Arrangement for the autonomous controlling of liquid levels in a plastic recycling method

Abstract

The invention relates to an arrangement for the autonomous controlling of liquid levels in a plastic recycling method, comprising at least one compensation container and at least one mixing container, wherein the compensation container and the mixing container are filled with a process water such that the compensation container has a first liquid level and the mixing container has a second liquid level, wherein the at least one compensation container is fluidically connected to the mixing container such that the process water can flow freely between the compensation container and the mixing container, as a result of which the first and the second liquid level of the at least one compensation container and the at least one mixing container are the same.

Description

[0001] Arrangement for the autonomous regulation of liquid levels in a plastics recycling process

[0002] The invention relates to an arrangement for the autonomous regulation of liquid levels in a plastics recycling process,

[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. From this, only 1.03 million tons of output were produced in a quality suitable for reuse in the plastics processing industry. This corresponds to a rate of just over 19%. The truth about Germany's performance in plastics recycling and the use of recycled materials is correspondingly sobering.

[0004] As of today, Germany lacks the necessary recycling infrastructure to economically and technically process the volumes of plastic waste generated here 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 Many processing plants currently do not meet state-of-the-art standards, are outdated, and have very weak economic foundations.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] Modern plastic waste processing processes involve numerous individual process steps in which an initially heavily contaminated plastic waste mixture, which may contain a wide variety of plastic types with varying compositions, is washed or cleaned, shredded, and finally separated with high precision according to the different plastic types. For the efficient and most precise separation of the various plastic fractions, high process reliability and stability are essential. One aspect concerns the most continuous provision of a specific volume flow of the plastic waste / process water mixture, which is required, for example, for the separation of the individual plastic fractions, for example, using a hydrocyclone.

[0008] It is therefore the object of the invention to provide an arrangement for regulating liquid levels in various containers in a plastics recycling process, which arrangement has a lower technical outlay and can be operated reliably and maintenance-free.

[0009] The problem is solved by the features of the independent claim. Further advantageous embodiments are specified in the subclaims.

[0010] Accordingly, it is provided that the arrangement comprises at least one compensation tank and at least one agitated tank, wherein the compensation tank and the agitated tank are filled with process water, so that the compensation tank has a first liquid level and the agitated tank has a second liquid level, wherein the at least one compensation tank is fluidically connected to the agitated tank, so that the process water can flow freely between the compensation tank and the agitated tank, whereby the first and second liquid levels of the at least one compensation tank and the at least one agitated tank are the same. The compensation tank can be an intermediate reservoir in which process water is collected before being discharged to one, expediently several, subsequent agitated tanks.The compensation tank can accordingly have a larger volume, in particular a larger cross-sectional area, than the stirred tank. The cross-section of the stirred tank and / or the compensation tank can be round. The liquid level can be set so that it lies above half, preferably above two-thirds, of the height of the compensation tank and / or the stirred tank. The compensation tank can be fluidically connected to the at least one stirred tank such that the water can flow freely, i.e., unhindered, between these tanks. Because the process water is a substantially homogeneous liquid and gravity and ambient air pressure are the same in both tanks, the water levels in both tanks always settle at the same height.

[0011] In particular, the process water can contain ground material from a plastic waste mixture that has an inhomogeneous bulk density. 2D materials, such as LDPE films, have a lower bulk density on average than 3D materials, such as hollow plastic bodies made of HDPE. This means that the bulk density correlates with the 2D or D content in the plastic waste mixture. For example, the bulk density can range from 10 grams / liter with a very high 2D material content to 475 grams / liter with a very high D material content.

[0012] It can be provided that the at least one compensation tank and the at least one agitated tank each have at least one vent opening above the respective liquid level. For example, both tanks can be open at the top.

[0013] It is conceivable that the compensation tank further comprises an inlet through which process water flows into the compensation tank, and the agitated tank further comprises an outlet through which process water flows out of the agitated tank.

[0014] Furthermore, the arrangement can comprise at least two or more agitated tanks fluidically connected to the compensation tank, wherein the second and any additional agitated tanks each have a liquid level equal to the first and second liquid levels. The advantage of the invention is, in particular, that there is no need to separately provide complex monitoring of the fill levels at each of the agitated tanks, with the associated control circuits including control, piping, and valves. Instead, the fill level monitoring can be limited to the compensation tank. The savings increase with each agitated tank connected to the compensation tank.

[0015] In particular, the at least two stirred tanks can be fluidically connected to the compensation tank via a respective pipeline. Alternatively, the stirred tanks can also be connected to each other via a pipeline located below the level.

[0016] In order for the first and second liquid levels of the at least one compensation tank and the at least one agitated tank to be equal, it is clear that the connections of the pipelines each open into the respective tank below the first and / or second predetermined liquid level.

[0017] It can be provided that the vessels, agitated vessels and compensation vessels, each have the same vessel height and that the connections open into the respective vessel at a height between half and two-thirds of the vessel height. Furthermore, the pipelines can each be flanged tangentially to the agitated vessels via their agitated vessel-side connections. This allows the process water to flow into the respective agitated vessel without generating a counterflow to the agitation direction if the agitation direction is selected accordingly. For this purpose, the agitated vessels can each have a stirring device which rotates about a substantially vertical axis. It can be provided that the agitation direction is selected such that it corresponds to the inflow direction of the process water flowing in from the compensation vessel.

[0018] The compensation tank may be provided with a level detection device and a control device configured to maintain the fill level in the compensation tank at a constant level. The level detection device may be implemented, for example, by a float or overflow. The control device may be connected to the level detection device via a data connection and control an actuator of a valve arranged at the inlet, via which the liquid level in the compensation tank can be regulated.

[0019] Furthermore, it can be provided that at least one centrifugal separator, such as a hydrocyclone, is connected downstream of each of the agitated tanks. This can have an inlet that is fluidly coupled to an outlet of a stirred tank. The at least one hydrocyclone can be configured to separate the ground material from the plastic waste mixture based on a predeterminable density cutoff. For this purpose, the hydrocyclone can have the aforementioned inlet for process water and furthermore a first outlet for a light fraction and a second outlet for a heavy fraction.

[0020] The density-based separation of the plastic waste mixture can be repeated several times to enrich a desired material fraction. It can therefore also be provided that the process water containing the plastic mixture passes through several hydrocyclones in succession. The concentration of the ground material is higher in the outlet for particles with a higher specific density of the hydrocyclone than in the outlet for particles with a lower specific density. Therefore, the density of the second stage of the hydrocyclone can be incrementally adjusted to be smaller or larger than the density of the first stage. The hydrocyclone has an upper, cylindrical segment with a tangential inlet and a lower, conical segment with an underflow or apex nozzle. Furthermore, the hydrocyclone can have a vortex finder or an overflow nozzle in the form of a dip tube that projects axially from above into the interior of the cyclone and ends below the tangential inlet.Through the tangential entry into the cylindrical segment, the liquid is forced onto a circular path and flows downwards in a downward vortex. The taper in the conical segment causes an inward displacement of volume and a build-up in the lower region of the cone, leading to the formation of an internal, upward vortex that escapes through the vortex finder or the overflow opening. The goal is the separation of the specifically heavier fraction (e.g., solids) on the wall of the cyclone and thus discharge through the underflow, while the specifically lighter fraction escapes through the overflow. The hydrocyclone can have a vertical flow that is directed downwards in the outer region (primary vortex) and upwards in the inner region (secondary vortex). The particles accumulating in these flows are thus fed either to the overflow or underflow opening.

[0021] Furthermore, it can be provided that the predeterminable density for separating the plastic waste mixture stream can be adjusted between i and 1.05 kg / dm3.

[0022] It can further be provided that the separation into two fractions comprises the enrichment of a light fraction in at least a first hydrocyclone and the enrichment of a heavy fraction in at least a second hydrocyclone. The hydrocyclones can be connected in series. For example, it can be provided that a first hydrocyclone performs a first separation cut into a light and a heavy fraction, and that a further light fraction hydrocyclone is provided which receives the light fraction and further enriches it and / or a further heavy fraction hydrocyclone is provided which receives the heavy fraction and further enriches the heavy fraction. The heavy fraction hydrocyclone can be a flat-bottom hydrocyclone.

[0023] Further details of the invention are explained with reference to the following figures.

[0024] Fig. 1 is a schematic plan view of an embodiment of the arrangement according to the invention; and

[0025] Fig. 2 is a schematic side view of an embodiment of the arrangement according to the invention.

[0026] Fig. 1 shows a schematic plan view of an embodiment of the arrangement according to the invention. This comprises a compensation tank 10 having an inlet 11 that can be regulated via a valve 13. The compensation tank 10 has a level detection device 12 for continuous level monitoring. This is coupled via a data connection to a control unit 14, which in turn is configured to control an actuator of the valve 13 to open or close it, depending on whether the level Pi of the process water W in the compensation tank 10 is below or above a setpoint. The compensation tank 10 is open at the top and therefore has an opening 5 through which the process water W in the compensation tank 10 is in contact with the ambient air.In the embodiment shown, two agitated tanks 20 are connected to the compensation tank, which are fluidically connected to the compensation tank 10 via respective pipelines 30. The pipelines have a first connection 31 on the compensation tank side and a second connection 32 on the agitated tank side, with both connections 31, 32 located below the liquid levels Pi, P2 of the compensation tank 10 and the agitated tank 20. The connections 31, 32 are each flanged laterally tangentially to the compensation tank 10 and the agitated tank 20, respectively. The agitated tanks 20 are also filled with process water W, with the water levels Pi and P2 being the same. The agitated tanks 20 are also open at the top and accordingly have an opening 5. Furthermore, the agitated tanks 20 each have a stirring device 21 having a vertical axis of rotation.The direction of rotation of the stirring devices 20 is selected such that the process water W flowing through the pipeline 30 into the respective stirring tank 20 flows in the stirring direction. The stirring tanks 20 further each have an outlet 22, downstream of which a hydrocyclone 40 is arranged to separate the plastic mixture contained in the process water along a predetermined density separation section into a light fraction 42 and a heavy fraction 43. The process water W flows into the hydrocyclone through an inlet 41.

[0027] Fig. 2 shows a schematic side view of the arrangement from Fig. 1. It can be seen that the liquid level Pi in the compensation tank 10 and the liquid level P2 in the agitated tank 20 are the same. This is achieved by the connection 31 of the connecting pipe 30 on the compensation tank 10 and the connection 32 on the agitated tank 20 opening into the respective tanks below the liquid levels Pi, P2, and the tanks 10, 20 are each open at the top or have an opening 5. In the exemplary embodiment shown, the tanks 10, 20 each have the same height Hi. The inlet 11 of the compensation tank 10 is located above the connecting pipe 30, the outlet 22 of the agitated tank 20 is located below the connecting pipe 30. The process water W initially flows through the inlet 11, depending on the position of the valve 13, into the compensation tank 10.The process water W flows through the connecting pipe 30 from the compensation tank 10 into the one or more agitated tanks 20. There, the process water is stirred by the stirring device 21 before flowing out of the outlet 22 of the agitated tank 20 toward the hydrocyclone 40. The hydrocyclone 40 for recovering polymers during density-based separation of the plastic waste mixture is located downstream of the agitated tank 20 and is at least indirectly connected to it. The mixture of process water W and the plastic waste mixture is fed to the hydrocyclone 40 and comprises, for example, PE, PP, PS, PET, PP-T, ABS, and other components. In the example shown, the hydrocyclone 40 is a conical hydrocyclone and divides the plastic waste mixture into a light fraction 42 and a heavy fraction 43. The hydrocyclone 40 separates the light fraction 41 and the heavy fraction 43, for example, at a density cut of 1 kg / dm. 3. The light fraction 41 thus contains, for example, PE and PP. The heavy fraction 43 accordingly comprises the remainder of the plastic waste mixture, namely PS, PET, PP-T, ABS and the other components. The light fraction 41 can then be fed to further (not shown) steps of the process, while the heavy fraction 43 can be fed to a second (not shown) hydrocyclone, which can be designed as a flat-bottom hydrocyclone. In this, for example, a density separation cut of up to 1.05 kg / dm 3 This can be done in such a way that a second light fraction can be separated from a second heavy fraction in the second hydrocyclone. The second light fraction can comprise PS, PP-T, and ABS, while the second heavy fraction can comprise PET and the other components. All fractions can then be fed separately to the next process steps after passing through the hydrocyclones.

[0028] 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.

[0029] List of reference symbols:

[0030] 5 Opening

[0031] 10 compensation tanks

[0032] 11 Entrance

[0033] 12 Level detection device

[0034] 13 Valve

[0035] 14 Control unit

[0036] 20 mixing tanks

[0037] 21 Stirring device

[0038] 22 Outlet

[0039] 30 connecting pipe

[0040] 31 Connection compensation tank

[0041] 32 Connection of agitated tank

[0042] 40 hydrocyclone

[0043] 41 Entrance

[0044] 42 light fraction

[0045] 43 Heavy fraction

[0046] Pi liquid level compensation tank

[0047] P2 Liquid level agitator tank w process water

Claims

Claims:

1. Arrangement for the autonomous regulation of liquid levels in a plastics recycling process, with at least one compensation tank (10) and at least one agitated tank (20), wherein the compensation tank (10) and the agitated tank (20) are filled with process water (W) such that the compensation tank (10) has a first liquid level (Pi) and the agitated tank (20) has a second liquid level (P2), wherein the at least one compensation tank (10) is fluidically connected to the agitated tank (20) such that the process water (W) can flow freely between the compensation tank (10) and the agitated tank (20), whereby the first and the second liquid levels (Pi, P2) of the at least one compensation tank (10) and the at least one agitated tank (20) are the same.

2. Arrangement according to claim 1, wherein the process water (W) contains ground material of a plastic waste mixture which has an inhomogeneous bulk density.

3. Arrangement according to claim 1 or 2, wherein the at least one compensation tank (10) and the at least one stirring tank (20) each have at least one vent opening (5) above the respective liquid level (Pi, P2).

4. Arrangement according to one of the preceding claims, wherein the compensation tank (10) further comprises an inlet (11) through which process water (W) flows into the compensation tank (10), and the agitated tank (20) further comprises an outlet (22) through which process water (W) flows out of the agitated tank (10).

5. Arrangement according to one of the preceding claims, which has at least two or more agitated containers (10) fluidically connected to the compensation container (20), wherein the second and optionally further agitated containers (10) each have a liquid level which is equal to the first and the second liquid level (Pi, P2).

6. Arrangement according to claim 5, wherein the at least two stirring vessels (10) are fluidically connected to the compensation vessel (10) via a respective pipeline (30).

7. Arrangement according to claim 6, wherein the connections (31, 32) of the pipes (30) each open into the respective container (10, 20) below the first and / or the second predetermined liquid level (Pi, P2).

8. Arrangement according to one of the preceding claims 6 or 7, wherein the containers each have the same container height (Hi) and the connections (31, 32) each open into the respective container (10, 20) at a height between half and two-thirds of the container height (Hl).

9. Arrangement according to one of the preceding claims 6 to 8, wherein the pipes (30) are each flanged tangentially to the stirred tanks (20) via their stirred tank-side connections (32).

10. Arrangement according to one of the preceding claims, wherein the compensation tank (10) has a level detection device (12) and a control device (14) which is designed to keep the fill level in the compensation tank (10) at a constant level.

11. Arrangement according to claim 10, wherein the control device (14) is connected to the level detection device (12) via a data connection and controls an actuator of a valve (13) arranged at the inlet, via which the liquid level (Pi) in the compensation container (10) can be regulated.

12. Arrangement according to one of the preceding claims, wherein at least one hydrocyclone (40) is connected downstream of the agitated vessels (20) in terms of process technology.

13. Arrangement according to claim 12, wherein the at least one hydrocyclone (40) is designed to separate the ground material of the plastic waste mixture depending on a predeterminable density separation cut. 14- Arrangement according to one of claims 12 or 13, wherein the hydrocyclone (40) has an inlet (41) for process water (41), a first outlet (42) for a light fraction and a second outlet (43) for a heavy fraction.

15. Arrangement according to one of the preceding claims, wherein the stirring containers (20) each have a stirring device (21) which rotates about a substantially vertical axis.

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