The principles of drying compressed air


Compressed air is a widely used power source. Though this powerful utility may be the most important part of your production process, it could contain water, dirt, wear particles, and even degraded substances, such as lubricating oil. These elements will form an unwanted condensate when using the compressed air, which is often acidic, and can be detrimental to any machinery, tools, or valves that it comes into contact with.

It is recommended that compressed air is treated before it’s used. By doing so, you remove the risk of further contamination. However, simply treating the compressed air may not be enough, as even modern production systems need a higher level of air quality. For the correct air quality needed, point-of-use filtration, and air dryers can provide beneficial results.

When compressed air contains water, the liquid can be removed using a process called “Drying”. Drying ranges from trapping the condensed water, to preventing condensation, to removing all the water present in the compressed air system. If too much water remains in the compressed air, the process has not been completed correctly, and the surrounding system can suffer from corrosion.

There are several drying methods available:

  • Aftercooler – Reduces the temperature and overall water content of the compressed air.
  • Bulk Liquid Separators – Removes bulk liquid that has been condensed in the distribution system.
  • Particulate Filters – Removes solid particle contaminants down to 5 micron and separates bulk liquids.

  • Coalescing Filters – Removes aerosol water and other liquids, which bypass the water traps.
  • Pressure Reduction – Drying through expansion.
  • Refrigeration Dryers – Drying to dewpoints of approximately 37°F (3°C)
  • Desiccant Dryers – Drying to dewpoints of approximately -40°F to -100°F (-40°C to -73°C).
  • Membrane Dryers – Variable drying capabilities to approximately -40°F (-40°C) dewpoint.

It should be noted that as refrigeration, adsorption, and membrane dryers are only designed to remove water vapor. They require the use of coalescing filters and possibly even a bulk liquid separator to work proficiently.

Figuring out which kind of dryer you need can be difficult. You should keep these points in mind:

  • Drying the entire compressed air supply in a factory to dewpoints less than -40°F (-40°C) is uneconomical.
  • Damage caused by wet air costs money in maintenance, downtime, and lost product.
  • A drying system which only contains an aftercooler and a coalescing filter could create problems with condensation.
  • For applications which use air at lower temperatures than the main compressed air line install filters at the point-of-use to maximise drying.
  • Use specific membrane dryers for those parts of the system which require dewpoints of 35°F to 52°F (2°C to 5°C) and flow rates up to 1200 SCFM.

  • Compressed air with a dewpoint of -40°F (-40°C) is reasonable for water vapor sensitive applications.

Drying the compressed air to be used in your system is crucial if you want to avoid any problems in the future. By using the correct dryers and drying processes, you can avoid any water vapour mishaps, and ensure that your compressed air is ready for any number of the applications you need it for.

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