Method for controlling a conveying device for feeding a mixed stream of plastic waste to a plastics recycling facility, and corresponding device

Abstract

The present invention relates to a method for controlling a conveying device for supplying a mixed stream of plastic waste to a plastics recycling facility, comprising: conveying the mixed stream of plastic waste at a predetermined feed rate, the mixed stream of plastic waste having a variable proportion of 2D material, a variable proportion of 3D material, and a variable bulk density, the proportions and bulk density changing over time; detecting at least one parameter of the mixed stream of plastic waste being conveyed; determining the bulk density of the mixed stream of plastic waste based on the detected at least one parameter; and controlling the feed rate as a function of the determined bulk density. The present invention further relates to a corresponding apparatus.

Description

[Technical Field]

[0001] The present invention is based on a method or apparatus for controlling a conveying device for feeding a plastic waste stream to a plastic separation facility, comprising conveying the plastic waste stream at a predetermined feeding rate, detecting the volume density of the conveyed plastic waste stream, and controlling the feeding rate in response to the detected volume density. [Background technology]

[0002] The rise in plastic waste will pose a major challenge for our society in the coming years. In 2019, around 5.35 million tonnes of post-consumer plastic waste was generated in Germany. Of this, only 1.33 million tonnes were sent for material recycling in German processing plants. Furthermore, from this, only 1.03 million tonnes were produced that were good enough for reuse in the plastics processing industry. This corresponds to just over 19%.

[0003] Germany currently lacks the recycling infrastructure needed to economically and technically process the large amounts of plastic waste produced into high-quality recycled products. Many of today's processing facilities are not up to date with cutting-edge technology and are outdated, leaving the country with a very weak economic base.

[0004] The increase in plastic waste and the tightening of national and international legislation regarding authorisation procedures, as well as the expansion of recycling quotas, the use of recycled products and restrictions on the import and export of waste, will pose major challenges for EU Member States, and in particular for plastic recycling companies, in the coming years. There is an urgent need for investment in processing capacities, and in particular the development of new processing methods to resolve the above challenges and problems.

[0005] One of the biggest challenges for plastic recyclers is the highly contaminated mix of plastic waste. Existing recycling processes and facilities currently only handle this waste to a limited extent. As a result, the majority of this waste is currently sent to thermal recycling. Furthermore, the majority of recycled products produced are unable to undergo stable plastic processing due to quality defects, making it unlikely that technologically demanding plastic products will be able to replace new products in a sustainable way.

[0006] The current situation calls for new approaches to processing and the creation of additional capacity in order to meet requirements already in place, such as those from VerpackG and KrWG, to increase material quotas in a sustainable way, and to provide the plastics processing industry with sufficient quantities of high-quality and consistent plastic recycled products in the future, especially as a replacement for primary plastics.

[0007] The development of concepts for the economical treatment of highly contaminated mixed plastic waste, which has so far mainly been thermally recycled, is of great importance. New modern treatment technologies have great potential to meet recycling quotas and, above all, to avoid taxes on plastic waste mixtures that have not been recycled in Germany so far, thereby mitigating the further economic and environmental burden caused by plastic waste that has not been physically recycled.

[0008] Plastics are often collected in a mixed state, but are only sent to reprocessing after undergoing complex dry mechanical sorting processes, such as ballistic and NIR sorters. However, so-called 2D materials, such as films, bags, and trays, are rarely sent to reprocessing and do not reach recycling, as existing methods and facilities do not allow them to be adequately cleaned or separated from other types of plastic. Therefore, sorting residues that are not recycled physically are recycled energetically, and the thermal energy they contain is used for electricity and district heating.

[0009] German Patent Application No. 10 2013 213 478 A1 discloses a method for separating and recovering plastics of uniform density. During the separation process, plastic particles are transported by a conveyor belt to a detection unit. Because a high particle density can negatively affect the sorting results and the purity of the desired plastic batch type, the speed of the conveyor belt is adjusted so that the distance between the plastic particles is favorable for subsequent separation. The particle density on the conveyor belt is detected by a camera and processed by a computer program installed in a control unit, which adjusts the speed of the conveyor belt accordingly.

[0010] However, the disclosed method has the drawback that while the volume flow rate of the transported waste is detected by detecting the particle density on the conveyor belt, the bulk density of the transported plastic waste is not detected. Therefore, this method is not suitable for separating plastics with a wide range of different densities, and in particular for the simultaneous processing of 2D and 3D materials. Summary of the Invention

[0011] The present invention is therefore based on the objective technical objective of further developing a method and apparatus for feeding a mixed plastic waste stream, which is capable of processing plastics with different densities and which allows for a higher yield of useful materials and a significantly higher purity of species in recycled products produced from the mixed plastic waste.

[0012] Accordingly, there is provided a method of controlling a conveying apparatus for supplying a mixed stream of plastic waste to a plastics recycling facility, the method comprising: conveying a mixed stream of plastic waste at a predetermined feed rate, the mixed stream of plastic waste having a variable proportion of 2D material, a variable proportion of 3D material, and a variable bulk density, the proportions and the bulk density varying over time; detecting at least one parameter of the conveyed mixed plastic waste stream; determining the bulk density of the mixed stream of plastic waste based on at least one of the detected parameters; controlling the feed rate as a function of the determined bulk density; Includes.

[0013] Providing a mixed plastic waste stream with a varying proportion of 2D and 3D materials also means that the supplied mixed plastic waste stream is significantly more heterogeneous than with conventional methods and, in particular, may be subject to large fluctuations in the individual proportions over time. In particular, it can be provided that the 3D portion is made up of bulky plastic waste, such as hollow bodies, and the 2D portion is made up of flat plastic waste, such as films.

[0014] The method according to the present invention therefore has the advantage of being able to process mixed plastic waste streams with varying 2D / 3D ratios at the time of input. In this case, processing 2D and 3D materials together results in a significantly higher yield of all material components useful for material recycling than methods known in the prior art. Therefore, the method according to the present invention can be used in particular in facilities that can obtain both HDPE (high-density polyethylene) ground material, PP (polypropylene) ground material, and PO (polyolefin) film ground material, as well as different types of polymers or thermoplastics.

[0015] The feed rate can be controlled to slow down when the predetermined bulk density is low and to speed up when the predetermined bulk density is high. Therefore, the feed rate can be controlled proportionally to the predetermined bulk density. This is because a lower gram-per-liter ratio is more effective in separating 2D and 3D plastic waste mixtures when the proportion of 2D material is imbalanced. This means that if a high proportion of 2D material is detected in the plastic waste mixture stream, the feed rate can be reduced to ensure that the individual plastic types can be consistently separated from each other at a downstream plastic recycling facility.

[0016] The step of sensing at least one parameter may include sensing the mass flow rate of the conveyed mixed plastic waste stream, for example, by a belt weigher.

[0017] Furthermore, the step of detecting at least one parameter can include, in particular, continuously optically detecting the composition of the transported mixed plastic waste stream, for example, using a line camera. In this case, because 2D materials have a lower bulk density than 3D materials on average, the bulk density can be determined based on the optically detected ratio of 2D to 3D material portions in the mixed plastic waste stream. This means that the bulk density correlates with the proportion of 2D or 3D material in the mixed plastic waste stream. For example, the bulk density can be between 10 grams / liter when the 2D material portion is predominant and 400 grams / liter when the 3D material portion is predominant.

[0018] Furthermore, determining the bulk density may include comparing the optically detected ratio of 2D material portions to 3D material portions in the conveyed mixed plastic waste stream with reference images stored in a database. The database may be stored in a memory of the control unit. Each reference image stored in the database may be assigned a target conveying speed used to control the feed rate. The assigned target conveying speed may be slower for reference images with more 2D portions and faster for reference images with fewer 2D portions.

[0019] The method may further include a step of flattening the mixed plastic waste stream to a predetermined height before the step of detecting at least one parameter of the mixed plastic waste stream being transported. In this case, the mixed plastic waste stream may be transported, for example, in the form of a single layer on a conveying belt. Avoiding peaks on the conveying belt may enable better image recognition. For example, flattening the mixed plastic waste stream may be performed using a vibration device before detecting at least one parameter of the mixed plastic waste stream being transported. Furthermore, the mixed plastic waste stream may be transported using a conveying means, for example, a conveying belt or a vibration device, and the plastic waste may be loaded onto the conveying means using multiple independent waste chutes arranged adjacent to each other perpendicular to the conveying direction of the conveying means and capable of loading across the entire width of the conveying means.

[0020] The method may further include, prior to the conveying step, grinding the plastic waste mixture to a predetermined material size. Homogenizing the plastic components to a predetermined size makes it easier to determine the 2D or 3D proportions, since repeating patterns of specific proportions are more visible.

[0021] The control of the supply rate may include controlling the supply rate of the mixed plastic waste stream to the conveying means. Further, the control of the supply rate may include controlling the conveying speed of the conveying means.

[0022] The invention further relates to a conveying device for carrying out a method according to any of the preceding claims, comprising a feeding device with conveying means, in particular a conveying belt, for feeding the mixed plastic waste stream, a detection device arranged on the conveying means for detecting at least one parameter of the mixed plastic waste stream, and a control unit configured to control the feeding speed of the feeding device, the control unit being configured to determine the bulk density of the mixed plastic waste stream based on the detected at least one parameter and to control the feeding speed of the feeding device as a function of the determined bulk density.

[0023] In this case, the supply rate can be controlled so that the supply rate is slow when the predetermined bulk density is low, and the supply rate is fast when the predetermined bulk density is high.

[0024] Furthermore, the detection device may comprise a belt weigher for detecting the mass flow rate of the plastic waste mixture on the conveying means.

[0025] Furthermore, the detection device may comprise optical detection means, such as for example a line camera, for detecting the composition of the mixed plastic waste stream on the conveying means.

[0026] The control unit can be configured to determine the bulk density based on an optically detected ratio of 2D material portions to 3D material portions within the mixed plastic waste stream.

[0027] The control unit can further be configured to compare the optically detected ratio of 2D to 3D material portions in the conveyed mixed plastic waste stream with reference images stored in a database to determine bulk density. In this case, each reference image stored in the database can be assigned a target conveying speed used to control the feed rate. The assigned target conveying speed can be slower for reference images with more 2D portions and faster for reference images with fewer 2D portions.

[0028] The feeding device may further comprise a feeding device for feeding the mixed plastic waste stream onto the conveying belt. The feeding device may comprise a plurality of independent waste chutes arranged adjacent to each other perpendicular to the conveying direction of the conveying means and capable of loading across the entire width of the conveying means. In addition, the feeding device may further comprise a device for flattening the mixed plastic waste stream. The device for flattening the mixed plastic waste stream may comprise a height limiting device arranged across the conveying path and above the conveying surface of the conveying means and configured to limit the passing mixed plastic waste stream to a predetermined height. The device for flattening the mixed plastic waste stream may further be configured so that the conveying means is configured in a trough shape and comprises a vibration device for vibrating and flattening the mixed plastic waste stream.

[0029] Furthermore, a crushing device for crushing the plastic waste mixture can be connected upstream of the feeding device, the crushing device being configured to crush the plastic waste mixture into a predetermined material size.

[0030] The control of the feeding rate may include controlling the feeding rate of the mixed plastic waste stream from the feeding device onto the conveying means. The control of the feeding rate may include controlling the conveying speed of the conveying means. Further, the control of the conveying speed of the conveying means may be performed using a frequency converter. The motor of the conveying means may be configured as a three-phase motor. [Brief explanation of the drawings]

[0031] Further details of the invention are explained on the basis of the following drawings. [Figure 1] 1 shows a schematic diagram of an embodiment of a transport device according to the present invention; [Figure 2] 1 shows a flow chart of one embodiment of a method according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0032] The conveying device 1 shown in FIG. 1 for supplying a mixed plastic waste stream 4 to a plastic recycling facility essentially comprises a feeder 2, a detection unit 5, a control unit 6, and a drive unit 21. The feeder 2 comprises a feeder 13 and a conveying means 3. The feeder 13 supplies the mixed plastic waste stream 4 to the conveying means 3 at the input side. In the illustrated embodiment, the feeder 13 comprises a plurality of independent waste chutes 14 arranged adjacent to each other perpendicular to the conveying direction X of the conveying means 3 and covering the entire width B of the conveying means 3. The amount of waste per unit time supplied to the conveying means 3 can be adjusted by setting the supply volume flow rate qA. This can be achieved by setting the speed of the supply and conveying means of the feeder 13 and / or by changing the passage cross-sectional area of ​​the feeder 13, for example, using a partition. Before transferring the plastic waste to the feeder 13, a crusher 19 can be used to crush the waste into a predetermined material chip size. In the illustrated embodiment, the conveying means 3 is configured as a belt conveyor. The mixed plastic waste stream 4 contains both 2D and 3D material portions 9 and 10, the proportions of which vary within the mixed plastic waste stream 4, as clearly indicated by the different intensities of hatching in the adjacent diagrams. This means that the 2D proportion is lowest in areas with little or no hatching and highest in areas with heavy hatching. Upon reaching the conveying means 3, the mixed plastic waste stream 4 may not have a constant height due to the formation of areas where waste accumulates and areas with low waste loads. This is clearly indicated in FIG. 1 by the contour of the height of the mixed waste stream 4 at the inlet area of ​​the conveying means. To flatten the pile, the conveying device 1 includes a height limiter 17 that crosses the conveying path X and is positioned above the conveying surface 16 of the conveying means 3. This limits the mixed waste stream 4 to a predetermined height H, thereby facilitating subsequent detection of the composition of the mixed plastic waste stream 4. The height limiter 17 may be height-adjustable.As a further device 15 for flattening the mixed plastic waste stream 4, the conveying means 3 is provided with a vibration device 18 which is able to vibrate the conveying surface 16 or the mixed plastic waste stream 4 so that any irregularities present can also be flattened thereby.

[0033] After passing through the height limiting device 17, the plastic waste mixed stream 4 has an essentially constant height H, as shown. Next, at least one parameter of the plastic waste mixed stream 4 is detected by the detection device 5. The detection device 5 can include, for example, a weight detection device such as a belt weigher 7, which constantly detects the weight of the plastic waste mixed stream 4. The detection device 5 can also include an optical detection device 8, such as a line camera. The detection device 8 detects the surface of the plastic waste mixed stream 4 to optically detect the composition of the plastic waste mixed stream 4, in particular to detect 2D and 3D proportions, each of which correlates with a specific bulk density. The detection devices 5, i.e., the belt weigher 7 and the camera 8, are connected to the control unit 6 and transmit the detected information to the control unit 6. The control unit 6 determines the current bulk density of the plastic waste mixed stream 4 on the conveying means 3 from the received information. In the case of optical detection, the control unit 6 includes a database 11 in which reference images 12 are stored. The control unit compares the image detected by the camera 8 with reference images 12 stored in a database 11 and determines which reference image 12 is most similar to the image currently detected by the camera 8. In this case, a target conveying speed vS is assigned to each reference image 12. Using this target conveying speed vS, the control unit 6 controls a drive 21 that drives the conveying means 3, and in the process, the feed speed v of the conveying means 3 is adjusted to the determined target conveying speed vS. In the illustrated embodiment, the speed control of the conveying means 3 is performed by a frequency converter 20 interposed between the control unit 6 and the drive 21 of the conveying means 3.

[0034] 2 shows a flowchart of one embodiment of the method according to the present invention. In this case, in a first step 100, plastic waste is crushed into a predetermined material chip size. Subsequently, in a second step 200, the plastic waste is fed onto a conveying means 3, which conveys 300 the plastic waste mixed stream 4 along a conveying direction X at a feeding speed v. The plastic waste mixed stream 4 conveyed on the conveying means 3 is flattened 400 using an appropriate device to limit it to a predetermined height H. After flattening 400, at least one parameter of the plastic waste mixed stream 4 on the conveying means 3 is detected 500 and transmitted to a control unit 6, which determines 600 the bulk density of the plastic waste mixed stream 4 from the at least one detected parameter. Finally, the feeding speed v of the conveying means 3 is controlled 700 based on the determined bulk density.

[0035] The features of the invention disclosed in the above description, in the drawings and in the claims may be essential both individually and in any combination for the realization of the invention. [Explanation of symbols]

[0036] 1. Conveyor device 2 Feeding device 3. Means of transportation 4. Mixed plastic waste stream 5. Detection device 6. Control Unit 7 Belt weigher 8 line camera 9 2D materials 10 3D materials 11 Database 12 Reference Images 13 Feeding device 14 Waste Chute 15. Equipment for flattening plastic waste 16 Conveying surface 17 Height restriction device 18 Vibration device 19 Crushing equipment 20 Frequency converter 21 Three-phase motor 100 Plastic waste crushing 200 Feeding of plastic waste onto conveyances 300 Conveying mixed plastic waste streams 400 Flattening of mixed plastic waste streams 500 Detection of mixed plastic waste streams 600 Determination of bulk density 700 Feed rate control v Feed rate vA feed rate vS Target conveying speed X Transport Route B Width H specified height

Claims

1. 1. A method for controlling a conveying device (1) for feeding a mixed plastic waste stream (4) to a plastics recycling facility, comprising the steps of: conveying a mixed plastic waste stream (4) at a feed rate (v), said mixed plastic waste stream (4) having a variable proportion of 2D material (9), a variable proportion of 3D material (10) and a variable bulk density, said proportions and said bulk density varying over time; detecting at least one parameter of the mixed plastic waste stream (4) being conveyed; determining the bulk density of the mixed plastic waste stream (4) based on at least one of the detected parameters; controlling the feed rate (v) as a function of the determined bulk density; A method comprising:

2. 2. The method of claim 1, wherein the feed rate (v) is controlled to be low when the predetermined bulk density is low and to be high when the predetermined bulk density is high.

3. 3. The method according to claim 1 or 2, wherein said detecting at least one parameter comprises detecting the mass flow rate of the conveyed mixed plastic waste stream (4), for example by means of a belt weigher (7).

4. 4. The method according to claim 1, wherein said detecting of at least one parameter comprises optically detecting the composition of the conveyed mixed plastic waste stream (4), for example by means of a line camera (8).

5. 5. The method of claim 4, wherein the bulk density is determined based on an optically detected ratio of the 2D material portion (9) to the 3D material portion (10) in the mixed plastic waste stream (4).

6. 6. The method according to claim 4 or 5, wherein the determination of the bulk density comprises comparing the optically detected ratio of the 2D material portions (9) to the 3D material portions (10) in the conveyed mixed plastic waste stream (4) with reference images (12) stored in a database (11).

7. 7. The method according to claim 6, wherein each of the reference images (12) stored in the database (11) is assigned a target conveying speed (vS) which is used to control the feed speed (v).

8. 8. The method according to claim 7, wherein the assigned target conveying speed (vS) is slow for reference images (12) with many 2D portions (9) and fast for reference images (12) with few 2D portions (9).

9. The method of any one of claims 1 to 8, wherein the bulk density is between 10 grams / liter and 400 grams / liter.

10. 10. The method according to any one of claims 1 to 9, further comprising flattening the mixed plastic waste stream (4) to a predetermined height (H) before detecting at least one said parameter of the conveyed mixed plastic waste stream (4).

11. The method according to any one of claims 1 to 10, further comprising flattening the plastic waste mixed stream (4) using a vibration device (18), preferably a vibrator, before detecting at least one said parameter of the conveyed plastic waste mixed stream (4).

12. 12. The method according to any one of claims 1 to 11, further comprising conveying the mixed plastic waste stream (4) using a conveying means (3), wherein the loading of the plastic waste onto the conveying means (3) is carried out using a plurality of independent waste chutes (14) arranged adjacent to each other perpendicular to the conveying direction (X) of the conveying means (3) and loading across the entire width (b) of the conveying means (3).

13. The method according to any one of claims 1 to 12, further comprising comminuting the plastic waste mixture to a predetermined material size before conveying the plastic waste mixture stream (4).

14. 14. The method according to claim 12 or 13, wherein the control of the feeding rate (v) comprises controlling the feeding rate (vA) of the mixed plastic waste stream (4) onto the conveying means (3).

15. The method according to any one of claims 11 to 14, wherein controlling the feeding speed (v) comprises controlling the conveying speed of the conveying means (3).

16. A conveying device (1) for carrying out the method according to any one of claims 1 to 15, comprising: a feeding device (2) comprising a conveying means (3), in particular a conveying belt, for feeding the mixed plastic waste stream (4); a detection device (5) arranged on the conveying means for detecting at least one parameter of the mixed plastic waste stream (4); a control unit (6) configured to control the feeding rate (v) of said feeding device (2); Equipped with The control unit (6) is configured to determine a bulk density of the mixed plastic waste stream (4) based on at least one of the detected parameters and to control the feeding speed (v) of the feeding device (2) as a function of the determined bulk density.

17. 17. The conveying device (1) of claim 16, wherein the supply speed (v) is controlled so that the supply speed (v) is low when the predetermined bulk density is low and the supply speed (v) is high when the predetermined bulk density is high.

18. 18. The conveying device (1) according to claim 16 or 17, wherein the detection device (5) comprises a belt weigher (7) for detecting the mass flow rate of the mixed plastic waste stream (4) on the conveying means (3).

19. The conveying device (1) according to any one of claims 16 to 18, wherein the detection device (5) comprises an optical detection means, for example a line camera (8), for detecting the composition of the plastic waste mixture stream (4) on the conveying means (3).

20. 20. The conveying device (1) according to claim 19, wherein the control unit (6) is configured to determine the bulk density based on an optically detected ratio of 2D material portions (9) to 3D material portions (10) in the mixed plastic waste stream (4).

21. 21. The conveying device (1) according to claim 19 or 20, wherein the control unit (6) is configured to compare the optically detected ratio of the 2D material portions (9) and the 3D material portions (10) in the conveyed plastic waste mixture stream (4) with reference images (12) stored in a database (11) in order to determine the bulk density.

22. 22. The conveying device (1) according to claim 21, wherein each of the reference images (12) stored in the database (11) is assigned a target conveying speed (vS) which is used to control the supply speed (v).

23. The conveying device (1) according to claim 22, wherein the assigned target conveying speed (vS) is slow for reference images (12) with many 2D portions (9) and fast for reference images (12) with few 2D portions (9).

24. A conveying device (1) according to any one of claims 16 to 23, wherein the feeding device (2) further comprises a feeding device (13) for feeding the mixed plastic waste stream (4) onto the conveying belt.

25. 25. The conveying device (1) according to claim 24, wherein the feeding device (13) comprises a plurality of independent waste chutes (14) arranged adjacent to each other perpendicular to the conveying direction of the conveying means and capable of loading across the entire width (b) of the conveying means (3).

26. Conveying device (1) according to any of claims 16 to 25, wherein the feeding device (2) further comprises a device (15) for flattening the mixed plastic waste stream (4).

27. 27. The conveying device (1) according to claim 26, wherein the device (15) for flattening the mixed plastic waste stream (4) comprises a height limiting device (17) arranged across the conveying path (X) and above the conveying surface (16) of the conveying means (3) and configured to limit the passing mixed plastic waste stream (4) to a predetermined height (H).

28. 28. The conveying device (1) according to claim 26 or 27, wherein the device (15) for flattening the mixed plastic waste stream (4) is further configured such that the conveying means (3) is configured in a trough shape and comprises a vibration device (18) for vibrating and flattening the mixed plastic waste stream (4).

29. A conveying device (1) according to any one of claims 16 to 28, wherein a crushing device (19) for crushing the plastic waste mixture is connected upstream of the feeding device (2) and configured to crush the plastic waste mixture into a predetermined material size.

30. The conveying device (1) according to any one of claims 24 to 29, wherein the control of the feeding speed (v) comprises controlling the feeding speed (vA) of the plastic waste mixture stream (4) from the feeding device (13) onto the conveying means (3).

31. The conveying device (1) according to any one of claims 16 to 30, wherein the control of the supply speed (v) includes control of the conveying speed of the conveying means (3).

32. 32. Conveying device according to claim 31, wherein the conveying speed of the conveying means (3) is controlled by means of a frequency converter (20).

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