PROCESS FOR DUST REMOVAL FROM FIBERS USING A DOUBLE-WALLED CYCLONIC PURIFIER

Abstract

The present invention relates to a dust removal method for treating a mixture (1) containing fibers (2) and dust (3) in order to collect a so-called "purified product" (4) which has a fiber (2) content higher than that of the mixture (1), during which a cyclonic separator (5) is used which comprises a first chamber (10) connected to a first collector (30), a second chamber (20) connected to a second collector (40), and a grid (16) which separates the second chamber from the first chamber, and during which a gaseous flow containing the mixture (1) is injected into the first chamber (10), so as to generate a swirling flow (F1) of gas, fibers (2) and dust (3), so that the dust (3) is ejected by centrifugal force through the grid (16) to enter the second chamber (20), from where said dust (3) falls into the second collector (40),while the fibers (2) which cannot pass through the grid (16) remain contained in said first chamber (10) and fall into the first collector (30). Figure for the abstract: Fig 1,

Description

Title of the invention: METHOD FOR DUST REMOVAL FROM FIBERS USING A DOUBLE-WALLED CYCLONIC PURIFIER

[0001] The present invention relates to the general field of processes intended to separate the different components of a mixture containing fibers on the one hand, and dust containing foreign bodies on the other hand, and this in particular with a view to recycling the material constituting said fibers.

[0002] The invention finds more particular application in the treatment of mixtures which are obtained from the grinding of pneumatic tires and which contain textile fibers, in particular polyethylene terephthalate, and dusts containing granules of rubber-based material.

[0003] Separation processes are already known according to which the components of the mixture are given electrostatic charges, for example by tribocharging, the sign of which is different depending on whether it is a fibre or a granule, and then the fibres are separated from the granules by passing the mixture thus charged through an electric field formed between two electrodes, each of which selectively attracts a type of component depending on the polarity of said component.

[0004] However, it is sometimes difficult to efficiently process large quantities of mixture in a limited time using known methods, especially when the aim is to obtain fibers with a high degree of purity, i.e. a very low impurity content, which sometimes requires several successive passes of the same mixture through the installation, each new pass improving the fiber content, and therefore the quality, of the product obtained from the mixture.

[0005] The objects assigned to the invention therefore aim to propose a method which makes it possible to improve the quality of a fiber-based product extracted from a mixture where the fibers are initially mixed with impurities, in particular small-sized impurities.

[0006] The objects assigned to the invention are achieved by means of a dust removal process intended to treat a mixture containing fibers and dust in order to collect a product called "purified product" which has a fiber content higher than that of the mixture and a dust content lower than that of the mixture, said process being characterized in that a cyclonic separator is provided which comprises: - a first chamber which extends along a central axis, which is delimited laterally by a first wall which surrounds the central axis, and into which opens a intake duct oriented in a direction tangential to said first wall, - a second chamber which is concentric with the first chamber and delimited by a second wall which surrounds the central axis, at a radially external distance from the first wall relative to the central axis, - a first collector connected to a low point of the first chamber, and intended to collect the purified product, - a second collector, separate from the first collector, and connected to a low point of the second chamber, in that the first wall which separates the second chamber from the first chamber is pierced with passage orifices putting the second chamber in communication with the first chamber, so as to form a grid, and in that a gaseous flow containing the mixture is injected into the first chamber through the inlet duct, so as to generate inside the first chamber, around the central axis, a swirling flow of gas, fibers and dust, so that the dust is ejected by centrifugal force through the grid to enter the second chamber, from where said dust falls into the second collector, while the fibers which cannot pass through the grid remain contained in said first chamber and fall into the first collector.

[0007] Advantageously, the invention makes it possible, by means of a simple, compact device, capable of handling a large flow rate of mixture, to rid the fibers of a large part, or even all, of the dust contained in the mixture, and in particular of the very small granules, for example rubber granules, which constitute all or part of said dust.

[0008] Other objects, characteristics and advantages of the invention will appear in more detail on reading the description which follows, as well as with the aid of the appended drawings, provided for purely illustrative and non-limiting purposes, among which:

[0009] [Fig.l] illustrates, in a front view in section in a vertical plane, the implementation of a method according to the invention, by means of a cyclonic separator.

[0010] [Fig.2] illustrates, in a perspective view with material cut away along a vertical section plane, the cyclonic separator of [Fig.l].

[0011] [Fig. 3] is a view of the section of the upper part of the cyclonic separator of figures 1 and 2, in a horizontal plane, normal to the central axis of the cyclonic separator.

[0012] The present invention relates to a dust removal method intended to treat a mixture 1 containing fibers 2 and dust 3 in order to collect a product called “purified product” 4 which has a fiber content 2 greater than the fiber content of the mixture 1 and a dust content 3 lower than the dust content of the mixture 1.

[0013] The content of a component 2, 3 considered, whether it is fibers 2 or dust 3, in a given quantity of mixture 1, or respectively in a given quantity of purified product, can be expressed by the ratio between the weight of the component considered and the total weight of the mixture, respectively by the ratio between the weight of the component considered and the total weight of the purified product.

[0014] The fibers 2 will have a thin and elongated shape, preferably substantially cylindrical.

[0015] At least a portion, preferably the majority of said fibers 2 present in the mixture 1 (i.e. more than 50% of the total number of fibers present), and more preferably all (100% of the total number of fibers present) of said fibers 2 which are present in the mixture 1 will have a length of between 1 mm and 10 mm, while the largest of their transverse dimensions, i.e. the largest of the dimensions considered perpendicular to their length, i.e. typically the diameter in the case of a cylindrical fiber, will be between 10 μm and 0.5 mm.

[0016] The method according to the invention is preferably designed to be able to separate and recover (at least) fibers of such dimensions, in the purified product 4.

[0017] More preferably, the fibers 2 will have a dimension, called length, which is clearly greater than the other two dimensions, called transverse dimensions, and more particularly will have a length at least 5 times, preferably at least 10 times, at least 20 times, or even at least 50 times or even 100 times greater than the largest of these two transverse dimensions, that is to say, typically, in the case of a fiber 2 of cylindrical shape, a length at least 5 times, preferably at least 10 times, at least 20 times, or even at least 50 times or even 100 times greater than the diameter of the fiber 2 concerned.

[0018] The fibers 2 may be made from a natural or synthetic textile material, and more preferably from a polymer or a combination of polymers from (non-exhaustive list): polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), nylon (PA).

[0019] The dusts 3 will preferably contain granules, in particular granules formed from an elastomeric material, preferably based on rubber.

[0020] These granules may have an equivalent diameter of less than 500 μm, and a form factor of between 1 and 2.

[0021] By “equivalent diameter”, we mean the diameter that a fictitious sphere would have which would occupy the same volume as the volume occupied by the granule 3 considered.

[0022] By "form factor" we mean the ratio between on the one hand the maximum Féret diameter, that is to say the maximum distance, observable for the granule considered, between two straight lines which are parallel to each other and tangent respectively to sides opposites of a planar projection of said granule considered, and on the other hand the minimum Féret diameter, that is to say the minimum distance, observable for the granule considered, between two straight lines which are parallel to each other and tangent respectively to opposite sides of said planar projection of said granule considered. This form factor makes it possible to give a good indication of the slenderness of the granules. As an indication, it is recalled that a sphere has a form factor equal to 1, and that a cube has a form factor equal to the square root of 2.

[0023] According to the method which is the subject of the invention, a cyclonic separator 5 is provided which comprises: - a first chamber 10 which extends along a central axis Z5, which is delimited laterally by a first wall 11 which surrounds the central axis Z5, and into which opens an intake duct 12 which is oriented in a direction tangential to said first wall 11, - a second chamber 20 which is concentric with the first chamber 10 and delimited by a second wall 21 which surrounds the central axis Z5, at a radially external distance from the first wall 11 relative to the central axis Z5; the second wall 21, solid, thus preferably forms the external wall of the cyclonic separator 5; - a first collector 30 connected to a low point 10B of the first chamber 10, and intended to collect the purified product 4, - a second collector 40, separated from the first collector 30, and connected to a low point 20B of the second chamber 20.

[0024] The first wall 11 advantageously extends over the entire height of the first chamber 10, considered along the central axis Z5, and more particularly over the entire height range common to the first chamber 10 and to the second chamber 20, so that the fibers 2 cannot go around said first wall 11 to end up in the second chamber 20.

[0025] The cyclonic separator 5 also comprises an exhaust duct 13 which opens into the first chamber 20, at a distance from the first wall 21. Said exhaust duct 13 may be centered on the central axis Z5.

[0026] Preferably, the central axis Z5 extends substantially or even exactly vertically, forming with the vertical an angle of inclination less than or equal to 30 degrees, 20 degrees, 10 degrees, 5 degrees, or even preferably a zero angle. This advantageously allows the cyclonic separator 5 to use the force of gravity so that it contributes to separating the components of the mixture 1.

[0027] The first wall 11 which separates the second chamber 20 from the first chamber 10 is pierced with passage orifices 15 putting the second chamber 20 into communication with the first chamber 10, so that said first wall 11 forms a grid 16.

[0028] As will be seen below, such a grid 16 will have the role of stopping the fibers 2 to retain them in the first chamber 10, while allowing the dust 3 to pass into the second chamber 20.

[0029] In accordance with the method according to the invention, a gas flow containing the mixture 1 is injected into the first chamber 10, through the intake duct 12, so as to generate inside the first chamber 10, around the central axis Z5, a swirling flow F1 of gas, fibers 2 and dust 3, as can be seen in FIGS. 1 and 3, so that the dust 3 is ejected by centrifugal force through the grid 16 to enter the second chamber 20, from where said dust 3 falls into the second collector 40, while the fibers 2 which cannot pass through the grid 16 remain contained in said first chamber 10 and fall into the first collector 30.

[0030] The fibers 2, driven by the swirling flow F1, and by the resulting centrifugal force, rub against the grid 16, which slows them down, and allows them to fall by gravity into the first collector 30, where said fibers 2, freed from at least part or even all of the dust 3, are thus concentrated into a purified product 4, as can be seen in [Fig.l].

[0031] At the same time, the dust 3 which has passed through the grid 16 finds itself trapped in the second chamber 20 and falls by gravity into the second collector 40.

[0032] The gas, freed from fibers 2 and dust 3, leaves the first chamber 10 via the exhaust duct 13.

[0033] Preferably, the access orifice of said exhaust duct 13 is located substantially in the center of the first chamber 20 relative to the central axis Z5, and preferably in an altitude range, considered along the central axis Z5, which is strictly between, and at a distance from, the altitude range occupied by the orifice of the intake duct 12 on the one hand, located above the opening of the exhaust duct 13, and the altitude range occupied by the first collector 30, located below the opening of the exhaust duct 13. This allows the exhaust duct 13 to capture the gas, avoiding sucking in the fibers 2 or the dust 3.

[0034] The exhaust duct 13 is further preferably oriented upwards in the direction of circulation of the gas through said duct, which facilitates a return, by gravity, of any components of the mixture 1 which would be captured by the exhaust duct 13.

[0035] It will be noted that, as much as the first wall 11, forming the grid 16, is permeable to gas and dust 3, the second wall 21 is advantageously full and impermeable to the gas used, so that said gas does not escape through the second chamber 20.

[0036] The gas stream is preferably a stream of nitrogen or air.

[0037] It will be noted in this respect that, more generally, the method according to the invention is advantageous preferably a dry process, which does not use liquid, nor in particular solvent, and which uses a flow of dry gas, preferably a flow of air or nitrogen.

[0038] Preferably, the mesh of the grid 16 is between 50 micrometers and 500 micrometers.

[0039] Such a mesh will advantageously allow the grid 16 to offer good selectivity, by retaining almost all or even all of the fibers 2 while allowing the fine dust 3 to pass through.

[0040] It will be noted in this respect that the size of the passage orifices 15, and therefore the mesh of the grid 16, have been deliberately exaggerated in figures 1 and 2 for a better understanding of the drawings.

[0041] Preferably, the first wall 11 which laterally delimits the first chamber 10 has, as can be seen in FIGS. 1 and 2, a truncated cone shape which tapers downwards.

[0042] Thus, the section of the first chamber 10, and more particularly the diameter of the first chamber 10, decreases as one approaches the low point 10B of said first chamber 10, thus converging towards the first collector 30.

[0043] The first chamber 10 will thus have a funnel shape, the neck of which forms the low point 10B.

[0044] Likewise, preferably, the second wall 21 which laterally delimits the second chamber 20 also has a truncated cone shape which narrows downwards, here therefore a diameter which decreases as one approaches the second collector 40.

[0045] The reduction in the diameter of the section of the first chamber 10 and / or of the second chamber 20 makes it possible to maintain a sufficient friction force against the walls 11, 21 to gradually reduce the speed of the mixture in the direction of their low point 10B, 20B to a speed sufficiently lower than that of the gas flow so that the components of the mixture 1 (fibers 2 and dust 3) fall into the collectors 30, 40.

[0046] Preferably, the radial distance, that is to say considered perpendicular to the central axis Z5, which separates the first wall 11 from the second wall 21, and therefore the radial thickness of the second annular chamber 20 which surrounds the first chamber 10, is constant over the height range of the frustoconical shape, and therefore preferably over the height range common to the first and second chambers 10, 20. Preferably, this distance represents less than 10% of the diameter of the frustoconical shape.

[0047] Preferably, as seen in Figures 1 and 2, the second collector 40 extends in a ring around a discharge conduit 41, preferably cylindrical with a circular base, which extends along the central axis Z5, preferably being centered on said central axis Z5, to connect the low point 10B of the first chamber 10 to the first collector 30.

[0048] Advantageously, this will make it possible to produce a particularly compact cyclonic separator 5, the first collector 30 being located vertically above the second collector 40, below the latter, and preferably fitting into the same cylindrical envelope, here with a circular base and centered on the central axis Z5, the two collectors 30, 40 therefore occupying the same projected surface in the horizontal plane. Such a configuration also offers the advantage of simplicity, with few mechanical parts being used, and therefore robustness and low cost.

[0049] It may be advantageous, in order to avoid possible tribocharging resulting in an accumulation of electrostatic charges which may attract the fibres 2 and result in clogging, to provide an electrical coupling of one or more metallic elements of the cyclonic separator 5 to a charge evacuation connection, and for example to earth.

Claims

1.

2.

3. Claims Dust removal method intended to treat a mixture (1) containing fibers (2) and dust (3) in order to collect a product called "purified product" (4) which has a fiber content (2) higher than that of the mixture (1) and a dust content (3) lower than that of the mixture (1), said method being characterized in that a cyclonic separator (5) is provided which comprises: - a first chamber (10) which extends along a central axis (Z5), which is delimited laterally by a first wall (11) which surrounds the central axis (Z5), and into which opens an intake duct (12) oriented in a direction tangential to said first wall (11), - a second chamber (20) which is concentric with the first chamber (10) and delimited by a second wall (21) which surrounds the central axis (Z5), at a radially external distance from the first wall (11) relative to the central axis (Z5), - a first collector (30) connected to a low point (10B) of the first chamber (10), and intended to collect the purified product (4), - a second collector (30), separate from the first collector (30), and connected to a low point (20B) of the second chamber (20), in that the first wall (11) which separates the second chamber (20) from the first chamber (10) is pierced with passage orifices (15) putting the second chamber (20) into communication with the first chamber (10), so as to form a grid (16), and in that a gas flow containing the mixture (1) is injected into the first chamber (10), through the intake duct (12), so as to generate inside the first chamber (10), around the central axis (Z5), a swirling flow (Fl) of gas, fibers (2) and dust (3), so that the dust (3) is ejected by centrifugal force through the grid (16) to enter the second chamber (20),from which said dust (3) falls into the second collector (40), while the fibers (2) which cannot pass through the grid (16) remain contained in said first chamber (10) and fall into the first collector (30)., Method according to claim 1 characterized in that the mesh of the grid (16) is between 50 micrometers and 500 micrometers. Method according to claim 1 or 2 characterized in that the first wall (11) which laterally delimits the first chamber (10), and preferably also the second wall (21) which laterally delimits the second chamber (22), has a truncated cone shape which tapers downwards.

4. Method according to one of the preceding claims, characterized in that the second collector (40) extends in a ring around a discharge conduit (41), preferably cylindrical with a circular base, which extends along the central axis (Z5) to connect the low point (10B) of the first chamber (10) to the first collector (30).

5. Method according to one of the preceding claims, characterized in that the radial distance which separates the first wall (11) from the second wall (21) is less than 10% of the diameter of the truncated cone shape over the height range of the truncated cone shape, and therefore preferably over the height range common to the first chamber (10) and to the second chamber (20).

6. Method according to one of the preceding claims, characterized in that the radial distance which separates the first wall (11) from the second wall (21) is constant over the height range of the truncated cone shape, and therefore preferably over the height range common to the first chamber (10) and to the second chamber (20).

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