How to Address Poor Dew Point Performance of Desiccant Air Dryers

Heatless Regenerative Desiccant Air DryersThree primary causes lead to unsatisfactory dew point for heatless dryers:
Temperature Factors

The inlet air temperature and ambient temperature must not exceed design values. Especially for dryers installed after air-cooled air compressors, 

optimize pipeline layout to lower the inlet temperature of the dryer as much as possible.

Solution: Take measures to reduce all temperature indicators. In particular, ensure adequate ventilation for air-cooled air compressors.
Purge Air Flow

Heatless regeneration belongs to pressure swing regeneration. If the pressure of the upstream air compressor remains stable, 

stable dew point can be achieved by maintaining a fixed purge air flow after commissioning. However, if the discharge pressure of the air compressor fluctuates, 

the calculation formula indicates that the purge air flow shall be increased when pressure drops; compressed air consumption can be reduced when pressure rises.

\(R=W/[(P+P_0)/P_1]\)
R = Purge air flow; W = Rated processing capacity; P = Operating pressure

\(P_0\) = Atmospheric pressure; \(P_1\) = Vacuum degreeSolution: Adjust the purge air flow to a proper value according to air compressor pressure. 

If the compressor pressure fluctuates drastically during operation, set parameters based on the minimum operating pressure or replace the dryer.

Excessively Long Adsorption Cycle

The working principle of heatless dryers can be understood as shallow-layer adsorption. An overly long adsorption cycle will cause relative saturation of adsorbents. 

The adsorbent cannot be fully desorbed during regeneration, resulting in deteriorated adsorbent performance.

Solution: After confirming this root cause, implement complete regeneration of desiccant, then set a reasonable cycle according to actual operating conditions. 

For heatless dryers equipped with dew point control, it is critical to set the maximum adsorption cycle; avoid unlimited extension of adsorption duration in any cycle.2. 

Heated Regenerative Desiccant Air DryersSimilarly, three major causes of poor dew point are listed below:

Same as above: adjust temperatures to the specified range.
Purge Air Flow

Thermal regeneration requires balance between regeneration heat and moisture adsorbed in one adsorption cycle. Therefore, professional technicians must complete equipment commissioning. 

Equipment operators shall only make adjustments within the scope authorized by the manufacturer.

Same as above: excessively long adsorption cycle. If the unit has sufficient monitoring points, activate regeneration exhaust monitoring to guarantee complete regeneration in every cycle, 

especially under dew point control mode.

3. Heat-of-Compression DryersTwo temperature parameters must be confirmed before commissioning heat-of-compression dryers: 

the inlet air temperature shall reach the design value, and cooling water temperature shall comply with specifications.

Heat-of-compression dryers are a special category of desiccant dryers. Zero-purge heat-of-compression dryers are widely promoted by manufacturers, yet many suppliers overstate their performance. 

For achievable dew points of zero-purge heat-of-compression dryers, refer to Atlas Copco MD and ND series specifications: MD represents zero-purge heat-of-compression dryers without heaters; 

ND represents zero-purge models equipped with heaters.Since many dryer manufacturers actively promote zero-purge heat-of-compression solutions, 

we analyze poor dew point issues for this type. Note that the dew point curve of heat-of-compression dryers fluctuates significantly and cannot remain constant.

Check the designed dew point of your zero-purge heat-of-compression dryer (verify the worst dew point on the dew point curve) and confirm whether it meets process requirements. 

If the designed dew point fails to satisfy the minimum process requirement, contact the manufacturer for modification. If the design specification cannot meet process air demands, 

on-site commissioning will hardly remedy the problem, and modification is mandatory.

Temperature Issues

Rectify conditions if dryer inlet temperature, adsorption inlet temperature or cooling water temperature fail to meet standards. 

Main measures include thermal insulation of pipelines between the dryer and air compressor, and optimization of cooling tower performance for circulating water. 

These temperature parameters are rigid indicators with no room for compromise. For equipment with long service time, clean and remove scale from the dryer cooler.

Drainage Issues

Similar to refrigerated air dryers, moisture in zero-purge heat-of-compression dryers is fully separated via drainage systems. Poor drainage performance will degrade overall unit performance. 

Remedying drainage faults in a timely manner can recover equipment performance.

Adsorption Cycle Problem
This is generally caused by missing maximum duration protection in dew point control settings. Carry out full regeneration of adsorbents and revise control parameters.

4. Blower Purge Regenerative Desiccant Air DryersRecommendation: In regions with high temperature and heavy rainfall in summer, 

avoid applying blower purge dryers if the ambient temperature and humidity around the dryer cannot be properly controlled. Do not expect high performance from this equipment during summer.

Reason: Regardless of closed-loop circulation design, regeneration air is sourced from ambient atmosphere. Hot and humid ambient air prevents effective regeneration of adsorbents. Standard units are designed for regeneration air conditions: 

inlet temperature 38°C, relative humidity 60~65% RH.

Temperature Issues

The air intake of the blower must avoid cross flow with exhaust air from air-cooled air compressors. All operating temperatures shall not exceed design limits. 

Cooling water temperature of zero-purge blower purge dryers must be strictly guaranteed.

Purge Air
Adjustment of purge air for blower purge dryers must be performed by qualified professionals. Regeneration requires balance between heat supply and adsorbed moisture within one cycle.


Adsorption Cycle
As mentioned above, unreasonable adsorption and regeneration cycles require professional adjustment and protection limit configuration for the dew point control system.

For other models such as combined dryers, troubleshoot following the above analysis items correspondingly.Summary of Troubleshooting Procedures for Poor Dew Point of 

Desiccant DryersAfter ensuring proper ventilation and water supply in the compressor station, conduct inspection step by step:

Step 1: Check whether adsorption inlet temperature, regeneration temperature and ambient temperature are normal.
Step 2: If temperature parameters are normal, inspect valves for internal air cross-leakage.
Step 3: Adjust purge air flow; for zero-purge dryers, verify if the drainage system can discharge condensate timely.

Step 4: Ask professional technicians to check if the adsorption cycle matches actual working conditions.If all parameters are within normal ranges, check whether the dryer design is reasonable. 

Another critical factor: confirm whether the adsorbent has exceeded its service life.