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The SORTICANTER® Centrifuge

The Flottweg SORTICANTER® is specifically designed for the plastics recycling industry. It is able to separate two plastics of different densities in a carrier medium such as water. To recycle plastics, the different components have to be separated according to their specific density. A simple “sink or float” process can be used to accomplish this task. This process, however, takes a long time and the performance in terms of residual moisture content as well as centrate clarity is not adequate for further processing. The challenge was therefore to design a solid bowl centrifuge that would separate solids according to their specific density and improve separation performance and lower residual moisture content. FLOTTWEG supplies complete systems for wet-mechanical sorting and washing of mixtures of various plastics. The plastics are separated using a liquid separation medium which is selected according to the table below. Solids with a lower density than the separation medium float while those with a higher density settle. The shift in density due to temperature changes is compensated by the system. Fully automatic operation – around the clock – is achieved through the optimum choice of system components and excellent control technology.

Polymer type

Density [kg/dm³]

  0.8       0.9        1.0       1.1       1.2       1.3       1.4
Soft natural rubber                              
Hard rubber                          

Materials other than plastics can also be separated. Some of these materials can be heavier than the liquid phase and others lighter (e.g. the contents of fat separators can be separated into fat, water and solid impurities). Separation liquids with a density different to water enable the separation zone to be shifted, thus providing more flexibility for complex separations. The SORTICANTER® can be operated by a hydraulic drive or a variable frequency drive (VFD). These allow the SORTICANTER® to be adjusted quickly to optimally accommodate varying feed conditions without interrupting operations. It is also possible to use the SORTICANTER® without modification for two phase separation, separating solids that just settle or just float on the liquid phase.

Mode of operation
The SORTICANTER® basically comprises a conical cylindrical bowl provided with a second cone at the end and a scroll tailored to the internal contours. The bowl and the scroll rotate at high speed in the same direction. The scroll rotates at a slightly different speed from the bowl to enable conveying. Plastic materials to be separated are firstly shredded to an edge length of 12 to 16 mm. Then adhesive impurities are eliminated by friction washers. The plastics slurry is conveyed to a tank with an agitator, homogenized and pumped to the SORTICANTER®. The mixture of solids and liquid is pumped through the feed pipe and passes through feed ports in the scroll into the rotating bowl. The product is then accelerated to the bowl speed to expose the suspension to centrifugal forces. Centrifugal force in a solid bowl centrifuge causes solids with a higher specific density than the liquid phase to settle against the bowl wall. The scroll conveys the separated solids up a conical beach where they are discharged through ports in the solids housing. Solids lighter than the liquid phase float and are carried with the liquid flow to the other end of the centrifuge. Before these floating solids reach the conical end, they are conveyed through a drying zone to a second port. The separation liquid (liquids with different densities can be used to make one solids phase float and one solids phase settle) is drained at the outer diameter of the second cone. The liquid is conducted to the impeller chamber and discharged by the impeller.

flottweg sorticanter three phase decanter centrifuge plastic recycling

Typical application
•Fibres and films
• Ground bottles
• Recovery of PET flakes
• Cable insulations
• Carpet fibres
• DSD films
• DSD mixed plasticss
• Separation of fats
• Heavy media separation of minerals
• Granulate from production waste and return materials