A new screen changer filter cartridge increases filter life in a PET recycling line

A screen changer filter cartridge designed to resist deformation and enhance polymer flow has enabled the operator of a high-throughput PET recycling line supplied by Starlinger recycling technology to reduce the frequency of filter replacement and improve pellet quality. Nordson Corp. will display the new cartridge at NPE2015 (booth W-6263).

Installed in a “bottle-to-bottle” recycling line at a European company, Starlinger’s recoSTAR PET 165 HC iV+ recycling line includes a Nordson Kreyenborg K-SWE-4K-75/RS screen changer situated between the extruder and the underwater pelletizer. The line, which operates “24/7/365,” converts PET bottle flakes to rPET with positive opinion by the European Food Safety Authority (EFSA) for re-use in bottles, with adjustable intrinsic viscosity levels depending on application.

The new Nordson Kreyenborg filter cartridge lengthened the filter life from eight to 72 hours, according to Christian Lovranich, head of process engineering at Starlinger recycling technology.

The new filter cartridge also addressed the requirements of high-throughput systems such as the 1.400 to 1.600 kg/h (3,086 to 3,527 lb./hr.) Starlinger line. “The larger filter area of the cartridge and the elimination of stagnation zones reduce pressure variations that can detract from pellet quality,” Lovranich said. “In addition, there is less material lost in backflushing, and there are no metal impurities.”

In addition to the considerable increase in screen life, a 40% reduction of the backflush amount compared to the previous system (a conventional backflush filter) was realized, the company stated. The resulting waste reduction alone led to a short pay-back of the replacement investment. The available filter area is 1.672 cm2 (260 sq.in.) and the filtration fineness is 50 mm with the used screens.

The stable structure of the new filter cartridge prevents pressure loss and deformation of the steel filter fabric, or screen medium, enabling it to withstand the high mechanical stresses encountered during production startup, noted Christian Schröder, research and applications engineer for Nordson PPS GmbH.

“Our new filter cartridge is an alternative to standard filter discs, in which surface area is increased through pleating of the filter fabric—that is, installation of the fabric in a wave or wrinkle pattern instead of being flat,” Schröder said. “The pleating makes the fabric susceptible to mechanical stresses, which can reduce the efficiency of melt filtration by causing the pleated layers to be pushed together or squeezed during processing. This also reduces the working life of the filter.”