Drying compressed air through adsorption is a purely physical process in which water vapor (adsorbate) is bound to the drying medium (adsorbent) through the binding forces of molecular adhesion. Adsorbents are solids in spherical and granular form which are permeated by an array of pores. The water vapor is deposited onto the internal and external surface of the adsorption medium without forming chemical compounds. Therefore, the adsorption medium does not have to be replenished, but periodically regenerated instead.
There are three main types of absorption desiccant air dryers:
The layout of Heatless Dryers and Externally Heated Dyrers is clear and simple. Compared to other desiccant air dryer systems, pressure dewpoints down to -100°F (-70°C) can be achieved without additional effort. Use in the higher pressure ranges and at low inlet temperatures causes the quantity of air needed for desorption to be reduced to an economical value. At low operating pressures, the demand for already dried compressed air for regeneration purposes is increased. This increase causes a large proportion of the prepared compressed air to no longer be available for productive purposes. Depending on the cycle, the quantity of air enclosed in the adsorber expands upon release at regular intervals with an emission noise level of about 90 - 95 dB(A). Given suitable noise attenuation measures, a reduction of the noise emission level to the region of 10 - 15 dB(A) can be accomplished.
Blower Purge Dryers, or desiccant air dryers with external heat regeneration and an ambient blower system, require only small quantities of processed and treated compressed air for purging and for building up pressure. The quantity of air required for regeneration is blown in (or drawn in) from the surrounding atmosphere by means of a blower. A desiccant air dryer with vacuum regeneration forms a logical and consistent further development. There is a growing tendency for using such systems, also in tower performance ranges, thanks to the efficiencies that can be realized. Operating by blower regeneration offers a wide-ranging freedom for adaptation to problematic marginal conditions. The regeneration system, consisting of a blower and a heater, is selected from a wide range of choices. Using different materials, customer-specific requirements can be met.