FR2860532A1 - DEVICE FOR DEVASEMENT WITHOUT POLLUTION OR NOTABLE WATER CONSUMPTION - Google Patents

Abstract

Device for the devastation without pollution or significant water consumption. The invention relates, in the field of civil engineering, the devastation of reservoirs and rivers. The usual techniques have several disadvantages, among others: polluting discharges, consumption of considerable water, difficulty in handling the displaced vase.The device according to the invention is, preferably, characterized by the combination of the following methods which makes it possible to remedy the mentioned drawbacks: vibration of the sludge to be treated; cutting of the vase by a cutter of sufficient speed to obtain, with addition of water, a homogeneous mixture; pumping the mixture; injection of a flocculant product causing, at the point of rejection, the segregation of the mixture; discharge or recovery of clear water; manipulation, without hydraulic drive, and reuse of the flocculated vase.Variants consist in modifying, depending on the case of species, the relative impact of the various combined processes.The device according to the invention is particularly suitable for the devastation of dam lakes .

Description

The present invention relates, in the field of civil engineering, a

  device to eliminate the accumulated mud in the water reservoirs (dams lakes in particular), without significant pollution or overall water consumption, and this, by successive modifications of the rheological behavior and manipulation of the vases.

  The deposit in the bottom of reservoirs and watercourses (also that the water stagnates or circulates) vases, especially from watersheds, reduces their capacity (up to more than 50% of the available volume) and shortens their capacity. lifetime. The solid part of this water-saturated sludge consists mainly of clays or silts (silts in English) whose elementary particle size is of the order of less than 1 to a few tens of microns.

  The technique usually used, as soon as the dimension of the restraint justifies a rational organization, shown schematically in FIG. 1, consists in cutting the surface in the vase (4) by a knife rotating about its axis, called a cutter (5). and mounted on a drag (1); and pumping water (3) loaded with these pieces of sludge in floating pipes (2), which reject this mixture generally downstream of the reservoir (6), from which flows the charged water microscopic particles of slime (7), while the remaining eroded slime accumulates (8).

  This device has serious disadvantages considerably increasing or preventing the operation, in particular: - To prevent the plugs clog the flow pipes, it is necessary to drive the cut pieces of sludge, rejected by the pipes, in a fort water flow, which induces a water consumption of a volume largely multiple of that of the vase in place evacuated with this volume of water (knowing that after the transitional phase of deposit, the vases of various geological origins reach a pseudo stable state characterized by a relatively uniform water content and cohesion, slowly increasing with the depth of silt). Not only is this water consumption expensive, but often it only works after short rainy periods.

  - The rejected mixture (6) is, in spite of a uniform color, of concentration (hereinafter the expression: concentration of the mud or of the mixture, signifies: ratio of the dry matter weight of a vase volume to that of the water concerned by this heterogeneous volume of sludge, or mixture), containing pieces of sludge (8) with a water content close to that of the sludge in place, and polluted water (7) by the particles of eroded vase pieces during transport, much less concentrated than (8), which is deposited in the course of the course of water (often on several kilometers, considering the small dimension of the solid particles) and causes a prohibitive pollution.

  - The vases are more or less thixotropic, that is to say that their resistance to shear at rest is higher than when they are in motion, which practically prevents their dredging and handling by shovels or shovels. buckets, and preferred their hydraulic transport, generally gravity.

  The device according to the invention consists in reducing or eliminating these disadvantages by the original combination of processes whose principle is known, but is not applied to the devastation, for lack of their combination. In its preferred form, represented in FIG. 2, it consists in: -a) submitting the sludge (4) to forced vibrations which reduce or destroy its resistance to shear (which, in the fine soils which constitute the majority of the silt , is comparable to its cohesion, that is to say to its shear strength without overload), by vibrating the cutter (10), and / or by supplying independent sources of vibration, preferably consisting of vibrating needles ( 9), arranged near the cutter, because the source of vibrations destroys the cohesion of the vase only in a limited radius.

  -b) Cut the vibrated vase with a cutter (10), vertical or tilting, rotating or not, but at high speed (which allows, at equal power, the reduction of the cohesion by the vibration) in order to obtain, by mixing with the water, simultaneously pumped from the reservoir (3) and / or injected separately (11), a homogeneous mixture (unlike water-driven mud pieces) whose water content is appropriate to the following the treatment.

  -c) Pump this homogeneous mixture (pump 12).

  -d) In the discharge line (13) of the pump, inject a flocculant product (of a chemical nature appropriate to that of the sludge), in preferentially liquid form by pumping from a reservoir (14), so that, preferably point of rejection (15) of the mixture thus treated, the particles of clays and silts accumulate in flocs (16) which, by their millimetric size, precipitate by gravity, causing the segregation of the flocculated flask and water released clear (17) which is recovered in the reservoir and / or discharged elsewhere, especially downstream.

  The yield of the flocculation clearly depends on the concentration of the treated mixture. Therefore, only a mixture of appropriate and relatively homogeneous concentration can be properly flocculated, hence the need for the previously described treatment. In addition, the distance between the flocculant injection point (s) and the segregation point between the flocculated flask and the released water must be optimally chosen so as to allow the flocs to be formed by mixing the mixture stream. (of the pump 12) and the flocculant stream (of the tank 14), without destroying them (at rest, or subjected to less turbulent manipulations, the flocs are stable).

  -e) Choose the mode and the deposit zone, as well as the destination, best suited to the case in question, knowing that flocculation, magnifying the elementary particles of the mixture of clay or silty origin, gives them an internal friction inhibits their thixotropic properties and improves their permeability, thus rendering the treated mixture manipulable not only by hydraulic drive, but for example by buckets, shovels or conveyor belts placed at the most appropriate place, with a view to its evacuation or reuse (eg agricultural or embankment). The mixture, flocculated according to the invention, has, in fact, mechanical characteristics superior to those of the vase displaced by the conventional method, and, backfilled out of the water table, it has an internal friction gradually sufficient to confer a behavior rubbing soil and carrying, which allows, among other things, to overcome, or overload, possibly after compaction.

  In Figure 2 is shown the application of the invention with evacuation by a conveyor belt (18) discharging into a truck (19). The mode of evacuation obviously depends on the particular case.

  In addition to the discharge of clear water, and its recovery, the invention allows, by improving the internal friction of the treated silt deposit relative to the initial slurry, its handling.

  The efficiency of flocculation depends on the recovery of water (especially in arid countries) and / or the discharge of clear water (essential against pollution by the charged water flowing from the silt deposit, which is observed in the usual technique to date), as well as the handling of the precipitated mixture, easier than the only hydraulic drive. And the effectiveness of the flocculation is conditioned by the initial phase of the invention, necessary to transform the original slime into a homogeneous mixture, whose appropriate concentration allows the application of flocculation under economic conditions.

  In its derived forms, the invention is characterized by adapting to the specific cases: by modifying those of its elements which do not prove indispensable in certain cases, for example by preserving (FIG. 3), after homogenization and adaptation of the concentration of the mixture, the driving in pipe (2), the injection of the flocculant (14) before its end, and the return of clear water (17) in the reservoir from downstream; or, if, locally, a weak cohesion of the vases (before the end of their sedimentation, or in case of weak clay component) makes it possible to be freed from its destruction by vibration or their dilution, to obtain an appropriate mixture following the treatment; or if, locally, a sandy silt allows the precipitation of the mixture without the addition of flocculants; - or by adapting - or completing - some of these elements to additional constraints, for example by using vibration to facilitate the movement of these elements (cutter, drag ...), to create channels, or to improve the use grids to stop large disruptive elements (trees and plants, blocks ...); or, in the absence of free water above the silt, initially injecting external water and reusing it.

  The invention is applicable, to move any cluster of soils with a preponderance of fine particles, without significant overall consumption of water or pollution, especially for the devastation of dam lakes.

Claims (9)

  1) Method for moving the accumulated vessels in reservoirs and streams, characterized by pumping the sludge and injecting flocculants into the pump discharge line.   2) Process according to claim 1, characterized in that the slurry is mixed with water during pumping.   3) Process according to any one of the preceding claims, characterized in that the vessel is subjected to sustained vibrations.   4) Process according to any one of the preceding claims, characterized in that all or part of the water released by the treatment is recovered.   5) Process according to claim 4, characterized in that all or part of the recovered water is sent into the silted zone.   6) Process according to any one of the preceding claims, characterized in that the flocculated mixture, separated from the free water, is manipulated and / or knocked down without hydraulic drive.   7) Method according to any one of claims 3, 4, 5 or 6, characterized in that the vibration sources are arranged and dimensioned to allow the movement of plant elements in the vase.   8) Backfilling of the product resulting from the treatment according to any one of the preceding claims.   9) Agricultural use of the product resulting from the treatment according to any one of the preceding claims.