“Turnkey solution particularly attractive for us”
When opting for Krones, Mpact adopted an approach of cautious due diligence. “Before we made the investment, we carried out detailed research,” explains John Hunt, Managing Director of Mpact Recycling. “We talked to operators of recycling systems, converters and beverage producers all over the world and looked at quite a few different models. The key criteria for placing the order with Krones was FDA approval, plus the system’s relatively favourable water and energy consumption. Krones was able to offer the PET recycling capability as a complete system, and not just delivering individual parts.” Mpact carefully reviewed the system Krones was proposing. “The washing module’s technology is excellent. Here, in our view, Krones is able to benefit from its long years of experience with bottle washers. And the decontamination module seems very dependable to us too. With Krones offering the front end as well, the system is an attractive turnkey solution for us,” says Ronald Fairbanks, General Manager Mpact Polymers. “Taking a long-term commercial view, the Krones recycling system was the best solution for us.”
MetaPure bottle-to-bottle PET recycling system at Mpact:
- Front end: The PET bottles, delivered in bales, are pre-sorted, coarsely cleaned and crushed.
- Washing module: The PET flakes are intensively cleaned, and foreign substances removed.
- Decontamination module: Food-hazardous contaminants are removed and the flakes turned into pellets.
Stage 1: Front end
In the facility’s courtyard, the PET bottles from the collection points are delivered in bales. The material is introduced to the front end, which opens them up in a bale-breaker to distribute bottles evenly on the conveyor. The first metal removal is performed using a permanent magnet to remove ferrous metal. The next unit is a ballistic separator, which in two stages removes flat contaminants like foils from the bottles, and lighter ones like dirt, dust and glass, etc. In the de-labeller unit, the containers are now fed between two drums, which mechanically remove labels, which are then separated out and disposed of in skips. A cascade-structured near-infra-red (NIR) sorting station detects coloured PET bottles and foreign plastics, and ejects them. At the end of this cascade, only transparent and light-blue PET bottles are then passed to the downstream process. As part of a dual checking system, the NIR sorting stage is followed by a manual sorting station. At the grinders, the final station in the front end, the bottles are shredded into small flakes.
“Thanks to dry removal of labels and dry grinding, the washing process has significantly lower water and energy consumption, in fact the water consumption is running at approximately 2.5 litres per kilogram of rPET, which is about 40 per cent lower than the industry’s standard figure,” explains Ronald Fairbanks.
Stage 2: Washing module
The shredded flakes are conveyed to a silo of the washing module, and then precleaned in a dry mixer and the downstream zigzag sifter, to remove light-weight fractions like dust or label residues. They come into contact with water for the first time in a pre-washer, where they are treated at moderate temperatures. Jets and mechanical friction remove any entrained dirt particles. In the downstream caustic bath, any remaining labels and adhesives are detached in a mixture of hot water and caustic. Due to the size of the system as a whole, two caustic washers are installed at Mpact Polymers. The caustic solution used is prepared in a two-stage caustic treatment system featuring the Parcival filtration system, enabling it to be subsequently re-used in consistent quality. Then, the polyolefins are removed from the flow as well, that is the material of the bottle closures. This is accomplished using a sink-float process in a density separator: the polyolefins float to the top, while the heavier PET falls to the bottom. This ensures very good flake quality. These PET flakes are then rinsed again with hot water in several stages and mechanically and thermally dried using hot air.
Stage 3: Decontamination module
In this step, the sorted and washed flakes are treated to create bottle-grade recyclate. For reasons of capacity, two decontamination modules with equal outputs were installed at Mpact Polymers. Tests conducted by the Fraunhofer Institute in Germany on the MetaPure recycling system operated at Mpact Polymers have confirmed that the material produced complies with regulations covering the safety of using rPET in food-grade packaging. The FDA certification for Krones’ decontamination process also underlines its general efficacy. The decontamination modules are, for reasons of hygiene, located in a separate room with a positive air pressure. From a buffer silo, the washed flakes are first of all pre-warmed in the first heating worm, then dried in the second worm, and brought up to process temperature, which is well below PET’s melting temperature. This is followed by the heart of the decontamination module: the vacuum reactor, where migrated constituents are expelled from the materials and the intrinsic viscosity (IV value) is increased.
"Very swift decontamination"
After this treatment, food-grade PET flakes are now ready for use. It’s precisely this stage, too, that accounts for the recycling system’s relatively low energy consumption. “In comparison to other recycling processes, the decontamination module works very swiftly, and therefore requires less energy. Thanks to this skilful combination, we are achieving values of less than one kilowatt-hour per kilogram of rPET” reports Ronald Fairbanks.
In the downstream extruder, the flakes are melted, extruded through a melt filter and pelletised. There, too, the energy consumption is lower in relative terms, because the flakes are already warm and dry from the decontamination process. The crystallisation of the pellets also utilises the residual heat, and does not require any additional energy input. Once the products have cooled down, they are packed in big bags, and undergo extensive and thorough quality checks
The system started operating in the middle of 2015, with installation being expeditious, “because lots of the kit had been pre-assembled before being stripped down and placed into containers”, says Ronald. After only six weeks from commissioning, the first decontamination module’s OEE (overall equipment effectiveness) was at 80 per cent. “Cooperation with the Krones team was very good right from the start, both with the sales people and with the technicians, fitters and the commissioning team,” says a content Ronald Fairbanks.