EXHAUST GAS AFTERTREATMENT SYSTEM IN AN EXHAUST GAS SYSTEM OF AN AMMONIA COMBUSTION ENGINE, METHOD AND USE THEREOF

Abstract

An exhaust gas aftertreatment system in the exhaust gas system of an ammonia combustion engine, wherein the exhaust gas system can be traversed by an exhaust gas flow of the ammonia combustion engine, including a passive SCR catalyst, an oxidation catalyst with which ammonia contained in the exhaust gas flow can be oxidized, and a regulated SCR catalyst. The oxidation catalyst is arranged in the exhaust gas system downstream of the passive SCR catalyst and the regulated SCR catalyst is arranged in the exhaust gas system downstream of the oxidation catalyst. The exhaust gas aftertreatment system further comprises at least one N2O decomposition catalyst arranged in the exhaust gas system upstream of the passive SCR catalyst or downstream of the passive SCR catalyst, the oxidation catalyst, and/or the regulated SCR catalyst.

Claims

1. An exhaust gas aftertreatment system in an exhaust gas system of an ammonia combustion engine, the exhaust gas system can be traversed by an exhaust gas flow of the ammonia internal combustion engine, comprising: a passive SCR catalyst, an oxidation catalyst with which ammonia contained in the exhaust gas flow can be oxidized, and a regulated SCR catalyst, wherein the oxidation catalyst is arranged in the exhaust gas system downstream of the passive SCR catalyst, and the regulated SCR catalyst is arranged in the exhaust gas system downstream of the oxidation catalyst, wherein the exhaust gas aftertreatment system further comprises at least one N.sub.2O decomposition catalyst that is arranged in the exhaust gas system upstream of the passive SCR catalyst or downstream of at least one of the passive SCR catalyst (14), the oxidation catalyst, or the regulated SCR catalyst.

2. The exhaust gas aftertreatment system according to claim 1, further comprising a metering unit for supplying ammonia to the exhaust gas flow upstream of the regulated SCR catalyst and wherein the at least one N.sub.2O decomposition catalyst is arranged in the exhaust gas system upstream of the metering unit or in the exhaust gas system downstream of the metering unit.

3. The exhaust gas aftertreatment system according to claim 1, wherein one of the components of the exhaust gas aftertreatment system is a combined catalyst which combines in one component two or more functions of the catalysts contained in the exhaust gas aftertreatment system.

4. The exhaust gas aftertreatment system according to claim 1, wherein, prior to the treatment with the exhaust gas aftertreatment system, the exhaust gas flow has a temperature in the range of 250 to 550 C.

5. The exhaust gas aftertreatment system according to claim 1, wherein, prior to the treatment with the exhaust gas aftertreatment system, the exhaust gas flow comprises up to 10,000 ppm ammonia and up to 5,000 ppm nitrogen oxides.

6. The exhaust gas aftertreatment system according to claim 1, wherein, prior to the treatment with the exhaust gas aftertreatment system, the exhaust gas flow comprises up to 500 ppm dinitrogen monoxide.

7. The exhaust gas aftertreatment system according to claim 1, wherein, prior to the treatment with the exhaust gas aftertreatment system, the exhaust gas flow comprises water in a proportion of 5 to 25 percent by volume.

8. The exhaust gas aftertreatment system according to claim 1, wherein the ammonia combustion engine has a power of 560 kW or more.

9. A method for the exhaust gas aftertreatment of an exhaust gas flow produced by an ammonia combustion engine in an exhaust gas aftertreatment system of claim 1, wherein a dinitrogen monoxide present in the exhaust gas flow is at least partially converted by an N.sub.2O decomposition catalyst.

10. A method of using an N.sub.2O decomposition catalyst in an exhaust gas aftertreatment system of an ammonia combustion engine of claim 1 to at least partially convert dinitrogen monoxide in an exhaust gas flow produced by the ammonia combustion engine.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0050] Further features and properties of the invention result from the following description of exemplary embodiments which are not to be understood in a limiting sense, and from the figures. In the figures:

[0051] FIG. 1 shows a first embodiment of an exhaust gas aftertreatment system according to the invention of an ammonia combustion engine,

[0052] FIG. 2 shows a second embodiment of the exhaust gas aftertreatment system according to the invention from FIG. 1,

[0053] FIG. 3 shows a third embodiment of the exhaust gas aftertreatment system according to the invention from FIG. 1,

[0054] FIG. 4 shows a fourth embodiment of the exhaust gas aftertreatment system according to the invention from FIG. 1,

[0055] FIG. 5 shows a fifth embodiment of the exhaust gas aftertreatment system according to the invention from FIG. 1, and

[0056] FIG. 6 shows a schematic flow diagram of the composition of an exhaust gas flow flowing through the exhaust gas aftertreatment system according to FIG. 1.

DETAILED DESCRIPTION

[0057] FIG. 1 schematically shows a first embodiment of an exhaust gas aftertreatment system 10 according to the present disclosure for an ammonia combustion engine 12.

[0058] The ammonia combustion engine 12 uses ammonia as fuel and converts it, generating an exhaust gas flow, which is indicated as arrow P in FIG. 1.

[0059] The ammonia combustion engine 12 is fluidly connected to the exhaust gas aftertreatment system 10, wherein the exhaust gas flow has a flow direction as shown by the arrow P in FIG. 1. In other words, components of the exhaust gas aftertreatment system 10 shown to the right of a respective reference point in FIG. 1 are located downstream of the respective reference point, and components of the exhaust gas aftertreatment system 10 shown in FIG. 1 to the left of a respective reference point are located upstream of the respective reference point.

[0060] The exhaust gas aftertreatment system 10 according to FIG. 1 comprises a passive SCR catalyst 14 along the flow direction of the exhaust gas flow, an oxidation catalyst 16, a metering unit 18 for supplying ammonia to the exhaust gas flow, a mixing module 20, a regulated SCR catalyst 22, and an N.sub.2O decomposition catalyst 24, which are each connected to one another in terms of flow and each form a component of the exhaust gas aftertreatment system 10.

[0061] The exhaust gas aftertreatment system 10 is used to clean the exhaust gas produced by the ammonia combustion engine 12 by chemically converting unwanted components of the exhaust gas flow.

[0062] The aim is to achieve as complete a conversion as possible of nitrogen oxides (NO.sub.x), ammonia (NH.sub.3), and dinitrogen monoxide (N.sub.2O) contained in the exhaust gas flow into nitrogen (N.sub.2), oxygen (O.sub.2), and water (H.sub.2O). This is made possible by the coordinated sequence according to the invention of the components of the exhaust gas aftertreatment system 10, described in more detail below.

[0063] Before the treatment with the exhaust gas aftertreatment system, the exhaust gas flow comprises in particular up to 10,000 ppm ammonia, up to 5,000 ppm nitrogen oxides, up to 500 ppm of dinitrogen monoxide, and water in a proportion of 5 to 25 percent by volume. It will be understood that the exact composition of the exhaust gas flow is dependent on the ammonia combustion engine 12 used and on the currently prevailing load state.

[0064] FIG. 6 shows a schematic flow diagram of the contents of selected constituents of the exhaust gas flow, namely nitrogen oxides (NO.sub.x), dinitrogen monoxide (N.sub.2O), and ammonia (NH.sub.3), the concentration of which is to be as low as possible at the end of the exhaust gas aftertreatment system 10 situated downstream in the exhaust gas flow, i.e., after the exhaust gas flow has flowed through the components of the exhaust gas aftertreatment system 10.

[0065] In FIG. 6, only the relative contents of the respective constituent of the exhaust gas flow are plotted in order to illustrate the function of the various catalysts of the exhaust gas aftertreatment system 10. It will be understood that different ratios of the different components in the exhaust gas flow can also be present, depending on the design and load situation of the ammonia combustion engine 12.

[0066] First, the exhaust gas flow meets the passive SCR catalyst 14, which removes nitrogen oxides from the exhaust gas flow, the ammonia present in the exhaust gas flow being partially consumed for the chemical conversion of the nitrogen oxides. However, the passive SCR catalyst 14 is inert, or tolerant, to dinitrogen monoxide.

[0067] As can be seen in FIG. 6, the passive SCR catalyst 14 can be designed such that the exhaust gas flow downstream of the passive SCR catalyst 14 is substantially free of nitrogen oxides while the content of dinitrogen monoxide remains substantially unchanged and the content of ammonia is only slightly decreased compared to the composition of the exhaust gas flow upstream of the passive SCR catalyst 14.

[0068] This ensures that the components of the exhaust gas aftertreatment system 10 arranged in the exhaust gas flow downstream of the passive SCR catalytic converter 14 are not adversely affected by excessively high nitrogen oxide concentrations present in the exhaust gas flow. In particular, it can be ensured that the concentration of nitrogen oxides in the exhaust gas flow downstream of the passive SCR catalyst 14 is substantially independent of the concentration of nitrogen oxides in the exhaust gas flow upstream of the passive SCR catalyst 14.

[0069] The oxidation catalyst 16 is arranged in the exhaust gas flow downstream of the passive SCR catalyst 14 in the exhaust gas flow. The oxidation catalyst 16 selectively oxidizes ammonia present in the exhaust gas flow so that downstream of the oxidation catalyst 16 the exhaust gas flow is substantially free of ammonia.

[0070] Depending on the achievable selectivity of such an oxidation catalyst, nitrogen oxides and dinitrogen monoxide can also be produced as undesired by-products of the ammonia oxidation, as shown by the increasing contents in FIG. 6.

[0071] The oxidation catalyst 16 is preferably operated passively, i.e., without regulation on the basis of a measuring probe assigned to the oxidation catalyst 16.

[0072] In order to remove the newly formed quantity of nitrogen oxides, which however will typically be lower than the concentration of nitrogen oxides in the exhaust gas flow before the treatment with the exhaust gas aftertreatment system 10, a regulated SCR catalyst 22 is provided in the exhaust gas flow downstream of the oxidation catalyst 16.

[0073] The operation of the regulated SCR catalyst 22 is controlled via a measurement sensor (not shown) which measures the concentration of nitrogen oxides in the exhaust gas flow.

[0074] For the regulated operation of the regulated SCR catalyst 22, ammonia is supplied downstream of the oxidation catalyst 16 and upstream of the regulated SCR catalyst 22 by means of the metering unit 18, which ammonia is distributed in the exhaust gas flow while flowing through the mixing module 20, which is designed for example as a connecting pipe.

[0075] The comparatively small quantity of ammonia metered in a targeted fashion in this way via the metering unit 18 is in turn decomposed in the regulated SCR catalyst 22.

[0076] As is clear from the illustration in FIG. 6, no decomposition of dinitrogen monoxide in the exhaust gas flow takes place via the passive SCR catalyst 14, the oxidation catalyst 16, or the regulated SCR catalyst 22.

[0077] Therefore, according to the present disclosure, at least one N.sub.2O decomposition catalyst 24 is additionally provided that oxidizes or reduces dinitrogen monoxide contained in the exhaust gas flow. In this way, the content of dinitrogen monoxide can be lowered and minimized compared to the composition of the exhaust gas flow before the treatment with the exhaust gas aftertreatment system 10 according to the present disclosure.

[0078] In the first embodiment, the N.sub.2O decomposition catalyst 24 is situated in the exhaust gas flow downstream of the passive SCR catalyst 14, the oxidation catalyst 16, and the regulated SCR catalyst 22. In this way, an N.sub.2O decomposition catalyst can be used that is incompatible with nitrogen oxides and ammonia.

[0079] In return, all components situated in the exhaust gas flow upstream of the N.sub.2O decomposition catalyst 24 are preferably tolerant to dinitrogen monoxide.

[0080] In this context, the expression incompatible with a constituent of the exhaust gas flow means that the desired chemical conversion carried out by the respective component cannot take place, or at least can take place only with reduced yield and/or selectivity, if the corresponding constituents of the exhaust gas flow are present in a concentration that is above a threshold value, for example in a concentration of more than 10 ppm.

[0081] In contrast, the expression tolerant to a component of the exhaust gas flow is used to mean that the desired chemical conversion carried out by the respective component can proceed substantially unchanged even if the corresponding component of the exhaust gas flow is present, or is present in a concentration which is above a second threshold value, for example in a concentration of more than 100 ppm.

[0082] Optionally, the exhaust gas aftertreatment system 10 can have an exhaust gas turbocharger (not shown) which is arranged in the exhaust gas flow upstream of the passive SCR catalyst 14 or between any two of the previously described components of the exhaust gas aftertreatment system 10. In this case, the position of the exhaust gas turbocharger is selected such that optimal operating conditions are set for the components of the exhaust gas aftertreatment system 10 that are used.

[0083] FIG. 2 shows a second embodiment of the exhaust gas aftertreatment system 10 according to the present disclosure.

[0084] The second embodiment substantially corresponds to the first embodiment so that only differences will be discussed below. Identical reference signs denote identical or functionally identical components, and reference is made to the above statements.

[0085] In the second embodiment, the N.sub.2O decomposition catalyst 24 is arranged in the exhaust gas flow downstream of the passive SCR catalyst 14 and upstream of the oxidation catalyst 16.

[0086] Accordingly, in this embodiment the passive SCR catalyst 14 is tolerant to dinitrogen monoxide and the N.sub.2O decomposition catalyst 24 is tolerant to ammonia, since the ammonia is first decomposed in the oxidation catalyst 16. It is also possible for the N.sub.2O decomposition catalyst 24 to be designed such that the amount of ammonia and/or nitrogen oxides still contained in the exhaust gas flow supports the function of the N.sub.2O decomposition catalyst 24.

[0087] In turn, the oxidation catalyst 16 and the regulated SCR catalyst 22 are not tolerant to dinitrogen monoxide, or the threshold value of these components with respect to dinitrogen monoxide can be selected lower, because the content of dinitrogen monoxide in the exhaust gas flow has already been at least lowered by the N.sub.2O decomposition catalyst 24 before the exhaust gas flow reaches the oxidation catalyst 16.

[0088] Optionally, a further N.sub.2O decomposition catalyst 24 can be arranged in the exhaust gas flow downstream of the regulated SCR catalyst 22, analogously to the first embodiment, which further catalyst decomposes residual contents of dinitrogen monoxide, or dinitrogen monoxide produced in the oxidation catalyst 16.

[0089] In principle, the passive SCR catalyst 14 and the N.sub.2O decomposition catalyst 24 may also be present in the form of a combined catalyst which not only converts nitrogen oxides with excess ammonia in the exhaust gas flow as described above, but at the same time at least partially converts the dinitrogen monoxide contained in the exhaust gas flow.

[0090] FIG. 3 shows a third embodiment of the exhaust gas aftertreatment system 10 according to the present disclosure.

[0091] The third embodiment substantially corresponds to the previous embodiments so that only differences will be discussed below. Identical reference signs denote identical or functionally identical components, and reference is made to the above statements.

[0092] In the third embodiment, the N.sub.2O decomposition catalyst 24 is arranged in the exhaust gas flow upstream of the passive SCR catalyst 14.

[0093] Thus, in the third embodiment the N.sub.2O decomposition catalyst 24 is the first component of the exhaust gas aftertreatment system 10 that is exposed to the exhaust gas flow produced by the ammonia combustion engine 12.

[0094] Therefore, in this case, the N.sub.2O composition catalyst 24 is designed to be tolerant to all components of the exhaust gas flow that are expected to be present due to the use of the ammonia combustion engine 12, and in particular tolerant to nitrogen oxides and ammonia.

[0095] In return, both the passive SCR catalyst 14, the oxidation catalyst 16, and also the regulated SCR catalyst 22 may be incompatible with dinitrogen monoxide, or at least their threshold value can be lowered with respect to dinitrogen monoxide.

[0096] FIG. 4 shows a fourth embodiment of the exhaust gas aftertreatment system 10 according to the present disclosure.

[0097] The fourth embodiment substantially corresponds to the previous embodiments so that only differences will be discussed below. Identical reference signs denote identical or functionally identical components, and reference is made to the above statements.

[0098] In the fourth embodiment, the N.sub.2O decomposition catalyst 24 is arranged in the exhaust gas flow downstream of the passive SCR catalyst 14 and the oxidation catalyst 16 and upstream of the metering unit 18 and thus of the regulated SCR catalyst 22.

[0099] In this embodiment, the N.sub.2O decomposition catalyst 24 does not have to be designed to be tolerant to ammonia, and can either be designed not tolerant to nitrogen oxides or at least to have a lower threshold value with regard to nitrogen oxides than in the third embodiment.

[0100] In addition, the regulated SCR catalyst 22 can be incompatible with dinitrogen monoxide, or at least its threshold value with regard to dinitrogen monoxide can be lowered.

[0101] On the other hand, in this embodiment both the passive SCR catalyst 14 and the oxidation catalyst 16 are tolerant to dinitrogen monoxide.

[0102] FIG. 5 shows a fifth embodiment of the exhaust gas aftertreatment system 10 according to the invention.

[0103] The fifth embodiment substantially corresponds to the previous embodiments, so that only differences will be discussed below. Identical reference signs denote identical or functionally identical components, and reference is made to the above statements.

[0104] In the fifth embodiment, the N.sub.2O decomposition catalyst 24 is arranged in the exhaust gas flow downstream of the passive SCR catalyst 14, the oxidation catalyst 16, and the metering unit 18, and upstream of the regulated SCR catalyst 22.

[0105] In this embodiment, the necessary design of the components that are used of the exhaust gas aftertreatment system 10 corresponds approximately to that of the fourth embodiment. However, the N.sub.2O decomposition catalyst 24 is at least tolerant to ammonia in the sense that the amounts of ammonia in the exhaust gas flow required for the operation of the regulated SCR catalyst 22 must not be above the threshold value of the N.sub.2O decomposition catalyst 24.

[0106] An arrangement of multiple N.sub.2O decomposition catalysts 24 at different positions within the exhaust gas flow is likewise within the meaning of the invention. The previously described embodiments can thus optionally be combined with one another.

[0107] Overall, the exhaust gas aftertreatment system 10 according to the invention is characterized in that the sequence of the components of the exhaust gas aftertreatment system 10 is coordinated with the components that are to be expected in the exhaust gas flow of an ammonia combustion engine and the proportions thereof, and at the same time with regard to the compatibility with these components.

[0108] While the disclosure has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.