Desiccant dryers are configured to provide the drying hopper a continuous stream of low dew point air for fast, effective drying of hygroscopic resins. To achieve this, dryers utilize an automatic process where part of the moisture removal capacity is “on line” providing the drying hopper with dry air, while the other part is “off line” in a regeneration mode, where heat is used to “bake out” the moisture trapped in the media.
Today, most dryer designs fall into two camps, wheel dryers and non-wheel dryers (2 or 4 desiccant beds). Although there are similarities in the two designs where they provide hot, dry air to the drying hopper, the methods that they use to achieve this desired output is quite different.
Wheel dryers contain a dense, desiccant encrusted wheel that is continuously rotating and two blowers. As the wheel rotates, sections of the wheel will pass through sections where regeneration heat, regeneration cooling, and drying cycles occur. The drying blower sends the wet air from the outlet of the drying hopper through a newly regenerated portion of the wheel where moisture is removed from the air. The resulting dry air is heated to the drying temperature and returned back to the drying hopper.
A second blower in the wheel design is solely used for regeneration of the wet section of the wheel. Its purpose is to blow heat directly into the wet section of the wheel and purge the trapped moisture out of the wheel. Since the wheel is dense and rotating at a relatively fast rate of speed, the regeneration blower, needs to be almost as large as the process blower. With this amount of airflow, a high wattage regeneration heater operates continuously. This high rate of air and heat is discharged directly into the room through a large, screened port typically saying “caution/high heat”. This vented regeneration air discharges all of the heat, dust, and particulate trapped in the wheel released during the regeneration cycle and directly into your clean room or molding area. This could create a high potential for airborne contamination.
Disadvantages to this design would be the nonstop electrical demand of the large regeneration blower and regeneration heater to be used to regenerate the wheel. Along with this significant amount of energy for the regeneration cycle, all of the dust, heat, and moisture from the dryer will be discharged into the clean environment making it difficult to keep clean.
The dryers with two or more beds and a single blower are configured with a stationary tower design. The airflow for process and regeneration are redirected through a zone switching valve. The airflow on this style dryer is similar to most dryers where the wet air is passed through a newly regenerated desiccant tower. Once the air gets through this process tower, most of the dry air will be heated with a process heater and returned to the drying hopper. The small amount of dry air, about 5% of the process air, that does not go to the process will be used in regeneration of the wet bed. Heating and cooling of the regeneration bed with this air eliminates the need for a second blower. This displaces much less heat, particulate and dust into your molding area or clean room. Other than keeping your clean room clean and free of contaminants, this design consumes much less energy in comparison to the other designs. The amount of energy save in the regeneration cycle is about 50% less than wheel dryers as smaller regeneration heaters are used with less regeneration air.
To further reduce the energy used by the dryer, we incorporate adaptive, on demand regeneration where we monitor and adjust the regeneration process based upon the amount of moisture in the beds. This design provides another 15% in energy savings as the regeneration cycle changes based on the demand placed on the drying system as it monitors throughput, moisture levels in the resin and the changing ambient conditions.
To find out more on how Dri-Air can assist you with your drying needs and keep your clean room clean, contact us at 860-627-5110 or sales@dri-air.com
