Moisture in the air causes contamination in the pneumatic system, leading to rust and blockages. It reduces quality in painting operations. In industries such as chemistry and electronics, it causes product damage. For this reason, moisture must be removed from the system. Dryers are used to remove moisture from the air in pneumatic systems. There are several methods for drying air:
Physical Drying Method
The physical drying method uses 2 separate vessels so the system doesn’t have to stop. Both vessels use materials such as silica gel that absorb and retain moisture.
With this method, drying is carried out physically. Air is passed through silicon dioxide. The desiccant material is in granular form. Silica gel changes color when it comes into contact with water vapor.
When the desiccant reaches a certain saturation level, it’s taken out of service and hot air is drawn through it, purifying it again. Meanwhile, the other vessel remains in service.
This method should be used in applications requiring precise drying. It has an effect roughly equivalent to cooling the air down to -60°C.
Refrigerated Drying Method
Before entering the dryer, humid air coming from the compressor passes through a pre-cooling chamber. Air arriving at approximately 25°C has its temperature lowered in a few stages. It’s then passed into the actual chiller, where its temperature is lowered to 4-5°C. Lower temperatures should be avoided to prevent icing.
A “water-trap filter” should be used near the outlet of the dryer to remove condensed moisture.
For energy recovery, the air leaving the dryer is passed back through the pre-cooling chamber, providing pre-cooling for the incoming hot air.
Because of its low cost and suitability for general use, it’s the most preferred drying method.
Refrigerated Dryer Dew Point
Refrigerated dryers typically lower the air’s dew point to between +2°C and +10°C.
Adsorption Dryer
Adsorption (chemical) dryers can achieve much lower dew points, down to below -40°C.
Desiccant Material Life
The silica gel or activated alumina materials used in adsorption dryers can be periodically regenerated and reused.
Chemical Drying Method
Compressed air is passed through tubes containing a substance that can bond with water. These tubes generally use sodium chloride (salt). Sodium chloride bonds with the water vapor in the air. This way, the harmful vapor in the compressed air is removed.
Related Questions
When the desiccant in one vessel absorbs moisture and reaches saturation, the other vessel is brought into service without stopping the system. Meanwhile, the saturated vessel is purged with hot air and prepared for reuse.
Silica gel changes color as it absorbs moisture, visually indicating its current saturation level. This makes it easy to tell when the desiccant needs to be replaced or regenerated.
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