FR2766812A1 - Device for purification of water by electrical treatment - Google Patents

Abstract

Device for electrical treatment of a liquid electrolyte, especially water to be purified, comprises at least one tubular element (1) consisting of a first insulating conduit (2) through which the liquid to be treated flows, made of a dielectric material capable of withstanding a high voltage of greater than 10<7> V/m and having a selected wall thickness (e1), a first conductive coating (3,4,5) surrounding the first dielectric layer constituting a high tension electrode, a second insulating conduit (6) having the same properties as the first insulating layer, surrounding the first conductive coating and serving to insulate the device from any external contact; and a second metallic conductive coating (7,8) surrounding the second insulating conduit and serving to ensure both the mechanical protection of the conduit and the safety of any operatives; a high tension electrical power source (9) of which one terminal is connected to the first conductive coating layer by way of a connector (11) to apply, between this conductive coating and the liquid which is maintained at earth potential, an electrical potential difference (V) of which the value is determined by wall thickness (e1) of the first insulating conduit (2), such that the electric field (E1 = V/e1) has as high a value as possible without reaching levels which would threaten the electrical breakdown resistance of the insulating conductor; and a connection (12) between the second electrical conductor (7,8) and earth. Preferably the first conduit layer is of PTFE, polyethylene or polypropylene

Description

Device for the electrical treatment of a liquid electrolyte, in particular of water to be purified.

The invention relates to the electrical treatment of liquid electrolytes, and in particular of water to be purified containing colloidal micelles (industrial, agricultural waste water, etc.).

A device for the electrical treatment of liquid electrolytes of high conductivity, in particular city water or river water, is already known from publication FR-A-2 640 655.

This known device essentially comprises a container suitable for being crossed by a flow of the liquid to be treated, at least one electrode arranged inside the container, coated with an insulating layer and of a shape chosen to increase the contact surface. with the liquid electrolyte, at least one counter-electrode arranged inside the container and comprising a bare surface or coated with an insulating layer, as well as a high voltage direct current supply whose positive and negative terminals are respectively connected to the electrode and the counter-electrode, the polarity used depending on the type of treatment to be carried out.

The treatment carried out in this known device involves a wall phenomenon in contact between the insulating layer which covers the electrode and the electrolyte to be treated. It is therefore essential that the surface of the electrode is as large as possible so that the contact surface between the insulating layer and the electrolyte to be treated is as extensive as possible.

This known device operates satisfactorily and is particularly suitable for treating city water or river water to prevent scale build-up in installations. It is also very effective for treating the water of the so-called wet cabins of industrial painting installations (automotive industry for example) in order to cause flocculation, on the surface of the tank which collects the flow, of the waste formed by the aerosols of paint falling on the water curtains of these cabins. This known device prevents scaling of the pipes and causes flocculation of the paint by promoting chemical reactions leading to the production of calcium carbonate microcrystals in suspension in the liquid. In the first application cited above, the deposit of scale occurs not on the walls of the installations, but on these micro-crystals; in the second, the micro-crystals, which have electrostatic charges of different sign, transfer these charges to the paint micelles which capture them; these micelles then assemble into fine dendrites. The paint clusters are structured in the form of very light sponges which float on the surface of the water (flocculation).

Thus, this known device involves the use of a container in which the treatment is carried out, the liquid circulating on the outer surface of one or more electrodes placed in this container. The presence of this container makes the structure of the device heavier, increases its bulk and its shortness.

The object of the invention is in particular to overcome the aforementioned drawbacks. It aims in particular to provide a treatment device operating according to the same physical principle as the aforementioned device but having the particular advantage of having a simplified structure, based on the principle of using the high-voltage electrode as a receptacle, and as a counterelectrode. the metal piping to the earth of the external distribution or circulation network for the liquid to be treated.

For this purpose, it proposes a treatment device of the type defined in the introduction, which comprises at least one tubular element comprising a first cylindrical insulating duct suitable for being traversed by the liquid to be treated and formed of a dielectric material suitable for withstanding an electric voltage. high (disruptive potential greater than 107 V / m) and having a wall of selected thickness e1; a first conductive coating surrounding the first conduit and suitable for constituting a high voltage electrode; a second insulating conduit with the same properties as the first, surrounding the first conductive coating and intended to isolate it from any external contact; a second conductive coating, metallic, surrounding the second insulating duct, and intended to ensure both its mechanical protection and the safety of any operators; a high voltage electric generator, one terminal of which is connected to the first conductive coating by a connection for applying between this coating and the liquid maintained at earth potential, an electric potential difference whose value V will be chosen according to the thickness e1 of the wall of the first duct so that the electric field E1 = V / e1 has the highest possible value, without reaching dangerous values for the voltage withstand of the insulating duct as well as a connection to the earth coupled to the second conductive coating.

Thus, the device of the invention has a structure or configuration which differs from those described in the aforementioned patent, essentially by the fact that the container in which the treatment is carried out disappears since it is replaced by one or more elements. formed of concentric tubes, the insulating tube adjacent to the liquid playing the role of the conductive coating of the high voltage electrode of the aforementioned patent, and the conductive coating which is superimposed on it playing the role of this electrode.

In summary, while in the configurations of the aforementioned patent, the liquid to be treated always circulates outside of electrodes covered with insulation, in the device of the invention, the liquid circulates inside one or more tubular elements. Each complete tubular element is structured around a hollow electrode formed by a conductive coating surrounding an insulating duct in which the liquid to be treated circulates.

As a result, the invention provides a simplified configuration, which does not include a container and which is formed by the assembly of one or more tubular elements, or pipes, through which the liquid to be treated passes.

This results not only in a simplification of the structure, but also in a reduction in size and a reduction in costs.

Each tubular element, or pipe, is formed by a coaxial assembly of four main elements, which can be fitted or fitted into each other.

The dielectric material of the first insulating conduit is preferably a polymer impermeable to water and obtainable by extrusion.

The polymer is advantageously chosen from polytetrafluoroethylene (PTFE), polyethylene and polypropylene.

According to another characteristic of the invention, the first insulating duct is treated on the outside to allow the wetting of a layer of adhesive or of conductive paint.

Indeed, the first coating advantageously comprises in its central part a layer of adhesive or conductive paint. This layer can either be used alone or be associated with a tubular metal casing. Used alone, this layer of conductive adhesive acts as a high voltage electrode. In association with a conductive tubular casing acting as a high voltage electrode, it avoids the drawbacks due to the presence of a high electric field in the layer of air trapped between the insulating tube and the conductive casing under voltage.

The second insulating conduit is preferably formed from a dielectric polymer, advantageously the same as that of the first conduit. Like the first and for the same reasons, the second insulating duct is preferably treated in order to receive on the inside on its central part and on the outside over its entire surface a conductive paint.

The conductive paint located inside is able to come into electrical contact with the first conductive coating. The conductive paint located on the outside of the second duct then serves to form, at least in part, the second conductive coating. For certain applications, for example during laboratory experiments carried out by qualified personnel, the second conductive coating may be formed only from this conductive layer. On the other hand, for any industrial or domestic application, the second coating will further comprise a solid metal tube surrounding the conductive layer and serving as a protective envelope, and possibly as a pressure vessel. In the latter case, for the reasons which have been explained previously, this second conductive coating, earthed for safety reasons, advantageously comprises a conductive layer deposited externally on the second insulating duct, in order to avoid the drawbacks due to the presence of a high electric field in the layer of air trapped between the insulating tube and the earthed metal casing.

In a preferred embodiment of the invention, the high voltage electric generator applies, between the electrolyte in electrical contact with the earth and the first conductive coating, a direct potential, positive or negative, or an alternating potential, capable of produce on the inner wall of the first conduit an electric field as high as possible, without reaching values liable to affect the voltage withstand of the dielectric material. To fix ideas, this electric field can reach values between 10 and 30 kV / mm.

In the case of an alternating potential, the electric field must have a peak value as high as possible, without however affecting the voltage withstand of the dielectric material. The electric field through the wall of the insulating duct can expect peak values between 10 and 30 KV / mm.

According to another characteristic of the invention, the device comprises several tubular elements arranged in a series and / or parallel connection and interconnected by connectors.

These fittings can be metallic and electrically connected to the earth and to the second conductive coatings of the tubular elements. Alternatively, they may be insulating fittings, in which case the second conductive coatings of the tubular elements must then be individually grounded.

The second conductive coating of the tubular elements can also be connected to the metal body of an installation, this metal body being connected to earth. It may for example be the body of a tank, the body of a circulation pump, etc.

In the following description, given only by way of example, reference is made to the accompanying drawings, in which - Figure 1 is a cross-sectional view of a device according to the invention - Figure 2 is a detail to scale enlarged of FIG. 1 showing the constituent elements of a tubular element; - Figure 3 is a perspective view of a device with several tubular elements mounted in series - Figure 4 is a perspective view of a device with several tubular elements mounted in parallel - Figure 5 is a side view of a device comprising two tubular elements, the outer casings of which are connected by a conductive connector; and - Figure 6 is another side view of a device comprising two tubular elements connected by an insulating chord.

Reference is firstly made to FIG. 1 which represents a device for the electrical treatment of a liquid electrolyte according to the invention, and comprising a tubular element 1 having a generally cylindrical shape of revolution.

This tubular element is formed by an assembly of several coaxial or concentric components. I1 firstly comprises a first insulating duct 2 which constitutes an inner tube suitable for coming into contact with the liquid L to be treated. The insulating pipe 2 is formed from a dielectric material, in the example a polymer capable of being obtained by extrusion, preferably polyethylene or else poltetrafluoroethylene (PTFE). This polymer is impermeable to water and is capable of withstanding high electrical voltages, that is to say generally a breakdown potential greater than 107 V / m. This duct 2 has a thickness e1 (FIG. 2) chosen to allow, as will be seen below, the production of an electric field as high as possible on the inner wall of the duct 2, without thereby reaching values that are dangerous for the voltage resistance of the insulating conduit 2.

The duct 2 is treated on the outside to allow the wetting of a layer of glue. This treatment can be carried out for example by the corona effect. Indeed, the insulating duct 2 is intended to subsequently receive, on its outer lateral surface, with the exception of the areas located in the vicinity of its ends, a layer of conductive adhesive 3 forming part of a first conductive coating surrounding the duct 2. The zones located in the vicinity of the ends must ensure sufficient insulation of the conductive coating with respect to the earth; for this, they must not be covered with conductive material.

For certain applications, the conductive coating may consist solely of the aforementioned conductive adhesive layer 3. In the particular example of Figure 2, the conductive adhesive layer 3 is combined with a metal casing 4. This conductive adhesive layer is intended to prevent ionization of the air trapped in the gaps possibly located between insulating tubes and conductive tubes acting as electrodes.

The insulating tube 6, plated around the metal casing 4, has undergone a treatment so as to be covered on the inside (except in the vicinity of its ends) and on the outside (over its entire lateral surface) with layers of conductive glue or paint, respectively 5 and 7, similar in their constitution to layers 3, and whose presence meets the same concerns as the presence of layer 3. The role of this tube is to electrically insulate all the elements 3, 4, and 5, connected to the high voltage terminal of the generator, of the assembly connected to earth and formed by the conductive layer 7 and by the metal tube 8 which surrounds it, this second assembly playing the role of electrode to earth. The tube 6 is formed from a dielectric material, preferably a polymer of the same type as that of the insulating duct 2; located between a set of high voltage elements and a set of earthed elements, it has a sufficient thickness e2 to avoid any risk of breakdown by disruption of the dielectric used. The inner wall of the metal tube 8, covered with the conductive adhesive 7, is in contact with the insulating tube 6. The tube 8 serves as a protective casing or pressure-resistant enclosure wall.

The device of the invention further comprises a high voltage electric generator 9 connected to the first conductive coating 3, 4, 5. In the example, it is a direct voltage generator of which one of the terminals 10 is connected to the conductive coating 3, 4, 5 by an electrical connection 11 which passes through an insulated bushing through the tubes 6 and 8 and the coating 7. The other terminal 13 of the electric generator 9 is connected to earth. This generator produces a high potential, for example between 5000 and 20,000 V, depending on the thickness e1 of the wall of the insulating duct 2. The values of the high voltage and of the thickness of the duct 2 are chosen so as to produce, on the inner wall of conduit 2, an electric field as high as possible, without however reaching a dangerous value for the voltage withstand of the insulating material. By way of example, it is possible to obtain an electric field with a value between 10 and 30 kV / mm for an insulating material of the non-charged PTFE type and of good quality, and even more for a polyethylene material. In an exemplary embodiment, the thickness e1 of the duct 2 is 1.5 mm and the applied potential is a continuous potential of 30 kV.

The device further comprises an electrical connection 12 connecting the second conductive coating 7, 8 to the earth. The electrical connection 12 is connected in the example to the tube 8 surrounding the conductive layer 7. In an alternative embodiment in which the tube 8 is not used, it is then the conductive layer 7 which is connected to earth by a conductive collar and. a suitable connection (not shown).

Reference is now made to FIG. 3 which shows an arrangement according to the invention comprising several tubular elements 1 mounted in series and connected in pairs by elbow connectors 13.

These tubular elements 1 can thus be passed through in series by a liquid to be treated entering through an inlet 14 and exiting through an outlet 15.

In the embodiment of FIG. 4, the device also comprises several tubular elements 1, but these are mounted in parallel and supplied jointly by a common connector 16 provided with a common inlet 17. Another connector (not shown) is mounted at the outlet of the tubular elements 1 to collect the liquid once treated.

Of course, it is possible to design different devices combining a series connection and a parallel connection according to the needs and the size or installation constraints.

Depending on the flow to be treated, the tubular elements are joined in series or in parallel by joints or elbows. It is thus possible to produce, from modular elements, structures resembling externally sets of boiler or radiator tubes for carrying out the treatment of liquid electrolytes.

The conductive coating worn at high voltage does not extend to the elbows or joints. A distance calculated to avoid the appearance of creeping loads in fact separates the edges of the conductive coating from the junction of the first insulating duct (interior duct) with the elbow or the joint. It follows that all the agreements are treated as parts to the ground, which considerably simplifies the realization of the connections in series or in parallel.

As shown in figure 5, the outer envelopes of two tubular elements 1 can be electrically connected by a metal connector 20 which is connected to earth by a connection 21. In this case, the tightness of the water circuit to be treated can be ensured by O-rings located between the tube 2 and the metal fittings 20, these fittings having an appropriate shape to be able, moreover, to participate in the continuity of the external electrical and mechanical protection of all the tubular elements 1.

In the case of FIG. 6, two tubular elements 1 are interconnected by an insulating connector 22 connected to the tube 2. In this case, the connection to the earth is effected directly on the outer casing of the tubular elements 1. D 'In general, the connection with the earth can be made either directly on an earth connection, or by means of a metallic body belonging to the installation, for example a tank or a circulation pump.

The device which is the subject of the invention has the advantage, compared with the devices of the prior art, of increasing, for the same liquid flow rate, at least by an order of magnitude the ratio of the active surface to the volume of the liquid. electrolyte, thus increasing in the same ratio the effectiveness of the treatment
The device which is the subject of the invention makes it possible to treat electrolytic liquids, such as city or river water, industrial water, domestic heating water, waste water or waste washing water.

This device finds different applications. It can be used to remove scale deposits in water distribution or domestic heating installations. I1 can also treat water and liquid electrolytes containing a colloidal phase that we want to flocculate in order to separate it from the rest of the liquid. As such, it can be used for the flocculation of paints collected in a wet cabin (automobile bodywork). It can also be used to improve the efficiency of flocculants used for the removal of various liquid residues mixed with washing water.

Claims (15)

Claims 1. Device for the electrical treatment of a liquid electrolyte, in particular of a water to be purified, characterized in that it comprises at least one tubular element (1) comprising a first insulating duct (2) suitable for being crossed by the liquid to be treated and formed of a dielectric material suitable for holding a high electrical voltage (disruptive potential greater than 107 V / m) and having a wall of selected thickness (el), a first conductive coating (3, 4, 5 ) surrounding the first insulating conduit and suitable for constituting a high voltage electrode, a second insulating conduit (6) with the same properties as the first, surrounding the first conductive coating and intended to isolate it from any external contact; and a second metallic conductive coating (7, 8) surrounding the second insulating duct, and intended to ensure both its mechanical protection and the safety of any operators a high voltage electric generator (9) of which one terminal (10) is connected to the first conductive coating via a connection (11) for applying between this coating and the liquid maintained at earth potential, an electric potential difference whose value (V) will be chosen as a function of the thickness (e1) of the wall of the first insulating duct (2) so that the electric field (E1 = V / el) has the highest possible value, without reaching dangerous values for the voltage withstand of the insulating duct; and finally a link (12) to earth coupled to the second conductive coating. 2. Device according to claim 1, characterized in that the dielectric material of the first insulating conduit (2) is a polymer impermeable to water and capable of being obtained by extrusion. 3. Arrangement according to claim 2, characterized in that the polymer is chosen from polytrafluoroethylene (PTFE), polyethylene and polypropylene. 4. Device according to one of claims 1 to 3, characterized in that the first insulating duct (2), treated externally on its central part to allow wetting, receives on this central part a layer of glue or paint conductive (3). 5. Device according to claim 4, characterized in that the conductive adhesive layer (3) is combined with a tubular metal casing (4). 6. Device according to one of claims 1 to 5, characterized in that the second insulating duct (6) is formed from a dielectric polymer, treated to allow wetting, receives inside and outside conductive paint layers (5) and (7). 7. Device according to claim 6, characterized in that the second coating further comprises a solid metal tube (8) surrounding the conductive layer and serving as a protective casing or a pressure vessel. 8. Device according to one of claims 1 to 7, characterized in that the high voltage electric generator (11) applies between the electrode in contact with the earth and the first conductive coating a direct potential, positive or negative, suitable in applying to the inner wall of the first insulating duct (2) an electric field as high as possible, without however affecting the voltage withstand of the dielectric material. 9. Device according to claim 8, characterized in that the electric field through the wall of the insulating conduit (2) reaches values between 10 and 30 kV / mm. 10. Device according to one of claims 1 to 7, characterized in that the high voltage electric generator (11) applies to the first conductive coating an alternating potential, suitable for applying to the inner wall of the first insulating conduit (2). an electric field with a peak value as high as possible, without however affecting the voltage withstand of the dielectric material. 11. Device according to claim 10, characterized in that the electric field through the wall of the insulating duct (2) reaches peak values of between 10 and 30 kV / mm. 12. Device according to one of claims 1 to 11, characterized in that it comprises several tubular elements (1) arranged in a series connection and / or in parallel and interconnected by connectors (15, 20, 22 ). 13. Device according to claim 12, characterized in that the connectors are metallic, electrically connected to earth and to the second conductive coatings (8) of the tubular elements (1). 14. Device according to claim 12, characterized in that the connections are insulating, and in that the second conductive coatings (8) of the tubular elements (1) are individually connected to earth. 15. Device according to one of claims 1 to 14, characterized in that the second conductive coatings (8) of the tubular elements (1) are connected to the metal body of an installation, this metal body itself being connected to earth. .