Many enterprise users adopt dryers, but even with dryers, it cannot be guaranteed that no moisture will condense in the compressed air. The following is an analysis of the various reasons for incomplete moisture removal from compressed air after passing through a dryer and the corresponding solutions based on practical situations.

Reasons and Solutions for Incomplete Dehydration of Compressed Air After Passing Through a Dryer

1. 90% of the moisture in compressed air is trapped by air storage tanks. Refrigerated dryers and heatless regenerative dryers can only handle the remaining small amount of moisture in gaseous form.Air storage tanks are the most important and primary equipment for drying and purifying compressed air.

2. However, air storage tanks can only separate liquid moisture. Compressed air can only be cooled below the pressure dew point corresponding to its pressure to allow the air storage tank to separate moisture. Therefore, the effect of aftercooling has a significant impact on the moisture content of compressed air.

3. The pressure dew point of a refrigerated dryer must be 10°C lower than the ambient temperature, but its optimal pressure dew point is 4°C. This is because water has the highest density at 4°C, making it easiest to separate, and it will not cause ice blockages.

4. In principle, heatless regenerative dryers can only handle gaseous moisture (i.e., water vapor). A large amount of liquid water entering a heatless regenerative dryer will seriously affect the machine's performance.

In summary, aftercoolers and air storage tanks are the most critical water removal equipment. Other drying equipment only play a supplementary role and should not be the focus of compressed air drying.

Specific Causes and Solutions

1. Clogged cooling fins

 Dust or other debris blocking the cooling fins will reduce the cooling efficiency of compressed air, increasing the pressure dew point. This adds difficulty to moisture removal for post-treatment equipment. In spring, for example, air compressor coolers are often clogged with willow catkins. **Solution**: Install filter sponges on the windows of the air compression station and regularly blow dust off the coolers to ensure effective cooling of compressed air and normal water removal.

2. Malfunction of the water-air separator (a water removal device in screw air compressors)

 If the air compressor uses a cyclone separator (with spiral baffles added inside to enhance separation efficiency, which may increase pressure drop), its separation efficiency is high only at the rated processing capacity. Deviations from the rated capacity will reduce efficiency and cause the dew point to rise. **Solution**: Inspect the water-air separator regularly and handle blockages or other faults promptly. If the separator fails to drain water in humid summer, check and repair it immediately.

3. Excessive compressed air consumption beyond the design range

 A large pressure difference between the air compression station and the user end leads to high airflow velocity, reducing the contact time between compressed air and adsorbents. This causes uneven distribution in the dryer, with excessive flow concentrated in the middle, leading to rapid saturation of adsorbents in that area. Saturated adsorbents can no longer absorb moisture, resulting in "channeling" (compressed air carrying a large amount of moisture through the central area), and liquid water at the user end. Additionally, rapid expansion of compressed air during transportation to the low-pressure end causes a significant temperature drop. If the temperature falls below the pressure dew point, water vapor condenses in a supersaturated state. In winter, this can quickly freeze on the inner walls of pipelines, gradually blocking them.

Solution: Increase compressed air flow. For example, supplement excess instrument air to process air, connect instrument air to the front end of the process air dryer with a control valve, and solve both the insufficient supply of process compressed air and the "channeling" issue in the dryer's adsorption tower.

4. Loose filling of adsorbents in adsorption dryers

 Adsorption dryers use activated alumina. If the filling is loose, the adsorbents will rub and collide under the impact of high-pressure compressed air, leading to pulverization. Pulverization increases gaps between adsorbents, allowing a large amount of compressed air to pass through without effective treatment, ultimately rendering the dryer ineffective. This issue is manifested by a large amount of liquid water and sludging in dust filters.

Solution: Fill activated alumina as tightly as possible, and inspect and replenish it regularly after use.

5. Oil in compressed air causing "oil poisoning" of activated alumina

 Screw air compressors use super coolants with high thermal conductivity to cool compressed air. If the coolant is not completely separated from the compressed air, the discharged air will carry oil. Oil adheres to the surface of activated alumina balls, blocking their capillary pores and disabling their moisture adsorption function (i.e., "oil poisoning").

 Solution: Replace the post-oil removal filter elements on schedule to ensure thorough oil-gas separation in the air compressor and effective post-oil removal. Additionally, avoid overfilling the super coolant in the unit.