The Importance of Air Treatment
Raymond Batkay, Channel Partner Manager, Northeast
Air is dirty, and depending on the season and your location in the world, the air is also wet. On a hot summer day in Louisiana, the humidity is so thick that you can almost see the air you’re breathing. Walk down Bourbon Street in mid-July, and it’s almost like walking through a cloud.
When we compress air, we take all that air is made of and condense it. There’s only 21% oxygen in the air. The rest of it is a mixture of earthly gases and water vapor. It’s not just gas and water vapor either; we also condense all the particulates, molecules, and microorganisms present in our atmosphere.
Consider the typical manufacturing facility in the United States. Even with the best housekeeping policies in place, dust, oil mist, and vapor are often palpably present. When these are compressed along with the air, oil and other particulates can form significant challenges to your equipment or product.
So how do we deal with these atmospheric hitchhikers? Line Filtration.
It is essential to distinguish the term “Air Filtration” from “Line Filtration.” Inside your air compressor are different types of filters, none of which directly treat the air. Line filters are designed to treat the air after it has gone through the compression process. This is why compressed air dryer systems and line filters are often referred to as “air treatment.”
What kind of air treatment is right for you?
The International Standard ISO 8573 Series classifies air quality in three separate categories:
– Solid Particulate (Dirt and Dust) Measured in Microns
– Water Vapor
– Oil (Liquid, Aerosol & Vapor)
Additionally, consider microbiological contaminants and other gaseous contaminants like CO, CO2, SO2, NOX, and Hydrocarbons in the range of C1 to C5.
It is crucial that if your system requires “validation” from a third-party organization, you know what ISO 8573 standard will be used. For instance, “Class 0” air is another way to describe oil-free air, and although with the right filtration system, you could get close, a business won’t get validated without an oil-free air compressor.
Do you need Class 0 air?
If you’re working in an autobody shop or a machine shop, chances are you don’t. However, that doesn’t mean you don’t need to filter your air. All those contaminants listed above can wreak havoc on your equipment and the products you’re producing.
For instance, consider oil carryover in an autobody shop. Once oil mixes with auto paint, your worker may experience “fish-eye” in the car’s finish. If the air used in the paint gun is improperly filtered, thousands of dollars and hours of work can be ruined.
You may not have to worry about the paint. Still, particulates in the air will damage sensitive machinery on the demand side of your manufacturing process, not to mention water vapor’s corrosive properties over time. Remember that black pipe scales easily when exposed to moisture. It is as simple as keeping your machines clean and maintained, which alleviates exorbitant amounts of maintenance.
To understand what you need, you must first understand the different types of filtration available to you.
Coalescing Filters: These filters are used for removing small amounts of water vapor and aerosols. Your System Specialist will rightfully tell you that most liquid coalescing filters remove small amounts of water and oil. I strongly recommend having a coalescing filter alongside a general filter in every Compressed Air System.
Dry Particulate Filters: Dry particulate filters are usually used to remove desiccant particles after an absorption dryer dries the compressed air. Best practices suggest that they can be implemented in a standard system to remove any corrosive particles from the system.
*All desiccant dryers must have a coalescing filter at the inlet and a particulate filter at the outlet. If you get oil or water on the desiccant, it will render it useless. The air also goes into the desiccant housing, disturbing desiccant beads and sometimes causing small pieces to break off. It would be wise to place a particulate filter to capture these little renegades before they contaminate your process.
Vapor Removal Filters (Adsorption): While lubricant aerosols are taken care of by your coalescing filter, lubricants that have not yet matured are still in a gaseous stage and will pass through the coalescing filter like a college sophomore with a fake idea. The best way to scrutinize your air quality is to employ the activated carbon housed in vapor removal filters. It’s the most effective and efficient way to “polish” your compressed air.
**BONUS** Mist Eliminator: A mist eliminator is based on a giant coalescing filter concept. A mist eliminator does not perform to the same level as its little brother does, but it offers a smaller pressure drop and requires much less maintenance. Additionally, the mist eliminator can act as a final fail-safe against a catastrophic oil carryover event. In turn, mist eliminators carry a higher CAPEX cost but require lower maintenance and care. Ask your System Specialist if a mist eliminator is the right alternative for you.
If you’re new to compressed air systems, you may be asking, “why don’t I order bunches of coalescing and particulate filters?” The answer is efficiency. You want to use the least amount of filtration as possible to get to your desired ISO class. Filters require maintenance, but each filter, depending on size and element, has different levels of pressure drop.
It’s important to note that you should never size a filter based on the size of its connections. NEVER go smaller than the pipe’s size, but understanding is vital to get the most of your filtration. It would be best if you sized your filters for the maximum rate of flow. Filters are rated in SCFM at operating pressure. Don’t be afraid to oversize your filter a little bit but keep in mind what the manufactures published limits are. It’s okay to give yourself a little bit of a buffer, and while it may cost you a few extra bucks initially, in the long run, you’ll be saving yourself by giving your air a little slack as it’s being cleaned.
My recommendation is always the same: compressor to the storage tank (wet tank), connected to coalescing filter to the dryer, to particulate filter, and where appropriate vapor removal filter to another storage (dry tank) to downstream. While the “wet tank” is not traditionally classified as an element of “air treatment,” the wet tank acts as a first-line knock-out punch as your air is being treated. By piping in the lower part of the tank and piping out at the top, gravity naturally pulls water and other heavy particulates/oil to the tank’s bottom to later be drained by an oil-water separator. It helps the dryer and filtration work a little less hard and decreases maintenance intervals.
These basic principles will ensure cool, dry, and clean air in the safe operation of your very healthy compressed air system. Having the right filter combination downstream of an appropriate air dryer can help you get cleaner, dryer air than that in the atmosphere.
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