In industrial applications, compressed air contains condensed water by its condensation. Since in compressed air systems the danger arises due to precipitant condensation, or if an application does not allow moisture for chemical-physical reasons, this water vapor must be removed and the compressed air dried.
The maximum water vapor content of a compressed air volume unit is caused by the temperature of the compressed air and almost completely independent of its pressure. The water vapor content is therefore theoretically clearly represented by the dew point, which clearly shows the temperature at which the actual water vapor quantity corresponds to a relative humidity of 100% and the condensation begins below it.
Drying in this context means a reduction of the dew point below the actual operating temperature. For drying to deepest dew points, essentially only processes such as adsorption, in which water vapor is sorptively bound to a solid phase, are suitable. By adsorption, therefore, is meant the addition of a substance, the adsorbate, to the surface of a solid body, of the adsorbent, with physical binding forces having an effect here. Since the absorption capacity of adsorbents decreases with increasing temperature and decreasing pressure, moisture can be desorbed again by heat supply or pressure reduction.
The adsorbents used in such a drying process are absolute high-tech drying agents and have an inner surface area of up to 1000 m2 / g, due to their pore structure of small and very small pores, of which steam can accumulate. For the drying of compressed air, use is made, in particular, of silica gels (dried beads), aluminum oxides (activated alumina) and zeolitic molecular sieves. These drying agents reach dynamic absorption capacities above 20% by weight and dew points up to -100 ° C can be achieved during drying.