TECHNOLOGY | WASHING
washing process for PET when it comes to separat- ing cap material from the PET itself,” adds Fried- laender. “In the washing process for polyolefins, its material characteristics require some procedural adjustment. However, the overall concept contin- ues to be based on PET washing technology. Based on trial results, we do mechanical and chemical modifications to meet the specific requirements of the application. A polyolefin recycling line looks different to a PET recycling line and uses some slightly different machinery. However, as with PET recycling, it is necessary to understand the input bale composition, which determines how the line should be designed.” Krones has constructed a pilot plant at its
Flensburg facility in Germany with a 50 kg/h throughput. Friedlaender adds that the plant was mainly set up to develop and test the company’s own equipment and includes a grinder, a washing module and a decontamination module. He says that the set-up represents the same process steps that are used in the commercial lines. The pilot plant is also used for customer trials and is cur- rently fully booked. Krones says that individual tried-and-tested units
were adapted to suit polyolefin-specific characteris- tics, but the process engineering features of the company’s washing technology remains un- changed. Trials in the in-house pilot plant firstly demonstrated good washing quality and then washing results were confirmed in external labora- tories and validated through the production of test specimens. A key task is to reduce the generation of unwanted odour after melting the washed material. Some of this results from impurities after the washing step, and here the Krones system has significant advantages because of its high washing quality, says the company.
The washing module for PET will in future be available on the market under the name of Meta- Pure W-PET, and that for polyolefins under Meta- Pure W-PO. As well as supplying individual mod- ules, Krones also designs and manufactures complete systems for polyolefin recycling. In these projects, Krones handles factory planning, engi- neering and all the service work required to create a complete recycling line.
PET technology In the MetaPure W-PET washing module, shredded PET flakes undergo a dry cleaning process to remove any loose contamination. Nozzles and mechanical friction then remove any dirt particles which have been carried along. Residual labels and adhesives are then removed during the subsequent caustic treatment process. Because of the difference in their specific weights, the polyolefin lid materials can be separated from the heavy PET flakes in a float-sink classifier during the float-sink sequence. Multi-stage post-washing with hot water is followed by a drying process. Finally, any individual pieces of metal remaining are then removed using all-metal separation. The entire washing process integrates the return
and recycling of used media. This includes the continuous recycling of the water used for washing using the water cascade and caustic filtration. In the water cascade, flakes are flooded with fresh water in the post-rinsing basin and this water is subse- quently used in the float-sink separator and in the pre-rinsing basin. Waste water is pH-monitored and, if free of solids, is then discharged. A highly efficient procedure ensures that the fresh-water current flows in the opposite direction to that which the PET flakes are conveyed. There is continuous flow and consistent water renewal in the basins. In the decontamination module, washed
flakes are turned into food grade recyclate. The cleaned material is heated gently and evenly in a heating conveyor. It is then dried and regulated to its final decontamination temperature, which is considerably lower than the PET melting temperature. This has a significant benefit from an energy view- point when compared to the processes used in pellet manufacture, which generally require higher temperatures. The actual cleaning process to remove migrated content takes place in the vacuum reactor of the Krones Meta-
Left: Krones has developed a washing technology for
polyolefins – the MetaPure W-PO 44 PLASTICS RECYCLING WORLD | July/August 2018
Pure recycling plant. In this phase, the intrinsic viscosity (IV) value is increased to meet the specific requirements. The result is food-grade recyclate which, depending on the layout of the system, can
www.plasticsrecyclingworld.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54
