JP2020516815A - Exhaust gas system - Google Patents

Abstract

The present invention relates to an exhaust gas system (1) for after-treatment of exhaust gas of an internal combustion engine, the catalyst (3) for oxidizing the exhaust gas, which is continuously arranged in the flow direction (2) of the exhaust gas. And/or a catalyst for storing nitrogen oxides, an introduction point (4) for supplying a reducing agent, an SCR catalyst (6) for selectively catalytically reducing nitrogen oxides, and a particulate filter The particulate filter (7) is arranged downstream of the SCR catalyst (6) when viewed in the flow direction (2), and is downstream of the particulate filter (7) when viewed in the flow direction (2). Relates to an exhaust gas system (1) in which a second SCR catalyst (8) and/or an ammonia slip catalyst is arranged.

Description

The present invention relates to an exhaust gas system for after-treatment of exhaust gas of an internal combustion engine, for storing a catalyst and/or nitrogen oxides for oxidizing the exhaust gas, which are arranged continuously in a flow direction of the exhaust gas. The present invention relates to an exhaust gas system including the catalyst, the introduction point for supplying the reducing agent, the SCR catalyst for selectively catalytically reducing nitrogen oxides, and the particulate filter.

Exhaust gas aftertreatment systems use various types of catalysts to ensure the most efficient and comprehensive conversion and removal of harmful substances contained in the exhaust gas. In particular, for example, a catalyst that absorbs nitrogen oxide (NO _x ) and binds thereto is used. Furthermore, catalysts are known which cause the conversion of nitrogen oxides into less harmful reaction products. Furthermore, a filter that removes particulates of a specific size from exhaust gas is also known.

A disadvantage of the device for purifying the exhaust gas of an internal combustion engine, which is well known in the prior art, is that the placement of the individual catalysts in the exhaust gas system is not optimal, and thus the individual catalysts exhibit the optimal effect according to their individuality. There is no point. In particular, in the devices known in the prior art, a so-called SCR catalyst for selectively catalytically reducing nitrogen oxides is often arranged downstream of the particulate filter. As a result, it is no longer possible to operate the SCR catalyst at its optimum operating point.

The object of the present invention is therefore to provide an exhaust gas system for the aftertreatment of the exhaust gas of an internal combustion engine, which system has an optimized arrangement of the individual catalysts and a further optimized configuration.

The above-mentioned problems relating to an exhaust gas system are solved by an exhaust gas system having the features of claim 1.

One embodiment of the invention is an exhaust gas system for the aftertreatment of the exhaust gas of an internal combustion engine, wherein a catalyst for oxidizing the exhaust gas and/or nitrogen arranged consecutively in the flow direction of the exhaust gas. A catalyst for storing oxides, an introducing point for supplying a reducing agent, an SCR catalyst for selectively catalytically reducing nitrogen oxides, and a particulate filter are provided, and the particulate filter has a flow direction. And the second SCR catalyst and/or the ammonia slip catalyst are arranged on the downstream side of the SCR catalyst in the flow direction and on the downstream side of the particulate filter in the flow direction.

By arranging the SCR catalyst on the upstream side of the particulate filter and arranging the SCR catalyst on the downstream side of the particulate filter, it is possible to provide a unit that functions better. In particular, the operating conditions of the SCR catalyst downstream of the particulate filter are based on the large volume that the particulate filter usually has and the cell geometry and cell density required to enable sufficient filtration of the exhaust gas. Getting worse.

This is because, for example, the temperature of the exhaust gas after it has passed through the particulate filter is significantly reduced, which negatively impairs the effect of the SCR catalyst. In addition, the particulate filter can cause a large pressure drop, which causes the exhaust gas to no longer have a sufficiently high flow rate for the SCR catalyst housed downstream to ensure optimum conversion. There isn't. For example, the incorporation of the SCR catalyst into the particulate filter by partial coating of the particulate filter is not optimal. This is because the cell densities and cell geometries of the honeycomb bodies of commonly used particulate filters are not optimal for the selective catalytic reduction of exhaust gas in SCR catalysts.

With the SCR catalyst housed upstream, a first aftertreatment of the exhaust gas can be carried out, in particular using the already introduced and vaporized reducing agent, which is typically composed of an aqueous urea solution, Nitrogen oxides can be converted into water and nitrogen.

Purification of the exhaust gas stream is achieved by the subsequent particulate filter. Then, the SCR catalyst connected to the downstream side of the particulate filter can convert the nitrogen oxides still contained in the exhaust gas. Particularly advantageously, the second SCR catalyst may therefore have a different cell geometry and/or cell density than the first SCR catalyst and also have a chemically different active coating. You can stay. Thereby, for example, the conversion of nitrogen oxides can be achieved even at relatively low temperatures and flow rates.

It is particularly advantageous if the first SCR catalyst arranged upstream of the particulate filter in the flow direction is electrically heatable. Electrical heating of the SCR catalyst is advantageous in order to heat the exhaust gas to the required operating temperature as quickly as possible so that selective catalytic reduction can be carried out.

It is also advantageous if the first SCR catalyst, viewed in the flow direction, has an extension length of up to 80 mm along the flow direction, the first SCR catalyst preferably being less than 50 mm. It has an extension length, particularly preferably an extension length of less than 40 mm. The relatively short extension length of the first SCR catalyst with respect to the particulate filter or the second SCR catalyst has a negligible effect on the flow to the subsequent particulate filter, and thus the particulate filter. It is advantageous to retain good removal results in.

In one preferred embodiment, the first SCR catalyst, viewed in the flow direction, is spaced from the particulate filter by a maximum of 20 mm along the flow direction, preferably less than 10 mm and particularly preferably less than 5 mm. It is characterized by being arranged. The smallest possible spacing is advantageous in order to be able to combine the pressure losses that occur due to the first SCR catalyst and the particulate filter. This facilitates the design of the exhaust system.

It is also preferable that the first SCR catalyst as viewed in the flow direction and the second SCR catalyst as viewed in the flow direction are formed as a module unit together with the particulate filter. This is advantageous for ease of installation.

Furthermore, it is advantageous if each SCR catalyst and the particulate filter are formed by one common honeycomb body. This is advantageous in that it keeps the number of mounted parts as small as possible, which simplifies the mounting.

Further, the honeycomb body of the particulate filter has a different cell geometry and/or cell density from the honeycomb body of the first SCR catalyst when viewed in the flow direction and the honeycomb body of the second SCR catalyst when viewed in the flow direction. It is advantageous to have This is particularly advantageous in order to optimally adapt the individual components to their respective applications and to achieve a pressure drop across the individual components which is as low as possible overall. Furthermore, the cell geometry can influence, for example, filter characteristics and velocity distribution.

Also, the cell geometry and/or cell density of the honeycomb body of the first SCR catalyst as viewed in the flow direction and/or the chemically active coating of the honeycomb body and/or the coating amount of the honeycomb body is It is also appropriate if the second SCR catalyst differs from the honeycomb body cell geometry and/or cell density and/or chemically active coating in view.

This is particularly advantageous, for example in order to be able to adapt the honeycomb body to the changed flow rate in the region of the second SCR catalyst. Also, in the area of the second SCR catalyst, changes in the exhaust gas composition must be taken into consideration. This is because the second SCR catalyst is housed on the downstream side of the particulate filter. This makes it possible, for example, to use relatively high cell densities or reduced cell cross-sections, without the risk of blockage of the flow channels formed in the honeycomb body. The coatings can also advantageously be adapted to normally relatively low ammonia-nitrogen oxide concentrations, yet still result in the most comprehensive nitrogen oxide conversion possible.

Preferably, the coating amount of the first SCR catalyst in the flow direction is greater than the coating amount of the second SCR catalyst in the flow direction.

Advantageous refinements of the invention are set out in the subclaims and in the description of the drawing below.

Hereinafter, the present invention will be described in detail based on an embodiment with reference to the drawings.

1 is a cross-sectional view of an exemplary exhaust gas system with multiple catalysts.

FIG. 1 shows a cross-sectional view of the exhaust gas system of the exhaust gas system 1. The exhaust gas system 1 comprises a plurality of catalysts which are arranged in a casing and are connected to each other by conduits so that the exhaust gas can pass through the catalysts.

In the embodiment shown in FIG. 1, when viewed in the flow direction 2 of the exhaust gas, first, the catalyst 3 for oxidizing the exhaust gas is arranged. Next, an introduction point 4 is provided in which a reducing agent such as urea aqueous solution can be introduced into the exhaust gas system. A vaporizing member 5 is arranged immediately next to the introduction point 4, and the reducing agent can be vaporized in the vaporizing member 5 and then reacted as nitrogen with nitrogen oxide in the exhaust gas.

Further downstream is a first SCR catalyst 6 in which nitrogen oxides in the exhaust gas react with ammonia and the chemically active coating of the SCR catalyst 6. Forms nitrogen and water.

A particulate filter 7 used for filtering exhaust gas is connected to the downstream side of the first SCR catalyst 6, and the particulate filter 7 particularly removes soot particulates from the exhaust gas.

A second SCR catalyst 8 follows the particulate filter 7. In the second SCR catalyst 8, the same reaction as in the first SCR catalyst 6 is chemically performed.

The advantage of such a configuration is that the nitrogen oxides in the exhaust gas have already been reduced before the exhaust gas flows into the particulate filter. Therefore, the exhaust gas flowing into the first SCR catalyst still has a particularly high temperature and the exhaust gas distribution over the cross section of the flow section has not yet been negatively impaired by the particulate filter. This allows a particularly effective conversion of nitrogen oxides in the exhaust gas. Often, large volume particulate filters significantly reduce the temperature of the exhaust gas, so that the chemical reactions within the SCR catalyst contained downstream do not usually proceed optimally. The second SCR catalyst is substantially used to reduce the nitrogen oxide moieties that have not yet been reduced in the first SCR catalyst.

Instead of or in addition to the second SCR catalyst, an ammonia slip catalyst may be attached which is capable of binding excess ammonia (NH ₃ ) that has not been converted when reducing the nitrogen oxides in the exhaust gas. . In this way, it is possible to avoid the breakthrough of ammonia into the exhaust gas, which can lead, for example, to ammonia leaking into the surrounding environment and causing odors or environmental pollution.

The embodiment shown in FIG. 1 has no particular limiting features and is used to demonstrate the idea of the invention.

Claims (8)

An exhaust gas system (1) for after-treatment of exhaust gas of an internal combustion engine, wherein the catalyst (3) and/or nitrogen for oxidising the exhaust gas, which are arranged continuously in the flow direction (2) of the exhaust gas. An exhaust gas system including a catalyst for storing oxides, an introduction point (4) for supplying a reducing agent, an SCR catalyst (6) for selectively catalytically reducing nitrogen oxides, and a particulate filter ( In 1),
The particulate filter (7) is arranged on the downstream side of the SCR catalyst (6) when viewed in the flow direction (2), and the particulate filter (7) of the SCR catalyst (6) is viewed in the flow direction (2). The exhaust gas system (1), characterized in that a second SCR catalyst (8) and/or an ammonia slip catalyst is arranged downstream. The exhaust gas system (1) according to claim 1, wherein the first SCR catalyst (6) arranged upstream of the particulate filter (7) in the flow direction (2) is electrically heatable. 1). The first SCR catalyst (6) when viewed in the flow direction (2) has a maximum extension length of 80 mm along the flow direction (2), and the first SCR catalyst (6) 3.) The exhaust gas system (1) according to claim 1 or 2, wherein) preferably has an extension length of less than 50 mm, particularly preferably less than 40 mm. Viewed in the flow direction (2), the first SCR catalyst (6) with respect to the particulate filter (7) is at most 20 mm along the flow direction (2), preferably less than 10 mm and especially The exhaust gas system (1) according to any one of claims 1 to 3, which is preferably arranged with a spacing of less than 5 mm. The first SCR catalyst (6) viewed in the flow direction (2) and the second SCR catalyst (8) viewed in the flow direction (2) are modules together with the particulate filter (7). Exhaust gas system (1) according to any one of claims 1 to 4, which is formed as a unit. The exhaust gas system (1) according to any one of claims 1 to 5, wherein the SCR catalyst (6, 8) and the particulate filter (7) are formed by one common honeycomb body. The honeycomb body of the particulate filter (7) is the same as the honeycomb body of the first SCR catalyst (6) when viewed in the flow direction (2), and the second body when viewed in the flow direction (2). Exhaust gas system (1) according to any one of claims 1 to 6, wherein the SCR catalyst (8) has a different cell geometry and/or cell density than the honeycomb body. Cell geometry and/or cell density of the honeycomb body and/or chemically active coating of the honeycomb body and/or the honeycomb of the first SCR catalyst (6) as viewed in the flow direction (2). The coating amount of the body differs from the cell geometry and/or cell density and/or the chemically active coating of the honeycomb body of the second SCR catalyst (8) when viewed in the flow direction (2). The exhaust gas system (1) according to any one of claims 1 to 7.

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