Method for separating a mixture of granules via the triboelectric effect
Patent Information
- Application Number
- EP2023757661
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-08-26
- Filing Date
- 2023-08-25
- Publication Date
- 2025-07-02
AI Technical Summary
Existing methods for separating mixtures of granules based on the triboelectric effect face challenges such as inefficient charging, low outlet flow rates, and difficulty in adjusting to changes in the mixture composition, leading to productivity issues and complex mechanical modifications.
A batch separation process involving a fluidization chamber where granules are initially at rest, then fluidized by an ascending fluid current, charged through the triboelectric effect, and subsequently passed through an electric field to separate the granules into distinct material-rich batches, with controlled fluid flow and evacuation to optimize charging and separation efficiency.
The process achieves effective and productive separation with high granule charging efficiency, reduced risk of clogging, and simplified management, even when the mixture composition changes, by controlling fluidization time and temperature, and air flow.
Smart Images
Figure 1.1
Abstract
Description
[0001] Process for separating a mixture of granules by triboelectric effect
[0002] The present invention relates to a method for separating a mixture comprising granules of at least a first material and a second material, the mixture being charged by triboelectric effect and passing through one or more electric fields to separate the mixture into at least a first mixture rich in granules of the first material and a second mixture rich in granules of the second material.
[0003] The invention also relates to a corresponding installation.
[0004] The triboelectric effect is an electrostatic phenomenon by which at least two materials of different nature electrify each other through contact. Electrons from one are transferred to the other and this situation persists. This is called static electricity. The lack of electrons in one creates a positive electric charge, while the excess electrons in the other creates a negative charge. It is known to then separate granules of these materials by passing them through an electric field, which applies opposing forces to the granules depending on their respective electric charges.
[0005] To enhance the triboelectric effect, mechanical energy is usually applied by rubbing the materials together for a period of time. The electrical charge increases gradually, at a rate that depends on the materials and surrounding conditions, including humidity. In some cases, the charge may decrease if the friction continues for too long.
[0006] In order to obtain a separation process with interesting productivity, it is known to continuously introduce the mixture to be separated into a stirring box. The particles are introduced at one end of the box and exit at the other end. However, the progression of the granular medium in the box, due to the movements of the box, its shape and its orientation, is difficult to control. It may happen that the granules at the outlet are insufficiently loaded, or that the outlet flow rate is low.
[0007] Furthermore, if the nature of the mixture to be separated changes, complex mechanical modifications must be made to again obtain a setting adapted to the new nature of the mixture.
[0008] In order to increase the loading speed and the flow rate of the mixture at the outlet, it has been proposed to continuously produce a fluidized bed in a reactor from the mixture to be separated. The fluidized bed is obtained by an ascending fluid stream, generally air. However, again, the extraction of granules and more generally the progression of the fluidized bed in the reactor proves difficult to manage. In addition, when the materials have a fairly long loading time, the fluidization reactor must be large, which results in significant costs for the blower producing the fluid stream, and for the possible heating of the fluid stream.
[0009] In WO 2010 / 109096, the fluidized bed is more or less static in the reactor, and the granules, once charged, are drawn out of the fluidized bed according to their charge by conveyor belts forming electrodes around the fluidized bed. Extraction is continuous, and the fluidized bed is continuously fed by the arrival of new granules. However, such a reactor is again very delicate to regulate, particularly with regard to the level of electrical charge. It may also happen that insufficiently charged granules accumulate in the reactor and block it.
[0010] An aim of the invention is therefore to provide a separation method solving all or part of the problems mentioned above, which is both effective from the point of view of separation and productive, while being simple to manage, in particular when the nature of the mixture to be separated changes.
[0011] To this end, the invention relates to a method for batch separation of a mixture comprising granules of at least a first material and a second material, comprising the following successive steps for each of the batches:
[0012] - introduction of one of the batches into a fluidization chamber defined by a reactor and obtaining an introduced batch,
[0013] - the granules of the introduced batch being initially at rest in the fluidization chamber, starting a fluidization and obtaining at least one fluidized bed in the fluidization chamber, the fluidization being obtained by at least one ascending fluid current passing through the introduced batch and putting at least a fraction of the granules of the introduced batch in suspension, the fluidized bed being charged by triboelectric effect,
[0014] - modification of the fluid flow and evacuation of at least 90% by mass of the introduced batch from the fluidization chamber and obtaining an evacuated batch, and
[0015] - passing the evacuated batch through one or more electric fields adapted to separate the evacuated batch into at least a first mixture rich in granules of the first material and a second mixture rich in granules of the second material.
[0016] According to particular embodiments, the method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:
[0017] - the modification of the fluid flow comprises a reduction in the flow rate of the fluid flow causing the granules of the fluidized bed to fall onto a receiving surface of the reactor;
[0018] - after the reduction of the flow rate of the fluid stream, the fluid stream has a non-zero residual flow rate in the fluidization chamber after the evacuation of the introduced batch; - the reactor is rotatably mounted relative to a frame between at least a first position occupied during fluidization, and a second position occupied during evacuation and in which the receiving surface is more inclined relative to the frame than in the first position, the evacuation comprising a displacement of at least 90% by mass of the introduced batch, by gravity, along the receiving surface towards the outside of the fluidization chamber;
[0019] - the modification of the fluid flow comprises an increase in the flow rate of the fluid flow, the evacuation comprising an ejection of at least 90% by mass of the fluidized bed from the fluidization chamber caused by the increase in the flow rate;
[0020] - the reactor comprises a casing defining: an inlet for introduction, the inlet being open for introduction, then closed after introduction, and an outlet for evacuating at least 90% by mass of the introduced batch, the outlet being open for evacuation, then closed after evacuation;
[0021] - the reactor defines at least one circuit forming a loop for the fluid flow, the reactor comprising at least one blower for obtaining the fluid flow in the circuit;
[0022] - the fluid stream is at a temperature between 45°C and 75°C; and
[0023] - the fluidization being obtained under given conditions, the granules of the introduced batch are maintained in the form of said fluidized bed for a predetermined duration, the granules of the first material taking on an electrical charge greater than 90% of a maximum electrical charge which can be obtained under the given conditions.
[0024] The invention also relates to an installation for batch separation of a mixture comprising granules of at least a first material and a second material, the installation comprising:
[0025] - a reactor defining a fluidization chamber intended to receive one of the batches to obtain an introduced batch, the reactor being adapted to create a fluidized bed in the fluidization chamber, the granules of the introduced batch being initially at rest in the fluidization chamber, the reactor being adapted to produce at least one ascending fluid stream passing through the introduced batch and putting at least a fraction of the granules of the introduced batch in suspension to obtain the fluidized bed, the fluidized bed being charged by triboelectric effect, the reactor being adapted to modify the fluid stream and evacuate at least 90% by mass of the introduced batch from the fluidization chamber to obtain an evacuated batch, and
[0026] - a separation unit adapted to create at least one or more electric field(s), the installation being adapted to pass the evacuated batch through the electric field(s) and separate the evacuated batch between at least a first mixture rich in granules of the first material and a second mixture rich in granules of the second material.
[0027] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings, in which:
[0028] - figure 1 is a general view, in perspective, of a separation installation according to the invention, making it possible to carry out a method according to the invention,
[0029] - figure 2 is a perspective view of a device for supplying the mixture of the installation shown in figure 1,
[0030] - figure 3 is a perspective view of a fluidization reactor of the installation shown in figure 1, the reactor being in a first occupied position during the fluidization of a batch,
[0031] - Figure 4 is a perspective view of the reactor shown in Figure 3, the reactor being in a second occupied position during the evacuation of a batch from the reactor, and
[0032] - Figure 5 is a perspective view of a separation unit of the installation shown in Figure 1.
[0033] With reference to Figure 1, an installation 10 according to the invention is described for separating a mixture 12 comprising granules (not shown) of at least a first material and a second material, into at least a first mixture 14 rich in granules of the first material and a second mixture 15 rich in granules of the second material.
[0034] The mixture 12 comprises for example as first material and second material:
[0035] - acrylonitrile butadiene styrene (ABS) and polystyrene (PS),
[0036] - polypropylene (PP) and polyethylene (PE), or
[0037] - polypropylene (PP) and polystyrene (PS).
[0038] The granules of the first material and the second material are capable of becoming electrically charged when rubbed against each other by the triboelectric effect.
[0039] The first mixture 14 is for example rich in granules of the first material, in the sense that it comprises, by mass, a higher rate of granules of the first material than in the second mixture 15. Similarly, the second mixture 15 is for example rich in granules of the second material, in the sense that it comprises, by mass, a higher rate of granules of the second material than in the first mixture 14.
[0040] Advantageously, the first mixture 14 comprises, by mass, a rate of granules of the first material greater than 95%.
[0041] Advantageously, the second mixture 15 comprises, by mass, a rate of granules of the second material greater than 95%. According to a variant not shown, the mixture 12 to be separated comprises granules of three distinct materials, or more than three materials.
[0042] Alternatively, the mixture 12 is for example quaternary (comprises four materials) and is separated into a first binary mixture 14 (rich in two of the materials) and a second binary mixture 15 (rich in the other two materials).
[0043] Advantageously, the first mixture 14 then comprises, by mass, a rate of granules of two of the materials greater than 95%, and the second mixture 15 then comprises, by mass, a rate of granules of the other two materials greater than 95%.
[0044] For example, the mixture 12 to be separated comprises the materials PS, ABS, PP and PE and is separated into a first mixture rich in PP / PE, a second mixture rich in ABS / PS, and a third undifferentiated mixture, of composition similar to the mixture 12.
[0045] The installation 10 is adapted to operate in batches at least at the level of a reactor 16 (figure 3) adapted to produce a fluidized bed 18 (figure 3) from the mixture 12. However, the batches of mixture to be separated advantageously follow one another at a high rate, which does not alter the productivity of the installation 10, quite the contrary, the installation being advantageously adapted to perfectly control the reactor 16, in particular the residence time of the granules in the reactor.
[0046] The installation 10 also comprises a separation unit 20 (figure 5). In the example, the installation 10 comprises a particular supply device 22 (figure 2), to constitute the batches introduced one by one into the reactor 16.
[0047] According to variants not shown, the batches are already formed and directly introduced into the reactor 16, or are produced in a manner known per se other than that permitted by the supply device 22.
[0048] In the example, the feed device 22 (figure 2) comprises a frame 24, a vibrating table 26 adapted to create a layer of granules from the mixture 12, a conveyor 28 to move the layer of granules relative to the frame 24, and two ionizing bars 30A, 30B placed above the conveyor.
[0049] Alternatively, the supply device 22 comprises only one ionizing bar, or more than two.
[0050] In the example, the feed device 22 comprises a hopper 32 containing the mixture to be treated, and an endless screw 34 for conveying the mixture 12 from the hopper to the vibrating table 26. The feed device 22 comprises, for example, a buffer hopper 36 located at the end of the conveyor 28.
[0051] The ionizing bars 30A, 30B are adapted to electrically discharge the mixture 12 to be separated. The ionizing bars 30A, 30B are, for example, activatable, and advantageously adjustable in frequency and distance from the conveyor. The frequency adjustment is advantageously carried out directly on the ionizing bars 30A, 30B.
[0052] The buffer hopper 36 is suitable for constituting a batch 38 of mixture, the mass of which is for example between 30 and 100 kg, and is advantageously approximately 50 kg.
[0053] The reactor 16 (figures 3 and 4) defines a fluidization chamber 40 adapted to receive a batch 38 introduced, in the example coming from the buffer hopper 36.
[0054] The reactor 16 is adapted to create the fluidized bed 18 in the fluidization chamber 40. The reactor 16 is adapted to produce at least one ascending fluid stream 42 passing through the introduced batch 38 to put at least a fraction of the granules of the introduced batch into suspension and obtain the fluidized bed 18.
[0055] The reactor 16 is adapted to modify the fluid stream 42 and evacuate at least 90% by mass of the introduced batch 38 from the fluidization chamber 40 to obtain an evacuated batch 44 (figure 4). Preferably, all, or almost all (more than 99% by mass), of the introduced batch 38 is evacuated.
[0056] The reactor 16 is for example configured so that the fluid stream 42 is at a temperature between 45°C and 75°C. This allows the fluid to be dried and promotes triboelectricity.
[0057] The reactor 16 defines for example a receiving surface 46, for example a grid, located under the fluidized bed 18 and intended to receive the granules if the flow rate of the fluid stream 42 is reduced, the fluidized bed falling back onto the receiving surface.
[0058] The reactor 16 is for example rotatably mounted relative to a frame 48 of the installation 10 between at least a first position (figure 3) occupied during fluidization, and a second position (figure 4), occupied during evacuation and in which the receiving surface 46 is more inclined relative to the frame 48 than in the first position.
[0059] The reactor 16 is for example mobile in rotation around an axis D which is advantageously horizontal.
[0060] The reactor 16 comprises for example a casing 50 defining an inlet 52 for the introduction of the mixture 12, the inlet being open for the introduction, then closed after the introduction. The casing 50 defines an outlet 54 for the evacuation of at least 90% by mass of the batch 38 introduced, the outlet being open for the evacuation, then closed after the evacuation.
[0061] In the example, the reactor 16 defines at least one circuit 56 forming a loop for the fluid stream 42, the reactor comprising at least one blower 58 for obtaining the fluid stream 42 in the circuit 56. The reactor 16 advantageously comprises a homogenization chamber 60 for homogenizing the fluid stream 42, and a heating system 62 adapted to heat the fluid stream 42. The reactor 16 advantageously comprises a recuperator 64 and a sheath 66 connecting the recuperator to the blower 58.
[0062] In the example, the circuit 56 includes the blower 58, the homogenization chamber 60, the heating system 62, the fluidization chamber 48, the recuperator 64 and the duct 66.
[0063] The fluidization chamber 40 is for example delimited at the bottom (in the first position) by the receiving surface 46, which is advantageously permeable to the fluid flow 42, laterally by the casing 50, advantageously having at least one transparent wall allowing the fluidized bed 18 to be seen, and above by the recuperator 64.
[0064] The homogenization chamber 60 extends for example between the blower 58 and the heating system 62. The homogenization chamber 60 has for example a shape that flares upwards (in the first position). The homogenization chamber 60 is advantageously delimited laterally by four flat faces.
[0065] The fluid is, for example, air, or previously dried air.
[0066] The recuperator 64 is advantageously adapted to filter the fluid stream 42 and remove fine particles (not shown) therefrom, so that the latter do not return to the blower 58.
[0067] The reactor 16 is advantageously adapted to operate in a closed circuit, or in fresh air. The duct 66 has, for example, an outlet 68 for the fluid stream 42 in “fresh air” mode. The blower 58 also has an air intake 70 for the same reasons.
[0068] In the first position, the receiving surface 46 is for example substantially horizontal. In the second position, the receiving surface 46 is for example inclined at approximately 45° (plus or minus 5°, or even 10°).
[0069] The separation unit 20 (Figure 5) comprises, for example, a hopper 72, a conveyor 74, and electrodes 76 adapted to create the electric field(s). The separation unit 20 comprises, for example, three separation compartments 76 and three endless screws 78 allowing three bags 80 to be filled at a time.
[0070] The operation of the installation 10 will now be described. It illustrates a method according to the invention.
[0071] The feed device 22 forms batches of the mixture 12. The endless screw 34 draws the mixture 12 from the hopper 32 and leads it to the vibrating table 26. The vibrating table 26 advantageously creates a layer of mixture on the conveyor 28, which conveys the layer to the buffer hopper 36 in which a batch 38 is formed. By passing under the ionizing bars 30A, 30B, the mixture 12 is electrically discharged. This advantageously involves carrying out electrical neutralization.
[0072] The reactor 16 is in the first position and the inlet 52 is open. The buffer hopper 36 introduces the batch 38 into the fluidization chamber 40.
[0073] The flow rate of the fluid stream 42 is then, for example, zero in the fluidization chamber 40. The granules of the introduced batch are initially at rest in the fluidization chamber 40.
[0074] According to an advantageous variant, the flow rate of the fluid stream 42 is not zero during introduction, but has a value such that the granules of the introduced batch 38 are at rest (no fluidized bed). This makes it possible, for example, to more easily maintain a desired temperature in the fluidization chamber 40.
[0075] Then the inlet 52 is closed and the flow rate of the fluid stream 42 is increased to a value making it possible to put at least a fraction of the granules, preferably all the granules, of the batch 38 introduced into suspension, to obtain the fluidized bed 18. The fluidized bed 18 is then charged by triboelectric effect.
[0076] Fluidization is obtained under given conditions (temperature of the fluid stream, humidity, flow rate of the fluid stream, etc.), the granules of the introduced batch 38 are advantageously maintained in the form of the fluidized bed 18 for a predetermined duration, the granules of the first material taking on an electrical charge greater than 90% of a maximum electrical charge which would be obtained under the same given conditions by maintaining the granules of the introduced batch 38 in the form of the fluidized bed 18 for a duration greater than the predetermined duration. In other words, one waits long enough to obtain an electrical charge greater than 90% of the maximum possible charge under the given conditions.
[0077] The maximum possible load under the given conditions can be determined by a person skilled in the art by simple measurements in the fluidization chamber 40, or in the laboratory.
[0078] Then the fluid stream flow rate 42 is reset to its reduced value, or reset to zero, and at least 90% by mass of the introduced batch 38, preferably the entire introduced batch, is evacuated from the fluidization chamber 40. For example, the granules of the fluidized bed 18 fall back onto the receiving surface 46.
[0079] The outlet 54 is opened and the reactor 16 is tilted from the first position to the second position. The receiving surface 46 tilts. The granules move, by gravity, along the receiving surface 46 and exit the fluidization chamber 40 through the outlet 54.
[0080] The evacuated batch 44 arrives in the separation unit 20. The outlet 54 of the reactor 16 is closed and the reactor is returned to the first position, in which it can receive a new batch of mixture 12.
[0081] In the separation unit 20, the discharged batch 44 is separated at least between the first mixture 14 and the second mixture 15. In the example shown, the discharged batch 44 is separated into three mixtures, the third being of undifferentiated composition, for example similar to that of the mixture 12 to be separated. The third mixture is generally recycled into the mixture 12 to be separated.
[0082] According to a variant of the method, the granules are not evacuated by reducing the flow rate of the fluid stream 42 and by tilting the reactor 16 relative to the frame 48, but by increasing the flow rate of the fluid stream 42. The evacuation then comprises an ejection of at least 90% by mass of the fluidized bed 18 from the fluidization chamber 40 via an outlet (not shown) provided in the circuit 56 of the fluid stream 42. Instead of the particles of the fluidized bed 18 falling back onto the receiving surface 46, they are pushed upwards by the increase in the flow rate of the fluid stream 42.
[0083] Thanks to the characteristics described above, the separation process is efficient from a separation point of view, because the granules are correctly electrically charged. Although carried out in batches in the reactor, the process remains productive. Indeed, the duration of fluidization is perfectly controlled and the risks of malfunction, such as clogging, are reduced. The process is simple to manage, even when the nature of the mixture to be separated changes, thanks to the easy parameterization of key factors (fluidization time, temperature, air flow rate).
Claims
CLAIMS 1. Method for batch separation of a mixture (12) comprising granules of at least a first material and a second material, comprising the following successive steps for each of the batches: - introduction of one of the batches into a fluidization chamber (40) defined by a reactor (16) and obtaining an introduced batch (38), - the granules of the introduced batch (38) being initially at rest in the fluidization chamber (40), starting a fluidization and obtaining at least one fluidized bed (18) in the fluidization chamber (40), the fluidization being obtained by at least one ascending fluid current (42) passing through the introduced batch (38) and putting at least a fraction of the granules of the introduced batch (38) in suspension, the fluidized bed (18) being charged by triboelectric effect, - modification of the fluid flow (42) and evacuation of at least 90% by mass of the batch (38) introduced from the fluidization chamber (40) and obtaining an evacuated batch (44), and - passage of the evacuated batch (44) through one or more electric fields adapted to separate the evacuated batch (44) into at least a first mixture (14) rich in granules of the first material and a second mixture (15) rich in granules of the second material.
2. The method of claim 1, wherein modifying the fluid stream (42) comprises reducing the flow rate of the fluid stream (42) causing granules from the fluidized bed (18) to fall onto a receiving surface (46) of the reactor (16).
3. Method according to claim 2, in which, after the reduction of the flow rate of the fluid stream (42), the fluid stream (42) has a non-zero residual flow rate in the fluidization chamber (40) after the evacuation of the introduced batch (38).
4. Method according to claim 2 or 3, in which the reactor (16) is rotatably mounted relative to a frame (48) between at least a first position occupied during fluidization, and a second position occupied during evacuation and in which the receiving surface (46) is more inclined relative to the frame (48) than in the first position, the evacuation comprising a displacement of at least 90% by mass of the batch (38) introduced, by gravity, along the receiving surface (46) towards the outside of the fluidization chamber (40).
5. The method of claim 1, wherein modifying the fluid stream (42) comprises increasing the flow rate of the fluid stream (42), evacuating comprising an ejection of at least 90% by mass of the fluidized bed (18) from the fluidization chamber (40) caused by the increase in flow rate.
6. Method according to any one of claims 1 to 5, in which the reactor (16) comprises a casing (50) defining: - an inlet (52) for introduction, the inlet (52) being open for introduction, then closed after introduction, and - an outlet (54) for the evacuation of at least 90% by mass of the introduced batch (38), the outlet (54) being open for evacuation, then closed after evacuation.
7. A method according to any one of claims 1 to 6, wherein the reactor (16) defines at least one circuit (56) forming a loop for the fluid stream (42), the reactor (16) comprising at least one blower (58) for obtaining the fluid stream (42) in the circuit (56).
8. A method according to any one of claims 1 to 7, wherein the fluid stream (42) is at a temperature between 45°C and 75°C.
9. Method according to any one of claims 1 to 8, in which, the fluidization being obtained under given conditions, the granules of the batch (38) introduced are maintained in the form of said fluidized bed (18) for a predetermined duration, the granules of the first material taking an electrical charge greater than 90% of a maximum electrical charge which can be obtained under the given conditions.
10. Installation (10) for batch separation of a mixture (12) comprising granules of at least a first material and a second material, the installation (10) comprising: - a reactor (16) defining a fluidization chamber (40) intended to receive one of the batches to obtain an introduced batch (38), the reactor (16) being adapted to create a fluidized bed (18) in the fluidization chamber (40), the granules of the introduced batch (38) being initially at rest in the fluidization chamber (40), the reactor (16) being adapted to produce at least one ascending fluid stream (42) passing through the introduced batch (38) and putting at least a fraction of the granules of the introduced batch (38) in suspension to obtain the fluidized bed (18), the fluidized bed (18) being charged by triboelectric effect, the reactor (16) being adapted to modify the fluid stream (42) and evacuate at least 90% by mass of the introduced batch (38) from the fluidization chamber (40) to obtain an evacuated batch (44), and - a separation unit (20) adapted to create at least one or more electric field(s), the installation (10) being adapted to pass the evacuated batch (44) into the electric field(s) and separate the evacuated batch (44) between at least a first mixture (14) rich in granules of the first material and a second mixture (15) rich in granules of the second material.