EP1064100B1 - Electrohydrodynamic spraying means - Google Patents

Abstract

The invention concerns electrohydrodynamic spraying means enabling electrohydrodynamic spraying, in the air and at atmospheric pressure, of liquids with high surface tension such as water. The means are characterised in that they comprise at least a liquid dispensing conduit (1) whereof the dimensions of the external diameter and of the internal diameter, at the liquid exit point, correspond to an appropriate ratio. Said means can be advantageously used for depolluting aerosol effluents, or transformable into aerosols.

Description

The present invention relates to electrohydrodynamic spraying means (hereinafter referred to as HDPE).

HDPE is a means of producing nebulisates of electrically charged millimeter, micron or submicron sized liquid droplets.

HDPE essentially consists of applying an electric field to a liquid so as to induce on the surface of this liquid electric charges of the same polarity as the voltage applied thereto. These charges, accelerated by the electric field, cause a transformation of the liquid drop into a cone. At the apex of this cone, a jet of liquid is produced which breaks up into droplets of millimetric, micron or submicron sizes (nebulisate or spray ).

Different modes of liquid fragmentation can be obtained and have been described in the prior art ( see in particular Cloupeau and Prunet-Foch, 1989, J. Electrostatics 22, pp 135-159). We can notably mention the "drop-by-drop" mode which produces millimetric drops, and the stable "jet-cone" mode which produces a bimodal particle size distribution of the nebulisate (micron drops and sub-micron satellites).

Various means have been described in the prior art in order to obtain a stable "cone-jet" mode HDPE (mode guarantor of bi-modal dispersion) for liquids whose surface tension at ambient temperature is less than or equal to 0.055 N / m such as ethanol, acetone, ethylene glycol. However, HDPE in "jet cone" mode is problematic for liquids with high surface tension such as water or liquids supplemented with reagents or surfactants.

The high surface tension of these liquids indeed imposes, for the realization of their HDPE, the application of strong potentials on the liquid, which creates a strong electric field in the gas surrounding the liquid and, consequently, the phenomena of ionization in the gas. In air, at atmospheric pressure, these electric discharges are mostly impulsive (darts), and prevent the establishment of a mode of fragmentation "cone-jet" in favor of a mode "cone-jet-glow ".

Thus, EP 0 258 016 discloses an electrostatic spraying system intended to allow the application of very thin surface coatings. This system is capable of spraying in air at atmospheric pressure liquids having a surface tension of less than 0.065 N / m, and preferably less than 0.050 N / m, but only to the extent that crown-type phenomena are avoided ("conc-jet" mode of fragmentation of the liquid). In the event of discharges, EP 0 258 016 indicates that its device must be placed in a gas other than air, or in an atmosphere different from the atmospheric pressure. The teaching of EP 0 258 016 thus leads the skilled person to avoid the phenomena of discharges, which are considered destabilizing spray.

Various solutions have been proposed in the prior art to stabilize the HDPE of such liquids by preventing the formation of pulses in the gas surrounding them. Two types of solutions can be identified: a first type of solution uses an increase in the dielectric strength of the gas surrounding the liquid by increasing the pressure of the gas and / or by using gases other than air such as CO ₂ or SF4, a second type of solution, uses an additional electrode placed near the cone and the liquid jet so as to reduce the radial electric field in the gas in the vicinity of the liquid. None of these two types of solutions is however industrially satisfactory: the first type imposes means of control of the atmospheric environment, and the second type imposes an additional high voltage source.

To the knowledge of the Applicant, none of the devices described in the prior art therefore allow, for liquids with high surface tensions such as water, HDPE in air and at atmospheric pressure, without generating a pulse regime. discharges, and without requiring the use of an additional electrode.

The present application relates to new ways to solve this problem, and to overcome the disadvantages of the means of the prior art.

The inventors have indeed for the first time established that a HDPE without pulse pulse regime could be established directly and in air and at atmospheric pressure for liquids whose surface tension, as measured at ambient temperature, is superior at 0.055 N / m and remarkably greater than 0.065 N / m. In particular, they established that such HDPE can be obtained using an HDPE device that meets certain operating parameters, and in a very essential way, using an HDPE device comprising at least a liquid distribution pipe 1 whose dimensions of outside diameter and internal diameter, at the exit point of the polarized liquid, correspond to a suitable relationship in a previously defined range of outside diameters ( see examples and chart in FIG. after). Such a relationship may notably correspond to a relationship between (diameter dimension outside) and (inside diameter dimension) greater than or equal to a fixed limit value.

• la forme du liquide, c'est-à-dire la géométrie du cône et du jet de liquide, et
• la chute de potentiel dans le liquide, c'est-à-dire le potentiel à la surface du liquide,

ceci afin de contrôler le divergent du champ dans le gaz (c'est-à-dire la variation du champ électrique dans le gaz).The inventors have indeed observed that the regime of discharges into the gas (continuous regime of discharges -glow stabilizer- or pulsed regime of discharges -dards destabilizing-) is directly connected to the divergent field in the gas. They have thus established that, for liquids whose surface tension is greater than 0.055 N / m, and remarkably greater than 0.065 N / m, it is essential, to achieve the desired HDPE in air at atmospheric pressure, to choose outside and inside diameters which allow to control:

• the shape of the liquid, that is to say the geometry of the cone and the jet of liquid, and
• the potential drop in the liquid, that is to say the potential on the surface of the liquid,

this in order to control the divergence of the field in the gas (that is to say the variation of the electric field in the gas).

The present application thus firstly relates to an electrohydrodynamic spraying device according to claim 1.

Various means are known to those skilled in the art to control the continuous nature of a discharge regime. These include the measurement of electric current using a fast oscilloscope, the visual control of the stability of the formed liquid cone, and / or granulometric measurements to verify the bi-modal character of the size distribution. droplets. Such a bi-modal distribution may in particular correspond to a first population, predominant (for example 90% of the volume of liquid sprayed), of larger average size droplets, and to a second minority population (for example 10% of the volume of liquid spray), droplets of medium size finer.

By electrohydrodynamic spraying device, we mean, in the present application, a device capable of generating a nebulisate (or dispersion, or spray ) of polarized liquid, that is to say a nebulisate of fragmented liquid, or pulverized, into droplets electrically charged. Such a device therefore comprises liquid supply and distribution means, and means for biasing electrically the surface of this liquid. The liquid distribution means are provided by a conduit 1, or capillary 1, at an outlet of which the polarized liquid forms a conical meniscus, the apex of which a jet then a dispersion of electrically charged liquid droplets.

By surface tension, we mean in the present application the surface tension as measured in air at ambient temperature and pressure.

The device according to the invention, designed to allow HDPE under a continuous regime of discharges, in air and at atmospheric pressure, liquids whose surface tension is greater than 0.055 N / m, and remarkably superior at 0.065 N / m, has the advantage of allowing, without modification of said device, the HDPE of liquids whose surface tension is less than or equal to 0.055 N / m.

préférentiellement supérieur ou égal à 1,5697 environ, plus préférentiellement supérieur ou égal à 1,6 environ, et encore plus préférentiellement supérieur ou égal à 1,8 environ.According to an advantageous arrangement of the invention, said means comprise, at least at said duct outlet 1, dimensions of outside and inside diameters which respond, when expressed in the same unit, to the following relation: $$\frac{\mathrm{dimension\; of\; outer\; diameter}}{\mathrm{inside\; diameter\; dimension}}\mathrm{greater\; than\; or\; equal\; to}\mathrm{}1,445\mathrm{}\mathrm{about},$$

preferably greater than or equal to about 1.5697, more preferably greater than or equal to about 1.6, and still more preferably greater than or equal to about 1.8.

The upper limit of the appropriate values for this ratio (outside diameter dimension) / (inner diameter dimension) is determined by different technical limits. It can be mentioned in particular the technical limits related to the machining of a very small internal diameter, or even those related to the pressure drop that may result from a smaller internal diameter and which then imposes in compensation hydraulic systems at higher pressure.

The lower bound of the appropriate values for the ratio (outside diameter dimension) / (inner diameter dimension) is obtained from experimental measurements (observation of the achievement of a stable HDPE based on a range of diameter values exterior and interior).

The lower bound value of course depends on the experimental conditions applied. Examples of suitable devices and their use are described in Figure 1 and in the "Examples" section below. Those skilled in the art can however design and implement variants. Thus, those skilled in the art can naturally take into account the material and / or the arrangement of the support supporting said conduit, or capillary, insofar as this material and / or this arrangement are likely to affect the electric field produced. It will be apparent to those skilled in the art that the choice of the presence or absence of such a support of conductive material, in particular when it is arranged perpendicularly to the axis of said duct 1, or capillary 1, substantially influences the experimentally measured lower bound of said appropriate ratio values (outside diameter dimension) / (inside diameter dimension). Thus, the aforesaid lower bound value 1.5697 is obtained from experimental measurements carried out in the presence of such a support, whereas the aforesaid lower bound value 1.445 is obtained from experimental measurements carried out under comparable conditions, but in the absence of such support.

It should also be emphasized that the measurements made, and hence the lower bound value obtained, also depend on the profile of the section at said conduit or capillary outlet. The aforesaid lower limit value 1,445 is thus obtained when said conduit, or capillary, has at least at said outlet a straight cross section (right face): the cross section perpendicular to the axis of said conduit 1 or capillary 1, at the of said outlet, has an annular profile. When the outlet section is not perpendicular to the edge of the duct 1 or capillary 1, the lower limit value obtained may be substantially different. Thus, when the outer face of duct 1 or capillary 1 appears, at least at said outlet longer than the internal face (non-straight face, that is to say, beveled type profile), the lower limit value may appear less high (a value of 1.38 could be obtained under these conditions, compared with the value of 1.445 obtained using an outlet section perpendicular to the edge of the duct 1 or capillary 1. Conversely, when the outer face appears, at least at said output, shorter than the internal face (beveled type profile), the lower limit value may appear higher (a value of 1.8 was thus obtained under these conditions, compared to 1.445 obtained using annular section clear sections, the skilled person can therefore choose to machine a particular profile on the section at said outlet conduit 1 or capillary 1.

avec D_max ladite valeur limite en m, et τ_q constante de relaxation électrique dudit liquide en s, ou, dans le cas d'un liquide à faible viscosité, à l'équation : $${\log }_{10}\left({\mathrm{D}}_{\max }\right)=0,37747\times {\log }_{10}\left({\mathrm{\tau }}_{\mathrm{q}}\right)+0,43141$$

avec D_max et τ_q comme ci-dessus définis.
Les termes "faible'' et "forte" viscosité sont entendus canformément aux notions communément admises par l'homme du métier. Typiquement, par "faible" viscosité, on entend une viscosité d'environ 1 mPa.s, tandis que par "forte" viscosité, on entend une viscosité supérieure d'environ deux ordres de grandeur (soit de l'ordre de 100 mPa.s environ).
Préférentiellement, la dimension dudit diamètre extérieur est inférieure à la moitié de cette valeur limite D_max. Lorsque lesdits diamètres extérieur et intérieur présentent des dimensions dont le rapport répond à une relation ci-dessus précisée (supérieur ou égal à 1,445 environ, préférentiellement supérieur ou égal à 1,5697 environ, plus préférentiellement supérieur ou égal à 1,65 environ, encore plus préférentiellement supérieur ou égal à 1,8 environ), la dimension dudit diamètre extérieur est préférentiellement inférieure au tiers de cette valeur limite D_max.An appropriate dimension for said outer diameter is in particular a function of the liquid electrical relaxation constant τ _q (which is itself a function of the conductivity of the liquid). It is lower than a limit value D _{max which} , in the case of a liquid with a high viscosity, has the equation: $${\log }_{10}\left({\mathrm{D}}_{\max }\right)=0,37793\times {\log }_{10}\left({\mathrm{\tau }}_{\mathrm{q}}\right)+0,34674$$

with D _max said limit value in m, and τ _q electrical relaxation constant of said liquid in s, or, in the case of a low-viscosity liquid, to the equation: $${\log }_{10}\left({\mathrm{D}}_{\max }\right)=0,37747\times {\log }_{10}\left({\mathrm{\tau }}_{\mathrm{q}}\right)+0,43141$$

with D _max and τ _q as defined above.
The terms "low" and "high" viscosity are understood to be in accordance with commonly accepted notions by those skilled in the art, typically "low" viscosity means a viscosity of about 1 mPa.s, while "high" is "Viscosity" means a viscosity greater than about two orders of magnitude (ie of the order of about 100 mPa.s).
Preferably, the dimension of said outer diameter is less than half of this limit value D _max . When said outer and inner diameters have dimensions whose ratio corresponds to a relationship specified above (greater than or equal to about 1.445, preferably greater than or equal to about 1.5697, more preferably greater than or equal to about 1.65, still more preferably greater than or equal to about 1.8), the dimension of said outer diameter is preferably less than one-third of this limit value D _max .

According to another advantageous aspect, the device according to the invention is capable of spraying, in air and at atmospheric pressure, a liquid whose surface tension is greater than 0.053 N / m, and remarkably greater than 0.065 N / m. m, in a stable mode of fragmentation of the liquid, especially in a mode of stable "cone-jet-glow" fragmentation (ie in a "jet cone" mode with continuous discharges superimposed). Those skilled in the art can verify obtaining a "cone-jet-glow" mode, that is to say the superposition of a continuous discharge regime and a spray-jet cone mode, to using known means. These include electrical measurements using a fast oscilloscope that make it possible to verify that the current is continuous (no pulses), and that it is greater than the theoretical "jet-cone" current.

By stable, we mean in the present application a permanent phenomenon (probability of occurrence in time greater than or equal to 0.9, preferably greater than or equal to 0.95, more preferably equal to 1).

The device according to the invention further comprises means for electrically biasing said liquid upstream or during its passage through said conduit 1, in particular means 2 for applying an electrical voltage to said liquid upstream or during its passage inside said conduit, so as to polarize it.

Any voltage to obtain a stable HDPE is appropriate. Its choice depends on the desired polarization. Advantageously, this voltage is continuous. The device according to the invention then produces nebulisates whose charge always has the same sign (that of the DC voltage applied, this voltage can be positive as well as negative, depending on the intended applications.) In an advantageous embodiment of the invention. said voltage is a DC voltage, preferably a positive DC voltage, such as a positive DC voltage of less than about 130 kV, and a person skilled in the art may choose a suitable voltage depending on the specific properties of the liquid used in the process. device according to the invention, in particular its properties of conductivity, viscosity, density, surface tension, and as a function of properties specific to the device, in particular the distance that separates said conduit outlet from the nearest mass point.

Advantageously, said means making it possible to apply such an electrical voltage to said liquid essentially consist of at least one high-voltage generator 2 which can be connected firstly to ground and which can be connected to said liquid either direct way upstream or during its passage inside said conduit, or indirectly through a conductive material in contact with said liquid upstream or during its passage inside said conduit. Said duct may indeed comprise an electrically conductive material on its inner surface, or on an internal thickness, and / or consists essentially of such a material.

In order to limit the current in said liquid resulting from the application of said voltage, the device according to the invention may further, for safety reasons, comprise a protection resistor 3 making it possible to limit the current in the sprayed polarized liquid, in particular a resistor protection device for limiting the discharge current of said liquid in the case of the passage of a very strong current. Such a resistor may advantageously be placed between said high voltage generator and its point of connection to said liquid.

According to a particular embodiment of the invention, said device further comprises means 5 for depolarizing said liquid after spraying, that is to say for discharging the droplets of liquid produced by contact on a surface to ground . According to an advantageous arrangement of this particular embodiment, said means 5 for depolarizing said liquid after spraying are placed at a distance D, hereinafter referred to as the inter-electrode distance, advantageously greater than the minimum distance that allows passage to the arc before the establishment of HDPE. Such means are however optional: when said device is used for the purpose of producing a nebulizer whose polarity must interact with components of inverse polarity, these means are not applicable.

According to an advantageous embodiment of the invention, said device further comprises means 4 allowing, during the spraying of said liquid, to collect a discharge current in the gas surrounding said polarized liquid, such as in particular a conductive material having an opening of shape and dimensions allowing the passage of the sprayed liquid while collecting said stream of gaseous ions created by electric discharges in the gas. Such means 4 are particularly suitable when said device is used for the purpose of producing a nebulizer whose polarity must interact with components of inverse polarity. They are also appropriate to ensure that the field at the liquid surface in the production area remains independent of the + and - charge densities under the ring (coagulation, charge modulation, and neutralization phenomena).

These means 4 then make it possible to eliminate gaseous ions having the same polarity as said nebulisate and which, as a result, could interfere with the desired nebulisate-component interaction, and thus reduce the efficiency of the device according to the invention. The device according to the invention is thus capable of controlling the discharge regime over a wide range of operation, typically over voltage ranges of the order of several thousand volts.

Such means 4 for collecting a discharge current make it possible in particular to collect the gaseous ions created by such a current of discharge, without collecting the droplets of liquid produced. Such a particularly suitable means 4 is constituted by a counter-electrode, or conductive material connected to the ground, placed at a distance d from said duct outlet, and having an opening allowing the passage of liquid droplets produced while collecting the ions. gaseous created by a discharge. Said distance d may in particular be evaluated by trial and error, by moving said means by translation along the axis of the fluid nebulisate produced to obtain a non-collection of the liquid droplets, and an effective collection of said current discharge. Such a means may in particular have an annular shape.

The device according to the invention further comprises means 6 for supplying said conduit with liquid. Said conduit may in particular be supplied with liquid using one or more pump (s), or with the aid of a reservoir which has a height of liquid suitable for controlling the flow rate.

• A étant une constante différente de 0 et de 1, comprise entre 0,1 et 10 environ et de préférence égale à 0,5 environ,
• r le rayon de gouttes désiré exprimé en m, et
• τ_q la constante de relaxation électrique dudit liquide exprimée en s.

According to another advantageous embodiment of the invention, said device further comprises means 6 for an average flow of operating fluid at the inlet or inside said duct of a value in m ³ .s ^-1 , which is within a range of about 10 between its upper and lower bounds, said range preferably including a value which can be of the following formula $$\mathrm{AT}\left[(4/3)\mathrm{\pi }{\mathrm{r}}^3\right]/{\mathrm{\tau }}_{\mathrm{q}},$$

• A being a constant different from 0 and 1, from about 0.1 to about 10 and preferably about 0.5,
• r the desired drop radius expressed in m, and
• τ _q the electrical relaxation constant of said liquid expressed in s.

For liquids whose surface tension is less than or equal to 0.055 N / m, that is to say in the absence of discharge problem, it is known those skilled in the art that the "jet cone" mode can be achieved by choosing an average operating flow rate equal to [(4/3) π r ³ ] / τ _q , where r is the desired drop radius (in m ), and τ _q the electrical relaxation constant (in s). It is recalled here that: τ _q = [ε ₀ ε _r ] / λ = [8,92.10 ^-12 ε _r ] / λ, λ being the conductivity of the liquid in s / m, ε ₀ the permittivity of the vacuum, ε _r the relative permittivity of the material (ε _r = the ratio between the absolute permittivity of the material and the permittivity of the vacuum).

For liquids whose surface tension is greater than 0.055 N / m, and remarkably greater than 0.065 N / m, the inventors have been able to establish that the appropriate average operating flow, for liquids with a surface tension of less than or equal to at 0.055 N / m at room temperature as indicated above, must be corrected by a constant factor A, different from 0 and from 1, between 0.1 and 10 approximately and preferably equal to 1/2, in order to to avoid a pulse regime of destabilizing discharges of the nebulisate.

• A étant une constante différente de 0 et de 1, comprise entre 0,1 et 10 environ et de préférence égale à 0,5 environ,
• r le rayon de gouttes désiré exprimé en m, et
• τ_q la constante de relaxation électrique dudit liquide exprimée en s.

The device according to the invention can therefore also comprise liquid supply means 6 allowing an average flow rate of operating liquid at the inlet of said duct whose value in m ³ .s ^-1 corresponds to the following formula: $$\mathrm{AT}\left[(4/3)\mathrm{\pi }{\mathrm{r}}^3\right]/{\mathrm{\tau }}_{\mathrm{q}},$$

• A being a constant different from 0 and 1, from about 0.1 to about 10 and preferably about 0.5,
• r the desired drop radius expressed in m, and
• τ _q the electrical relaxation constant of said liquid expressed in s.

According to another aspect of the invention, said device further comprises means for measuring the particle size of the dispersion produced by the spraying of said polarized liquid, and in particular an LDA (Laser Doppler Anemometry ) type system, and / or means for measuring the electric current carried by the dispersion produced by spraying said polarized liquid, and in particular an oscilloscope. Such means make it possible in particular to follow the evolution of the particle size of the droplets produced and / or the evolution of said stream during the spraying of said liquid.

According to an advantageous aspect of the invention, said liquid is essentially a solution (solvent and solute (s) neutral (s) or ionic (s), organic (s) or mineral (with)), or a mixture of solutions chosen ( s) from the group consisting of water, ultrapure water, distilled water, water comprising conductive salts, an organic solvent supplemented with surfactant molecule (s), ethanol supplemented with surfactant molecule (s), acetone supplemented with terzioactive molecule (s), ethylene glycol supplemented with surfactant molecule (s).

The device according to the invention has many applications of interest. They encompass all known applications of HDPE devices in general, such as coating or surface deposition, to which are added new applications now achievable with the aid of the device according to the invention because of its ability to spray. , in air and at atmospheric pressure, a liquid whose surface tension is greater than 0.055 N / m, and remarkably greater than 0.065 N / m, without generating a pulse pulse regime. There may be mentioned applications in the field of electric washing of particles, and in the biological field.

According to a preferred embodiment of the invention, said device is applied to the collection of particles, and in particular polluting particles, present in an aerosol (dedusting). This applies to any aerosol effluent or any effluent that can be aerosolized. Such collection takes place by electrical coagulation of said particles to be removed from said droplets of liquid produced by the device according to the invention; for such coagulation to be operative, said device is then applied to the production of liquid droplets of inverse polarity to the polarity (natural or induced) of said particles to be eliminated.

The device according to the invention is therefore, in a preferred embodiment of the invention, disposed on a vein of industrial effluent to be dusted, in which it can produce a reverse polarization nebulisate of that of the particles of the aerosol effluent. from liquid (s) with a surface tension greater than 0.055 N / m, and remarkably greater than 0.065 N / m, such as water. Particularly advantageously, there is a plurality of devices according to the invention on such a stream of effluents.

Compared with the devices of the prior art for the collection of aerosols such as in particular fluidized bed and wet scrubber, the device according to the invention has the particular advantage of producing charged liquid droplets of finer sizes and, in the case an application for collecting pollutant particles in an aerosol, to limit the volume of wastewater resulting. The device according to the invention also has the advantages of increasing the collection area per unit volume of collecting liquid (increase of inter-particle electrostatic forces, collecting droplets of medium size finer), to avoid the problem of reduction. the efficiency of electrostatic precipitator systems related to the accumulation on the collecting electrodes of insulating dusts, not to require a pressurization system or mechanical system and thus to avoid the problems of pressure drop of a filtration system at the output of the process (inertial collection is possible with the device according to the invention).

The device according to the invention also has, in general, the advantages of reducing installation costs, energy costs, wastewater treatment costs (due to the low flow rates of wastewater produced by the device according to the invention. the invention, from the liter to the cubic meter per hour). It also has the advantage of reliability: the percolation of the collecting droplets on the walls used for the inertial collection makes it possible to avoid the accumulation of the products collected on the electrodes, as observed by using said devices of the prior art. . The device according to the invention allows a particularly advantageous way of working continuously.

According to a particularly preferred embodiment of the invention, said device is therefore applied to the inertia collection, following electric coagulation on larger droplets, particles whose initial size is less than or equal to one micron, and in particular pollutant particles of this size, present in an aerosol, or in an effluent transformable aerosol.

Such particles, because of their small sizes, could previously be effectively removed from an aerosol by inertial collection after their coagulation with the collecting droplets. The device according to the invention, by allowing the control of the (or) size (s) of charged droplets produced, makes it possible to produce charged droplets whose size (s) is (are) optimal (s) for causing, after coagulation with said particles to be eliminated, their fall by simple inertia in a controlled and effective manner. With the device according to the invention, it is not necessary to use, for said collection, filtration systems. The pressure losses related to the use of such filtration systems are thus avoided. The device according to the invention also makes it possible to control the volume of water necessary for this growth, and thus the volume of wastewater to be treated.

One means for varying the size (s) of droplets produced by the device according to the invention consists in particular in varying the flow rate of the liquid, that is to say to vary the mechanical flow of liquid by varying the rate of supply of liquid to the inlet, or inside, of said conduit, and / or to vary those liquid properties that influence its flow rate, including its conductivity properties (that this either by modifying the properties of a single basic liquid, or by using different liquids of specific properties).

Said effluent or aerosol can in particular be from an incineration plant, a chemical industry, metallurgy, a glass industry, a boiler or a thermal power station, a road tunnel, a vehicle, in particular a diesel vehicle.

The present application also relates to a method of HDPE characterized in that it implements at least one device according to the invention. It also relates to a process for the depollution of aerosol effluents, as described in claim 10.

Claims (10)

1. A device for the electrohydrodynamic spraying of a liquid comprising at least one duct (1) at an outlet of which said liquid can be sprayed and means including means (2) allowing the application of a voltage to said liquid upstream or while it is flowing inside said duct, so as to bias it, characterized in that at least at said outlet of the duct (1), the dimensions of the external and internal diameters of the duct (1) correspond, when they are expressed in the same units, to the following relationship:

   (external diameter dimension) / (internal diameter dimension) greater than 1.445, preferably greater than 1.5697, more preferably greater than 1.6;

   the dimension of the external diameter of the duct (1) being less than a limiting value D_max corresponding to the formula: $${\log }_{10}\mathrm{\hspace{1em}}\left({\mathrm{D}}_{\max }\right)=0.37793\times {\log }_{10}\mathrm{\hspace{1em}}\left({\mathrm{\tau }}_{\mathrm{q}}\right)+0.34674$$

   

   when said liquid has a high viscosity,
   or to the equation: $${\log }_{10}\mathrm{\hspace{1em}}\left({\mathrm{D}}_{\max }\right)=0.37747\times {\log }_{10}\mathrm{\hspace{1em}}\left({\mathrm{\tau }}_{\mathrm{q}}\right)+0.34141$$

   

   when said liquid has a low viscosity, with
   D_max said limiting value in m, and τ_q the electrical relaxation constant of said liquid in s,
   said device allowing the spraying, in the air and at atmospheric pressure, of a liquid the surface tension of which is greater than 0.055 N/m while generating a continuous discharge regime such as a glow regime or a Hermstein regime.
2. Device according to claim 1, characterized in that said means comprise, at the at said outlet, dimensions of external and internal diameters of a duct (1) which correspond, when they are expressed in the same units, to the following relationship:

   (external diameter dimension) / (internal diameter dimension) greater than approximately 1.8.
3. Device according to claim 1, characterized in that said voltage is a DC voltage, in particular a positive DC voltage such as a DC voltage less than approximately 30 kV.
4. Device according to any one of the preceding claims, characterized in that it also comprises means (5) allowing said liquid to be unbiased after spraying, such as an earthed electricity-conducting material.
5. Device according to any one of the preceding claims, characterized in that it also comprises means (4) allowing, during the spraying of said liquid, the collection of a discharge current in the gas surrounding said biased liquid, such as in particular a conducting material having an opening of a shape and a size which allows the sprayed liquid to flow while collecting said discharge current.
6. Device according to any one of the preceding claims, characterized in that it also comprises means for feeding with liquid (6) allowing a mean operating liquid flow rate at the inlet or inside said duct of a value in m³.s^-1 which is comprised within a range varying by a factor of approximately 10 between its upper bound and its lower bound, said range comprising, preferably centrally, a value which can correspond to the following formula: $$\mathrm{A}\left[(4/3)\mathrm{\hspace{1em}}\mathrm{\pi \hspace{1em}}{\mathrm{r}}^3\right]/{\mathrm{\tau }}_{\mathrm{q}},$$

   

   A being a constant different from 1, comprised between approximately 0.1 and 10 and preferably equal to approximately 0.5 with

   r the desired drop radius expressed in m,

   τ_q the electrical relaxation constant of said liquid expressed in s.
7. Method for electrohydrodynamic spraying using a device according to one of claims 1 to 6, characterized in that a liquid which is biased at the outlet of the duct (1), and the surface tension of which is greater than 0.055 N/m, and in a remarkable manner greater than 0.065 N/m, is sprayed in the air at atmospheric pressure setting up a continuous discharge regime.
8. Method according to claim 7, characterized in that said liquid the surface tension of which is greater than 0.055 N/m is essentially a solution (solvent and neutral or ionic, organic or mineral solute(s)), or a mixture of solutions selected from the group constituted by water, ultra pure water, distilled water, water containing conducting salts, an organic solvent to which one or more surfactant molecule have been added, ethanol to which one or more surfactant molecule have been added, acetone to which one or more surfactant molecule have been added, ethylene glycol to which one or more surfactant molecule have been added.
9. Use of a device according to any one of claims 1 to 6 according to a continuous discharge regime, in order to produce droplets of liquid, said liquid having a surface tension greater than 0.055 N/m, for the collection of particles, and in particular polluting particles, present in an aerosol, and in particular inertial collection, following the electrocoagulation on said larger droplets, of particles the initial size of which is smaller than or equal to a micron, and in particular of polluting particles present in an aerosol and the size of which is less than or equal to a micron.
10. Method for the pollution control of aerosol effluents, or effluents which can be converted into aerosols, in which it is sought to remove the polluting particles, characterized in that it comprises the stages of:

    - biasing said polluting particles present in the aerosol,

    - producing a dispersion of liquid droplets with reverse polarity using at least one device according to any one of claims 1 to 6 setting up a continuous discharge regime, said liquid having a surface tension greater than 0.055 N/m,

    - bringing said dispersion of liquid droplets and said biased polluting particles into contact, so as to allow the electrocoagulation of these polluting particles onto said liquid droplets,

    - collecting the polluted liquid droplets inertially.

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