Even when specialized conveying procedures are used, it is not possible to entirely eliminate increased dust production caused by abrasion and particle destruction during the pneumatic transport of bulk material – and in the plastics industry, even the smallest amount of dust in plastic pellets can cause problems during processing. Separators are used to remove the dust from the pellets, thereby improving product quality.

With ever-expanding market requirements to be satisfied, there has been an explosive increase in the variety of plastics used as well as the associated diversity of properties they have. The quality of an end-product is significantly dependent on selecting the right product cleaning system to conclude the pneumatic conveying process, as high dust levels may cause plastic films to be prone to tearing, or may prevent the desired level of transparency from being achieved in plastic glazing, for example. Even in sophisticated conveying systems, it is not possible to entirely prevent abrasive dust formation. Separators have proven valuable for removing dust fines and short streamers, helping to achieve top product quality before packing, loading or processing.

Zeppelin offers five basic types of separator; the company’s product range also includes static screens and drum screens for the removal of long streamers and angel hairs. GTS or GSE counterflow pellet cleaners are most frequently used in storage silos at the end of conveying, wherein the pellets to be cleaned are accelerated by a stream of conveying gas and then subjected to an opposing gas stream. This causes a high relative velocity between the product and the countercurrent, allowing dust particles and streamers to be reliably separated from the pellets on account of their lower kinetic energy. The newer GSE generation of separators uses an integrated expansion zone to improve separation efficiency; less tall than their GTS predecessors, they also require less energy for operation. Both separators are designed for throughputs of 3 to 120 metric tons per hour, and can reduce dust content from over 1,000 ppm to less than 50 ppm.

The FVS is another type of separator that is used underneath silos in gravity chutes, and which can optionally be integrated into truck container loading and handling arrangements. This separator is suitable for throughputs of 3 to 500 metric tons per hour, and it has a compact design that makes it ideal for retrofitting. Separators offer a simple means of significantly improving product quality before processing, packing and loading. While the FVS separator was being tested under one of several loading silos, one of the receiving plastic processors was so impressed by the improved quality of the product it received that the customer requested to be supplied exclusively from that silo in future – additional silos have since been retrofitted with the separator. Which separator to use depends on the facility design and the product to be processed itself, as VGS or KWS separators are best for fragile products, for example. This illustrates why the system supplier’s process expertise is decisive when choosing the ideal solution and ensuring the right combination of conveying and separation processes. This is the only way to ensure high-quality products in the plastics industry.