WO2006097131A1

WO2006097131A1 - Honeycomb body comprising means for supplying a reactant and corresponding method and waste gas system

Info

Publication number: WO2006097131A1
Application number: PCT/EP2005/002904
Authority: WO
Inventors: Rolf BRÜCK; Peter Treiber
Original assignee: Emitec Gesellschaft Für Emissionstechnologie Mbh
Priority date: 2005-03-16
Filing date: 2005-03-18
Publication date: 2006-09-21
Also published as: DE102005012066A1

Abstract

The invention relates to a honeycomb body (1) comprising a first honeycomb structure (2) which can be crossflown by a fluid, and a second honeycomb structure (3) which can be crossflown by a fluid and which is arranged in a radial manner on the outside of the first honeycomb structure (2), said second honeycomb structure being at least concentric in relation to the first honeycomb structure (2). The first (2) and the second honeycomb structures (3) are separated from each other by means of an intermediate pipe (4). Said intermediate pipe (4) protrudes at least on one side in a first axial direction (5) between X and Y cm, in relation to a front side (6) of at least one of the honeycomb structures (2, 3). Means (7) for adding a reactant are formed inside (8) of the intermediate pipe (4). The inventive honeycomb body enables waste gas systems to be formed in an advantageous manner, wherein the waste gas flow divides and is guided through various honeycomb structures (2, 3). The present invention is particularly advantageous in the formation of an SCR-system, wherein the first honeycomb structure (2) is used as a hydrolysis catalyst and the second honeycomb structure (3) is used as an oxidation catalyst.

Description

Honeycomb body with Reaktanderizufuhr and corresponding method and exhaust system

The present invention is a honeycomb body with various honeycomb structures, and a corresponding method and exhaust system.

In many states there are legal limits that have to comply with the concentrations of certain pollutants in the exhaust gas of motor vehicles or motor vehicles. To reduce the concentration of nitrogen oxides (NO _x ), various methods have been established. One of these methods is the SCR process (Selective Catalytic Reduction). This is based on the introduction of a reducing agent such as urea in the exhaust gas stream, by means of which selectively acting catalysts corresponding to oxides of nitrogen (NO _x ) to nitrogen (N ₂ ) and water (H ₂ O) are implemented.

From DE 199 13 462 Al a process for the thermal hydrolysis and metering of urea or aqueous urea solution in a reactor is known, in which a partial stream of an exhaust gas is passed through a hydrolysis catalyst. After hydrolyzation, the partial exhaust gas streams are brought together again and a selective catalytic reduction of nitrogen oxides is carried out. The disadvantage here is that a separate housing and a separate partial exhaust gas line must be formed for the hydrolysis.

Proceeding from this, the object of the invention is to propose a honeycomb body and a corresponding method and exhaust system in which partial gas flow can be subjected to different catalytic reactions without the need for an additional housing or an additional carrier. A further object of the invention is to propose a honeycomb body which, in order to save space, has a plurality of hydrodynamically separated reaction chambers. includes zones. Furthermore, a corresponding exhaust system and a corresponding method to be proposed.

These objects are achieved by a honeycomb body with the features of claim 1, an exhaust system having the features of claim 12, and a method having the features of claim 16. Advantageous developments are the subject of the respective dependent claims.

The honeycomb body according to the invention has a first honeycomb structure through which a fluid can flow. Furthermore, the honeycomb body comprises a second honeycomb structure, which can be flowed through radially outside the first honeycomb structure, through which a fluid can flow. The first and the second honeycomb structure are separated from one another by at least one intermediate tube, wherein the at least one intermediate tube protrudes at least on one side in a first axial direction between 5 and 15 centimeters beyond an end face of at least one of the honeycomb structures. It is preferred here that the at least one intermediate tube protrudes by 5 to 10 cm beyond an end face of at least one of the honeycomb structures. According to a preferred embodiment, there are two intermediate tubes, which lie inside each other.

By the one side, the end face of at least one honeycomb structure superior intermediate tube is a separation of the gas streams that can flow through the honeycomb body. It is a first partial gas flow - a central flow - formed, which flows through the first honeycomb structure and a second partial gas flow - an edge flow - which flows through the second honeycomb structure. The two honeycomb structures are separated from each other by the intermediate tube, that no exchange can take place through the intermediate tube. This allows the formation of different reaction zones in a honeycomb body, without having to provide additional components and / or strands of an exhaust pipe. According to the invention, the two reaction zones can be formed in a single honeycomb body. In particular, this is advantageous if, due to the boundary conditions in use, the two reaction zones are strictly separated from one another. must be separated, but a mixing after flowing through the reaction zones is desired or necessary.

In principle, however, it is also advantageous if at least one intermediate tube of the honeycomb body protrudes on the opposite end face. It is preferred that such a pipe socket is provided with an extension which is different from a length of the overhang of the intermediate tube of 5 to 15 cm, in particular smaller. Thus, the extension is advantageously chosen in a range of 0.5 to 2.0 cm. Such a pipe socket can serve, for example, for fastening a support structure, so that a bilateral bearing of the honeycomb body is made possible via the at least one intermediate tube. In this context, it should be noted that all intermediate tubes may be formed with different lengths with respect to the overhang and / or extensions of the pipe socket.

The honeycomb structure has cavities which can be flowed through at least for a fluid. That is, the cavities can be formed with a freely flow-through cross-section such as channels but alternatively or additionally, cavities, which can not be freely roughened, but the verschlos- sen or at least partially closed, with a gas stream passing through the wall of the cavity can. Such a honeycomb body can be used for example as a diesel particulate filter.

The honeycomb structures may be formed in different ways. On the one hand, the training is at least partially possible from high temperature resistant stainless steel materials. For this purpose, at least partially metallic layers are formed, which are at least partially structured and optionally wound with at least one substantially smooth layer. Another possibility consists of stacking at least one at least partially structured at least partially metallic layer and optionally at least one substantially smooth at least partially metallic layer to form a layer. stack and twist at least one stack. Under a layer can be understood in particular a thin sheet metal foil made of high temperature resistant corrosion-resistant stainless steel in particular a chromium-nickel stainless steel. Thicknesses of the layers of less than 100 .mu.m, preferably less than 80 .mu.m, particularly preferably less than 60 .mu.m, particularly preferably less than 40 .mu.m and particularly preferably less than 30 .mu.m are preferred. Weiterbin it is also possible to form the position at least partially made of a fiber material. This may be a metallic and / or ceramic fiber material, which may for example be reinforced with sheet metal layers. The fiber materials can be produced by different processes, in particular by sintering or the layered structure. For layers which are at least partially constructed of fiber materials, the preferred layer thickness is less than 2 mm, preferably less than 1.5 mm, particularly preferably 1 mm or less. When constructed from layers, the structured regions of the layers with other smooth or structured regions form the cavities or channels. The layers are positively, positively and / or materially connected to one another in connection regions, with a material connection such as welding or brazing being preferred. Brazing is here understood to mean a high-temperature brazing process in which, in particular, chromium-aluminum or nickel-chromium steels are brazed to a corresponding brazing alloy, for example a nickel-containing brazing material, preferably a nickel-based brazing alloy.

Both honeycomb structures can be made similar or different. In particular, it is also possible in an advantageous manner to form at least one honeycomb structure made of ceramic material, in particular as an extruded ceramic honeycomb body. This is particularly preferred for the centrally located inner first honeycomb structure.

The cross sections of the honeycomb structures are preferably circular, but other shapes are possible. In particular, here polygonal shapes or can The cross sections of the two honeycomb structures do not have to have the same geometry, in particular, for example, a first honeycomb structure with a circular cross section may be formed in an oval honeycomb structure as the first honeycomb structure formed concentric with each other.

According to an advantageous development of the honeycomb body according to the invention comprises means for adding a reactant in the interior of the intermediate tube.

By the means for adding a reactant, reactants can be introduced into the gas stream in previously determinable amounts such that exactly one honeycomb structure receives the gas stream enriched with the reactant. For example, when forming a hydrolysis catalyst coating for SCR catalysis, it is possible to introduce reducing agents such as, in particular, urea in aqueous solution onto the first honeycomb structure. If the second honeycomb structure comprises an oxidation catalyst coating in this case, it is highly sensitive to even low concentrations of the reducing agent, in particular of urea. In particular, coatings may be present on the second honeycomb structure, which are poisoned by the reducing agent, so that serious damage to the honeycomb body may occur upon contact of the first honeycomb structure with reducing agent.

The means for supplying a reactant may consist, for example, in a nozzle with a feed line, wherein the nozzle is formed in the interior of the intermediate tube so as to ensure that in operation only the first honeycomb structure comes into contact with the reactant. A feed line can be formed, which connects the means for adding a reactant to a jacket tube, which may be formed outside the first honeycomb structure, with a reactant reservoir. Particularly preferred and suitable is the honeycomb body according to the invention for use in the exhaust system of a motor vehicle. Under a motor vehicle is to be understood in particular an automobile, a motorized bicycle or a water or aircraft. Especially advantageous is the combination of a small motor vehicle such as a passenger car or a motorcycle with a honeycomb body according to the invention. A passenger car with a honeycomb body according to the invention has particular advantages in terms of space savings in the exhaust system of this motor vehicle. Preferred here is a passenger car with diesel engine.

The protrusion of the intermediate tube over at least one end face of the first and / or second honeycomb structure of 5 to 10 centimeters has proven to be particularly advantageous, since such a projection on the one hand ensures that the introduced by the means for introducing a reactant reactant is evenly distributed, before it strikes the front of the first honeycomb structure. This allows the most uniform possible reaction of the first honeycomb structure. On the other hand, this overhang of the intermediate tube is so small that nevertheless a compact and small construction of the honeycomb body according to the invention is possible. Also particularly advantageous are overhangs of the intermediate tube of 5 to 10 centimeters, more preferably from 6 to 8 centimeters.

By dimensioning the honeycomb structures and the intermediate tube, an advantageous distribution of a gas flow during operation of the honeycomb body to the individual honeycomb structures can be achieved. Particularly advantageous is a distribution of the gas flow has proven, in which the first honeycomb structure is acted upon by about one third of the exhaust gas flow rate, while the second honeycomb structure is acted upon by about two-thirds of the exhaust gas volume flow. When used in an SCR system in which the first honeycomb structure has a hydrolysis catalyst coating and the second honeycomb structure comprises an oxidation catalyst coating, it can thus be ensured that that sufficient ammonia is provided behind the honeycomb structures in order to allow as complete a conversion of the nitrogen oxides as possible. Depending on the design of the corresponding SCR coating, a certain proportion of nitrogen dioxide (NO ₂ ) may be required, which is obtained by oxidation of the nitrogen monoxide (NO) normally present in the exhaust gas to nitrogen dioxide in the oxidation catalyst, ie in the second honeycomb structure. The exact distribution of the gas flow to the two honeycomb structures can be achieved on the one hand solely by the dimensioning of the intermediate tube and the honeycomb structures. In this case, various parameters can be changed, which ultimately determine the flow resistance of the respective first and second honeycomb structures. These are in particular the cell densities in the respective honeycomb structures and the wall thicknesses of the cavities or channels of the honeycomb structures.

In particular, first and / or second honeycomb structures have proven to be advantageous, which are wound or twisted from metallic sheet metal foils. In particular, the first honeycomb structure has metallic walls of a thickness of less than 80 or 60 μm, preferably less than 40 μm and particularly preferably less than 30 μm. Preferred cell densities for the first honeycomb structure are 200 to 800 cpsi (cells per square inch, cells per square inch), preferably 400 to 600 cpsi. The second honeycomb structure is preferably constructed of metallic layers. When sheet metal foils are used, thicknesses of sheet metal foils of less than 60 μm, preferably less than 40 μm, particularly preferably less than 30 μm, are preferred. Here, cell densities of the second honeycomb structure are preferably those in the range of 200 to 1000 cpsi, preferably in the range of 400 to 600 cpsi. In this case, it is preferred that the layers (for example sheet-metal foils or layers of materials permeable to a fluid), from which the first honeycomb structure is at least partially formed, are thicker than the layers from which the second honeycomb structure is formed. Preference is given to ply-thicknesses in the first honeycomb structure of up to 100 micrometers, preferably of up to 120 micrometers, more preferably of up to 150 micrometers. Furthermore, it is also advantageously possible to provide additional means for flow division or flow distribution. These can be formed on the projecting part of the intermediate tube. In this case, on the one hand static means are possible, such as, for example, as a widening or narrowing of the intermediate tube in the form of a funnel. On the other hand, it is alternatively or additionally possible to provide movable means for flow division or distribution, for example, in the simplest form, flaps which can change the flow-through cross section. Thus, for example, a pivotable flap can be formed on or in the intermediate tube whose opening angle determines the proportion of the gas flow which flows through the first and the second honeycomb structure. Thus, very accurate control loops can be formed, which lead, when used in an SCR catalytic system as set out above, for example, that the ammonia or Stickstoffdioxidanteil in the gas behind the honeycomb structures can be determined very accurately. This can thus be matched exactly to the currently given needs in the exhaust. Thus, in particular, changes in the catalytically active coatings of the first and / or the second honeycomb structure can be taken into account so that, for example, the change in the conversion rate due to the aging of the catalyst in the first and / or second honeycomb structure can be taken into account. Thus, even with aging of the first and / or the second honeycomb structure good results in the implementation of nitrogen oxides in the exhaust gas can be achieved.

The first and the second honeycomb structure preferably have a length of 50 to 150 mm, preferably 80 to 120 mm. The first and second honeycomb structures may have different lengths. The first and the second honeycomb structure may be formed offset from each other. Regardless, it is preferable that the honeycomb structures at least partly overlap each other in a radial direction. Thus, in this embodiment there is in each case an area, in particular at least a portion of the honeycomb body, in which a section in a radial direction perpendicular to the first axial direction is, includes both parts of the first honeycomb structure and parts of the second honeycomb structure.

The at least partial permeability of the first and second honeycomb structures is preferably made possible by the formation of channels extending through the honeycomb structures. These channels can be at least partially closed, wherein preferably at least partially through-flow walls are formed between these at least partially closed channels for a fluid. The formation of cavities whose cross section is greater than dimensions of the channels is possible and according to the invention, for example by forming holes in layers, from which the first and / or the second honeycomb structure is formed.

According to a preferred embodiment of the honeycomb body according to the invention, a third honeycomb structure is formed behind the first and second honeycomb structures in a second direction, which is substantially opposite to the first axial direction.

Particularly preferred here is the formation of the third honeycomb structures at a defined distance behind the corresponding end face of the first and / or the second honeycomb structure. Particularly preferred here is a distance of 30 to 50 mm, in particular from 35 to 45 mm behind the end face of the first and / or the second honeycomb structure. Alternatively, it is possible to determine the distance as a function of the outer diameter, in particular of the second honeycomb structure, so that, in particular, a monotonously increasing course of the distance is realized as a function of the diameter. Alternatively and / or additionally, the length of the overhang of the intermediate tube can also take place via the corresponding end face of the first and / or the second honeycomb structure, depending on the diameter of the intermediate tube and / or the configuration of the means for supplying a reactant. Depending on the configuration and in particular the distribution characteristic of the means, in particular a nozzle include, the overhang can be made shorter or longer. In principle, the more uniformly the means for supplying a reactant distribute the reactant until impact with the end face of the first honeycomb structure, the shorter the overhang. In particular, the means for supplying a reactant may comprise a point or annular nozzle. Alternatively or additionally, means for distributing the reactant between the means for supplying the reactant and the end face of the first honeycomb structure may be formed. This may be, for example, a baffle plate or the like. These means for distributing the reactant ensure a possibly uniform distribution of the reactant in the central flow flowing through the first honeycomb structure.

When using a honeycomb body according to the invention in a system for SCR conversion of nitrogen oxides and also in other fields of application, this gap between the first and / or second honeycomb structure on the one hand and the third honeycomb structure on the other hand serves to mix the partial gas streams which are in operation through the first and the second Honeycomb stream. When used in an SCR system so the formation of a gas mixture can be promoted, which consistently contains a very homogeneous concentration of ammonia. For this purpose, it is advantageous if the third honeycomb structure has an SCR coating.

Particularly preferably, at least one of the honeycomb structures has a catalytically active coating. This consists, for example, in a catalyst material (such as, for example, noble metal catalysts such as platinum, rhodium, ruthenium, palladium and the like), which is applied in a ceramic coating. Particularly advantageous in this case is the application of coating in the form of a ceramic washcoat. The additional or alternative application of aluminosilicates such as in particular zeolites such as zeolites of the X, Y, A, Faujasit or ZSM type is possible according to the invention. Particularly preferred is a honeycomb body which can be used in an SCR system for the selective catalytic reduction of nitrogen oxides. In such a case, the first honeycomb structure particularly preferably has a hydrolysis catalytic converter coating. Furthermore, the second honeycomb structure preferably comprises an oxidation catalyst coating. The third honeycomb structure has in particular an SCR coating.

In the third honeycomb structure, a reaction of nitrogen monoxide (NO) and optionally nitrogen dioxide (NO ₂ ) with ammonia (NH ₃ ) and optionally with oxygen to nitrogen (N ₂ ) and water (H ₂ O) preferably takes place during operation. Side reactions are possible, with the main reaction being the desired reaction. Due to the sometimes very restrictive legal regulations with regard to ammonia, this can not be carried directly on board an automobile but must be obtained from other reactants. In particular, the production of ammonia from urea ((NH ₂ ) ₂ CO) in aqueous solution has proved to be advantageous. Thus, it is necessary to produce ammonia from urea. This is preferably done in the first honeycomb structure, which has a corresponding catalytically active coating. In the first honeycomb structure, a hydrolysis is carried out in addition to a hydrolysis. The thermolysis causes a temperature-induced reduction of urea to ammonia and an intermediate such as isocyanic acid (HCNO). In the hydrolysis, this isocyanic acid is in turn catalyzed with water to form ammonia and carbon dioxide (CO ₂ ).

On the other hand, between the third honeycomb structure on the one hand and the first and / or second honeycomb structure on the other hand, a minimum distance of 2.5 centimeters, preferably a distance of between 3 centimeters and 5 centimeters or 3.5 to 4.5 centimeters, is particularly preferred. It is possible, on the one hand, for this region to be designed essentially free of installation, so that mixing of the gas streams, which in each case pass through the first and second honeycomb structures during operation, can take place in this region. On the other hand Alternatively or additionally, flow influencing means may be formed in this area, which require a faster mixing of these two gas streams. As a result, the corresponding distance can also be shortened. In particular, such means for influencing the flow are internals such as, for example, one or more diaphragms or corresponding baffles. In any case, the means for influencing the flow are designed so that a turbulent flow as possible is generated in this region, which leads to good mixing of the two Gas flows leads.

According to a further advantageous embodiment of the honeycomb body according to the invention, the intermediate tube comprises a first intermediate tube and a second intermediate tube lying at least partially outside the first intermediate tube.

An intermediate pipe lying at least partially outside the first intermediate pipe means in particular that, for example, the overhang is formed by only one intermediate pipe. In this case, a connection of the inner first honeycomb structure to the first intermediate tube and a connection of the outer second honeycomb structure to the second intermediate tube are preferred. In particular, there is a positive, positive and / or cohesive connection between at least one honeycomb structure and at least one intermediate tube. Particularly preferred is an embodiment in which the intermediate tubes are in intimate contact with each other, in particular non-positively, positively and / or cohesively connected to each other. In particular, a cohesive connection, for example by welding or high-temperature brazing is preferred. Such a connection allows on the one hand advantageously a simple construction of the honeycomb body according to the invention, in which the two honeycomb structures are constructed independently of each other and then subsequently the intermediate tubes can be connected to each other. On the other hand, an intimate connection of the intermediate tubes allows a good heat exchange between the two honeycomb structures, which can be particularly advantageous if larger ones Amounts of liquid reactants lead to a spranghaften cooling of the first honeycomb structure.

According to a further advantageous embodiment of the honeycomb body according to the invention, a gap is formed between the first intermediate tube and the second intermediate tube.

Such a gap may be advantageous if, during operation, a cooling of the second honeycomb structure by the first honeycomb structure, which in turn can be cooled by a liquid reactant, should be prevented as far as possible, for example because the second honeycomb structure has a catalytically active coating which has a has high light-off temperature. Gap widths of 2 to 5 mm are preferred here. In the through-flow direction, the gap can be sealed by a sealing means, in particular a high-temperature and corrosion-resistant sealing means, in order to prevent a part of the exhaust gas from flowing past the honeycomb structures during operation in the exhaust system of a motor vehicle.

According to a further advantageous embodiment, the first and / or the second intermediate tube is provided with support means for supporting on other components.

A system such as that shown above without the formation of support means may be highly sensitive to vibrations, depending on the frequency spectrum of the corresponding internal combustion engine in whose exhaust system the honeycomb body is to be used. By regularly compared to the channel walls very thick at least one intermediate tube with a large mass, there is a system which has resonances especially at low frequencies. However, a corresponding resonance can disturb or damage the entire system. Therefore, it is advantageous to provide support means here, which support the intermediate pipe, in particular on a jacket pipe or on other components such as the exhaust pipe. As support means, for example, rod-shaped support elements can be formed here, which are in particular attached to the front side of the intermediate tube are formed. Furthermore, it is possible, alternatively or additionally, to support a support of the intermediate tube via the feed line to the means for adding a reactant to a jacket tube or another component. For this purpose, a corresponding bore can be provided in the at least one intermediate tube through which the supply line passes and with which it is in particular connected in a materially bonded manner. For this purpose, it is advantageous to form the feed line of a material as stable as possible, such as a metal, in particular a stainless steel tube. Furthermore, it is advantageous to form the feed line of a corrosion-resistant material, which is also correspondingly temperature-stable. Alternatively or additionally, it is also possible that the supply line is provided with a corresponding coating.

In addition to rod-shaped support means can also be sheet-shaped so planar support means may be formed. The support means can also serve as a flow distribution means, which lead to a corresponding distribution of the exhaust gas flow to the two honeycomb structures during operation of the honeycomb body at the same time. The support means are preferably formed at locations where the at least one intermediate tube without training of the support means would have a correspondingly large oscillation amplitude. These are particularly preferably the protruding end regions of the intermediate tube.

According to a further advantageous embodiment of the honeycomb body according to the invention, at least the second honeycomb structure is arranged in a jacket tube and at least one intermediate tube is connected to the jacket tube via support means. This means in particular that no additional connections, such as welding or brazing, between jacket tube and the second honeycomb structure are provided. The second honeycomb structure is then essentially fixed to the adjacent intermediate tube and is thus inserted into the jacket tube. The alignment of the intermediate tube to the shell is now via the support means, so that a permanently substantially equal forces acting on the second honeycomb structure from the jacket. The formation of an intermediate tube with support means advantageously increases the durability of a corresponding honeycomb body. In particular, when using a honeycomb body according to the invention with proppants in the exhaust system of an automobile with a diesel engine, the support means can be designed and configured at appropriate locations, taking into account the corresponding resonant frequencies and high vibration amplitudes in these engines.

According to a further aspect of the inventive concept, an exhaust system for a motor vehicle is proposed which comprises at least one honeycomb body according to the invention. The exhaust gas system has a throughflow direction, which is formed at least one intermediate tube in the flow direction upstream of an end face of at least one of the first and second honeycomb structure protruding. In the flow direction in front of the honeycomb structures, a supply line for a reactant is formed by the jacket tube or by the jacket tube and the at least one intermediate tube.

According to an advantageous embodiment of the exhaust system according to the invention, the liquid supply with a reactant reservoir, in particular Re- duMionsmittelreservoir, preferably a reservoir for urea in aqueous solution, connected. In particular, this is a tank or a reservoir for urea in aqueous solution. Preferably, also conveying means, in particular controllable conveying means such as pumps, are formed, through which a reducing agent can be fed through the feed line into the means for adding a reactant. In particular, urea injections can take place continuously or else in dependence on the current operating state of the engine and / or the exhaust system. This can be done in particular depending on the concentrations of NO and / or NO ₂ . According to a further advantageous embodiment of the exhaust system according to the invention, a second honeycomb body through which a fluid can flow is formed with an SCR coating in the flow direction behind the first and the second honeycomb structure. In this connection, it is particularly preferred that flow mixing means are formed between the first and the second honeycomb structure and the second honeycomb body for mixing a first gas flow flowing through the first honeycomb structure and a second gas flow flowing through the second honeycomb structure.

An exhaust system designed in this way can advantageously be used as an S CR exhaust system, with hydrolysis and thermolysis taking place in the first honeycomb structure as explained above. The flow mixing means particularly preferably ensure that as homogeneous a mixing as possible of the gas streams which can flow through the first and the second honeycomb structure can take place, so that the most uniform possible conversion in the SCR catalyst takes place in the third honeycomb structure and / or in the second honeycomb body can.

According to a further aspect of the inventive concept, a method is proposed for reducing the proportion of nitrogen oxides (NOx) in an exhaust gas stream, comprising the following steps: a) splitting the exhaust gas stream into a peripheral and a central flow, b) oxidizing at least part of the fraction of nitrogen monoxide (NO) in the boundary stream; c) hydrolysis of at least a portion of the portion of urea ((NH ₂ ) ₂ CO) in the central stream; d) mixing the boundary and central flows into a total flow; e) reduction of nitrogen oxides in the total flow.

In this case, the steps b), c) and e) are preferably carried out in honeycomb bodies or honeycomb structures, which are formed with a corresponding coating, such as this has been explained above with reference to a honeycomb body according to the invention. Preference is given in step e) to a selective catalytic reduction of nitrogen oxides.

According to an advantageous embodiment of the method according to the invention urea is introduced into the central flow in aqueous solution.

According to a further advantageous embodiment of the method according to the invention, steps b), c) and e) take place when flowing through in each case a honeycomb structure and / or in each case a honeycomb body.

The statements made above on a honeycomb body according to the invention apply in the same way to the exhaust system according to the invention and can be transferred from the honeycomb body to the exhaust system and vice versa. All the advantages mentioned above in connection with the honeycomb body according to the invention also occur in the exhaust gas system according to the invention and vice versa. The details and advantages disclosed above in particular for the honeycomb body according to the invention and for the exhaust system according to the invention can also be transferred to the method according to the invention and in each case vice versa. In particular, the method according to the invention can be carried out using a honeycomb body according to the invention or an exhaust gas system according to the invention.

In the following, the invention will be explained in more detail with reference to the figures, without the invention being limited to the exemplary embodiments shown there. Show it:

1 shows schematically a longitudinal section through a first exemplary embodiment of a honeycomb body according to the invention; 2 shows schematically a longitudinal section through a second embodiment of a honeycomb body according to the invention,

3 shows a cross section through the first exemplary embodiment of the honeycomb body according to the invention;

4 shows a cross section of a honeycomb body according to the invention;

5 is a schematic longitudinal section through an exhaust system according to the invention;

6 schematically shows a cross section through a third embodiment of a honeycomb body according to the invention; and

Fig. 7 shows schematically a cross section through a fourth exemplary embodiment of a honeycomb body according to the invention.

FIG. 1 shows schematically in longitudinal section a honeycomb body 1 according to the invention with a first honeycomb structure 2 through which a fluid can flow and a second honeycomb structure 3 which can be flowed through radially outside the first honeycomb structure 1. The second honeycomb structure is coaxial with the first honeycomb structure 2 in the present exemplary embodiment. The first 2 and the second honeycomb structure 3 are separated from each other by an intermediate tube 4. The intermediate tube 4 protrudes on both sides in a first axial direction 5 by between 5 and 15 centimeters and in the opposite direction by 0.5 to 2 cm beyond the end faces 6 of the honeycomb structures 2, 3 addition. Furthermore erfϊndungsgemäß means 7 for adding a reactant in the interior 8 of the intermediate tube 4 are formed.

The second honeycomb structure 3 is held in a jacket tube 9. Due to the projecting beyond the end faces 6 intermediate tube 4 takes place during operation of the

Honeycomb body 1 in the exhaust system of an automobile, a division of the exhaust gas flows through the first honeycomb structure 2 and the second honeycomb structure 3. Depending on the design of the honeycomb structures 2, 3 can be achieved by adjusting the diameter of the intermediate tube and the parameters of the honeycomb structures 2 and 3, in particular with regard to cell density, wall thickness and shape of the individual cells a very accurate distribution of the exhaust gas flow. In particular, it is advantageous here to divide the exhaust gas flow such that about two thirds of the exhaust gas flow through the outer second honeycomb structure 3, while about one third of the exhaust gas flow is conducted via the first inner honeycomb structure 2. Furthermore, it is possible and according to the invention, in addition to provide separate upstream Gasstromteilungseinrichtungen, which may for example consist of corresponding funnels or flaps. Furthermore, it is possible to make these distribution devices controllable. In particular, a correspondingly designed movable flap can be provided, with which the ratio of the gas flows, which flow through the first 2 and second honeycomb structure 3 in operation, can be adapted to the current circumstances.

In particular when a hydrolysis catalyst coating is formed on the first honeycomb structure 2, if appropriate a special oxidation catalyst coating on the second honeycomb structure 3 and injection of reducing agent, in particular urea in aqueous solution by the means 7 for addition of a reactant, the quantities can be produced by the distribution devices hydrolyzed urea and thus the amount of ammonia formed can be controlled as needed in a downstream SCR catalyst.

The embodiment shown in Fig. 1 comprises two honeycomb structures 2, 3 which are not only formed coaxially, but also have the same length. In principle, the honeycomb structures 2, 3 can also be formed offset in different lengths and / or against each other. In particular, it is also possible that the honeycomb structures 2, 3 overlap in the first direction 5, but these honeycomb structures 2, 3 can be offset in the first direction 5 relative to one another be educated. However, it is particularly preferred here for at least one subregion to consist in which a section in a radial direction 10 through the honeycomb body 1 comprises both a part of the first honeycomb structure 2 and a part of the second honeycomb structure 3.

When the honeycomb body 1 in the exhaust system of an automobile is installed, 8 of the intermediate tube 4 can through the feed line 11, a reducing agent from an unshown reducing agent reservoir through the means 7 for adding a reactant in the indoor ^■ cavities are input. Preferably, the addition of liquid reducing agents or of reducing agent is at least partially as at least one aerosol. If the first honeycomb structure 2 is provided with a hydrolysis catalyst coating, conversion of the reducing agent can take place here. In particular, when urea is used as the reducing agent, hydrolyzing and thermolysis of the urea occur in the first honeycomb structure, resulting in the formation of ammonia (NH ₃ ). This ammonia may be used for selective catalytic reduction in a suitably designed downstream catalyst. In this case, a conversion of nitrogen oxides (NO _x) to nitrogen (N ₂ ) takes place upon release of water. If the region of the second honeycomb structure 3 is at least partially provided with an oxidation catalyst coating, which may possibly catalyze the formation of additional nitrogen dioxide from nitrogen monoxide, there is a risk of damage or destruction of this region if the reducing agent comes into contact with this region , Therefore, it is advantageous to form the means 7 for adding a reactant in the interior 8 of the intermediate tube 4, since this ensures due to the flow conditions in the exhaust system that no reactant b: zw. no reducing agent comes into contact with the second honeycomb structure 3. Thus, it is advantageously ensured that damage to the oxidation catalytic converter region of the second honeycomb structure 3 is effectively avoided. The length 13 of the projecting region 14 of the intermediate tube 4 is selected so that, together with the specific configuration of the means 7 for adding a reactant, the most uniform possible reactant distribution 12 is ensured when it encounters the end face 6 of the first honeycomb structure.

In the illustrated embodiment, the intermediate tube 4 of the honeycomb body 1 also projects on the opposite end face 6. It is preferred that such a pipe socket 32 is provided with an extension 33 which is in the range of 0.5 to 2 cm. This offers the possibility of fastening support structures 20 in order to enable bilateral support of the honeycomb body 1 in the jacket tube 9.

Fig. 2 shows a further embodiment of a honeycomb body according to the invention in longitudinal section. In addition to the components shown in FIG. 1, this honeycomb body 1 has a third honeycomb structure 15. The third honeycomb structure 15 may be both part of a single honeycomb body 1 together with the second honeycomb structure 3 and the first honeycomb structure 2. Alternatively, the third honeycomb structure 15 may be housed in a separate honeycomb body, in which case the third honeycomb structure 15 is formed downstream of the first honeycomb structure 2 and the second honeycomb structure 3 with respect to a flow direction 16. Between the first 2 and / or the second honeycomb structure 3 and the third honeycomb structure 15, a region 17 without honeycomb structures is formed. This region 17 has an axial length 18. The axial length 18 is chosen so that in this area under normal operating conditions in the exhaust system of a motor vehicle, a mixing of the two gas streams can be achieved, which flow through the first honeycomb structure 2 and the second honeycomb structure 3, so that the third honeycomb structure 15 with a possible well-mixed gas stream is flowed. Alternatively and / or additionally, flow mixing means 19 may be formed, which lead to the best possible mixing of the two gas streams mentioned above. These flow mixing means 19 may, for example in the form of a baffle plate, one or more straight or rounded plates, which are optionally formed offset from each other, be formed with and / or without holes and optionally also in the form of a conventional known based on a honeycomb mixer structure. The axial length 18 is preferably in a range of 30 to 50 mm, particularly preferably in the range of 35 to 45 mm, particularly preferably 40 mm in length.

The exemplary embodiment of a honeycomb body according to the invention shown in FIG. 2 can be used particularly advantageously in a space-saving manner as a system for selective catalytic reduction (SCR) of nitrogen oxides (NO _x) . In particular, the honeycomb body according to the invention allows the implementation of a selective catalytic reduction in which only a partial flow of the exhaust gas is subjected to a hydrolysis in a simple manner particularly space-saving, without additional housing for carriers and complex gas ducts are to be formed. Thus, in particular the honeycomb body 1 according to the invention can be used in a passenger vehicle or the like, ie in areas in which the available installation space for a unit represents a serious restriction for additional exhaust gas components. Here, a very good implementation of the nitrogen oxides can be carried out in a simple manner, without additional components are needed.

Fig. 3 shows a cross section along the section line shown in Fig. 1. Evident is the first honeycomb structure 2, which is formed coaxially with the second honeycomb structure 3. The first honeycomb structure 2 and the second honeycomb structure 3 are separated from each other by the intermediate pipe 4. The second honeycomb structure 3 is held in a jacket tube 9. In the present exemplary embodiment, the honeycomb structure 2, 3 are constructed from at least partially structured layers 25 and essentially smooth layers 26, which form channels 27. The honeycomb structures 2, 3 can be constructed of layers as well as ceramic as a monolith. In particular, at least partially metallic layers 25, 26 are to be understood here as layers, in particular high-temperature-resistant layers Sheet metal or fiber layers. Layers 25, 26 produce a honeycomb structure in which they are wound and / or stacked and subsequently wound. For this purpose, various possibilities are known from the prior art.

4 schematically shows a perspective view of a part of a honeycomb body 1 according to the invention in the projecting region 14 of the intermediate tube 4. In this projecting region 14, support structures 20 are formed, which connect the intermediate tube 4 to the jacket tube 9. The support structures 20 - shown here by way of example as four rod-shaped elements - are preferably designed so that vibrations in the coupled system of intermediate tube and jacket tube are prevented as effectively as possible. One possibility here is to provide the support structures 20 at or adjacent to the end of the projecting region 14 facing away from the honeycomb structures 2, 3. As a result, vibrations of the system can be effectively prevented. It is also possible to form a plurality of support structures 20 in the first axial direction 5, which may preferably also be designed to be offset from one another in the radial direction. The support structures 20 are not limited in their form to stabformige support structures 20, the training in the form of, for example, sheets is possible and according to the invention.

Fig. 5 shows a further exemplary embodiment of a honeycomb body according to the invention in longitudinal section. In the following, only the differences to the embodiments shown above will be listed here. The projecting region 14 of the intermediate tube 4 is provided with means for dividing the flow in this exemplary embodiment. This is on the one hand a rigid funnel 21, which is attached to the intermediate pipe 4 and on the other hand, a movable flap 22 which can be pivoted in the direction of arrow 23. These two measures are exemplary and can also be cumulative or alternative. In particular, the pivotable flap 22 allows a very precise control of the proportions of a gas flow, which flow through the first honeycomb structure 2 and the second honeycomb structure 3. So is a very precise control of the ammonia and / or nitrogen dioxide content in the gas stream after the honeycomb structures 2, 3 possible if corresponding coatings on the honeycomb structures 2, 3 are formed.

Furthermore, FIG. 5 shows schematically the connection of the agent 7 for adding a reactant via a feed line 11 with a reactant reservoir 24.

In the present exemplary embodiment, honeycomb structures 2, 3 are shown which are formed coaxially and overlapping each other, wherein there are partial areas which have no overlap. The honeycomb structures 2, 3 have different lengths and are offset relative to one another. This is also possible in addition to the measures indicated in the embodiments shown above.

6 shows schematically a cross section through a third exemplary embodiment of a honeycomb body 1 according to the invention with a first honeycomb structure 2 and a second honeycomb structure 3. The honeycomb structure each have channel walls 28 which delimit channels 27. The channel walls 28 may be formed as described above by layers 25, 26 or also of ceramic material. For clarity, in both honeycomb structure 2, 3, the channel walls 28 and channels 27 are shown only by way of example.

The first honeycomb structure 2 and the second honeycomb structure 3 are formed by a first intermediate tube 29 and a second intermediate tube 30 located outside the first intermediate tube 29. In the third embodiment, the intermediate tube 29, 30 are separated by a gap 31, which represents an air gap insulation. The width of the gap 31 is preferably in the range of 2 to 5 mm.

7 shows schematically a cross section through a fourth exemplary embodiment of a honeycomb body 1 according to the invention, which differs essentially from the third exemplary embodiment shown in FIG. 6 in that no gap is cut out between the first intermediate tube 29 and the second intermediate tube 30. is formed, but these are in intimate contact. Preferably, the intermediate tubes 29, 30 are positively, positively and / or materially connected. In particular, a cohesive connection by high-temperature brazing and / or welding is advantageous because a heat exchange between the two honeycomb structure 2, 3 can take place here in an advantageous manner.

The honeycomb body according to the invention advantageously enables the formation of exhaust gas systems in which the exhaust gas flow is divided and guided through different honeycomb structures 2, 3. This is particularly advantageous for forming an SCR system in which the first honeycomb structure 2 serves as the hydrolysis catalyst and the second honeycomb structure 3 serves as the oxidation catalyst.

LIST OF REFERENCE NUMBERS

1 honeycomb body

2 first honeycomb structure

3 second honeycomb structure

4 intermediate pipe

5 first axial direction

6 front side

7 means for adding a reactant

8 Interior of the intermediate pipe

9 casing pipe

10 radial direction

11 supply line

12 Reactant distribution

13 Length of the overhang

14 outstanding area

15 third honeycomb structure

16 flow direction

17 area

18 axial length

19 flow mixing agent

20 support structure

21 funnels

22 flap

23 direction

24 reactant reservoir

25 at least partially structured situation

26 substantially smooth position

27 channel

28 duct wall

29 first intermediate pipe second intermediate pipe gap pipe socket extension

Claims

claims

1. honeycomb body (1) with a first fluid-flow through a honeycomb structure (2) and a radially outside of the first honeycomb structure (2) lying second fluid-flow through a honeycomb structure (3), wherein the first (2) and the second Honeycomb structure (3) by at least one intermediate tube (4, 29, 30) are separated from each other, characterized in that the at least one intermediate tube (4, 29, 30) at least on one side in a first axial direction (5) by between 5 and 15 cm protrudes beyond an end face (6) of at least one of the honeycomb structures (2, 3).

2. honeycomb body (1) according to claim 1, wherein the means (7) for adding a reactant in the interior (8) of the intermediate tube (4, 29, 30) are formed

3. honeycomb body (1) according to claim 1 or 2, wherein in a second direction substantially opposite to the first axial direction (5) behind the first (2) and the second honeycomb structure (3), a third honeycomb structure (15) is formed.

4. honeycomb body (1) according to any one of the preceding claims, wherein at least one honeycomb structure (2, 3, 15) has a catalytically active coating.

The honeycomb body (1) according to claim 4, wherein the first honeycomb structure (2) comprises a hydrolysis catalyst coating.

A honeycomb body (1) according to claim 4 or 5, wherein the second honeycomb structure (3) comprises an oxidation catalyst coating.

7. honeycomb body (1) according to one of claims 4 to 6, wherein the third honeycomb structure (15) has a SCR (selective catalytic reduction) coating.

8. honeycomb body (1) according to one of the preceding claims, wherein the intermediate tube (4) comprises a first intermediate tube (29) and at least partially outside the first intermediate tube (29) lying second intermediate tube (30).

9. honeycomb body (1) according to claim 9, wherein between the first intermediate tube (29) and the second intermediate tube (30), a gap (31) is formed.

10. honeycomb body (1) according to any one of the preceding claims, wherein the first (29) and / or the second intermediate tube (30) is provided with support means (20) for supporting on other components.

11. honeycomb body (1) according to one of the preceding claims, wherein at least the second honeycomb structure (3) in a jacket tube (9) is arranged and at least one intermediate tube (4, 29, 30) via support means (20) with the jacket tube (9 ) connected is.

12. An exhaust system for a motor vehicle, comprising at least one honeycomb body (1) according to one of claims 1 to 11, with a flow direction (16), wherein the at least one intermediate tube (4, 29, 30) in the flow direction (16) upstream of a Front side of at least one of the first (2) and second honeycomb structure (3) protrudes and in which in the flow direction (16) in front of the honeycomb structures (2, 3) a feed line (11) for a reactant through the jacket tube (9) or - the jacket tube ( 9) and the at least one intermediate tube (4, 29, 30) is formed, wherein the supply line (11) is connected to a means (7) for supplying a reactant in the interior of the intermediate tube (4, 29, 30).

13. The exhaust system of claim 12, wherein the liquid supply is connected to a reactant reservoir (24).

14. The exhaust system according to any one of claims 12 or 13, wherein a second fluid-permeable honeycomb body (1) with an SCR coating in the flow direction (16) behind the first (2) and the second honeycomb structure (3) is formed ,

15. An exhaust system according to claim 14, wherein between the first (2) and the second honeycomb structure (3) and the second honeycomb body (1) Strömungsverniischungsmittel (19) for mixing one through the first

Honeycomb structure (2) flowing through the first gas stream and a through the second honeycomb structure (3) flowing through the second gas stream are formed.

16. A method of reducing the level of nitrogen oxides (NOx) in an exhaust gas stream, comprising the steps of: a) dividing the exhaust gas stream into a peripheral and a central flow, b) oxidizing at least a portion of the proportion of nitrogen monoxide (NO) in the boundary stream ; c) hydrolysis of at least a portion of the portion of urea ((NH ₂ ) ₂ CO) in the central stream; d) mixing the boundary and central flows into a total flow; e) reduction of nitrogen oxides in the total flow.

17. The method of claim 16, wherein urea is introduced into the central stream in aqueous solution.

18. The method of claim 16 or 17, wherein the steps b), c) and e) when flowing through each of a honeycomb structure (2, 3, 15) and / or in each case a honeycomb body.