Method for obtaining fine material from plastic containers to be recycled

Abstract

NOT VISIBLE DUE TO STATUS OF PATENT

Description

[0001] Process for recovering fines from plastic containers to be recycled

[0002] Field of the invention

[0003] The invention relates to a method for recovering the fine material resulting from the comminution and washing process from plastic containers to be recycled, which are used to produce PCR (Post Consumer Recycled) granules.

[0004] State of the art

[0005] Processing methods for producing plastic recyclates are known from the state of the art. These involve converting baled post-consumer containers into a plastic material that is used to manufacture new plastic containers. In particular, used PET bottles are used to produce rPET, which is used to produce post-consumer recycled (PCR) granules and the resulting new PET bottles.

[0006] Depending on the input material used, usually only 70% + / - 10% of the PET bottle material can be recycled. Residual amounts in the bottle, labels and sleeves, adhesives, caps, and other contaminants must be separated. Polyolefin (PO)-based caps can be recycled as a separated PO stream.

[0007] During each sorting and separation step, a small portion of good material, such as PET and polyolefins, is inevitably unintentionally separated as a loss.

[0008] A recycling process is therefore measured by how well it removes contaminants, or rather, how clean the recycled material is after decontamination. Of course, a recycling system is also measured by its yield of the target polymer and whether the separated side streams can be used as valuable materials or recycled.

[0009] The common method for separating polyolefins from PET is density separation using water as the separation medium. The polyolefin cap material and labels float to the surface, while the PET sinks. Both fractions are collected separately and further processed or sold as products. Foreign polymers, mineral substances, and metals with a density greater than 1.0 g / cm 3cause major problems in recycling operations. These foreign substances are trapped in the sediment along with the PET flakes during density separation with water and can subsequently only be separated using sensor-assisted flake sorting, magnetic separation, or eddy current separation. PVC labels, in particular, pose a challenge due to their similar properties to PET flakes, as the required upper quality limit is sometimes very low. By using alcohols, ketones, or alkanes as density separation media, densities of less than 1.0 g / cm3 can be used to separate polyolefins from foreign substances.

[0010] Fine-grained fractions in the product stream typically contain higher levels of foreign matter and cannot currently be processed efficiently or economically using sensor-based sorting machines. Therefore, the separation of fine-grained fractions in the product stream is typically carried out using dewatering centrifuges. The PET or polyolefin flakes are dewatered after each washing and separation step and discharged in the main stream. The fine fractions leave the centrifuges with the wash water. Remaining adhesive residues and stuck-on contaminants are dissolved or separated in hot wash steps with washing chemicals at temperatures of up to 95°C and discharged.

[0011] The water is separated by dewatering centrifuges, usually through 3 mm holes, although holes between 1 and 4 mm are also common. The water emerging from the centrifuges contains contaminants and fines. Before being returned to the process, it must undergo solid / liquid separation. For this purpose, dewatering screens with a pore size of 200 μm to 800 μm, usually 400 μm, are used. The fines, small PET or polyolefin particles, cap material, label adhesive residues, and ink residues, remain trapped on the screen lining. The process water is recirculated, and the fine-grained fraction is usually finally separated as "fines" or a fines stream, and sold or disposed of.

[0012] However, the PET or polyolefin content in this fraction is significant and can account for up to 10 wt% of the input stream in the wash, which is missing from the yield and thus lost during the recycling process.

[0013] Object of the invention

[0014] The disadvantages of the described prior art give rise to the task of creating an improved processing method in which the lost PET and polyolefin quantities in the fine fractions produced in the shredding and washing process are significantly reduced and the effectiveness of the recycling process is thereby improved.

[0015] Description

[0016] The stated problem is solved by a method for recovering the fine material resulting from the comminution and washing process of recycled plastic containers used to produce PCR (Post-Consumer Recycled) granules, by the features stated in the characterizing portion of patent claim 1. Further developments and / or advantageous embodiments are the subject of the dependent patent claims.

[0017] The invention is preferably characterized in that the fines stream is separated into sinking material and floating material by wet-mechanical density separation at an adjustable separation density. This density separation enables small particles of the target polymer, which have a grain diameter of up to approximately 4 mm, to be separated from the fines stream, since the target polymer has a different density compared to other polymers and impurities present in the fines stream. This allows the target polymer present in the fines stream to be recovered. This can be up to 10 wt% of the input stream of the target polymer. The provision of wet-mechanical density separation therefore improves the yield of the target polymer and the efficiency of the entire recycling process. Furthermore, density separation is a mechanical process that is virtually maintenance-free and reliable.By adjusting the separation density, the density separation can be easily adapted to the density distribution in the fines stream. Depending on its density and the densities of the other substances in the fines stream, the target polymer can be separated from the other substances in the floating or sinking material.

[0018] In a particularly preferred embodiment of the invention, a centrifugal force is used as the driving force for the mechanical density separation. This centrifugal force ensures rapid and reliable density separation, even when the density differences between the substances to be separated are very small.

[0019] It is particularly advantageous if the separation density is adjusted using a density medium, whereby the separation density can be adapted to the density of the target polymer to be separated. By adjusting the density of the density medium between the density of the target polymer and the remaining substances in the fines stream, the target polymer, for example, migrates into the floating material, and the remaining substances migrate into the sinking material during density separation. When separating the target polymer PET from PVC, the PET material migrates into the floating material and the PVC material into the sinking material if the separation density is set to 1.39 g / cm 3 is set.

[0020] It is preferred if the density medium is water, and the density of the density medium is adjusted by adding a salt. This allows the density of the density medium to be adjusted precisely to the required value for precise separation with little effort.

[0021] It is advantageous if the salt is zinc chloride, sodium iodide, sodium chloride, or preferably potassium carbonate. With these salts, a density of the density medium between 1 and 1.5 g / cm 3 Potassium carbonate, in particular, is environmentally and safety-friendly, inexpensive, has good solubility, and is easy to store and dose. These salts, and especially potassium carbonate, maintain a stable density once set, and the density is easily readjustable should it change after several cycles of the density medium.

[0022] In a further preferred embodiment, the density medium is an alcohol, a ketone, or an alkane. These substances can achieve densities of 0.8 to 1 g / cm 3 to reach.

[0023] In a particularly preferred embodiment of the invention, the mechanical density separation takes place in a centrifugal separator. In the centrifugal separator, a sediment and a float can be generated by a liquid density medium and removed separately. Both comprise the applied density medium and substances with different densities. The target polymer can be separated from the remaining substances depending on the density of the remaining substances in the sediment or the float.

[0024] It is particularly useful if the centrifugal separator comprises a pipe that is inclined relative to the horizontal, and the centrifugal force is generated by the density medium being fed tangentially into the centrifugal separator. The geometry and the openings create a liquid and air vortex in which a settling phase forms in the liquid and a floating phase at the interface between the liquid and air. The substances present in the fines stream are quickly separated between the two phases by the centrifugal force generated. The settling phase leaves the pipe at its upper end, and the floating phase leaves the pipe at its lower end. This type of centrifugal separator is particularly reliable and low-maintenance, as the pipe has no moving parts. Furthermore, the unit represents a cost-effective separator.

[0025] The material is fed into the inclined pipe via the upper end of the pipe, independently of the separation fluid, directly into the inner air vortex. In contrast, with hydrocyclones, the material must be pumped in tangentially together with the separation fluid. The advantage of the inclined pipe is that no solid material needs to be pumped, only the fluid. This protects both the pump and the material, since, unlike a hydrocyclone, conveying with a pump impeller has no abrasive effect on the pumped material, as the fluid is conveyed free of solid, abrasive material. In addition, the inclined pipe enables more precise and flexible feed into the separation unit. Furthermore, no agitator tanks are required, simplifying the system technology.

[0026] With vertical hydrocyclones, only limited throughput is possible due to their conical shape, as the separation depends on the geometry depending on the application. This requires the use of "hydrocyclone spiders," in which many hydrocyclones are connected in parallel to achieve the required throughput. The inclined pipe does not have this disadvantage, as the diameter can easily be increased without significantly compromising the separation efficiency.

[0027] In a further particularly preferred embodiment of the invention, the separation density can be between 0.8 and 1.5 g / cm 3 This makes it possible to separate the target polymer from almost all polymers and impurities present in the fines stream. If the separation density is between 1.39 and 1.40 g / cm 3 If set, even the PET particles as the target polymer can be separated from PVC particles which originate from PVC labels.

[0028] The sediment is conveniently fed into a first centrifuge, where a first solid fraction is separated from the density medium and particles with a maximum particle size of 1 mm. This dewaters the sediment, and the first solid fraction contains no worthless particles with a particle diameter smaller than 1 mm. If the first solid fraction contains the target polymer, it can be further processed, increasing the yield of the target polymer by up to 10 wt%.

[0029] It is also advisable to feed the floating material to a second centrifuge, where a second solid fraction is separated from the density medium and particles with a maximum particle size of 1 mm. If no target polymer is present in the second solid fraction, this fraction can be discarded, as the valuable target polymer is present in the first solid fraction. It is also conceivable that the densities of the substances in the fines stream are greater than the density of the target polymer, and the target polymer therefore constitutes the second solid fraction.

[0030] In a further preferred embodiment of the invention, the density medium and the particles with a maximum grain size of 1 mm from the first and second centrifuge are fed to a dewatering screen, and the particles are separated from the density medium. This frees the density medium from the finest particles, allowing it to be regenerated and fed back to the separator. The finest particles with a maximum grain size of 1 mm represent no value for the recycling process, primarily because they are primarily contaminants. These can be disposed of.

[0031] The cleaned density medium is conveniently returned to the centrifugal separator. This allows for resource-efficient use of the density medium and, after cleaning in the dewatering screen and possible adjustment of the density, it can be recirculated several times.

[0032] It is advantageous if the purified density medium is stored in a storage tank before being returned to the centrifugal separator, and the density of the density medium is adjusted in the storage tank. There is always sufficient density medium in the storage tank to allow the centrifugal separator to operate smoothly and continuously. The density of the density medium can be precisely adjusted in the storage tank before it is fed to the centrifugal force separator. Precise adjustment of the density or density cutoff is particularly important when there is a slight difference between the density of the target polymer and the remaining substances to be separated.

[0033] Further advantages and features will become apparent from the following description of an exemplary embodiment of the invention with reference to a schematic flow diagram. Figure 1 shows a flow diagram of a process for recovering the fine material produced during the comminution and washing process from plastic containers to be recycled, which are used to produce PCR (Post-Consumer Recycled) granules.

[0034] A fines stream 11 is assumed, which is created by separating the fines washed out in the washing medium from the washing medium. The plastic fines inevitably created during the shredding of the plastic containers into flakes and the intensive washing of the flakes are washed out with the washing medium and are thus lost to the main stream of the target polymer. According to the state of the art, the fines stream 11 is not further purified and is sold or disposed of. However, in addition to impurities (metals, paper fibers, adhesives, etc.), the fines stream contains up to 10 wt% of the valuable material or the target polymer (e.g., PET or PO fines), which are missing from the main stream. This reduces the efficiency of known recycling processes.With this innovative process, the valuable material can be separated from the fines stream 11, making the process significantly more efficient than conventional recycling processes. The fines stream 11 consists of moist, dewatered solids with a residual moisture content of 1 to 15 wt%.

[0035] The fines stream 11 is fed to a centrifugal separator 13. The centrifugal separator 13 enables the fines stream to be separated into a sinking material 15 and a floating material 17 at a set separation density, and the valuable material or the target polymer is separated from the impurities. The sinking material 15 has a higher density than the separation density, and the floating material 17 has a lower density than the separation density. The centrifugal separator 13 enables a sharp and precise separation according to density. Therefore, the plastic fines of a plastic type remain in the same fraction (sinking material or floating material) regardless of the particle size, since all particles have the same density. This means that the fines are not lost and can be further processed. For example, the material stream of recycled PET material from PET bottles orthe yield of the recycling process can be increased by up to 10 wt% because the PET fines washed out with the washing water can be recovered by the centrifugal separator 13.

[0036] The centrifugal separator 13 preferably comprises an inclined tube 19 defining a separation chamber 20. In the centrifugal separator 13, a centrifugal force is generated by the tangential introduction of a density medium 25. This quickly establishes equilibrium between the sinking material and the floating material, even though the density difference between the materials to be separated may be very small (see PET and PVC above).

[0037] The centrifugal separator 13 separates the product stream 11 with a high density separation efficiency into the sediment 15 and the floating material 17, which exit the centrifugal separator at different points. The sediment 15 exits the centrifugal separator 13 at the upper end and the floating material 17 at the lower end. The sediment 15 is fed to a first centrifuge 21, and the floating material 17 is fed to a second centrifuge 23.

[0038] The separation density of the centrifugal separator 13 is adjusted by the density medium 25, which is introduced tangentially into the centrifugal separator 13 as described above. Preferably, the density medium is the treated wash water, which is collected in a storage tank 27. Before the density medium 25 is returned to the centrifugal separator, the required density of the density medium 25 is adjusted to achieve the required separation density in the centrifugal separator 13. This adjustment can be achieved, for example, by adding a salt, in particular potassium carbonate.

[0039] In the first centrifuge 21, the sediment 15 is separated into a first solid fraction 29 and the density medium 25 or wash water. The separated density medium 25 also contains particles smaller than 1 mm. The first solid fraction 29 is filled, for example, into first big bags 35 in a first filling station 33.

[0040] In the second centrifuge 23, the floating material 17 is separated into a second solid fraction 31 and the density medium 25 or wash water. The density medium 25 separated by the second centrifuge 23 also contains particles smaller than 1 mm. The second solid fraction 31 is filled in a second filling station 37, for example, into second big bags 39.

[0041] The density medium 25, which is separated from the first and second centrifuges 21, 23, is passed through a dewatering screen 41. The dewatering screen 41 cleans the density medium 25 of the particles 43, which can be fed to a collection point 45 and disposed of.

[0042] Surprisingly, even fines with small density differences can be separated in the centrifugal force separator 13. The following example illustrates this: In addition to PET fines, the fines stream 13 also contains fines from PVC labels, polyolefins (PO), and paper fibers. The density of PO and the paper fibers is lower than the density of the PET fines, which allows them to be easily separated from each other in the centrifugal separator 13.

[0043] Although the densities of PVC and PET are close to each other, these two materials can be separated. For the separation of PVC from PET, a separation density of between 1.39 and 1.40 g / cm 3proved to be ideal. For this, the density medium must be adjusted to this density. Water, in which the appropriate amount of potassium carbonate (K2CO3) is dissolved to adjust the density, is suitable for this purpose. K2CO3 is particularly preferred as a salt because it is safe, inexpensive, easy to store, and highly soluble. Furthermore, it maintains the adjusted density, thus keeping the density of the density medium 25 stable.

[0044] The water with the dissolved K2CO3 is fed tangentially into the tubular centrifugal separator 13, whereby the geometry and openings create a liquid vortex on the outside and an air vortex on the inside, generated by a centrifugal force field. The resulting sediment 15 comprises PVC particles, mineral substances, metals, and density medium 25. The fine particles have a grain size of up to approximately 4 mm. In the first centrifuge 21, these substances are separated as the first solid fraction 29 from the density medium 25 and the fine particles 43. The first centrifuge features a sieve with a 1 mm mesh width, resulting in particles 43 having a maximum grain size of 1 mm.

[0045] By extracting the first solid fraction 29, impurities with a density greater than the PET material (target polymer) can be separated. This material can be sold or disposed of according to current technology. However, the first solid fraction 29 no longer contains any PET fines.

[0046] The separated floating material 17, which contains PET and PO, is separated in the second centrifuge 23 into the dense medium (water with K2CO3) and the second solid fraction 31. For this purpose, the second centrifuge 23 also has a sieve with a mesh width of 1 mm. The second solid fraction, which contains PET fines and PO larger than 1 mm, can yield up to 10 wt% more PET material (target polymer) as a valuable product.

[0047] In the dewatering screen, the water with dissolved K2CO3 is separated from the particles 43 and, in a treated state, is fed to the storage tank 27. In the storage tank 27, the density can be adjusted as needed by adding K2CO3. Particles 43 with a maximum particle size of 1 mm can be disposed of or sold. If, in this exemplary embodiment, impurities are present that enter the floating material 17 because they have a lower density than PET (e.g., paper fibers), they can be separated from the PET fines by a further cleaning cycle. To do this, a new separation density must be set for the density medium 25 by adding less K2CO3. The PET

[0048] Fine material is then in the sinking material 15 and the impurities are in the floating material 17.

[0049] Legend:

[0050] 11 Fine material flow

[0051] 13 centrifugal separators

[0052] 15 Sinking debris

[0053] 17 Floating debris

[0054] 19 pipe

[0055] 20 Separation chamber

[0056] 21 First centrifuge

[0057] 23 Second centrifuge

[0058] 25 Density medium

[0059] 27 Storage tank

[0060] 29 First solid fraction

[0061] 31 Second solid fraction

[0062] 33 First filling station

[0063] 35 First Big Bags

[0064] 37 Second filling station

[0065] 39 Second Big Bags

[0066] 41 Drainage sieve

[0067] 43 particles

[0068] 45 collection point

Claims

1 . A method for recovering the fine material resulting from the comminution and washing process of plastic containers to be recycled, which are used to produce PCR (Post Consumer Recycled) granules, comprising the following process steps (a) Crushing the containers into flakes, (b) washing the flakes with a washing medium, (c) feeding the product stream comprising the flakes and the washing medium to a dewatering device for separating the washing water from the flakes, (d) generating a fine material stream (11) by separating the fine material washed out in the washing medium from the washing medium, characterized in that the fine material stream (11) is separated into a sinking material (15) and a floating material (17) by a wet-mechanical density separation at an adjustable separation density.

2. Method according to claim 1, characterized in that a centrifugal force is built up as the driving separation force of the mechanical density separation.

3. Method according to claim 1 or 2, characterized in that the separation density is adjusted by a density medium (25), whereby the separation density can be adapted to the density of the target polymer to be separated.

4. Method according to one of the preceding claims, characterized in that the density medium (25) is water and the density of the density medium (25) is adjusted by the addition of a salt.

5. Process according to claim 4, characterized in that the salt is zinc chloride, sodium iodide, sodium chloride or preferably potassium carbonate.

6. Method according to one of claims 1 to 3, characterized in that the density medium (25) is an alcohol, a ketone or an alkane.

7. Method according to one of the preceding claims, characterized in that the mechanical density separation takes place in a centrifugal separator (13).

8. Method according to claim 7, characterized in that the centrifugal separator (13) comprises a tube (19) inclined relative to the horizontal and the centrifugal force is generated by the density medium (25) being fed tangentially to the centrifugal separator.

9. Method according to one of the preceding claims, characterized in that the separation density is between 0.8 and 1.5 g / cm 3 can be set.

10. Method according to one of the preceding claims, characterized in that the sinking material (15) is fed to a first centrifuge (21) and in the first centrifuge (21) a first solid fraction (29) is separated from the density medium (25) and particles (43) with a maximum grain size of 1 mm. 11 . Method according to one of the preceding claims, characterized in that the floating material (17) is fed to a second centrifuge (23) and in the second centrifuge (23) a second solid fraction (31) is separated from the density medium (25) and particles (43) with a maximum grain size of 1 mm.

12. The method according to claim 11, characterized in that the density medium (25) and the particles (43) with a maximum grain size of 1 mm from the first and second centrifuge (21, 23) are fed to a dewatering sieve (41) and the particles (41) are separated from the density medium (25).

13. Method according to one of claims 7 to 12, characterized in that the purified density medium (25) is returned to the centrifugal separator (13).

14. Method according to one of claims 7 to 13, characterized in that the purified density medium (25) is stored in a storage tank (27) before being returned to the centrifugal separator (13) and the density of the density medium (25) is adjusted in the storage tank (27).