressed air require the same level of filtration, that is why having this information is the first step to choose the correct filter. If you are using compressed air in the manufacturing of electronics or creating of food or food packaging, you will want a higher quality of compressed air with as little contaminates as possible. If you are using compressed air to power pneumatic tools or fill tires, the compressed air can be slightly less "clean" and still protect your equipment.

Let us firstly get a better understanding of what contaminants are and how they affect the compressed air system. Contaminants within a compressed air system can originate from ambient air that is utilized, as well as the system (compressor) itself. There are three main contaminants that are found in compressed air: particulates, aerosols and vapors.

Particulates: Particulates in compressed air system are small pieces of solid material such as dust, dirt and or pollen from the ambient air, as well as loose metal particles that can be caused by pipe corrosion. Depending on the sensitivity of your application and or process, contact with particles can be damaging to the end product, therefore causing delays in production and quality control issues, not to mention potentially unsatisfied customers. 

Aerosols: Aerosols consist of small droplets of liquid that can be found within the compressed air system, especially in those using oil-injected compressors. Aerosols are created from the lubricant, in this case, the oil used in the compressor and can be harmful to both products and people if not treated properly. 

Vapors: In the compressed air system, vapors consist of lubricants as well as any other liquid that has converted to a gas. Such vapors require a special carbon activated filter in order to be removed from the system.

Now that we have a better understanding of the contaminants above, let us take a look at what types of filters are used in eliminating each type of contaminant. The different filter types are as follows:

Coalescing filters are used for removing water and aerosols. Small droplets are caught in a filter media and merged into larger droplets that are then taken out of the filter. A re-entrainment barrier prevents these droplets from reentering the air. Most of the liquid coalescing filters remove is water and oil. These filters also remove particulates from compressed air, trapping them within the filter media, which can lead to pressure drops if not changed regularly. Pressure drop means an energy loss in the compressed air system. Every 1 bar of differential pressure an air compressor must overcome is equal to approximately 7% increase in electrical consumption. Coalescing filters remove most contaminants very well, reducing particulate levels down to 0.1 micron in size and liquids down to 0.01 ppm.

A mist eliminator is a low-cost alternative to a coalescing filter. While it does not produce the same level of filtration as coalescing filters, a mist eliminator offers a smaller pressure drop (about 1 psi), allowing systems to operate at lower pressure, thus saving on energy costs. These are typically best used with liquid condensate and aerosols in lubricated compressor systems.

Adsorption filters are typically used to remove gaseous lubricants that will go through the coalescing filter. Water and aerosols will quickly saturate this type of filter, rendering it useless in a matter of hours. Sending air through a coalescing filter prior to the adsorption filter will prevent this damage. The adsorption process uses activated carbon granules, carbon cloth or paper to capture and remove contaminants. Activated charcoal is the most common filter media because it has a large open pore structure; a handful of activated charcoal has the surface area of a football field. Because of the use of activated charcoal, however, a dust filter needs to be used after this type of filter to remove the dust particulate. 

Dust removal filters are usually used to remove desiccant particles after an adsorption dryer. They can also be implemented at point of use to remove any corrosion particles from the compressed air. Dust removal filters operate in a similar technique as a coalescing filter, capturing and retaining particles within the filter media to provide up to 99.9999% particle removal efficiency. However, they do not remove liquids or aerosols.

At different points of use, different compressed air purities might be needed, depending on the application. The various air purity classes are provided in the table below, which clearly shows the various Atlas Copco filters and dryers that meet all the different classes.

In conclusion, filtration plays an important role within the compressed air system. Picking out a right inline filter is not an art, but it could be confusing if you do not ask the right questions or understand the process that requires filtration. 

The problem with filtration, however, is the pressure drop, and therefore installation running costs. You can learn about ways to minimize these in this article about 2-in-1 filters.