Considerations in Buying a Used Desiccant Dryer for Plastic Resin

Initial investment, operating cost and production considerations are all factors that affect which desiccant dryer you should purchase. There are several different types of dryers to choose from: desiccant, hot-air, straight compressed-air dryers, etc.    Desiccant dryers are the most prevalent and most likely to be seen on the used market.  Desiccant Dryers are typically used for drying hydroscopic material- any material that attracts moisture from the air.

The Twin Tower Desiccant Design is typical of desiccant beds dryers.  While one bed is drying product, the other bed is regenerating.  These machines typically have a dew point of -40 F degrees, but lower dew points can be reached with certain units.   There are Heatless Desiccant Air Dryers, Heated Desiccant Dryers and Blower Purge Desiccant Dryers.

Heatless Desiccant Air Dryers use a blast of dry air from the online tower to regenerate the offline tower.  While the compressed air is being dried in one tower, the desiccant in the other tower is being regenerated.  These machines tend to have the lowest initial investment cost but can be expensive to operate because of the large amount of compressed air consumed during the regeneration process. Heated Desiccant Dryers have a heating element either inside or outside of the desiccant beds; the heater either dries the desiccant bed directly (internal) or dries the purge air blowing through the bed (external).  These units have a very low energy cost for operation but have a higher initial investment. Blower Purge Dryers are similar to heated dryers.  In blower purge dryers, the purge air is atmospheric air supplied by an electric motor that has been supplemented with heat. Operating expenses for blower purge dryers falls in between the heated and heatless units. Desiccant Dryer Installation Factors 

Machine Mounted Dryers tend to be utilized the best in applications where there are infrequent material changes and/or where floor space is limited.  These dryers tend to be smaller in size but can be more difficult to service based on accessing it on top of the machine.  Most machine mounted dryers are dual desiccant beds fed with a continuous stream of air.  The hopper is either mounted on the machine or mounted beside the press.

Portable or beside the press dryers are more convenient to service but are a little more costly than machine mounted dryers. Floor space will help determine if you want a dual bed (smaller) or a multi-bed unit (larger).  These dryers are typically used in longer-running jobs with limited changeovers.  Casters for mobility allow the dryer to be moved from various production lines as needed.  For larger units the hoppers are usually placed next to the unit and fed to the process.  An option to consider for smaller dryers is the self-contained portable drying system.  These units have the, controls, dryer and hopper mounted on the same frame.  This allows for greater mobility and ease of use; material can be dried away from the press and brought to the press once it is ready to be introduced to production.

Central Drying Systems are desired in large operations feeding large numbers of presses or operations making many material changes.  Various materials can be dried using one dryer and several hoppers.  Hoppers can be configured with additional heaters to maintain the temperature and vacuum loaders to feed individual machines.