Desiccant Dryers: Heat of Compression Type

Desiccant Dryers

Desiccant dryers come in different forms.  They are designed for water sensitive areas as they can reach a dew point to -40oF (-40oC) and below.  That means that water will not condense in the compressed air lines until the temperature is below the dew point.  The desiccant inside these units will adsorb the water vapor as compressed air passes through a bed.  Once the desiccant bed is full of water vapor, it will have to be regenerated.

A typical system will use two towers that will switch back and forth.  One tower is used to remove the water from the compressed air system, and the other is used to regenerate the desiccant.  In this blog, I will cover how the desiccant can be regenerated with a Heat of Compression (HOC) type of desiccant dryer.

An air compressor is not an efficient device.  For every eight horsepower of energy to make compressed air, only one horsepower is used as work.  And for compressed air drying, the type of desiccant dryer is important.  Regeneration of desiccant beads can be done either with non-heated or heated means. The non-heated, or heatless version will use 15% of your compressed air to purge through the regeneration tank.  The air escapes into the atmosphere with the water vapor and is wasted.

With the heated type desiccant dryers, they come in three different categories.  One type uses a heater to increase the temperature of the compressed air. At the elevated temperature, the purge requirement can be reduced to 7% for the regeneration of desiccant.  But, still compressed air is wasted.  To cut the purge to zero, a blower-type heated desiccant dryer can be used.  Instead of heating the compressed air, the blower will push ambient air through a heater to regenerate the desiccant bed.  But can you get more efficient than that?

Well, what if you can remove the heater and the blower?  The heat of compression type of desiccant dryers can do that.  Remember above when I mentioned that “for every eight horsepower of energy to make compressed air, only one horsepower is used as work”.  The seven horsepower of energy that is lost is given off as heat.  The HOC dryer uses that heat to regenerate the desiccant bed.  So, the overall energy is reduced even further.  There is a restriction when using this type of dryer.  The air compressor will have to be oil-free because oil will coat the desiccant beads and stop the adsorption rate.

When the air is compressed, heat is generated.  This heated air can reach around 200oF (93oC).  With the higher temperature, air can hold more water vapor.  As the heated air passes through the desiccant bed that needs to be regenerated, the water vapor is picked up from the desiccant beads.  The saturated air would then pass through an aftercooler.  The aftercooler reduces the air temperature below 100oF (38oC) which will cause the water to drop out.  From the aftercooler, the air will then pass through the desiccant bed in the drying tower.   When the cycle time is reached, the towers will switch to regenerate the second tower.

Line Vacs can convey many things.

With these types of dryers, the desiccant beads will start to degrade from regeneration.  To help replace them, EXAIR offers a Line Vac.  Instead of climbing a ladder with many bags of desiccant, the Line Vac can do this safely and ergonomically.   EXAIR Line Vacs use a small amount of compressed air to generate a powerful vacuum by a Venturi effect.  The unique design of the generators creates a high velocity of air to create a low pressure on one side and a powerful thrust on the other.  The Line Vac can pick up and move solid material vertically up to 20 feet (6 meters).  You can watch a video on the operation of a Line Vac HERE.  The EXAIR Line Vacs are very quiet, compact, rugged, and powerful.  To replace the desiccant, it can do it quickly and safely.

If you need to convey solid materials in a quick and easy way, an EXAIR Line Vac could be a solution for you.  We have them in a variety of materials and designs to match your application.  Ergonomically, they can save the back-wrenching labor of picking up bags, climbing stairs, and dumping material into towers.  If you want to know if the EXAIR Line Vac could work for you, an Application Engineer at EXAIR can help to recommend the best unit for you.

John Ball
Application Engineer

Email: johnball@exair.com
Twitter: @EXAIR_jb

 

Photo: Heated Desiccant Dryer by Compressor1Creative Commons Attribution-No Derivs 2.0 Generic

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