Clean PET Flakes Through Use of Filtration
The quality of recycled PET flakes improves considerably when the hot wash solution is filtered. A new process can be adapted to various system concepts.
When recycling PET materials, the so-called hot wash stage is of prime importance for removing contaminants. Most recycling systems, however, do not employ any type of treatment for the hot wash solutions used. Once the contaminants in the washing solution reach a certain concentration, the cleaning action diminishes. In addition, adhesives and printing inks that have been loosened are carried over increasingly into subsequent process stages, where they recontaminate – primarily at lower process temperatures – the previously cleaned flakes.
ÖHMI Consulting GmbH has developed a new type of process to filter the hot wash solutions in which the washing solution is cleaned in a bypass arrangement. In this process, a defined amount of the washing solution is diverted from the hot washer and filtered. The amount diverted depends on the quality of the incoming material and the material throughput, and is usually about 10-15 %. A system with a throughput of 0.5 - 1 m3/h has been in operation at MultiPET Gesellschaft für PET Recycling mbH in Bernburg since 2003; a second system was installed at Texplast GmbH in Wolfen in May 2005.
Economical and nonpolluting
The filtration systems remove paper fibres, particulate matter and adhesives from labels from the bypass stream completely. Even the printing inks contained in the washing solution are removed almost entirely. The fraction of adhesive-containing flakes drops significantly and the discolouration due to recontamination that was observed previously no longer occurs. As a result, filtration of hot wash solutions now represents an economical and nonpolluting technique for improving the quality of recycled PET flakes.
Previously, the entire hot wash solution was usually replaced instead of being cleaned. This entailed additional costs for the necessary chemicals and increased the amount of wastewater. In addition, production had to be interrupted for several hours.