Filters play a vital role in the compressed air process. Depending on the end use, strict purity standards require a variety of contaminants to be removed, including oil aerosols, vapors and particulates. Contaminants can enter the compressed air from a variety of sources. Intake air can introduce dust or pollen particulates, while corroded pipes can add harmful particulates from within the compressor system. Oil aerosols and vapors are often a byproduct of using oil-injected compressors and must be filtered out before end use. There are distinct purity requirements for different compressed air applications, but the presence of contaminants can surpass acceptable levels, leading to damaged products or unsafe air. Filters fall into three categories: coalescing filters, vapor removal filters and the dry particulate filters. While each type ultimately produces the same result, they each operate on different principles.
Coalescing Filters: 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. 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.
Vapor Removal Filters: Vapor removal filters are typically used to remove gaseous lubricants that will go through the coalescing filter. Because they use an adsorption process, vapor removal filters should not be used to capture lubricant aerosols. Aerosols will quickly saturate the filter, rendering it useless in a matter of hours. Sending air through a coalescing filter prior to the vapor removal 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.
Dry Particulate Filters: Dry particulate filters are usually employed 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. Dry particulate filters operate in a similar manner as a coalescing filter, capturing and retaining particles within the filter media.
Knowing the needs of your compressed air system can help you chose the right filter. Whether your air need a high level of filtration or basic contaminants removed, cleaning your air is an important step in the compressed air process. Check out Atlas Copco’s line of filters today or call a representative and learn how Atlas Copco can help you achieve cleaner, safer air.
