A desiccant air dryer for compressed air uses special drying agent beads like silica gel and activated alumina to absorb water vapor from an air stream. These air dryer units are often regenerative so that the drying agent doesn’t need replacing in order to provide vapor-free compressed air consistently. Wet air passes directly through the desiccant medium which adsorbs the moisture. The desiccant medium has a finite capacity for adsorbing moisture before it must be dried out, or regenerated. To do this, the tower containing saturated desiccant medium is depressurized and the accumulated water is driven off. How this happens depends on the type of desiccant air dryer, The desiccant in air dryers has always consisted of loose beads made of activated alumina, molecular sieves or silica gel. However, new technologies are emerging to provide more efficient alternatives.
