Compressed Air Dryers : your guide continued

Desiccant air dryers are the next type of Compressed Air Dryers we are looking at.

A Desiccant Air Dryer is a type of 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. Adsorption dryers are used when the compressed air application requires a pressure dew point below 0°. The pressure dew point they can achieve can be sized to produce dew points from -20°C to as low as -70°C

Desiccant Air Dryers are better suited for second stage drying as the hygroscopic medium would otherwise get saturated too quickly. That means they are often the second step after a primary dryer like a refrigerated dryer.

There are 2 main types of desiccant air dryer:

Single canister dryers

These 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 desiccant air dryer

The regenerative desiccant dryers consist of two pressure vessels. Both vessels are filled with desiccant.

The first vessel is removing moisture from the compressed air. Wet air passes directly through the desiccant bed which adsorbs the moisture. When this vessel is saturated with moisture, the valves will switch and lead the air to the other standby vessel. During adsorption in the other vessel, the first vessel will be regenerated. It's a cyclic process.

The desiccant medium has a limited capacity for adsorbing the moisture in your compressed air supply before it must be dried out or regenerated. To do this, the tower containing the saturated desiccant medium is depressurized and the accumulated water is driven off. How this happens depends on the type of dryer.

A heatless desiccant dryer loses about 20% of output to purge. This is because if a desiccant dryer experiences a high pressure drop, the compressor discharge pressure must be set higher, which increases energy and operating costs. Therefore, it is important to select desiccant dryers that offer an exceptionally low pressure drop – below 0.2 bar for most models – as well as the most efficient regeneration process.

A zero-purge desiccant dryer does not lose any of its air output to purge and could save 20% in energy compared to a heatless desiccant

Why choose a desiccant 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 exceptionally low dew points

Next Up will be Membrane Air Dryers.

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