FR2884857A1 - Internal combustion engine`s exhaust gas particle filtering and eliminating device for motor vehicle, has recuperating module with particle tanks coupled to particle-gas separation units to collect recuperated agglomerated particles - Google Patents

Abstract

The device has an electrostatic agglomeration module (10) with internal and external electrodes (9, 3), and a module for recuperating mass of particles agglomerated by the module (10). The recuperating module has independent particle tanks (13), each associated to a particle-gas separation unit (14) through a centrifugal/cyclone concentrator type inertial or aero-kinetic path to collect the recuperated agglomerated particles through the unit (14).

Description

Inertial separation element device for filtering

  and the removal of particles contained in exhaust

  The invention relates to the treatment of polluting components contained in a gaseous medium and, in particular, to the field of devices for filtering the exhaust gases of an internal combustion engine.

  More particularly, the invention relates to a device for filtering and removing particles contained in the exhaust gas of a motor vehicle internal combustion engine which comprises an electrostatic agglomeration module and a recovery module of particles agglomerated by the electrostatic agglomeration device.

  The electrostatic agglomeration modules generally use an electric field to cause an attraction of electrically charged particles to a substrate on which the particles are attached.

  In this regard, reference may be made to the patent application WO 00/02549 which describes an electrostatic particle agglomeration device comprising a corona-type electrostatic filter comprising a cylindrical cage inside which the exhaust gases enter. view of their filtering.

  Reference can also be made to US Pat. No. 4,478,613, which describes another type of particle agglomeration device comprising an electrostatic filter and a mechanical particle separator.

  The electrostatic filter comprises a tubular element having one of its closed ends, inside which there is a stack of disks concentric with respect to the axis of the tube. The tube is maintained at a zero potential while the discs are connected to a negative potential. The exhaust gases enter the tube through an opening and flow axially to exit through an opposite opening on the side. Discs carried at a negative potential constitute an emissive structure for generating an electric field between the inner surface of the tube and the discs. The exhaust gases pass through this field, the particles contained in the exhaust gas being electrically charged. The particles thus charged move radially under the effect of the electric field created to go to be deposited on the inner face of the tube where they accumulate in layers.

  Similarly, French Patent Application No. 02 06304 also describes an exhaust gas filtering device provided with such an electrostatic agglomeration module. In this device, the filtering is carried out by means of an entanglement of gas-permeable metal fibers which internally delimit a passage for the gases and which are capable of mechanically retaining particles. This entanglement also constitutes an electrode which, together with a wire electrode disposed along the axis of the passage, creates a transverse electric field sufficient to deflect the particles carried by the exhaust gases to the external electrode at which they are located. agglomerate.

  But it is then necessary to eliminate the trapped particles.

  This is usually achieved by using a particle cluster recovery module which collects and stores the clusters of particles that break off as soon as they reach a size sufficient for the friction forces exerted by the exhaust gases snapped.

  In view of the above, the object of the invention is to provide a recovery module capable of efficiently recovering and storing the clusters of particles created during the trapping of the particles by the upstream electrostatic agglomeration module.

  The subject of the invention is therefore a device for filtering and eliminating particles contained in the exhaust gases of an internal combustion engine of a motor vehicle, comprising an electrostatic agglomeration module comprising an internal electrode and an external electrode. between which is created an electric field, the outer electrode being made of porous material capable of passing the exhaust gases as well as clusters of particles during the passage of the exhaust gas through the porous material, and a module of recovery of particle clusters.

  The recovery module comprises a plurality of particle reservoirs independent of each other, each reservoir being associated with a particle-gas separation element (14) by inertial or aerokinetic means, in particular of the centrifugal or cyclone concentrator type, for collecting the particles. agglomerates recovered by said particle-gas separation element.

  In one embodiment, the recovery module comprises a first rigid part assembled on a second rigid part, the first part comprising, for each separating element, a central hub, fins arranged around the hub and a cylindrical or conical skirt. extending downstream of the fins in the flow direction of the exhaust gas.

  As regards the second part, it comprises, for each separating element, a passage for the gases which communicates with a corresponding separating element and an annular zone forming a storage tank for the agglomerated particles able to receive the particles entrained in rotation by the fins.

  With regard to the second part, it is provided, on both sides of the cylindrical wall and the annular storage area, and downstream of the latter, passages for the circulation of a secondary flow of gas.

  In another particular embodiment, possibly combinable with the embodiments defined above, the recovery module comprises filters adapted to stop the soot or micrometer particles in the vicinity of the tank. The filters may be placed upstream of one of said passages but may also be placed at the periphery of the recovery module so as to filter the gases at the output of said module.

  In another embodiment, the second part comprises means for electrostatically trapping soots or micrometric particles comprising a circular electrode forming anode coaxial with the cylindrical wall and, on either side of the circular electrode, annular metal filters. forming cathode capable of trapping soot and micrometric particles deviated by the effect of the anode.

  As regards the recovery module of the filtering device, it also advantageously comprises regeneration means of the stored particles in order to eliminate, for example periodically, the clusters of particles stored therein.

  According to yet another embodiment, also combinable with the other embodiments defined above, the agglomeration module comprises several parallel filtering stages each associated with a particle reservoir and a separation element, each stage comprising said internal electrode and said outer electrode of porous material.

  The separation module can be placed directly downstream of the agglomeration module or the separation module and the agglomeration module can be placed at a distance from one another in separate functional units of the motor vehicle.

  According to yet another embodiment, also combinable with the embodiments mentioned above, the particlegaz separation elements are at least partially placed in parallel, the agglomeration module and the recovery module being connected by conduits supplying each one or more cyclones elements.

  However, the particle-gas separation elements can be disposed in a closed enclosure supplied with gas from the agglomeration module.

  Advantageously, the recovery module will be made from a material adapted to withstand a temperature of at least 600 ° C. and capable of withstanding corrosion and oxidation, in particular stainless steel or zamak.

  Other objects, features and advantages of the invention will appear on reading the following description, given solely by way of nonlimiting example, and with reference to the accompanying drawings, in which: FIG. 1 is a sectional view of FIG. a particle filtering and removal device according to the invention; FIG. 2 is a detailed view illustrating an example of arrangement of the recovery module; FIG. 3 illustrates an embodiment of a particle filtering and removal device comprising an agglomeration module and a particle cluster recovery module comprising several stages placed in parallel; FIG. 4 is a perspective view illustrating the constitution of the recovery module; FIG. 5 is a detailed view of the module of FIG. 4; FIG. 6 illustrates a particular embodiment of the recovery module; Figure 7 illustrates yet another variant of the recovery module; - Figure 8 shows another variant of the recovery module; - Figure 9 illustrates yet another variant of the recovery module; Figure 10 illustrates yet another variant of the recovery module; FIG. 11 illustrates a mode of arrangement of several cyclone elements in parallel; FIG. 12 shows an example of association of several cyclone elements; FIG. 13 illustrates yet another mode of arrangement of the cyclone elements; and FIG. 14 illustrates yet another mode of association of several cyclone elements.

  Referring to Figure 1, we will first describe the general structure of a device for filtering and removing particles contained in the exhaust gas of a motor vehicle internal combustion engine.

  This device essentially comprises a particulate filter 10 consisting of an electrostatic agglomeration module ensuring entrapment and agglomeration of the particles carried by the exhaust gases and a module 12 for recovering agglomerated particle clusters extracted from the agglomeration module 10. , which leads to an outlet S of gas evacuation.

  In this figure 1, the arrows F represent the flow of the exhaust gas.

  As can be seen in FIG. 1, the electrostatic agglomeration module comprises an agglomeration unit 1 in which the particles conveyed by the exhaust gases are trapped and a collector 2 ensuring the recovery of the clusters of agglomerated particles and released by the agglomeration unit as soon as they reach a sufficiently large size.

  The agglomeration unit 1 comprises an outer electrode 3 of generally cylindrical shape made from fibers or metal son. It delimits internally an axial passage 4 through which the exhaust gases and the particles they contain are introduced into the filter.

  The external electrode 3 is maintained in axial position in the agglomeration module 10 by two end plates 5 and 6, respectively upstream and downstream. The upstream end flange 5 is provided with an axial hole 7 coaxial with the passage 4 for the admission of the exhaust gases into the agglomeration unit 1 while the downstream flange 6 is provided with radial holes, such as 8, through which exhaust gases as well as clumps of agglomerated particles are supplied to the recovery module 12.

  The agglomeration module 10 also comprises a central electrode 9 made in the form of a rod coaxial with the external electrode 3 and one end of which is mounted on the downstream end flange 6, while the other end is end is connected to a high-voltage power supply ramp 11.

  Thus, in operation, the particulate-laden exhaust gases enter the axial passage 4 of the outer electrode 3, in which the gases are ionized, thus making it possible to electrically charge soot particles.

  As is conceivable, the end flange 6 prevents the axial passage of the exhaust gas. These gases are then deflected radially and pass through the external electrode 3, which is permeable to gas.

  The external electrode 3 is maintained at a zero potential, the internal electrode 9 being, in turn, brought to a positive or negative potential. The potential difference created between the external electrode 3 and the internal electrode 9 generates an electric field in the axial passage 4. If this electric field has a sufficient intensity, in particular in the very close vicinity of the internal electrode 9, it Partial or total ionization of the gases between the inner and outer electrodes occurs.

  For example, in the case of an internal electrode 9 brought to a negative potential, the particles present in the exhaust gases are mainly charged by collision and combination with free electrons.

  Moreover, the almost homogeneous electric field in the inter-electrode space deflects the charged particles that migrate towards the porous electrode. The electric field is heterogeneous only near the two electrodes. When the particles are in the vicinity of the porous electrode, i.e., about 1 millimeter, the electric field lines converge toward the fibers of the porous electrode. The particles are then precipitated against the fibers by the strong local increases of this electric field. The charged particles are then deposited on the inner face of the electrode and agglomerate by electrostatic interactions and under the action of Van der Waals forces. The particle clusters then grow to a size sufficient for the friction forces exerted by the exhaust gases tear them. The masses of particles then ejected are recovered by the collector to be transmitted, downstream, to the recovery module 12, to be stored in a reservoir 13.

  As can be seen in FIG. 1, in addition to the reservoir 13, the recovery module 12 comprises a particle-gas separation element 14 by inertial or aerokinetic means, for example of centrifugal or cyclone concentrator type. In the remainder of the description, this element will be designated by the term of inertial element. This element comprises a pipe 15, for example with an axis parallel to the general axis of the agglomeration module 10 and which comprises a first generally cylindrical upstream portion 16 and a second slightly frustoconical skirt-shaped downstream portion 17 which opens towards the tank 13.

  The first part 16 is provided with a central hub 18 and a set of fins 19 inclined circumferentially to apply to a stream of air entering axially into the recovery module 12 a rotational movement in addition to the axial movement, conferring and a helical movement which allows a centrifugation of the clusters of particles contained in the gases from the electrostatic agglomeration module 10 and thus their plating against the inner peripheral surface of the inertial element 14.

  For the storage of the centrifuged particles, the reservoir 13 comprises a cylindrical wall 20 of diameter slightly smaller than that of the skirt 17 and which is inserted into the latter to form, with the inner surface of the skirt 17, a passage 21 for the centrifuged particles and, internally, an axial passage 22 for the exhaust gas.

  The cylindrical wall 21 is extended radially by a generally annular recovery zone Z in which the clusters of particles separated from the exhaust gases are stored.

  Thanks to this arrangement, the clusters of centrifuged particles, animated by a helical movement, propagate along the inertial element 14 by being pressed against its wall and are then transferred to the reservoir 13 via the passage 21.

  Referring now to FIGS. 2 and 3, it can be seen that, preferably, the electrostatic agglomeration module 10 and the recovery module 12 each comprise several stages placed in parallel.

  Thus, with regard to the agglomeration module, the latter comprises, in the exemplary embodiment shown, five stages, each formed of a cylindrical electrode 3-1, 3-2, 3-3, 3-4 and 3-5 identical to the electrode 3 described above with reference to Figure 1 which defines internally an axial passage 4-1, 4-2, 4-3, 4-4 and 4-5.

  This electrode is connected to ground. In addition, a wired electrode 9-1, 9-2, 9-3, 9-4 and 9-5 extends in the axial passage. This electrode is supplied with high voltage via the ramp 11.

  As in the embodiment described above, the cathode electrodes 3-1, ..., 3-5 and the anode forming electrodes 4-1, ..., 45 are carried by the two upstream end plates and downstream 5 and 6. The upstream end flange 5 is provided with a set of holes 7-1, 7-2, 73, 7-4 and 7-5 coaxial with the passages 4-1, 4-2, 4- 3, 4-4 and 4-5, respectively, while the downstream flange 6 is provided with a number of holes such as 8-1, 8-2, 8-3, 8-4 each disposed between two cylindrical electrodes consecutive to transmit, downstream, the exhaust gas and the agglomerated particles to the recovery module 12.

  Regarding the recovery module 12, it also comprises several cyclone elements Cl, ..., Cn in parallel each associated with a tank R1, ..., Rn.

  As seen in Figure 2, each recovery stage is identical to the recovery module described above with reference to Figure 1 and comprises an inertial element Ci associated with a reservoir Ri. Downstream, the exhaust gas freed from clumps of particles, are recovered by the vehicle exhaust line.

  Referring now to FIG. 4, according to this embodiment, according to which the particle filtering and removal device comprises a particle recovery module comprising several stages, the module is in the form of a cassette 23. formed by the combination of two pieces 24 and 25. These parts are made of metal alloy resistant to temperatures that can rise above 600 C and to an environment of oxidation and corrosion related to the use considered, with regard to the evacuation of motor vehicle exhaust. Thus, for example, we will use materials allowing mass production by a molding process. For example, ferritic stainless steels or zamac, an alloy of zinc and aluminum, which is particularly resistant and malleable, will be used. However, any other suitable material for the intended use may also be used.

  As regards the part 24 constituting one of the walls of the cassette 23, it is pierced with a plurality of circular holes, such as 26, arranged in staggered rows, or, as can be seen in FIG. linear. The holes 26 are here arranged in the form of three rows of four holes.

  Each hole delimits, internally, the hub 18 (FIG. 1) and is provided with fins 19 serving to rotate the exhaust gases and the clusters of particles they contain.

  In each circular hole is disposed an inertial element carried by the other piece 25.

  As seen in Figure 5, and as described above with reference to Figure 1, facing each inertial element, the second part 25 is provided with axial passages in a number equal to the number of cyclone elements. These passages have a diameter smaller than that of the second portion 17 of the cyclone elements (FIG. 1) to form a purified air outlet. The edge of the peripheral wall at the hole 22 is raised towards the cyclone elements to form the cylindrical wall 20 of the reservoir thus providing the annular passage 21 between the free end of a corresponding inertial element and the annular rim 20, allowing the net of centrifuged air and the particles of particles thus transported to escape into the reservoir 13. A peripheral wall P delimits laterally the reservoir 13.

  Preferably, between the first and second parts 24 and 25 is interposed a sealing sheet (not shown) provided with perforations.

  Note that, in one embodiment, the agglomeration module 10 and the recovery module 12 are joined to each other to form a unitary assembly. In this case, the upstream end of the recovery module 12 and the downstream end of the agglomeration module 10 are separated by a distance of between approximately 50 and 100 mm so as to obtain a homogeneous distribution of the flow rate to be treated on the set of cyclone elements.

  However, it is also possible to position the recovery module 12 remotely, in a functional unit structurally distinct from a unit integrating the agglomeration module 10.

  It will also be noted that, with respect to the exhaust gas, the soot particle density is several milligrams per cubic meter on weakly loaded engine operating points. It can however reach several tens or even hundreds of milligrams per m3 for points of high load.

  Moreover, the range of exhaust gas flow rates as well as the relatively low agglomerated particle density necessitate relatively large storage volumes and also the coupling of the agglomerators and the reservoirs of a regeneration device in order to Periodically, regeneration phases are used to burn the particles stored in the tanks.

  It will therefore be provided, as will be recalled later, regeneration devices, for example integrated tank.

  Reference will now be made to FIGS. 6 to 10, of other embodiments of the recovery module 10 according to the invention, and in particular of the storage tank 13.

  Referring firstly to Figure 6, for the purpose of generating and controlling a secondary flow in the tank 13, there is provided, in the bottom of the latter, orifices for maintaining a secondary flow D of gas. exhaust in the tank and in particular in the recovery zone. The secondary flow can however be generated in the direction of the arrows D '. In this case, no orifice will be provided.

  The bottom of the tank can thus be provided with a number of orifices 27 and 28 disposed on either side of the outlet S of the inertial element 15. It is thus easier to recover the agglomerated particles, in particular in reducing turbulence at the tank inlet.

  Referring now to Figure 7, it is possible to provide an annular filter 29 in the tank 13, upstream of the orifices 27 and 28, creating an obstacle preventing any exit of agglomerated particles through these orifices.

  This filter 29 may, as shown in FIG. 7, have a cylindrical shape and thus constitute a wall delimiting externally the reservoir 13. Alternatively, as shown in FIG. 8, the filter 29 may have a generally annular shape and come to seal the orifices 27 and 28.

  Referring now to FIG. 9, it is also possible, in a variant, to produce the filters in the form of two annular plates 29 'and 29 "coaxial with the cylindrical wall 20 of the reservoir and facing one of the another so as to delimit between them an annular channel for the passage of the secondary flow of the exhaust gas, and realizing these plates 29 'and 29 "of metallic material capable of trapping the agglomerated particles.

  These filters are associated with electrostatic trapping means. Indeed, a circular anode 30 placed between the plates 29 'and 29 "and connected to a source of high voltage makes it possible to create an electric field enabling the particle clusters to be deflected towards the surface. one or other of the plates 29 'and 29 ". This configuration allows both to load the particles and deflect them on the filters and thus ensure their capture.

  In the various embodiments described above, the secondary gas flows are created for each inertial element. It is also possible, alternatively, to create a secondary flow of gas for all the cyclones placed in parallel and to establish fluid communication between the elementary reservoirs to an outlet located at the periphery. In this case, as shown in FIG. 10, the filter (s) 29 are then situated at the periphery, at this output.

  Referring now to Figures 11-14, various types of arrangement of the cyclone elements will be described.

  An inertial element induces a back pressure in the exhaust line in which it is located. This penalizes the power of the motor and increases the consumption. The level of back pressure in the exhaust line therefore becomes a parameter used for sizing cyclone elements. Therefore, the respect of a back pressure in the exhaust line imposes a minimum diameter of the clusters of particles below which it is possible that some clusters of particles are not retained in the tank.

  In order to overcome this drawback, several cyclone elements arranged in parallel are used in order to divide the volume flow rate of the gas stream to be treated while maintaining the same incident velocity. Indeed, a lower volume flow rate corresponds to a smaller distance to travel for the particles in order to reach the cylindrical wall of the inertial element and, consequently, a decrease in the cutoff diameter, that is to say extended efficiency to smaller particles.

  In addition, a multiplication of cyclone elements makes it possible to increase the compactness of the system.

  As can be seen in FIGS. 11 to 14, various variants can be used to parallel cyclone elements.

  Referring first to FIG. 11, as well as to FIG. 12 which is a side view of the arrangement visible in FIG. 11, it is possible to arrange the cyclone elements in the form of two groups G1 and G2 cyclone elements placed in parallel, each group G1 and G2 comprising several cyclone elements placed in series. The cyclone elements are here grouped in the form of two groups G1 and G2 of three cyclone elements placed in series. The cyclone elements of each group are fed from two lines 30 and 31 which collect the incident gas flow at the outlet of the collector 2.

  As a variant, as shown in FIG. 13, the cyclone elements C1,..., Cn are disposed in a closed closed enclosure 32 subjected to the influence of the gas flow at the outlet of the collector 2. As can be seen in FIG. 13 the cyclone elements are differently oriented to recover the incident flux in different orientations. Likewise, as can be seen in FIG. 14, the cyclone elements can be placed at different heights, as a function of the stream flow lines inside the enclosure.

  Finally, note that in the various embodiments, the recovery module 12 may be associated with regeneration means, for example controlled, in order to periodically implement or when the reservoirs 13 are full, regeneration phases.

  Various regeneration means can be used for this purpose. For example, heating resistors can be used to raise the temperature of the internal volume of the tank to a temperature allowing combustion of the particles.

  However, any other type of regeneration means suitable and within the reach of a person skilled in the art may also be used.

Claims (14)

  A device for filtering and removing particles contained in exhaust gases of an internal combustion engine of a motor vehicle, comprising an electrostatic agglomeration module (10) having an internal electrode (9) and an external electrode (3) between which is created an electric field, the outer electrode being made of porous material capable of passing the exhaust gases as well as agglomerated particle clusters during the passage of the exhaust gas through the porous material, and a module (12) for recovering clusters of particles, characterized in that the recovery module comprises a plurality of tanks (13) of particles independent of each other, each reservoir being associated with a particle-gas separation element (14) by inertial or aerokinetic means, in particular centrifugal concentrator or cyclone type, for collecting the agglomerated particles recovering by said particle-gas separation element.   2. Device according to claim 1, characterized in that the recovery module comprises a first rigid part assembled on a second rigid part, the first part comprising, for each particle-gas separation element, a central hub (18), fins (19) disposed around the hub and a cylindrical or conical skirt (17) extending downstream of the fins in the flow direction of the exhaust gas.   3. Device according to claim 2, characterized in that the second part comprises, for each particle-gas separation element, a passage (22) for the gas which communicates with a corresponding separating element and an annular zone (Z) forming agglomerated particle storage tank adapted to receive the particles driven in rotation by the fins.   4. Device according to one of claims 2 and 3, characterized in that the second part is provided on either side of the cylindrical wall and the annular storage area, and downstream of the latter, passages ( 27, 28) for the circulation of a secondary flow of gas.   5. Device according to any one of claims 2 to 4, characterized in that the recovery module comprises filters (29) adapted to stop the soot or micrometer particles in the vicinity of the tank.   6. Device according to claim 5, characterized in that the filters are placed each upstream of one of said passages.   7. Device according to one of claims 5 and 6, characterized in that the filters are placed at the periphery of the recovery module so as to filter the gas output of said module.   8. Device according to one of claims 3 and 4, characterized in that the second part comprises means for electrostatically trapping soots or micrometric particles, comprising a circular electrode (30) forming anode coaxial with the cylindrical wall and from and other of the circular electrode, annular metal filters (29 ', 29 ") forming a cathode capable of trapping the soot and micrometric particles deviated by the effect of the anode.   9. Device according to any one of claims 1 to 8, characterized in that the recovery module comprises means for regenerating the stored particles.   10. Device according to any one of claims 1 to 9, characterized in that the agglomeration module comprises several filter stages in parallel each associated with a particle reservoir (13) and a particle-gas separation element ( 14), each stage comprising said inner electrode and said outer electrode of porous material.   11. Device according to any one of claims 1 to 3, characterized in that the separation module is directly positioned downstream of the agglomeration module or away from the agglomeration module, the agglomeration module and the module of recovery being placed in separate functional units of the motor vehicle.   12. Device according to any one of claims 1 to 11, characterized in that the particle-gas separation elements are at least partly placed in parallel, the agglomeration module (10) and the recovery module (12). being connected by conduits (30, 31) each supplying one or more particle-gas separation elements.   13. Device according to any one of claims 1 to 12, characterized in that the particle-gas separation elements are placed in a closed chamber (32) supplied with gas from the agglomeration module.   14. Device according to any one of claims 1 to 13, characterized in that the recovery module is made of a material adapted to withstand a temperature of at least 600 C and resistant to corrosion and oxidation, in particular stainless steel or zamak.