PET Washing Plants

Left: PET film with coating / Right: PET film after washing process, coating removed

The basic principle of the highly efficient process in the STF PET Washing Plant is as follows:

The hot screw washer as well as the hot washer work with a medium of a 4-5% caustic soda solution. Both are heated by electrical heating plates in order to achieve an ideal cleaning effect. Instrumentation and control systems monitor water temperature and leach concentration.

The PET flakes are brought into the screw washer with the help of a cyclone including a rotary valve. The flakes are brought forward by parallel running and very slowly rotating screws. An ideal cleaning effect is achieved by the increased retention time in the medium (adhesives and dirt are dissolved and resolved). After that, in the friction cleaner, the material is separated from the water that contains adhesives and dirt.

With a blower, the material is brought to the hot washer. The removed leach is pumped back into the circulation container.

Hot Washer

The flakes are brought into the hot washer via cyclone with rotary valve. They are then intensively washed by a stirrer producing high turbulences. In a downstream friction cleaner, the water mixed with the caustic soda solution is separated. Due to the produced friction, put-on and adhering adhesives are removed.

The washing water containing the removed dirt is pumped to the fiber separator of the circulation container. A blower carries the dried material to the post washer.

Post Washing Stage

The material in the post washer is again intensively cleaned by  a stirrer producing high turbulences. The material is introduced by a cyclone with rotary valve. In the post washer, leftover caustic soda solution that originates from the hot washing stages, is removed.

The clean material is brought into a friction cleaner via the washer overflow. In the friction cleaner, the washing water is separated from the material. The dried flakes are then blown into the second separation stage. The water, together with the detached dirt, is pumped into the collection container of the second separation stage.