As we head in to the colder months here in Ohio, I will soon be getting my humidifier out of the basement and set up in my bedroom. The dry air that accompanies the onset of winter chaps my lips, cracks the skin on my knuckles, affects my nasal passages, and oftentimes makes me wake up with a sore throat…something I definitely don’t want to happen in the middle of a pandemic! So I put some water vapor in my home’s air, on purpose, to take care of all of that.
Moisture in an industrial compressed air system, however, isn’t good for anything. It’ll corrode your pipes, get rust in your pneumatic tools, motors, and cylinders, and spit out of your blow off devices, all over whatever you’re using your air to blow off. Depending on the type of compressor, where, and how, it’s used, there are different types of dryers. Today, dear reader, we’re taking a look at one of the most basic moisture removal systems: the deliquescent dryer. The principle of operation is as follows:
Deliquescent dryer: how it works (1)
Incoming compressed air enters near the base, where a form of mechanical separation occurs…the air flows back & forth, around trays of desiccant. The simple act of changing direction causes a certain amount of free liquid to just fall out and collect in the bottom.
The air then flows upwards through the desiccant bed. The desiccant in a deliquescent dryer absorbs moisture (as opposed to the adsorption that occurs in a regenerative desiccant dryer) until they get so wet, they dissolve.
The desiccant level has to be monitored (commonly via a sight glass) so it can be replaced as it’s consumed.
After the desiccant does its job, moisture free air flows out the top, and gets on with it’s work.
Deliquescent dryers, owing to their simplicity, are the least expensive air dryers. They have no moving parts and no electricity, so the only maintenance involved is replacing the desiccant media as it’s consumed. This makes them especially popular in mobile/on-site applications involving portable or tow-behind, engine driven compressors, since they don’t need power to run.
There are several disadvantages, also owing to their simplicity:
The deliquescent media has to be periodically replenished. If you don’t stay on top of it, you can find yourself shut down while you go back to the shop to get a big bag of salt. That’s time your boss can’t charge your customer for. Also, the cost of the new media is a continual operating cost of the dryer…something you don’t have to account for with the regenerative desiccant models.
Disposal of the waste media can be a concern…you definitely want to check your local environmental regulations before dumping it in the garbage. Your boss won’t like talking to the EPA about THAT either.
They have to be equipped with a particulate filter on the discharge to keep the deliquescent media (which, being a salt, is corrosive in nature) from entering your system. That would be even worse than water moisture…which this is there to prevent in the first place.
They don’t get near as low of a dewpoint as other dryers – the best you can hope for is 20°F to 30°F. Which is fine, given the above mentioned nature of applications where these are commonly used. You just wouldn’t want to use them to supply a product like an EXAIR Vortex Tube…which can turn that in to -40°F cold air, causing the water vapor to turn to liquid, and then to ice. In a hurry.
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Russ Bowman Application Engineer EXAIR Corporation Visit us on the Web Follow me on Twitter Like us on Facebook
Most of EXAIR’s line of Intelligent Compressed Air Products have no moving parts and require no maintenance. The caveat to the “no maintenance” aspect is proper filtration at the point of use. Many products have very tight orifices that could get clogged from any contaminants such as particulate, condensate, and lubricant. EXAIR recommends point of use filtration to be installed just upstream of any EXAIR Product for this purpose.
There are three primary types of compressed air filters: particulate, coalescing, and adsorption. Each have their own inherent characteristics and can be used in conjunction with one another. Each style is used to handle a different form of contaminant that’s present within the distribution system of your compressed air supply.
EXAIR Model 9001 Auto-Drain Filter
Particulate filters – Particulate filters are available with different filtering mechanisms that allow you to control the particulate size that will be filtered out. The higher the level of filtration, the greater the pressure drop you’ll experience at the outlet of the filter. Styles are also available with either a polycarbonate bowl or metal bowls, depending on the application and environment.
Any filter with a polycarbonate bowl should have a metal guard on the outside to provide protection for personnel should a failure occur. In these styles of filters, compressed air is forced through a filter element that blocks any particulate contained within the air supply.
These filter elements are generally a sintered bronze material with filtration levels from 40-5 micron possible. Over time, the filter elements can clog and increase the pressure drop at the discharge of the filter. They’re relatively inexpensive and should be replaced yearly to maintain optimum performance and mitigate pressure drop. They also remove liquid drops as well from the air supply, containing them within the bowl. Styles with both manual-drains and automatic-drains are available that will drain the bowl of excess moisture automatically through the bottom of the filter.
EXAIR Model 9005 Oil Removal Filter
Coalescing Filters – The coalescing filter is used to remove very fine water vapor as well as any residual oil. These filters are highly recommended to be installed just prior to any dryer that contains a media that would be compromised by any lubricant passing through it. Coalescing filters utilize an element typically made up of glass fibers that “coalesce”, or combine, the fine water vapor and oil aerosols until the droplet size becomes large enough that it drops off into the bowl or filter housing. With a coalescing filter, the most common cause of pressure drop increase is due to particulate clogging the filter element. Because of this, a particulate filter should always be installed just prior to any coalescing filters.
Adsorption Filters – The final type of compressed air filter is the adsorption filter. Where the particulate filters can remove the majority of contaminants and the coalescing filters the residual oil, they are not capable of removing lubricant vapors or oil. That’s where the adsorption filter comes in. In addition to removing the finest oil vapors, they also can eliminate odors from the compressed air supply. The oil vapors and odors adhere to activated carbon within the filter, removing them from the air supply. These filters are commonly found within the food processing industry, where any contaminants in the air supply could impact the integrity of the product.
EXAIR has a line of Automatic Drain Filter Separators and Oil Removal Filters, available from stock, to make sure the quality of your air supply is sufficient for proper operation of any EXAIR product. Feel free to give us a call and any of our Application Engineers will be happy to assist you.
EXAIR’s Super Air Knife is THE best solution for compressed air blowoff operations that require a wide sheet of compressed air. We’ve been manufacturing Air Knives for over 35 years, with the Super Air Knife making its first appearance back in 1997. Since then, the Super Air Knife has undergone a few enhancements over the years as we’re constantly trying to not only introduce new products but also improve on the ones we have. We’ve added new materials, longer single piece knives, as well as additional accessories. But, by and large, the basic design has remained the same. As the saying goes: “If it ain’t broke, don’t fix it!”.
The Super Air Knife utilizes a source of compressed air to create a laminar sheet of high velocity air. This supplied compressed air mixes with ambient air that is entrained into the primary airstream. The Super Air Knife entrains ambient air at a rate of 40:1, making it VERY effective in a variety of drying, cleaning, and cooling applications. Available in lengths ranging from 3”-108” and in a variety of different materials of construction, there’s a Super Air Knife available for just about any application.
Any time you have product moving along a conveyor that needs to be cleaned, dried, or cooled off, a Super Air Knife is the ideal fit. I recently worked with our Argentinian Distributor on an application involving drying off plastic bottles just prior to applying a label to the outside. After the bottles are molded, they go through a washing operation to remove contaminants from the inside and outside of the bottles before they’re filled. After filling, a label must be applied to the outside of the bottle. Before installation of the Super Air Knives, they were allowing the bottles to air dry. As they moved along the conveyor, most of the residual water did come off and wasn’t causing any issues.
They were looking to increase production rates so that they could keep up with demand, however when they increased the speed of the conveyor there was still a good amount of residual water remaining on the bottles. This prevents the label from adhering properly to the outside of the bottle. Not only did this result in an added step to inspect the bottles, but those that weren’t labeled properly had to have the label removed and cleaned off before a new one could be put on. This actually ended up being less productive than just running the conveyor at a slower speed.
They came across the EXAIR Super Air Knife and decided to try (2) 110036 aluminum Super Air Knives to remove excess moisture just prior to labeling. The plant handles a wide variety of different sized bottles, so they also utilized the Universal Mounting System so that they could easily adjust the positioning of the knife based on the job. With the Super Air Knives in place, they were able to effectively run the operation nearly 20% faster without any problems.
With the quiet and efficient Super Air Knives in place, they were able to increase production rates in order to fulfill their orders on time. If there’s an application in your facility that could necessitate the use of an EXAIR Super Air Knife, give us a call. With 16 different lengths available from stock in 4 different materials, same day shipping with orders placed by 3:00 ET, AND our unconditional 30 day guarantee, there’s no excuse not to give one a try!
