Purge Economizer Controls is an energy management system which allows the air dryer user to operate at a specified outlet dewpoint, and maintain that dewpoint level within a close tolerance, while reducing the volume of purge air required. The volume of purge air will vary proportionally with the volume of air being dried. Standard timed based controls do not allow for purge adjustment due to demand fluctuations, or reduction in dryer loading. Purge flow must be fixed for a maximum dryer inlet capacity based on an anticipated operating pressure with standard time based controls.
Purge Economizer Controls purging, is based on the dewpoint level measured at the outlet of the dryer-not by moisture or thermal sensors placed in the centre of the desiccant chambers. If the outlet dewpoint does not warrant taking the drying chamber off line at the end of each purging/repressurization period, the tower positions are maintained in a ""Purgeless"" condition until the outlet dewpoint rises to the set level of the hygrometer. This ""Purgeless"" period may continue for an extended period of time if very little air is being processed by the dryer. As the dewpoint level is considered prior to each tower switching, a ""Purgeless"" period is likely to occur prior to inlet switching. Therefore, the overall time cycle of the dryer is extended, resulting in fewer valve switching operations, and reduced wear and tear on valves. As the controls operate based on outlet dewpoint, system changes such as variation in operating pressures, and aging of desiccant (reducing its capacity), are automatically taken into consideration. Over time, due to desiccant aging, ""Purgeless"" periods will become increasingly shorter, providing the user with an indication that the desiccant requires changing.
All new APPL twintower regenerative air dryers can be supplied with ""Purge Economizer Controls"", or existing models may be converted. This control system can also be applied to most competitive twintower dryers.
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