EP2673076B1 - Expanding device for combining a liquid species and a particulate solid species - Google Patents

Description

The invention relates to a device for contacting a liquid species and a growing solid species, applicable to the treatment of industrial and urban wastewater charged with particulates and which it is desired to homogenize, and to the treatment of purification of water intended for consumption or industrial processes requiring particularly clean water.

The invention applies in particular to the treatment by flocculation of a fluid to be treated. For example, it applies to the technology of Actiflo® which is a settling system using an addition of microsand and flocculant polymer to the effluent to cause weighted flocculation, that is to say a growth flocs around a ballast constituted by microsand particles. The water is stirred by a paddle stirrer to create adhesion. Prior to treatment, a coagulant such as ferric chloride can be added to remove the colloid load.

The invention is also applicable to industrial wastewater precipitation treatment intended for recovery in the form of crystals of mineral matter such as gypsum or limestone. Homogenization of the fluid is desired, to allow a control of the particle size. In a similar way, water softening processes aimed at removing limestone therein for a specific industrial use are also based on the precipitation of limestone.

In these systems, agitation is used to ensure homogenization. It is necessary that this agitation be compatible with the growth of the aggregates of the solid species, and this despite the obstacles that constitute the side walls of the tank, against which the aggregates abut if they are driven by a speed with a significant radial component.

To meet these specifications, it is possible to choose a paddle stirrer adapted to provide a thrust that is more longitudinal than radial. In addition, it is possible to insert the paddle stirrer in a guide-flow tube whose axis is aligned with that of the paddle stirrer. The guide-flow tube ensures the compartmentalization of the tank between the inside of the guide-flow tube where the current is down, and the outside of the guide-flow tube where the current is rising. The radial component of the currents is greatly diminished, which ensures a harmonious growth of solid species aggregates that do not strike the side walls.

Thus, an optimized version of Actiflo®, called Turbomix®, is based on a single vat comprising a flow-guide tube, a stirrer in the flow-guide tube and a spider opposing the rotation of the flow coming out of the guide tube-flow, which allows a decrease in the size of the installations, energy saving and a facilitated reprocessing of the flocs. It is described in the document WO 2005/065832 .

In the various situations of bringing into contact of a liquid species and a growing solid species mentioned, with a view to improving the techniques available, a possible improvement remains the most complete possible elimination of residual shear effects in known methods. These shears, unrecognized by the prior art, have the effect of dislocating the flocs or crystals and therefore oppose the smooth running of the growth process thereof. More particularly, vortices appear in certain configurations, and they have the double disadvantage of unnecessarily dissipating energy and causing shearing in the tank.

To solve this problem, the present invention consists of a device for contacting a liquid species and a growing particulate solid species, according to claim 1.

By external transverse dimension is meant here the dimension extending from one side to the other of the outer surface in axial section (a diameter in the case of a form of revolution), and not the distance to the axis of such or such point of this surface (a ray in the aforementioned case of a form of revolution).

This device provides a homogenization of the efficient mixture with low energy consumption, and a reduction of the shear effects observed in the prior devices. The solid particles follow U-shaped trajectories with moderate curvature and rise rapidly along the side walls of the tank, and do not remain deposited in the extension of the agitator. The particulate solid species grows rapidly, and it is possible to decrease the stirring speed.

The implantation of a static obstacle in the extension of an agitator combined with a guide-flow tube was already known from the document KR 2006/0114644 which describes an instantaneous dissolution device including a lower stirrer outside the guide-flow tube combined with an enlargement of the guide-flow tube at its lower mouth, essential for creating the random movements necessary for the rapid dissolution of the introduced solid species; it is understood that, since the lower mouth of the flow-guide tube is flared, only part of the downward flow intercepts this lower stirrer while another part of this flow flows horizontally at the outlet of the tube, which causes turbulence favorable to dissolution when these two parts are telescoping; a small element arranged in the extension of the axis contributes to the flow guidance. It should be noted that since this document relates to an instantaneous dissolution device, its elements are designed so as to cause significant turbulence to promote dissolution, which goes against the invention which aims instead to preserve a phase solid growth.

We also know from the document US - 6,345,810 a ventilation device comprising an agitator in the extension of which is disposed a dome in the center of which opens an air injection channel; the agitator, whose motor prevents vertical flow along the axis to bottom, is intended to brew laterally the liquid while causing a bursting of air bubbles so as to optimize the effect of aeration. The dome has a profile whose slope with respect to the axis decreases while moving away. Since this document aims to spray incoming air bubbles, its elements are not compatible with a device to preserve a growing solid phase.

According to advantageous characteristics, the agitator and the static obstacle are shaped and / or dimensioned and / or positioned according to each other.

Thus, advantageously, the static obstacle is capped axially by the stirrer and / or the guide-flow tube when it exists; in other words, the flow being in practice downward, the agitator and / or the guide-flow tube at least descend at least by their lowest part, at the highest part of the static obstacle; the styling effect of the stirrer and / or the guide-flow tube results from the fact that their respective lower parts are in practice located at a distance from the axis whereas the highest part of the static obstacle is in central configuration .

Preferably, the static obstacle and the stirrer are at least at a point (of an axial plane) distant longitudinally by a distance less than the longitudinal dimension of the stirrer. This characteristic guarantees the minimum character of the counter-current velocity components at the axis between the agitator and the static obstacle and optimizes the synergy between the stirrer and the static obstacle to ensure a continuous transition of the trajectories of the machine. downstream flow.

According to another advantageous characteristic of the invention, the maximum value of the external transverse dimension of the static obstacle is at least equal to the maximum transverse dimension of the agitator and / or the flux guide tube when it exists. This ensures that the entire flow supplied by the agitator or the flow guide tube is intercepted by the obstacle and is progressively guided towards soft U-shaped trajectories.

According to another advantageous characteristic of the invention, the axial dimension of the static obstacle is at most equal to half the value maximum of said external transverse dimension, or at most equal to one-third of this value. This ensures that the obstacle provides flow guidance until it imposes a significant radial component.

According to another advantageous characteristic of the invention, the external surface of the static obstacle has, in any plane passing through the axis, an average inclination of at least 45 ° with respect to this axis; this contributes to the aforementioned effects; in fact, when the static obstacle has a high part of small section, possibly blunt-shaped tip, the previous feature is in practice also carried out.

According to another advantageous characteristic of the invention, the external surface of the static obstacle connects to the bottom of the tank at least approximately tangent, with an angle of at most 15 °. This helps to optimize the synergy between the static obstacle and the wall to which it is attached, in practice the bottom of the tank, in the flow guide in its U-shaped trajectories.

The slope of the external surface of the static obstacle can, in a particularly simple geometric configuration, be constant, from the top of the obstacle to the wall to which this obstacle is fixed; however, according to another advantageous characteristic, the external surface of the static obstacle comprises at least one zone which, in an axial plane, is curved with a concavity oriented away from the axis. In fact, the more the outer surface of the static obstacle is curved, the greater the effect of guiding and accompanying the flow is important.

According to an advantageous characteristic, a radius of curvature of the static obstacle, called the first radius of curvature, taken in a plane comprising the axis is between a quarter of a transverse reference dimension of the vessel and once, or a times and half said reference transverse dimension of the vessel. By reference transverse dimension is generally meant a transverse dimension of the tank volume in which the agitator extends its influence; this is in practice, for reasons of space minimization, of the minimum transverse dimension of the tank, for example one side of the bottom of this tank, when it is rectangular or square. This feature, which aims at a precise dimensioning of the static obstacle in relation to the dimensions of the base of the tank, makes it possible to minimize the counter-current speed components in the extension of the axis of the stirrer, allowing the particulate solid species to grow rapidly, and the operator to decrease the stirring speed.

According to an advantageous characteristic of the invention, the curved appearance of the external surface results from the fact that the external surface of the static obstacle comprises an axial succession of portions of constant slopes, these slopes increasing (with respect to the axis) from one portion to another while moving away from the agitator. Such a configuration may have advantages in terms of manufacturing.

According to another advantageous characteristic, the static obstacle has a generally regular shape around the axis, for example a form of revolution. This helps to obtain good axial symmetry of the curvature of the trajectories of the various fractions of the downflow. In such a case, the static obstacle comprises along its outer surface at least two ribs. These move away from the central portion of the static obstacle, radially or even both radially and circumferentially. There is preferably a rib at the corner of the base of the tank, each corner being in the extension of a rib, which makes it possible to reduce the shear phenomena by making the best use of the space of the tank. There may be more ribs than corners of the bottom of the tank.

According to another possible form of the external surface of the static obstacle, this external surface of the static obstacle has the shape of a pyramid formed of a circumferential succession of facets separated by edges. It should be remembered that the notion of pyramid implies the presence of facets, flat or curved, in any number that can be equal to 4, or even lower (3 facets) or higher (often in even numbers, such as 6 or 8). It is understood that such a configuration leads to a certain ease of manufacture. When the facets are curved, they are advantageously formed of cylinder portions in the mathematical sense of the term, that is to say portions of a surface formed by the displacement of a straight line. (parallel to the bottom of the tank) along a generator (here located in practice in a plane containing the axis). Such a configuration combines simplicity of manufacture and good flow guidance.

In a particularly advantageous manner, the bottom comprises, at least in the extension of the edges, ribs moving away transversely from the axis. It is understood that these ribs, when they are integral with the static obstacle, can contribute to the good fixing of the static obstacle at the bottom of the tank; Moreover, when these ribs extend to corners of the bottom, it is understood that these ribs may further contribute to a good position in position of the static obstacle relative to the corners of the bottom.

Preferably, the blades are twisted, that is to say that their inclination relative to the axis varies from the axis towards the ends of these blades, for example in an increasing direction. According to an alternative, the blades are folded, that is to say they comprise, separated by a fold line deviating globally from the axis (but not necessarily coplanar with this axis), two upstream and downstream portions constant slopes relative to the axis.

Whatever the particular shape of the blades, they advantageously have, at least at their ends, an angle of attack of between 35 ° and 55 ° with respect to the axis; this angle of attack is the angle of inclination of the blades near their attack, namely here near their upper edges. This contributes to a good axial flow drive.

According to another advantageous characteristic of the invention, the maximum value of the external transverse dimension of the static obstacle represents at least one-third of the smallest transverse dimension of the bottom to which this static obstacle is fixed (it is a order of magnitude, so that this condition includes a value of some 30%). This ensures a flow guiding effect on a substantial fraction of the surface area of this bottom.

According to yet another characteristic of the invention, a guide-flow tube is actually present, that is to say that the stirrer is inserted at least partially (or completely) into a guide-flow tube. When the agitator is inserted only partially into a guide-flow tube, then, according to an advantageous characteristic, it exceeds the mouth of the guide-flow tube by at least 5% and at most 60% of its dimension measured parallel to the axis, and preferably at least 15% and at most 45%. This characteristic makes it possible to limit the shearing related to the meeting of the walls of the guide-flow tube with the radial component of the currents created by the blades, which exists even if the stirrer has been carefully designed.

According to another advantageous characteristic, in a plane comprising the axis, the inner surface of the blades has a projection parallel to the external surface of the static obstacle. This characteristic makes it possible to limit the shear phenomena in the space between the obstacle and the blades. It is preferably implemented over the greatest possible distance.

According to another advantageous characteristic, in a plane comprising the axis, the outer surface of the blades has a circular projection whose radius of curvature, said second radius of curvature, is between one eighth of a reference transverse dimension of the tank and half of said reference transverse dimension of the vessel.

In general, this characteristic which aims at a dimensioning of the blades in relation to the dimensions of the base of the tank, makes it possible to limit the phenomena of shear at the end of the blade.

According to another advantageous characteristic, in a plane comprising the axis, the outer surface of the blades has a circular projection whose radius of curvature said second radius of curvature is between half of a radius of curvature said first radius of curvature of the outer surface of the static obstacle and twice said radius of curvature said first radius of curvature of the outer surface of the static obstacle.

In general, this characteristic which aims at a dimensioning of the blades in relation to the dimensions of the static obstacle, makes it possible to limit the phenomena of shearing and the formation of vortices.

The invention also relates to a method for contacting a liquid species and a particulate solid species growing in a tank, in which, by means of a paddle stirrer rotating about a axis, the stirrer possibly being provided with a guide-flow tube, the two species are mixed and driven along this axis, towards a static obstacle generally centered around said axis in the extension of the agitator, characterized in that imposes on these mixed species generally U-shaped trajectories by means of this static obstacle, this static obstacle having an external transverse dimension which increases as one moves away from the agitator parallel to said axis, with a slope by relative to this axis which is constant or increasing.

The invention also relates to the method of dimensioning the assembly formed by the contacting vessel, the stirrer and a static obstacle installed in the vessel.

• La figure 1 représente un agitateur utilisé, de manière générale, dans les dispositifs de mise en contact.
• La figure-2 représente les flux hydrauliques dans une cuve selon l'art antérieur.
• La figure 3 représente les variations de vitesse mesurées en un point de la cuve selon la figure 2.
• La figure 4 représente les zones de faible pression dans une cuve selon l'art antérieur.
• Les figures 5 et 6 représentent deux obstacles statiques utilisables, selon l'invention, en fond de cuve.
• Les figures 7 et 8 représentent un premier mode de réalisation de l'invention.
• Les figures 9 et 10 représentent plus précisément un mode de réalisation d'un obstacle statique utilisé en fond de cuve dans ce premier mode de réalisation de l'invention.
• Les figures 11 et 12 représentent plus précisément l'agitateur utilisé dans ce mode de réalisation de l'invention.
• La figure 13 représente les vitesses des flux dans une cuve incorporant l'invention.
• La figure 14 représente les zones de basse pression dans une cuve selon l'invention.
• La figure 15 représente en perspective d'un second mode de réalisation d'un dispositif selon l'invention.
• La figure 16 en est une vue en élévation.
• La figure 17 est une vue en perspective de l'obstacle statique, avec des nervures dans le prolongement des arêtes.

The invention will now be described in relation to the appended figures.

• The figure 1 represents an agitator used, in general, in the contacting devices.
• FIG. 2 represents the hydraulic flows in a tank according to the prior art.
• The figure 3 represents the variations of speed measured at a point of the tank according to the figure 2 .
• The figure 4 represents the zones of low pressure in a tank according to the prior art.
• The Figures 5 and 6 represent two static obstacles that can be used, according to the invention, at the bottom of the tank.
• The Figures 7 and 8 represent a first embodiment of the invention.
• The Figures 9 and 10 more precisely represent an embodiment of a static obstacle used at the bottom of the tank in this first embodiment of the invention.
• The Figures 11 and 12 represent more precisely the agitator used in this embodiment of the invention.
• The figure 13 represents the flow rates in a tank incorporating the invention.
• The figure 14 represents the zones of low pressure in a tank according to the invention.
• The figure 15 represents in perspective a second embodiment of a device according to the invention.
• The figure 16 is an elevation view.
• The figure 17 is a perspective view of the static obstacle, with ribs in the extension of the edges.

In figure 1 , there is shown a stirrer 100 generally usable in a tank for contacting a liquid species and a solid species. This agitator comprises an axis 110 around which it is driven by a rotational movement (for example due to the action of a motor not shown) and blades 120 distributed in general in a regular manner about the axis 110 and whose shape and arrangement, generally identical for all the blades, allow the rotating agitator to exert an axial thrust 130 (also called longitudinal thrust) on the liquid in which it is immersed. The number of blades of the agitator 100 is at least two, but the more the agitator comprises blades, the more the device is efficient.

In general, such an agitator can be placed in a guide-flow tube, which is a device consisting essentially of a cylinder, generally of hollow circular base, separating an inner zone in which flows a fluid driven by the thrust axial 130 and an outer zone in which the fluid is generally driven in a movement parallel to the axial thrust 130, but in the opposite direction. The presence of such a guide-flow tube makes it possible to reduce the speed of rotation of the stirrer. Indeed, the flux guide tube transforms a portion of the radial thrust created by the agitator in axial thrust.

In figure 2 , there is shown a contacting vessel 200 comprising a stirrer 100 and a guide-flow tube 210. Here, the blades 120 of the agitator are entirely present inside the inner space of the flow guide tube 210 The axes of the flux guide tube 210 and the stirrer 100 are aligned. The tank 200 is concrete or is a civil engineering work.

On the figure 2 , the lower part of the tank 200 in the extension of the guide-flow tube 210 and the stirrer 100 is occupied by a cross as described in the international patent application WO 2005/065832 . It consists of two rectangular walls perpendicular to each other intersecting on a line parallel to their short side and located midway along their long side. This cross is arranged so that the line of intersection of the walls is in the extension of the common axis of the flux guide tube 210 and the stirrer 100. The cross is referenced 230.

Always in figure 2 , the tank 200 is shown with the velocity vectors of the fluid in motion that it contains.

In figure 3 , the variability over time of the axial speed in the area referenced 240 in FIG. figure 2 . This zone is located inside the flow-guide tube 210 at the height of the blades of the stirrer 100. figure 3 shows the great variability of this speed, synonymous with useless energy consumption and risks of shearing of the solid species present in zone 230.

In the space 250 between the center of the blades of the stirrer 100 and the central axis of the spider 220, the mean direction of circulation of the fluid is from the spider 220 to the stirrer 100, unlike the circulation in the rest of the spider. inside the flow guide tube 210.

In figure 4 the iso-pressure surfaces of static pressure equal to -100 Pa relative to the mean are represented in the space of the tank 200. There is a continuous ring around the spider 220, as well as vortices extending in each of four quarters of space defined by the spider 220, from the bottom of the stirrer 100.

These original findings paved the way for the improvement of existing systems.

In addition, these simulation results are validated by comparison with the axial velocity values obtained experimentally as a function of the distance with respect to the axis (not shown).

Various propellers have been tested for the agitator 100. In particular, propellers with four and eight blades including or not an outer cylinder crimping the blades, and the eight-blade configuration with or without a central dome. These various propellers were tested in a tank 200 provided with a flux guide tube 210 and a spider 220, the latter being then replaced by either an eight-sided pyramid as shown in FIG. figure 5 , whose faces extend to the tip, is the same eight-sided pyramid but with a truncated vertex as shown in FIG. figure 6 . The faces (or facets) of the pyramids are here identical, corresponding to an axial symmetry, and can be either flat or curved upward and opposite to the axis.

Thus, a static obstacle having a generally regular shape around the axis, for example a form of revolution, has been chosen. But more particularly a form of revolution makes it possible to obtain excellent results, in particular by avoiding the formation of vortices at the level of the edges noted with the angular forms. It may be noted that, in the case of axial symmetry with a pyramid shape, we come closer to an exact form of revolution because there are a large number of facets.

In Figures 7 and 8 a complete embodiment of the invention is shown. This comprises in a tank 200 an agitator 800 with eight blades 820 regularly distributed around the axis of rotation 810 actuated by the top of the tank (not shown). A flux guide tube 210 identical to that shown in the preceding figures is present and the blades 820 protrude slightly at their distal ends from the lower part of the flux guide tube.

The presence of a guide-flow tube is not essential, but in general, the agitator is configured, in association with its eventual flow guide tube, to ensure the development of essentially longitudinal currents. If there are several agitators, each of them is configured to ensure the development of essentially longitudinal currents.

A static obstacle 830 is disposed at the bottom of the tank 200. This static device 830 has a general shape of revolution with a top pointing towards the agitator and a diameter increasing along the longitudinal axis when one moves away from the agitator 800 (This obstacle therefore has a circular section unlike those of Figures 5 and 6 ). The maximum diameter of the static device 830 is reached in contact with the bottom of the tank 200. This obstacle here has a non-conical or frustoconical shape, but a flared shape away from the axis, with a curvature, constant or not, turned to the outside. Preferably, the radius of curvature of the obstacle 830 in a plane comprising the axis 810 is substantially constant over the greatest possible distance. It is chosen as a function of the dimensions of the base (or bottom) of the tank 200, so as to minimize the shearing in the bottom of the tank, an area where it is desired that the fluid and the aggregates it carries follow from Globally U-shaped trajectories, soft and without loss of energy or shear.

In Figures 7 and 8 , the geometry of the bottom of the tank is represented with a square shape as well as the height of the tank which is approximately twice the height of the guide-flow tube. The flux guide tube 210 is placed in the embodiment shown at equal distances from the bottom and the top of the tank. In other arrangements, the blades of the agitator could protrude at one or other of the ends or mouths of the guide-flow tube (see being outside thereof). The diameter of the agitator (and any associated guide-flow tube) is typically at least about one-third of the smallest width of the bottom of the tank.

In figure 9 , which is a view in a plane perpendicular to the axis 810 and 10, which is a view in a plane containing the axis 810, the geometry of the static device 830 is shown in more detail. Its summit can be sharp, or on the contrary blunted. We observe the rounded end 831 which has essentially the shape of a sphere.

Also shown are four ribs 832 rising from the surface of the static device 830 and running therefrom from an intermediate cross section to its outer cross section. Each of the ribs 832 is tangentially tangential to the perimeter of the intermediate cross section. These ribs 832, unlike the rest of the static device 830, do not have a geometry of revolution. They each constitute a projection of projecting dimension parallel to the longitudinal axis and of substantially constant projection height over the entire length of the rib. Finally, the path of each rib 832 along the surface of the static obstacle 830 is projected in a transverse plane as shown in the upper part of FIG. figure 9 , slightly curved with respect to a straight line, each of the ribs 832 tending, in the embodiment shown, towards one of the corners of the square base of the tank 200 (not shown). The height of each of the ribs 832 is here substantially constant. These ribs may contribute to attenuating the rotational components induced by the agitator to the downward fluid flow.

In figure 11 an example of precise geometry of the blades 820 of the agitator 800 is shown. Three views of the same blade are represented in three planes offset from each other by 90 °. Axis 810 is shown in all three views. The blade 820 is a thin plate of material. Outside its junction with the axis 810, it is delimited by three visible edges in figure 11 . Its surface is inclined at its junction with the axis 810 of an angle A1 of 60 ° relative to the transverse plane perpendicular to the axis. At its distal end 822 (defined by the single edge that does not open on the axis 810), the blade 820 is inclined relative to the transverse plane perpendicular to the axis of an angle A2 of 45 ° only (indeed , the inclination A1 near the axis is advantageously greater than the inclination at the distal ends of the blades.This angle variation between the axis 810 and the distal portion 822 of the blade comes from the twisted character of the blade , adapted to produce a longitudinal thrust of constant intensity as a function of the distance to the axis.It may be noted that, since the blades here, in each section parallel to the axis, a constant slope (which decreases as and when as we move away from the axis), this slope is equal to the angle of attack (ie the inclination of the blades at their leading edge (upper edge).

More generally, at least one blade of the agitator is twisted, and preferably all the blades are twisted, for example in the same manner. Shears and vortices are globally diminished.

The height D of the distal portion 822 of the blade has been shown parallel to the longitudinal axis. In figure 8 , the blades 820 protrude from the lower mouth of the guide-flow tube by about a quarter of the height D.

In Figure 12, there is shown the section of the static device 830 and the projected blade 820 in the plane AA 'shown in FIG. figure 11 . The radius of curvature R2 of the outer surface of the projected blade 820 is substantially constant. It is chosen according to the dimensions of the base of the tank, so as to limit the shear phenomena at the end of the blade. Alternatively or in combination, it is chosen according to the dimensions of the static obstacle 830, to limit shearing and vortex formation.

The internal surface 823 of the projected blade is, for its part, parallel to the surface of the static obstacle 830, these two curves both having a constant radius of curvature R1. With this configuration, the trajectories of the fluid and aggregates it carries do not encounter any obstacle.

Parallel to the axis 810, these two curves are separated by a few tens of millimeters, this distance being denoted D '. It is chosen in relation to the dimension of the agitator parallel to the axis 810, for example the height D represented in FIG. figure 11 so that, in view of this dimension of the agitator, it is not disposed too far from the static obstacle 830, thus guaranteeing the synergistic effect that exists due to the adaptation of their reciprocal sizing and which manifests itself in the absence of countercurrent flow in the extension of the axis of the agitator.

The figure 13 shows the excellent results obtained with the static device 830 and the stirrer 800 implemented in the guide-flow tube 210 of the tank 200. The figure shows the velocity vectors of the fluid, and it is found that it in all tangent points by its trajectory the surfaces that it meets.

The figure 14 presents the isobaric surface of the fluid of the figure 14 for the pressure value equal to -100 Pa. It is found that this isobaric surface is present only in the guide-flow tube and above it. Compared to the representation of the figure 4 , in particular the disappearance of the ring surrounding the static device and vortices extending from the agitator to the bottom of the tank.

The Figures 15 to 17 represent another embodiment of a device for contacting a liquid species and a growing particulate solid species.

Elements similar to those of the first embodiment are designated by reference signs which are deduced from those used for this first embodiment by adding the number 100.

This device thus comprises a vessel provided with a stirrer 900 with blades 920 and a static obstacle 930 disposed in the extension of the axis thereof, downstream thereof (in practice at a lower level, since, in the examples shown here, the flow generated by the agitator is towards the bottom). This stirrer 900 may be surrounded, as previously, by a flux guide tube 210; it can however be noted that this agitator does not overflow the guide-flow tube. It may further be noted that the flux guide tube is here represented with vertical walls which protrude from its external vertical surface (which contribute to ensuring a good linear flow upwards, outside the this tube).

As before, the blades 920 have an angle of attack which, at least at the ends is of the order of 45 ° (here 43 °). However, unlike blades 820, these blades 920 are not twisted but have fold lines transverse to the axis (but not perpendicular thereto or coplanar with the axis), separating flat portions high (upstream ) and low (downstream), the upper part (helping to define the angle of attack especially at the distal end) having a lower slope with respect to the axis than the lower part (by which these blades are fixed to the axis, more precisely to a hub 910A mounting on the axis).

These blades are here six in number and in projection in a plane transverse to the axis overlap each other, giving a recovery rate of about 110%, which helps to ensure a good workout of the flow.

Other numbers of blades may be chosen, preferably but not necessarily even, with an angle of attack of preferably between 35 ° and 55 °.

As before the agitator (this is also the case of the flow guide tube) covers the static obstacle, that is to say that the lowest part of the blades (near their distal ends) descend in the immediate vicinity from the highest part of the static obstacle (its central part), or even lower (see figure 16 ). It may be noted that, in this embodiment too, the static obstacle and the stirrer are, at least at one point, longitudinally distant from a distance less than the longitudinal dimension of the stirrer.

While the static obstacle 830 has, precisely, a form of revolution about the axis, the static obstacle has the shape of a pyramid, with facets that are advantageously identical, which corresponds to an axial symmetry . More precisely, this obstacle 930 is a pyramid with four facets 934 separated by edges 936, hence a square outline at its junction at the bottom of the tank. However, as before, this obstacle has, in axial section, a concavity oriented upwards and opposite the axis; this concavity is furthermore, as in the first embodiment, constant with a radius of curvature which is constant from the top to near the bottom.

Preferably, the facets of the pyramid are cylinder portions in the mathematical sense of the term, that is to say that they are formed by a straight line (horizontal that is to say perpendicular to the axis ) moving parallel to itself along a generator (ie the line of greatest slope, in axial section). Alternatively, these facets may have a double curvature, for example concave upwards and opposite the axis in axial section and convex in cross section; however, we understand that represented configuration may be simpler to achieve than such a double curvature configuration.

This radius of curvature of the static obstacle in a plane including the axis is here also between one quarter of a reference transverse dimension of the tank and one and a half times said reference transverse dimension of the vessel.

We can check that here too (see figure 15 ), the maximum value of the external transverse dimension of the static obstacle (diagonal of the square section close to the bottom) is at least equal to the maximum transverse dimension of the agitator and / or guide-flow tube when exist ; likewise, the axial dimension of the static obstacle (its height) is at most equal to half of the maximum value of said external transverse dimension (in fact, in the example shown, this axial dimension is even at most equal to half of the 938 side of this static obstacle near the bottom (see figure 16 ).

As before, it can be noted that the external surface of the static obstacle has, in any plane passing through the axis (see in particular the figure 16 ), an average inclination of at least 45 ° with respect to this axis.

Similarly, the external surface of the static obstacle is connected to the bottom of the tank, here also, at least approximately tangent, with an angle here of at most 15 ° (the connection angle to the bottom is here substantially lower than for obstacle 830).

In a variant not shown, the curved shape upwardly and away from the axis can be approximated by an axial succession of portions of constant slopes, these slopes increasing from one portion to the other while moving away from the 'stirrer.

By analogy with the obstacle 830, the static obstacle may comprise ribs along its outer surface.

However, advantageously, such ribs can be dispensed with on the outer surface of the obstacle in the case of such a pyramid formed by a circumferential succession of facets separated by ridges, while arranging along the surface of the bottom of the tank. Such ribs 932 are advantageously arranged in the extension of at least some of the edges of the pyramid, preferably in the extension of each of them (with a possible curvature away from this obstacle). These ribs are advantageously attached to the static obstacle.

These ribs can extend from the corners of the static obstacle to the corners of the bottom of the tank, thus contributing to easy positioning of this obstacle vis-à-vis the bottom. In addition these ribs can be both attached to the static obstacle and the bottom of the tank, which helps to strengthen the attachment of this obstacle to the bottom of the tank.

For example, for a square bottom tank with a side length of 2 m and a height of 2 m, the square base static obstacle has 1 m of side along the bottom and a height of 35 cm (the assumed radius of curvature constant deduces from this).

The invention can be implemented without a flux guide, in a tank having a base whose dimensions are large relative to the diameter of the blades of the stirrer, or with a paddle stirrer adapted to exert a thrust whose longitudinal component is significantly larger than the radial component.

The embodiment that has been presented uses a square base tank 200. But if the base of the vessel 200 is a circle, the reference transverse dimension to be used for sizing the agitator 800 or 900 and the static obstacle 830 or 930 is the diameter of the base of the vessel. If the base of the tank is a rectangle, then it's the small side of it. If the base of the tank is a polygon, we will favor the hydraulic diameter of it.

The invention is not limited to the embodiments presented but extends to all variants within the scope of the skilled person within the scope of the main claims; in particular, characteristics of the two embodiments that have been described can be combined.

Claims (14)

1. Device for bringing a liquid species into contact with a growing particulate solid species, comprising a vat (200) in which a blade stirrer (800, 900) is arranged in rotation about a shaft (810, 910), the stirrer being optionally provided with a flow-guide tube (210), the vat (200) comprising moreover a static obstacle (830, 930) generally centred about said shaft in the extension of the stirrer, the static obstacle (830, 930) having an outer surface having, in a plane passing through the shaft, an outer transverse dimension (610; 710; 835) that increases moving away from the stirrer (800, 900) parallel to said shaft (810, 910), with a constant or increasing slope with respect to the shaft, characterized in that the static obstacle (830) comprises at least two ribs (832) along its outer surface.
2. Contact device according to claim 1, in which the static obstacle (830, 930) is covered axially by the stirrer (800, 900) and/or by the flow-guide tube (210) if it exists.
3. Contact device according to claim 1, characterized in that the static obstacle (830, 930) and the stirrer (800, 900) are, at least at one point, longitudinally separated by a distance (D') smaller than the longitudinal dimension (D) of the stirrer.
4. Contact device according to any one of claims 1 to 3, in which the maximum value of the outer transverse dimension of the static obstacle (830, 930) is at least equal to the maximum transverse dimension of the stirrer (800, 900) and/or of the flow-guide tube (210) when it exists.
5. Contact device according to any one of claims 1 to 4, in which the axial dimension of the static obstacle (830, 930) is at most equal to half of the maximum value of said outer transverse dimension.
6. Contact device according to any one of claims 1 to 5, in which the outer surface of the static obstacle (830, 930) has, in any plane passing through the shaft, an average inclination of at least 45° with respect to this shaft.
7. Contact device according to any one of claims 1 to 6, in which the outer surface of the static obstacle (830, 930) is connected to the bottom of the vat at least approximately tangentially, at an angle of at most 15°.
8. Contact device according to any one of claims 1 to 7, in which the outer surface of the static obstacle (830, 930) comprises at least one zone which, in an axial plane, is dished with a concavity orientated away from the shaft.
9. Contact device according to claim 8, characterized in that a radius of curvature (R1) of the static obstacle in a plane comprising the shaft (810, 910) is comprised between one quarter of a reference transverse dimension (L) of the vat (200) and one and a half times said reference transverse dimension (L) of the vat (200).
10. Contact device according to one of claims 1 to 9, characterized in that the static obstacle (830) has a generally regular shape about the shaft (810), for example a rotational shape.
11. Contact device according to any one of claims 1 to 9, in which the outer surface of the static obstacle has the shape of a pyramid formed by a circumferential succession of facets separated by edges.
12. Contact device according to claim 11, in which the bottom comprises, at least in the extension of the edges, ribs moving transversally away from the shaft.
13. Contact device according to any one of claims 1 to 12, in which the blades (820, 920) have an angle of attack comprised between 35° and 55°.
14. Method of bringing a liquid species and a growing particulate solid species into contact within a vat (200) with a device according to claim 1, according to which, using a blade stirrer (800, 900) rotating about a shaft, the stirrer being optionally provided with a flow-guide tube (210), the two species are mixed along this shaft, towards a static obstacle (830, 930) generally centred around said shaft in the extension of the stirrer, characterized in that generally U-shaped paths are imposed on these mixed species via the static obstacle.

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