FR3030318B1 - DEVICE FOR PRETREATMENT OF SEDIMENTS FROM A BACKGROUND OF A LIQUID MEDIUM COMPRISING SUCCESSIVE SIEVE STAGES - Google Patents

Abstract

The invention relates to a device (1) for the pretreatment of sediments taken from a bottom of a liquid medium, comprising at least two successive sieving stages, each of the sieving stages comprising a screening basket (3) having mesh size predetermined, can be rotated inside a receptacle (5), so as to separate filtrates, passing through the mesh of the basket (3), and residues not passing through the mesh. According to the invention, at least one of the sieving stages comprises means for projecting a fluid under pressure on the periphery of the screening basket (3), from the outside to the inside thereof.

Description

The invention relates to the field of cleaning the bottom of liquid media, for example maritime or fluvial media, and more precisely the treatment and recovery of sediments deposited on the bottom of liquid environments such as estuaries, ports, lakes, ponds, rivers, rivers or water retaining structures and treatment plants. In particular, the present invention relates to the pretreatment of such sediments, once extracted from the liquid environment in which they rested. 2. Prior Art

Streams carry many sediments, the deposition of which naturally causes the siltation of funds. This phenomenon can be amplified by erosion processes, low flows, a flat topography as well as industrial and urban discharges. Closed environments (ponds, ponds ... or almost closed (ports, dams ...) are even more subject to this problem.

For this reason, it is necessary to clean the funds of these environments, I or dredging. Classically, dredging operations of these areas are periodically carried out in order to evacuate the sludge or sediment accumulated therein, which can eventually disrupt human activities (societal, commercial, tourist, leisure, etc.). and / or ecological balances.

Such dredging operations must be reproduced regularly, for example every 3 to 5 years, since the siltation is continuous, each time causing a stop or a disruption of the activities of the zone concerned.

These dredging works are usually carried out by specialized boats, called dredges, or by public works machinery, from the shore. The equipment used often combines, on the one hand, a mechanical or hydraulic system making it possible to mix the sediments accumulated on the bottom to be cleaned, and on the other hand a system making it possible to extract the brewed sediments, generally a suction pump.

Following their extraction, the sediments must be evacuated, and preferably at least partly reused and recovered. They are usually transported and undergo pre-treatment prior to their use. This pretreatment aims on the one hand to separate the sludge particles from undesirable elements (detritus, ...) recovered during the dredging operation, and to dry the sediments by dissociating the dry matter from the water. There are different types of pretreatment, the most commonly used being screening (ie the passage of sediments through a grid), sieving, (ie the passage of sediments to through a sieve) or draining (that is, natural drainage of sediments by migration of excess water).

There is currently no effective system for dealing with large quantities of sediment. As a result, the thousands of m3 of sediment recovered during dredging operations are generally not treated. The waste is thus stored on land in depots or transported by pipeline, barge or other means of transport far from the coast and released at sea. These operations can be harmful for the environment by contributing to water pollution because of the toxic substances contained in such waste.

Many studies nevertheless show the potential of valorization of dredged sediments, as for example in the manufacture of concrete, in road works (embankments, pavements ...), in the industry (glassworks, foundry ...) or in agronomy.

There is therefore a need for a system that would ensure effective sediment drying, while being able to handle larger amounts of incoming material, and that would contribute to the reduction of the mass of waste stored on land or dumped into 3. Presentation of the invention

The present invention aims to overcome these disadvantages of the prior art.

This objective, as well as others which will appear more clearly later, are achieved by means of a pre-treatment device for sediments taken from a bottom of a liquid medium, comprising at least two successive sieving stages, each sieving stages comprising a sieving basket having meshes of predetermined size, being rotatable inside a receptacle, so as to separate filtrates, passing through said meshes of said basket, and residues not passing through said sieves; sts.

According to one aspect of the invention, at least one of the sieving stages comprises means for projecting a pressurized fluid onto at least a portion of the periphery of the sieving basket, from the outside to the inside thereof. this.

The projection of fluid under pressure on the periphery of the basket makes it possible to unclog the meshes of the basket forming the filter. The pressure exerted by the fluid off the particles obstructing the filter, and puts them back in motion so that the sieving operation can be continued and the filtrates are evacuated.

Filtration, and therefore sorting and drying of sediments, is thus more efficient. The presence of the cleaning system ensures a continuity in the operation of the pretreatment device, and thus to handle larger amounts of sediment.

According to a first embodiment, the projection means comprise a plurality of nozzles distributed over the height of the periphery.

Thus, when the basket is set in motion and rotates, the entire outer surface of the basket, that is to say from the bottom end of the basket to its upper end, is sprayed. This ensures that all meshs in the basket are unclogged, and ensures maximum efficiency.

According to a particular embodiment, the sieving basket has a frustoconical shape with an upper edge wider than the lower edge.

According to another embodiment, the basket is flared near its upper edge.

This specific form facilitates the ejection of residual sediment out of the basket, when the rotational speed thereof is increased.

According to a particular embodiment, the basket is mounted on an axis of rotation therethrough, movable relative to the receptacle.

In particular, the upper end of the axis of rotation is driven by a motor.

Starting the motor causes rotation of the axis, and therefore the basket inside the receptacle. The technique used is simple and inexpensive.

According to another embodiment, the receptacle has an inclined bottom guiding the filtrates to transfer means.

In particular, the filtrate transfer means comprise a discharge nozzle.

Thus, the filtrates having crossed the mesh of the basket flow naturally towards the bottom of the receptacle, the discharge nozzle allowing their precise guidance to the next filter basket.

According to another embodiment, the receptacle is fixed inside a tank receiving the residues.

Thus, the recovery of residues, not having crossed the mesh of the basket, is carried out in a simple manner, within the device itself.

According to another embodiment, the tank has, under the receptacle, a funnel-shaped shape, guiding the residues towards discharge means.

This allows the residues to be naturally guided towards the bottom of the tank, and are collected in order to be evacuated to a storage tank, for example.

According to another embodiment, the sediment pre-treatment device comprises control means controlling the setting in rotation and / or the speed of rotation of said baskets and / or the distribution of said fluid under pressure.

Thus, the sediment treatment cycle can be completely automated to gain performance.

According to another embodiment, the sediment pre-treatment device comprises three successive sieving stages.

The incoming sediments thus undergo three successive treatments, the size of the meshes of the sieving baskets reducing gradually as the stages of sieving. In this way, three types of residues can be recovered and recovered, the "ultimate" residues taking the form of very fine particles. In addition, the "ultimate" filtrates, evacuated at the end of operations are liquid and can be discharged directly into the starting environment. The device is thus efficient, since there is no "ultimate" waste to be stored.

In addition, the pretreatment operations can be carried out "in situ" on the actual site of extraction of the sediments, unlike the solutions of the prior art that require transport of the sediments to a treatment zone. This makes it possible to considerably reduce the carbon footprint of transport operations since only the sediments that are freed of their water (and possibly packaged) are transported. The invention also relates to a pretreatment stage for a device for sieving sediments taken from a bottom of a liquid medium, comprising a screening basket having meshes of predetermined size, which can be rotated inside a receptacle, so as to separate filtrates, passing through the mesh of the basket, and residues not passing through the mesh.

Advantageously, the stage comprises means for projecting a fluid under pressure on the periphery of the sieving basket, from the outside towards the inside thereof. The invention also relates to a pretreatment process of sediments taken from a bottom of a liquid medium, comprising at least two successive sieving phases.

Advantageously, each of the sieving phases implements operations of: rotating a screening basket having meshes of predetermined size, inside a receptacle, so as to separate filtrates, passing through the meshes of the basket, and residues not passing through the mesh; projecting a fluid under pressure on the periphery of the sieving basket, from outside to inside thereof.

Such a method allows efficient and simple sorting and dewatering of the sediments. It may in particular comprise the following steps, for a treatment cycle of one of said stages: extraction of the filtrates, by rotating said basket at a first speed of rotation; discharging residues, by rotating said basket at a second rotational speed, greater than said first speed; unclogging the basket, by rotating said basket at a third speed, lower than said second speed and activating the fluid projection. 4. List of Figures Other features and advantages of the invention will appear more clearly on reading the following description of embodiments, given by way of simple illustrative and non-limiting examples, and the appended figures, among which: Figure 1 shows a three-dimensional view of the sieving device; Figure 2 shows the holding structure of the sieving device according to a first embodiment; Figure 3 shows the sieving device according to a particular embodiment; Figure 4 shows a sectional view of a sieving stage according to this particular embodiment; Figure 5 is a three-dimensional view of a screening basket and the associated high pressure cleaning system; Figure 6 shows a variant of the high pressure cleaning system; FIG. 7 illustrates an exemplary implementation method according to the invention. 5. DESCRIPTION OF AN EMBODIMENT OF THE INVENTION 5.1 GENERAL PRINCIPLE The invention relates to a device for pretreatment of sediments taken from a bottom of a liquid medium, for example a river, a lake, a pond or a pond comprising at least two successive sieving stages. In some particular cases, a single stage can be implemented.

Such floors can for example be arranged in columns, steps or side by side. The sediment sieving device according to the invention allows the sediments to be progressively dewatered by dissociation of the solid particles and the liquid, sucked up during the sediment sampling.

Each of the sieving stages comprises a sieving basket having meshes of predetermined size, this basket being able to be rotated inside a receptacle, so as to separate filtrates, passing through the meshes of the basket, and residues, not going through the cracks.

At least one of the sieving stages comprises means for projecting a fluid under pressure on the periphery of said sieving basket from the outside to the inside of the basket.

This projection of pressurized fluid allows in particular the cleaning of the cells, or meshes, of the basket. The particles obstructing the cells of the screening basket are thus effectively set in motion, and these cells are uncorked continuously. The fluid projection means may comprise a single nozzle or a plurality of nozzles (for example aligned), delivering as many jets, over the entire height, or at least a large part thereof. They can be fixed or mobile with respect to the receptacle and / or the basket. 5.2 Description of an embodiment

FIGS. 1 and 2 show a sediment pre-treatment device 1 comprising three successive sieving stages 11, 12, 13. This device is used for example following a sediment sample taken from a bottom of a liquid medium. for example a lake, a harbor or a pond. Such sediments generally having a powdery or loamy appearance, include a liquid phase and a solid phase, and need to be dried in order to be stored or recovered.

The pretreatment device 1 thus comprises three stages 11, 12, 13 each forming a centrifuge system allowing gradual drying of the sediments, by sieving sediment particles smaller and smaller. The stages 11, 12, 13 are assembled in stairs in the embodiment described, but could as well be assembled in column or side by side.

As illustrated in FIG. 2, the stages 11, 12, 13 can be fixed to a structure 2 comprising one or more walls 21 and one or more roofs 22, forming a shelter, and intended to rest on the ground or on a barge. The wall 21 of this structure 2 comprises in particular on its inner face projecting elements 23, 24, 25 now fixed each of the sieving stages relative to each other, and relative to the ground. Other holding structures can be envisaged as a perforated structure.

Figure 3 shows the stages 11, 12, 13 sieving the device according to a preferred embodiment. In particular, each stage comprises a hood closed tank, provided with a high pressure cleaning system, a discharge and a discharge pipe, as described more precisely to follow, in correspondence with Figure 4.

A first screening stage 11 forming a first centrifuge system thus comprises a basket 3 provided with meshes on its surface, so as to form a filter allowing only a certain particle size to pass. The basket 3 preferably has a frustoconical shape, the perimeter of its high edge being greater than the perimeter of its low edge, the basket 3 thus being flared in its high edge. The basket 3 is also provided with an ejector rim 31 in its upper part as shown in FIG. 5. The size of such a basket is in correspondence with the volumes of sediment to be extracted during the entire cycle.

Such a basket 3 may also have any other form facilitating the drying out and the ejection of the sediments. One can for example implement a basket capable of changing inclination depending on the treatment phase. Thus, the basket has a nominal diameter in a dewatering phase, and a larger diameter in a sediment ejection phase. This can for example be provided by three sliding means at 120 ° in the upper part of the basket.

This basket 3 is secured to an axis 4 adapted to be actuated in rotation by a motor 8, preferably electric. Thus, the base of the basket is advantageously mounted tight around the axis of rotation 4, but a mechanical connection by belt or reducer can also be considered.

A receptacle 5, of a diameter slightly greater than the basket and provided with an inclined base 51, receives the screening basket 3, the lower end of the axis 4 being connected to the base 51 of the receptacle 5. To do this, the lower end of the axis 4 is provided with a base 41 comprising a ball bearing 42, and cooperates with a bearing support 52 emerging in the center of the base 51 of the receptacle 5.

The receptacle 5 is mounted in a tank 6, which can take any type of shape (cylindrical, cubic, frustoconical ...). In the embodiment described, the vessel has a substantially frustoconical shape, having under the receptacle 5, a funnel-shaped element for discharging residues. By residues is meant the sediments deposited in the sieving basket 3 and too large to cross the mesh of the basket.

The tank 6 is provided with a cover 7 pierced at its center to receive the axis 4 which is secured to the screen basket 3. The motor 8, to turn this axis 4 and to activate the centrifugation process, is located at the upper end of the axis 4, and above the cover 7.

Furthermore the receptacle 5 is fixed by different points to the tank 6, the receptacle 5 and the tank 6 forming a fixed assembly. Thus, after a certain centrifugation time, and because of an increase in the speed of rotation, the residues that are too large to pass through the meshes of the basket 3 are ejected outside the basket 3 via the ejector flange 31 and fall into the tank 6, then are conveyed for conditioning by gravitation to the end 61. The residues may optionally then be recovered in a storage tank, as shown in Figures 1 and 2.

Moreover, the receptacle 5 is in connection with means for discharging the filtrates, which may for example take the form of a discharge nozzle 9 (or a tube, a channel, etc.) placed in the end the lowest of the receptacle. Filtrates are the set of liquid and sedimentary particles, having crossed the mesh during the rotation of the basket 3.

The receptacle 5 is also provided with means for projecting a fluid under pressure, which comprise in the embodiment described a channel 10 for transporting the fluid (preferably water, but possibly also oil or petrol). ) provided with a plurality of nozzles 101 over part of its height. These nozzles are shown in more detail in FIGS. 6 and 7. The channel 10 is inserted inclined through the cover 7 of the tank 6 and the receptacle 5 so as to orient the nozzles 101 for projecting the fluid perpendicularly to the outer surface of the basket 3 and all the way up. The nozzles 101 are thus positioned so as to come close to the outer surface of the basket 3. In an alternative embodiment, a single movable nozzle moves along the channel 10 in order to project the fluid between the low edge and the high edge of the basket filter 3. In another embodiment, shown in FIG. 6, the nozzles 101 are uncovered and respectively covered by a rotation of a sealing envelope 20 around the channel 10, so as on the one hand to allow (and respectively to prevent ) the projection of high pressure fluid arriving in the channel and also prevent the particles passing through the basket 3 during centrifugation to obstruct the nozzles. For example, the rotation of the envelope may naturally be initiated by the rise in pressure of the channel. Of course, the means for projecting the fluid under pressure are not limited to the examples mentioned above.

The fact of projecting the pressurized fluid over the entire outer surface of the basket 3 and towards the inside of the basket, allows in particular to unclog the meshes of the filter having been obstructed by the sediments, and to restart the particles. The sieving stage 11 is connected to the sieving stage 12 by the overflow nozzle 9 guiding the filtrates from the receptacle 5 to the next sieving basket. As represented in FIGS. 1 and 2, the different sieving stages 11, 12, 13 of the device 1 can also communicate with each other via a piping system comprising, in the case of a staircase assembly, elbow outlet tubes. 201, 202, 203. In the case of column mounting, these discharge tubes would be straight. The sediments are thus discharged into the screen sieve 3 of the first stage 11 by means of a first evacuation tube 200.

The tank 6 of the first stage 11 is open on a second discharge tube 201 which makes it possible to evacuate the filtrates. This tube 201 is oriented by a bend towards the sieving basket of the second sieving stage 12. A third tube 202 similarly discharges the filtrates from the second stage 12 to the third stage 13. Finally, a fourth tube 203 emerges from the tank the last stage 13 and pours the filtrates, which are at this liquid stage, to a reservoir or in the starting environment (port, lake, pond ...).

Each of the stages 11, 12, 13, regardless of the embodiment, therefore has a similar structure, forming a centrifuge system. Only the size of the mesh of the sieving basket varies so that the filtering of the sediments is gradually refined as and when the stages are crossed. Thus, in the embodiment described, the first sieving stage 11 retains large particles larger than 5 mm, the second stage 12 filters residues of average size between 1 and 5 mm, and the third stage 13 treats small particles smaller than a millimeter in size. At each stage pass, the residues can be ejected to a storage bin 21, 22, 23 corresponding, and recovered for recovery. For example, large-scale waste (pebbles, gravel ...) can be used for road sub-layers, medium-sized waste (sand) can be assembled into large bags, and waste fine size valued in agronomy. 5.3 Description of operation

The operation of the device is described in connection with FIGS. 1 to 5.

Such a device 1 sieving sediment can rest on the ground or be installed on a barge, on the surface of a liquid medium (port, pond, lake ...), the latter configuration allowing sediment not to go through a stage of "waste".

The sediments, of pulverulent type, recovered during a dredging operation, for example, are automatically dumped inside the first screening basket 3 of the first stage 11.

As illustrated in FIG. 7, the process of the invention implements, for each sieving stage, successive sieving cycles. A sieving cycle comprises several phases, or steps, after the first stage sieve has received (step 70) a sediment dose to be treated:

During a first phase 71, of a duration appropriate to the desired drying, the electric motor 8 is actuated, driving in rotation the axis 4 which is secured to the basket 3. The rotation of the basket, in the manner a centrifuge, increases the gravity field around the sediments: they are pressed against the hole surface of the basket 3, and water and particles smaller than the size of the holes are projected through the basket 3 , and join the receptacle 5 and the tip 9, preferably placed above a second sieve basket of the next sieving stage to undergo a second treatment, the second sieving basket having meshes of smaller size.

In a second phase 72, the speed of rotation of the basket 3 is then increased so as to project the residues that have not passed through the holes, along the inclined walls of the basket and towards the ejection edge 31 at the top of the basket. The residues, due to the speed acquired during the rotation of the basket, are ejected into the tank 6 and join the funnel 61 for the purpose of being transferred and possibly stored in storage bins.

A third phase 73 of rotation of the basket 3, slower, is accompanied by the startup of nozzles 101 for spraying fluid under pressure. The fluid is thus projected over the entire height of the basket 3, and because of its rotation over its entire periphery. The pressure exerted makes it possible to unclog the holes of the basket 3 by pushing the particles obstructing the filter towards the center of the basket. Thus, the following sieving operations do not lose in effectiveness.

Finally, during a fourth phase 74, the supply of the nozzles 101 cut off projection and the motor 8 is stopped, the rotation of the basket is thus stopped. A new sediment spill in the basket 3 can also be envisaged, it operates with a slow speed of rotation, so as not to completely stop the engine 8.

The cleaning fluid flowing in the receptacle 5 causes the remainder of sediment particles filtered towards the tip 9, then to the second stage 12 sieving. Each sieving stage reproduces these same phases constituting a sieving cycle. All sieving stages can operate at the same time, only the filling of the highest basket is automatically performed before each rotation. Furthermore, the rotation of the baskets, the speed of rotation of the baskets and the distribution of the cleaning fluid are advantageously automated so as to make the sediment treatment operations more fluid and efficient.

When the three stages 11, 12, 13 of sieving have been crossed, the ultimate filtrates are preferably substantially liquid and can be returned to the environment in which the sediments have been removed or transferred to a treatment zone, if polluted.

Claims (14)

1. Device (1) for the pretreatment of sediments taken from a bottom of a liquid medium, comprising at least two successive sieving stages, each of said sieving stages comprising a sieving basket (3) having meshes of predetermined size, capable of being rotated inside a receptacle (5), so as to separate filtrates, passing through said meshes of said basket (3), and residues not passing through said meshes, characterized in that at least one of said sieving stages comprises means for projecting a pressurized fluid onto at least a portion of the periphery of said sieving basket (3), from the outside towards the inside thereof, and in that said basket (3) 3) sieving has a frustoconical shape with an upper edge wider than the lower edge. 2. Device (1) for pretreatment of sediments according to claim 1, characterized in that said projection means comprise a plurality of nozzles (101) distributed over the height of said periphery. 3. Device (1) sediment pretreatment according to any one of claims 1 to 2, characterized in that said basket (3) is flared near its upper edge. 4. Device (1) for pretreatment of sediments according to any one of claims 1 to 2, characterized in that said basket (3) is mounted on an axis (4) of rotation therethrough, and movable relative to said receptacle ( 5). 5. Device (1) sediment pretreatment according to claim 4, characterized in that the upper end of said axis (4) of rotation is driven by a motor (8). 6. Device (1) for pretreatment of sediments according to any one of claims 1 to 5, characterized in that said receptacle (5) has an inclined bottom (51) guiding said filtrate to transfer means. 7. Device (1) for pretreatment of sediments according to claim 6, characterized in that said filtrate transfer means comprise a discharge nozzle (9). 8. Device (1) for pretreatment of sediments according to any one of claims 1 to 7, characterized in that said receptacle (5) is fixed inside a tank (6) receiving said residues. 9. A pretreatment device for sediment according to claims 1 to 8, characterized in that said vessel (6) has, under said receptacle (5), a funnel-shaped, guiding said residues to evacuation means (61). 10. Device (1) for pretreatment of sediments according to claims 1 to 9, characterized in that it comprises control means controlling the rotation and / or speed of rotation of said baskets (3) and / or the distribution said fluid under pressure. 11. Device (1) for pretreatment of sediments according to claims 1 to 10, characterized in that it comprises three successive sieving stages (11, 12, 13). 12. Pretreatment stage for a device (1) for sieving sediments taken from a bottom of a liquid medium, comprising a sieve basket (3) having meshes of predetermined size which can be rotated inside a receptacle (5), so as to separate filtrates, passing through said meshes of said basket (3), and residues not passing through said meshes, comprising means for projecting a fluid under pressure on at least a portion of the periphery of said sieve basket (3), from the outside to the inside thereof, characterized in that said sieve basket (3) has a frustoconical shape with an upper edge wider than the lower edge. 13. A pretreatment process for sediments taken from a bottom of a liquid medium, comprising at least two successive sieving phases, characterized in that each of said sieving phases comprises operations of: rotating a basket (3) sieve of frustoconical shape having meshes of predetermined size, inside a receptacle (5), so as to separate filtrates, passing through said meshes of said basket (3), and residues not passing through said meshes, projection a fluid under pressure on at least a portion of the periphery of said sieve basket (3), from the outside to the inside thereof. 14. pretreatment process according to claim 13, characterized in that it comprises the following steps, for a treatment cycle of one of said stages: extraction of the filtrates, by rotating said basket (3) at a first speed of rotation; discharging residues, by rotating said basket (3) at a second rotational speed, greater than said first speed; unclogging the basket (3), by rotating said basket (3) at a third speed, lower than said second speed and activating the fluid projection.