How to Choose Between Different Types of Compressed Air Dryers

Refrigerated air dryers and desiccant air dryers are both widely adopted compressed air drying equipment. However, no single dryer type suits all working conditions.

Selection and matching schemes shall be determined mainly based on drying requirements and operating costs to satisfy customer demands.

Refrigerated Drying Method

The refrigerated drying process employs refrigerant to cool compressed air down to a specific dew point, condense excess saturated moisture,

and separate liquid water via a water-oil separator to realize air drying. Nevertheless, the outlet pressure dew point of such equipment cannot drop below the freezing point of water.

Distinct features: continuous operation, no regeneration required, low energy consumption.
Adsorption Drying Method

The adsorption drying method uses adsorbents such as silica gel, activated alumina and molecular sieve to capture moisture from compressed air.

This technology can easily achieve a pressure dew point below the freezing point of water. Since adsorbents have limited moisture adsorption capacity,

twin-tower or multi-tower alternating adsorption is adopted to sustain continuous compressed air drying.

There are various desiccant dryers available on the market; all operate on the principle of moisture adsorption, differing only in regeneration modes.
Selection Guidelines
Based on Performance Requirements
The primary and most critical selection principle is compliance with customer requirements.

Refrigerated air dryers feature lower energy consumption and running costs compared with desiccant dryers, yet they cannot deliver deeply dried compressed air.

The pressure dew point of refrigerated dryers is normally above 3°C PDP, which meets demands for general manufacturing processes.

For applications requiring higher dryness of compressed air, desiccant air dryers should be selected.
Based on Installation Environment
Refrigerated air dryers have weak adaptability to ambient conditions. Excessively high or low ambient temperature impairs unit operation:
High ambient temperature raises the refrigerant condensing pressure of air-cooled refrigerated dryers, reduces cooling capacity and increases the outlet pressure dew point.
When ambient temperature drops below 0°C, ice blockage easily occurs during condensate drainage of refrigerated dryers.

Desiccant air dryers tolerate a wider range of ambient temperatures. During model selection, attention should be paid to the impact of high air compressor outlet temperature under maximum ambient temperature,

which will push up the pressure dew point of incoming compressed air.

Based on Maintenance Costs
Refrigerated air dryers adopt a hermetic refrigeration system where refrigerant is isolated from the atmosphere, resulting in low system maintenance costs.
Desiccant dryers involve frequent valve switching between adsorption towers; heat-regenerative types additionally cycle between high and low temperatures, leading to higher maintenance expenses for valves.

Moreover, most desiccant dryers are matched with oil-injected compressors at the front end. Compressor lubricant may easily cause desiccant oil poisoning,

requiring periodic adsorbent replacement and further increasing maintenance expenditure.

Based on Procurement Costs
From current market prices, desiccant air dryers of the same air handling capacity are sold at a higher price than refrigerated dryers of the same brand.
Based on Operating Costs

These two types of dryers achieve different dew point levels and cannot be simply interchanged, so their operating costs are not directly comparable.

Cost comparison is only meaningful within the same dryer category:

Comparison among refrigerated dryers with different heat exchangers, refrigerants and gas-liquid separation structures;
Comparison among desiccant dryers with different regeneration modes.
Our Recommendations

If the temperature in pipeline areas stays below 2°C for a long time, and the required compressed air pressure dew point is at least 5°C lower than the minimum annual ambient temperature,

a standalone desiccant dryer is recommended.

Clarify the actual dew point requirement for compressed air usage, compare it with item 1, and adopt the lower dew point value. Equipment selection must satisfy this dew point target first;

then energy-saving configurations within the same dryer category can be considered. Otherwise, investment returns will be unsatisfactory.

It is advisable to install a refrigerated dryer upstream of the desiccant dryer. The refrigerated dryer removes most moisture and oil from compressed air,

lowering the dehumidification load of the desiccant dryer, stabilizing its drying effect, and allowing selection of a smaller-sized desiccant dryer. Meanwhile,

it reduces contamination of adsorbents by oily impurities, maintains stable drying performance for longer periods and extends the adsorbent replacement cycle.