46 TRADE SHOW REVIEW PETplanet Insider Vol. 22 No. 10/21 www.petpla.net Herbold Meckesheim GmbH Your Partner for Plastics Wash Lines www.herbold.com As a one-stop supplier, we provide all relevant process components: Pre-washing units Hydro-cyclone separation systems Friction washers Mechanical and thermal driers Water treatment As a specialist for plastics recycling we are your contact for complex applications. We have the long lasting expertise in washing, separation and drying - to recycle new, used and contaminated plastics waste. Thanks to our modular technology, we are able to develop customized overall concepts or to optimize your already-existing plant. Key points for your profitability: Best flake quality High energy efficiency Minimized fresh water quantities Low downtimes and labour utilization Durable equipment made for tough applications fi bre applications in order to extend the working life of the screen packs on the spinning line. In bottle-to-bottle recycling, fi nenesses are now increased from a typical former level of 60 μm or more up to 40 μm or less. By comparison, a young, healthy human eye cannot distinguish particles fi ner than 50 μm. Minimal losses of polymer: The widely used “backfl ush” screen changer ejects some of the polymer melt as part of the process of removing contaminants. Over time, the amount of material loss can be substantial. One goal of innovation in screen changers is to reduce such losses. Energy efficiency: In conventional underwater pel let ising systems, three phases where an energy input is required are 1) maintenance of the tempered water system circulating through the pelletiser; 2) drying of pellets; and 3) crystallisation. One goal of innovation is to reduce energy consumption in these stages. High product ivi ty: The maximum throughput now considered the state of the art in producing rPET pellets for bottle applications is approaching 5 t/h. For post-extrusion components, achieving these rates depends on three factors: 1) component designs that yield streamlined fl ow properties; 2) enhanced control over melt pressure and temperature; and 3) reduction in downtime for troubleshooting and maintenance. Gear pump The gear pump shifts part of the job of building melt pressure from the extruder, thereby reducing stress on the extruder and on the processed material while delivering melt at the pressure level required by the screen changer and the following downstream equipment. In addition, the gear pump provides uniform fl ow, reducing surges and other process variations that can negatively affect the pelletising process and pellet uniformity. With use of a gear pump, the degassing system of an extruder can be made more reliable, and the extruder length can be reduced. Screen changer While typically deployed immediately downstream of the extruder and upstream of the screen changer, the gear pump may be preceded by an additional screen changer that provides “pre-fi ltration” at a fi neness level down to 1,000 μm, removing large particles that can cause excessive wear to the gear pump. At this particle size, the contamination level is less than 0.1%, provided that there has been effi cient washing and sorting prior to extrusion. Otherwise, the contamination level is larger. For the main fi ltration step in PET processing, a piston-actuated system with a self-cleaning feature based on a hydraulically powered process called backfl ushing is state-of-the-art. In a screen changer with four screen cavities, for example, melt fl ow is split into four streams. Backfl ushing starts automatically when the pressure differential caused by contaminant build-up increases to a pre-set level. Melt is then compressed and discharged
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