A desiccant compressed air dryer uses a special material, called desiccant to dry the compressed air. This desiccant is made of a material that attracts water, the water sticks to the surface of the desiccant. Every once in a while, the desiccant needs to be dried, or ‘regenerated’, to remove the water again.
A desiccant dryer is used where a higher quality (i.e. of that of a Fridge Dryer) of dry air is required.
How a Desiccant Dryer Works:
A desiccant dryer usually has two identical towers, filled with desiccant. One tower is used to dry the compressed air, while the other tower is regenerated.
Every once in a while (controlled by a central control unit) the dryer switches towers. The compressed air is now dried by the second tower, while the first tower, filled with wet, saturated desiccant is dried.
On most dryers, there is a small sight-glass. Behind the glass you can see small beads. This is not the drying-desiccant, but an indicator. It will change colour when the air the is too wet.
When the desiccant has done its job for some time, it has absorbed all the water from the compressed air and is saturated with water. It cannot hold any more water. In order to re-use the desiccant, we need to get rid of all that water. This is called regeneration.
The regeneration process is done in one of the two towers of the air dryer, the one that is not operational. There are two ways the desiccant can be regenerated: by hot air or by dried compressed air.
With the hot air method, a separate system consisting of a fan with an electric heater is used to blow hot air through the desiccant to dry it. This is just normal air drawn from the compressor room.