STF Maschinen und Anlagenbau GmbH
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PET-Recycling-Plant (Texplast)

PET recycling plants

  Material introduction

After the packaging wire has been removed, the bottles which are compressed to bales or briquettes are introduced into the debaler using a forklift. There, the PET bottles are detangled and fall into the dosing screw which transports them continuously and evenly to the elevating belt. The plant throughput is determined by adjusting the speed of the screw. The elevating belt is equipped with a non-magnetic area, over which a permanent over-belt magnet is installed. So ferromagnetic materials which are in the input are removed. The elevating belt then transports the bottles to the sorting belt.

  Manual sorting

The sorting belt is mounted on a stage and is designed for 4 manual sorting places.

The built-in detection coil recognizes metals and stops the belt. The sorting personnel is thereby given the opportunity to remove the metals and to restart the belt. The sorting stage is mounted on a high base frame that contains bunkers where the rejected materials are collected and can be removed with the forklift.

The sorted material then directly gets into the cutting mill.

  Cutting and pre-cleaning

The cutting mill is essentially a wet-shredding and cutting mill. With the help of adding an abundant amount of water, the shredding process in this stage provides a combination of cutting and cleaning effects. The machine interior is covered with a highly wear-resistant material (Hardox). This interior shielding, along with the stator blade covers, is completely replaceable.

During the shredding process, 95% of all paper labels are dissolved.

The cut material is introduced into a friction cleaner. Inside the frictional cleaner unit, the washing water along with the therein contained paper and dirt is separated from the material to be processed and pumped to the fibre separator of the circulation container no. 1. The material is transported towards the vertical air-stream separator with the help of a blower unit.

Within the vertical air-stream separator, the PET and PO flakes are separated from other materials contained in the mill output like labels, paper, dust and other suspended solids. The material is transported into the air-stream separator by a cyclone with rotary valve. The heavier PET and PO flakes descend to the bottom and are transported by another blower to the cyclone of separation stage no. 1.
The lightweight particles are vacuumed off the top and are blown to the labels filling station. The selectivity can be adjusted over the label blower.

  Separation stage 1

The separation stage consists of a stirring and a separating container. The material is brought into the stirring container with the help of a cyclone with rotary valve and is blended into the separating medium (water). The homogenous mixture is then pumped into a separating container that is entirely filled with water. Due to a laminar flow, the heavier particles sink to the bottom and the lightweight particles move towards the top. The principle behind this separation is that the plastics have a different density than water. Since PET has a higher density than water, it sinks to the bottom and is pumped into a friction cleaner. The dried material is transported to the next station by a blower.

The polyolefines (PE, PP etc.) and other foreign materials that have a lower density than water move to the top where they get into a friction cleaner. The PO flakes are moved to the PO filling station through a blower.

The friction cleaner and drier remove the water from the material. The washing water that contains the resolved dirt is pumped to the fibre separator of the circulation container no. 2.

  Hot screw washer

Both hot screw washer and hot washer use a medium of 4-5% caustic soda solution. They are heated by electrical heating plates in order to achieve an ideal cleaning effect. Measuring and regulating systems control water temperature and leach concentration.

The PET flakes are transported to the screw washer by a cyclone with rotary valve. They are then brought forward by parallel running and very slowly rotating screws. Through the longer time the material is exposed to the medium, an optimal cleaning process is obtained. (dissolving and resolving of adhesive and dirt). In the following friction cleaner the material is separated from the water that contains adhesives and dirt.

The material is then blown to the hot washer and the removed leach is pumped back into the circulation container no. 4.

  Hot washing stage

The flakes are transported into the hot washer through a cyclone with rotary valve. They are intensively cleaned by the turbulences produced by a stirrer.

A downstream friction cleaner removes the water that is mixed with the caustic soda solution. The produced friction also removes adhering adhesives.

The washing water that contains the resolved dirt is pumped to the fibre separator of the circulation container no. 5.

A blower transports the dried material to the post washer.

  Post washing stage

The material is intensively cleaned in the post washer by the high turbulences produced by a stirrer. The material is introduced through 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 is transported to a friction cleaner through the washer overflow. There, the washing water is removed. The dried flakes are then brought into the second separation stage by a blower and the washing water with the dissolved dirt is pumped into the collection container of separation stage no. 2.

  Separation stage 2

The second separation stage is mainly used as a security separation for the leftover and removed labels from the hot washer.

It uses the same principle as the first separation stage. However, the material stream that moves towards the top of the flow is not dried and processed, but merged with the removed water from the other stream and then pumped to the fibre separator of the third circulation system.

At the underflow, the sinking stream is pumped to a two-stage friction cleaner. In the first stage, most of the contained water is separated from the PET flakes and they are dried again in a second stage.
Then, the material is moved into the post processing stage (for PET).

  Post processing of the heavy fraction (PET)

A vertical air-stream separator cleans the material, which is introduced through a cyclone with rotary valve, again. The lightweight particles (mainly respirable dust) are blown to a cyclone for waste and the heavy particles are blown to the cyclone of the first vibration chute.

The first stage consists of a vibration chute and a magnetic drum. The vibration chute consists of two layers, whereas the first one strains oversize grains and the second one separates the material for the following magnetic drum which removes magnetic foreign materials.

The grained PET falls onto another vibrating chute, is separated and then passes through a combinatory separator, where non-magnetic metals like aluminium and stainless steel parts are removed.

The combinatory separator additionally post separates the material by colour, reducing the manual sorting stage's error rate. Small amounts of PET are also removed.

The cleaned material falls into a blower funnel and is transported to the PET filling station.

The material that has been rejected with the help of the magnetic drum and the flakes sorter is also filled into big bags.

  PET filling station

It consists of a stage that is designed for holding two big bags. Above it, a dispensing silo is mounted that has a discharging screw for each big bag. The material is introduced with a cyclone. Three sensors which control the filling level are mounted at the silo. The filling funnels for the big bags also contain sensors which detect a completely full big bag and automatically switch to the filling of the other one, which enables a continuous filling process. The filling station also has a pneumatic vibrating unit which is responsible for compacting the material and for an optimal filling of the big bags.

  PO filling station

This station consists of a cyclone, a silo with rotary valve and a base frame with working platform. A sensor is mounted in the filling funnel for the big bags that recognizes a full big bag and stops the feeding through the rotary valve. Until the big bag has been replaced by an empty one, a storage silo holds back the material flow. After that, the rotary valve can be started again.

  Filling station for metals / colored PET

This station consists of a cyclone, a silo with rotary valve and a base frame with working platform. Inside the filling funnel, a sensor is mounted that recognizes a full big bag and stops the material feed through the rotary valve. The storage silo holds back the material until the full big bag is replaced. Then, the rotary valve can be restarted.

  Labels filling station

It consists of two stages which are designed to hold one big bag each. Each one consists of a cyclone, a rotary valve and a base frame with operating platform. The filling funnels contain sensors which recognize a full big bag. In this case, the pneumatic gate switches to the second big bag.

This station is also equipped with a pneumatic vibrating unit which compacts the material in the big bags.