All regenerative desiccant dryers dry air in the same manner. The aftercooled saturated compressed air enters the drying tower and any water vapor in the compressed air is absorbed into the desiccant beads until the beads are saturated.
The desiccant dryers we will discuss differ in the regeneration process.
Purge air occurs when air that is of low relative humidity picks up moisture from the bed and flows out of the tower to dry the bed. The following dryers differ by what amount of purge air is used, and how much is lost compressed air.
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What are Desiccant Dryers?
Desiccant dyers, also referred to as absorption dyers, work by absorbing water vapor into a porous media with an attraction to water.
Heatless Dryers
Heatless dryers usually operate on a 5 – 10 minute tower switch cycle. They use no auxiliary heat and require 15% to 20% of the rated flow at full load in dried compressed air to the regenerating tower. This purge compressed air absorbs moisture and removes it from the tower. This air does not go to the system.
External Heat Dryers
External heat dryers normally operate on a four-hour (3 hours of heating and 1 hour of cooling) tower switch cycle. They make use of an auxiliary heater to heat the dry purge air, reducing the relative humidity even more. This allows the removal of the moisture load with less dry compressed air. Again, this purge air doesn’t go into the system.
Blower Purge Dryers
Blower purge dryers also operate on a four-hour cycle (3 hours of heating and 1 hour of cooling). They use an auxiliary heater but not dry compressed air to purge as the surge is supplied by a blower that runs during the drying cycle.
Heat Of Compression Dryers
Heat of Compression (HOC) dryers work in the same way as other dryers but have a few differences. They can only be used in oil-free compressors. While the drying cycle is the same the regenerator cycle uses the captured heat of compression in the discharge air prior to the after-cooler. This removes the moisture from the compressed air.
Looking For More Information?
If you have any questions about the different types of desiccant dryers, or anything air related, we would love to hear from you. We would be happy to help address your concerns and answer any questions you may have. CDA Systems has represented SPX Flow Pneumatic Products and Hankinson products for many years.
CDA can even provide a service program to meet your company’s needs. Rely on CDA’s Factory Trained Service team and book a site visit today: 925.667.3400/sales@cdasystems.com