FR2663864A1 - Electrode for an electrostatic fluid-treatment device and treatment device incorporating the said electrode - Google Patents

Abstract

According to the invention, the electrode comprises a thin-walled structure (24) made of insulating material covered with an electrically conductive coating (26) on one of its faces. The insulating material is a polymer, while the conductive coating consists of a film of natural or synthetic resin filled with a metal powder. The invention also relates to an electrostatic fluid-treatment device comprising an above-defined electrode.

Description

ELECTRODE FOR ELECTROSTATIC TREATMENT DEVICE
OF FLUIDS AND TREATMENT DEVICE INCORPORATING
THE SAME ELECTRODE
The invention relates to an electrode for electrostatic treatment devices for fluids used in particular for water treatment and for the treatment of fuels for internal combustion engines.

An electrostatic treatment cell has a set of electrodes, at least one of which is isolated from the liquid to be treated by a layer of insulating material. It is known, in particular from patent GB-A-1,274,902 to use treatment electrodes constituted by a metallic core of planar or cylindrical shape covered with a layer of insulating material of constant thickness. The technical realization of this type of electrodes is delicate and expensive. It is most often carried out by injection molding a plastic material on the metallic core or by the use of retractable sheaths of polyfluorethylene.

The object of the invention is to propose improved fluid treatment electrodes in terms of manufacturing, cost and efficiency.

More particularly, the invention provides an electrode for an electrostatic treatment device for fluids, characterized in that it comprises a thin-walled structure of insulating material covered with an electrically conductive coating on one of its faces, said face being intended to be isolated from the fluid to be treated.

Advantageously, the insulating material is a plastic material, preferably a polymer chosen from the group of polystyrenes, ABS, polycarbonates, PVC, PTFE and FEP. The wide choice of usable materials makes it possible to obtain, at low cost, thin-walled structures of the most suitable form for the intended application from conventional plastics processes, polymers, such as injection, extrusion, blowing and thermoforming.

According to a first embodiment of the invention, the electrically conductive coating is constituted by a film of natural or synthetic resin charged with a powder of electrically conductive material, preferably of metal.

Advantageously, the conductive coating consists of acrylic resin loaded with nickel powder.

The resin film, which is initially liquid, is applied like a paint or varnish, after being mixed with a solvent. By choosing a solvent compatible with the plastic material constituting the thin-walled structure, it ensures perfect contact between this insulating material and the conductive film, which significantly improves the passage of electrical charges through the metal-polymer interface and thereby even the electrostatic treatment properties of the electrode.

The invention also relates to an electrostatic treatment device comprising at least one electrode according to the invention defined above, said electrode preferably having a geometry allowing or promoting a turbulent flow of the fluid to be treated.

According to a first embodiment of a device according to the invention usable for the treatment of sanitary water, at least one electrode having an elongated shape is mounted in a central position in the tubular body of a water collector, so as to very quickly create the treatment by contact and by t # rbulence of the fluid to be treated.

Advantageously, the electrode is in the form of a cylindrical sleeve closed at one end and of which the other ex-trematated is secured to a plug mounted at the end of the body of the bull.

According to another embodiment of a device according to the invention, the device comprises means for scanning the active surface of the electrode, the latter being mounted coaxially in a cylindrical body. Advantageously, the scanning means comprise brushes capable of a relative movement of rotation relative to the surface to be cleaned. This embodiment is well suited for the treatment of industrial water.

According to yet another embodiment of the invention, the device comprises, in the passage of the fluid to be treated, means forming a deflector and a fluid mixer to promote turbulent flow of said fluid in the vicinity of the electrode and to rapidly obtain a mixture homogeneous double layers electrically treated with the rest of fluid.

Other advantages and characteristics of the invention will appear on reading the description which follows and which refers to the attached drawings in which
FIG. 1 is a schematic representation in longitudinal section of an electrostatic treatment device according to the invention, FIG. 2 is a schematic representation, according to two variants, of another embodiment of a device according to the invention , and FIG. 3 is an exploded diagrammatic representation of a third embodiment of a device according to the invention.

The electrostatic fluid treatment device illustrated in FIG. 1 comprises a cylindrical tubular body 12 closed at each end by a set of plates 14 and 16. The body has two orifices 18 and 20 for connection to the circuit of fluid to be treated, a closed circuit of industrial water by way of nonlimiting example. The body 12 is preferably made of PVC.

Arranged axially to the body 12, there is an electrode 22 said to be emissive of charges suitably connected to the high voltage HT.

 According to the invention, the electrode 22 is composed of a thin-walled structure 24 made of insulating material reccuserted on one of the faces by an electrically conductive coating 26 (shown for convenience in FIG. 1 by a thick line voluntarily enlarged). In the example described here by way of nonlimiting example, the structure 24, consisting of a closed hollow tubular element, carries the conductive coating 26 on its internal face intended to be isolated from the fluid to be treated. This coating and connects to the high voltage HT by a conductive wire 28 suitably insulated and one end of which is welded to the coating 26. The tubular structure 24 is held in position in the body 12 by means of an axis of my base 27 .

Still within the framework of the invention, the insulating material of the wall of the electrode is a plastic material preferably of the polymer type chosen from the group of polystyrenes,
ABS, polycarbonates, polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE) and the tetrafluoroethylene-perfluoroprene copolymer (FEP).

When the thin-walled structure of the electrode has very high dielectric qualities such as PTFE or FEP which have a dielectric strength of 34 KV / mm for a thickness of lmm with an electric constant at 106 Hz of 2.1, the thickness can be of the order of 0.5 to 1 mm at 10 KV.

The use of PVC for example, which has poorer dielectric strength and poorer dielectric constant requires a thickness of 3 to 5 mm at 10 KV.

In general, the better the dielectric qualities of the polymer, the more the thickness of the electrode wall can decrease.

Before closing the PVC tube constituting the structure 24, an electrically conductive coating film was applied in liquid form, such as a paint or a varnish. the coating is composed of a binder in natural or synthetic resin charged with a powder of electrically conductive material, such as a metal or carbon.

By way of nonlimiting example, the coating is composed of an acrylic resin charged with a nickel powder. The application of the coating is facilitated by mixing a solvent also compatible with the constituent polymer (here PVC) of structure 24, for example a solvent based on ketones or acetates. This results in perfect contact at the coating-insulating interface as a result of the dissolution of the surface layers of the polymer.

The geometry of the electrode relative to the passage 30 left to the fluid to flow through the body 12 is also important. A large electrode area will not be sought. The geometry of the electrode will also condition the effectiveness of the treatment which will not depend on the surface but on the shape which will increase the turbulence.

The electrode must make it possible to promote turbulence in the flow while creating a contact surface phenomenon necessary for the treatment of the fluid, whether this fluid is of high conductivity or dielectric. This electrode can take in the cell a helical, cruciform, cylindrical or planar form (for example in the form of a hollow plate), of one or more cylinders positioned transversely or parallel to the flow, or of any form making it possible to create the turbulence without detachment of the fluid vein. In all cases, a large surface contact between the electrode and the fluid will not be sought, although not being incompatible with the invention.

This appropriate geometry will make it possible to pass very quickly from the laminar flow to the turbulent flow by reducing the so-called transition zone and by promoting the instability of the boundary layer by making it vortex.

The turbulence of the fluid will also be generated by the geometry and the roughness of the wall of the electrode.

The roughness state causes local turbulence agitation which is higher the roughness is greater.

The treatment cell is implemented by applying a high potential difference (5 to 10 KV for aqueous liquids) between the coating and the liquid to be treated circulating between the orifices 18 and 20 depending on the direction Fi -> F2 or vice versa. This liquid will have the same potential as the mass of the generator ET (not shown) itself connected to the general mass of the installation. In the device presented (provided with a PVC body 12), the liquid is earthed to the installation by a metal pipe 32 secured to the inlet orifice 18, and which acts as a counter-electrode.

When a potential difference is applied between the electrically conductive coating and the earth of the installation, a surface phenomenon occurs between the insulator and the fluid to be treated.

With or without voltage, the contact between the fluid to be treated and the electrode reveals a double layer which is due to the phenomena of preferential absorption.

This double layer is composed of a compact layer attached to the wall, the thickness of which is always extremely small (of the order of the ionic radius) and of a diffuse layer, the size of which, linked to the conductivity, can vary from a fraction of a micrometer, in the case of aqueous solutions, to several centimeters in the case of highly purified hydrocarbons or liquefied gases.

When the electrode is put under maintenance, the dielectric coating is subjected to an electric field insufficient to cause its deterioration, but strong enough to cause the migration of electric charges in the impurities of the crystal network of the dielectric.

At this stage, the qualities of the metallic film-polymer contact obtained by the electrodes according to the invention is essential.
This migration causes a surface phenomenon in contact between this insulating layer and the fluid to be treated.

This surface phenomenon results in the appearance of a charge density at the polymer-fulde interface in the double layer. This charge density causes a concentration of ions in the diffuse layer, a concentration which has the effect of accelerating, in the case of water treatment, the reactions of crystallization of CaC03 germs (elevation of bicarbonate ions C03H-, hydroxyl OH- and calcium Ca ++ in the layer in contact with the polymer).

Insofar as the speed of passage of the fluid in the treatment cell maintains a turbulent flow along the emissive electrode (with movements of the fluid transverse with respect to the general flow of the fluid inside the body 12), the surface of the emissive electrode may be weak. Indeed; such transverse movements cause a greater migration of charges in the fluid to be treated.

 It should be noted that the ease of application of the conductive coating in the liquid form makes it possible to use the most diverse and also the most suitable forms of electrodes according to the invention, without risk of point defects during application. This feature makes it possible to fully use the capacities for obtaining shapes offered by polymer plastics (injection, extrusion, etc.).

According to an advantageous characteristic of the embodiment of the invention illustrated in FIG. 1, the treatment cell includes means for scanning the active surface of the electrode 22. These means are constituted by the association of one or more brushes mounted flush with the electrode 22 and secured to the cylindrical body 12 along a generator, and the rotational mounting of the electrode 22 / axis 27 assembly relative to the body 12. For this purpose, the axis 27 projects outside the body 12 and carries a manual actuating flywheel 36 capable of reciprocating rotational movement according to arrow F3.

This cleaning crew is particularly interesting for large installations operating in a closed circuit such as industrial painting installations.

Indeed, the negative ions present in the vicinity of the electrode favor the production of calcium carbonate germs in the vicinity thereof (thus avoiding the crystallization of tartar on the walls of the ducts of the installation) and thereby - even the deposition of colloidal mud on the active surface of the electrode. Regular cleaning thus keeps the tartar in suspension.

Without departing from the scope of the invention, other embodiments use an electric motor or the current of fluid flowing in the treatment cell to actuate the axis 27. In the latter case, the brush of helical shape is mounted free to rotate around the electrode 22.

It should be noted that this cleaning allows the diffusion in the double layers of the charges emitted by the electrode.

FIG. 2 shows two variants 100 and 200 of another embodiment of the invention. In these variants, the emlsslve electrode is produced directly from a portion 12, 202 of insulating material (for example PVC) from the pipe of the fluid to be treated (variant 100 is single-tube 104 while variant 200 has several tubes 204 of reduced diameter). The external face of the tubes 104 and 204, isolated from the fluid to be treated, 106 and 206 on which a connection wire is welded, is covered with an electrically conductive coating 108 and 208 at the HV generator. The conductive coating is of the type presented previously. The conductive coating is protected and insulated from the outside by an external dielectric jacket, for example a varnish (not shown in FIG. 2). Finally, the ground electrode consists of a metal part 110, 210 of the fluid line suitably connected to the general ground of the installation.

The device according to the invention 100 of the monotube type represented in FIG. 2 comprises means forming a deflector and a fluid mixer.

 Blus in particular, a static e 210 mixer composed of one or more mixing elements offset by 900 relative to each other and fixed longitudinally in the body 104 of the treatment cell makes it possible to very quickly obtain a homogeneous mixture of the layers double electrically treated with the rest of the fluid, and significantly decrease the size of the cell.

The static mixer 210 improves the processing efficiency by dividing the flow, sweeping and constant mixing of the electrically treated double layers present at the polymer-fluid interface and makes it possible to reduce the size considerably. of the cell. Indeed, in a drolt tube, not equipped, the turbulence is not enough to obtain a perfect homogeneous mixture between the double layers and the rest of the solution; a tube length of the order of 100 times its diameter is required for turbulent mixing of the constituents having no difference in density.

The static mixer 210 can take the form of dihedra, of helical or oblique elements which cross, or of open and crossed flow channels, generating an intense radial mixing with a reduced axial dispersion by homogenization of the velocity profile.

In another variant, not shown, of the invention, the tube (s) forming the electrode is (are) provided with internal radial projections, for example spikes (possibly offset) to promote the turbulent flow of the fluid through the tube (s).

FIG. 3 shows an exploded view of a third embodiment of the invention usable in sanitary water distribution installations. The reference 300 relates to the metallic tubular body of a manifold, one end of which 301 receives the orifice 302 for the inlet of the water. Outlet orifices 304 are mounted in regular spacing on the body 300 of the collector itself connected to the ground of the installation.

The emissive electrode 306 consists of a hollow tube of insulating material 308 closed at one end and the other end of which is secured to a plug 310 which can be screwed onto the available end 303 of the tubular body 300. The internal face of the hollow tube 308 is covered with the insulating coating 309 connected to the HT generator by a connection wire 312 passing through the plug 310. After mounting the electrode 306, the latter is placed in the body 300 in a coaxial manner substantially vis-à-vis the outlet orifices 304, the axial length of the active surface of the electrode (covered with the coating 309) being dimensioned accordingly.

The dimensions of the electrode 306 and its arrangement relative to the body 300 are chosen to rapidly create the contact and turbulence treatment of the fluid to be treated. The cleaning of the electrode 306 is easily done by dismantling the plug 310. Without departing from the scope of the invention, the electrode 306 can be replaced by a plurality of electrodes (not shown) integral with the plug 310.

The invention is not limited to electrostatic treatments of aqueous fluids but also applies to all fluids sensitive to electrostatic treatments, in particular to petroleum products, in particular to fuels for internal combustion engines.

 Indeed, the phenomena which come into play to improve the pulverization of the fuel in the combustion chamber do not call upon electromagnetic or electric fields through the fluid, but start from the phenomenon of transport of electric charges and polarization by flow and by contact with a liquid dielectric.

The potential difference which is of the order of 5 to 10 kv between the treatment electrode and the mass of the installation for aqueous fluids will be 30 to 50 kv for petroleum fuel products in order to increase the concentration of charged elements on the electrode surface, and to generate charge transport.

This charge transport is due to the convection of a part of the double electric layer appearing in the fluid-insulating contact inside the treatment cell.

In this case, the jet of combustible electrically treated per and reach the edge of the combustion chamber in diesel thermal engines and improve the quality of spraying for petrol engines or burners.

 The turbulent flow of fuel in the cell will disturb the charge distribution given by the insulator within the diffuse layer.

To improve turbulence and promote mixing of the boundary layer, alternative embodiments incorporate marks forming a deflector and a fluid mixer, for example of the type presented with reference to the device illustrated in FIG. 2.

The invention is also applicable to improving the efficiency of the spraying of phytosanitary products during agricultural spreading. In fact, the electrostatic treatment has the effect of electrically charging the sprayed droplets and of finely dividing the spreading.

Claims (12)

1 / Electrode for electrostatic fluid treatment device characterized in that it comprises a thin-walled structure (24, 104, 204, 308) made of insulating material covered with an electrically conductive coating (26, 106, 206, 309) on one of its faces, said face being intended to be isolated from the fluid to be treated. 2 / An electrode according to claim 1 characterized in that the insulating material is a plastic, preferably a polymer selected from the group of polystyrenes, ABS, polycarbonates, PVC, polytetrafluoroethylene (PTFE) and the tetrafluoroethylene-perfluoroprene (FEP) copolymer. 3 / Electrode according to one of the preceding claims characterized in that the electrically conductive coating consists of a film of natural and synthetic resin loaded with a powder of electrically conductive material, preferably made of metal. 4 / electrode according to claim 3, characterized in that the conductive coating consists of acrylic resin charged with nickel powder. 5 / An electrode according to claims 2 and 3, characterized in that the conductive coating is applied to the plastic wall in liquid form after mixing with a solvent compatible with the resin and the plastic used.  60 Electrode according to one of the preceding claims, ca actérlsée in that the insulating material structure is in the form of a thin-walled hollow structure (24, 308) whose inner face is covered with the conductive coating (26, 309). 7 / electrode according to one of claims 1 to 5, characterized in that the insulating material structure is in the form of a tube (104, 204) whose outer wall is covered with the conductive coating (106, 206) itself protected by an outer shell of dielectric material. 8 / electrode according to claim 7, characterized in that the tube is provided with internal radial projections (possibly offset) to promote the turbulent flow of the fi through the tube forming electrode. 9 / Device for electrostatic treatment of fluids, characterized in that it comprises at least one electrode (22, 100, 200, 306) defined according to one of the preceding claims, said electrode preferably having a geometry allowing turbulent flow of the fluid to be treated. 10 / Device according to claim 9, characterized in that it comprises at least one electrode (306) having an elongated shape and is mounted in a central position in the tubular body (300) of a water collector.  it / Device according to claim 10, characterized in that said electrode (306) is in the form of a cylindrical sleeve (308) closed at one end and the other end of which is integral with a plug (310) mounted at the end of the tubular body (300) of the manifold.  12 / Device according to claim 9 of the type in which said electrode (22) is mounted coaxially in a cylindrical body characterized in that it comprises means for scanning the active surface (34, 36) of said electrode (22 ). 13 / Device according to claim 12, characterized in that said scanning means comprise brushes (34) capable of a relative movement of rotation relative to said surface (24) to be cleaned. 14 / Device according to claim 9, characterized in that it comprises in the passage of the fluid to be treated means deflector and fluid mixer to promote a turbulent flow of said fluid in the vicinity of the electrode, and to obtain quickly a homogeneous mixture of the electrically treated double layers with the rest of the fluid.