In some industry (electronics, pharmaceutical, food preparation, pneumatic conveying, etc.) or for installations with external pipe work, a pressure DewPoint of +3°C from a refrigerant dryer is not sufficient.
For these applications, a heatless adsorption dryer is required supplying compressed air at a pressure DewPoint of down -70 °C. Heatless dryers are compact and have low purchase and maintenance costs.

The HDT heatless adsorption dryers consist of two parallel vessels filled with adsorption material (molecular sieve).
While compressed air is dried in one tower, the second saturated tower, having just come off line, is regenerated. A small amount of dried compressed air is used for this purpose.
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Dryers are supplied with 0.01 micron oil removal filter (with automatic drain) on the inlet and a 1 micron dust filter on the outlet.

Both filters are fitted with a pressure differential gauge, offer easy access for maintenance and are contained within the dryer footprint.

 
The change over spool valve designed by FRIULAIR is simple and reliable. Access to the valves is extremely easy and they have a large cross sectional area for low pressure drop. The aluminium valve bodies are anodized internally and externally to prevent corrosion and sticking. The low maintenance valves can be quickly and easily disassembled and reassemble if required.

From HDT 300 model, the dryer is supplied with butterfly selector valves with spheroidal graphite cast iron body and stainless steel selector lens, controlled by a pneumatic actuator.
Carbon steel towers are built in compliance with current European directives and powder coated. ASME Section VIII Div. 1 is available on request. The volume of each vessel is designed to give optimum velocity over the desiccant bed and a low pressure drop (Dp 0.21 bar max.).
Accurate packing density prevents desiccant material movement and dusting. Compressed air flow is upwards through the desiccant bed to protect it from contamination. Heavy particles or water droplets will stay at the bottom of the vessel and be discharged during the regeneration process.
Each adsorption tower has an inner and outer stainless steel diffuser to ensure maximum distribution of the compressed air over the desiccant materials.
The operation phase of each tower in indicated by an easy to read pressure gauge.
Lower socket for quick and simple removal of exhaust desiccant material.
Upper socket for quick and simple replacement of desiccant material.
Orifice to ensure constant and uniform flows during both regeneration cycles. Access to this orifice is easy to allow replacement for different working conditions and requirements.
The correct operation of the dryer is constantly checked and monitored by an electronic controller. HDT 3-25 dryers are supplied with DDC12 electronic instrument. From model HDT 30 the dryers are equipped with DDC15 electronic instrument.
Each tower is fitted with a safety pressure relief valve (from model HDT 30 included).
The silencers are placed in the lower part of the dryer for ease of access and for easy disassembling and/or replacement. Made in aluminium melting, they ensure maximum security during de-pressurization phase. They can be regenerated with detergent and hot water washing.