When it comes to the pelletising of PET, an energy-saving process as well as a certain degree of crystallisation is very important. Econ launched an underwater pelletiser especially adapted to these requirements. The result is the Econ PET-edition, which has been optimised for PET and rPET. With the help of the Econ patented Thermal Insulation Technology, a safe start-up process is obtained. By preventing heat transfer from the die plate unit into the process water, not only is the freezing of die holes prevented, but a considerable amount of energy is saved. In addition, special attention has been paid to an appropriate insulation of the water tank and the piping in order to achieve an end temperature of the pellets of at least 140 °C. Depending on a customer’s requirements, Econ provides a tailor-made solution to ensure the required pellet end temperature. Not only is the pelletiser engineered to operate with minimum energy consumption, but the downstream equipment ECS (Econ Crystallisation System for PET) is as well. This uses the intrinsic heat of the pellets for crystallisation and is therefore one of the most efﬁcient methods of crystallising PET, says Econ. The system is designed to keep the PET pellets at a constant temperature and to achieve a degree of crystallisation of 30-40 %. In the crystallisation channel, the pellets are conveyed further by gentle vibration and mixed to prevent sticking during crystallisation. The high degree of crystallisation enables a faster pre-drying of the pellets before further processing (e.g. injection moulding), which saves a considerable amount of time.
In the food sector, a low acetaldehyde (AA) content of recycled PET is required in order to meet the legal guidelines. “Our goal in the development of the Econ PET-Edition was to achieve a significantly improved value in comparison to conventional pelletising systems,” explains Dominik Neumann, team leader of the R&D department. By reducing the pressure build-up at the die plate by 40 %, a lower AA content of 30-40 % was achieved directly after pelletising. Previous tests have shown that a lower energy input can be expected during dehydration, since the reduced AA content represents a different starting position.