Method for separating granular mixtures by triboelectric effect

Abstract

The present invention relates to a method for separating a mixture containing granules of at least two materials in batches, comprising the steps of: - introducing the batch into a fluidization chamber (40) defined by a reactor (16) to obtain an introduced batch (38); - the batch of granules is initially at rest and starts to be fluidized to obtain at least one fluidized bed (18) in the fluidization chamber, the fluidization being achieved by at least one ascending fluid flow (42) that suspends at least a small portion of the batch of granules introduced therein, the fluidized bed being electrically charged by the triboelectric effect; - modifying the fluid flow (42) and expelling at least 90% by mass of the batch introduced from the fluidization chamber; - passing the discharged batch through one or more electric fields intended to separate the discharged batch; The present invention relates to a method, including:

Description

[Technical Field]

[0001] The present invention relates to a method for separating a mixture comprising granules of at least a first material and a second material, wherein the mixture is charged by triboelectric effect and passed through one or more electric fields to separate the mixture at least between a first mixture enriched in granules of the first material and a second mixture enriched in granules of the second material.

[0002] The invention further relates to a corresponding installation. [Background technology]

[0003] The triboelectric effect is an electrostatic phenomenon whereby at least two materials of different nature conduct electricity to each other upon contact. Electrons from one are transferred to the other and remain so. This is called static electricity. A lack of electrons in one creates a positive charge, while an excess of electrons in the other creates a negative charge. It is then known to separate granules from such materials using the passage of an electric field, which exerts opposing forces on the granules according to their respective charges.

[0004] To increase the triboelectric effect, mechanical energy is applied, usually by rubbing the materials together for a period of time. The charge gradually builds up at a rate that depends on the material and the surrounding conditions, specifically the humidity level. In some cases, if the friction continues for too long, the charge can decrease.

[0005] To obtain a separation method with advantageous productivity, it is known to continuously feed the mixture to be separated into an agitated box. The particles are fed at one end of the box and exit at the other end. However, the progress of the granular medium within the box is difficult to control due to the movement of the box, its shape and orientation. Insufficient charging of the granules at the outlet or low outlet flow rates can also occur.

[0006] Furthermore, if the properties of the mixture being separated change, complex mechanical corrections must be made to regain the adjustments appropriate to the new properties of the mixture.

[0007] In order to increase the charging speed and flow rate of the mixture at the outlet, it has been proposed to continuously create a fluidized bed in the reactor from the mixture being separated. The fluidized bed is obtained by an upward fluid flow, usually air. However, even in this case, the extraction of the granules, and more generally the progression of the fluidized bed in the reactor, proves to be difficult to manage. Furthermore, if the material has a fairly long charging time, the fluidized reactor must be large, which necessarily involves considerable costs for the blower that generates the fluid flow and for the possible heating of the fluid flow.

[0008] In WO 2010 / 109096, the fluidized bed is stationary to a variable extent within the reactor, and the granules are charged and then drawn out of the fluidized bed according to their charge by a conveyor belt that forms an electrode around the fluidized bed. The extraction is carried out continuously, and the fluidized bed is continuously fed by the arrival of new granules. Nevertheless, such a reactor is still very difficult to regulate, especially with regard to the charge level. It is also possible that insufficiently charged granules accumulate in the reactor and clog it. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2010 / 109096 Summary of the Invention [Problem to be solved by the invention]

[0010] The object of the present invention is therefore to provide a separation method that solves all or some of the problems mentioned herein above, which is both effective from the point of view of separation and productivity, while being simple to manage, in particular when the properties of the mixtures to be separated change. [Means for solving the problem]

[0011] To this end, the subject of the present invention is a method for separating a mixture comprising, per batch, at least granules of a first material and of a second material, comprising, for each batch, the following successive steps: - feeding one of the batches into a fluidization chamber defined by a reactor to obtain a fed batch; - the fed batch of granules is initially stationary in the fluidization chamber, starting fluidization to obtain at least one fluidized bed in the fluidization chamber, the fluidization being obtained by at least one ascending fluid flow passing through the fed batch and suspending at least a small portion of the fed batch of granules, the fluidized bed being electrically charged by triboelectric effect; - modifying the fluid flow and expelling at least 90% by mass of the fed batch from the fluidization chamber to obtain a fed batch; - passing the discharged batch through one or more electric fields suitable for separating the discharged batch into at least a first mixture enriched in granules of the first material and a second mixture enriched in granules of the second material; A separation method comprising:

[0012] According to particular embodiments, the method has one or more of the following features, taken individually or in all technically possible combinations: - modifying the fluid flow includes reducing the flow rate of the fluid flow to cause the granules in the fluidized bed to fall onto a receiving surface of the reactor; - after the reduction in the flow rate of the fluid flow, the fluid flow has a non-zero residual flow rate in the fluidization chamber after the step of discharging the fed batch; - the reactor is rotatably mounted relative to the frame between at least a first position, which is assumed during fluidization, and a second position, which is assumed during discharging and in which the receiving surface is more inclined relative to the frame than in the first position, and the discharging step includes displacing at least 90% by mass of the fed batch by gravity along the receiving surface towards the outside of the fluidization chamber; - modifying the fluid flow includes increasing a flow rate of the fluid flow, and the pumping step includes discharging at least 90% by mass of the fluidized bed out of the fluidization chamber due to the increased flow rate; - the reactor comprises a shell defining an inlet for feeding, the inlet being open for feeding and then closed after feeding, and an outlet for discharging at least 90% by weight of the fed batch, the outlet being open for discharging and then closed after discharging; - the reactor defines at least one circuit forming a loop for the fluid flow, the reactor including at least one blower for obtaining the fluid flow in the circuit; - the fluid stream has a temperature comprised between 45°C and 75°C; - fluidization is obtained under predetermined conditions, the fed batch of granules being maintained in the form of said fluidized bed for a predetermined period of time, and the granules of the first material being charged with more than 90% of the maximum charge obtainable under the predetermined conditions.

[0013] The present invention relates to an installation for separating a mixture comprising granules of at least a first material and a second material in batches, the installation comprising: - a reactor defining a fluidization chamber intended to receive one of the batches to obtain a fed batch, the reactor being suitable for creating a fluidized bed in the fluidization chamber, the granules of the fed batch being initially stationary in the fluidization chamber, the reactor being suitable for generating at least one ascending fluid flow passing through the fed batch and suspending at least a small portion of the granules of the fed batch to obtain the fluidized bed, the fluidized bed being charged by the triboelectric effect, and the reactor being suitable for modifying the fluid flow and for discharging at least 90% by mass of the fed batch outside the fluidization chamber to obtain the fed batch; - a separation unit suitable for generating at least one or more electric fields, the installation being suitable for subjecting a discharged batch to the electric field and for separating the discharged batch at least between a first mixture enriched in granules of a first material and a second mixture enriched in granules of a second material; Includes.

[0014] The invention will be better understood on reading the following description, given purely by way of example, and on referring to the accompanying drawings, in which: [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a perspective view of an overall separation installation according to the invention, which serves to carry out the method according to the invention; [Figure 2] 2 is a perspective view of a system for conveying a mixture of the installation shown in FIG. 1. FIG. [Figure 3] 2 is a perspective view of the fluidization reactor of the installation shown in FIG. 1, the reactor in a first position assumed during fluidization of the batch. [Figure 4] FIG. 4 is a perspective view of the reactor shown in FIG. 3, with the reactor in a second position assumed during discharge of the batch from the reactor. [Figure 5] FIG. 2 is a perspective view of a separation unit of the installation shown in FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0016] Referring to FIG. 1, an apparatus 10 according to the present invention is described for separating a mixture 12 comprising granules of at least a first material and a second material (not shown) into at least a first mixture 14 enriched in granules of the first material and a second mixture 15 enriched in granules of the second material.

[0017] The mixture 12 may include, for example, the following as the first material and the second material: - acrylonitrile butadiene styrene (ABS) and polystyrene (PS), - Polypropylene (PP) and polyethylene (PE), or - Polypropylene (PP) and Polystyrene (PS) Includes.

[0018] Granules of the first and second materials tend to become electrically charged when the granules rub against each other due to the triboelectric effect.

[0019] The first mixture 14 is enriched in granules of the first material, for example, in the sense that the first mixture 14 contains a higher mass proportion of granules of the first material than the second mixture 15. Similarly, the second mixture 15 is enriched in granules of the second material, for example, in the sense that the second mixture 15 contains a higher mass proportion of granules of the second material than the first mixture 14.

[0020] Advantageously, the first mixture 14 comprises a proportion of granules of the first material that is higher than 95% by weight.

[0021] Advantageously, the second mixture 15 comprises a proportion of granules of the second material that is higher than 95% by weight.

[0022] According to a variant (not shown), the mixture 12 to be separated comprises granules of three distinct materials or four or more materials.

[0023] In a variant, the mixture 12 is, for example, four (comprising 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).

[0024] The first mixture 14 advantageously comprises more than 95% by weight of granular components of two of the materials, and the second mixture 15 advantageously comprises more than 95% by weight of granular components of the other two materials.

[0025] For example, the mixture 12 to be separated contains the materials PS, ABS, PP, and PE and is separated into a first mixture that is rich in PP / PE, a second mixture that is rich in ABS / PS, and a third undifferentiated mixture having a composition similar to mixture 12.

[0026] The installation 10 is suitable for operating batch by batch in at least a reactor 16 (FIG. 3) suitable for producing a fluidized bed 18 (FIG. 3) from the mixture 12. However, it is advantageous for the batches of mixture to be separated to follow one another at a high rate, without impairing the productivity of the installation 10; on the contrary, it is advantageous for the installation to be suitable for full control of the reactor 16, and in particular the residence time of the granules in the reactor.

[0027] The facility 10 further comprises a separation unit 20 (FIG. 5). In this example, the facility 10 comprises a special conveying system 22 (FIG. 2) to form batches that are fed into the reactor 16 one by one.

[0028] According to a variant (not shown), the batch is either already formed and fed directly into the reactor 16 or produced in a manner known per se, other than that made possible by the conveying system 22.

[0029] In this example, the conveying system 22 (FIG. 2) includes a frame 24, a vibration table 26 suitable for creating a granular layer from the mixture 12, a conveyor 28 for moving the granular layer relative to the frame 24, and two ionization bars 30A, 30B positioned above the conveyor.

[0030] In a variant, the transport system 22 comprises only one ionization bar or three or more ionization bars.

[0031] In this example, the conveying system 22 includes a hopper 32 containing the mixture to be processed and a worm screw 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.

[0032] The ionization bars 30A, 30B are suitable for discharging the mixture 12 to be separated. The ionization bars 30A, 30B can, for example, be activated and advantageously adjusted in frequency and distance relative to the conveyor. The frequency is advantageously adjusted directly on the ionization bars 30A, 30B.

[0033] The buffer hopper 36 is suitable for forming batches 38 of the mixture, the mass of which is for example comprised between 30 kg and 100 kg, advantageously being about 50 kg.

[0034] The reactor 16 (FIGS. 3 and 4) defines a fluidization chamber 40 suitable for receiving an incoming batch 38 , which in this example comes from a buffer hopper 36 .

[0035] The reactor 16 is suitable for creating a fluidized bed 18 in a fluidization chamber 40. The reactor 16 is suitable for generating at least one ascending fluid flow 42 passing through the fed batch 38 in order to suspend at least a small portion of the granules of the fed batch and for obtaining the fluidized bed 18.

[0036] The reactor 16 is suitable for pumping at least 90% by weight of the fed batch 38 out of the fluidization chamber 40 to modify the fluid flow 42 and obtain the pumped batch 44 (FIG. 4). Preferably, all or almost all (greater than 99% by weight) of the fed batch 38 is pumped out.

[0037] Reactor 16 is configured, for example, so that fluid stream 42 is at a temperature comprised between 45° C. and 75° C., thereby allowing the fluid to dry and enhance triboelectricity.

[0038] The reactor 16 is e.g. large and defines e.g. a receiving surface 46 below the fluidized bed 18 and intended to receive the granules when the flow rate of the fluid stream 42 is reduced and the fluidized bed falls back onto the receiving surface.

[0039] The reactor 16 is mounted to rotate relative to the frame 48 of the equipment 10, for example, at least between a first position (FIG. 3) that is assumed during fluidization and a second position (FIG. 4) that is assumed during delivery and in which the receiving surface 46 is more inclined relative to the frame 48 than in the first position.

[0040] The reactor 16 is movable, for example in rotation about an axis D, which is advantageously horizontal.

[0041] Reactor 16 includes, for example, a shell 50 defining an inlet 52 for the introduction of mixture 12, the inlet being open for introduction and then closed after introduction. Shell 50 defines an outlet 54 for the delivery of at least 90% by weight of the delivered batch 38, the outlet being open for introduction and then closed after introduction.

[0042] In this example, reactor 16 defines at least one circuit 56 forming a loop for fluid flow 42, and reactor includes at least one fan 58 for drawing fluid flow 42 into circuit 56. Reactor 16 advantageously includes a homogenization chamber 60 for homogenizing fluid flow 42 and a heating system 62 suitable for heating fluid flow 42. Reactor 16 advantageously includes a recuperator 64 and a sheath 66 connecting the recuperator to fan 58.

[0043] In this example, the circuit 56 includes a fan 58 , a homogenization chamber 60 , a heating system 62 , the fluidization chamber 40 , a recuperator 64 , and a sheath 66 .

[0044] The fluidization chamber 40 is bounded at the bottom (in a first position) by a receiving surface 46 which is advantageously permeable to the fluid flow 42, advantageously having at least one transparent wall which allows the fluidized bed 18 to be seen, laterally by a shell 50 and upwardly by a recuperator 64.

[0045] 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). Advantageously, the homogenization chamber 60 is laterally bounded by four planes.

[0046] The fluid is, for example, air or pre-dried air.

[0047] Advantageously, the recuperator 64 is adapted to filter the fluid flow 42 and remove particulates (not shown) therefrom so that they do not return to the blower 58 .

[0048] The reactor 16 is advantageously suitable for operation in a closed circuit or in fresh air. The sheath 66 has, for example, an outlet 68 for the fluid flow 42 in "fresh air" mode. The blower 58 further includes an intake 70 for the same reason.

[0049] 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 about 45° (plus or minus 5°, or even 10°).

[0050] The separation unit 20 (FIG. 5) includes, for example, a hopper 72, a conveyor 74, and electrodes 76 suitable for generating an electric field. The separation unit 20 includes, for example, three separation compartments 76 and three worm screws 78 that allow three bags 80 to be filled at once.

[0051] We will now describe the operation of the installation 10. This operation describes the method according to the invention.

[0052] Conveying system 22 forms batches of mixture 12. Worm screw 34 draws mixture 12 from hopper 32 and conveys mixture 12 to vibrating table 26. Vibrating table 26 advantageously creates a layer of mixture on conveyor 28, which conveys the layer to buffer hopper 36 where batches 38 are formed.

[0053] The mixture 12 is discharged by passing under the ionizing bars 30A, 30B. The challenge is to advantageously carry out electrical neutralization.

[0054] The reactor 16 is in the first position and the inlet 52 is open. The buffer hopper 36 is feeding the batch 38 into the fluidization chamber 40.

[0055] The flow rate of the fluid flow 42 is, for example, zero within the fluidization chamber 40. The fed batch of granules is initially stationary within the fluidization chamber 40.

[0056] According to an advantageous variant, the flow rate of the fluid flow 42 is not zero during the feeding, but has a value such that the granules of the fed batch 38 are stationary (no fluidized bed), thereby making it possible, for example, to more easily maintain the desired temperature in the fluidization chamber 40.

[0057] The inlet 52 is then closed and the flow rate of the fluid stream 42 is increased to a value that allows suspending at least a small portion, preferably all, of the granules of the fed batch 38, to obtain a fluidized bed 18. The fluidized bed 18 is then electrically charged by the triboelectric effect.

[0058] Advantageously, fluidization is obtained under predetermined conditions (temperature of the fluid stream, humidity, flow rate of the fluid stream, etc.) and the granules of the fed batch 38 are maintained in the form of a fluidized bed 18 for a predetermined period of time, and the granules of the first material are charged with more than 90% of the maximum charge that would be obtained under the same predetermined conditions by maintaining the granules of the fed batch 38 in the form of a fluidized bed 18 for a period longer than the predetermined period of time. In other words, wait long enough to obtain a charge that is more than 90% of the maximum charge possible under the predetermined conditions.

[0059] The maximum possible charge under given conditions can be determined by one skilled in the art by simple measurements in the fluidization chamber 40 or in a laboratory.

[0060] The flow rate of fluid stream 42 is then reset to its reduced value or reset to zero, and at least 90% by weight of fed batch 38, preferably the entire fed batch, is pumped out of fluidization chamber 40. For example, granules in fluidized bed 18 fall back onto receiving surface 46.

[0061] The outlet 54 is open and the reactor 16 is tilted from the first position to the second position. The receiving surface 46 is tilted. The granules move along the receiving surface 46 due to gravity and leave the fluidization chamber 40 via the outlet 54.

[0062] The outgoing batches 44 arrive in the separation unit 20 .

[0063] The outlet 54 of the reactor 16 is closed and the reactor is returned to the first position where it can receive a new batch of mixture 12 .

[0064] In separation unit 20, the output batch 44 is separated into at least a first mixture 14 and a second mixture 15. In the example shown, the output batch 44 is separated into three mixtures, the third of which is an undifferentiated composition, e.g., similar to the composition of the mixture 12 to be separated. The third mixture is generally recycled into the mixture 12 to be separated.

[0065] According to a variant of the method, the granules are not pumped out by decreasing 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 pumping step comprises discharging at least 90% by mass of the fluidized bed 18 out of the fluidization chamber 40 via an outlet (not shown) provided in the circuit 56 for the fluid stream 42. Instead of the particles in the fluidized bed 18 falling back onto the receiving surface 46, the particles are pushed upward by increasing the flow rate of the fluid stream 42.

[0066] The separation method is effective from the separation point of view, since the granules are precisely charged thanks to the features explained hereinabove. Although the method is carried out in batches in a reactor, the method remains highly productive. In fact, the duration of fluidization is fully controlled, reducing the risk of breakdowns such as clogging. The method is easy to adapt to changes in the properties of the mixture to be separated, due to the facilitated parameterization of the main factors (fluidization time, temperature, air flow rate). [Explanation of symbols]

[0067] 10 Equipment 12 mixture 14 First mixture, first binary mixture 15 Second mixture, second binary mixture 16 Reactor 18 Fluidized Bed 20 Separation Unit 22 Transport System 24, 48 frames 26 Shaking table 28, 74 Conveyor 30A, 30B Ionizing Bar 32, 72 Hopper 34, 78 Worm screw 36 Buffer hopper 38 Batch, fed batch, mixed batch 40 Fluidization Chamber 42 Upward fluid flow, fluid flow 44 batches sent out 46 Receptive Surface 50 Outer structure 52 Entrance 54, 68 exit 56 circuits 58 Blowers and fans 60 Homogenization Chamber 62 Heating System 64 Recuperator 66 Sheath 70 Air intake 76 Separation compartment, electrode 80 bags D-axis

Claims

1. A method for separating a mixture (12) comprising granules of at least a first material and a second material by batches, the method comprising the steps of: - feeding one of said batches into a fluidization chamber (40) defined by a reactor (16) to obtain a fed batch (38); - the granules of the fed batch (38) are initially stationary in the fluidization chamber (40), and initiating fluidization to obtain at least one fluidized bed (18) in the fluidization chamber (40), the fluidization being obtained by at least one ascending fluid flow (42) passing through the fed batch (38) and suspending at least a small portion of the granules of the fed batch (38), the fluidized bed (18) being electrically charged by the triboelectric effect; - modifying the fluid flow (42) and discharging at least 90% by mass of the fed batch (38) from the fluidization chamber (40) to obtain a fed batch (44); - passing said discharged batch (44) through one or more electric fields suitable for separating said discharged batch (44) into at least a first mixture (14) enriched in granules of said first material and a second mixture (15) enriched in granules of said second material; A method comprising:

2. 2. The method of claim 1, wherein the step of modifying the fluid flow (42) comprises reducing a flow rate of the fluid flow (42) to cause the granules from the fluidized bed (18) to fall onto a receiving surface (46) of the reactor (16).

3. 3. The method of claim 2, wherein after the reduction in the flow rate of the fluid flow (42), the fluid flow (42) has a non-zero residual flow rate in the fluidization chamber (40) after the step of discharging the fed batch (38).

4. 4. The method of claim 2 or 3, wherein the reactor (16) is rotatably mounted relative to the frame (48) at least between a first position assumed during the fluidization and a second position assumed during the unloading in which the receiving surface (46) is more inclined relative to the frame (48) than in the first position, and wherein the unloading step includes displacing at least 90% by weight of the fed batch (38) by gravity along the receiving surface (46) toward the outside of the fluidization chamber (40).

5. 2. The method of claim 1, wherein modifying the fluid flow (42) comprises increasing the flow rate of the fluid flow (42), and wherein pumping comprises discharging at least 90% by mass of the fluidized bed (18) out of the fluidization chamber (40) due to the increase in flow rate.

6. The reactor (16) - an inlet (52) for the feeding, the inlet (52) being opened for the feeding and then closed after the feeding; an outlet (54) for the discharge of at least 90% by weight of the fed batch (38), the outlet (54) being opened for the discharge and then closed after the discharge; a shell (50) defining 6. The method according to any one of claims 1 to 5.

7. 7. The method of claim 1, wherein the reactor (16) defines at least one circuit (56) forming a loop for the fluid flow (42), and the reactor (16) includes at least one blower (58) for directing the fluid flow (42) into the circuit (56).

8. The method according to any one of claims 1 to 7, wherein the fluid stream (42) is at a temperature comprised between 45°C and 75°C.

9. 9. The method according to claim 1, wherein the fluidization is obtained under predetermined conditions, the granules of the fed batch (38) being maintained in the form of the fluidized bed (18) for a predetermined period of time, and the granules of the first material being charged with more than 90% of the maximum charge obtainable under the predetermined conditions.

10. An apparatus (10) for separating a mixture (12) comprising granules of at least a first material and a second material in batches, the apparatus comprising: a reactor (16) defining a fluidization chamber (40) intended to receive one of the batches (38) to obtain an inflow batch (38), the reactor (16) being suitable for creating a fluidized bed (18) in the fluidization chamber (40), the granules of the inflow batch (38) being initially stationary in the fluidization chamber (40), the reactor (16) being suitable for generating at least one ascending fluid flow (42) passing through the inflow batch (38) and suspending at least a small portion of the granules of the inflow batch (38) to obtain the fluidized bed (18), the fluidized bed (18) being electrically charged by triboelectric effect, the reactor (16) being suitable for modifying the fluid flow (42) and for pumping at least 90% by weight of the inflow batch (38) out of the fluidization chamber (40) to obtain an outflow batch (44); a separation unit (20) suitable for creating at least one or more electric fields, the installation (10) being suitable for introducing the discharged batch (44) into said electric fields and for separating the discharged batch (44) at least between a first mixture (14) enriched in granules of the first material and a second mixture (15) enriched in granules of the second material; and Including, equipment (10).

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