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Nordson BKG (formerly Kreyenborg BKG) has released an integrated system that uses the thermal energy of the molten polymer created during PET pelletising for subsequent crystallisation. The group’s claim is that this “eliminates problems caused by the agglomeration of amorphous material and substantially reduces energy costs for compounding or recycling”.
Called CrystallCut, the patented process removes the requirement to cool PET after pelletising and then reheat it for crystallisation. As an integrated network that incorporates underwater pelletising, drying, and crystallising, Nordson says it is designed for precise control of material temperatures throughout the process, preventing production and quality problems caused by insufficient crystallisation and excess levels of amorphous material. The group claims that the energy efficiency of the CrystallCut system can save more than €3,000,000 in annual energy costs for a typical PET resin plant and nearly €200,000 for an extrusion line recycling PET bottle flakes. These figures are based on examples cited by Nordson BKG from actual commercial installations (see graph in the slider above for an example relating to polymerisation).
“The CrystallCut system provides substantial relief to the cost pressure on PET polymerisation and recycling, particularly as prices for PET fall,” said Ralf Simon, Managing Director of Nordson BKG. “In addition, because the system utilises residual thermal energy within the material to crystallise pellets from the inside out, it yields an enhanced crystalline structure that results in lower energy costs for re-melting the material.”
In the CrystallCut system, hot PET granulate produced by the face cutter of the underwater pelletiser is transferred rapidly to the pellet dryer in hot water (up to 95°C) through closed conveying pipes, where pellet cooling and solidifying takes place. The system preserves heat from the melt due to a combination of closed conveying pipes and the relatively short distance between die head and dryer.
Nordson claims that the temperature of the pellets are between 150-160°C when they exit the dryer onto a vibrating conveyor. This keeps the pellets in constant motion, generates a uniform distribution of thermal energy, and prevents pellets from sticking together. At the end of the process, the pellets have a temperature of approximately 180°C, have reportedly achieved up to 40% crystallinity, and may be transferred directly to solid state polycondensation (SSP).
In addition to saving energy costs and preventing amorphous PET clumping, the CrystallCut system yields an almost dust-free product and increases bulk density by 8% in comparison with a conventional process, according to the manufacturer.
Assuming an average energy cost of 12 cents/kWh, Nordson BKG estimates that the CrystallCut system yields energy savings of up to 125 kWh or €15 per tonne of PET in a modern PET polymerisation plant. Based on Nordson’s claim that such a plant can achieve a production capacity of 600 tonnes per day, these savings amount to €9,000 daily and €3,200,000 per year. This would be an annual energy saving of more than 26 gigawatt hours, or 26,000 megawatt hours.
Another example cited by Nordson BKG is that of an extrusion line which recycles PET bottle flakes at a rate of 1,500 kg/h. The savings reported to be achievable with the CrystallCut system exceed 180 kWh, or more than 1.4 cents/kg. In a 365/24 operation this equates to €190,000 per year.