Method for separating mixture of particles by triboelectric effect

Abstract

The present application relates to a method for separating a mixture in batches, said mixture comprising particles of at least two materials, for each batch, said method comprising the following consecutive steps: feeding one of the batches into a fluidization chamber (40) defined by a reactor (16) and obtaining a feed batch (38),-the particles of said batches are initially in a stationary state,-the particles of said batches are initially in a non-stationary state, and-the particles of said batches are initially in a non-stationary state. The fluidization is started and at least one fluidized bed (18) is obtained in the fluidization chamber, the fluidization is carried out by at least one rising fluid flow (42), which causes at least a portion of the particles of the feed batch to be in a suspended state, the fluidized bed being charged by the triboelectric effect,-the fluid flow (42) is altered, and the fluid flow (42) is changed into the fluidized bed (18). And discharging at least 90% by mass of the feed batch from the fluidization chamber,-passing the discharged batch through one or more electric fields, intended to separate the discharged batch.

Description

[0001] The present application relates to a method for separating a mixture, the mixture comprising particles of at least a first material and a second material, the mixture being charged by the triboelectric effect and passing through one or more electric fields to separate the mixture between a first mixture rich in particles of the first material and a second mixture rich in particles of the second material.

[0002] The present application also relates to a corresponding device.

[0003] The triboelectric effect is an electrostatic phenomenon in which at least two materials of different natures are charged by contacting each other. Electrons are transferred from one material to the other, and this situation persists. Therefore, it is called static electricity. The lack of electrons in one material generates a positive charge, while the excess of electrons in the other material generates a negative charge. It is known to subsequently separate the particles from this material using a channel through an electric field, the electric field applying opposite forces to the particles according to their respective charges.

[0004] To increase the triboelectric effect, mechanical energy is usually provided by rubbing the materials against each other for a period of time. The charge gradually increases, and its speed depends on the materials and the surrounding conditions, especially the humidity level. In some cases, if the rubbing duration is too long, the charge may decrease.

[0005] To obtain a separation method with favorable productivity, it is known to continuously feed the mixture to be separated into a stirring tank. The particles are fed at one end of the stirring tank and discharged at the other end. However, due to the movement of the stirring tank, it is difficult to control the progress of the particle medium in the stirring tank in terms of its shape and direction. It may happen that the particles at the outlet are insufficiently charged, or the outlet flow rate is low.

[0006] Furthermore, if the properties of the mixture to be separated change, complex mechanical processing modifications must be carried out in order to obtain an adjustment suitable for the new properties of the mixture again.

[0007] To increase the charging speed and the flow rate of the mixture at the outlet, it has been proposed to continuously generate a fluidized bed from the mixture to be separated in a reactor. The fluidized bed is obtained by an upward fluid flow (usually air). However, the extraction of the particles and more generally the progress of the fluidized bed in the reactor have again proven difficult to manage. In addition, when the material has a relatively long charging time, the fluidized reactor must be large, which requires significant costs for the blower for generating the vertical fluid flow and for the possible heating of the fluid flow.

[0008] In the document WO 2010 / 109096, the fluidized bed is more or less static in the reactor, and once the particles are charged, they are attracted out of the fluidized bed according to their charge by a conveyor belt that forms an electrode around the fluidized bed. The extraction is continuous, and the arrival of new particles continuously feeds the fluidized bed. However, this reactor is difficult to readjust, especially in terms of the charge level. It is also possible that insufficiently charged particles accumulate in the reactor and clog the reactor.

[0009] Therefore, the object of the present application is to provide a separation method that solves all or part of the above problems, which is effective from the perspectives of separation and production, and is easy to control, especially when the properties of the mixture to be separated change.

[0010] To this end, the subject of the present application is a method for batch-separating a mixture, the mixture comprising particles of at least a first material and a second material, and for each batch, the method comprising the following successive steps:

[0011] - Feeding one of the batches into a fluidization chamber defined by a reactor and obtaining a fed batch,

[0012] - The particles of the fed batch are initially at rest in the fluidization chamber, start to fluidize and obtain at least one fluidized bed in the fluidization chamber. The fluidization is obtained by at least one upward fluid flow passing through the fed batch, and at least a part of the particles of the fed batch are in a suspended state. The fluidized bed is charged by the triboelectric effect.

[0013] - Changing the fluid flow and discharging at least 90% by mass of the fed batch from the fluidization chamber and obtaining a discharged batch, and

[0014] - Passing the discharged batch through one or more electric fields adapted to separate the discharged batch into at least a first mixture rich in particles of the first material and a second mixture rich in particles of the second material.

[0015] According to a specific embodiment, the method has one or more of the following features taken alone or according to all technically possible combinations:

[0016] - The changing of the fluid flow includes reducing the flow rate of the fluid flow so that the particles from the fluidized bed fall onto the receiving surface of the reactor;

[0017] - After reducing the flow rate of the fluid flow and after discharging the fed batch, the fluid flow has a non-zero residual flow rate in the fluidization chamber;

[0018] - The reactor is rotatably mounted relative to the frame between at least a first position and a second position. The first position is occupied during the fluidization process, and the second position is occupied during the discharging process. In the reactor, the receiving surface is more inclined relative to the frame than in the first position. The discharging includes the displacement of at least 90% by weight of the feed batch under the action of gravity along the receiving surface towards the outside of the fluidization chamber;

[0019] - The changing of the fluid flow includes increasing the flow rate of the fluid flow. The discharging includes the 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 includes a housing that defines: an inlet for feeding, which is opened during feeding and then closed after feeding; and an outlet for discharging at least 90% by mass of the feed batch, which is opened during discharging and then closed after discharging;

[0021] - The reactor defines at least one loop that forms a loop for the fluid flow. The reactor includes at least one blower for obtaining a fluid flow in the loop;

[0022] - The temperature of the fluid flow is from 45°C to 75°C; and

[0023] - Under given conditions, fluidization is obtained, and the particles of the feed batch are maintained in the form of a fluidized bed for a predetermined time. The charge carried by the particles of the first material is greater than 90% of the maximum charge that can be obtained under the given conditions.

[0024] This application also relates to a device for separating a mixture in batches, the mixture containing at least particles of a first material and a second material. The device includes:

[0025] - A reactor that defines a fluidization chamber, which is intended to receive one of the batches to obtain a feed batch. The reactor is adapted to generate a fluidized bed in the fluidization chamber. The particles of the feed batch are initially at rest in the fluidization chamber. The reactor is adapted to generate at least one upward fluid flow through the feed batch and suspend at least a part of the particles of the feed batch to obtain a fluidized bed, which is charged by the triboelectric effect. The reactor is adapted to change the fluid flow and is adapted to discharge at least 90% by mass of the feed batch from the fluidization chamber to obtain a discharged batch, and

[0026] - A separation unit that is adapted to generate at least one or more electric fields. The device is adapted to pass the discharged batch through the electric field and separate the discharged batch into at least a first mixture rich in particles of the first material and a second mixture rich in particles of the second material.

[0027] The present application will be better understood by reading the following description given by way of example only and with reference to the accompanying drawings, in which:

[0028] - Figure 1 is a general perspective view of a separation device according to the present application, which is used to implement the method of the present application,

[0029] - Figure 2 is for conveying Figure 1 a perspective view of a system for the mixture of the device shown,

[0030] - Figure 3 is Figure 1 a perspective view of a fluidized bed reactor of the device shown, the reactor being in a first position occupied during a batch fluidization process,

[0031] - Figure 4 is Figure 3 a perspective view of the reactor shown, the reactor being in a second position occupied during the process of discharging a batch from the reactor, and

[0032] - Figure 5 is Figure 1 a perspective view of a separation unit of the device shown.

[0033] With reference to Figure 1 , a device 10 according to the present application is described, which is used to separate a mixture 12 of particles (not shown) containing at least a first material and a second material into at least a first mixture 14 rich in particles of the first material and a second mixture 15 rich in particles of the second material.

[0034] The mixture 12 includes, for example, as the first material and the second material:

[0035] - acrylonitrile butadiene styrene (ABS) and polystyrene (PS),

[0036] - polypropylene (PP) and polyethylene (PE), or

[0037] - polypropylene (PP) and polystyrene (PS).

[0038] When the particles of the first material and the second material rub against each other by the triboelectric effect, they tend to become electrically charged.

[0039] The first mixture 14 is, for example, rich in particles of the first material, and relatively speaking, the proportion of particles of the first material contained therein by mass is higher than that of the second mixture 15. Similarly, the second mixture 15 is, for example, rich in particles of the second material, and relatively speaking, the proportion of particles of the second material contained therein by mass is higher than that of the first mixture 14.

[0040] Advantageously, the first mixture 14 comprises particles of a first material in an amount greater than 95% by mass.

[0041] Advantageously, the second mixture 15 comprises particles of a second material in an amount greater than 95% by mass.

[0042] According to a variant (not shown), the mixture 12 to be separated comprises particles of three different materials or more than three materials.

[0043] In a variant, the mixture 12 is, for example, a quaternary mixture (comprising four materials) and is separated into a first binary mixture 14 (rich in two materials) and a second binary mixture 15 (rich in two other materials).

[0044] Advantageously, the first mixture 14 then comprises particles containing two materials in an amount greater than 95% by mass, while the second mixture 15 comprises particles containing two other materials in an amount greater than 95% by mass calculated on the basis of mass.

[0045] For example, the mixture 12 to be separated comprises 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 having a composition similar to the composition of the mixture 12.

[0046] The device 10 is adapted to operate batchwise at least in a reactor 16 ( Figure 3 ), the reactor being adapted to generate a fluidized bed 18 from the mixture 12 ( Figure 3 ). However, the batches of the mixture to be separated advantageously follow one another at a high rate, which does not impair the productivity of the device 10. On the contrary, the device is advantageously adapted to perfectly control the reactor 16, in particular the residence time of the particles in the reactor.

[0047] The device 10 further comprises a separation unit 20 ( Figure 5 ). In this example, the device 10 comprises a special conveying system 22 ( Figure 2 ) for forming multi-batch one-by-one feeding into the reactor 16.

[0048] According to a variant (not shown), the batches have been formed and directly fed into the reactor 16, or are produced in a manner known per se, rather than in the manner allowed by the conveying system 22.

[0049] In this example, the conveying system 22 ( Figure 2 ) comprises a frame 24; a vibrating table 26 adapted to generate a layer of particles from the mixture 12; a conveyor 28 for moving the layer of particles relative to the frame 24; and two ionization rods 30A, 30B placed above the conveyor.

[0050] In one variant, the conveying system 22 comprises only one ionization rod, or more than two ionization rods.

[0051] In this example, the conveying system 22 includes a hopper 32 for accommodating the mixture to be processed, and a worm 34 for conveying the mixture 12 from the hopper to the vibrating table 26. The conveying system 22 includes, for example, a buffer hopper 36 located at the end of the conveyor 28.

[0052] The ionization rods 30A, 30B are adapted to electrically discharge the mixture 12 to be separated. The ionization rods 30A, 30B can be, for example, activated and advantageously adjusted in terms of frequency and distance relative to the conveyor. This frequency is advantageously adjusted directly on the ionization rods 30A, 30B.

[0053] The buffer hopper 36 is adapted to form a batch 38 of the mixture, the mass of which is, for example, 30 to 100 kg, and advantageously about 50 kg.

[0054] The reactor 16 ( Figure 3 and Figure 4 ) defines a fluidization chamber 40, which is adapted to receive the fed batch 38, which in this example comes from the buffer hopper 36.

[0055] The reactor 16 is adapted to generate a fluidized bed 18 in the fluidization chamber 40. The reactor 16 is adapted to generate at least one upward fluid flow 42 through the fed batch 38 to suspend at least a portion of the particles of the fed batch and to obtain the fluidized bed 18.

[0056] The reactor 16 is adapted to vary the fluid flow 42 and to discharge at least 90% by mass of the fed batch (38) out of the fluidization chamber (40) to obtain a discharged batch 44 ( Figure 4 ). Preferably, all or almost all (more than 99% by mass) of the fed batch 38 is discharged.

[0057] The reactor 16 is configured, for example, such that the temperature of the fluid flow 42 is 45 °C to 75 °C. Thus, the fluid can be dried and the triboelectricity can be enhanced.

[0058] The reactor 16 defines, for example, a receiving surface 46, such as a grid, which is located below the fluidized bed 18 and is intended to receive particles if the flow rate of the fluid flow 42 decreases and the fluidized bed falls back onto the receiving surface.

[0059] For example, the reactor 16 is mounted to be rotatable relative to the frame 48 of the device 10 between a first position, which is occupied during fluidization ( Figure 3 ), and a second position, which is occupied during discharging ( Figure 4), and in the reactor, the receiving surface 46 is more inclined relative to the frame 48 than in the first position.

[0060] The reactor 16 can rotate, for example, about an axis D, which is advantageously horizontal.

[0061] The reactor 16 includes, for example, a housing 50 that defines an inlet 52 for feeding the mixture 12, which is open during feeding and then closed after feeding. The housing 50 defines an outlet 54 for discharging at least 90% by mass of the feed batch 38, which is open during discharging and then closed after discharging.

[0062] In this example, the reactor 16 defines at least one circuit 56 that forms a circuit for the fluid flow 42. The reactor includes at least one blower 58 for obtaining the fluid flow 42 in the circuit 56. The reactor 16 advantageously includes a homogenization chamber 60 for homogenizing the fluid flow 42 and a heating system 62 suitable for heating the fluid flow 42. The reactor 16 advantageously includes a recuperator 64 and a sheath 66 connecting the recuperator to the fan 58.

[0063] In this example, the circuit 56 includes the fan 58, the homogenization chamber 60, the heating system 62, the fluidization chamber 48, the recuperator 64, and the sheath 66.

[0064] The fluidization chamber 40 is defined, for example, at the bottom (in the first position) by a receiving surface 46 that advantageously permeates the fluid flow 42; the sides are defined by the housing 50, which advantageously has at least one transparent wall so that the fluidized bed 18 can be seen, and the top is defined by the recuperator 64.

[0065] The homogenization chamber 60 extends, for example, between the blower 58 and the heating system 62. The homogenization chamber 60 has, for example, an upwardly flared shape (in the first position). The homogenization chamber 60 is advantageously defined laterally by four planes.

[0066] The fluid is, for example, air or pre-dried air.

[0067] The recuperator 64 is advantageously suitable for filtering the fluid flow 42 and for removing fine particles (not shown) therefrom so that the latter do not return to the blower 58.

[0068] The reactor 16 is advantageously suitable for operating in a closed circuit or in fresh air. The sheath 66 has, for example, an outlet 68 for the fluid flow 42 in the "fresh air" mode. For the same reason, the blower 58 also includes an air inlet 70.

[0069] In the first position, the receiving surface 46 is, for example, substantially horizontal. In the second position, the receiving surface 46 is inclined, for example, by approximately 45° (plus or minus 5°, even 10°).

[0070] The separating unit 20 ( Figure 5 ) includes, for example, a hopper 72, a conveyor 74, and an electrode 76 adapted to generate an electric field. The separating unit 20 includes, for example, three separating compartments 76 and three worms 78, so as to be able to fill three bags 80 simultaneously.

[0071] The operation of the device 10 will now be described. The method according to the present application is also shown.

[0072] The conveying system 22 forms multiple batches of the mixture 12. The worm 34 withdraws the mixture 12 from the hopper 32 and conveys it to the vibrating table 26. The vibrating table 26 advantageously forms a layer of the mixture on the conveyor 28, and the conveyor 28 conveys the mixture layer to the buffer hopper 36, where a batch 38 is formed.

[0073] By passing under the ionization rods 30A, 30B, the mixture 12 is electrically discharged. This is a matter of advantageously performing electrical neutralization.

[0074] The reactor 16 is in the first position and the inlet 52 is open. The buffer hopper 36 feeds the batch 38 into the fluidization chamber 40.

[0075] The flow rate of the fluid flow 42 in the fluidization chamber 40 is then, for example, zero. The batch-fed particles are initially stationary in the fluidization chamber 40.

[0076] According to an advantageous variant, the flow rate of the fluid flow 42 is not zero during the feeding process, but has a value such that the particles of the fed batch 38 are in a stationary state (no fluidized bed). Thus, for example, it is possible to more easily maintain the desired temperature in the fluidization chamber 40.

[0077] Then the inlet 52 is closed, and the flow rate of the fluid flow 42 is increased to a value such that at least a part of the particles of the fed batch 38, preferably all the particles, are in a suspended state to obtain a fluidized bed 18. Then the fluidized bed 18 is charged by the triboelectric effect.

[0078] Fluidization is obtained under given conditions (temperature of the fluid flow, humidity, flow rate of the fluid flow, etc.), and the particles of the fed batch 38 are advantageously maintained in the form of the fluidized bed 18 for a predetermined time, and the charge carried by the particles of the first material is greater than 90% of the maximum charge, and the maximum charge is obtained by maintaining the particles of the fed batch 38 in the form of the fluidized bed 18 for a time longer than the predetermined time under the same given conditions. In other words, anyone waits long enough to obtain a charge greater than 90% of the maximum charge possible under the given conditions.

[0079] A person skilled in the art can determine the maximum possible charge amount under given conditions through the fluidization chamber 40 or simple measurements in the laboratory.

[0080] Then, the flow rate of the fluid stream 42 is reset to its reduced value or to zero, and at least 90% by mass of the feed batch 38 is discharged from the fluidization chamber 40, preferably the entire feed batch is discharged. For example, the particles of the fluidized bed 18 fall back onto the receiving surface 46.

[0081] The outlet 54 is opened, and the reactor 16 is tilted from the first position to the second position. The receiving surface 46 is tilted. The particles move along the receiving surface 46 under the action of gravity and leave the fluidization chamber 40 through the outlet 54.

[0082] The discharge batch 44 reaches the separation unit 20.

[0083] The outlet 54 of the reactor 16 is closed, and the reactor returns to the first position, where it can receive a new batch of the mixture 12.

[0084] In the separation unit 20, the discharge batch 44 is separated into at least a first mixture 14 and a second mixture 15. In the example shown, the discharge batch 44 is separated into three mixtures, and the composition of the third mixture is undifferentiated, for example, similar to the composition of the mixture 12 to be separated. The third mixture is generally recycled to the mixture 12 to be separated.

[0085] According to a variant of the method, the particles are not discharged 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. Then, the discharge includes ejecting 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 for the fluid stream 42. By increasing the flow rate of the fluid stream 42, the fine particles of the fluidized bed 18 are pushed upward instead of falling back onto the receiving surface 46.

[0086] Due to the above features, from the perspective of separation, the separation method is effective because the particles are correctly electrically charged. Although the method is carried out batchwise in the reactor, the method is still productive. In fact, the duration of fluidization is perfectly controlled, and the risk of failures (such as blockages) is also reduced. Due to the promotion of the parameterization of the key factors (fluidization time, temperature, air flow rate), the method is easy to control even when the nature of the mixture to be separated changes.

Claims

1. A method for batch separation of a mixture (12), the mixture comprising particles of at least a first material and a second material, for each batch, the method comprising the following sequential steps: - Feeding one of the batches into a fluidized chamber (40) defined by a reactor (16) and obtaining a fed batch (38), - The particles of the fed batch (38) are initially at rest in the fluidized chamber (40), start to fluidize and obtain at least one fluidized bed (18) in the fluidized chamber (40), the fluidization is obtained by at least one upward fluid stream (42) passing through the fed batch (38), and at least a part of the particles of the fed batch (38) are in a suspended state, and the fluidized bed (18) is charged by triboelectric effect, - Changing the fluid stream (42) and discharging at least 90% by mass of the fed batch (38) from the fluidized chamber (40) and obtaining a discharged batch (44), and - Passing the discharged batch through one or more electric fields, the electric fields being adapted to separate the discharged batch (44) into at least a first mixture (14) rich in particles of the first material and a second mixture (15) rich in particles of the second material.

2. The method according to claim 1, wherein changing the fluid stream (42) comprises reducing the flow rate of the fluid stream (42), causing the particles from the fluidized bed (18) to fall onto the receiving surface (46) of the reactor (16).

3. The method according to claim 2, wherein after reducing the flow rate of the fluid stream (42), after discharging the fed batch (38), the fluid stream (42) has a non-zero residual flow rate in the fluidized chamber (40).

4. The method according to claim 2 or 3, wherein the reactor (16) is mounted to be rotatable relative to a frame (48) between at least a first position and a second position, the first position is occupied during fluidization, the second position is occupied during discharging, and in the reactor the receiving surface (46) is more inclined relative to the frame (48) than in the first position, and the discharging comprises a displacement of at least 90% by weight of the fed batch (38) along the receiving surface (46) towards the outside of the fluidized chamber (40) under the action of gravity.

5. The method according to claim 1, wherein changing the fluid stream (42) comprises increasing the flow rate of the fluid stream (42), and the discharging comprises ejecting at least 90% by mass of the fluidized bed (18) out of the fluidized chamber (40) caused by the increase in flow rate.

6. The method according to any one of claims 1-5, wherein the reactor (16) comprises a housing (50), the housing defining: - An inlet (52) for feeding, the inlet (52) being opened during feeding and then closed after feeding, and - An outlet (54) for discharging at least 90% by mass of the fed batch (38), the outlet (54) being opened during discharging and then closed after discharging.

7. The method according to any one of claims 1 - 6, wherein the reactor (16) defines at least one loop (56) that forms a loop for the fluid stream (42), and the reactor (16) includes at least one blower (58) for obtaining the fluid stream (42) in the loop (56).

8. The method according to any one of claims 1 - 7, wherein the temperature of the fluid stream (42) is from 45 °C to 75 °C.

9. The method according to any one of claims 1 - 8, wherein fluidization is obtained under given conditions, and the particles of the feed batch (38) are maintained in the form of a fluidized bed (18) for a predetermined time, and the charge carried by the particles of the first material is greater than 90% of the maximum charge that can be obtained under the given conditions.

10. An apparatus (10) for batch - separating a mixture (12) comprising at least particles of a first material and a second material, the apparatus (10) comprising: - a reactor (16) that defines a fluidization chamber (40) which is intended to receive one of the batches to obtain a feed batch (38), the reactor (16) being adapted to produce a fluidized bed (18) in the fluidization chamber (40), the particles of the feed batch (38) being initially at rest in the fluidization chamber (40), the reactor (16) being adapted to produce at least one upward fluid stream (42) passing through the feed batch (38) and to suspend at least a portion of the particles of the feed batch (38) to obtain a fluidized bed (18), the fluidized bed (18) being charged by the triboelectric effect, the reactor (16) being adapted to vary the fluid stream (42) and to discharge at least 90% by mass of the feed batch (38) out of the fluidization chamber (40) to obtain a discharge batch (44), and - a separation unit (20) that is adapted to generate at least one or more electric fields, the apparatus (10) being adapted to pass the discharge batch (44) through the electric field and to separate the discharge batch (44) into at least a first mixture (14) rich in particles of the first material and a second mixture (15) rich in particles of the second material.

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