Centrifugal dissolver

Abstract

The invention relates to an arrangement (1), comprising a centrifuge (10) having a vertical axis of rotation (X) and a container (20) which has a bottom (21) and a side wall (22) and is suitable for containing a liquid (90), and which also has an outlet (32) for the liquid. The centrifuge (10) comprises a mixer (50) which can be inserted into the container (20) in an operating position in which, during rotation of the centrifuge (10), a portion (51) of the mixer (50) is located in the ring (91) of liquid (90) that forms along the side wall (22).

Description

Description Title: Centrifugal Dissolver

[0001] The field of the invention is chemical engineering, and more specifically the separation between a solid and a liquid and the dissolution of a solid in a liquid.

[0002] Dissolution is the physicochemical process by which a solid incorporated into a solvent forms, after dissolution, a homogeneous mixture called a solution, containing the dissolved solid (called the solute). The kinetics of dissolution, and therefore the time required for the solid to dissolve, depend in particular on the nature of the solid and the solvent, the size of the solid particles, the surface area of ​​contact between the solid and the solvent, and the temperature of the solvent.

[0003] In certain situations, after a predetermined dissolution time (i.e., the time elapsed since the solid was introduced into the solvent), the goal is to extract (separate) from the solution the undissolved solid particles, known as undissolved solids. These undissolved solids consist of particles from the solid whose initial size was too large to dissolve within this predetermined time and / or particles whose physicochemical nature prevents them from dissolving in the solvent. This separation between the undissolved solids and the solution can be achieved, for example, by decantation. In decantation, the undissolved solids naturally settle (by gravity alone) to the bottom of the container holding the solution and can then be separated from it (for example, using a filter). The solution is then removed from the container without these undissolved solids.This removed solution, which no longer contains any indissoluble particles but only dissolved particles, is called the clarified solution.

[0004] When high separation performance is required, a centrifuge is used. A centrifuge is a liquid / solid separator in which a container spins at high speed around an axis of rotation. Under the influence of centrifugal force, the liquid in the container collects in the outermost radial portion of the container, near the side wall, forming a ring of liquid. The particles in this ring of liquid accumulate in the region closest to the side wall under the influence of this same force. centrifugal force. The portion of the liquid outside this region can then be removed from the container. Thus, a centrifuge allows for the retention of solid particles larger than a certain size threshold, known as the "cutoff threshold," and insoluble particles within the container. The goal is to ensure that the portion of liquid removed from the container does not contain any particles larger than this cutoff threshold. In other words, the aim is for the liquid removed from the container to contain only a clarified solution (liquid in which all particles are dissolved) and particles smaller than the cutoff threshold. This cutoff threshold depends, in particular, on the particle density, the physicochemical properties of the solvent (especially its density and viscosity), the residence time of the particles in the solvent, and the centrifuge's rotational speed.The centrifuge is used in particular when the cut-off threshold is low (e.g. 1 pm (micron)), because decantation does not allow for effective separation between particles below and above the cut-off threshold.

[0005] The present invention relates to a device comprising a centrifuge with a vertical axis of rotation and which includes a container with a bottom and a side wall and suitable for containing a liquid, and with an outlet for this liquid.

[0006] During operation, the centrifuge vessel rotates at a high speed. The liquid introduced into the vessel, under the influence of centrifugal force, moves towards the side wall of the vessel, forming a ring that extends the full height of the vessel and has a radial thickness. Particles are continuously introduced into the vessel as a suspension or as a solid and circulate within this liquid ring. The dissolution process begins as soon as the solvent contacts the particles. Liquid (solvent) is continuously added to the vessel to continue the dissolution process. In practice, the particles are observed to agglomerate, as expected, against the side wall of the vessel, forming a layer. However, it is observed that the solvent circulates less easily within this layer, and consequently, the dissolution of the particles within this layer is slowed.Furthermore, the liquid in this layer tends not to renew itself because it has a slightly higher density than the liquid introduced gradually. measurement in the container. Indeed, the liquid in this layer is densified by the dissolution of the particles present there. As a result, the quantity of dissolved particles is too low, particularly particles whose initial size is above the cutoff threshold, whereas the goal is for a majority of these particles to be dissolved. Description of the invention

[0007] The present invention aims to remedy these drawbacks.

[0008] The invention aims to provide a device that allows the separation, in the most efficient way possible and in the shortest possible time, of a liquid containing particles into, on the one hand, a clarified solution (in which all the particles are dissolved) and particles whose size is less than a fixed cut-off threshold, and on the other hand, particles insoluble by their physicochemical nature and particles whose size at the end of this time is greater than this cut-off threshold, while allowing the dissolution within this time of the majority of the particles whose initial size is greater than this cut-off threshold.

[0009] This goal is achieved thanks to the fact that the centrifuge includes a mixer which is suitable for insertion into the container in an operating position in which, during the rotation of the centrifuge, a portion of the mixer is located in the ring of liquid which forms along the side wall.

[0010] This device disrupts the flow of liquid in this part of the container, causing particles to circulate throughout the entire thickness of the liquid ring. This promotes the dissolution of particles of all sizes. Furthermore, the device creates a region of liquid where insoluble particles and / or particles larger than the cutoff threshold are collected and can be easily separated from the rest of the solution. In addition, the device is compact, making it easy to use.

[0011] For example, the portion of the mixer, in its operating position, presents in a radial half-plane of the container that passes through the mixer, a surface area that is less than 10% of the surface area of ​​the liquid in the radial half-plane.

[0012] Thus, the mixer disturbs the flow of liquid less in the ring, and as a result, the ejection of liquid out of the container during its rotation is minimized or prevented.

[0013] For example, the mixer has a blade and the portion of the mixer includes the distal part of the blade.

[0014] For example, the outlet is located opposite the portion of the mixer in its operating position, according to the direction of the axis of rotation.

[0015] Thus, the dissolution of particles by the renewal of the diffusion layer is improved.

[0016] For example, the outlet is located at the top of the container and the mixer portion is located near the bottom of the container in its operating position.

[0017] For example, the device also includes a mechanism for changing the temperature of the liquid during the rotation of the centrifuge.

[0018] The invention also relates to a method of separation between a liquid and solid particles located in that liquid.

[0019] According to the invention, the process comprises the following steps (a) A centrifuge is provided with a vertical axis of rotation and which includes a container with a bottom and a side wall and suitable for holding a liquid and with an outlet for the liquid, and which includes a mixer which is inserted into the container; (b) The container is partially filled with a liquid; (c) The centrifuge container is rotated into an operating position in which a ring of liquid forms along the side wall and a portion of the mixer is located in the ring; (d) Liquid is introduced into the container at a fixed rate; (e) Solid particles are introduced into the container; (f) The centrifuge container is kept rotating for a certain period of time; (g) The liquid containing any dissolved particles is discharged through the outlet.

[0020] For example, from step (e) the gas or gases released by the dissolution of the particles are removed.

[0021] For example, all the particles are soluble in the liquid.

[0022] For example, none of the particles are soluble in the liquid.

[0023] The invention will be better understood and its advantages will become more apparent upon reading the following detailed description of embodiments shown by way of non-limiting examples. The description refers to the accompanying drawings in which:

[0024] [Fig. 1] Figure 1 is a perspective view of a container of the device according to the invention.

[0025] [Fig. 2] Figure 2 is a radial plane cross-sectional view of the container in Figure 1.

[0026] [Fig. 3] Figure 3 is a schematic illustration of the device according to the invention.

[0027] [Fig. 4] Figure 4 is a perspective view of the mixer of the device according to the invention.

[0028] [Fig. 5] Figure 5 is a schematic illustration of another embodiment of the device according to the invention. Detailed description of the invention

[0029] The device 1 according to the invention comprises a centrifuge 10, a liquid / solid separator including a container (also called a bowl) 20 that rotates at high speed eu around an axis of rotation X, which is generally vertical. The rotation speed eu is, for example, between 50 and 3500 revolutions per minute. For example, the rotation speed eu is constant during the operation of the centrifuge 10 (except, of course, during the start-up and shutdown phases). In practice, for a given diameter of container 20, the rotation speed is high enough to form a ring of liquid against the lateral wall 22 of the container 20 (see below). The terms "upper" and "lower" are defined with respect to this upwardly oriented axis of rotation X. The terms "internal" and "external" refer to an element or a place radially closer or further respectively from this axis of rotation X. Such a centrifuge 10 is shown in perspective in figure 1.

[0030] The container 20 (bowl) comprises a base 21 and a side wall 22. The base 21 joins the lower edge of the side wall 22. The container 20 has a shape of revolution about the axis of rotation X. For example, the side wall 22 is a cylinder. The container 20 has an opening 23, which is located at the upper edge of the side wall 22. For example, the opening 23 is the entire circular space enclosed by this upper edge. Alternatively, as shown in Figure 1, the side wall 22 extends radially inward by means of a rim 24 at its upper edge.

[0031] The container 20 is intended to hold a liquid 90 which is to be centrifuged. Under the effect of the centrifugal force generated by the high-speed rotation of the container 20, the liquid 90 present in the container 20 collects in the outermost radial part of the container 20 to form a ring 91. The ring 91 is formed near and along the side wall 22 and extends over a distance D measured radially from the side wall 22, this distance D being the thickness of the ring 91. In addition, the particles 95 present in the liquid 90 accumulate against the side wall 22 under the effect of this same centrifugal force. Thus, these particles 95 and this liquid 90 can then easily be separated from each other, either by extraction of the liquid 90, or by recovery of the particles 95. As illustrated in figures 1 to 3, the ring 91 is covered by the rim 24 which helps to keep the liquid 90 in the container 20.

[0032] The container 20 includes an inlet 31 through which the liquid is introduced into the container. For example, the inlet 31 is a tube that passes through the opening 23. The container 20 includes an outlet 32 ​​through which the liquid is able to exit the container 20. Figure 2 is a radial cross-sectional view of the centrifuge 10 in operation.

[0033] The container 20 operates at room temperature. Optionally, the device 1 includes a mechanism for modifying the temperature of the liquid 90 contained in the container 20. This mechanism is a heating and / or cooling mechanism for the liquid 90. For example, this mechanism modifies the temperature of the container 20. For example, this mechanism is a conduit embedded in the wall of the container 20 through which a heating and / or cooling fluid circulates. For example, this mechanism is a heating element integrated into the wall of the container 20.

[0034] The centrifuge 10 includes a mixer 50 which is inserted into the container 20 in an operating position. This operating position is achieved when the centrifuge 10 is running, i.e., rotating. The mixer 50 includes a rod 53 by means of which it is inserted and held in the container 20.

[0035] The operation of device 1 according to the invention is now described, with reference to figure 3. The associated process allows the separation between a liquid 90 and solid particles 95, and allows the dissolution of a part of the solid particles 95 in the liquid 90.

[0036] First, a centrifuge 10, as described above, is provided (step (a)). Then, container 20 is partially filled with a liquid 90 (step (b)), and container 20 is rotated (the centrifuge 10 is then in operation), in which a ring 91 of the liquid 90 forms against the side wall 22 (step (c)). The liquid 90 is supplied through the inlet 31, which is connected to a first container 81 containing this liquid 90.

[0037] Liquid 90 is introduced into container 20 at a fixed flow rate (step (d)). This flow rate depends, in particular, on the liquid 90 (for example, this liquid is a solvent) and the nature of the particles 95. This introduction allows the container to be supplied with liquid in parallel with the introduction of solid particles 95 into container 20 (step (e)) at a controlled flow rate. The particles 95 are supplied via a second container 82 which is connected to container 20. Step (c) can take place before, during, or after steps (d) and (e). For example, steps (d) and (e) take place at least partially simultaneously. In all cases, the particles 95 and the liquid 90 mix. Figure 2 illustrates the ring 91 and the particles 95 which tend, under the effect of rotation, to accumulate in the region of the ring 91 which is closest to the lateral wall 22 to form a layer 96.

[0038] When the centrifuge 10 is running, a portion 51 of the mixer 50 is located within the ring 91. This situation is illustrated in Figures 2 and 3. Thus, the mixer 50 creates turbulence in a part of the ring 91. This turbulence helps to dislodge the particles 95 from the layer 96 where they tend to accumulate under the effect of centrifugal force. This results in a distribution of the particles 95 throughout the thickness of the ring 91, and therefore an exposure of the particles 95 to the virgin liquid (i.e., without particles 95) that has just been introduced into the container 20 through the inlet 31. In this way, the particles 95 are more easily dissolved. The container 20 is kept rotating for a certain time t (step (f)) and this rotation is stopped after this time t. Steps (d) and (e) therefore take place during step (f). This duration t depends on various criteria.The aim is for the liquid exiting container 30 through outlet 32 ​​to consist solely of a clarified solution (in which all particles are dissolved) and particles 95 whose size is less than a critical dimension (which corresponds to the cutoff threshold). For example, the particle size distribution of the solution exiting container 20 through outlet 32 ​​is determined (see step (g) below), and the rotation of container 20 is stopped when a majority of the soluble particles 95 whose size is less than the critical dimension are dissolved. Ideally, all the soluble particles 95 whose size is less than this critical dimension are dissolved after this time t. The size of a particle 95 is defined as its maximum dimension (this dimension is the diameter in the case of a spherical particle).Alternatively, the container (bowl) 20 is kept rotating until there are no more solid particles 95 to be introduced into the bowl 20, or until there is no more liquid (e.g., solvent) to be introduced into the bowl 20. Thus, it is understood that the duration t of rotation, while finite, is in some cases not known in advance and therefore cannot be fixed. The expression "a certain duration" covers all cases of use of the centrifuge according to the invention and cannot be further specified without restricting the scope of the invention in a detrimental manner. In tests carried out by the inventors, compared to the prior art situation where the centrifuge 10 does not include a mixer 50, a greater proportion of dissolved particles 95 was obtained for the same residence time of these particles 95 in the bowl 20. In particular, more particles 95 were dissolved whose size was greater than the critical dimension of and which tended to remain in the 96 layer and therefore never be dissolved.

[0039] A radial half-plane P is defined, extending radially from the axis of rotation X, which forms its boundary, and passing through the mixer 50. The portion 51 of the mixer (50), in its operating position, presents a surface area in this radial half-plane P that is less than a percentage Y of the surface area of ​​the ring 91 in the radial half-plane P. Indeed, tests carried out by the inventors have shown that the mixer 50 must, during operation, sufficiently disturb the flow of the liquid 90 in the ring 91, but not so much as to prevent the liquid 90 from being expelled from the container 20 through the top opening 23. For example, this percentage Y is equal to 10%. For example, this percentage Y is equal to 5%. For example, this percentage Y is equal to 1%.

[0040] The mixer 50 can have various geometries. For example, as illustrated in Figure 4, the mixer 50 has a blade 52 located at the end of the shaft 53. Portion 51 of the mixer 50 comprises the distal part of the blade 52. This portion 51 lies to the right of a plane shown in dashed lines. In the operating position, the blade 52 extends in a plane parallel to the bottom 21 and has a thickness measured in the radial half-plane P. The surface area of ​​portion 51 in the radial half-plane P is then the product of the thickness of the blade 52 and the length of the distal part of the blade 52. For example, portion 51 of the mixer 50 consists of the entire blade 52. The surface area of ​​portion 51 in the radial half-plane P is then the product of the thickness of the blade 52 and the length of the blade 52.

[0041] The solution, comprising liquid 90, particles 95 dissolved in this liquid 90, and possibly undissolved particles 95, exits container 20 through outlet 32 ​​(step (g)). For example, outlet 32 ​​is located at opening 23. This solution flows into a casing 60 surrounding container 20, which is in fluidic communication with a third container 83. As shown below, thanks to the mixer 50, the particles 95 dissolve more rapidly, so that the third container 83 does not contain any particles 95 larger than the critical size. The possible particles 95 which have not been dissolved before the stop of the rotation of the bowl 20, either because their initial size was too large, or because they are not chemically soluble in the liquid 90, remain in the container 20. After step (g), the contents of the container 20 are recovered (step (h)).

[0042] Advantageously, the device 1 is configured such that the outlet 32 ​​is located opposite the portion 51 of the mixer 50 in its operating position, along the direction of the axis of rotation X. During their tests, the inventors realized that, in this configuration, the solution exiting the container 20 through the outlet 32 ​​contains a minimum of undissolved particles 95. For example, the outlet 32 ​​is located at the top of the container 20 and is then formed by the opening 23, and the portion 51 of the mixer 50 is located near the bottom 21 of the container 20 in its operating position. Alternatively, the outlet 32 ​​is located near the bottom 21 of the container 20 and the portion 51 of the mixer 50 is located in the upper region of the container 20, just below the opening 23.

[0043] Advantageously, in addition to the first 81, second 82, and third 83 containers, the device 1 includes a fourth container 84 containing a solution that is poured into container 20 after step (g) in order to stop the dissolution reaction of the particles 95. Thus, observation and measurement of the remaining particles 95 in the bowl is possible. For example, the liquid remaining in container 20 is poured into a fifth container 85 (step (h)).

[0044] In some cases, one or more gases are released by the dissolution of the particles 95 in the liquid 90. These gases are the result of the chemical reaction between the particles 95 and the liquid 90. It is necessary to remove these gases. Device 1 then includes a gas removal mechanism, which operates from step (e) and also possibly in step (f), i.e., for the entire duration of the rotation of the bowl 20. For example, this removal mechanism 70 includes a condenser 71 that cools these gases to produce a condensate and a bubbler 72 that then traps this condensate. The final product of this treatment is then stored or released into the atmosphere. Figure 3 shows this removal mechanism 70 in the application example described above. In this case, the reaction between the Copper and acid produce NOx. Bubbler 72 contains sodium hydroxide, which reacts with the condensed NOx.

[0045] Depending on the nature of the particles 95, the process described above, with reference to Figure 3, varies. In the first specific case, where all the particles 95 are soluble, the process is a pure dissolution process. In the second specific case, where all the particles 95 are chemically insoluble in the liquid 90, the process is a pure liquid / solid separation process. In yet another specific case, during the dissolution of the particles 95 in the liquid 90, which is a solvent, one or more chemical species are formed through chemical reactions between these particles 95 and the solvent 90. These species may be liquids or solid particles.

[0046] Examples of implementation of the invention by the inventors are described below.

[0047] A first example is a pure dissolution. Liquid 90 is an acid introduced into container 20 (with a maximum capacity of 5 liters) at a flow rate of 2 liters / hour. Particles 95 are copper with a particle size ranging from 10 µm to 50 µm (particle size refers to the size of particles 95). The rotational speed w of container 20 is 1000 rpm. This process is illustrated in Figure 3. At the end of the test, a sodium nitrate solution with a density greater than that of the solution in ring 91 is introduced into container 20 at a high flow rate of 100 liters / hour. Tests carried out by the inventors show, through analysis of the remaining solution in container 20, that all the particles 95 have dissolved.

[0048] A second example is a pure liquid / solid separation. Liquid 90 is water introduced into container 20 at a rate of 2 liters / hour. Particles 95 are copper particles with a particle size of less than 1 µm. Therefore, particles 95 are not soluble in liquid 90. The rotational speed w of container 20 is either 1000 rpm or 2000 rpm. This process is illustrated in Figure 5, which shows a simplified version of device 1 in Figure 3. Tests carried out by the inventors show a separation efficiency greater than 98%. This separation efficiency is defined as the ratio {[MCU(E) - M eu(S)] / MCU(E)} where MCU(E) is the mass of copper in the liquid entering container 20 (i.e., i.e. in the first container 81) and Mcu(S) is the mass of copper in the liquid at the outlet of container 20 (i.e. in the third container 83).

[0049] In certain embodiments, for example, when the particles 95 consist of a first group of insoluble particles of a first density and a second group of insoluble particles of a second density, these two densities being different, a solid residue is observed at the end of the liquid / solid separation test in the container 20, consisting of a stacking of a layer of the first particles and a layer of the second particles. Such a stacking is also observed when the particles 95 consist of a first group of insoluble particles and a second group of soluble particles, some of which have a size greater than the critical threshold. In this case, a stacking of a layer of insoluble particles and a layer of soluble particles larger than the critical threshold is observed.The process according to the invention is thus particularly useful for segregating particles, in this case by separating these particles into distinct layers according to their nature. In particular, this process is useful in the nuclear industry for reprocessing radioactive waste where it is necessary to treat a solution containing soluble particles (uranium oxides UO2, U3O8) and insoluble particles (plutonium oxide PuC and insoluble dissolution particles, called "dissolution fines," such as metals and oxides).

[0050] List of references: 1: device - 10: centrifuge - 20: container or bowl - 21: bottom of container - 22: side wall of container - 23: opening of container - 24: rim - 31: inlet - 32: outlet - 50: mixer - 51: portion of mixer - 52: mixer blade - 53: mixer shaft - 60: housing - 70: discharge mechanism - condenser 71 - 72: bubbler - 81: first container - 82: second container - 83: third container - 84: fourth container - 85: fifth container - 90: liquid - 91: liquid ring - 95: particles - 96: layer.

Claims

Demands [Claim 1] Device (1) comprising a centrifuge (10) with a vertical axis of rotation (X) and comprising a container (20) with a bottom (21) and a side wall (22) and capable of containing a liquid (90), and with an outlet (32) for said liquid, said centrifuge (10) being characterized in that it comprises a mixer (50) which is capable of being inserted into said container (20) in an operating position in which, during the rotation of said centrifuge (10), a portion (51) of said mixer (50) is located in the ring (91) of liquid (90) which forms along said side wall (22), said portion (51) of the mixer (50), in its operating position, having in a radial half-plane (P) of said container (20) which passes through said mixer (50), a surface whose area is less than 10% of the area of ​​the liquid in said radial half-plane (P). [Claim 2] Device (1) according to claim 1 wherein said mixer (50) comprises a blade (52) and wherein said portion (51) of the mixer (50) comprises the distal part of said blade (52). [Claim 3] Device (1) according to claim 1 or 2 such that said outlet (32) is located opposite said portion (51) of the mixer (50) in its operating position, along the direction of the axis of rotation (X). [Claim 4] Device (1) according to any one of claims 1 to 3 wherein said outlet (32) is located at the top of said container (20) and said portion (51) of the mixer (50) is located near the bottom (21) of said container (20) in its operating position. [Claim 5] Device (1) according to any one of claims 1 to 4 further comprising a mechanism for changing the temperature of said liquid during the rotation of said centrifuge (10). [Claim 6] A method for separating a liquid from solid particles located in that liquid, characterized in that it comprises the following steps: (a) A centrifuge (10) is provided with a vertical axis of rotation (X) and comprising a container (20) with a bottom (21) and a side wall (22) and suitable for containing a liquid (90), and with an outlet (32) for said liquid, and comprising a mixer (50) which is inserted into said container (20); (b) The said container (20) is partially filled with a liquid (90); (c) The container (20) of said centrifuge (10) is rotated into an operating position in which a ring (91) of said liquid (90) is formed along said side wall (22) and a portion (51) of said mixer (50) is located in said ring (91), said portion (51) of the mixer (50), in its operating position, presenting in a radial half-plane (P) of said container (20) which passes through said mixer (50), a surface whose area is less than 10% of the surface area of ​​the liquid in said radial half-plane (P); (d) The said liquid (90) is introduced into the said container (20) at a fixed flow rate; (e) Solid particles (95) are introduced into said container (20); (f) The container (20) of said centrifuge (10) is kept in rotation for a certain duration (t); (g) The liquid (90) containing, where applicable, the dissolved particles (95) is discharged through said outlet (32). [Claim 7] A method according to claim 6 such that from step (e) the gas or gases released by the dissolution of said particles (95) are evacuated. [Claim 8] A method according to claim 6 or 7 such that all of said particles (95) are soluble in said liquid (90). [Claim 9] A method according to claim 7 such that none of said particles (95) are soluble in said liquid (90).

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