WO1997047379A1

WO1997047379A1 - Solids separation and solids flow control device

Info

Publication number: WO1997047379A1
Application number: PCT/FR1997/001076
Authority: WO
Inventors: Jean Leybros; Christian Oriol; Thierry Prevost
Original assignee: Compagnie Generale Des Matieres Nucleaires
Priority date: 1996-06-14
Filing date: 1997-06-13
Publication date: 1997-12-18
Also published as: AU3348397A; SK170198A3; EP0904149A1; JP2000511821A; FR2749776B1; FR2749776A1

Abstract

A solids separation and solids flow control device particularly suitable for use in apparatuses, devices and equipment for continuously contacting a solid with a liquid, especially fluidised-bed and moving-bed columns (1), is disclosed. The device includes separating means (2) for cyclically and controllably separating the accumulated solids, means (e.g. a bypass circuit (7, 8) or an air-lift) for generating a flow or stream of liquid by means of a hydraulic imbalance to transfer solids in a working fluid from the apparatus to metering means (3) via the separating means, and transfer means (4, 40, 5, 6) for hydraulically and sequentially transferring the solid in the working fluid from the metering means (3) to the solid-liquid separation means. A plant including said separating device for continuously contacting a solid with a liquid, and an apparatus for continuously contacting a solid with a liquid, e.g. a fluidised-bed or moving-bed column, are also disclosed.

Description

SOLID STORAGE AND SOLID FLOW CONTROL DEVICE

The present invention relates to a device for withdrawing solids which also makes it possible to control the flow rate of solids which applies more particularly to apparatus, devices and apparatus for continuously contacting a solid and a liquid, in particular to columns moving bed and fluidized bed.

The invention also relates to the installation for continuously contacting a solid and a liquid comprising such a withdrawal device and an apparatus for continuously contacting a solid and a liquid.

The solids can be in particular mineral or organic compounds, for example solid ion exchangers such as ion exchange resins or zeolites and others, generally being in the form for example of grains or beads.

In the field of material transfer taking place between a liquid and a solid, it is known that the exchange reaction being balanced, in order to achieve a suitable transfer rate and a suitable exhaustion in solute of one or the other phase. , it is necessary to ensure a relative movement between the two solid and liquid phases present. We therefore turned to methods and devices aimed at making mobile one or the other of the two solid and liquid materials in the presence or even both.

The most commonly used technique is that of the "fixed bed" which has been used in particular to extract compounds present in low content, as is the case in particular for demineralization of water.

This technique consists in passing the liquid through the solids which are in the form of a fixed bed of grains contained in a column. The liquids, in particular the solutions to be treated, are circulated through these beds of solid which are charged as and when the passages of liquids to be treated. Such a technique has, inter alia, the disadvantage of being applicable only if the liquid to be treated is perfectly clear because, in fact, if the latter contains solid particles in suspension, as is the case in particular for a pulp , these are stopped by the grains and cause, in the more or less long term, a clogging of the bed.

In addition, when the bed is fully loaded, namely when, for example, the heat exchanger grains or others have reached their maximum extraction capacity, it is necessary to stop feeding the column and isolate it in order to proceed with the unloading of the solids inside the column, αui then, generally, are treated, for example to remove the fixed compounds, and regenerated to be returned to their initial form in order to garnish the column again.

Such an operation requires frequent stops which can be extended over a fairly long period, and in order to be able to have a treatment installation operating continuously, it will be necessary to use two or even three columns, or more and a set of valves. allowing the circulation of the liquid to be modified, one of the columns of the installation being in the withdrawal or regeneration phase of the solid phase, while the others fulfill their / 47379 PC17FR97 / 01076

normal role of treatment. This type of installation thus requires the provision of several columns and valves to allow permutation, which is very unfavorable from the economic point of view. Finally, in fixed solid beds, preferential paths of the liquid are generally created which seriously affect the efficiency of the exchange operation.

Because of the numerous drawbacks present by the "fixed bed" methods and devices, we have sought to overcome them by developing techniques in which it is possible essentially to bring them into continuous contact with a single column. . Thus was developed the technique called "moving bed" in column, that is to say a system where not only the liquid, but also the solid particles, for example the exchanger grains are put moving, relative to the column wall. The article by M.J. SLATER, in BRIT. CHEM.

ENG. , 14, (1), 41, (1969) reviews the various methods and apparatuses implementing the technology of the moving bed.

These processes and devices can be classified into two main categories: on the one hand, that or the bed is said to be "cup" or "sliding", because the movement is obtained by a succession of displacements each bearing on a quantity more or less large of grains, and that the bed moves by successive glides, on the other hand those where the bed is said to be "fluidized", because the grains behave like a fluid.

In most of the devices and apparatuses operating according to the principle of the moving bed, the solid which is supplied at the top of a column, circulates by gravity and against the flow of the liquid, down the column, where it is withdrawn by various devices. Thus, the article by HIESTER in Chem. Eng. Prog., 50, (3), 139, (1954) and document US-A-2 671 714 do they describe withdrawal devices in the form of rotary metering valves which allow the transfer of the ion exchange material from the base of a first column equipped with a first of these valves to the top of a second column, under the action of suction created by streams of water under pressure. In the second column, provided at its base with a second rotary valve, the ion exchange material descends by gravity, brakes by a series of perforated plates, and is recycled in the first column passing through the second rotary valve.

The document GB-A-947 166 and the document FR-A-1 176 525 likewise describe tubular columns in which the granular solid material circulates from the top to the bottom of the column against the current of the liquid introduced at the base of the column, then this solid maceration is drawn off at the base of the column by means of a discharge orifice, a perforated plate, and an extraction member, for example a valve rotary.

In most of the "moving bed" methods and devices of the prior art, trays are therefore used and the displacement of the grains from the top to the bottom of the column is carried out by cyclic stopping of the fluidization, in bypassing part of the liquid flow, by interrupting the flow of the liquid or by reversing the direction of flow of this liquid.

Certain other methods and devices of the prior art such as those described in the document FR-A-1 176 525 involve a liquid purge at the bottom of the column using a pump; such devices have the disadvantage that it is mandatory to provide a grid at the base of the column to retain the grains.

The methods and devices mentioned and described above have many drawbacks: first, the cyclic cessation of fluidization decreases the time during which the liquid-solid contact can actually occur, which consequently reduces the efficiency of the column.

Then the withdrawal of solids requires equipping the installation with a series of automatic valves with programmed opening, the control of which by electronic or electromagnetic timer is complex and expensive. In addition, the conduct of such sets requires careful and delicate control. Solid flow control is often unreliable. Furthermore, this equipment requires significant maintenance due to the very presence of solids which promotes abrasion wear. They are subject to a risk of blockage or significant clogging.

The document EP-A-0 060 207 relates to a method and to a device operating in a completely continuous manner for the extraction of ions from a clear liquid or containing suspended matter by contact with a bed of grains. exchangers.

The device described in this document comprises a fluidization column which does not include any tray or grid capable of hindering the grading by density of the grains as a function of their ion charge, under the action of cyclic pulses generated by a pulsation generator operating by sampling at the top of the column and reinjection by jerks at the base of the column; such a device has as a major drawback the use of a valve for withdrawing the grains resulting in random control of this withdrawal and a significant risk of clogging.

Certain other hydraulic withdrawal devices also have the defect of disturbing the bed of the column by backwashing and thus modifying the performance of said column. In a nuclear type application, for example, this type of process and device, although effective, is often prohibited due to the various drawbacks mentioned above.

The object of the present invention is therefore to provide a device for withdrawing solids which overcomes the drawbacks of the devices of the prior art, that is to say a device which can be used continuously, which does not require the presence of neither trays nor grids and which, when the solid phase is in the form of particles or grains, does not cause any clogging, abrasion, wear and grain entrainment phenomena

The aim of the present invention is also to provide a device which is easy to implement, easy to service and maintain, of minimum complexity, having a processing capacity equal to, or even greater than, that of the existing racking devices and making it possible to control the quantity of solid withdrawn from the column Such a device is, according to the invention, preferably applied to a column with a “moving bed” or a fluidized bed in which the solids circulate against the current of the liquids under the gravity action, but it can also be applied to any device, device, equipment or appliance in which it is necessary to implement such a device for withdrawing solids, that is to say to any device in which solids accumulate, for example it can be applied to any apparatus, device, equipment or device for treatment or bringing a liquid phase into contact with a solid or a solid with a liquid phase, such an apparatus preferably operating continuously.

In all that follows and for the convenience of the description, the apparatus, device or other to which the drawing-off device according to the invention is applied, is generally designated by the term column, but it is obvious that this apparatus can take on a any shape and size which can be readily determined by one skilled in the art.

The withdrawal device for apparatus in which solids are accumulated, according to the invention, comprises withdrawal means intended to withdraw in a cyclic and controlled manner the solids accumulated in an apparatus, in particular it may be the solids collected by gravity in a column, generally at its lowest point, means for generating a flow or current of liquid under the action of a hydraulic imbalance for transferring / transporting, essentially by suction, into a working fluid, the solids collected from the device, for example the device for contacting a solid and a liquid such as a column to dosing means (also called capacity or dosing zone), by means of withdrawal means , and finally transfer means for hydraulically and sequentially transferring the solid into the working fluid generally in the form of a solid suspension, from the metering means to solid-liquid separation means.

Such a device does not have the drawbacks of the prior art because, in particular, that it does not have a disc, a grid or a plate, that the number of moving mechanical parts, inducing pressure losses is very small. even non-existent. This device is extremely simple because it does not use any complex transfer device, since the transfer of solids is essentially induced by a modification of the hydraulic balance.

Finally, the supply of liquid to the device in which solids accumulate, in particular to the device for bringing a solid and a liquid into contact, such as a column, is permanently maintained and does not undergo any interruption during withdrawal, which results in a significant increase in the effective treatment capacity of the column and allows continuous operation with a single column.

The solids are preferably in the form of particles such as grains, granules or beads and are generally of an average size of 0.2 mm to 2 mm. The solids preferably consist of materials generally used in apparatuses for bringing liquid and solid into contact: they may be mineral or organic compounds, for example solid ion exchangers such as exchange resins of ions or zeolites and other divided solids

The liquid may be any liquid capable of undergoing a liquid-solid exchange operation, it may for example be an aqueous liquid such as an aqueous effluent from various industrial operations (for example rinsing of installations), or resulting from nuclear installations (such as reprocessing factories, power stations, laboratories) .... The liquid is charged with various elements, for example in suspension or in solution, which one wishes to eliminate or separate by the contacting operation. These elements to be eliminated, or to be separated, can for example be in the form of salts of various cations, in particular of metal cations, in particular of radioelements such as cesium, strontium and others, but they can also be anions or organic complexes. The concentration of these elements can be very variable: from the trace state (ppb) to concentrated solutions (a few tens of g / 1). For example, for the salts of the radioactive cations mentioned above, it is generally from 0.01 to 1000 mg / 1.

On the other hand, the drawing off operation is generally carried out under normal conditions of temperature and pressure, but it is obvious that other temperatures and pressures can be used.

The withdrawal means can take any suitable form known to those skilled in the art, but they generally comprise a pipe, tubing, pipe or other conduit which connects on the one hand the device in which solids are accumulated, in particular the apparatus for contacting a solid and a liquid such as a column, and on the other hand the metering means. The withdrawal means are connected to the apparatus in which solids have accumulated, in particular to the apparatus for bringing a solid and a liquid into contact at the point of this apparatus, or the solids in particular have accumulated. from this device where the solids are collected by gravity, that is to say essentially at the low point of the apparatus for contacting a solid and a liquid such as a column. The withdrawal means can for example penetrate obliquely into the apparatus such as the column and be directed towards the bottom of the said apparatus of the said column and the accumulated solids, for example by gravity, can be removed via a calibrated orifice, but such an arrangement is given only by way of illustration; the withdrawal means can of course be adapted according to the desired application and the device to which they must be connected or connected.

It is preferable that, during the transfer procedure as described below, the introduction, for example injection, of the working fluid into the system does not disturb the flows which take place inside of the apparatus in which the solids accumulate, in particular of the apparatus for contacting a solid and a liquid such as a column.

For example, in the case where the apparatus for contacting a solid and a liquid is furnished with a moving bed, it is desirable that neither lifting nor backwashing occur. For this purpose, the withdrawal means connecting the device such as a column to the metering means (at the metering capacity) and which are, as already described above, for example in the form of a pipe or a suction pipe, are preferably made in such a way that their pressure drop is greater than that necessary to carry out the transfer of the solids generally being in the form of a solid suspension.

The metering means or measuring means generally take the form of a "capacity metering ", namely for example an essentially vertical tubing or pipe generally calibrated, thus making it possible to precisely measure the quantity of solids - generally in the form of a suspension of solids - withdrawn into the apparatus in which s accumulate solids such as a column.It is obvious that these metering or measuring means can be in any form for metering or measuring the solids sampled and ensuring precise control of the flow of solids.

The means for generating a flow or current of liquid, under the action of a hydraulic imbalance, and for transporting, essentially by suction, in a working fluid, the solids collected from the apparatus in which the solids accumulate, in particular from the apparatus for bringing a solid and a liquid such as a column into contact with the metering means, by means of the withdrawal means, comprise, in a first embodiment, a circuit for bypass also called "by-pass" circuit placed on the metering means, and provided with sealing means consisting for example of a "by-pass" valve. This "bypass" circuit preferably connects, on the one hand the metering means, and on the other hand the transfer means to the solid-liquid separation means.

The collection of solids is therefore carried out in this embodiment by creating between the point αe the apparatus such as the contacting apparatus, where the solids are collected and collected, essentially under the action of gravity (by example the bottom of the column) and the metering means (capacity or metering area) a liquid stream or stream, by opening the sealing means such as the "by-pass" valve of the "by-pass" circuit preferably connecting the metering means and the transfer means to the solid-liquid separation means, thereby inducing a hydraulic imbalance.

The part of the transfer means or terminates the "by-pass" circuit preferably comprises a pipe, tubing or essentially vertical descending pipe or any other known means allowing the delivery of a fluid.

The current or flow of liquid can be obtained by placing the bypass circuit at a point located on the metering means, at a level lower, preferably significantly lower, than the level of the liquid in the device, a know at the level of the liquid leaving the top of the device, for example the contacting device of a solid and a liquid such as a column. This liquid leaves for example in a conventional manner via a weir.

According to a second preferred embodiment of the present invention, which will find its application for example in the field of the nuclear industry or in any field of the industry where the presence of parts such as tap valves or the like poses serious problems of maintenance, the "by-pass" bypass system comprising closure means such as a valve, and allowing the withdrawal of solids in the apparatus where solids accumulate such as a column, can advantageously be replaced by a so-called "air-lift" device placed on the metering means.

The function of this so-called "air-lift" device is to empty the liquid present in the upper part of the metering means (metering capacity), which creates a hydraulic imbalance, which tends to be compensated by a liquid flow or current, coming from the point (in general at a low point) of the apparatus where solids accumulate, for example from the setting apparatus contact of a solid and a liquid, or are collected, accumulates the solids generally by gravity, this flow or current of fluid being preferably directed towards the means or the metering capacity. Said flow or current makes it possible as 0 previously with the bypass system to draw off the solid phase at the point of the apparatus, for example from the apparatus for bringing a solid and a liquid into contact. , where solids are accumulated and collected, in particular by gravity, namely at the foot of the:> column.

The "air lift" device is placed on the metering means at a point situated at a lower level, preferably markedly lower than the level of the liquid in the device, namely at the level of the liquid coming out from the top of the device. , for example 1 apparatus for contacting a solid and a liquid (weir of the column) The means for generating a flow or current of liquid under the action of a hydraulic imbalance, for transferring into a D driving fluid the solids from the device in which the solids are accumulated towards the metering means, are not limited to the two embodiments indicated above, but can on the contrary be constituted by any other means making it possible to create a 0 hydraulic imbalance between the apparatus in which solids are accumulated such as in a column, and the metering means, in particular the metering capacity

As an example of these means, we can mention a siphoning system, a hyαroejector,:> etc According to the invention, the withdrawal is cyclic and controlled, that is to say that the means for generating a flow or current of liquid under the action of a hydraulic imbalance are actuated at regular intervals, for example every hour. for a predetermined time, for example one to 5 minutes. The actuation of these means consists, for example, in putting the air lift into operation or in opening the shutter means of the "bypass" bypass system. The withdrawal is controlled, that is to say that when the quantity of solids desired to be withdrawn is reached, the means for generating a flow or current of liquid are ceased to operate and the transfer procedure is initiated by the means of transfer described below.

Thus, when the solid, generally in the form of a suspension of solids in the working fluid reaches a sufficient level in the metering means, corresponding to the quantity of solids to be drawn off, the closure device with which the circuit is provided. "bypass" is closed and the next transfer procedure is activated.

The transfer means, for hydraulically and sequentially transferring the solid into the working fluid, generally in the form of a solid suspension from the metering means to the solid-liquid separation means preferably essentially comprise means for introduction, injection of a current or flow of working fluid into the metering or measuring means (capacity or area). These means may for example include a tapping into which opens a pipe or tubing supplied with working fluid by a working fluid circuit provided with regulation and control means such as a valve with controlled opening making it possible to regulate the flow, the number, the timing ... of the injections of engine fluid and thus obtain an effectively sequential transfer.

The working fluid can be any fluid suitable for such a use, but it is advantageously constituted by the liquid circulating in the apparatus where solids accumulate, in particular in the apparatus for continuously contacting a solid and of a liquid such as a column. The transfer means also include load breaking means conventionally constituted by a tank, also called "load breaking pot". These load breaking means or "load breaking pot" are preferably located at a point the level of which ("altitude") is determined by balancing the pressure losses which occur in the apparatus in which solids accumulate, in particular in the apparatus for contacting a solid and a liquid such as a column, for example, in the bed of solids which is in such a column.

The transfer means further comprise routing means comprising for example pipes, tubes, etc. connecting for example the metering means and the load breaking means, and the load breaking means and the solid-liquid separation means.

The shape of these conveying means can be easily determined by a person skilled in the art, for example the metering means and the load breaking means can be connected by an essentially vertical ascending pipe, then by a bent pipe and finally by an essentially horizontal pipe terminating in the load-breaking "pot"; load breaking means (load-breaking "pot") and the liquid-solid separation means can be connected by an essentially vertical downward pipe preferably starting from the bottom of the load-breaking means and ending in the liquid-solid separation means. Said downward pipe is preferably substantially parallel to the metering and measuring means and to the vertical upward pipe mentioned above, and is connected in the first embodiment of the invention, to the metering means by the "by -pass "preferably preferably essentially horizontally.

Said hydraulic and sequential transfer from the metering or measuring means (capacity or metering zone) to the solid-liquid separation means, therefore preferably comprises injection for a predetermined period preferably between one or a few seconds and a few minutes, for example 1 sec. 10 min. a current or flow of working fluid at a sufficient speed, preferably between 1 and 100 cm / s and in an amount sufficient to hydraulically transport the solids generally in the form of a suspension to the load breaking means or load breaking capacity and towards the separation means.

Generally, the quantity of working fluid injected will allow the transfer of an equivalent quantity of solids (generally expressed in volume) thus forming a suspension of solids which is transferred.

The solid-liquid separation means can comprise any device known to those skilled in the art such as a settling tank or the like allowing the separation of the solid and liquid phases. According to a particularly advantageous characteristic of the present application, after having been separated in the solid-liquid separation means, the fluid or liquid having served for the transfer of the solid from the apparatus such as a column to the metering means (zone or metering capacity), as well as the driving or transfer fluid for the hydraulic and sequential transfer from the metering means (capacity or metering zone) to the separation means, in other words for emptying the metering capacity, is recovered to be introduced into the apparatus in which solids accumulate, in particular the apparatus for contacting a solid and a liquid such as a column. As already indicated above, the device according to the invention can, in particular, but not exclusively, be applied to any apparatus, device, equipment or apparatus for continuously contacting a solid and a liquid, in particular to a moving bed or fluidized bed column and it then makes it possible to take advantage of the advantages of a fixed bed column, in particular maximum loading or unloading of the solid, maximum contact capacity, while retaining the benefits of continuous operation.

On the other hand, the device according to the invention has neither tray, grid, or other device impeding the flow; no pump or other is necessary to transport and transfer the solid or the solid suspension, moreover in the case where an "air lift" system is used, the valves, taps and others can be completely deleted.

The invention also relates to the installation comprising a device or apparatus for bringing a liquid and a solid into contact with the withdrawal device according to the invention.

According to a preferred embodiment of the installation according to the invention, the withdrawal device is applied to the columns operating in a fluidized bed by creating a flaring in the lower part of the column in which the solids, in particular in the form of grains, come accumulate. In this part of the column, the solid bed then has the behavior of a packed moving bed whose linear pressure drop is sufficient to allow the device of the invention to be used without disturbing the fluidized bed during the sequences of solid transfer. It is obvious that any means other than a flaring allowing said accumulation of solids also falls within the scope of the invention.

Other characteristics and advantages of the invention will be better understood on reading the following description, given by way of illustrative and nonlimiting example, this description being made with reference to the accompanying drawings in which: FIG. 1 is a vertical section view schematically illustrating a movable bed column equipped with the withdrawal device according to the present invention; FIG. 2 is a vertical section view schematically illustrating another embodiment of the device according to the invention applied as in FIG. 1 to a column with a moving bed, but in which the circulation of the solid is carried out by an "air-" device. lift "instead of a" by-pass "system. FIG. 3 is a vertical section view schematically illustrating a fluidized bed column equipped with the withdrawal device according to the present invention in the embodiment according to FIG. 2, that is to say provided with an "air-lift" device.

In Figure 1, there is shown very schematically an installation comprising a movable bed column (1) equipped with the device according to the invention. This device comprises a suction tube for the solids (2) penetrating obliquely into the lower part of the column (1) and oriented towards the bottom of the said column and connected to a vertical capacity (3) allowing the dosage of the solid withdrawn. A liquid supply pipe (4) is fixed at the low point of the metering capacity (3) which is itself connected at one point to a load breaking capacity (5) The load breaking capacity is equipped a tube (6) allowing the transfer of the solid-liquid suspension to a separation equipment (not shown) such as a screen, filter or other.

At a determined height, a bypass pipe (7) provided with a remote-controlled valve (8) connects the metering capacity (3) to the transfer pipe (6).

Furthermore, the column (1) is continuously supplied by the liquid phase at point (17). The liquid phase after having passed from bottom to top the solid bed leaves by overflow at point (18) do the column (1) which also has a pipe (9) for supplying the solid. The tubing (7) is placed so as to be located under the outlet point (18) of the liquid.

In operation, the solid is withdrawn sequentially from column (1) in the manner next. The remote-controlled valve (8) is open, the pipe (7) being situated at an altitude lower than that of the point of exit of the liquid (18) from the column, the liquid will tend to circulate towards the tube (2) thus creating a liquid flow whose speed is sufficient to suck the solids from the column (1) to the metering capacity (3). A solid level measuring device placed at (30) controls the closing of the remote-controlled valve (8). Then we introduce through the pipeline

(4) a flow of liquid controlled by a time delay device (40) allowing the transfer of the solid towards the load breaking capacity (5). When the transfer of solid, in the form of a suspension of solids, is carried out, fresh solid is introduced via the tube (9), the level of solid in the column being monitored by a device for measuring level (20) which controls the supply of solid. In Figure 2, a very schematically shows a movable bed column similar to that shown in Figure 1 equipped with the device according to the invention. The references used in the installation illustrated by this figure will therefore be the same as those in FIG. 1. In this embodiment, the device according to the invention comprises, as means for generating a flow or current of liquid allowing the circulation of solids, an "air lift" device instead of a "bypass" system.

The circulation of the solid through the pipe (?) Is thus carried out by an air-lift device (/ 0) controlled by the level measurement device (30) In FIG. 3, the withdrawal device of the present invention already shown in FIG. 2 is applied to a fluidized bed column instead of a moving bed column. In this variant of installation in which the bed is fluidized, the solid is accumulated in the flaring (10) at the bottom of the column from which it can be withdrawn using the device of the invention.

It is obvious that the withdrawal device of Figure 1 (a bypass) could also be applied to a fluidized bed column.

Of course, the invention is not limited to the embodiments which have just been described above, but on the contrary covers all possible variants.

The invention will now be illustrated by means of the following implementation example, of course, is given by way of illustration and not limitation. EXAMPLE:

A column with a diameter of 500 mm and a height of 7.0 m is used. The column contains a bed of 1.2 m ^J of a solid ore exchanger having a grain size of 0.8 mm capable of fixing metal salts contained in an aqueous solution The bed is not fluidized and occupies a height of 6.0 m column. The solution admitted into the column at a rate of 0.5 m ³ / h contains approximately 20 mg / 1 of metal salts. The grains sampled at a rate of 15 l / h contain approximately 660 mg / l of metal salts and the solution at the outlet of the column contains only 0.02 mg / l of metal salts.

The grains are removed every hour according to the following sequence operation of the racking air-lift for 3.5 minutes, flushing for 45 seconds of 15 liters of solids using 15 liters of solution.

It emerges from this example where we find ourselves in the embodiment of FIG. 2, that the withdrawal device according to the invention allows absolutely continuous operation, at maximum capacity, without disturbing the flow inside. of the column, maintenance and upkeep being reduced to a minimum.

Claims

1. withdrawal device for apparatus in which solids accumulate, characterized in that it comprises withdrawal means intended to withdraw in a cyclic and controlled manner the accumulated solids, means for generating a flow or current of liquid under the action of a hydraulic imbalance to transfer the solids into a working fluid from the apparatus to metering means, via the withdrawal means, transfer means for hydraulically and sequentially transferring the solid into the fluid motor, from the metering means to the solid-liquid separation means 2 Device according to claim 1, characterized in that the means for generating a flow or current of liquid under the action of a hydraulic imbalance, for transferring into a driving fluid the solids from the apparatus in which the solids are accumulated towards the metering means include a bypass circuit placed on the metering means at a point situated at a level below the level of the liquid in the apparatus, this circuit being provided with closure means, the opening of which generates said flow or current of liquid.

3. Device according to claim 1, characterized in that the means for generating a flow or current of liquid under the action of a hydraulic imbalance, for transferring the solids into a working fluid from the device in which the solids are accumulated towards the metering means, comprise a so-called "air-lift" device placed on the metering means at a point situated at a level below the level of the liquid in the apparatus 4. Device according to any one of claims 1 to 3, characterized in that the solids are in the form of grains, granules or beads. 5. Device according to any one of claims 1 to 4, characterized in that the accumulated solids are removed by a calibrated orifice.

6. Application of the device according to claim 1 to the withdrawal of solids in the continuous contacting apparatus of a solid and a liquid.

7. Installation for continuously contacting a solid and a liquid comprising an apparatus for continuously contacting a solid and a liquid and a withdrawal device, characterized in that said withdrawal device is the withdrawal device according to any one of claims 1 to 5.

8 Installation according to claim 7, characterized in that the apparatus for continuously contacting a solid and a liquid is a moving bed column

9 Installation according to claim 7, characterized in that the apparatus for continuously contacting a solid and a liquid is a fluidized bed column.

10. Installation according to claim 9, characterized in that the bottom of the column operating in a fluidized bed is flared to allow the accumulation of solids before they are drawn off

11. Installation according to any one of claims 7 to 10, characterized in that the working fluid used to transfer the solids from the apparatus for continuously contacting a solid and a liquid to the metering means , and since metering means to the solid-liquid separation means consists of the liquid circulating in the apparatus for continuously contacting a solid and a liquid.