PETpla.net Insider 06 / 2020

MATERIALS / RECYCLING PETplanet Insider Vol. 21 No. 06/20 www.petpla.net 44 Energy-saving inline crystallisation For the bottle-to-bottle recycling process, systems have been devel- oped that reduce energy costs by combining the pelletising and crys- tallisation step in a single integrated process. This technology uses the thermal energy of the molten poly- mer in PET pelletising for subsequent crystallisation, avoiding the need to cool PET after pelletising and then reheat it for crystallisation. The inline crystallisation system developed by Nordson, called Crys- tallCut, is designed to work with the spherical pellets generated by UWPs and is an integrated network incor- porating pelletiser, dryer, and crys- tallising unit. rPET pellets achieve a crystallisation level of up to 32% (in production of virgin polymer, by com- parison, the figure is approximately 40%, depending on the initial quality of the material). Subsequently, a solid state polycondensation (SSP) reactor raises the IV of the polymer and car- ries out a final decontamination step by removing trace substances like acetaldehyde, which have a deleteri- ous effect on taste in food applica- tions. Pellet temperature in the Crystall- Cut system is maintained at 140- 180 °C. The system eliminates the intervening step of holding pellets in a silo at a maximum 60 °C (to avoid pel- lets sticking together) and a separate pre-crystallisation step before the pel- lets are transferred to the SSP reac- tor. Alternatively, by adjusting process parameters, it is possible to bypass the CrystallCut step or to produce amorphous polymer. Compared with a traditional operation with UWP and SSP operating at 2.5 t/h, the CrystallCut system provides thermal energy savings of 30 to 50 kWh/t, electri- cal energy savings of 10 kWh/t, a reduction in cooling water of up to 40%, and a reduction in fresh water for refill of up to 90%. As energy costs vary from region to region globally, plant operators need to calculate their cost savings indi- vidually. The system can be used to yield rPET with near-virgin properties. Because process heat is retained in the core of the pellets, crystal- lisation takes place uniformly from the core to the outside surface. By means of process optimisation, it is possible to achieve this crystallin- ity at small pellet sizes, making the rPET more compatible with virgin PET when blended. At the same time the higher bulk density of the rPET increases SSP capacity and reduces costs for transportation and packaging. Complete polymer processing systems Polymer processing systems for PET recycling are available individu- ally, but there are benefits in sourcing them from a single company. Apart from the obvious one of reducing the number of interfaces during the engineering and purchasing phase, single-sourcing enables the sup- plier to design a system to maximise the efficiency with which the various equipment components interact. For example, the pressure demands of the screen changer and pelletiser affect the selection of the gear pump. Another advantage of working with a single supplier is that of using a single control or software solution to inte- grate the entire post-extrusion system. With UWPs, the operator can use a single interface on the pelletising system to access the extruder, feed- ing equipment, screen changer, and melt pump. To meet the surge in demand anticipated for rPET, the recycling industry will have to achieve massive increases in new capacity. Along with the extensive equipment needed for producing high-quality flake from post- consumer PET bottles, recycling com- panies will have to invest in extrusion and post-extrusion systems capable of yielding rPET with properties as close as possible to those of virgin material. In helping these companies to supply a fast-growing market for rPET, new-generation post-extrusion systems will be key to increasing pro- ductivity and profitability. www.nordson.com Spherical pellets CrystallCut installation