An integrated system that uses the thermal energy of the molten polymer in PET pelletizing for subsequent crystallization eliminates problems caused by the agglomeration of amorphous material and substantially reduces energy costs for compounding or recycling, according to Nordson BKG™. Called CrystallCut®, the patented* process avoids the need to cool PET after pelletizing and then reheat it for crystallization. As an integrated network that incorporates underwater pelletizing, drying and crystallizing, it is designed for precise control of material temperatures throughout the process, preventing production and quality problems caused by insufficient crystallization and excess levels of amorphous material. The energy efficiency of the 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, according to examples cited by Nordson BKG™ based on actual commercial installations (see graph for an example relating to polymerization). “The CrystallCut system provides substantial relief to the cost pressure on PET polymerization and recycling, particularly as prices for PET fall,” said Ralf Simon, managing director of Nordson BKG™. “In addition, because the system utilizes residual thermal energy within the material to crystallize pellets from the inside out, it yields an enhanced crystalline structure that results in lower energy costs for re-melting the material.” In the system, the hot PET granulate produced by the face cutter of the underwater pelletizer is transported rapidly to the pellet dryer in hot water (up to 95 °C) through closed conveying pipes, where pellet cooling and solidifying takes place. This conveying medium and the short distance between die head and dryer are keys to conserving the heat from melt processing. The pellets are at a temperature in the 150 to 160 °C range 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 completion of the process, the pellets have a temperature of approximately 180 °C, have 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. Benefits |
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