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Atlas Copco Desiccant Dryer

What’s the Difference: Absorption dryer vs Desiccant/Adsorption Dryer


All atmospheric air contains some amount of moisture. When the air is compressed, its water concentration rises. To avoid product contamination or future problems with your compressed air system it is important to treat this air and draw the moisture out. To do this, you will need the help of an air compressor dryer. Learn the differences of an absorption dryer and a desiccant/adsorption dryer.

Absorption drying

Absorption drying is a chemical process in which water vapor becomes bound to absorption material. The absorption material can either be a solid or a liquid. Commonly sulfuric acid or sodium chloride are used, but that also means that the possibility of corrosion exists. This method involves a high consumption of absorbent materials and is generally not recommended.

Desiccant or adsorption dryer

A desiccant is a material that absorbs moisture. Desiccant air dryers work by allowing the moist air to flow over hygroscopic material (silica gel, molecular sieves, and activated alumina) and becomes dry. When the water vapor changes from moist compressed air to hygroscopic material or “desiccant,” the desiccant becomes gradually saturated with the absorbed water.

Since a desiccant absorbs water, it is important to regenerate the desiccant regularly to regain its drying capacity. That is why Adsorption air dryers are typically built with two drying vessels. One vessel will dry the incoming air while the second one regenerates. The vessels switch tasks as one becomes completely regenerated.

There are four ways to regenerate desiccant, the method used will depend on the type of adsorption dryer.

  1. Purge regenerated adsorption dryers (heatless-type dryers): These dryers are best suited for smaller air flow rates.
  2. Heated purge regenerated dryers: These dryers heat up the expanded purge air by means of an electric air heater.
  3. Blower regenerated dryers: Ambient air is blown over an electric heater and brought into contact with the wet desiccant to regenerate it.
  4. Heat of compression dryers (“HOC” dryers): In HOC dryers the desiccant is regenerated by using the available heat of the compressor.

Desiccant dryers are the most popular choice for energy-efficiency and reducing operating costs. It usually takes a desiccant dryer to achieve the lower pressure dew points and meet the most stringent air quality standards making it the more common choice.

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If you have more questions on Absorption, desiccant or adsorption dryers please reach out to one of our experts today.

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