Method for controlling a conveyor device for feeding a plastic waste mixture stream to a plastic recycling plant, and corresponding device

Abstract

The invention relates to a method for controlling a conveyor device for feeding a plastic waste mixture stream to a plastic recycling plant, comprising the steps of: conveying a plastic waste mixture stream at a feed rate, wherein the plastic waste mixture stream comprises a variable fraction of 2D material, a variable fraction of 3D material and a variable bulk density, wherein the fractions and the bulk density vary over time; detecting at least one parameter of the conveyed plastic waste mixture stream; determining the bulk density of the plastic waste mixture stream on the basis of the at least one detected parameter; controlling the feed rate on the basis of the determined bulk density. The invention also relates to a corresponding device.

Description

[0001] Method for controlling a conveying device for feeding a plastic waste mixture stream to a plastic recycling plant and corresponding device

[0002] The invention is based on a method and a device for controlling a conveying device for feeding a plastic waste stream to a plastic separation plant, comprising conveying a plastic waste stream at a feed speed, detecting the volume density of the conveyed plastic waste stream, and controlling the feed speed as a function of the detected volume density.

[0003] Rising amounts of plastic waste pose enormous challenges for our society in the coming years. In 2019, approximately 5.35 million tons of post-consumer plastic waste were generated in Germany. Of this, only 1.33 million tons were recycled in processing plants within Germany. This, in turn, ultimately produced only 1.03 million tons of output suitable for reuse in the plastics processing industry. This corresponds to a rate of just over 19%.

[0004] As of today, Germany lacks the necessary recycling infrastructure to economically and technically process the resulting volumes of plastic waste into high-quality recyclates. Many processing plants currently do not meet state-of-the-art standards, are outdated, and have very weak economic foundations.

[0005] Rising plastic waste volumes, tightened national and international legislation on permitting procedures and increasing recycling rates and the use of recyclates, as well as waste import and export restrictions, pose enormous challenges for EU member states and especially for plastics recycling companies in the coming years. Investments in processing capacities and, in particular, the development of new processing methods to address these challenges and problems are urgently needed.

[0006] One of the greatest challenges for plastics recyclers is heavily contaminated plastic waste mixtures. Existing recycling processes and facilities currently offer very limited material processing options for these fractions. Therefore, a large portion of this waste currently finds its way into thermal recycling. Furthermore, due to quality deficiencies, a large proportion of the recycled materials produced do not permit stable plastics processing and therefore rarely replace virgin materials in technically sophisticated plastic products.

[0007] The current situation calls for new approaches to processing and creating additional capacities in order to meet the requirements already in force, including those stipulated in the Packaging Act and the Recycling and Waste Management Act, to sustainably increase material quotas and to provide the plastics processing industry with sufficient quantities of plastic recyclates, particularly of high and consistent quality, as a substitute for primary plastics in the future.

[0008] The development of economically viable concepts for the material processing of heavily contaminated and mixed plastic waste, which has previously been predominantly thermally recycled, is critical. New and modern processing technologies offer great potential for meeting recycling quotas and, among other things, avoiding levies on mixed plastic waste not yet recycled in Germany and reducing further economic and ecological burdens caused by non-materially recycled plastic waste.

[0009] Plastics are often collected mixed together and only recycled after undergoing complex dry mechanical separation steps, such as ballistic separators or NIR sorters. However, because films, bags, and trays, so-called 2D materials, are difficult to clean and separate from other types of plastic in these existing processes and systems, a large proportion of them are not recycled but are lost for recycling. These non-recycled sorting residues are therefore recovered for energy recovery, and the thermal energy they contain is used to generate electricity and district heating.

[0010] DE 102013213478 Ai discloses a method for separating and recovering plastics, where the plastics have a similar density. For the separation process, plastic particles are transported to a detection unit via a conveyor belt. The speed of the conveyor belt is controlled to ensure a favorable spacing between the plastic particles for subsequent separation, since particles that are too close together negatively impact the sorting result and the purity of the desired plastic batches. The particle density on the conveyor belt is recorded by a camera and processed by a computer program installed on a control unit, which regulates the speed of the conveyor belt accordingly.

[0011] However, the disclosed method has the disadvantage that, while the conveyed waste volume flow is detected by detecting the particle density on the conveyor belt, the bulk density of the conveyed plastic waste is not. Thus, the method is not suitable for separating plastics with a wide range of different densities, and thus, in particular, not for the simultaneous processing of 2D and 3D materials.

[0012] The invention is therefore based on the objective technical problem of further developing a method and a device for feeding a plastic waste mixture stream in such a way that plastics with different densities can be processed with it and that a higher yield of valuable materials and a significantly increased purity of the recyclates produced from plastic waste mixtures can be achieved.

[0013] Accordingly, the method for controlling a conveying device for feeding a plastic waste mixture stream to a plastic recycling plant comprises:

[0014] Conveying a plastic waste mixture stream at a feed rate, wherein the plastic waste mixture stream has a variable proportion of 2D material, a variable proportion of 3D material and a variable bulk density, wherein the proportions and the bulk density vary over time;

[0015] Detecting at least one parameter of the conveyed plastic waste mixture stream; determining the bulk density of the plastic waste mixture stream based on the at least one detected parameter;

[0016] Control the feed rate depending on the determined bulk density.

[0017] Providing a mixed plastic waste stream with variable proportions of 2D and 3D material can imply that the supplied mixed plastic waste stream is significantly more heterogeneous than conventional processes and, especially over time, can be subject to significant fluctuations in the individual proportions. In particular, it can be provided that the D portion comprises voluminous plastic waste such as hollow bodies, and the 2D portion comprises flat plastic waste such as films.

[0018] The process according to the invention thus has the advantage of being able to process a mixed plastic waste stream with fluctuating 2D / 3D proportions in the input. The combined processing of 2D and 3D materials leads to a significantly higher yield of all valuable material components for material recycling compared to the prior art process. Thus, the process according to the invention can be used in particular for plants that produce HDPE (high-density polyethylene) regrind, PP (polypropylene) regrind, PO (polyolefin) film regrind, and various types of polymers or thermoplastics.

[0019] The feed rate can be controlled in such a way that the feed rate is low for a low determined bulk density and high for a high determined bulk density. This allows the feed rate to be controlled proportionally to the determined bulk density. Sorting of 2D and 3D plastic waste mixtures is more effective the lower the gram / liter ratio, when there is a disproportionate proportion of 2D material. This means that if a high 2D proportion is detected in the mixed plastic waste stream, the feed rate is reduced so that the individual plastic types can be separated from one another in the downstream plastic recycling plant with a consistently high degree of separation accuracy.

[0020] It is conceivable that the detection of the at least one parameter comprises the detection of the mass flow of the conveyed plastic waste mixture stream, for example by means of a belt scale.

[0021] Furthermore, the detection of the at least one parameter can comprise, in particular, continuous optical detection of the composition of the conveyed mixed plastic waste stream, for example using a line scan camera. The bulk density can be determined based on the optically detected ratio of the 2D material content to the 3D material content in the mixed plastic waste stream, since 2D materials on average have a lower bulk density than 3D materials. This means that the bulk density correlates with the 2D or 3D content in the mixed plastic waste stream. The bulk density can, for example, be between 10 grams / liter with a very high 2D material content and 400 grams / liter with a very high D material content.

[0022] Furthermore, determining the bulk density can include comparing the optically recorded ratio of the 2D material content to the D material content in the conveyed mixed plastic waste stream with reference images stored in a database. The database can be stored in a memory of the control unit. Each reference image stored in the database can be assigned a target conveying speed, which is used to regulate the feed speed. The assigned target conveying speed can be low for reference images with a high 2D content and high for reference images with a low 2D content.

[0023] It can be provided that the method further comprises leveling the mixed plastic waste stream to a predefined height before detecting the at least one parameter of the conveyed mixed plastic waste stream. The mixed plastic waste can be conveyed, for example, in the form of a monolayer on the conveyor belt. Better image recognition can be achieved by avoiding mounds on the conveyor belt. For example, the mixed plastic waste stream can be leveled using a vibrating device before detecting the at least one parameter of the conveyed mixed plastic waste stream.In addition, the conveying of the plastic waste mixture stream can be carried out by means of a transport means, for example a conveyor belt or a vibrating chute, wherein the feeding of the transport means with plastic waste can be carried out by means of several separate waste chutes arranged side by side perpendicular to the conveying direction of the transport means, via which the transport means can be fed across its entire width.

[0024] The method may further comprise comminuting the plastic waste mixture to a predetermined material size before conveying the plastic waste mixture stream. By homogenizing the plastic pieces to a predetermined size, the 2D or D fraction can be determined more easily, as recurring patterns of specific fraction amounts become more visible.

[0025] It can be provided that controlling the feed speed includes controlling the feed speed of the mixed plastic waste stream onto the transport means. Furthermore, controlling the feed speed can include controlling the conveying speed of the transport means.

[0026] The invention further relates to a conveying device for carrying out the method according to one of the preceding claims, comprising a feed device which has a transport means, in particular a conveyor belt, for feeding the plastic waste mixture stream; a detection device for detecting at least one parameter of the plastic waste mixture stream located on the transport means, a control unit which is configured to regulate the feed speed of the feed device, wherein the control unit is configured to determine the bulk density of the plastic waste mixture stream based on the at least one detected parameter and to regulate the feed speed of the feed device depending on the determined bulk density.

[0027] The feed speed can be controlled in such a way that the feed speed is low when the determined bulk density is low and high when the determined bulk density is high.

[0028] Furthermore, the detection device can comprise a belt scale for detecting the mass flow of the plastic waste mixture on the transport means.

[0029] In addition, the detection device can comprise an optical detection means, for example a line scan camera, for detecting the composition of the plastic waste mixture stream on the transport means.

[0030] The control unit can be configured to determine the bulk density based on the optically detected ratio of the 2D material portion to the D material portion in the plastic waste mixture stream.

[0031] The control unit can further be configured to determine the bulk density by comparing the optically detected ratio of the 2D material content to the D material content in the conveyed mixed plastic waste stream with reference images stored in a database. A target conveying speed can be assigned to each of the reference images stored in the database, which is used to control the feed speed. The assigned target conveying speed can be low for reference images with a high 2D content and high for reference images with a low 2D content.

[0032] The feed device can further comprise a feed device for feeding the mixed plastic waste stream onto the conveyor belt. The feed device can comprise several separate waste chutes arranged side by side perpendicular to the conveying direction of the conveyor, via which the conveyor can be fed across its entire width. Furthermore, the feed device can further comprise a device for leveling the mixed plastic waste stream. The device for leveling the mixed plastic waste stream can comprise a height-limiting device that crosses the conveying path and is arranged above a transport surface of the conveyor, which is designed to limit the passing mixed plastic waste stream to a predefined height.The device for leveling the plastic waste mixture stream can further be designed such that the transport means is trough-shaped and has a vibrating device for vibratingly leveling the plastic waste mixture stream.

[0033] Furthermore, a comminution device for comminuting the plastic waste mixture can be arranged upstream of the feed device, which is designed to comminute the plastic waste mixture to a predetermined material size.

[0034] Controlling the feed speed can include controlling the feed speed of the mixed plastic waste stream from the feed device to the transport means. Controlling the feed speed can include controlling the conveying speed of the transport means. Furthermore, controlling the conveying speed of the transport means can be achieved using a frequency converter. The motor of the transport means can be designed as a three-phase motor.

[0035] Further details of the invention are explained with reference to the following figures.

[0036] Fig. i is a schematic representation of an embodiment of the conveying device according to the invention; Fig. 2 is a flow diagram of an embodiment of the method according to the invention.

[0037] The conveying device 1 shown in Figure 1 for feeding a mixed plastics waste stream 4 to a plastics recycling plant essentially comprises a feed device 2, a detection unit 5, a control unit 6 and a drive 21. The feed device 2 comprises a feeding device 13 and a transport means 3. By means of the feeding device 13, a mixed plastics waste stream 4 is fed onto the transport means 3 on the inlet side. In the embodiment shown, the feeding device 13 has several separate waste chutes 14 arranged side by side perpendicular to the conveying direction X of the transport means 3, via which waste chutes the transport means 3 is fed across its entire width B. By setting the feed volume flow qA, the amount of waste fed onto the transport means 3 per unit of time can be adjusted.This can be achieved by adjusting the speed of a feed conveyor of the feed device 13 and / or by changing the passage cross-section of the feed device 13, for example by means of a bulkhead. Before the plastic waste is transferred to the feed device 13, the waste can be reduced to a predetermined material chip size by means of a comminution device 19. In the illustrated embodiment, the transport means 3 is designed as a belt conveyor. The mixed plastic waste stream 4 has both a 2D material portion 9 and a 3D material portion 10, with the portions varying within the mixed plastic waste stream 4, which is illustrated by the different hatching strengths according to the adjacent diagram. This means that the 2D portion is lowest in areas with little or no hatching and maximum in areas with heavy hatching.The mixed plastic waste stream 4 may have an inconsistent height upon reaching the transport means 3, which is due to the formation of areas with waste accumulations and areas with a lower waste load. This is indicated in Figure 1 by the height profile of the mixed waste stream 4 in the mouth area of ​​the transport means. To level the accumulations, the conveying device 1 has, on the one hand, a height limiting device 17 which crosses the conveying path X and is arranged above the transport surface 16 of the transport means 3, by which the mixed waste stream 4 is limited to a predefined height H, thereby facilitating the subsequent determination of the composition of the mixed plastic waste stream 4. The height limiting device 17 can be designed to be height-adjustable.The transport means 3 has a vibrating device 18 as a further device 15 for leveling the plastic waste mixture stream 4, by means of which the transport surface 16 or the plastic waste mixture stream 4 can be vibrated, so that any unevenness present can also be leveled.

[0038] After passing the height-limiting device 17, the mixed plastic waste stream 4 has a substantially constant height H, as shown. At least one parameter of the mixed plastic waste stream 4 is then recorded by a recording device 5. The recording device 5 can have a weight recording device, such as a belt scale 7, by means of which the weight of the mixed plastic waste stream 4 is constantly recorded. The recording device 5 can further have an optical recording device 8, such as a line scan camera. This records the surface of the mixed plastic waste stream 4 for optically detecting the composition of the mixed plastic waste stream 4, in particular for detecting the 2D portion and the D portion, which each correlate with a specific bulk density.The detection device 5, i.e., the belt scale 7 and the camera 8, are connected to a control unit 6 and send the detected information to it. The control unit 6 uses the received information to determine the current bulk density of the mixed plastic waste stream 4 on the transport means 3. In the case of optical detection, the control unit 6 has a database 11 in which reference images 12 are stored. The control unit compares the images captured by the camera with those in the database.

[0039] 11 stored reference images 12 and determines which of the reference images 12 the image just captured by the camera 8 is most similar to. Each reference image

[0040] 12 is assigned a target conveying speed vs. Using this target conveying speed vs, the control unit 6 controls a drive 21, which drives the transport means 3, whereby its feed speed v is adjusted to the determined target conveying speed vs. In the illustrated embodiment, the speed of the transport means 3 is controlled by means of a frequency converter 20, which is interposed between the control unit 6 and the drive 21 of the transport means 3.

[0041] Figure 2 shows a flow diagram of an embodiment of the inventive

[0042] Method. In a first step 100, plastic waste is shredded to a predetermined material chip size. Subsequently, in a second step 200, the plastic waste is fed onto a transport means 3, which conveys the mixed plastic waste stream 4 at a feed speed v along a conveying direction X 300. The mixed plastic waste stream 4 conveyed on the transport means 3 is then leveled 400 by means of a suitable device in order to limit it to a predetermined height H. After leveling 400, at least one parameter of the mixed plastic waste stream 4 located on the transport means 3 is recorded 500 and transmitted to a control unit 6, which determines 600 the bulk density of the mixed plastic waste stream 4 from the at least one recorded parameter. Finally, the feed speed v of the transport means 3 is controlled 700 based on the determined bulk density.

[0043] The features of the invention disclosed in the above description, in the drawings and in the claims may be essential for the realization of the invention both individually and in any combination.

[0044] List of reference symbols

[0045] 1 conveyor device

[0046] 2 Feeding device

[0047] 3 means of transport

[0048] 4 Mixed plastic waste stream

[0049] 5 Recording device

[0050] 6 Control unit

[0051] 7 Belt scale

[0052] 8 line scan camera

[0053] 9 2D material io D material ii database

[0054] 12 reference images

[0055] 13 Feeding device

[0056] 14 waste chutes

[0057] 15 Device for leveling the mixed plastic waste stream

[0058] 16 Transport area

[0059] 17 Height limiting device

[0060] 18 vibrating device

[0061] 19 Shredding device

[0062] 20 frequency converters

[0063] 21 three-phase motor

[0064] 100 Shredding of plastic waste

[0065] 200 Placing plastic waste on means of transport

[0066] 300 Conveying the mixed plastic waste stream

[0067] 400 Leveling of the mixed plastic waste stream

[0068] 500 Recording the mixed plastic waste stream

[0069] 6oo Determining the bulk density

[0070] 700 feed speed rules

[0071] V Feed speed

[0072] VA feed speed

[0073] Vs Target conveying speed

[0074] X Conveyor path

[0075] B Width

[0076] H predefined height

Claims

Claims Method for controlling a conveying device (1) for feeding a plastic waste mixture stream (4) to a plastic recycling plant; conveying a plastic waste mixture stream (4) at a feed rate (v), wherein the plastic waste mixture stream (4) has a variable proportion of 2D material (9), a variable proportion of 3D material (10) and a variable bulk density, wherein the proportions and the bulk density vary over time; Detecting at least one parameter of the conveyed plastic waste mixture stream (4); Determining the bulk density of the plastic waste mixture stream (4) based on the at least one detected parameter; Controlling the feed rate (v) as a function of the determined bulk density. Method according to claim 1, wherein the control of the feed rate (v) is carried out such that the feed rate (v) is low for a low determined bulk density and high for a high determined bulk density. Method according to claim 1 or 2, wherein the detection of the at least one parameter comprises detecting the mass flow of the conveyed plastic waste mixture stream (4), for example by means of a belt scale (7). Method according to one of claims 1 to 3, wherein the detection of the at least one parameter comprises optically detecting the composition of the conveyed plastic waste mixture stream (4), for example by means of a line scan camera (8). Method according to claim 4, wherein the determination of the bulk density is carried out based on the optically detected ratio of the 2D material portion (9) to the 3D material portion (10) in the plastic waste mixture stream (4).Method according to claim 4 or 5, wherein determining the bulk density comprises adjusting the optically detected ratio of the 2D material portion (9) to the. 3D material portion (10) in the conveyed plastic waste mixture stream (4) with reference images (12) stored in a database (11). - Method according to claim 6, wherein the reference images (12) stored in the database (11) are each assigned a target conveying speed (vs), which is used to regulate the feed speed (v). . Method according to claim 7, wherein the assigned target conveying speed (vs) is low for reference images (12) with a high 2D portion (9) and high for reference images (12) with a low 2D portion (9). . Method according to one of the preceding claims, wherein the bulk density is between 10 grams / liter and 400 grams / liter.

0. Method according to one of the preceding claims, further comprising leveling the mixed plastic waste stream (4) to a predefined height (H) before detecting the at least one parameter of the conveyed mixed plastic waste stream (4). 1.Method according to one of the preceding claims, further comprising leveling the mixed plastic waste stream (4) by means of a vibrating device (18), preferably a vibrating chute, before detecting the at least one parameter of the conveyed mixed plastic waste stream (4).

2. Method according to one of the preceding claims, further comprising conveying the mixed plastic waste stream (4) by means of a transport means (3), wherein the transport means (3) is fed with plastic waste by means of several separate waste chutes (14) arranged side by side perpendicular to the conveying direction (X) of the transport means (3), via which waste chutes the transport means (3) is fed across its entire width (b). . Method according to one of the preceding claims, further comprising comminuting the mixed plastic waste stream to a predetermined material size before conveying the mixed plastic waste stream (4). - Method according to one of claims 12 or 13, wherein the control of the feed speed (v) comprises the control of the feed speed (v A) of the plastic waste mixture stream (4) onto the transport means (3). Method according to one of claims 11 to 14, wherein controlling the feed rate (v) comprises controlling the conveying speed of the transport means (3).Conveying device (1) for carrying out the method according to one of the preceding claims, comprising: a feed device (2) which has a transport means (3), in particular a conveyor belt, for feeding the plastic waste mixture stream (4); a detection device (5) for detecting at least one parameter of the plastic waste mixture stream (4) located on the transport means, a control unit (6) which is designed to regulate the feed speed (v) of the feed device (2), characterized in that the control unit (6) is designed to determine the bulk density of the plastic waste mixture stream (4) on the basis of the at least one detected parameter and to regulate the feed speed (v) of the feed device (2) as a function of the determined bulk density.Conveying device (1) according to claim 16, wherein the feed speed (v) is controlled such that the feed speed (v) is low for a low determined bulk density and high for a high determined bulk density. Conveying device (1) according to claim 16 or 17, wherein the detection device (5) comprises a belt scale (7) for detecting the mass flow of the plastic waste mixture (4) located on the transport means (3). Conveying device (1) according to one of claims 16 to 18, wherein the detection device (5) comprises an optical detection means, for example a line scan camera (8), for detecting the composition of the plastic waste mixture stream (4) located on the transport means (3). Conveying device (1) according to claim 19, wherein the control unit (6) is configured to determine the bulk density based on the optically detected ratio of the 2D material portion (9) to the D material portion (10) in the mixed plastic waste stream (4). Conveying device (1) according to claim 19 or 20, the control unit (6) is configured to compare the optically detected ratio of the 2D material portion (9) to the D material portion (10) in the conveyed mixed plastic waste stream (4) with reference images (12) stored in a database (11) in order to determine the bulk density. Conveying device (1) according to claim 21, wherein the reference images (12) stored in the database (11) are each assigned a desired conveying speed (vs), which is used to regulate the feed speed (v).Conveying device (1) according to claim 22, wherein the assigned target conveying speed (vs) is low for reference images (12) with a high 2D component (9) and high for reference images (12) with a low 2D component (9). Conveying device (1) according to one of claims 16 to 23, wherein the feed device (2) further comprises a feeding device (13) for feeding the mixed plastic waste stream (4) onto the conveyor belt. Conveying device (1) according to claim 24, wherein the feeding device (13) has a plurality of separate waste chutes (14) arranged side by side perpendicular to the conveying direction of the transport means, via which waste chutes the transport means (3) can be fed across its entire width (b). Conveying device (1) according to one of claims 16 to 25, wherein the feed device (2) further comprises a device (15) for leveling the mixed plastic waste stream (4). Conveying device (1) according to claim 26, wherein the device (15) for. Leveling the plastic waste mixture stream (4) and the conveying path (X) intersecting and arranged above a transport surface (16) of the transport means (3), which is designed to limit the passing plastic waste mixture stream (4) to a predefined height (H). Conveying device (1) according to one of claims 26 or 27, wherein the device (15) for leveling the plastic waste mixture stream (4) is further designed such that the transport means (3) is trough-shaped and has a vibrating device (18) for leveling the plastic waste mixture stream (4) by vibrating. Conveying device (1) according to one of claims 16 to 28, wherein a comminution device (19) for comminution of the plastic waste mixture is arranged upstream of the feed device (2), which is designed to comminute the plastic waste mixture to a predetermined material size.Conveying device (1) according to one of claims 24 to 29, wherein the control of the feed speed (v) comprises the control of the feed speed (v. A ) of the plastic waste mixture stream (4) from the feed device (13) to the transport means (3). Conveying device (1) according to one of claims 16 to 30, wherein the control of the feed speed (v) comprises the control of the conveying speed of the transport means (3). Conveying device according to one of claims 31, wherein the control of the conveying speed of the transport means (3) is effected by means of a frequency converter (20).

Images