Gala Centrifugal Dryers

HOW IT WORKS

The pellets emerging from the pelletizer cutting chamber are carried by the process water through piping to an agglomerate catcher at the inlet of the centrifugal dryer. The agglomerate catcher protects the dryer by removing larger pellet clusters(agglomerates) that may be produced during start-up before they enter the dryer rotor.

In dryers with water rates less than 20 M3/h, all the process water is separated inside the rotor section of the dryer. Larger systems are equipped with a predewatering system in which up to 95% of the process water is separated from the pellets.

The pellets and residual water flow into the rotor section of the dryer. Both the speed of rotation and the design of the lifters inside the rotor cause the pellets to ricochet between lifters and screens while being conveyed by centrifugal action up the dryer rotor in a helical path. The water is separated through the screens and the pellets are continuously conveyed into the upper section of the dryer where they are discharged from the resin outlet.

The drying process reduces the residual moisture, depending on the polymer. Final drying is achieved in the upper two-thirds of the screen surface and in the pellet outlet chute of the dryer. Dry countercurrent air flow generated by an external exhaust fan removes the residual surface moisture from the pellets, assisted by the pellet internal temperature. The exhaust fan produces a slight vacuum which prevents humid air from exiting into the room or condensing in downstream equipment components.

The pellets leave the dryer continuously at a residual moisture of 0.05% (LDPE). The length of the water transport line impacts the residual moisture of the pellets and determines the pellet temperature entering the dryer. Additional factors that influence residual moisture are pellet size and shape, pellet surface and hygroscopic characteristics. In some cases additional cooling, post-drying or classification may be utilized.