Desiccant Air Drying Technologies
Twin Tower Heatless Desiccant Dryers
The CompAir AX-Series uses twin desiccant towers and strategically positioned valves to dry the compressed air.
The compressed air produced is thoroughly dried as it is directed through the on-line desiccant-filled tower of the dryer. As the desiccant in this tower adsorbs moisture from the air, the desiccant in the dryer’s offline tower is purged of moisture and readied for use.
Advantages at a glance:
High Reliability - proven technology used in thousands of applications and installations worldwide.
Low Capital Investment - large range, available for precise sizing to suit your needs.
High Air Quality - pre and post filter included, helping you to meet stringent air quality requirements.
Energy Efficient - with the optional high efficiency Energy Management System (EMS) offers even greater efficiency.
Standard features include:
High Efficiency Pre Filter and Dust Filters
IP54 electrical enclosure
Digital controller
Tower pressure gauges
Colour change moisture indicator
Optional features include:
Energy Management System (EMS) with dew point display
Fail-to-Shift alarm - Monitors the dryer sequencing functions to ensure proper dryer operation by sensing the pressure in each tower, sending an alarm in case of anomalies. This option is available from models 1000m3/h and above
IP65 electrical rating plus stainless steel control box
4-20 mA signal (requires EMS) is available should you need to get 4-20mA to your SCADA system
Different tower vessels design code
Stainless steel control air tubing
Filter monitoring - Differential pressure switches installed on filter monitor performance. Display options include analog and digital
-70˚C pressure dew point
No air loss drain for filters with alarm
Marine paint
A desiccant air dryer is equipment that removes moisture from compressed air by adsorption — a physical process where water vapor sticks to the surface of a porous material (desiccant). This results in very low pressure dew points (typically -40 °C to -70 °C), far lower than what refrigerated dryers can achieve.
⭐ Twin Tower Heatless Desiccant Dryers — Overview
Twin Tower Heatless Desiccant Dryers are the simplest and most common form of desiccant dryers used in industry. They consist of two pressurized towers filled with desiccant material (often activated alumina or molecular sieves). One tower dries compressed air, while the other regenerates the saturated desiccant — enabling continuous 24/7 operation.
📌 Key Advantages
Ultra-low dew point (standard -40 °C; optional up to -70 °C) for moisture-sensitive applications.
Simple, proven technology with reliable, long-term performance.
Lower capital cost compared to more complex heated or blower-purge designs.
No external heaters required — reduces electrical and mechanical complexity.
📌 Typical Applications
Used where very dry compressed air is essential, such as:
Pharmaceuticals
Electronics and semiconductors
Food & beverage
Precision pneumatic machinery
Packaging and automation systems
Petrochemicals and chemical processing
🔍 Principle of Operation
🌀 1. Adsorption (Drying) Phase
Moist compressed air enters the on-line tower filled with desiccant.
Water vapor adheres to the desiccant surface, producing dry compressed air.
Dry air exits with a very low dew point (-40 °C or lower).
🔄 2. Regeneration (Purging) Phase
At the same time, the off-line tower is depressurized and regenerated using purge air:
A small portion (typically ~10 – 15 % of dry compressed air) is expanded to atmospheric pressure.
This purge air flows counter-current through the saturated desiccant, stripping away moisture and exhausting it to the atmosphere.
🔁 3. Cycle Switching
After a preset time/fixed cycle (e.g., ~5–10 min), valves switch towers.
The regenerated tower becomes the drying tower, and vice-versa.
This alternating cycle ensures continuous dry air delivery.
📊 Core Components
Component Function
Dual desiccant towers Provide alternating drying and regeneration
Desiccant media (e.g., Activated alumina, Mol. sieve) Adsorbs moisture from air
Pneumatic valves / solid-state controller Controls tower switching
Prefilters / afterfilters Remove particulates & oil aerosols before/after drying
Purge line & muffler For regeneration air and moisture exhaust
Pressure gauges / moisture indicator System monitoring and safety
📌 Performance & Technical Specs
🔹 Pressure Dew Point
Standard: -40 °C at rated flow (typical industry requirement).
Ultra-dry options: -70 °C for specialized applications.
🔹 Flow Capacity
Range spans from small (e.g., ~10 scfm / ~20 m³/h) to very large systems (thousands of scfm) depending on model and manufacturer.
🔹 Operating Pressure
Typically suitable for industrial compressed air pressures — often up to 10–16 bar(g) or higher with engineered designs.
🔹 Purge Loss
Heatless dryers use 10–15 % of dry air for regeneration. This is the main operatio
