5.4.5. Sorption by Absorption


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Fig. 5.10: Absorption dryer with solid drying agent
With absorption drying the moisture is separated by a chemical reaction with a hygroscopic drying agent. Since the absorption properties of the drying agent diminish over time, periodic renewal is necessary.

There are 3 different types of drying agent. The soluble agents liquify with increased absorption. The solid and liquid agents react with the moisture without changing their aggregate status.
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<BR>Operating principle

During absorption the compressed air flows upwards through a drying middle bed. During this it gives up some of its moisture to the drying agent. A drain directs the condensate to a floor tank. The pressure dew point is lowered by 8- 12 %.

Example

Compressed air enters a dryer operating with calcium chloride at a temperature of +30 °C. The pressure dew point achieved here is between 18 and 22 °C.


Features
    • Low entry temperature.
      High temperatures soften the drying agent and bake it together.
    • Very corrosive drying agents.
      The dried compressed air can take drying agent with it into the pneumatic system. This can cause considerable damage.
    • No input of outside energy.
Due to its properties, absorption drying has only become established in fringe applications of pneumatic engineering. One example of this is its use for compressed treatment air in laboratories.