EP1919626A1 - Device for air/water extraction by semi-humid electrostatic collection and method using same - Google Patents

Abstract

The invention concerns a device for air/water extraction by semi-humid electrostatic collection, comprising a chamber (7) containing a discharge electrode (1) for generating an ion flow from an ionized gas accumulation surrounding the discharge electrode (1) and a counter-electrode (2), an inlet (3) for mixing air and aerosol to be extracted which contains liquid or solid particles, a steam supply tube (8) and an outlet (4) for cleansed air. The invention is characterized in that the device enables stream to be introduced through said steam supply tube (8) in the gap between the discharge electrode (1) and the counter-electrode (2) so as to form a steam sheath (10) enclosing the discharge electrode over its entire length, such that the treated air is not steam-saturated.

Description

Seekers: Atomic Energy Commission 31-33, rue de la Federation 75752 PARIS CEDEX 16

CNRS

3 Michelangelo Street

75794 PARIS CEDEX 16

Device for extracting air / water by semi-wet electrostatic collection and method using this device

The invention relates to an air / water extraction device by wet electrostatic collection, in particular semi-wet, comprising a chamber containing a discharge electrode for creating an ion flow from a pocket of ionized gas surrounding the discharge electrode and a counter electrode, an inlet for the air and aerosol mixture to be treated which contains liquid or solid particles, a vapor inlet tube and an outlet for the treated air, and a method using these measures. Below, these devices will be mentioned under the term ^"ESP".

It is of great importance to be able to separate the particulate constituents of the gases in the atmosphere, either to clean the treated air (for example near industrial buildings), or to analyze the particles it carries. A very important method of separation is the electrostatic separation of impurities in an electrostatic precipitator. In the case of air cleaning, however, large structures are needed to obtain collection electrodes having the largest possible area, in order to increase the efficiency of cleaning. Large structures are then necessary and electrofilters of this size require for this purpose large amounts of electrical energy for the creation and maintenance of electrostatic fields. Such electrostatic filters can therefore only be used on fixed supports. In the present case, where it is desired to use the electrostatic filter to analyze the particles contained in the air, mobile instruments are more advantageous since the monitoring areas of interest are not necessarily fixed or close to a source of electricity. In this case, it is essential to have a very good collection rate to be able to detect particles even in very small quantities.

There are currently two types of devices, dry electrostatic precipitators (simply called electrostatic precipitators) and wet electrostatic precipitators:

An electrostatic precipitator (ESP) is a device that cleans the gas using the electrostatic forces produced by an electric field through which the particles pass. This electric field, which is high (several tens of kV per cm) and non-uniform, is induced by two electrodes. More precisely, it has two effects: it creates an ion flux from an ionized gas pocket surrounding one of the electrodes, typically in the form of a tip or wire, brought to a high potential: this phenomenon is called a corona effect. The particles that are passed through this flow of ions are then coated with these ions and charged. They become sensitive to the Coulomb forces that drag them onto the cylindrical or planar against electrode, brought to the ground. The efficiency of an electrostatic precipitator is remarkable for all sizes with a minimum generally below the micron. Devices operating on this principle can be found commercially

(for example at United Air Specialists, Inc.). The advantages are compactness and a yield of about 1 for particles larger than one micron. The main disadvantage of these systems lies in the collection of submicron particles, whose performance is poor.

The second family of electrofilters consists of wet electrostatic precipitators. In this case, the air to be treated containing the particles is premixed with water vapor introduced in the form of droplets in a unit upstream of the collection unit. The objective here is to increase the size of the droplets by condensation and to make the smallest particles more sensitive to electric fields. There are also such systems commercially (for example at Wheelabrator Air Pollution Control Inc.). These systems, although allowing the collection of very small particles with excellent efficiency, are intended for industrial use and require very large quantities of water (several tens of liters per hour). They are therefore not suitable for portable applications.

WO-2004/041440 discloses a portable electrofilter comprising:

an air inlet system consisting of an ^air passage having an inlet and an outlet at its ends and an air pump, for sucking air through said inlet through said passage air then out of said outlet, thereby creating a flow of air through said air passage; an ionization section located in said air inlet system near said inlet, which is capable of ionizing the analytes in the air stream; and

a collection electrode located in said air inlet system between the ionization section and the outlet of said air inlet system, wherein said collection electrode comprises a vertical tubular electrode and is exposed to said flow of air. air.

^The electrostatic filter of WO-2004/041440 further comprises a reservoir containing a liquid which is hydraulically connected to the collection electrode; a liquid pump for pumping said liquid from said reservoir into the collection electrode, such that said liquid flows on the outside of said collection electrode and is returned to the reservoir. The liquid serves to clean the collection electrode continuously or periodically, which avoids stopping the electrostatic filter to clean or replace the electrodes. The liquid is typically transported to a waste management system, where it will be filtered or at least cleaned.

The electrofilter of WO-2004/041440 is therefore not a wet electrostatic precipitator, the water intervenes only during the recovery of residues at the counter electrode and not during the collection. The defect of this device is that of all dry precipitators: it has a low efficiency for small particles.

U.S. Patent No. Re. 35990 (Reissue) discloses a method and a device for treating residues. These residues are incinerated in an oxygen-rich atmosphere to produce ash and residual gases and these gases are burned in an oxygen deficient atmosphere to produce burned residual gases. An electrostatic filtration module is used to purify the flue gas entering it, making it more environmentally acceptable.

GB 2403 672 discloses an electrostatic precipitator in which the droplets produced by an ultrasonic droplet generator can be used to prevent the formation of solid particles in the porous collection electrode. As a result, drops of water can usually be added to the aerosol before being introduced into the electrostatic precipitator.

These last two solutions involve a consumption of water and energy that is incompatible with portable use.

FR 201249 A discloses an electrostatic precipitator of droplets for removing dust and other pollutants from the gas stream. The electrostatic force at the electrostatic field sucks the fluid out of the nozzle and causes the fluid to break into small droplets. The droplets having a very high load-to-mass ratio undergo a very high acceleration due to the field prevailing between the nozzles and the collecting plate. The moving droplets can meet the particles in the gas stream and strike them in the gas stream by pulling them toward the header plate. The residence time of the droplets in the gas stream is very low, but thanks to the high speed the probability of collision with particles is very important. A small amount of vapor present in the reduced gas is therefore sufficient to obtain improved collection efficiency compared to a dry electrostatic precipitator. In order to avoid a vapor gain between the discharge electrode along its entire length, the water droplets according to FR 201249 A are accelerated out of the nozzles forming the discharge electrodes and are then distributed in all the gas streams. . Steam is reduced by a steam inlet tube in the space between the discharge electrode and the counter electrode. A characteristic of FR 201249 A is that the discharge electrode is formed by the nozzles themselves, which at the same time serve as the steam inlet tube.

US 4,544,382 A discloses an electro-filter which may especially be used at elevated temperatures. The particles present in a stream of gas to be cleaned are charged to a specific region of the filter. The principle of the device according to US 4,544,382 A is that the compressed air and wet enters the device quickly and in the wet gas a corona discharge is between a needle and the nozzle. In the narrowed portion of the injector, the compressed and wet air expands creating ice microparticles that exit the injector and trap the charged particles in the discharge crown.

The object of the present invention is therefore to provide a system for the collection of particles suspended in a gas by a system of electrostatic precipitators with high efficiency, in particular the collection of liquid or solid particles of size between 10 nm and 100 μm, and consumption of energy and products (eg water) compatible with portable use. On the other hand, this invention aims to allow the efficient collection of submicron particles suspended in the air for their analysis. This device also allows portable applications and has a consumption of energy and products (mainly water) low enough to have a suitable autonomy.

The present invention thus relates to a wet electrostatic collection air / water extraction device, comprising a chamber containing a discharge electrode for creating an ion flow from an ionized gas pocket surrounding the discharge electrode and a counter-electrode, an inlet for the air and aerosol mixture to be extracted which contains liquid or solid particles, a steam inlet tube and an outlet for the cleaned air, characterized in that the device makes it possible to introduce the steam by said vapor inlet tube in the space between the discharge electrode and the counter-electrode so as to form a steam sheath surrounding the discharge electrode over its entire length, so that the treated air is not saturated with steam.

The present invention also relates to a process for the collection by wet electrostatic method of liquid or solid particles of size between 10 nm and 100 μm suspended in a gas using the device described above, characterized in that

(a) the steam is introduced into the space between the counterelectrode and the discharge electrode to establish a steam sheath around the discharge electrode,

(b) an air and aerosol mixture is introduced in the form of a flow in the space between the discharge electrode and the counter-electrode, (c) the vapor molecules are ionized by the discharge electrode,

(d) the ionized vapor molecules charge particles,

(e) the charged particles grow to form droplets, and

(f) said droplets are fed to the counter electrode and are precipitated thereon,

(g) the droplets are recovered and transported for analysis.

Other features and advantages of the invention will emerge from the description which follows, with reference to the figures of the accompanying drawings. The exemplary embodiments described with reference to the accompanying drawings are in no way limiting.

Figure 1 illustrates the principle of the dry electrofilter according to the state of the art.

Figure 2 illustrates the principle of the wet electrofilter according to the state of the art.

FIG. 3 illustrates the operating principle of the semi-wet electrostatic collector of a device according to the present invention.

Figure 4 shows an exploded view of a possible embodiment of the device according to the present invention.

Figure 5 shows that a rotating flow in the chamber containing a discharge electrode and a counter-electrode stabilizes the jet of steam. Figure 5 illustrates the use of tangential air intakes to the walls of the main channel ("mainline") to create a helical airflow.

Figure β shows a device according to the present invention with a particle collection system having impacted the counter-electrode using microfluidic channels.

Figure 7 shows a device according to the present invention with a particle collection system having impacted the counter-electrode using a systematic electrowetting of the counter-electrode.

FIG. 8 illustrates an exemplary embodiment of the present invention in which a helical channel can be machined on the inside of the chamber of the device according to the present invention containing electrodes (main channel) for collecting the particles, and forming an interlacing with the against electrode, it also consists of a helical wire.

FIG. 9 describes an exemplary embodiment of the present invention with the use of a plane counter-electrode that can be envisaged to facilitate the collection of particles.

FIG. 10 shows another exemplary embodiment according to the present invention (second example of possible planar configuration) for guiding the vapor / aerosol mixture.

In the figures, identical reference indices are used for the designation of identical parts.

Figure 1 illustrates the principle of the dry electrofilter according to the state of the art. In Figure 1, 1 refers to the discharge electrode, 2 to the counter-electrode, 3 to the inlet for the air and aerosol mixture, 4 to the outlet for the cleaned air and 5 to the direction of the ionic wind resp. charged particles of the discharge electrode 1 on the counter electrode 2. Due to the physical effects involved, the particles that are subjected to the ionic wind created at the electrode 1 (corona discharge) are charged. Then the charged particles are transported to the counterelectrode 2 (electrostatic collector). It is possible to charge the particles upstream at the inputs, in which case the only collection - which requires a much lower voltage - is through the device opposite. This method makes it possible to optimize the two physical phenomena independently, while losing in compactness. The use of such a method further requires that the path of the air treated between the charging unit and the collection unit is very short so as not to allow the particles time to discharge.

Figure 2 illustrates the principle of the wet electrofilter according to the state of the art. In Fig. 2, 6 refers to a container for a liquid, usually water, which will be used for droplet formation. Thanks to the physical mechanisms involved, we obtain a nucleation of drops around the particles that we want to collect. A fog is forming. Particles encapsulated in the droplets are collected by electrostatic force.

This electrostatic filter makes it possible to collect very efficiently small particles that are artificially magnified. But it has the disadvantage that the amount of solvent (usually water) necessary for nucleation around submicron particles is very important. Thus to treat 500 1 / min by capturing the particles of 1 micron, consumes 200 1 of water per day. Figure 3 illustrates the operating principle of the air / water extraction device by semi-wet electrostatic collection of the present invention. The wet electrostatic collection air / water extraction device of the present invention comprises a chamber 7 containing a discharge electrode 1 for creating an ion flow from a pocket of ionized gas surrounding the discharge electrode 1 and a counter-electrode 2, an inlet 3 for the air and aerosol mixture to be cleaned which contains liquid or solid particles, a steam inlet tube 8 and an outlet 4 for the cleaned air, characterized in that the device allows introducing the steam through said steam inlet tube 8 into the space 9 between the discharge electrode 1 and the counter-electrode 2 so as to form a steam sheath 10 surrounding the discharge electrode 1 over any its length, so that the treated air is not saturated with steam. In Figure 3, numbers 6 and 12 refer to the steam generator (water). 6 indicates the solvent tank and 12, heating to produce steam from the solvent. 11 indicates a pump which drives the air and aerosol mixture through the device.

The solvent vapor (preferably water) is produced from a reserve located upstream 6. It is conducted within the chamber 7. The discharge electrode 1 is preferably located in the axis of the tube. steam inlet 8 and brought to high voltage by a mobile power supply (which is not shown here). The voltage is generally 5 to 10 kV. The discharge electrode 1 may be either a tip or a wire. It can be held and guided from the steam inlet tube or from the pipe.

The main air flow containing the particles (the air and aerosol mixture) penetrates to 3 at the periphery of the electrode of discharge 2. Thus, a steam sheath 10 surrounds the discharge electrode 1 over its entire length. In this way, the discharge is in the vapor, and the ions created are in the case of the water of the ions H ₃ O ⁺ . If another solvent is used, ^other ions may be formed. These ions will charge the particles present in the flow as in a conventional electrofilter. The flow rate is such that the flow of air and aerosol in the pipeline remains preferably laminar. The speed of the gas stream will be determined by ^the action of the pump 11.

At the edge of the steam (water) sheath 10, droplets form and encapsulate the particles, as in a wet electrostatic precipitator. Then, when these droplets are brought to the counter-electrode, they drag with them all the particles they encounter.

In the present invention, the vapor droplets are formed very late. First, the steam is introduced through the nozzle at the end of the steam inlet tube 8 into the space between the electrodes and is worked in an unsaturated atmosphere. It is only at the end of the vapor sheath that the droplets form.

This is preferably achieved in the device according to the present invention by virtue of the following properties of the nozzle:

the end of the discharge electrode is at a distance from the nozzle which is smaller than the diameter of the nozzle. the flow of water vapor leaving the nozzle is between a few thousandths and five hundredths of the air flow rate. In addition, the outlet of the nozzle must be located between the discharge electrode 1 and the counter-electrode 2 so that the collected droplets pass through the entire space containing the air and aerosol mixture.

It is particularly advantageous that the steam leaving the nozzle has the following properties: Pressure slightly greater than or equal to atmospheric pressure, temperature equal to the boiling point (100 ^° C. at atmospheric pressure) or greater, flow rate less than five hundredths air flow. Thus, the air to which the steam mixes will not be saturated.

The advantage of the present invention (device and method) is to benefit from the gain in collection efficiency similar to that of wet electrofilters, while using a quantity of the solvent (preferably water) much less important, since This is not a question of saturating all treated air with water vapor.

Different solvents can be used in the present invention, as long as they can be vaporized in the device and the particles present in the vapor can be at least partially ionized. Examples of suitable solvents: ethanol, acetone, water. These can be used alone or - if possible - in a mixture. Since water is preferably used, the vapor is therefore water vapor in the device and in the process according to the present invention.

The solvent (preferably water) which has impacted the counterelectrode 2 only has to be recovered for analysis. In the case of a biological or chemical analysis, it is important that the volume of the solvent thus recovered is also as small as possible to avoid too much dilution and to promote detection.

Figure 4 shows an exploded view of a possible embodiment of the device according to the present invention. It can be seen in particular that the discharge electrode 1 can be fixed indifferently to the frame in which the main flow takes place or be integrated with the steam ejection nozzle 13. In both cases, the discharge electrode 1 can be short and relatively thick, in which case the discharge will be solely at the tip of the discharge electrode 1; or it can be fine and pass through the entire chamber 7 (the pipe), in which case the discharge takes place over the entire length of the discharge electrode 1 (it is called wire discharge). 14 indicates a low voltage electrical control box and indicates a detection device (the analysis unit !?).

The discharge electrode 1 is generally in the middle of the chamber 7. Preferably, the discharge electrode is located in the axis of the vapor inlet tube.

The discharge electrode 1 may have different shapes, for example a comb shape or a square section. It is necessary to generate a localized discharge that it has one or more zones whose radius of curvature is small enough to initiate the discharge. It is preferable that the discharge electrode is a tip or a wire.

The electrodes 1 or 2 may be constituted by different conductive materials, for example stainless steel or conductive plastics. The counterelectrode 2 may consist of a compact or porous conductive material, generally metal. If a porous conductive material is used, it can be in various forms: perforated metal, porous sintered metal, one or more layers of wire mesh preferably rolled into a cylinder shape, a cushion of fibers or metal wires in the form of cylinder, etc. As the gas flows into the porous medium, the particles are transported near the surface of the conductive elements, thus allowing the charged particles to actually deposit on the surface of the conductive elements of the porous medium. If solid collection electrodes are used, such as a solid tube surrounding the central discharge electrode, the charged particles must be precipitated by the electrical force through the fluid boundary layer adjacent to the inner surface of the tube which surrounded.

In a preferable embodiment of the present invention, the counter-electrode 2 is provided with a cooling system.

It is preferable according to the particle recovery method that the counter-electrode 2 is rendered hydrophilic or hydrophobic by a surface treatment. This treatment may consist of a grooving (which makes the surface very wetting by capillarity) or chemical deposition.

The present device is very effective and achievable in small format. The cylindrical shape with circular cross section is the most suitable form in many applications. However, it is not necessary ^to have a cross section of circular shape to take advantage of the many benefits of the invention. Cross sections Rectangular, elliptical or other shapes may be used in the device according to the present invention.

The device of the present invention may be in different sizes. Thus in the embodiment of Figure 4, the diameter of the cylinder (against electrode) is 50 mm and the outer diameter of the nozzle is 5 mm and the inner diameter of 4 mm. But this diameter does not have an essential influence on the formation of the droplets.

In the context of the present invention it is advantageous that the main air flow containing the particles penetrates tangentially to the walls of the channel (chamber 7) so as to obtain a helical flow. This flow makes it possible, on the one hand, to bring the larger particles towards the counter-electrode 2 by the centrifugal force, and on the other hand, to stabilize the flow of vapor generated around the discharge electrode to ensure a cylindrical steam sheath surrounds the discharge electrode 1 over its entire length.

FIG. 5 shows that a rotary flow makes it possible to stabilize the jet of steam leaving the steam inlet tube 8. FIG. 5 illustrates the use of tangential inlets to the main channel in order to create a helical air flow in the chamber 7. 3 indicates an inlet for the air and aerosol mixture. This makes it possible to stabilize the vapor zone which is thus confined in a cylinder surrounding the discharge electrode 1. In addition, it is possible, in this way, to separate the collector (against electrode 2) into two zones: In zone I, the largest particles are collected by cyclone effect (they are driven outwards by centrifugal force):

In Zone II, smaller particles are harvested using electrostatic forces.

The use of a helical main flow makes it possible to stabilize the steam flow and to collect the larger particles quickly. It is therefore preferable that the air and aerosol flow tangentially to the walls of the chamber 7 to create a helical flow.

On the other hand, it is advantageous for the collection electrode (against electrode 2) to undergo a surface treatment (grooving or other similar treatment) in order to render it very hydrophilic and to standardize the deposition of the droplets over the entire surface. by a kind of film. FIG. 6 shows a device according to the present invention with a system for collecting particles having impacted the counter-electrode 2 using microfluidic channels 14. The structuring of the counter-electrode 2 makes it possible to permanently keep a liquid film wetting the surface without have to feed it continuously.

It is furthermore advantageous that the counterelectrode 2 is partially immersed in a tank containing a solvent. The solvent is preferably water. In this case, the counter-electrode 2 is partially in a reservoir containing solvent for wetting the counter-electrode 2 with a film of this solvent. This solvent is preferably water which may contain additives. It is therefore advantageous to bathe a counter-electrode end 2 in a water tank. In this variant, the water will then cover the entire surface due to the capillary forces, and it is not necessary to continuously supply the surface to keep it moist. Thus, a film of water is formed on the entire surface of the counter-electrode 2 on which the particles arrive. This film can be set in motion by means of a solenoid valve to collect the collected particles continuously and carry out the treatment in real time. Such a device does not impose any flow constraint, it being understood that the higher the output rate, the more the particles will be diluted.

In a preferable variant, the collected particles are fed after their recovery to the analysis unit 15 which can be combined with the device of the present invention. The particles are continuously collected in the film covering the counter-electrode, from which a small amount of water to be analyzed can be taken at regular intervals. The output of the device is preferably in the aqueous phase to allow analysis.

Figure 6 shows the wetting device of the collection electrode. When excess water is brought into the upper reservoir, it flows by siphon effect along the counter-electrode 2: this gives a controlled flow rate, while keeping the electrode 2 permanently wet. The Peltier cell 16 is used to cool the film of water to prevent it from evaporating while preheating the water to be vaporized. 15 indicates a detection device.

The water used for vaporization around the discharge electrode 1 should be pure to ensure that the drop nucleation is only around the particles of interest (for example germs), while the water used to wet the counterelectrode 2 may contain additives (surfactants, pH buffer).

To limit the evaporation of the solvent (for example a film of water) on the counter-electrode, it is advantageous to put a cooling system on the counter-electrode. It is advantageous to use a Peltier cell 16 whose hot source will be the water intended to be vaporized. This water is thus preheated and the energy necessary for the vaporization is limited.

In addition, a cooling of the walls of the collection unit may be advantageous for accelerating the condensation of the water vapor around the solid particles which are thus trapped in droplets whose radius increases as and when they transit axial and radial.

The device according to the present invention may further comprise collection means using the capillarity, the gravity or the shear of the air.

FIG. 7 shows a device according to the present invention with a particle collection system having impacted the counter-electrode 2 using a systematic scanning by electrowetting of the counter-electrode 2.

It is advantageous, if the surface of the collection electrode is not incompatible (for example by grooving), to have an electrode grid 17 therein (see Fig. 7). Figure 7 illustrates the possibility of using an addressable electrode array in position by a sufficiently high voltage to cause the displacement of a drop of water (containing any additives) to scan the entire surface of the collection electrode. It is then possible, by successively bringing these electrodes 17 to a potential of the order of a few tens of volts (typically: 60 volts), to move a drop on the surface of the counterelectrode 2 by electrowetting. It is thus possible to sweep with a single drop the entire surface of the electrode 2, drastically reducing the quantity of water necessary to collect the particles or droplets.

Depending on the time that the drop of water passes through the device, it may be necessary to add a cooling system, for example a Peltier cell 16 (see Figure 6).

Finally, the complete system can use several modules, such as the one described above, to increase the flow of air to be treated while preferably keeping a laminar flow inside each module since the flow treated by each modules remain the same. Each of the modules typically measures a few cm in diameter, for one or several tens of cm in height.

FIG. 8 illustrates that a helical groove 18 can be machined on the inner face of the main pipe (chamber 7) to collect the particles and form an interlacing with the counter-electrode 2, also consisting of a helical wire. This solution makes it possible to limit the surface of the counter-electrode and thus not to have to functionalize the latter.

FIG. 9 illustrates that the use of a planar counter-electrode 2 is conceivable to facilitate the collection of the particles. FIG. 10 shows a second example of a planar configuration that can be envisaged. 8 refers to a steam inlet tube and to a detection device (the analysis unit). 19 indicates the collection areas (counter-electrode 2), 20 indicates a bin, 21 indicates a reagent and 22 indicates the electrodes for moving the drops by electrowetting.

The device of the present invention may contain gravity-type collection means (the droplets sink below the counter electrode due to gravity) or air shear (the droplets are carried along the counter-electrode by the flow of air present in the device).

The most common applications of the present invention are the extraction of particles suspended in the air for their subsequent analysis (monitoring of pollution, prevention of bioterrorism). Any constituent of air such as gases, microbes (including microorganisms such as spores, bacteria, fungi), dust or any other particles that are entrained or transported by air, can be ionized by the electrostatic field, collected by the collection electrode and, if necessary, analyzed.

The main object of the invention is an implementation, the objective of which is to collect the particles in as small a volume of water as possible, for subsequent biological analyzes. This is called microbiological extraction devices. The present invention provides several specific advantages. The device envisaged differs from conventional devices in several respects:

Using water vapor instead of fog

(droplets, as is the case in conventional wet electrofilters) increases the collection efficiency of submicron particles. This remains valid if another solvent that water is used for steam formation. The use of water vapor ensures that the condensation in droplets is around the particles present in the air.

The water vapor is confined to a small volume, the water consumption is low enough to have a range of at least one day with a main tank containing a few liters of water.

The small format of the device allows to use a large number in parallel while keeping the portable system. It is thus easy to calibrate the final system according to the needs of the analysis by varying the number of modules used in parallel.

The invention will be useful in particular for the establishment of mobile air analysis beacons for detecting submicron particles present as traces in the atmosphere (bacteria and viruses). For example, it is conceivable to place such tags at the exit of risky industries to detect in real time the presence of legionellosis.

The device of the present invention allows the separation of liquid or solid particles of size between 10 nm and 100 μm suspended in a gas by a system of electrostatic precipitators. It allows in particular the collection of particles measuring between 50 nm and 10 microns with great efficiency, and a consumption of energy and water compatible with portable use.

In addition, the proposed invention allows the efficient collection of submicron particles suspended in air for analysis. The device can also be transportable, and have a consumption of energy and products (mainly water) low enough to have a suitable autonomy.

Claims

claims An air / water extraction device by semi-wet electrostatic collection, comprising a chamber 7 containing a discharge electrode 1 for creating an ion flow from an ionized gas pocket surrounding the discharge electrode 1 and a counter-electrode 2, an inlet 3 for the air and aerosol mixture to be extracted which contains liquid or solid particles, a steam inlet tube 8 and an outlet 4 for the cleaned air, characterized in that the device allows introducing steam through said vapor inlet tube 8 into the space between the discharge electrode 1 and the counterelectrode 2 so as to form a steam sheath 10 surrounding the discharge electrode 1 over its entire length, so that the treated air is not saturated with steam. 2. Device according to claim 1, characterized in that the counter-electrode 2 is partially immersed in a reservoir containing a solvent. 3. Device according to claim 2, characterized in that the solvent is water. 4. Device according to one of claims 1 to 3, characterized in that the discharge electrode 1 is located in the axis of the steam inlet tube 8. 5. Device according to one of claims 1 to 4, characterized in that the discharge electrode 1 is a tip or a wire. 6. Device according to one of claims 1 to 5, characterized in that the counter-electrode 2 is provided with a cooling system 16. 7. Device according to one of claims 1 to 6, characterized in that the counter-electrode 2 is made hydrophilic by a surface treatment. 8. Device according to claim 7, characterized in that the treatment is a grooving. 9. Device according to one of claims 1 to 8, characterized in that said device further comprises collecting means using the capillarity, gravity or shear air. 10. Method for the collection by wet electrostatic method of liquid or solid particles of size between 10 nm and 100 μm suspended in a gas using the device according to one of claims 1 to 9, characterized in that (a) the steam is introduced into the space between the counterelectrode 2 and the discharge electrode 1 to establish a steam sheath 10 around the discharge electrode 10, (b) an air and aerosol mixture is introduced in the form of a flow in the space between the discharge electrode 1 and the counterelectrode 2, (c) the vapor molecules are ionized by the discharge electrode 1, (d) the ionized vapor molecules charge particles, (e) the charged particles grow to form droplets, and (f) said droplets are fed to the counter electrode 2 and are precipitated thereon, (g) the droplets are recovered and transported for analysis. 11. Process according to claim 10, characterized in that the vapor is water vapor. 12. The method of claim 10, characterized in that said flow of air and aerosol is laminar. 13. The method of claim 12, characterized in that said air flow and aerosol between tangentially to the walls of the chamber 7 to create a helical flow. 14. Method according to one of claims 10 to 13, characterized in that the counter electrode 2 is partially in a tank containing solvent for wetting the electrode against 2 with a film of this solvent. 15. Method according to one of claims 10 to 14, characterized in that the solvent is water may contain additives.