WHAT IS DESICCANT ?
Desiccant keeps things dry by adsorbing moisture in the surrounding air. There are many kinds of desiccants. Desiccants are hydrophilic materials including silica gel, activated carbon, molecular sieve, and activated alumina. You have probably seen packets of silica gel in the packaging of various consumer products to keep them dry during storage and transportation. Activated alumina is the most commonly used desiccant compound for compressed air dryers, formed into beads. Activated alumina beads look like spheres but are in fact highly porous and have a high surface area to volume ratio. This enables them to adsorb a lot of water vapor within a small volume.
Most have two towers of desiccant, which take turns drying and regenerating based on timers and moisture sensors. Technically, when desiccant captures moisture vapor, it releases energy in the form of heat. An equal amount of heat energy must be applied to regenerate the desiccant.
A critical aspect of some regeneration dryers is purge loss. This refers to the amount of dry compressed air that the dryer diverts to the moisture saturated tower to pull the water out of it and prepare it for the next drying cycle. After the moisture is stripped from the desiccant into the passing air, the wet air is released into the atmosphere. This is the purge. When sizing air systems with regeneration dryers that purge, you must consider the dryer as one of the uses for compressed air. This can be a significant air demand depending on the size of the system since the purge rate (cfm) is based on the capacity of the dryer, not on the amount of air going through it. So oversizing a heatless dryer will purge/consume extra air that could be used for production (or that doesn’t need to be made at all). The higher the air flow, the higher the operating cost.
A critical aspect of some regeneration dryers is purge loss. This refers to the amount of dry compressed air that the dryer diverts to the moisture saturated tower to pull the water out of it and prepare it for the next drying cycle. After the moisture is stripped from the desiccant into the passing air, the wet air is released into the atmosphere. This is the purge. When sizing air systems with regeneration dryers that purge, you must consider the dryer as one of the uses for compressed air. This can be a significant air demand depending on the size of the system since the purge rate (cfm) is based on the capacity of the dryer, not on the amount of air going through it. So oversizing a heatless dryer will purge/consume extra air that could be used for production (or that doesn’t need to be made at all). The higher the air flow, the higher the operating cost.
