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Desiccant Air Dryers 101: A Beginner's Guide

Desiccant Air Dryers 101: A Beginner's Guide

Hidden from the naked eye, water vapor, oils, and other contaminants can be found floating in the air ready to wreak havoc on your system. The best defense? Installing compressed air treatment equipment to maximize its performance and increase its longevity, such as desiccant air dryers.

Desiccant air dryers are industrial pieces of equipment that remove moisture from an air stream with the use of desiccant material. As air travels through the desiccant media, moisture is absorbed by the desiccant; allowing the dry air to flow downstream.

But, desiccant dryers are not one-size-fits-all. There are a few different kinds to explore and help you decide what is best for your system.

Discussed in this article:

  1. How Desiccant Works
  2. How to Replace or Reuse Desiccant
  3. Types of Desiccant Dryers

 

hOW DOES Desiccant WORK?

Desiccant is a type of material with the ability to attract and hold liquids and other gases. You’ve most likely seen desiccant being put to work in your shoe box, medication package, or any electronic (hint: it’s the mesh bag that says “DO NOT EAT”).

In an air dryer, desiccant beads are used to adsorb water vapor to provide dry air downstream. This works great in achieving very low dew points early on in the drying cycle, but as the desiccant beads continue capturing moisture, their performance begins to diminish.

just desiccant sieve

 

What Happens when Desiccant Becomes Saturated?

When the desiccant beads are saturated, they are no longer able to absorb moisture. At this point, the moisture trapped by the desiccant must be removed by one of three methods.

  • Manually change the desiccant
  • Regenerate using dry air from the dryer; common in heatless/heated desiccant regenerative dryers
  • Regenerate using heated air; commonly found in heated blower purge dryers

 

3 Types of Desiccant Dryers

Now that we understand the basics of desiccant, let's dive into the types of desiccant dryers. There are three common types of desiccant dryers, and they have their own advantages and disadvantages.

  1. Manual change desiccant pots
  2. Heatless regenerative desiccant dryers
  3. Heated blower purge desiccant dryers

 

1. Manual Change Desiccant Pots

Manual desiccant dryers, more commonly known as desiccant pots, are single tower dryers with replaceable desiccant cartridges, or pour-in beads that remove moisture from an air stream. As the air flows through the media, the desiccant adsorbs the moisture. These types of dryers require the user to change the desiccant every so often, typically by visual inspection of a moisture indicator.

manual change desiccant pot

Advantages:

  • Dew points down to -40°F
  • Desiccant comes in cartridges or free-flowing beads for easy replacement

Disadvantages:

  • The performance will drop once the desiccant begins to become saturated
  • Humidity indicators are not precise; colors may not begin to change until the air quality exceeds 20% relative humidity
  • Replacement cartridges require constant servicing and can be costly
  • Post-filtration is required to capture desiccant dusting from the media

2. Heatless Regenerative Desiccant Dryers

Heatless desiccant dryers use regenerative technology to purge the moisture off the water-saturated desiccant. These dryers come with a minimum of two towers: one tower will be drying the air while the other is drying out the saturated desiccant. A small amount of sweep air is used from the air stream to perform the regeneration cycle.

 

heatless regenerative desiccant dryer

Advantages:

  • Dew points consistently down to -40°F
  • Regeneration cycles swap dryer towers every 2-5 minutes
  • The desiccant lasts for 3-5 years (on average) before needing replacement

Disadvantages:

  • Purge air, or sweep air, is required for the regeneration cycle
  • Purge air consumes small % of CFM (see manufacturers specification)


3. Heated Blower Purge Desiccant Dryers

Heated blower purge desiccant dryers force a stream of heated air up through the water-saturated desiccant tower to eliminate the moisture. Unlike heatless (or heated) regenerative dryers, the air is taken from the ambient environment, heated and blown through the media. Although no compressed air is consumed for the regeneration process, this drying technique requires a fan and an electric heater to dry the desiccant.

 

regenerative dryer

Advantages:

  • Dew points consistently down to -40°F
  • Regeneration technology swaps dryer towers every 2-5 minutes
  • The desiccant lasts for 3-5 years (on average) before needing replacement

Disadvantages:

  • Higher electrical demand; additional utility costs will occur
  • More system components means more opportunity for points of failure

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Filtration Requirements for Desiccant Dryers

21999-0255 50 CFM 3 Stage Filtration NEW web-1

Without proper pre-filtration, the desiccant can become contaminated with oils, water and particulates from the compressor; rendering the technology useless over time. Make sure to install a quality oil coalescing filter to the dryer inlet if the dryer does not already come with one.

Optimally, the pre-filtration will consist of both a water separator and an oil coalescing filter.

 

Ready to get startes with desiccant air dryers?

Finding the perfect filter and air dryer to meet your needs is a tough decision. Our team of engineering experts is standing by awaiting all of your dry air questions.

Get in touch today to learn more about which solution would best suit your needs or shop online!

 

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