The dryer is an important part of the compressed air system that often gets overlooked. Along with filters, it ensures that the air being used in your final application is clean and free of moisture. Moisture in the air can cause fish-eyes in paint and clogged media blaster nozzles. The two main types of dryers are refrigerated and desiccant. The main difference between these two types is the drying agent inside the machine.

How to Select a Dryer for your Compressed Air System: First Steps

To choose an air-drying system for an air compressor, start with an analysis of the air compressor, plant environment, and applications. The best solution will depend on a few key factors:

Dew point. The dew point is the moment when the air reaches a temperature that leads to condensation and moisture saturation. It varies with temperature and pressure but is a key rating to consider when selecting an air dryer.
Temperature. The compressed air temperature required by your application will affect the dew point. The ambient air temperature will affect the type of air dryer most that is best suited for conditions.
Compressed air use. Keep in mind how often you will use the compressed air and how that flow will fluctuate. This can help determine whether a cycling or non-cycling dryer is appropriate.
Location. The location of the air compressor can determine what type of dryer is a best fit. If the compressor is outdoors in fluctuating temperatures, or indoors in a cramped area, the best air dryer will need to accommodate those conditions.
Air compressor specifications. Generally, dryers are rated to pair with a compressor system with certain pressure (psig) and flow (scfm) ratings. Actual air pressure and flow will vary from factory rated pressure and flow.
Tolerances. Moisture tolerance levels of the machines, and processes that use compressed air, determine how dry the air needs to be, and at what temperature and pressure.

Some moisture is always present in a compressed air system, regardless of the degree of drying. Air that may be considered dry for one application may not be dry enough for another. ISO 8573-1 establishes the standard for air quality classes for pollutants. For moisture content, the standards are:

an ISO 8573.1 table for moisture in air treatment

Refrigerated Dryers

Refrigerated dryers are split into two sub categories, cycling and non-cycling. Non-cycling runs all the time, whereas a cycling dryer cycles on to cool a secondary cooling fluid, then shuts off while the cooled fluid does the work of drying the air.

Refrigerated dryers are the lower cost option in terms of set-up, operation and maintenance. A benefit of these dryers is that they are resistant to airborne oil particles, but the disadvantage is that they have minimal dew point capacity. Dew point is the temperature when the water in the air lines will condense.

Desiccant Dryers

Desiccant dryers can be heatless, heated internal or heated external. In a desiccant dryer the air flows through one of two towers filled with a drying agent that absorbs any moisture. The opposing tower is offline and being regenerated with purge air.

Desiccant dryers have better dew point capacity than refrigerated dryers and they can be used in remote and hazardous environments. They tend to have high set-up costs, the desiccant bed needs to be replaced every 3-5 years, they require more filtration for airborne oil vapor and particulate carry over, and often need purge air. Most often they consume purge air, making them less efficient than refrigerated.

RELATED: HOW TO SELECT THE RIGHT DRYER FOR YOUR COMPRESSED AIR SYSTEM

Tips for Choosing Air Dryers

To specify the right dryer for a compressed air installation, keep the following information in mind:

Avoid over-specifying. Drying the entire supply of compressed air to dew points less than -40°F can be a waste of energy. One possibility is to subdivide the compressed air supply by application, and then treat each point of use as needed for the downstream application served.
Avoid under-specifying. Design the drying system to meet your specific needs to avoid damage caused by wet air.

Selecting the right dryer for your air compressor depends mainly on the air quality requirements for the process. In nearly all compressed air applications, dryers play a vital role by providing clean, dry air for reliable operations. Dry air helps prevent costly shutdowns, product contamination, and equipment failures. Finding the right drying system brings substantial savings over the lifetime of the equipment.

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