The closed-system regeneration design
does not use any process air or gas for purge so there is not process air/gas loss.  The purge gas in these systems is re-circulated minimizing loss and cost. 

The heat-of-compression reactivation dryer
relies heavily on the heat of compression to reactivate the bed.  Compressors that are cycling or in intermittent operations are not suited for this type of dryer.

Split-stream, closed-system dryers
are best suited for specialized gas applications. They typically special engineered for a specific application.  Because a blower is not used in the reactivation system they can be used in very high process flow applications.



Closed-system regeneration dryers use either the external heater system, heat of compression, or a split-stream concept.

An externally heated, closed-system dryer heats a captive volume of air with electricity or steam and then sends the heated air through the regenerating bed to carry off the adsorbed water.

The heat-of-compression reactivation dryer uses part or all of the heated air from the main compressor to purge the tower being reactivated. The air is then cooled using a condenser/separator and then redirected back to the inlet process air, where it is dried along with process air.

Although efficient, they have the lowest bed capacities; and designs typically are well above the typical -40°F designs.  They can be designed for lower dew points, however, capital cost rises quickly.  These types of dryers are best suited for high process flow rates.

A split-stream, closed-system dryer diverts part of the compressed air from the dryer inlet through a heater, then through the idle bed of desiccant, where the air purges out the moisture from the desiccant.  This portion of air then goes through a regeneration cooler and into the active desiccant bed for drying.

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