STF Maschinen und Anlagenbau GmbH
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Separating plants

Our separating plants have been developed especially for the separation of PET and PO (PE, PP etc.) in PET bottle recycling plants. In combination with two friction cleaners, a separating plant is formed that can be perfectly integrated into every existing recycling plant in order to increase quality.


  The process

The separating stage uses the principle of density separation. Materials with different densities can be separated with the use of a medium where the density lies between these materials. The most common examples are PET/PO with the separating medium "water" or PS/PP with the separating medium "brine" (salt water).

  Operating mode (with the example of PET/PO separation)

The separating plant consists of a stirring and separating container. The material gets into the stirring container by a cyclone with rotary valve (pneumatic transport) or a screw conveyor, for example. A stirrer mixes the plastics with the separating medium "water" and the homogeneous mixture is pumped into a separation container that is entirely filled with water. Due to a laminar flow, the heavier particles sink to the bottom and the lighter particles move to the top of the flow. The principle behind this separation mechanism is the difference in density of the materials to be separated. Since PET has a higher density than water, it sinks to the bottom and is pumped into a friction cleaner where it is dried. Polyolefin plastics like PE, PP etc. and all other less dense materials (compared to water) float on top where they are introduced into a friction cleaner and dried also.

  Construction
  • separate stirring and separating container, made of stainless steel
  • big containers for high throughput and ideal separating results
  • base frame consisting of a stable all steel welded construction, galvanized to protect against corrosion
  • stainless-steel piping
  • discharge can be controlled by measuring tools installed at entry and underflow of the separation container