Tag: deliquescent

Intelligent Compressed Air: What You Need To Know About Deliquescent Dryers

Published on by Russ BowmanLeave a comment

Moisture free air is a “must” for industrial use, for a number of reasons:

  • An awful lot of distribution systems incorporate iron pipe. It’s inexpensive, readily available, easy to work with, rated for pressure, and has a long history of successful installations. Iron pipe will also oxidize (make rust) in the presence of water:
Here’s what we find a lot of the time inside a Reversible Drum Vac that’s been sent in for refurbishment because it’s not drawing effective vacuum anymore.
  • Regardless of what your distribution lines and components are made of, water droplets can erode them. Compressed air itself is a gas; it follows the curves in elbows, and flows around valve discs & regulator diaphragms. Water droplets, on the other hand, run full speed INTO those things, often at high velocity. This eventually causes pitting, which is bad enough…those pits, though, are little pockets for salts, acids, or alkalines to effect their destructive little chemical reactions.
  • When used for blow off applications, anything in your compressed air will get on anything you’re blowing off. If the intent is to remove moisture from a surface, moisture in your compressed air supply decidedly works against your goal.
  • Water can freeze as it is carried along with air flow through orifices. This can quickly block the flow of air. The US Navy lost a submarine, USS Thresher (SSN-593) and all hands in 1963. A number of factors contributed to the sinking, but a significant one was that compressed air being blown into the ballast tanks (to create negative buoyancy) had higher than permissible moisture content, and froze in orifice plates in the lines. The ballast tanks stayed full of water, and 129 sailors & shipyard personnel died as the boat passed crush depth.

There are a number of types of air dryers that are commonly fitted to industrial air compressors to take care of moisture problems. The least expensive one of these is the Single Tower Deliquescent Dryer. Here’s how they work:

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 some of the water 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.
  • After the desiccant does its job, moisture free air flows out the top, and gets on with it’s work.

In addition to the low price tag, other things to like about them are:

  • Low pressure drop.
  • No moving parts or electrical components.
  • Can be used outdoors, and in hazardous, mobile, dirty, or corrosive environments.

Of course, there are things to NOT like about them as well:

  • Limited suppression of dew point – because they are drying the air to a specific relative humidity, as opposed to a specific dew point, the attainable dew point is dependent on the incoming air temperature, the chemical composition of the desiccant salt, and the ambient temperature where it’s installed. Unless you use some sort of specialty salt desiccant, the typical dew point is only 20-25ºF lower than the air inlet temperature.
  • Desiccant carryover – speaking of those specialty salts, they’re even more corrosive than the basic sodium chloride that’s often used. Any carryover will wreak havoc on your distribution system and air operated devices.

Deliquescent dryers’ particular set of “pros and cons” presents challenges for their use in industrial settings, for sure. But if the primary concern is preventing pipes from freezing up, then their low cost, low maintenance, and simplicity make them a great choice.

At EXAIR Corporation, we’re keen on compressed air efficiency. The attention to detail we pay to our products – from design, to manufacturing & assembly, to availability, and right on through to technical support – bears out our commitment to helping you get the most out of your compressed air system. If you’ve got questions, we can talk about this all day long…and most of the time, we do. Give me a call.

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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Image courtesy of Brian S. Elliott, Wikimedia Commons Creative Commons Attribution-Share Alike 4.0 International License

Compressed Air Supply Side: What Is A Deliquescent Dryer, And When Would You Use One?

Published on by Russ BowmanLeave a comment

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.

EXAIR Corporation is in the business of helping you get the most out of your compressed air.  If you want to learn more, please follow our blog.  If you have specific questions, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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(1) – Deliquescent Dryer Image: VMAC Air Innovated: The Deliquescent Dryer – https://www.vmacair.com/blog/the-deliquescent-dryer/

Supply Side Review: Deliquescent Type Dryers

Published on by Brian FarnoLeave a comment

As mentioned in my post last week.  The supply side of compressed air systems within a facility is critical to production.  The quality of air produced by your compressor and sent to the demand side of the system needs to be filtered for both moisture and particulate.  One method to dry the air, that is the topic for this blog, is deliquescent type dryers.

These dryers operate like an adsorbent dryer such as a desiccant medium dryer.  The main variance is that the drying medium (desiccant) actually undergoes a phase change from solids to liquids.  Because of this the material is used up and cannot be returned to its original state for reuse.   The liquids formed by the desiccant dissolving in the removed water vapor are then filtered out of the air stream before it is passed on to the demand side of the air system.

There are many compounds that are used to absorb the moisture in the wet compressed air.  A few options are potassium, calcium, or sodium salts and many that contain a urea base.  The desiccant compound must be maintained at a minimum level for the dryer to contain enough media to successfully dry the air.

These dryers are generally a single tank system that is fed with compressed air from a side port near the bottom of the tank.  The air then travels up past drip trays where the desiccant and water mixture fall and ultimately ends up in the bottom of the tank.  The air then goes through a material bed that must be kept at a given level in order to correctly absorb the moisture in the air.  The dry air is then pushed out the top of the tank.

As the desiccant material absorbs the liquid from the compressed air flowing through the tank it falls onto the drip trays and then into the bottom of the tank where it is drained out of the system.  This process can be seen in the image below.

 

Deliquescent type compressed air drying system
How a deliquescent air dryer works – 1(VMAC Air Innovated, 2017)

 

The dew point that this style dryer is able to achieve is dependent on several variables:

  • Compressed air temperature
  • Compressed air pressure / velocity
  • Size and configuration of the tank
  • Compression of the absorption media
  • Type of absorption media and age of media

These dryers are simplistic in their design because there are no moving parts as well as easy to install and carry a low startup cost.

Some disadvantages include:

  • Dewpoint range 20°F – 30°F (Again this is according to the media used.)
  • Dissolved absorption material can pose a disposal issue as it may not be able to be simply put down a drain
  • Replacement of the absorption material

Even with disadvantages the ability to supply the demand side of a compressed air system for a production facility is key to maintaining successful operations.  If you would like to discuss any type of compressed air dryer, please contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

 

1 – Deliquescent Dryer Image: VMAC Air Innovated: The Deliquescent Dryer – https://www.vmacair.com/blog/the-deliquescent-dryer/