Technically, “CrystallCut” is an integrated system that uses the thermal energy of the molten polymer in PET pelletizing for subsequent crystallization that eliminates problems caused by the agglomeration of amorphous material and substantially reduces energy costs for compounding or recycling. “CrystallCut” (U.S. Patent No. 8,324,339 B2) is a registered trademark of Nordson BKG.
The 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 the precise control of material temperatures throughout the process, preventing possible production and quality problems caused by insufficient crystallization and excess levels of amorphous material.
CrystallCut System Equipment (photo: Nordson BKG)
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).
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 ton of PET in a modern PET polymerization plant. Since such a plant can achieve a production capacity of 600 tons per day, these savings amount to € 9,000 daily and € 3,200,000 per year. This represents 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 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.
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.