STF Maschinen und Anlagenbau GmbH
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Washing plants

Hot screw washer

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 get into the screw washer with the help of a cyclone with 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). In the following friction cleaner, the material is separated from the water that contains adhesives and dirt.

With a blower, the material gets to the hot washer and the removed leach is pumped back into the circulation container no. 4.

  Hot washer

The flakes also get into the hot washer via cyclone with rotary valve. They are then intensively washed by the high turbulences produced by a stirrer. 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 fibre separator of the circulation container no. 5.

A blower carries the dried material to the post washer.

  Post washing stage

The material in the post washer is intensively cleaned by high turbulences which are produced by a stirrer. 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 cleaned material gets into a friction cleaner via the washer overflow. In the friction cleaner, the washing water is separated from the material and 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 separation stage no. 2.