EP2616646B1 - Device for treating soot particle-containing exhaust gases - Google Patents

Description

The present invention relates to a device for the treatment of soot particles containing exhaust gas, in particular with a so-called electrostatic filter or electrostatic precipitator. The invention finds particular application in the treatment of exhaust gases of mobile internal combustion engines in the automotive sector, in particular in the treatment of exhaust gases resulting from diesel fuel.

In motor vehicles with mobile internal combustion engines and especially in motor vehicles with diesel engines are regularly amounts of soot particles contained in the exhaust gas of the internal combustion engine, which must not be discharged into the environment. This is predetermined by corresponding exhaust regulations that specify limit values for the number and mass of soot particles per exhaust gas weight or exhaust gas volume and in some cases also for an entire motor vehicle. Soot particles are in particular unburned carbons and hydrocarbons in the exhaust gas.

A large number of different concepts for removing soot particles from exhaust gases of mobile internal combustion engines have already been discussed. In addition to mutually closed wall-flow filters, open bypass filters, gravity separators, etc., systems have also been proposed in which the particles are electrically charged in the exhaust gas and then deposited by means of electrostatic attraction forces. These systems are known in particular under the name "electrostatic filter" or "electrostatic precipitator".

In "electrostatic precipitators", the provision of an electric field and / or a plasma causes an agglomeration of small soot particles into larger soot particles and / or an electric charge in soot particles. Electrically charged soot particles and / or larger ones Soot particles are usually much easier to separate in a filter system. Soot particle agglomerates are transported carrier in an exhaust gas flow due to their greater inertia and thus deposit at deflection of an exhaust gas flow easier. Electrically charged soot particles are drawn to surfaces due to their charge, to which they attach and release their charge. This also facilitates the removal of soot particles from the exhaust stream in the operation of motor vehicles.

Thus, for such electrostatic filters, a plurality of spray electrodes and collector electrodes are regularly proposed, which are positioned in the exhaust pipe. In this case, for example, a central spray electrode, which runs approximately centrally through the exhaust pipe, and a surrounding jacket surface of the exhaust pipe as a collector electrode used to form a capacitor. With this arrangement of the spray electrode and the collector electrode, an electric field is formed transversely to the flow direction of the exhaust gas, wherein the spray electrode, for example, can be operated with a high voltage which is in the range of about 15 kV. As a result, in particular corona discharges can be formed by which the particles flowing with the exhaust gas through the electric field are charged in a unipolar manner. Due to this charge, the particles migrate to the collector electrode due to the electrostatic coulombic forces.

In addition to systems in which the exhaust pipe is designed as a collector electrode, systems are also known in which the collector electrode, for example, is designed as a wire grid. In this case, the attachment of particles takes place on the wire grid for the purpose of possibly combining the particles with other particles, so as to realize an agglomeration. The exhaust flowing through the grid then rips the larger particles with them and leads them to classic filter systems.
In the regeneration of filter systems, in addition to the intermittent regeneration by brief heating, that is, burning of the soot (catalytically motivated, oxidative conversion), also known To convert carbon black by means of nitrogen dioxide (NO ₂ ). The advantage of continuous regeneration with nitrogen dioxide is that the conversion of soot can already take place at significantly lower temperatures (in particular less than 250 ° C.). For this reason, continuous regeneration is preferred in many applications. However, this leads to the problem that it must be ensured that the nitrogen dioxide in the exhaust gas comes into contact with the deposited soot particles to a sufficient extent.

Also in this context, there are technical difficulties in the realization of a permanent operation of such exhaust systems in motor vehicles, the different loads of the internal combustion engines lead to different exhaust gas streams, exhaust gas compositions and / or temperatures.

In addition, it should be noted that in the provision of such components for such a soot deposition system as simple as possible components should be used, especially those that can be produced inexpensively in the context of mass production. In addition, especially in the design of the electrodes to take into account that they may need to be positioned aligned in the exhaust pipe, in particular so that an undesirably high dynamic pressure or an undesirable turbulence of the exhaust gas in the region of the electrode does not occur.

Even if the systems described above have proven to be suitable for the treatment of soot particles, at least in tests, the implementation of this concept for series production in motor vehicles poses a great challenge. In particular, the electrical insulation of the electrode and the counter electrode to the exhaust pipe soot particles, whereby a soot particle layer can lead to a short circuit.

GB 1 022 714 discloses an ionizing device having a housing serving as a counter electrode and an electrode disposed therein. The electrode is secured in the housing by means of an insulator. Compressed air is introduced into the region of the insulator fixed in the electrode so that no particles from the exhaust gas of an internal combustion engine are deposited on the insulator.

From the post-published WO 2011/029728 A1 For example, an exhaust treatment device is known in which two electrically conductive honeycomb bodies are spaced apart by a gap. Between the honeycomb bodies, an electric potential is formed so that soot particles in the gap are ionized and deposited on the downstream honeycomb body. The upstream honeycomb body has a plurality of electrodes extending into the gap. The honeycomb bodies are arranged insulated from one another, wherein the insulation is covered by a cover so that a deposition of soot particles is at least partially avoided.

On this basis, it is an object of the present invention, at least partially solve the problems described with reference to the prior art. In particular, an apparatus for the treatment of soot particles containing exhaust gas is to be specified, which prevents the formation of short circuits on electrical insulation of time. These objects are achieved with a device according to the features of claim 1. Further advantageous embodiments of the device are specified in the respective dependent formulated claims. The description, in particular in conjunction with the figures, explains the invention and provides additional embodiments.

• mindestens ein Ionisierungselement zur Ionisierung von Rußpartikeln,
• mindestens ein Filterelement, wobei an mindestens einem Abschnitt des Filterelements ein elektrisches Potential anlegbar ist,
• mindestens eine Strömungsleiteinrichtung, die eine Strömung des Abgases so beeinflussen kann, dass eine Ablagerung der Rußpartikel an mindestens dem Ionisierungselement, einer elektrischen Isolierung des Ionisierungselements oder einer elektrischen Isolierung des Filterelements verhindert und beseitigt werden kann.

The device according to the invention for treating exhaust gas containing soot particles comprises at least

• at least one ionization element for the ionization of soot particles,
• at least one filter element, wherein an electrical potential can be applied to at least one section of the filter element,
• at least one flow guide, which can influence a flow of the exhaust gas so that a deposition of the soot particles on at least the ionization element, an electrical insulation of the ionization element or an electrical insulation of the filter element can be prevented and eliminated.

The device proposed here may in particular be part of an exhaust system of a motor vehicle which has a diesel engine and is arranged in particular in an exhaust pipe of the exhaust system.

Accordingly, the exhaust gas containing the soot particles flows through an ionization element, which comprises at least one electrode, to which an electrical High voltage between 3 kV [kilovolts] and 50 kV, preferably between 5 kV and 25 kV, can be applied. The tension becomes particular adjusted or controlled so that there is a corona discharge between the electrode and a counter electrode. The ionization element can be formed as a simple spray electrode or rod electrode, but it is preferred that the ionization element comprises a honeycomb body with a plurality of channels through which at least one electrode is arranged at its inlet region or outlet region, which is oriented in or against the flow direction. The honeycomb body may in particular, at least partially, preferably be formed entirely from an electrically conductive material, so that an electrical potential can be applied to the honeycomb body and thus simultaneously to the electrodes.

The at least one ionization element may also preferably have an outer tube and an inner tube arranged concentrically therewith, which form a gap traversed by the exhaust gas, wherein at least one annular electrode having a plurality of electrode tips protruding radially into the intermediate space is arranged on the inner tube on the inner tube.

The at least one filter element is preferably designed as a surface separator having a plurality of channels, which are permeable to the exhaust gas and extending between an inlet region and an outlet region. By virtue of the electrical potential which can be applied to at least one section of the filter element, the filter element can be used as a counterelectrode to the electrode of the ionization elements and the soot particles deposited in the filter element can be neutralized.

Particularly preferably, the at least one filter element is a so-called open bypass filter, in which there are no completely closed flow channels. Rather, the filter element is formed with a metallic fleece and metallic corrugated layers in which openings, guide structures, etc. are provided. The guide structures form flow bottlenecks in the flow passages, so that the residence time or impact probability for soot particles in the interior of the filter element is increased. In this context, reference is made to the applicant's well-known patent publications, which can be used to further characterize the filter element and / or its regeneration; In particular, reference is made in full to the description of the following documents: WO-A-01/80978 ; WO-A-02/00326 ; WO-A-2005/099867 ; WO-A-2005/066469 ; WO 2006/136431 ; WO 2007/140932 ,

The regeneration of such a filter element is preferably carried out continuously based on the CRT method. For this purpose, the device z. B. upstream of an oxidation catalyst in which (also) nitric oxide is oxidized to nitrogen dioxide, which then reacts with the soot in the filter element. In addition, it is also possible that such an oxidatively acting coating is realized in the filter element itself, either in a zone thereof or in all areas of the filter element.

The at least one flow-guiding device is arranged in the flow direction of the exhaust gas in front of the at least one ionization element or in front of the at least one filter element. The flow-guiding device comprises elements which deflect at least one (spatially limited) part of the exhaust gas, in particular in that a part of the exhaust gas flows around the flow-guiding device at least in sections, so that the deflection is influenced only by the shape of the flow-guiding device. The deflection of the partial exhaust gas flow takes place in such a way that soot particles either do not reach the ionization element or in particular an electrical insulation of the ionization element or the electrical insulation of the filter element, or meet in such a way that the exhaust gas flow there acts so that An addition of soot particles is not possible. The avoidance of a soot layer on the electrical insulation and / or the ionization element also causes the formation of a short circuit between the ionizing element and / or the filter element with the exhaust pipe prevented.

• mindestens einen Strömungsgleichrichter,
• mindestens ein Umlenkblech.

Preferably, the flow guiding device comprises at least one element of the following group:

• at least one flow straightener,
• at least one baffle.

Under flow rectifier is a device to understand that at least partially reduces the turbulence in a flow or the exhaust flow laminarized and thus produces a more uniform velocity distribution of the exhaust gas over the cross section of the exhaust pipe. This can be done, for example, by a honeycomb body with a plurality of channels through which the exhaust gas can flow.

It is particularly advantageous if the flow-guiding device is adjustable. Thus, by adjusting the flow-guiding device, the flow direction of a part of the exhaust gas leaving the flow-guiding device can be changed. In particular, after predeterminable intervals or due to vehicle parameters, the flow-guiding device is adjusted such that alternating regions of the ionization element or the filter element are flowed through by the exhaust gas, whereby deposition of soot particles on the ionization element or the electrical insulation is prevented or entrained soot particles and thus entrained be eliminated.

In order to prevent deposition of the soot particles on the ionization element or the electrical insulation of the filter element, the Strömungsleiteinrichtung advantageously forms a flow-through diameter, which is smaller, preferably at least 10% smaller, more preferably at least 25% smaller than a diameter in the flow direction downstream ionizing element or filter element. In this way, the exhaust gas does not even reach the ionizing element or the electrical element surrounding the filter element Insulation. A deposition of the soot particles thus does not take place. In particular, in the case of a deflection of the soot particles by the electric field of the ionization element, the charged soot particles can not reach the ionization element and / or the electrical insulation of the filter element.

In a development of the invention, it is proposed that the at least one flow-guiding device contains a catalytic reactor. In this way, the exhaust gas flowing past the flow-guiding device can be catalytically converted.

Preferably, the at least one flow guide is attached directly to an exhaust pipe, so that can be dispensed with further fastening elements for the flow guide.

A further development of the invention provides that the at least one flow guide forms a flow shadow in the region of the electrical insulation, which also prevents deposition of the soot particles at least on the ionization element or the electrical insulation of the filter element. The flow guide is thus arranged in the exhaust gas flow, that the exhaust gas does not flow through the ionization element or the electrical insulation of the filter element.

In order to prevent deposition of soot particles at least on the ionization element or the electrical insulation and to eliminate already deposited soot particles, it is also proposed that the at least one flow guide device forms a concentrated flow in the region of the electrical insulation with an increased exhaust gas velocity. The exhaust gas velocity is thus increased in relation to the average exhaust gas velocity or the exhaust gas velocity over the cross section of the exhaust gas line without the flow guiding device. This pulse increase of the exhaust gas ensures that already deposited particles at least from the ionizing element or the electrical insulation can be eliminated and located in the exhaust particles can not accumulate.

According to a further preferred embodiment, a device is proposed, in which the flow guide is arranged upstream of the ionization element, and the flow guide has a flow-through range which is dimensioned so that ionized soot particles in the exhaust stream of an electric field generated by the ionization element at least not to a surface get the ionization element or the electrical insulation of the filter element. This embodiment is particularly preferably combined with an ionization element in which the outer tube and the inner tube concentrically arranged form an intermediate space through which the exhaust gas can pass, wherein at least one annular electrode with a plurality of electrode tips protruding radially into the intermediate space is arranged on the inner tube. This means, in particular, that a flow obstacle is arranged radially starting from at least the outer tube or the inner tube, whose radial extent is selected in dependence on a length of the electric field of the ionization element in the flow direction, the strength of the electric field and the exhaust gas velocity so that ionized At least during operation, soot particles do not reach the surface of the ionization element or the electrical insulation of the filter element. The main flow of the exhaust gas is therefore limited to a limited part of the gap, with the walls of the ionizing element forms only a small flow of exhaust gas.

Fig. 1:

eine Ausführungsform der erfindungsgemäßen Vorrichtung, und

Fig. 2:

eine weitere Ausführungsform der erfindungsgemäßen Vorrichtung,

Fig. 3:

noch eine weitere Ausführungsform der erfindungsgemäßen Vorrichtung.

The invention and the technical environment will be explained by way of example with reference to the figures. It should be noted that the figures show particularly preferred embodiments of the invention, but this invention is not limited thereto. They show schematically:

Fig. 1:

an embodiment of the device according to the invention, and

Fig. 2:

a further embodiment of the device according to the invention,

3:

Yet another embodiment of the device according to the invention.

Fig. 1 schematically shows a cross section through a device 1 according to the invention in an exhaust pipe 16. In the flow direction 15 of the exhaust gas containing soot particles 2, an ionization element 3 and a filter device 4 is arranged behind a flow guide 8. The flow guiding device 8 comprises a deflecting plate 11, which is fastened to the exhaust gas line 16 via fastening elements (not shown). The ionization element 3 has an electrically conductive honeycomb body 17, which is connected to the exhaust gas line 16 via a first electrical insulation 9.1. At the back of the honeycomb body 17 in the flow direction 15, a plurality of electrodes 14 are arranged, which can be acted upon by a first electrical connection 13.1 with an electrical voltage. The filter element 4 has a plurality of channels 5 through which the exhaust gas can flow and which extend between an inlet region 6 and an outlet region 7. The filter element 4 is isolated from the exhaust pipe 16 with a second electrical insulation 9.2. The filter element 4 can be acted upon by a second electrical connection 13.2 with an electrical voltage.

During operation, the exhaust gas containing soot particles 2 flows toward the ionization element 3 and is at least partially deflected by the deflecting plate 11. By the baffle 11, a portion of the exhaust gas is accelerated and hits at an increased speed on the first electrical insulation 9.1, whereby the soot particles 2 can not settle on the first electrical insulation 9.1 or already released on the first electrical insulation 9.1 settled particles become.

The exhaust gas also flows through the honeycomb body 17 of the ionization element 3, wherein the flow is at least partially laminarized. In the area between the electrodes 14 and the filter element 4, at least part of the soot particles 2 are ionized in a corona discharge between the electrodes 14 and the filter element 4. The charged soot particles 2 are accelerated toward the filter element 4 and deposited therein due to their charge at a higher deposition rate.

Fig. 2 schematically shows a cross section through a further embodiment of the device according to the invention 1. This embodiment of the device 1 according to the invention is similar in construction as the embodiment according to Fig. 1 so that only the differences are discussed here. In this embodiment, the flow guide 8 is designed as a flow rectifier 10. The flow rectifier 10 has a flow-through diameter 12 which is smaller than a flow-through diameter of the downstream ionization element 3. In the flow rectifier 10, the exhaust gas flow is at least partially laminarized and reduced to the diameter 12 of the flow rectifier 10 through which it can flow. With a sufficient difference in the diameters 12 of the flow rectifier and the ionizing element 3, it is thus achieved that the soot particles 2 in the exhaust gas do not reach the first electrical insulation 9.1 of the ionization element 3. A deposit on the electrical insulation 9.1 is thus avoided.

Fig. 3 schematically shows a sectional view of another embodiment of the device 1 according to the invention, wherein in the following only on the differences from the embodiment according to Fig. 2 will be received. The flow guide device 8 has a honeycomb body 17, which holds a counterelectrode 22 of the ionization element 3. The honeycomb body 17 has in an outer and an inner region closed channels 18, which with a radial extension 20 a Prevent flow through the honeycomb body 17 in these areas. Thus, a flow-through region 19 of the honeycomb body 17 is formed. The ionization element 3 has an annular electrode 14 assigned to the exhaust gas line 16 with a multiplicity of electrode tips. Centrally in the exhaust pipe 16, a tubular counter electrode 22 is arranged, which is held by the honeycomb body and possibly isolated from this. Thus, over a length 21, an electric field may be formed between the annular electrode 14 and the tubular counter electrode 22.

The radial extent 20 of the closed channels 18 is selected such that ionized soot particles 2 can not be distracted so far from the electric field present between the annular electrode 14 and the counterelectrode 22 that they can reach a surface of the ionization element 3. The size of the radial extent 20 thus depends essentially on the length 21, the electric field strength and the exhaust gas velocity.

The present invention effectively prevents soot particles from being deposited on electrical insulation of exhaust gas cleaning components, thereby preventing the formation of a short circuit. Safe operation of the exhaust system is thus ensured.

LIST OF REFERENCE NUMBERS

1

contraption

2

soot

3

Ionisierungselement

4

filter element

5

channel

6

entry area

7

exit area

8th

flow guide

9.1

first electrical insulation

9.2

second electrical insulation

10

Flow straightener

11

baffle

12

diameter

13.1

first electrical connection

13.2

second electrical connection

14

electrode

15

flow direction

16

exhaust pipe

17

honeycombs

18

closed channels

19

permeable area

20

radial expansion

21

length

22

counter electrode

Claims (9)

1. Device (1) for treating exhaust gas containing soot particles (2), comprising at least

   - at least one ionization element (3) for ionizing soot particles (2),

   - at least one filter element (4), wherein an electrical potential can be applied to at least one section of the filter element (4),

   - at least one flow-directing device (8) which can influence a flow of the exhaust gas in such a way that depositing of the soot particles (2) on at least the ionization element (3), electrical insulation (9.1) of the ionization element (3) or electrical insulation (9.2) of the filter element (4) can be prevented and removed.
2. Device (1) according to Patent Claim 1, wherein the flow-directing device (8) comprises at least one element of the following group:

   - at least one flow rectifier (10), and

   - at least one baffle (11).
3. Device (1) according to one of the preceding patent claims, wherein the flow-directing device (8) is adjustable.
4. Device (1) according to one of the preceding patent claims, wherein the flow-directing device (8) forms a diameter (12) through which exhaust gas can flow, which diameter (12) is smaller than a diameter of the ionization element (3) or filter element (4) positioned downstream in the flow-direction (15), through which diameter there can be a flow.
5. Device (1) according to one of the preceding patent claims, wherein the at least one flow-directing device (8) contains a catalytic reactor.
6. Device (1) according to one of the preceding patent claims, wherein the at least one flow-directing device (8) is attached to an exhaust gas line (16).
7. Device (1) according to one of the preceding patent claims, wherein the at least one flow-directing device (8) forms a flow shadow in the region of the electrical insulation (9.1, 9.2).
8. Device (1) according to one of Patent Claims 1 to 6, wherein the at least one flow-directing device (8) forms a concentrated inflow in the region of at least one surface of the ionization element or of the electrical insulation (9.2) with an increased exhaust gas speed.
9. Device (1) according to Claim 4, wherein the flow-directing device (8) is arranged upstream of the ionization element (3), and the flow-directing device (8) has a region through which there can be a flow, which region is dimensioned in such a way that ionized soot particles in the exhaust gas stream from a field generated by the ionization element (3) do not arrive at a surface of the ionization element (3) or of the electrical insulation (9.2) of the filter element (4).

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