What is a compressed air dryer and how does it work?

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What is a compressed air dryer and how does it work?

Compressed air dryers are crucial components in your compressed air treatment, along with other elements like air filters and oil-water separators. But what exactly is a compressed air dryer? And how does it work? That’s what you’ll learn here.

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What is a compressed air dryer?

Compressed air dryers are filtering systems that rid your compressed air of moisture created during the compression process. It makes sure that your compressed air is high-quality and free of harmful moisture that could damage your equipment or have a negative effect during use.

Compressed air filters, on the other hand, filter the air from other impurities like dust and gases.

How do compressed air dryers work?

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How your compressed air dryer works depends on the type of air dryer you have. Each uses a different technique to the same result: providing clean and dry compressed air for you to work with.


The most common compressed air dryers and their basic working principles:

  • Refrigerated air dryers are the most common type of compressed air dryer. They work by cooling the air down until the moisture condenses, extracting it from the air. They are also known as refrigerant air dryers.
  • Adsorption air dryers are usually used as a second stage dryer. They use hydrophilic substances to extract moisture from the air. Well-known sub-groups are desiccant and deliquescent air dryers.
  • Membrane air dryers contain a hydrophilic membrane for the air to pass over moisture builds up on the membrane and migrates along the length of the membrane before being expelled.

Curious for more? Discover in detail what the different types of compressed air systems are and how they work.

What compressed air dryer systems are there?

  1. Refrigerated air dryers
  2. Desiccant air dryers
  3. Deliquescent air dryers
  4. Membrane air dryers

1. Refrigerated air dryers

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Refrigerated air dryers or refrigerant dryers cool down the air to approximately 3°C or 35°F. At this temperature, known as the dew point, the moisture in the air condenses after which it is drained.

The cooled air is reheated to room temperature upon exiting the dryer and before being used.

The are 2 main subtypes of refrigerant dryers:

  • Non-cycling refrigerant air dryers continuously refrigerate and thus maintain a consistent temperature. They are very reliable and easy to maintain, but you cannot turn them off. They keep running even if your business is closed.

  • Cycling refrigerant air dryers produce the amount of cold needed and then shut off until the core temperature reaches a certain level. They automatically turn off and on as needed, making them the more environmentally friendly option. The extra parts needed for this way of working, however, could result in a slightly higher need for maintenance and it does not offer a stable pressure dew point.

Why choose a refrigerated air dryer?

Refrigerated air dryers are the most common type of compressed air dryer. They are perfect for most manufacturing and service applications, provided you just need dry air without any perceptible moisture.

A few benefits of refrigerant air dryers 

  • Cost-effective in purchase and maintenance
  • Environmentally friendly and can be combined with the Energy Box to save even more energy
  • Reliable and consistent

In need of a compressed air dryer system capable of lower dew points? Then a desiccant air dryer is a better fit for you.

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2. Desiccant air dryers

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desiccant air dryer is a subtype of the adsorption air dryer system. They use a porous hygroscopic medium like activated alumina and silica gel to extract moisture from the air and dry it. They have a dew point of around -40°C or -40°F.


As stated in this succinct guide to air dryers, desiccant air dryers are better suited for second stage drying as the hygroscopic medium would otherwise get saturated too quickly. That means they are usually the second step after a primary dryer like a refrigerated dryer.


There are 2 main types of desiccant air dryer:

  • Single canister dryers are most often used for point-of-use applications. It contains a granular hygroscopic medium through which the air is pushed and where it is filtered of moisture. Single canister dryers are easy to use and efficient in their energy use.

  • Twin tower dryers are also known as regenerative dryers. They contain 2 canisters.

The first canister contains a hygroscopic medium through which the air passes. When the medium becomes saturated, the air flows to the second canister for the same treatment.

The first canister then heats up a small amount of air to purge the first medium from moisture and expels it into the atmosphere, resetting the medium.

The regeneration of the medium uses 1 of 2 working principles:

  • Heatless regeneration uses a small amount of compressed air to dry the hygroscopic medium, causing a 17-20% loss of air.

  • Heated regeneration or blower purge uses hot atmospheric air, reducing air loss to less than 7%.

Why choose a dessicant air dryer?

The regenerative nature and low dew point of desiccant dryers, make it perfect to compress air at or below the freezing point.

Some advantages of a desiccant air dryer

  • Easy to maintain and clean
  • Perfect for second stage drying
  • Versatile and capable of very low dew points
Looking for a different type of adsorption dryer? Then maybe a deliquescent air dryer is for you.
 

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3. Deliquescent air dryers

The second type of adsorption dryer systems is the deliquescent air dryer. Like desiccant dryers, they pass the air through a hygroscopic medium to dry it.

Contrary to desiccant air dryers, deliquescent air dryers use soluble salt tablets instead of a medium that needs regeneration. The resulting brine needs to be drained and the tablets replaced every so often.

Deliquescent air dryers’ dew point fluctuates depending on the temperature of the atmospheric air coming in.

Why choose a deliquescent air dryer?

Deliquescent air dryers are perfect for remote or hazardous environments like landfills, asphalt factories, wood working factories and similar, often industrial, environments.

Benefits of deliquescent air dryers

  • Perfect for specialised applications with contaminated air, natural gases and waste gases.
  • Easy maintenance because of its design
  • No electricity required

Because of the added maintenance costs and minimal range of use, Mark decided not to provide deliquescent air dryers.

For a consistent dew point, refrigerant dryers and desiccant dryers will better serve you.

Download your copy of our guide to adsorption air dryers.

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4. Membrane air dryers

The final type of air dryer for your compressor, is the membrane air dryer. As the name indicates, it runs incoming air over a hygroscopic membrane to rid it of moisture.

The air builds up on the membrane until it migrates through to the other side, which is low pressure. A dry gas is then run through, carrying the moisture away for expulsion.

Like deliquescent air dryers, membrane air dryers’ dew point depends on the temperature of incoming air, although a proper setup will result in incredibly low dew points. They are often a second or even third stage dryer.

Why choose a membrane air dryer?

Membrane air dryers are a popular choice for medical use thanks to the low dew point in a controlled environment resulting in small amounts of high-quality air. If you need an air dryer for a laboratory, dentist’s office or hospital, this is your best bet.

Reasons to go for a membrane air dryer

  • Operate continuously without using electricity
  • Quiet and reliable
  • High-quality air compression
In need of a point-of-use air dryer for industrial use? Then the desiccant dryer is more likely to fit your needs.

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The importance of a compressed air dryer in (industrial) air compressors

In some industries a regular flow of dry and/or clean air is required for particular industrial processes. For these application, a compressed air dryer can offer the perfect solution. This section will cover the specifications and precise use of an air dryer. 

Type of compressed air dryer: desiccant compressed air dryer

Moisture can always occur while using standard piston and/or screw compressors, simply because the specific process of compressing the air produces water vapour. This moisture might have damaging and corrosive effects on your compressor systems or end-product.


In certain industries dry air is essential to the specific process. That is why compressed air dryers are widely used to make sure the compressed air remains completely dry. There are three different types of compressed air dryers:

1. Refrigerating compressed air dryers

These types of dryers work by cooling the air to low temperatures and condensing the bulk of the water vapour. Some water vapour does however remain in the air, so this specific type of compressed air dryer is not to be used in applications that are water-sensitive.

2. Desiccant compressed air dryers

Desiccant dryers use a certain amount of desiccant material to remove the water particles from the air. While one part of the desiccant material is absorbing water, the other part is drying. There are two types of desiccant dryers: heated and heatless.

Heated dryers use heat to remove water from the desiccant material. These dryers operate on steam or electricity.

Heatless desiccant dryers use the dry air of the compressor itself to remove water vapour from the desiccant material. The advantage of this type of desiccant dryer is that there is less outside energy needed. 

3. Membrane compressed air dryers

These dryers use membrane microtubes that let through water vapour. The compressed air goes through the tubes, and the water vapour diffuses through the membrane. The same dry air is used to remove the moist air from the membrane.

These dryers require little maintenance, and are explosion-proof. They are mostly used in rooms where an extreme temperature (heat or cold) is required. 

 


How do I choose the right air dryer?

When looking for an industrial air dryer, there are many different models to choose from and it’s easy to get lost. If you follow these tips, you’re on your way to the perfect air compressor and treatment for your business:

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  • Stick to the air quality you need for your business, no higher or lower.

  • Make sure you take into account the longevity of your systems. Investing in high-end systems now will cut down costs tremendously in the long run, saving time and money.

  • Get support from experts to make sure you can trust your choice.

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Advice for your compressed air drying system

Choosing the right compressed air drying system for your business can be a complicated task. If you’re curious for more information or looking for some personal advice, get in touch with our experts. They’ll gladly help you along the way.

Read more about air dryers in related articles

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