The desorption of the drying medium of adsorption dryers with heatless regeneration takes place in a counter current direction, in parallel and simultaneously with adsorption, making use of a purge of dried compressed air. The mode of operation of pressure change desorption corresponds to almost isothermal desorption through partial pressure drop in the adsorbing component by means of pure purge gas. In parallel to the outflow side of the adsorption dryer (Fig. 5.3.3.1), there is a by-pass line with integrated perforated screen (item 5). As soon as the exhaust valve (item 6) is opened, the part-current of dried compressed air, restricted by the perforated screen, flows from the pressure side of the system, through the adsorber to be desorbed, to the atmosphere. The part-current used for desorption, which is depressurised down to atmospheric pressure, is approximately equal to the volumetric flow with which the moisture is fed into the adsorber during adsorption. The moisture content of the air always depends on the effective temperature.
Figure 5.3.3.1
At constant temperature, equal volumes of air, if saturated, contain equal quantities of moisture. The volume flow of atmospheric air needed for desorption is, therefore, about equal to the volumetric flow during adsorption. The bigger the difference between operating and atmospheric pressure, the smaller is the regeneration volume flow in proportion to the total. Upon pressure release, the total humidity in the dried part-current remains constant, however, the air volume change after depressurisation leads to a reduction of relative humidity in proportion to the pressure drop then extremely dry partcurrent or regeneration air current has a very steep gradient of partial pressure drop in relation to the bed of drying medium. The moisture from the bed of drying medium is re-entrained by the regeneration air current and carried into the open air via the opened exhaust valve and silencer (item 7).
