DE102013007014A1 - Exhaust after-treatment device for an exhaust system and exhaust system - Google Patents

Abstract

The invention relates to an exhaust gas aftertreatment device (10) for an exhaust system of a vehicle with a carrier material (14) arranged in a housing (12) of the exhaust gas aftertreatment device (10). The carrier material (14) is provided with at least one first catalytically active substance (18) and with at least one second catalytically active substance (20). These substances are arranged alternately in a flow direction (30) of the exhaust gas in the exhaust gas aftertreatment device (10). For this purpose, the carrier material (14) is wound up in the housing (12) to form a roll (16), a base body (26) of the roll (16) through which the exhaust gas can flow in the radial direction forms a channel (28) from which the Exhaust gas can be transferred through the base body (26) into the vicinity of the roller (16). The invention also relates to an exhaust system with such an exhaust gas aftertreatment device (10).

Description

The invention relates to an exhaust gas aftertreatment device for an exhaust system of a vehicle. In a housing of the exhaust aftertreatment device, a carrier material is arranged, which is provided with a first catalytically active substance and with a second catalytically active substance. In a flow direction of the exhaust gas, the two catalytically different effective substances are arranged alternately. Furthermore, the invention relates to an exhaust system with such an exhaust gas aftertreatment device.

The DE 10 2006 031 659 A1 describes an exhaust system for reducing nitrogen oxides in the exhaust gas of internal combustion engines. In this case, downstream of an SCR catalyst, an ammonia oxidation catalyst is arranged, wherein this sequence of an SCR catalyst and this downstream ammonia oxidation catalyst is repeated several times. The alternately arranged SCR catalysts and ammonia oxidation catalysts with their different catalyst compositions may in this case be arranged on a common carrier.

From the prior art, it is also known to apply SCR catalysts (SCR = selective catalytic reduction, selective catalytic reduction) with comparatively much ammonia in order to achieve the greatest possible reduction of the nitrogen oxide content of the exhaust gas. This can be done, for example, by adding an aqueous urea solution in excess upstream of the SCR catalyst. For example, 120% of the amount of urea to be provided stoichiometrically for the conversion of the nitrogen oxides can be metered in.

From the urea forms in the hot exhaust gas ammonia, which is converted in the subsequent SCR catalyst in a selective catalytic reduction reaction with the nitrogen oxides contained in the exhaust gas to nitrogen and water. In an overdose described above, however, there is an undesirable slippage of ammonia, ie an occurrence of ammonia downstream of the SCR catalyst. This is undesirable because of ammonia-based odor nuisance and is not allowed.

The DE 10 2008 026 178 A1 describes a way to prevent the slippage of ammonia by dividing the exhaust stream and fed to an oxidation catalyst. In this nitrogen oxides are formed from the ammonia, which are then reacted in another SCR catalyst with the remaining ammonia to nitrogen and water. However, this is relatively expensive.

Object of the present invention is therefore to provide an exhaust gas aftertreatment device and an exhaust system of the type mentioned, by means of which can be achieved in a particularly simple manner, a particularly high efficiency in the exhaust gas treatment.

This object is achieved by an exhaust aftertreatment device having the features of patent claim 1 and by an exhaust system having the features of patent claim 8. Advantageous embodiments with expedient developments of the invention are specified in the dependent claims.

In the exhaust aftertreatment device according to the invention, the carrier material is wound into a roll in the housing. In this case, a main body of the roller through which the exhaust gas can flow in the radial direction forms a channel, from which the exhaust gas can be transferred through the main body into an environment of the roller. The alternately arranged in the flow direction of the exhaust gas arranged different catalytically active substances are thus flowed through, when the exhaust gas passes radially through the main body of the roller. Such an exhaust aftertreatment device can be produced particularly inexpensively.

In addition, the volume of the catalytically active substances having base body increases in the radial direction. Thus, it is ensured that for a given volume flow, an increasingly larger volume flowed through is present, so that the residence time of the exhaust gas increases in the radial direction. With increasing dwell time or decreasing space velocity is accompanied by a particularly good implementation of the exhaust gas constituents. Namely, the temperature and the pressure of the exhaust gas decrease over the radius of the main body, and the volume which can be flowed through increases. At this adjusting space velocity, a particularly high efficiency of the exhaust aftertreatment device can be achieved.

In an advantageous embodiment of the invention, an annular space permeable by the exhaust gas is formed between the roller and the housing. This makes it possible to achieve a particularly uniform flow through the body from the channel to the annulus.

The alternating sequence of the different catalytically can be particularly simple reach effective substances when a first side of the carrier material with the at least one first catalytically active substance and a second side of the carrier material is provided with the at least one second catalytically active substance.

However, it is also possible for one and the same side of the carrier material to be provided alternately with the at least one first catalytically active substance and with the at least one second catalytically active substance. In this case, in particular a length of each provided with one of the two substances portion may be sized so that this length corresponds exactly to a circumference of a winding of the roll.

The carrier material can be wound up in a particularly simple manner into the roll if the carrier material is formed from a metal. However, even with a ceramic carrier material, it is possible in the not yet solidified state to bring this into the shape of the roll.

It is also possible, for example, to dope the ceramic carrier material in the raw state, that is to say to activate it in a certain way, so that only the correspondingly doped or activated regions of the material assume the coating in a subsequent coating.

Finally, it has proven to be advantageous if the at least one first catalytically active substance for oxidizing exhaust gas components and the at least one second catalytically active substance for reducing nitrogen oxides is formed. In this case, ammonia can be applied in excess to the first substance effective as the oxidation catalyst, and the ammonia passing through this oxidation catalyst is then subsequently reduced with the nitrogen oxides formed in the oxidation catalyst with the aid of the second catalytically active substance. Due to the alternating sequence of several such layers of different effective catalytic substances, the nitrogen oxides can be particularly largely removed from the exhaust gas without causing a slip of ammonia. It is thus also possible to realize combustion processes which lead to high levels of nitrogen oxides in the exhaust gas, that is to say so-called "high-NOx" combustion processes, without the limit values applicable to the nitrogen oxides being exceeded.

The exhaust system according to the invention has at least one exhaust aftertreatment device according to the invention. Upstream of the at least one exhaust aftertreatment device, a further exhaust gas aftertreatment device is arranged, which has the at least one second catalytically active substance. By means of such an exhaust system can be achieved particularly high efficiencies in terms of the conversion of exhaust components.

The advantages and preferred embodiments described for the exhaust gas aftertreatment device according to the invention also apply to the exhaust system according to the invention and vice versa.

The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or in the figures alone can be used not only in the respectively specified combination but also in other combinations or in isolation, without the scope of To leave invention.

Further advantages, features and details of the invention will become apparent from the claims, the following description of preferred embodiments and from the drawings. Showing:

1 strongly schematized a catalyst in which effective as oxidation catalyst layers and layers of exhaust gas as SCR catalyst are successively flowed through, wherein a carrier material is arranged with these layers wound into a radially from the inside to the outside by a roll in a housing of the catalyst;

2 schematically the winding of a carrier material having the two catalytically active substances to the roll; and

3 the arrangement of in 1 shown catalyst in an exhaust system downstream of an SCR catalyst.

In 1 is schematically a catalyst 10 shown as an example of an exhaust aftertreatment device of a vehicle. This is in a housing 12 of the catalyst 10 a carrier material 14 to a role 16 wound. A first side of the substrate 14 is coated with a first catalytically active substance, which is designed for oxidizing exhaust gas constituents. This coating is hereinafter referred to as the oxidation catalyst layer 18 referred to, because it has the property of an oxidation catalyst. A second side of the substrate 14 is coated with a second catalytically active substance, which is designed for reducing nitrogen oxides. This coating is hereinafter referred to as SCR layer 20 as it is designed to be in a selective catalytic reduction reaction Convert ammonia with nitrogen oxides to nitrogen and water.

The catalyst 10 is exposed to exhaust gas, which previously in another SCR catalyst 22 which was treated as well as the catalyst 10 in an exhaust system 24 of the vehicle is arranged (see 3 ). This SCR catalyst 22 is operated in such a way that there is a slip of ammonia. In other words, upstream of this SCR catalyst 22 an ammonia-forming substance in the exhaust gas is added in excess, for example urea in the form of an aqueous urea solution. This causes the nitrogen oxides contained in the exhaust gas to a particularly large extent in the SCR catalyst 22 be converted with ammonia to nitrogen and water. In the present case, however, it is prevented that in the exhaust gas ammonia remains, which the exhaust system 24 with the SCR catalyst 22 and in 1 shown catalyst 10 leaves. To achieve this, the downstream of the SCR catalyst 22 nor ammonia-containing exhaust gas in the catalyst 10 according to 1 further treated.

The carrier material with the coatings applied on both sides, namely with the oxidation catalyst layer 18 and the SCR layer 20 is so important to the role 16 wound up, that it is a comparatively compact body 26 the role 16 forms. Through this body 26 is in the catalyst 10 a - in this case axial - channel 28 formed as an inlet for that of the SCR catalyst 22 upcoming exhaust serves. From this axial channel 28 from then flows through the exhaust gas in the radial direction of the body 26 , This flow of exhaust gas in the catalyst 10 from the inside to the outside, so the radial flow through the body 26 , is in 1 through flow arrows 30 illustrated.

The oxidation catalyst layer 18 and the SCR layer 20 are comparatively thin, and the role 16 has a plurality of windings. This results in that during the radial flow through the body 26 the role 16 the exhaust gas first through the oxidation catalyst layer 18 , then through the SCR layer 20 , then again through the oxidation catalyst layer 18 and again through the SCR layer 20 passes. Depending on the number of windings can also significantly more than in 1 only shown by way of example number of alternately arranged coatings with the different catalytically active substances may be provided.

When radial flow through the body 26 the role 16 Thus, the exhaust gas first passes through the first thin oxidation catalyst layer 18 therethrough. This will be part of the upstream of the catalyst 10 in the exhaust gas existing ammonia to nitrogen oxides, among other things converted to nitrogen dioxide. In the following SCR layer 20 Then these nitrogen oxides are reacted with a portion of the ammonia in the selective catalytic reduction reaction to nitrogen and water. These successive reactions of the oxidation of ammonia to nitrogen oxides and the subsequent reaction of the nitrogen oxides with remaining ammonia are repeated in the subsequent oxidation catalyst layers 18 and SCR layers 20 ,

With a sufficient number of layer sequences remains in the exhaust gas, which is the main body 26 has flowed through, no more ammonia, and the nitrogen oxides are completely removed. The design of the coatings is chosen so that in particular the first oxidation catalyst layer 18 so to speak, with ammonia is run over, so not immediately all ammonia in the first oxidation catalyst layer 18 is oxidized. This leaves enough ammonia in the exhaust gas to in the subsequent SCR layers 20 for complete removal of both the ammonia and the oxidation catalyst layer 18 formed nitrogen oxides from the exhaust gas.

So can in the exhaust, which is the SCR catalyst 22 is supplied, the urea solution or a similar ammonia-releasing or ammonia-containing reducing agent are introduced in an overdose, without resulting in a slippage of ammonia.

Characterized in that in the radial direction, the volume of the body 26 the role 16 increases, results for the catalyzed reactions particularly favorable residence time of the exhaust gas in the body 26 , The pressure and the temperatures take over the radius of the roll 16 as the volume increases. Thus, at a particularly favorable space velocity, a high efficiency of the catalyst 10 be achieved.

Out 1 It is further evident that between the role 16 and the housing 12 an annulus 32 is formed, in which the exhaust gas after flowing through the body 26 arrives. Through this an exhaust gas outlet is provided, the exhaust gas thus leaves the catalyst 10 over the annulus 32 , Spacers (not shown) may be provided around the roller 16 at a distance from the shell 12 hold.

In 2 is by a motion arrow 34 rolling up with the oxidation catalyst layer 18 and the SCR layer 20 provided carrier material 14 illustrated. As a carrier material 14 In particular, a metallic material comes in Question, but can also be a ceramic material to the role 16 wind up as long as the ceramic material is still malleable.

In the in 3 shown exhaust system 24 illustrate flow arrows 36 the flow of exhaust gas. In one area 38 upstream of the SCR catalyst 22 are in the exhaust gas overdosed ammonia and nitrogen oxides. In one area 40 downstream of the SCR catalyst 22 the exhaust gas contains unreacted ammonia. This exhaust gas flows into the channel 28 of in 1 shown catalyst 10 and occurs after a radial flow through the body 26 the role 16 over the annulus 32 again from this catalyst 10 out.

In one area 42 the exhaust system 24 downstream of the catalyst 10 Thus, the exhaust gas is purified both in terms of nitrogen oxides and with respect to the ammonia. The exhaust system 24 This is particularly simple in construction, since the entire exhaust gas flow through the catalyst 10 with the alternately arranged oxidation catalyst layers 18 and SCR layers 20 is directed.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006031659 A1 [0002]
• DE 102008026178 A1 [0005]

Claims (8)

Exhaust after-treatment device for an exhaust system ( 24 ) of a vehicle, with one in a housing ( 12 ) of the exhaust aftertreatment device ( 10 ) arranged carrier material ( 14 ), which contains at least one first catalytically active substance ( 18 ) and with at least one second catalytically active substance ( 20 ), which in a flow direction ( 30 ) of the exhaust gas alternately in the exhaust aftertreatment device ( 10 ) are arranged, characterized in that the carrier material ( 14 ) in the housing ( 12 ) to a role ( 16 ) is wound, wherein a flow-through of the exhaust gas in the radial direction body ( 26 ) of the role ( 16 ) a channel ( 28 ), from which the exhaust gas passes through the parent body ( 26 ) through into an environment of the roll ( 16 ) is convertible. Exhaust after-treatment device according to claim 1, characterized in that between the roller ( 16 ) and the housing ( 12 ) an annular space through which the exhaust gas can flow ( 32 ) is trained. Exhaust after-treatment device according to claim 1 or 2, characterized in that a first side of the carrier material ( 14 ) with the at least one first catalytically active substance ( 18 ) and a second side of the substrate ( 14 ) with the at least one second catalytically active substance ( 20 ) is provided. Exhaust after-treatment device according to one of claims 1 to 3, characterized in that one side of the carrier material ( 14 ) alternately with the at least one first catalytically active substance ( 18 ) and with the at least one second catalytically active substance ( 20 ) is provided. Exhaust after-treatment device according to one of claims 1 to 4, characterized in that the carrier material ( 14 ) is formed of a metal or ceramic. Exhaust after-treatment device according to one of claims 1 to 5, characterized in that the carrier material ( 14 ) at least in regions with the at least one first catalytically active substance ( 18 ) and the at least one second catalytically active substance ( 20 ) is coated. Exhaust after-treatment device according to one of claims 1 to 6, characterized in that the at least one first catalytically active substance ( 18 ) for oxidizing exhaust gas constituents and the at least one second catalytically active substance ( 20 ) is designed for reducing nitrogen oxides. Exhaust system with at least one exhaust aftertreatment device ( 10 ) according to one of claims 1 to 7, wherein upstream of the at least one exhaust aftertreatment device ( 10 ) a further exhaust aftertreatment device ( 22 ), which contains the at least one second catalytically active substance ( 20 ) having.

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