PETpla.net Insider 09 / 2015

MATERIAL / RECYCLING 18 PET planet insider Vol. 16 No. 09/15 www.petpla.net melt, offers an option for removing even more contaminants than that for flakes. Washing module and decontamination module A bottle-to-bottle recycling line from Krones basically consists of a washing module and a decontami- nation module. Pre-sorting, i.e. the process for removing foreign materi- als, can be handled either manually or automatically, and takes place in the neighbouring plant, as does bottle comminution. The ground flakes are then passed through a multi-stage washing process comprising pre- washing, intensive washing, and post- washing. Before the material is dried, the closures, foreign substances and fine PET parts are removed. But what we are looking at here is still non- food-grade flakes, which may well be used in the textile industry, for exam- ple, but definitely not for any applica- tions where they come into contact with food and beverages. In order to qualify the recyclate for use in making beverage bottles, the next step is to remove all of the con- taminants contained in the PET mate- rial. This decontamination process from Krones is performed in stages: two heat exchangers warm up the flakes, whereupon they are decon- taminated in the downstream vacuum reactor. As the process continues, any coloured flakes still present, plus any metal particles, are removed, and any fine parts remaining are filtered out. It’s only after completion of this pro- cess that we’re looking at food-grade flakes. Additional sorting in the washing module The line installed for Roxpet contains some additional features: for example, Roxpet had one further unit installed upstream of the wash- ing module, which removes a high percentage of all non-ferrous metals, such as aluminium. This unit pro- cesses more than 2,000kg/h, which means it’s big enough for both recy- cling lines. Each of the washing mod- ules in the two lines, moreover, incor- porates an all-metal sorting system, which serves yet again to remove any metal residues by means of mag- nets. And downstream of the wash- ing module, a laser sorting system for the cleaned flakes has additionally been installed, likewise adequately dimensioned for serving both the recycling lines. It operates with four channels, two for each line, with one million measurements being taken per second. In this system, each flake is inspected for its material charac- teristics. Depending on the quality of the raw flakes supplied, the machine handles some umpteen thousand rejects per minute. Average wastage at Roxpet is between 7 and 8%. Plasticising and inline crystallisation The flakes, after having been cleaned and sorted in this way, are now passed to the decontamination module containing even more special features. An extruder screw has been linked up directly to the decontamina- tion reactor, which serves to remove any contaminants from the flakes, thus creating food-grade quality. In this extruder screw, the material is liquefied and plasticised. Immediately downstream, the PET melt is passed through a filtration unit with 50-μm filter sheets, which arrest any parti- cles still present. To ensure uninter- rupted line operation, four filters have been installed here, which are back- washed at regular intervals with liquid PET. The flow of PET is now passed through a perforated plate, at the exit of which rotating blades cut it up into pellets. These pellets travel onwards into a mechanical centrifugal drier, removing the water, so that it can be re-used. The still-hot pellets continue to be amorphous, and are slowly cooled down in the inline crystallisation unit. It is in this step of the process that the so-important crystallisation of the PET pellets takes place, which is a vital precondition if they are to be suc- cessfully used in a preform injection- moulding machine. A second identical line After the first recycling line had gone into operation, in late 2011, Roxpet installed a second identical line rated at 1,000kg/h, which was commissioned in April 2012. The two lines together provide an annual capacity totalling around 14,000 tons of food-grade pellets. This enables Roxpet to supply Groupe Alma’s preform-making operations in north- ern France, using silo-trucks. In total, throughout France, the group needs more than 100,000 tons of PET each year in order to produce preforms and PET containers for its water products. Pierre Papillaud would like to use up to 30% of recycled PET for bottle production. “Anyone contaminating the natural environment should be made to pay for it” There is still not enough raw material from collections available on the market. “Germany’s mandatory deposit has been the target of much The flakes are decontaminated in the vacuum reactor.