Mechanism for autonomous control of liquid level in plastic recycling processes

Abstract

The present invention relates to a mechanism for autonomously controlling liquid levels in a plastic recycling method, comprising at least one compensation vessel and at least one stirring vessel, wherein the compensation vessel and the stirring vessel are filled with process water, whereby the compensation vessel has a first liquid level and the stirring vessel has a second liquid level, and the at least one compensation vessel is fluidly connected to the stirring vessel, whereby process water can flow freely between the compensation vessel and the stirring vessel, whereby the first and second liquid levels in the at least one compensation vessel and the at least one stirring vessel are equal.

Description

[Technical Field]

[0001] The present invention relates to a mechanism for autonomously controlling liquid levels in plastic recycling processes. [Background technology]

[0002] The ever-increasing amount of plastic waste will pose a severe challenge to our society in the future. In 2019, Germany generated approximately 5.35 million tonnes of post-consumer plastic waste. Of this, only 1.33 million tonnes were sent for physical reuse in domestic reprocessing plants. Furthermore, only 1.03 million tonnes were output in a quality suitable for reuse in the plastics processing industry. This corresponds to just over 19%. The facts about Germany's capabilities in plastic recycling and the use of recycled materials are quite telling.

[0003] As things stand today, Germany does not have the recycling infrastructure necessary to economically and technically reprocess the volume of plastic waste it generates into high-quality, high-value recyclable materials. Many reprocessing facilities are currently outdated, outdated and on a very weak economic footing.

[0004] The ever-increasing volume of plastic waste, increasingly stringent national and international legislation regarding approval procedures and increasing reuse rates and the use of recycled materials, as well as restrictions on waste imports and exports, will pose severe challenges for EU Member States and especially for plastic recycling companies. There is an urgent need for investment in reprocessing capacities and in particular in the development of new reprocessing methods to overcome the challenges and issues mentioned above.

[0005] One of the biggest challenges for plastic recyclers is highly contaminated plastic waste mixtures. Existing recycling processes and equipment currently only allow for a very limited amount of material reprocessing of such fractions. Therefore, the vast majority of such waste currently goes for thermal reuse. Furthermore, the vast majority of recycled materials produced have qualitative shortcomings that do not allow for stable plastic processing processes, and therefore rarely provide a sustainable replacement for new, technically demanding plastic products.

[0006] Modern plastic waste reprocessing processes involve numerous individual process steps, in which initially highly contaminated plastic waste mixtures, which may contain a wide variety of plastic types in various compositions, are washed or cleaned, crushed, and finally separated into the different plastic types with high precision. High process reliability and stability are essential for efficient and as accurate a separation of the different plastic fractions as possible. One aspect is to provide, as continuously as possible, the specific volumetric flow rates of plastic waste, process water, and the mixture required for the separation of the individual plastic fractions, for example, by hydrocyclones. Summary of the Invention [Problem to be solved by the invention]

[0007] It is therefore an object of the present invention to provide a mechanism for controlling the liquid level in different containers in a plastics recycling process which has relatively low technical costs and can operate reliably and maintenance-free. [Means for solving the problem]

[0008] This problem is solved by the features of the independent claims. Further preferred embodiments are set forth in the respective dependent claims.

[0009] According to the invention, the mechanism is intended to have at least one compensation vessel and at least one stirring vessel, the compensation vessel and the stirring vessel being filled with process water, such that the compensation vessel has a first liquid level and the stirring vessel has a second liquid level, and the at least one compensation vessel being fluidly connected to the stirring vessel, such that the process water can flow freely between the compensation vessel and the stirring vessel, whereby the first and second liquid levels in the at least one compensation vessel and the at least one stirring vessel are equal.

[0010] The compensation vessel may be one, or, meaningfully, several, intermediate reservoirs in which the process water collects before being released into the subsequent stirred vessel. Accordingly, the compensation vessel may have a larger volume, particularly a larger average area, than the stirred vessel. The cross section of the stirred vessel and / or the compensation vessel may be circular. The liquid level may be adjusted to be located above half, preferably above two-thirds, of the height of the compensation vessel and / or the stirred vessel. The compensation vessel may be fluidly connected to at least one stirred vessel so that water can flow freely, i.e., unhindered, between these vessels. Since the process water is a substantially homogeneous liquid and gravity and the ambient air pressure are equal in both vessels, the level position in both vessels always rises and falls to the same height.

[0011] In particular, the process water may be intended to contain a pulverized plastic waste mixture with a non-uniform bulk density. 2D materials, such as films made of LD-PE, have, on average, a lower bulk weight than 3D materials, such as hollow plastic bodies made of HD-PE. That is, the bulk density correlates with the 2D or 3D proportion in the plastic waste mixture. The bulk density is, for example, between 10 grams / liter at a very high proportion of 2D material and 475 grams / liter at a very high proportion of 3D material.

[0012] The at least one compensation vessel and the at least one stirring vessel may each have at least one ventilation opening above the respective liquid level, for example, both vessels may each be open upwards.

[0013] It is contemplated that the compensation vessel further has an inlet through which process water enters the compensation vessel, and the agitation vessel has an outlet through which process water exits the agitation vessel.

[0014] Furthermore, the arrangement may be provided for having at least two or more stirred vessels fluidly connected to the compensation vessel, the second and possibly further stirred vessels having liquid levels equal to the first and second liquid levels, respectively. The advantage of the present invention is that it is not necessary to provide for separate, costly monitoring of the fill level in each stirred vessel, in particular with associated control circuits with controls, piping, and valves. Instead, the fill level monitoring can be limited to the compensation vessel only. The more stirred vessels connected to the compensation vessel, the greater the savings.

[0015] In particular, at least two stirred vessels may be fluidly connected to the compensation vessel via respective piping, or alternatively, the stirred vessels may be connected to one another via piping located below level.

[0016] It is clear that in order to ensure that the first and second fluid levels in the at least one compensation vessel and the at least one stirring vessel are equal, the piping connections communicate with the respective vessels below the first and / or second predetermined liquid levels, respectively.

[0017] Each vessel, i.e., the stirred vessel and the compensation vessel, may each have the same vessel height, and the connections may each communicate with the respective vessel at a height between half and two-thirds of the vessel height. Furthermore, the pipes may be tangentially flanged to the stirred vessels via the connections on the respective stirred vessel side. This allows the process water to flow into each stirred vessel without generating a backflow in the stirring direction when the stirring direction is selected accordingly. To this end, the stirred vessels may each have a stirring device that rotates around a substantially vertical axis. The stirring direction may be selected to match the inflow direction of the process water on the compensation vessel side.

[0018] The compensation vessel may have a level detection device and a control device set up to keep the filling level of the compensation vessel at a constant level. The level detection device may be embodied, for example, by a float or an overflow. The control device may then be connected to the level detection device via a data connection and may activate an actuator of a valve arranged at the intake, via which the liquid level in the compensation vessel can be controlled.

[0019] In addition, at least one centrifugal separator, such as a hydrocyclone, may be provided downstream of each stirred vessel in terms of process engineering. This may have an inlet fluidly connected to the outlet of the stirred vessel. The at least one hydrocyclone may be configured to separate the crushed plastic waste mixture according to a predeterminable density separation fraction. To this end, the hydrocyclone may have the aforementioned inlet for process water and may further have a first outlet for the light fraction and a second outlet for the heavy fraction.

[0020] Density-based separation of the plastic waste mixture can be repeated multiple times to concentrate the desired material fraction. It may also be contemplated that the process water containing the plastic mixture may be passed sequentially through multiple hydrocyclones. The concentration of the ground material is higher at the hydrocyclone outlet for particles with a relatively high specific gravity than at the outlet for particles with a relatively low specific gravity. Therefore, the density of the second stage of the hydrocyclone can be adjusted to be progressively lower or higher than that of the first stage. The hydrocyclone has an upper cylindrical segment with a tangential outlet and a lower conical segment with an underflow or apex nozzle. The hydrocyclone may also have a vortex finder or overflow nozzle in the form of a dip tube that enters the cyclone axially from above and terminates within the tangential outlet. Entering the cylindrical segment tangentially forces the liquid to follow a circular path, forming a downward-directed vortex that flows downward. The tapering of the conical segments causes a downward displacement of the volume and a blockage in the lower region of the taper, which leads to the formation of an upward-directed inner vortex, which escapes through the vortex finder or overflow opening. The aim is to separate the specific heavy fraction (e.g. solids) at the cyclone wall and thus discharge it via the underflow, while the specific light fraction escapes through the overflow. Hydrocyclones can have vertical flows that are downward-directed in the outer region (primary vortex) and upward-directed in the inner region (secondary vortex). The particles collected in these flows are fed either to the overflow or underflow opening.

[0021] Furthermore, the predeterminable density for separating plastic waste mixtures is between 1 and 1.05 kg / dm 3 It may be intended to be adjustable between

[0022] Furthermore, the separation into two fractions may include concentrating the light fraction in at least one first hydrocyclone and concentrating the heavy fraction in at least one second hydrocyclone. These hydrocyclones may be connected in series. For example, a first hydrocyclone may perform a first separation into a light fraction and a heavy fraction, followed by a separate light fraction hydrocyclone that receives and further concentrates the light fraction, and / or a separate heavy fraction hydrocyclone that receives and further concentrates the heavy fraction. The heavy fraction hydrocyclone may be a flat-bottom hydrocyclone. [Brief explanation of the drawings]

[0023] Further details of the invention will be described with reference to the following drawings, in which: FIG. 1 is a schematic plan view showing an embodiment of a mechanism according to the present invention.

[0024] FIG. 2 is a schematic side view showing an embodiment of a mechanism according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] FIG. 1 shows a schematic plan view of an embodiment of the arrangement according to the invention. The arrangement comprises a compensation vessel 10 with an inlet 11 that can be controlled via a valve 13. The compensation vessel 10 comprises a level detection device 12 for continuous level monitoring. This is linked via a data connection to a control unit 14, which is further set up to operate the actuator of the valve 13 to open or close it depending on whether the level P1 of the process water W in the compensation vessel 10 is above or below a target value. The compensation vessel 10 is open upward and thus has an opening 5 through which the process water W in the compensation vessel 10 comes into contact with the ambient air. In the illustrated embodiment, two stirred vessels 20 are connected to the compensation vessel 10, which are fluidly connected to the compensation vessel 10 via pipes 30. These pipes have a first connection 31 on the compensation vessel side and a second connection 32 on the stirred vessel side, both connections 31, 32 being located below the liquid levels P1, P2 in the compensation vessel 10 and the stirred vessel 20. The connections 31, 32 are laterally and tangentially flanged to the compensation vessel 10 and the stirred vessel 20, respectively. The stirred vessel 20 is also filled with process water W, and the water levels P1 and P2 are equal. The stirred vessel 20 is also open upward and has an opening 5. Each stirred vessel 20 further has a stirrer 21 with a vertical axis of rotation. The direction of rotation of the stirrer 20 is selected so that the process water W flowing into the respective stirred vessel 20 from the pipe 30 flows in the stirring direction. Each stirred vessel 20 further has an outlet 22 followed by a hydrocyclone 40 for separating the plastic mixture contained in the process water into a light fraction 42 and a heavy fraction 43 according to a predetermined density separation section. The process water W flows into the hydrocyclone through an inlet 41.

[0026] FIG. 2 shows a schematic side view of the arrangement of FIG. 1. It can be seen that the liquid level P1 in the compensation vessel 10 and the liquid level P2 in the stirred vessel 20 are equal. This is achieved because the connection 31 of the connecting pipe 30 to the compensation vessel 10 and the connection 32 to the stirred vessel 20 communicate with the respective vessels below the liquid levels P1 and P2, and because the vessels 10 and 20 are open upward or have openings 5. In the illustrated embodiment, the vessels 10 and 20 each have the same height H1. The inlet 11 of the compensation vessel 10 is located above the connecting pipe 30, and the outlet 22 of the stirred vessel 20 is located below the connecting pipe 30. Depending on the position of the valve 13, the process water W first flows into the compensation vessel 10 through the inlet 11. The process water W flows from the compensation vessel 10 through the connecting pipe 30 into one or more stirred vessels 20. There, the process water is stirred by the stirring device 21 and then flows out of the stirred vessel 20 through the outlet 22 in the direction of the hydrocyclone 40. The hydrocyclone 40 for obtaining polymers in the course of density-based separation of the plastic waste mixture is arranged downstream of the stirred vessel 20 and is at least indirectly connected thereto. A mixture of the process water W and the plastic waste mixture is fed to the hydrocyclone 40, which contains, for example, PE, PP, PS, PET, PP-T, ABS, and other components. The hydrocyclone 40 is a conical hydrocyclone in the illustrated example and separates the plastic waste mixture into a light fraction 42 and a heavy fraction 43. The hydrocyclone 40 has a density of, for example, 1 kg / dm 3 The light fraction 41 is then fed to another step (not shown) of the process, while the heavy fraction 43 is fed to a second hydrocyclone (not shown), which may be configured as a flat-bottom hydrocyclone, in which a maximum of 1.05 kg / dm3 is fed. 3A density separation section can be performed under a pressure of 1000 kJ / cm 2 , whereby a second light fraction can be separated from a second heavy fraction in a second hydrocyclone. The second light fraction can then contain PS, PP-T, and ABS, and the second heavy fraction can contain PET and other components. All fractions can then be fed separately from each other to the next process step after passing through the hydrocyclone.

[0027] The constituent elements of the present invention disclosed in the above description, drawings, and claims can be essential parts for realizing the present invention either alone or in any combination. [Explanation of symbols]

[0028] 5 Opening 10 Compensation container 11 Intake 12 Level detection device 13 Valve 14 Control Unit 20 Stirring vessel 21 Stirring device 22 Outlet 30 Connecting pipe 31 Compensation vessel connection 32 Mixing vessel connection 40 Hydrocyclone 41 Intake 42 Light Fraction 43 Heavy Fraction P1 Compensation vessel liquid level P2 Mixing vessel liquid level W Process water

Claims

1. 1. A mechanism for autonomously controlling liquid levels in a plastic recycling process, comprising at least one compensation vessel (10) and at least one stirring vessel (20), wherein the compensation vessel (10) and the stirring vessel (20) are filled with process water (W), whereby the compensation vessel (10) has a first liquid level (P1) and the stirring vessel (20) has a second liquid level (P2), and the at least one compensation vessel (10) is fluidly connected to the stirring vessel (20), whereby process water (W) can freely flow between the compensation vessel (10) and the stirring vessel (20), whereby the first and second liquid levels (P1, P2) in the at least one compensation vessel (10) and the at least one stirring vessel (20) are equal.

2. 10. The system of claim 1, wherein the process water (W) comprises a pulverized mixture of plastic waste having a non-uniform bulk density.

3. 3. The arrangement according to claim 1, wherein the at least one compensation vessel (10) and the at least one stirring vessel (20) each have at least one ventilation opening (5) above the respective liquid levels (P1, P2).

4. 4. The mechanism according to claim 1, wherein the compensation vessel (10) further comprises an inlet (11) through which process water (W) flows into the compensation vessel (10), and the stirring vessel (20) further comprises an outlet (22) through which the process water (W) flows out of the stirring vessel (10).

5. 5. The arrangement according to claim 1, comprising at least two or more stirred vessels (10) in fluid connection with the compensation vessel (20), the second and possibly further stirred vessels (10) having liquid levels equal to the first and second liquid levels (P1, P2), respectively.

6. 6. The arrangement according to claim 5, wherein at least two of the stirring vessels (10) are fluidly connected with the compensation vessel (10) via respective piping (30).

7. 7. The arrangement according to claim 6, wherein the connections (31, 32) of the piping (30) communicate with the respective vessels (10, 20) below the first and / or second predetermined liquid levels (P1, P2), respectively.

8. 8. A mechanism according to claim 6 or 7, wherein each of the containers has the same container height (H1), and each of the connection parts (31, 32) communicates with each of the containers (10, 20) at a height between half and two-thirds of the container height (H1).

9. 9. An arrangement according to any one of claims 6 to 8, wherein the pipes (30) are tangentially flanged to the stirring vessel (20) via respective stirring vessel-side connections (32).

10. 10. The arrangement according to any one of claims 1 to 9, wherein the compensation vessel (10) comprises a level detection device (12) and a control device (14) set up to keep the liquid level in the compensation vessel (10) at a constant level.

11. 11. The arrangement according to claim 10, wherein the control device (14) is connected to the level detection device (12) via a data connection and is able to actuate an actuator of a valve (13) arranged at the intake and to control the liquid level (P1) in the compensation vessel (10) via this valve.

12. 12. The arrangement according to claim 1, wherein the stirred vessels (20) are each followed in process engineering fashion by at least one hydrocyclone (40).

13. 13. The arrangement according to claim 12, wherein the at least one hydrocyclone (40) is set up to separate the crushed material of the plastic waste mixture depending on a predeterminable density separation section.

14. 14. The arrangement according to claim 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. 15. An arrangement according to any one of claims 1 to 14, wherein the stirred vessels (20) each have a stirring device (21) which rotates about a substantially vertical axis.

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