Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/32—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by electrical effects other than those provided for in group B01D61/00
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/10—Single element gases other than halogens

Definitions

• the invention relates to a method and a device for treating electrically volatile gaseous volatile organic effluents at low pressure and at low temperature.
• this technique consists in generating an electric arc AR between two divergent electrodes, a flow of gas containing the VOCs being directed towards these electrodes.
• An electric arc AR starts at the neck of the electrodes A, in accordance with Paschen's law, moves by sliding towards the flared part B under the action of the gas flow.
• the electrical voltage drop across the arc increases with the length of the arc.
• the displaced electric arc is short-circuited and extinguished by a new arc, the process is repeated according to an oscillatory relaxation phenomenon.
• the purpose of the preionization process is to increase the conductivity of the flame, in the absence of any addition of additive liable to present a risk of pollution.
• a solution described in French patent application 2,577,304 published on August 14, 1986 in the name of ELECTRICITE DE FRANCE and STEIN-HEURTEY implements a nozzle, the pre-ionization process being carried out by creating electric arcs between an axial electrode and one or more annular electrodes, forming a nozzle.
• the arcs generated and the lively combustion produced are produced at high temperature, above 2000 ° K.
• the electric arcs generated are arcs in thermodynamic equilibrium at high temperature and the phenomenon of expansion, and the correlative lowering of gas caused by the nozzle effect is substantially obscured by the aforementioned significant temperature increase .
• nitrogen oxide NO x is important. Indeed, this production is essentially of thermal origin, the maximum of the level of emission of nitrogen oxide NO x being located at a temperature close to 3500 ° K.
• the present invention relates to the implementation of a method and a device for the treatment by electrical discharge of gaseous volatile organic effluents at low pressure and at low temperature making it possible to notably avoid the formation of nitrogen oxide NO X.
• the subject of the present invention is a method and a device for treatment by electrical discharge of gaseous volatile organic effluents at low pressure and at low temperature using a phenomenon of electric discharge outside local thermodynamic equilibrium, the treatment of these effluents, therefore, being carried out at low temperature and at low pressure, which makes it possible substantially to avoid the formation of nitrogen oxide NO x .
• Another object of the present invention is also the implementation of a method and a device for treatment by electrical discharge of gaseous volatile organic effluents, containing hydrogen, the treatment leads to low pressure allowing in these effluents to release hydrogen radicals having, due to the low pressure surrounding them, a lifetime ten times greater than that of these same hydrogen radicals subjected to atmospheric pressure.
• the method of treatment by electrical discharge of volatile organic gaseous effluents, object of the present invention is remarkable in that it consists at least in subjecting these effluents to an expansion at low pressure, in order to generate a lowering of temperature.
• the device for the treatment by electrical discharge of gaseous volatile organic effluents at low pressure and at low temperature is remarkable in that it comprises, at least, an intake stage for these effluents, a stage of the same effluents allowing to generate a relaxation at low pressure and a lowering of the temperature of these effluents to a temperature between 150 ° K and 173 ° K.
• an electrical discharge generator stage between a high voltage electrical potential and a low voltage electrical potential is provided, this electrical discharge being applied to these effluents at low pressure and at low temperature to cause rupture of the hydrocarbon chains of these latter, in the absence of creation of nitrogen oxide compound NO x .
• the process and the device which are the subject of the present invention find application in the destruction of volatile organic effluents, in the production of hydrogen radicals with increased lifetime in hydrocarbon products, in particular in the cracking of hydrocarbons used or produced by industry. petroleum, in the absence of crippling production of nitrogen oxide.
• FIG. 2a shows, by way of illustration, a functional diagram of the steps for implementing the method of treatment by electrical discharge of gaseous volatile organic effluents at low pressure and at low temperature, object of the present invention
• FIG. 2b represents, by way of illustration, a functional diagram of the stages of an alternative implementation of the method of treatment by electrical discharge of gaseous volatile organic effluents at low pressure and at low temperature, object of the present invention, in which, by repeating the steps of the process which is the subject of the invention as illustrated in FIG. 2a, a synergistic effect is however obtained;
• FIG. 3a shows, by way of illustration, a sectional view, along a plane of radial symmetry, of the device for treatment by electrical discharge of gaseous volatile organic effluents at low pressure and at low temperature, object of the present invention
• FIG. 3b ⁇ , 3b 2 , 3b 3 and 3b 4 show diagrams illustrating the principle of the different flow regimes in a nozzle such as that used in the device object of the invention illustrated in Figure 3a;
• FIG. 4a shows, by way of illustration, a sectional view, along a plane of radial symmetry, of an alternative embodiment of the device for treatment by electrical discharge of gaseous volatile organic effluents at low pressure and at low temperature, object of the present invention, this variant embodiment being more particularly suitable for implementing the method which is the subject of the present invention as illustrated in FIG. 2b;
• Figure 4b shows a diagram of the profile of the relative pressures recorded in the flow produced in the device object of the present invention as shown in Figure 4a;
• FIG. 4c shows a diagram giving the position of the shock wave generated in a nozzle of the device object of the present invention shown in Figure 4a as a function of the gas flow
• FIG. 4d represents a diagram of the values of the Paschen parameter, product of the pressure in a straight section of the flow and of the electrical distance, likely to generate an electric discharge in this section, this diagram making it possible to locate the position of the electric discharge for the minimum value of this parameter;
• FIG. 5a shows, by way of illustration, a sectional view along a radial plane of symmetry of the central electrode equipping the device object of the present invention as illustrated in Figure 3a or 4a;
• - Figure 5b shows, by way of illustration, a preferred diagram of connection and electrical supply of the electrodes fitted to the device object of the present invention as illustrated in Figure 4a;
• FIG. 6a shows a preferred non-limiting embodiment of the device object of the invention as illustrated in Figure 3a;
• FIG. 6c shows another preferred non-limiting embodiment of the device object of the invention as shown in Figure 3a or 6a.
• the process which is the subject of the present invention consists in treating the abovementioned effluents when these are accompanied by a carrier gas, these effluents then being able to correspond to aerosols, vapors or other gases which are in suspension, respectively mixed with the abovementioned carrier gas.
• the carrier gas can consist of air, ambient air, which, taking into account the proportion of nitrogen contained in the ambient air above, implies, in the absence of special precautions, the risk of creating nitrogen oxide NO x .
• this consists, in a step A, in subjecting the volatile organic gaseous effluents to an expansion at low pressure, in order to generate a lowering of the temperature of these effluents, the latter being brought to a temperature between 150 ° K and 173 ° K.
• low pressure expansion means any expansion of organic effluents, and of course of the carrier gas, at a pressure less than or equal to 350 millibars for example.
• step B The aforementioned gaseous volatile organic effluents having been brought to the state of low pressure and of reduced temperature are then subjected, in step B, to a treatment by electric discharges.
• This procedure makes it possible to treat the aforementioned volatile organic gaseous effluents by breaking the chains. constituent hydrocarbons of the latter, in the absence of creation of nitrogen oxide compounds NO X , as will be described and illustrated later in the description.
• step A must be carried out prior to step B or, where appropriate, at least concomitantly.
• the electric discharge treatment operation makes it possible to crack the carbonaceous bonds CH and to generate hydrogen radicals whose lifespan in the atmosphere at low pressure mentioned above is lengthened significantly. It has been observed during investigations that for a low pressure of the order of 300 millibars, the lifetime of the hydrogen radicals is approximately ten times greater than at atmospheric pressure.
• the electrical discharges generated are formed by electrical discharges at low temperature, that is to say in the medium of gaseous volatile organic effluents brought to the temperature between 150 ° K and 173 ° K, these electrical discharges being generated in an environment outside of local thermodynamic equilibrium, which makes it possible to maintain the environment of the discharge atmosphere at a temperature substantially lower than the temperature room. For this reason, the level of nitrogen oxide emission from the nitrogen contained in the carrier gas is significantly reduced and, under certain experimental conditions, practically negligible, as will be described later in the description.
• step Ai of subjecting the gaseous organic effluents to steps A and B shown in FIG. 2a, that is ie respectively at a low pressure expansion step by lowering the temperature to a temperature between 150 ° K and 173 ° K, and, concomitantly or successively, subjecting the cooled and low temperature effluents to discharges electrical under conditions similar to those explained above in the description in conjunction with Figure 2a.
• Step i can then advantageously be repeated, this repetition making it possible, from gaseous organic effluents having already undergone a treatment during the implementation of step Ai, in particular from ozone 0 3 and oxygen radicals generated by the emanations of the electrical discharge carried out in step B of the aforementioned step Ai, to further submit the effluents gaseous organics treated with a phenomenon of enhanced oxidation by means of ozone and the oxygen radicals thus created.
• step Ai is meant the repetition of steps A and B constituting it at least qualitatively, the conditions for implementing these steps can however be modified according to specific criteria related to the mode of production of the low pressure expansion processes during the repetition, as will be described in more detail later in the description.
• the relaxation carried out during the repetition may be less intense, the pressure and the temperature reached being able to be greater than in the case of the first relaxation, the repeated relaxation being consequently less strong, as will be described later in the description.
• the device which is the subject of the present invention comprises at least one stage 1 for admitting the effluents volatile organic gases with which an expansion stage 2 for these effluents is associated, this expansion stage making it possible to generate expansion at low pressure, pressure less than 350 to 400 millibars for example, and a lowering of the temperature of these effluents to a temperature between 150 ° K and 173 ° K.
• the device which is the subject of the present invention comprises an electrical discharge generator stage, marked with the reference 3, between a high voltage electrical potential and a low voltage electrical potential.
• the electric discharge is applied to volatile organic effluents at low pressure and at low temperature, this operating procedure making it possible to treat volatile organic effluents by breaking the hydrocarbon chains constituting them in the absence of the creation of oxide compounds. 'nitrogen NO x .
• the expansion stage 2 is constituted by a supersonic nozzle under the operating conditions which will be described later in the description.
• the device which is the subject of the invention can advantageously be made up and comprise at least, in a tube T provided with a pipe for admitting the carrier gas, this pipe bearing the reference 10, a central electrode EC of revolution, this central electrode extending substantially along the longitudinal axis of the tubing T. More specifically, it is indicated that the central electrode EC can be produced by a cylindrical rod of electrically conductive material, such as copper, stainless steel for example.
• the device which is the subject of the invention successively comprises, and arranged substantially in revolution around the central electrode EC so as to form the expansion stage 2, a chamber d 'inlet, denoted CA, volatile organic gaseous effluents, the inlet chamber CA constituting in fact a reservoir of the buffer tank type of the carrier gas and volatile organic gaseous effluents contained in the latter.
• a chamber d 'inlet denoted CA
• volatile organic gaseous effluents volatile organic gaseous effluents
• the inlet chamber CA constituting in fact a reservoir of the buffer tank type of the carrier gas and volatile organic gaseous effluents contained in the latter.
• the device which is the subject of the invention comprises a nozzle 20 comprising a nozzle neck and forming a duct of the Venturi duct type, for example, the intake face of the nozzle being in direct engagement in the inlet chamber CA.
• the nozzle 20 surrounds the central electrode EC and constitutes with the latter a supersonic flow channel, if necessary subsonic, for the gaseous volatile organic effluents and the carrier gas contained in the inlet chamber CA.
• the assembly consisting of the carrier gas and the effluents VOC is subjected to a flow causing a shock wave accompanied by the expansion and the decrease in temperature of gaseous volatile organic effluents mentioned above, as will be described later in the description.
• the nozzle 20 and the nozzle neck consist of an electrically conductive material, such as copper or stainless steel, and formed by a tube of revolution having a convergent / divergent profile.
• the central electrode EC and the revolution tube constituting the nozzle 20 are coaxial to form the cylindrical expansion channel of the carrier gas and organic VOC effluents.
• the central electrode EC and the nozzle neck as well as the complete nozzle 20 are connected to an electric voltage generator to form the electric discharge generator stage 3 between the central electrode EC and the nozzle 20.
• the electric voltage generator is not shown, only the connections to the latter, 200 and 201, of the nozzle 20, respectively of the central electrode EC being shown, so as not to unnecessarily overload the drawing .
• the inlet chamber CA can be produced directly in the tube T formed by a cylindrical sleeve, a shutter 11 forming a shim for holding the central electrode EC and made of electrically insulating material being provided so as to maintain and center the above-mentioned central electrode EC.
• FIG. 3a the direction of flow e of the carrier gas and of the organic VOC effluents is shown.
• this can be held by a mechanical piece of insulating material denoted 21, fixed directly to the internal wall of the tube T.
• the connection of the nozzle 20 and the nozzle neck to the external electric generator by the connection 200 can then be produced in a manner known as such by a sealed electrical crossing making it possible to ensure the passage through the body of the tubing T of the conductor 200 under suitable electrical insulation conditions.
• the central electrode EC can be maintained if necessary by any suitable device, not shown in the drawing, and located outside a part of the tubing T and the nozzle 20 for example. Indeed, it is indicated that, beyond the termination end of the nozzle in the direction of flow e, the VOC effluents and the carrier gas are, for example, at atmospheric pressure Patm, as shown in FIG. drawing and that will be explained in more detail later in the description.
• FIG. 3b ⁇ there is shown the profile of a nozzle type Laval nozzle convergent / divergent, the neck of the nozzle being noted C on the abscissa Xc.
• the profile is defined by the radius r of any straight section of the nozzle, each section having an area A and the section at the neck of the nozzle having an area A c .
• the inlet chamber CA is deemed to constitute a large upstream reservoir where the organic VOC effluents and the carrier gas are at a pressure P 0 and have a specific mass po as well as an original temperature T 0 .
• atmospheric pressure Patm prevails.
• the P / Po ratio of the pressure in any section of the nozzle to the generating pressure Po and the Mach number M are represented along the nozzle of the abscissa 0 corresponding to the inlet face of the nozzle 20 up to 'at' the abscissa Xs, termination of the nozzle, as mentioned previously in the description, these representations being given in FIGS. 3b 2 and 3b 3 .
• P N and P P denote particular values of the pressure of the external medium.
• the calculation of the position of the shock wave in the divergent part of the nozzle can be carried out in the following manner.
• Mi is the Mach number immediately upstream of the shock wave considered.
• the shutdown temperature which is equal to the flow generating temperature, remains the same on either side of the shock wave.
• the flow downstream of the shock wave can be considered as an isentropic flow from the reservoir with a generating temperature T ' 0 equal to the previous temperature T 0 but with a generating pressure p' 0 less than p 0 .
• the number of Mach Mi upstream of the shock wave can then be calculated for a ratio A ⁇ / A c given from relation (2).
• the ratio p / p'o and the number of Mach M for the area A considered are then determined from the relations ( 1) and (2) above.
• the temperature ratio for any section of the flow is then deduced from the Mach number from relation (3).
• FIG. 4a A more detailed description of a device according to the object of the present invention, more particularly intended for the implementation of the method illustrated in FIG. 2b, will now be given in conjunction with FIG. 4a and the following figures 4b to 4d.
• the expansion stage 1 can be completed by another expansion stage 4 ensuring an analogous function and making it possible to repeat step Ai of the process described above in connection with the Figure 2b.
• the additional expansion stage 4 can be formed by another nozzle 40 of revolution around the central electrode EC and arranged in cascade with the nozzle 20.
• the nozzle 20 constituting the expansion stage 2 and the nozzle 40 constituting the additional expansion stage 4 are cascaded around the central electrode EC via a passage chamber forming a mixing chamber and denoted CB.
• the passage chamber CB may comprise an intake outlet for gaseous volatile organic effluents passing through the wall of the tube T and bearing the reference D.
• the passage chamber CB forming a mixing chamber, makes it possible to introduce turbulence at the level flow, which has the effect of promoting the treatment of VOCs.
• the nozzles 20 and 40 can be constituted by Laval nozzles.
• the inlet chamber CA can be constituted by a cylindrical chamber with a diameter between 30 and 70 mm. In the inlet chamber A there reigns the pressure generating Po of the flow.
• the opening angle of the nozzle 20, that is to say of the divergent thereof, can be taken equal to a value between 2 and 5 °.
• the passage chamber CB also of cylindrical shape, may have a length between 30 and 70 mm and a diameter between 30 and 80 mm.
• the neck of the first nozzle 20 may have a length of a few tens of millimeters and a constant diameter over this length of between 17 mm and 20 mm
• the neck of the second nozzle 40 is preferably a neck of radius greater than that of the neck of the first nozzle 20, but of neck length, over which the radius of the neck is substantially constant, less than that of the first nozzle.
• the central electrode can have a diameter between 13 and 16 mm.
• the aforementioned dimensioning parameters can be adapted according to the industrial application chosen.
• a filtering system is provided before injection.
• the air flow constituting the carrier gas can then be between 20 and 200 Nm 3 / h. It is recalled that 1 Nm 3 denotes a volume of 1 m 3 of gas measured under normal conditions of temperature and pressure.
• FIG. 4a it is thus possible, as shown in FIG. 4a, to obtain a shock wave phenomenon in the divergent part of the first, 20, respectively the divergent part of the second nozzle 40.
• This operating mode then allows the implementation of the method which is the subject of the present invention according to the embodiments shown in FIG. 2a and / or 2b.
• the first nozzle 20 can be a supersonic or subsonic nozzle while the second nozzle 40 can be supersonic or subsonic, conditionally to the flow regime of the first nozzle 20.
• the experimental results are given in FIG.
• FIG. 4c represents the position ⁇ x of the shock wave with respect to the neck as a function of the volume flow rate D g of the gas admitted into the intake chamber CA.
• the gas flow rates are expressed in Nm 3 / h and the position difference ⁇ x in mm.
• the voltage required to initiate each discharge is directly related to the inter-electrode distance noted as di- Generally, it is indicated that the initiation voltage at the neck is equal to the breakdown voltage according to Paschen's law .
• an optimum operating mode of the device which is the subject of the present invention in fact corresponds to a cut-off of the discharge by at least one reboot at the neck when the power dissipated in the plasma cord corresponds substantially to the charge adaptation with the generator. It is in fact understood that under these conditions, the efficiency of the energy transfer is then optimal.
• the phenomenon of extinction of each discharge which corresponds substantially to a phenomenon of relaxation oscillation under the conditions indicated previously in the description, can be achieved in three different ways: the discharge voltage reaches the breakdown voltage at the throat of the nozzles .
• the priming zone is then the space where the electrodes, central electrode and corresponding nozzle, are closest and where the electric field is sufficient, taking into account the flow conditions. This new discharge short-circuits the old one which is no longer maintained and then ends up going out.
• This operating mode is the operating mode when the supply by the electric generator is a continuous supply.
• the length, and the resistance, of the discharge increases over time, as well as the energy necessary to maintain it. From a critical length, the power supply can no longer provide enough energy to maintain the plasma.
• the conductivity of the discharge decreases and eventually cancels, leading to the extinction of the above-mentioned discharge.
• the discharge voltage then increases suddenly to reach the no-load voltage of the generator and a new ignition occurs at the neck of the nozzle. - When the voltage generator is an alternating generator, the passage through the zero value of the current / 00330
• the initiation of the discharge must be done at the point of the nozzle where the product P x deiec / that is to say the product of the pressure P of the gas or gas mixture for a section of any given nozzle, by the inter-electrode distance and the distance between the central electrode EC and the convergent / divergent body of the nozzle, is the smallest.
• FIG. 4d shows the evolution of the product P x die for different gas flow rates or gas mixture. From the observation of FIG. 4d above, it appears that the breakdown must occur, in particular at the level of the shock wave OC, where the product P xd é i ec is the weakest.
• the shock wave is pushed back into the divergence of the first nozzle 20 and the product P x deiec then passes through its minimum upstream of the shock. In this case, the discharge begins upstream of the above-mentioned shock wave.
• This embodiment is more particularly suitable for fine adjustment of the position of admission of the organic effluents to be treated with respect to the position of the shock wave generated in the first nozzle 20, if necessary in the second nozzle 40.
• the aforementioned preferred embodiment will be described in connection with FIG. 3a with respect to the first nozzle 20, all of the elements being able to be taken up similarly with respect to the second nozzle 40.
• the central electrode EC is formed by an electrode hollow whose end, in the direction of flow of the gas mixture comprising the organic effluents to be treated VOC, is completely closed.
• the central electrode EC thus forms an intake channel for organic effluents by means of an intake intake, denoted PRA, situated at the other end, that is to say at the upstream end of the hollow electrode EC.
• PRA an intake intake
• the hollow electrode thus constituted EC can be advantageously mounted between the sealing and holding shutter 11 and a holding device 12, located at the terminal end of the hollow electrode EC outside the tubing T and mechanically connected to the latter.
• the holding device 12 can be constituted, by way of nonlimiting example, by a ring holding the end of the hollow electrode EC firmly, this ring being attached by fixing lugs to the tubing T.
• the hollow central electrode EC has holes passing through the side wall of the latter, these holes forming a nozzle on at least one cross section of the above-mentioned central electrode EC.
• the holes forming the nozzle bear the reference 13. They can be diametrically opposite, a number of two holes being represented in FIG. 5a, or on the contrary offset by 120 ° in the cutting plane QQ represented in FIG. 5a cited above.
• the admission of the VOC effluents to be treated can be carried out via the PRA intake socket, transmitted by the channel formed by the hollow electrode EC and distributed. at the nozzles 13 under optimal distribution conditions, as will be explained below.
• the pressure of the VOC effluents to be treated at the PRA intake outlet can be between 0.35 and 5 bars.
• This embodiment allows, thanks to the nozzles 13, to determine the pressure in a given section of the entire device, even in the presence of electrical discharges without however requiring the introduction of a Pitot tube, which, taking into account the small cross-section of the gas mixture at each nozzle would be likely to significantly disturb the field of flow velocities.
• the diameter of the holes constituting the nozzles 13 can be between 0.5 and 1 mm. The nozzles 13 also make it possible to inject the VOC effluents into the flow.
• the embodiment represented in FIG. 5a is particularly advantageous insofar as, taking into account the displacement ⁇ x of the shock wave as a function of the flow rate D g as represented in FIG. 4c, it is advantageous to admit the organic effluents to treat VOC in a neighborhood upstream or downstream of the effective position of the above-mentioned shock wave, depending on the treatment to be applied to organic effluents introduced via the carrier gas. Under these conditions, as shown in FIG.
• the central electrode EC hollow electrode
• the shutter and holding systems 11, respectively 12 can advantageously be provided with a guide system of the rolling guide type 110, respectively 120, allowing sliding mounting.
• this must be maintained at the level of the only holding and sealing system 11 by the intermediate seals, which are not shown in the drawing.
• the upstream end of the central electrode EC that is that is to say in the vicinity of the holding and sealing device 11, can advantageously be provided with a system for translational movement of the central electrode EC formed, for example, by a micrometric screw VM, which, from a suitable thread of the external end of the central electrode EC, allows the displacement of the aforementioned central electrode in translation along the axis of symmetry XX of the latter.
• the micrometric screw device VM will not be described in detail since it corresponds to a device known from the state of the art.
• the electrodes are supplied from a direct current generator, such a generator can be produced from the supply of the three-phase network. It can then include, in cascade, an autotransformer, a step-up transformer, a rectifier assembly and a filter cell for example. The average value of the no-load voltage can be adjusted by acting on the autotransformer so as to reach a maximum value of 4.5 kV.
• the production of such a generator will not be described in detail since the mode of implementation thereof corresponds to the use of elements known from the state of the art.
• the generator In the presence of the electrical discharge, the generator is then subjected to the periodic transition from a short-circuit regime to an idle operating regime, with numerous instabilities due to the almost simultaneous extinction and re-ignition.
• the supply generator is a periodic supply generator
• the generator is constituted in the form of a high sinusoidal voltage supply delivering a voltage of 10 kV at a frequency of 50 Hz for example.
• the generator is then constituted by a high voltage transformer with magnetic leaks, the magnetic leaks of such a transformer making it possible to maintain a practically sinusoidal current whose effective value remains constant and of the order of 0.14 amperes for a primary voltage. of 220 volts.
• An alternative implementation in alternative power supply may consist in using a high voltage electronic power supply delivering a periodic voltage at 25 kHz. Under these operating conditions, the maximum value of the current delivered can reach 180 mA.
• Each of the aforementioned supply generators can be used to supply one or the other of the nozzles 20, respectively 40.
• This preferred mode of supply consists in using an alternating generator at a frequency of 50 Hz making it possible to initiate the discharge in one or the other of the nozzles 20 or 40 without limitation of flow rate.
• the corresponding supply mode as shown in FIG. 5b then consists in connecting the tubing T and finally the second nozzle 40, which is not electrically isolated from the body of the tubing T, at the reference voltage or ground voltage.
• the first nozzle 20, electrically isolated from the tubing body T by the fixing and isolation piece 21 shown diagrammatically in FIG. 5b, consists in applying the alternating voltage between the central electrode and the first nozzle 20.
• the supply diagram shown in this figure allows to secure the device whose tubing body T is then brought to the reference potential, that is to say to the mass.
• the body of the second nozzle 40 may be provided with a coating 401 of material oxidation catalyst, increasing the yield of VOC treatment.
• the expansion channel formed by the central electrode EC and the wall of the second nozzle 40, in particular the coating 401 mentioned above, can be subdivided into elementary expansion channels CD delimited by radial and concentric walls for example comprising elements made of oxidation catalyst material.
• the oxidation catalysts which may be used, mention may be made of platinum-iridium, silica-alumina, for example.
• FIGS. 6a, 6b ⁇ , 6b 2 and 6c A non-limiting preferred embodiment of the device for the treatment by electrical discharge of VOC effluents will now be described in conjunction with FIGS. 6a, 6b ⁇ , 6b 2 and 6c, relating to specific elements making it possible to improve the stability of the zone of electric shock in the nozzles used.
• the intake chamber CA if necessary the passage chamber CB, can comprise a deflecting part 14 making it possible to print with a jet of gas or of gaseous mixture, coming from the intake pipe gas 10, a substantially vortex movement in a plane substantially orthogonal to the longitudinal axis XX of the inlet chamber CA or passage CB and the nozzle 20 or 40. This movement swirling stabilizes the electric discharge zone in the vicinity of the above-mentioned plane.
• the deflecting part 14 can be made of an electrically insulating, molded material, such as PVC, substantially of revolution, comprising a central orifice 140 allowing the passage of the central electrode. EC.
• deflection and injection orifices formed in the thickness of the deflecting part 14 provide, with the internal side wall of the inlet chamber CA or passage CB, a profile of radial deflection towards the internal side wall of each chamber, in order to allow a tangential injection of the gas jet or gas mixture in the vicinity of the abovementioned internal side wall.
• the gas jet admitted from the pipe 10 upstream of the deflecting part 14 is subdivided into elementary transverse jets directed towards this internal side wall.
• the deflecting part 14 can be installed by means of a spacer 14a. Under these conditions, the electric discharge, initiated radially in the absence of vortex movement of the gas or gas mixture, is on the contrary driven in rotation in the original discharge plane and maintained in the latter. This allows, on the one hand, to stabilize the abscissa of the electric discharge plane and, on the other hand, to delocalize the points of electric discharge impacts on a circle, intersection of the discharge plane and the central electrode EC, respectively of the nozzle.
• the stabilizing effect of the electric discharge zone can also be obtained, or reinforced, thus as shown in Figure 6c, thanks to the implementation of a CO coil generating a magnetic field B collinear with the longitudinal axis XX of the inlet chamber CA or passage CB and the nozzle.
• the CO coil can advantageously be placed outside the tubing T.
• the magnetic field B is of substantially constant and stationary amplitude, over a distance corresponding to the extent of the dimension of the chamber CA or CB, increased at least the length, in this same direction, of the distance from the inlet of the nozzle to the outlet of the nozzle.
• the existence of this magnetic field makes it possible to cause the electric discharge in rotation, constituted by the plasma cord forming a current tube, according to a magnetron effect.
• the rotary drive is located substantially in a plane orthogonal to the longitudinal axis XX.
• the superimposed magnetic field is continuous, while when the discharge current is sinusoidal, the superimposed magnetic field is sinusoidal, at the same frequency and in phase or in phase opposition with the discharge current.
• the pipe 10 for supplying carrier gas and effluents can be formed in the body of the tubular T and lead to the flat face of the latter by an intake orifice OR, in order to allow the installation of the CO coil on the surface of revolution of the tubing T, without major obstacle. Due to the significant improvement in the stability of the electrical discharge zone, it is then possible to provide an alternative electrical supply of the electrodes, central electrode EC and nozzle, at significant frequencies up to 25 kHz or more, and thus obtaining a reduction in the production of nitrogen oxide NO x .
• the range of use of the electrochemical cell was between 0 and 2000 ppm and the measurement accuracy was plus or minus 20 ppm for concentrations below 400 ppm and 5% for higher concentrations. With regard to nitrogen oxides, it is indicated that the measurement system gave an indication of all the NO X detected.
• a higher NO x emission concentration is noted in the case of the second operating nozzle subsonic with respect to the first nozzle operating in supersonic regime.
• the characteristic decay time ⁇ for which the number of hydrogen atoms has been divided by 10 is itself approximately multiplied by a factor 10.

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