FR2891006A1 - Exhaust gas particles filtering and eliminating device for e.g. heat engine, has concentrator with central outlet allowing lightest part of gas to pass through it and annular outlet allowing heaviest part of gas to pass through it - Google Patents

Abstract

The device has a particle filter (2) presented in the form of an axial cylinder. A set of centrifugal concentrators (3) is circumferentially distributed around the filter and connected to the filter. The concentrators are placed parallel to each other and receive an exhaust gas flow to be processed. Each concentrator has a central outlet (5) and an annular outlet (6), where the outlet (5) allows the lightest part of the gas to pass through it. The outlet (6) allows the heaviest part of the gas to pass through it. A plate has a central passage in which the filter is placed.

Description

Device for filtering and eliminating particles contained in

  exhaust gases improve particle capture

  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 filtering device.

  Electrostatic filtering modules generally use an electric field to cause an electrically charged particle attraction to a substrate onto which the particles are attached.

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

  Reference can also be made to US Pat. No. 4,478,613, which describes another type of particle filtering 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, and the particles contained in the exhaust gases are charged by ionic drift. 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.

  Likewise, French Patent Application No. 2,839,903 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. Particles trapped on the outer electrode may progressively as the deposit increases to be released into the flow. To avoid this, the regeneration frequency can be important and therefore expensive in energy.

  But it is then necessary to eliminate the trapped particles.

  This is usually achieved by using a particle cluster recovery module that collects and stores the clusters of particles that break off as soon as they reach a size sufficient for the friction and pressure forces exerted by the gases. exhaust snatch them. In this regard, French Patent Application No. 2,861,803 proposes to send the particles to a recovery tank to burn them, then to send the residue to the combustion chamber of the engine. To return the particles to the combustion chamber of the engine, this involves generating a favorable pressure differential: by installing an exhaust flap to increase the pressure of the exhaust line, resulting in a high energy cost, - by reinjecting a compression current with a risk of degradation and breakage of it.

  In view of the foregoing, one object that the invention proposes to achieve is to improve the filtering of clusters of agglomerated particles from an electrostatic agglomeration module.

  Another object that the invention proposes to achieve is to efficiently filter particles of large particle size.

  The device for filtering and removing particles contained in an exhaust gas of an internal combustion engine of a motor vehicle comprises a particle concentration module and a particulate filter. The concentration module includes a particulate depleted gas outlet and a particulate enriched gas outlet connected to the inlet of the particulate filter. It can be expected that the flow rate of the particulate depleted gas outlet is of the order of 80 to 90% of the total flow of exhaust gas. The flow of particulate enriched gas passing through the particulate filter is then relatively low. For the regeneration of the particulate filter, it is possible to provide a combustion of the particles by heating the gases entering the filter at the combustion temperature of soot. Due to the reduced flow rate in the particulate filter, the energy required for heating is greatly reduced.

  Particle filter means a device capable of retaining the particles and allowing the gases to pass. Since the particulate filter tends to become clogged with particle accumulation, it is desirable to regenerate it from time to time.

  In one embodiment, the concentration module comprises a centrifugal concentrator. Centrifugal concentrator means an element generally provided with a tubular body provided with inclined blades tending to rotate the gas passing through said body, resulting in a centrifugation effect, the heavier particles than the gas being driven primarily to the 2891006 4 from which they can be removed while the centrally located gas streams are substantially free of particles.

  Advantageously, the concentration module comprises a plurality of centrifugal concentrators.

  In one embodiment, at least a portion of the centrifugal concentrators are arranged in parallel. It is thus possible to use several small centrifugal concentrators.

  In one embodiment, at least a portion of the centrifugal concentrators are arranged in a ring. The particulate filter can be mounted between the centrifugal concentrators, in particular in a ring of centrifugal concentrators. Each centrifugal hub of the ring may include an inwardly particulate enriched gas outlet in the direction of the particulate filter.

  In one embodiment, each centrifugal concentrator includes a central particulate depleted gas outlet and an annular particulate enriched gas outlet. The annular outlet may be associated with a border directing the particle-enriched gas stream in a preferred direction, for example towards the inside of a ring of centrifugal concentrators in the direction of a particulate filter.

  In one embodiment, the annular outlets meet at the center of the ring.

  Advantageously, the device comprises a particle agglomeration means arranged upstream of the concentration module. The particle agglomeration means may comprise an electrostatic filter.

  Thanks to the invention, a particle filtering and removal device is provided capable of concentrating the particles in a first gas stream and generating a second stream of particulate-depleted gas, the first gas stream being then directed to a particulate filter capable of retaining the particles by leaving the first stream of purified gas and can then join the second gas stream.

  The particulate filter can be regenerated thermally. A relatively low power particle filter heating element can be provided. Particle filter heating causes the particles stored in it to burn, the power required for heating being all the smaller as the first gas flow is small. However, it can be expected that the first gas flow has a lower flow rate than the second gas flow. More precisely, the second gas flow can represent on the order of 10 to 30% of the total flow of exhaust gas, resulting in a considerable reduction in the cooling caused by the gas flow rate in the particulate filter compared to a conventional particulate filter to pass all the exhaust.

  The present invention will be better understood on studying the detailed description of some embodiments taken as non-limiting examples and illustrated by the appended drawings, in which: FIG. 1 is a diagrammatic view in axial section of the device of FIG. filtering and disposal; and FIG. 2 is a schematic front view corresponding to FIG.

  As can be seen in the figures, the filter and particle elimination device referenced 1 as a whole comprises a particle filter 2 in the form of an axial cylinder, and a ring 3 comprising a plurality of Centrifugal concentrator elements 5 circumferentially regularly distributed around the particle filter 2. The centrifugal concentrators 4 are arranged parallel to each other and receive as input the entire flow of the exhaust gas to be treated. Each centrifugal concentrator 3 has a central outlet 5 and an annular outlet 6. The central outlet 5 sees the lightest portion of the exhaust gas passing while the annular outlet 6 passes the heavier part of the exhaust gas comprising almost all soot particles. The ring 4 is provided with a collector in the form of a plate 7 provided with a central passage in which the particle filter 2 is arranged and ensuring the connection between the annular outlet 6 of each centrifugal concentrator 3 and the inlet of the particulate filter 2.

  The particle filter 2 is equipped with a heating wire 8 arranged on the upstream side in the direction of flow of the exhaust gas and capable of heating up to the combustion point the particles agglomerated on the upstream face of the particulate filter 2 .

  It will be understood that the annular outlet 6 of each centrifugal concentrator 3 tends to direct the flow of particle-laden gas radially outwardly of the centrifugal concentrator and consequently both inwardly and outwardly of the device 1 taken as a whole. As can be seen in Figure 2, the plate 7 is extended by a border 9 surrounding each centrifugal concentrator 3 on an angular sector of the order of 180 on the outer side and preventing the flow of charged gas (the particles to spread to the outside of the device 1. The particle-laden gas flow is thus forced to move inwardly of the device 1 and then to pass through the particle filter 2.

  A centrifugal concentrator element 4 comprises a pipe 10 parallel to the conduits of the other centrifugal concentrator elements and to the general axis of the device. The pipe 10 comprises a cylindrical upstream portion 10a, a frustoconical intermediate portion 10b converging downstream and a substantially cylindrical downstream portion 10c. The centrifugal concentrator element 4 also comprises a plurality of fins 11 and a hub 12 disposed in the cylindrical upstream part 10a of the pipe 10. The hub 12 is a circular solid part coaxial with the pipe 10 and leaving free a zone of shape in which the fins 11 are arranged. The fins 11 are inclined circumferentially to apply to a stream of gas entering axially into the pipe 10 from upstream a rotational movement in addition to the axial movement, thus giving the gas streams a movement helical which allows a centrifugation of the particles contained in the exhaust gas and heavier than the exhaust gas itself.

  The plate 7 comprises a plurality of holes distributed around the central passage, each hole forming the central outlet 5 associated with a corresponding centrifugal concentrator element 4. Near the central outlet 5, the plate 7 is deformed into a tubular rim 7a having a diameter slightly smaller than the bore of the downstream portion 10c of the pipe 10. The flange 7a is slightly projecting axially within the the downstream portion 10c and thus provides an annular passage forming the annular outlet 6 between the flange 7a from the plate 7 and the downstream portion 10c of the pipe 10, thus allowing the centrifuged gas streams and the soot particles thus transported s escape to the outside of the centrifugal concentrator element 4 while being retained by the plate 7 and the border 9, and therefore directed towards the particle filter 2. On the contrary, the gas streams remained close to the axis of the centrifugal concentrator element 4 are very poor in soot particles and escape directly through the central outlet 5.

  Such a centrifugal concentrator element is particularly suitable for treating a gas loaded with particles of particle size of the order of one to several tens of microns. As shown by the respective areas of the central outlet 5 and the annular outlet 6, a very high proportion of exhaust gas passes through the central outlet 5, for example about 80% and only a small proportion of exhaust gas charged. in particulate passes through the outlet 6 and is then purified by the particulate filter 2. When supplying the heating wire 8 with electrical energy for the regeneration of the particulate filter, the flow rate of gas passing through the particulate filter tends to cool the particles or at least slow their rise in temperature. The flow rate of gas passing through the particulate filter 2 is reduced by about 80% compared to a conventional particulate filter which passes all the exhaust gas of a heat engine, the combustion of soot particles is much faster because of the lower energy loss and the energy consumed for the regeneration of the particulate filter 2 is very much lower. In addition, the heating wire 8 may be more dimly dimensioned, which proves to be economical.

  In addition, when the soot particles from the heat engine have a particle size too small to be effectively treated by a particulate filter and / or by centrifugal concentrating elements, the device for filtering and removing particles 1 may comprise a electrostatic filter 13, for example of the type described in document FR-A-2 839 903 to which the reader is invited to refer, ensuring an agglomeration of the particles, for example of a particle size of about 100 nm to a particle size distribution of the order of 1 to a few microns. Centrifugal concentrator elements are considerably more effective at treating particles having a particle size of this order of magnitude.

Claims (10)

  1. Device for filtering and eliminating (1) particles contained in an exhaust gas of an internal combustion engine of a motor vehicle, characterized in that it comprises a particle concentration module (3) and a particle filter (2) disposed downstream of the concentration module, considering the flow direction of the exhaust gas, the concentration module (3) comprising a particulate depleted gas outlet and a particulate enriched gas outlet connected to the inlet of the particulate filter (2).   2. Device according to claim 1, wherein the concentrating means comprises a centrifugal concentrator.   3. Device according to claim 1 or 2, wherein the concentrating means (3) comprises a plurality of centrifugal concentrators (4).   4. Device according to claim 3, wherein at least a portion of the centrifugal concentrators (4) are arranged in parallel.   5. Device according to claim 3 or 4, wherein at least a portion of the centrifugal concentrators (4) are arranged in a ring.   6. Device according to any one of claims 3 to 5, wherein the particle filter (2) is mounted between the centrifugal concentrators (4).   7. Device according to any one of claims 3 to 6, wherein the particle filter (2) is mounted in a ring of centrifugal concentrators (4).   8. Device according to any one of claims 2 to 7, wherein each centrifugal concentrator (4) comprises a central outlet (5) of particulate depleted gas and an annular outlet (6) of particulate enriched gas.   9. Device according to claim 8, wherein the annular outlets (6) meet at the center of a ring.   10. Device according to any one of the preceding claims, comprising a particle agglomeration module mounted upstream of the concentration module.