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Compressed air drying


In recent years, dryer technology has evolved significantly — resulting in improvements such as:

  • dryers that are smaller, saving space.
  • better controllers that simplify and enhance system management.
  • advanced connectivity that enables remote monitoring and service.

And while all of the above-mentioned advances are important, none of them are as globally consequential as simultaneous advancements in another area — the continued development of refrigerant dryers with Variable Speed Drive (VSD).

The reason for the latter advances’ heightened importance is both environmental and economical. This is because, while a traditional air compressor in most industrial operations always runs at full capacity — despite an ever-fluctuating demand for compressed air — VSD technology saves energy and money by automatically adjusting motor speed to match air demand. Another substantial breakthrough has been the development of a completely new type of desiccant, a substance that is used in some compressed air systems to remove moisture.

Choosing the right compressed air dryer

When selecting the correct size of dryer for your process requirements, six major factors must ultimately be considered, and calculation tools can help once they’re determined. These include:

  1. Maximum air flow in standard cubic feet per minute (scfm)
  2. Desired pressure dew point
  3. Inlet air pressure
  4. Inlet air temperature
  5. Ambient air temperature (and water temperature, if your condenser is water-cooled)
  6. Installation environment of the dryer

Desiccant dryers can provide an ultra-low dew point, typically around -40°C/-40°F. Refrigerant dryers typically achieve a dew point of about 3°C/ 37°F, but they cost less to buy, operate and maintain than desiccant dryers.

How a refrigerant dryer works

For any operations that require dry compressed air, a refrigerant dryer is a critical air system component. To reduce the compressed air temperature, compressed air is passed through an air-to-refrigerant heat exchanger. This causes water vapor in the air to condense into liquid so it can be trapped and removed.

Conventional refrigerant air dryers typically employ a piston compressor operating at one fixed speed — creating an “on or off” scenario that wastes energy. Conversely, a VSD refrigerant air dryer uses a scroll compressor driven by an inverter that can vary speeds to match demand, saving energy.

How a desiccant dryer works

With desiccant air dryers, moist air flows over a material (desiccant) that readily takes up and retains water to be dried. Because the desiccant absorbs water, it needs to be regenerated regularly to regain its drying capacity.

There are four types of desiccant dryers, with the main difference between them being how they regenerate the desiccant:

  • Purge regenerated adsorption dryers (“heatless-type dryers”) use expanded compressed air to purge moisture from the desiccant.
  • Heated purge regenerated dryers heat the expanded purge air to improve purge efficiency and reduce energy consumption by 25% vs. heatless-type dryers.
  • Blower regenerated dryers blow heated ambient air to regenerate wet desiccant. No compressed air is used, reducing energy consumption by 40% vs. heatless-type dryers.
  • Heat of compression dryers regenerate desiccant with the heat naturally given off by the compressor, eliminating the need for any additional energy consumption.

A revolutionary desiccant development

Compared to traditional granular desiccants, Cerades — a revolutionary new solid desiccant developed and patented by Atlas Copco — delivers higher air quality, lower energy and service costs, and substantial health and environmental benefits.

Compressed air flows straight through the Cerades structure, saving energy by reducing pressure drop (up to 70%) in the dryer. Cerades also handles higher air flow than granular desiccant, so the dryer can be much smaller. Further, Cerades is vibration-resistant, can be mounted horizontally, lasts longer, delivers longer cycle times to improve energy efficiency and process productivity, and doesn’t decay and break down into dust — all big advantages over granular desiccant.


Want to learn more about compressed air drying efficiency — and how Atlas Copco’s VSD and Cerades technologies can improve yours? Download Atlas Copco’s recently released whitepaper, An Overview of Compressed Air Drying, to take a deeper dive into these topics and a range of related ones. 

To help you discover how to boost both your energy efficiency and your bottom line, the whitepaper answers questions such as:

  • Is it best to buy an air compressor with a built-in dryer?
  • If I have a VSD compressor, should I choose a VSD dryer? Conversely, if I have a fixed-speed compressor, should I have a fixed-speed dryer?
  • How important is dryer choice in overall system efficiency?

Download the whitepaper today to get answers to these questions and more. 

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