Desiccant Dryers

A compressor takes in Atmospheric Air, loaded with Moisture and contaminants.

At 24°C / 75°F and 75% relative humidity, a 500 SCFM/850 NM³/HR Air Compressor takes in about 340 litres of water in vapour form during a 24-hour period.

The Compressor After Cooler Condenses about half the amount of water.
As the air flows from the compressor into an Air Receiver and Air Distribution lines, it cools.
The vapour condenses causing rust, scale, in The Air Receiver and ultimately leaks in pipes, valves, instruments, and air-operated tools and equipment.

Moreover, when exposed to freezing temperatures, the moisture in airlines will freeze and restrict airflow.
A typical OXAIR Desiccant Dryer pays for itself in less than a year by reducing and eliminating maintenance costs and downtime.
Clean, dry air makes your operation more productive
As long as the compressed air is not exposed to temperatures below the temperature the air was Dried to in the dryer, (the dew point temperature),

No troublesome liquid will form in downstream air lines and equipment.
Dry air keeps pneumatic equipment running at peak efficiency and extends the service life of air tools, motors, and cylinders. Dry air allows pneumatic instruments, valves, and controls to operate reliably, and helps ensure product and process quality.

NB: Dryer Air is Critical in Most Air Separation Applications

• Designed for consistent-pressure dew points
• Eliminate water and freeze-up in low ambient temperatures
• Come completely assembled, piped and wired, with a full charge of activated Alumina Desiccant
• Only hook-up of utilities is needed for operation
• Include structural steel frame, complete with floor stand
• With SUPER QUIET MUFFLER

Desiccant dryers lower the dew point of compressed air by Adsorbing the water vapour in the compressed air onto the surface of the desiccant.

• Twin towers allow the inlet air to be dried in one tower while the desiccant in the other tower is being regenerated (dried).
• These dual-tower regenerative desiccant dryers are an economical and reliable way to dry compressed air to dew points below the freezing point of water or to reduce the moisture content of compressed air for use in critical process applications.

Compressed air is continuously dried through the use of two Identical Towers, each with a Desiccant Bed. While one tower is on-stream drying the compressed air, the other tower is off-stream being regenerated (dried out). The inlet air is fed via Pneumatic Actuated Valves controlled by a PLC.

The towers are alternated in this manner so that dry desiccant is always in contact with the wet compressed air, resulting in a continuous supply of dry air downstream.

All dryers should be installed with Pre-Filters and an After-Filter.

1250 SCM Dryer

Principle

The Oxair desiccant dryer is specifically designed to remove moisture in vapour form. The Dryer’s PLC controlled system is fully automatic, alternately cycling air flow through the dryer’s twin Desiccant Towers. Cycling between the two towers accomplishes the adsorption and regeneration processes and provides a continuous flow of air.

The compressed air laden with moisture vapour enters a tower and flows upward through the desiccant bed. The desiccant has a great affinity for moisture vapour; therefore it adsorbs or removes moisture from the air and holds it on its surfaces.

The adsorption process is an exothermic process meaning heat is produced as moisture is adsorbed on the desiccant surface. At the end of the drying cycle, the desiccant in the tower is Regenerated – or the moisture that the desiccant Adsorbed is removed by Dry, Warm Air. A small portion of the dry gas is expanded to near atmospheric pressure by passing through an orifice specifically designed for the Regeneration (Purge) stream to strip the previously Adsorbed moisture vapour.

The exothermic reaction from the previous drying cycle contributes to the regeneration of the desiccant bed. The heat is picked up by the Regeneration stream, which in turn increases the moisture Adsorption capacity of the Regeneration stream.

Operation Cycle

The wet compressed air enters the dryer via left hand side Inlet Valve DV-01,

• The right Tower Purge (regeneration) exhaust valve DV-04 will open depressurising the off-line tower and
• Purge Valve DV-06 will open,
• The purge flow will continue for a period of approximately three minutes and fifty-five seconds.
• When regeneration of the off-line tower is complete,
• The purge exhaust Valve DV-04 will close,
• Initiating a forty-five second re-pressurisation phase through the purge valve DV-05 and DV-06.

After Re-Pressurisation is complete:

• The PLC will switch inlet valves and the inlet air/gas stream will divert from the left tower to the right tower through DV-02.
• Exhaust Valve DV-03 will also open De-Pressurising the off-line tower to begin the regeneration cycle.
• The left Tower Lower Purge Valve DV-05 diverting a portion of the dry air down through the top of the Left Hand Tower and out through the exhaust through the lower Purge Valve V-03.

The desiccant dryer will continuously cycle through the sequence described above until power is removed from the dryer, or the air pressure drops to a point where an alarm is triggered forcing the dryer to pause its cycling. Complete standard operating cycle is ten minutes (5 minutes each side) Under normal conditions and during normal operation; the dryer should provide an outlet pressure dew point (PDP of – 40°C or below.)