Exhaust gas aftertreatment system in an exhaust gas system of an ammonia combustion engine, method for exhaust gas aftertreatment, and use of an N2O decomposition catalyst

Abstract

An exhaust gas system of an ammonia combustion engine, in the exhaust gas aftertreatment system in the exhaust gas system through which the exhaust gas flow of the ammonia combustion engine can pass, includes a passive SCR catalyst (14), an oxidation catalyst (16) capable of oxidizing ammonia contained in the exhaust gas flow, and a controlled SCR catalyst (22). The oxidation catalyst (16) is disposed in the exhaust gas system downstream of the passive SCR catalyst (14), and the controlled SCR catalyst (22) is disposed in the exhaust gas system downstream of the oxidation catalyst (16). The exhaust gas aftertreatment system further includes at least one N2O decomposition catalyst (24) disposed in the exhaust gas system upstream of the passive SCR catalyst (14) or downstream of the passive SCR catalyst (14), the oxidation catalyst (16), and / or the controlled SCR catalyst (22). In addition, a method for exhaust gas aftertreatment and the use of an N2O decomposition catalyst (24) are shown.

Description

Technical Field

[0001] The present invention relates to an exhaust gas aftertreatment system in an exhaust gas system of an ammonia combustion engine, a method for exhaust gas aftertreatment of an exhaust gas stream generated by an ammonia combustion engine, and the use of an N2O decomposition catalyst.

Background Art

[0002] An ammonia combustion engine is an internal combustion engine that uses ammonia as fuel and is a typical alternative to a "classical" internal combustion engine that uses hydrocarbons such as natural gas, gasoline, or diesel as fuel. The use of an ammonia combustion engine is particularly desirable when replacing hydrocarbon-derived from fossil resources with so-called "green" ammonia as fuel.

[0003] In this context, the term "green ammonia" refers to ammonia produced based on hydrogen generated by electrolysis, and the electrical energy required for the electrolysis is obtained from a renewable energy source such as wind or solar energy. As a result, by using an ammonia combustion engine, it is possible to reduce carbon dioxide emissions and thus minimize greenhouse gas emissions.

[0004] However, an ammonia combustion engine produces an exhaust gas stream that is fundamentally different from that produced by a classical internal combustion engine. In particular, it is important to prevent the ammonia combustion engine from simply emitting other greenhouse gases that have a greenhouse gas coefficient equal to or higher than that of carbon dioxide instead of carbon dioxide.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, an object of the present invention is to enable at least reducing the emission of compounds having a greenhouse gas coefficient higher than that of carbon dioxide in the exhaust gas aftertreatment of the exhaust gas flow generated by an ammonia combustion engine, particularly.

Means for Solving the Problems

[0006] The object of the present invention is achieved in the present invention by an exhaust gas aftertreatment system in an exhaust gas system of an ammonia combustion engine, wherein the exhaust gas flow of the ammonia combustion engine can flow through. The exhaust gas aftertreatment system includes a passive SCR catalyst, an oxidation catalyst capable of oxidizing ammonia contained in the exhaust gas flow, and a controlled SCR catalyst. The oxidation catalyst is disposed in the exhaust gas system downstream of the passive SCR catalyst, and the controlled SCR catalyst is disposed in the exhaust gas system downstream of the oxidation catalyst. The exhaust gas aftertreatment system further includes at least one N2O decomposition catalyst located in the exhaust gas system upstream of the passive SCR catalyst or downstream of the passive SCR catalyst, the oxidation catalyst, and / or the controlled SCR catalyst.

[0007] It has been recognized that the exhaust gas flow generated by an ammonia combustion engine contains nitrous oxide, i.e., dinitrogen monoxide (also called "laughing gas" or N2O), in a related proportion. However, since the greenhouse effect that nitrous oxide can cause exceeds 250 times the greenhouse effect that carbon dioxide can cause over a time scale of 100 years, the emission of nitrous oxide should be avoided as much as possible or must be avoided as much as possible.

[0008] For this reason, in the present invention, at least one N2O decomposition catalyst that at least partially chemically converts nitrous oxide contained in the exhaust gas flow is used in the exhaust gas aftertreatment system. That is, the N2O decomposition catalyst is provided to at least partially oxidize (reduce) nitrous oxide contained in the exhaust gas flow.

[0009] Furthermore, in the present invention, the N2O decomposition catalyst is arranged in the exhaust gas aftertreatment system such that the composition of the exhaust gas flow when flowing through the N2O decomposition catalyst is adapted to the N2O decomposition catalyst and the conversion rate and selectivity of the N2O decomposition catalyst are optimized.

[0010] Suitable N2O decomposition catalysts are selected, for example, from zeolites (in particular iron-supported zeolites), spinel compounds, hexaaluminate compounds, perovskite compounds, and rhodium-containing catalysts. Cordierite can be used as the carrier of the N2O decomposition catalyst.

[0011] The term "SCR catalyst" refers to a catalyst used for the selective catalytic reduction of nitrogen oxides (NO x ).

[0012] A passive SCR catalyst is an uncontrolled SCR catalyst. A passive SCR catalyst acts without being controlled based on the measurement data of a measurement probe (a reducing agent is added based on the measurement data of the measurement probe). Instead, a passive SCR catalyst uses ammonia contained in the exhaust gas flow, that is, ammonia discharged from an ammonia combustion engine without being burned, to reduce nitrogen oxides contained in the exhaust gas flow.

[0013] A passive SCR catalyst is, in particular, for reducing the content of nitrogen oxides in the exhaust gas flow expected at the start of exhaust gas aftertreatment, so that the functions of each component of the exhaust gas aftertreatment system arranged in the exhaust gas flow downstream of the passive SCR catalyst are not impaired by nitrogen oxides present in the exhaust gas flow.

[0014] In addition, since a passive SCR catalyst does not depend on the measurement data of a measurement probe, it can be arranged at a position in the exhaust gas system where the concentration of nitrogen oxides in the exhaust gas flow is too high to perform measurements or cannot be performed precisely enough.

[0015] Moreover, the passive SCR catalyst can function as a highly cost-effective scavenger for catalyst poisons that may be contained in the exhaust gas stream. A catalyst poison is a compound that limits the functionality of the catalyst, at least temporarily and especially permanently, such that the catalyst can no longer perform its intended function. Catalyst poisons contained in the exhaust gas stream can be derived from the lubricating oil and / or the ignition jet fuel of an ammonia combustion engine.

[0016] The oxidation catalyst disposed in the exhaust gas stream downstream of the passive SCR catalyst acts to remove ammonia contained in the exhaust gas stream. In an ammonia combustion engine, ammonia slip is expected to occur. That is, unreacted ammonia can enter the exhaust gas stream from the combustion chamber of the ammonia combustion engine. Therefore, the oxidation catalyst is provided to enable the function and accurate control of each component of the exhaust gas aftertreatment system and to prevent or at least minimize the emission of unwanted ammonia.

[0017] At the same time, the oxidation catalyst can function to remove any other oxidizable gases, such as hydrogen (H2) and / or hydrocarbons, that may be contained in the exhaust gas stream and that did not burn or did not burn completely. These components can occur in the exhaust gas stream as residues of so-called "pilot fuel".

[0018] According to the present invention, the oxidation catalyst is disposed upstream of the controlled SCR catalyst in the exhaust gas stream. This prevents or at least reduces the controlled SCR catalyst from being affected by the fluctuating ammonia concentration in the exhaust gas stream.

[0019] In contrast to the passive SCR catalyst, the controlled SCR catalyst operates based on the measurement data of a measurement probe assigned to the controlled SCR catalyst to determine the nitrogen oxide concentration in the exhaust gas stream. This enables accurate control of the nitrogen oxide concentration in the exhaust gas stream downstream of the controlled SCR catalyst.

[0020] Furthermore, a metering supply unit for supplying ammonia to the exhaust gas flow can be provided upstream of the control SCR catalyst. In that case, the at least one N2O decomposition catalyst is arranged in the exhaust gas system upstream or downstream of the metering supply unit.

[0021] The ammonia content in the exhaust gas flow can be adjusted via the metering supply unit, thereby controlling the catalytic conversion of nitrogen oxides still present in the exhaust gas flow in the control SCR catalyst arranged downstream of the metering supply unit.

[0022] In particular, the metering supply unit further includes a mixing module for mixing the ammonia supplied into the exhaust gas flow by the metering supply unit and other components of the exhaust gas flow. For example, the mixing module is a connecting pipe fluidly connecting the metering supply unit and the control SCR catalyst.

[0023] Therefore, the exhaust gas aftertreatment system according to the present invention is characterized in that, in particular, the types and arrangements of the components of the exhaust gas aftertreatment system can be optimally adapted to each component present in the exhaust gas flow, i.e., to the chemical composition of the exhaust gas flow, at the position of each component in the exhaust gas flow.

[0024] It is also possible to position the N2O decomposition catalyst within the exhaust gas aftertreatment system such that each component contained in the exhaust gas flow at the position of the N2O decomposition catalyst has the effect of promoting the reaction by the N2O decomposition catalyst. Thereby, a synergistic effect in the conversion of undesirable constituents of the exhaust gas flow is obtained by the intended arrangement of the components of the exhaust gas aftertreatment system.

[0025] In a variant, at least two components of the exhaust gas aftertreatment system that are consecutive in the exhaust gas flow are housed in a common functional module.

[0026] For example, a passive SCR catalyst and an N2O decomposition catalyst, a controlled SCR catalyst and an N2O decomposition catalyst, or an oxidation catalyst and an N2O decomposition catalyst form a common functional module.

[0027] In another modification, at least one of the components of the exhaust gas aftertreatment system is a composite catalyst that combines two or more functions of each of the catalysts included in the exhaust gas aftertreatment system into one component.

[0028] As an example, the composite catalyst may be, for example, a combination of an N2O decomposition catalyst and an SCR catalyst that simultaneously decomposes nitrogen oxides and nitrous oxide according to the reaction equation N2O + NO → N2 + NO2, and then selectively catalytically reduces the resulting NO2.

[0029] The composite catalyst can also be, for example, a combination of an N2O decomposition catalyst and an oxidation catalyst that simultaneously decomposes ammonia and nitrous oxide according to the reaction equation 3N2O + 2NH3 → 4N2 + 3H2O.

[0030] In the exhaust gas aftertreatment system, it is also possible to use or have a plurality of N2O decomposition catalysts. In this case, depending on the position of the N2O decomposition catalyst within a series of components of the exhaust gas aftertreatment system, an N2O decomposition catalyst optimally designed for the composition of the exhaust gas flow expected at the location of each N2O decomposition catalyst in the exhaust gas system can be used.

[0031] Before the treatment by the exhaust gas aftertreatment system, the temperature of the exhaust gas flow may be in the range of 250°C to 550°C. Therefore, the arrangement of the components of the exhaust gas aftertreatment system according to the present invention in the direction of the flow of the exhaust gas flow is designed to convert undesirable constituents in the exhaust gas flow, such as ammonia, nitrogen oxides, and nitrous oxide, into environmentally compatible substances by subjecting the exhaust gas flow with an initial temperature in the range of 250°C to 550°C to a series of assumed reactions.

[0032] The exhaust gas aftertreatment system may include an exhaust gas turbocharger through which the exhaust gas discharged from the cylinder of the ammonia combustion engine, i.e., the exhaust gas flow, passes. The exhaust gas turbocharger enables at least partially utilizing the thermal energy contained in the exhaust gas flow. Thereby, by additionally affecting the temperature of the exhaust gas flow as intended, each component of the exhaust gas aftertreatment system used in the exhaust gas flow downstream or upstream of the exhaust gas turbocharger can be operated within an optimal temperature range.

[0033] The exhaust gas turbocharger can be used at any suitable position within the exhaust gas aftertreatment system. For example, the exhaust gas turbocharger can be positioned in the exhaust gas flow upstream or downstream of the passive SCR catalyst, downstream of the oxidation catalyst, downstream of the controlled SCR catalyst, or downstream of the N2O decomposition catalyst.

[0034] The exhaust gas turbocharger has the effect of reducing the temperature of the exhaust gas flow. This means that the temperature of the exhaust gas flow is lower downstream than upstream of the exhaust gas turbocharger. Therefore, when arranging the exhaust gas turbocharger within the exhaust gas aftertreatment system, in particular, each component of the exhaust gas aftertreatment system that operates at a higher temperature is arranged upstream of the exhaust gas turbocharger in the exhaust gas flow, and each component of the exhaust gas aftertreatment system that operates at a lower temperature is arranged downstream of the exhaust gas turbocharger in the exhaust gas flow. Thereby, surely, all components of the exhaust gas aftertreatment system can be operated within an optimal temperature range.

[0035] The exhaust gas turbocharger is in particular a single-stage turbocharger.

[0036] In addition, before the treatment by the exhaust gas aftertreatment system, the exhaust gas stream may contain ammonia up to 10,000 ppm, in particular up to 8,000 ppm of ammonia, for example up to 5,000 ppm of ammonia, and up to 5,000 ppm of nitrogen oxides.

[0037] All numerical values in ppm (parts per million) represent volume concentrations under process conditions.

[0038] In addition, before the treatment by the exhaust gas aftertreatment system, the exhaust gas stream may contain up to 500 ppm of nitrous oxide.

[0039] Before the treatment by the exhaust gas aftertreatment system, the exhaust gas stream may contain water in a proportion of 5 to 25 volume percent, in particular 10 to 25 volume percent, for example 10 to 20 volume percent.

[0040] The pressure of the exhaust gas stream is in particular at most 5 bar.

[0041] Thus, the components of the exhaust gas stream observed at a particular point during the operation of an ammonia combustion engine can vary widely depending on the load situation. Even under such conditions, a series of components of the exhaust gas aftertreatment system provided in the present invention and related to each other enable optimal exhaust gas aftertreatment.

[0042] In addition, the composition of the exhaust gas stream to be treated is fundamentally different from the composition of the exhaust gas stream of a classical internal combustion engine and from the composition of the exhaust gas stream during a technical process such as the production of nitric acid where nitrous oxide is likewise produced as a by - product.

[0043] In a given operating mode, it is also possible to configure the exhaust gas aftertreatment system so as not to use an N2O decomposition catalyst. The given operating mode is determined in particular based on the fact that the exhaust gas stream contains no nitrous oxide at all or, if it does, at a concentration below a predefined operating mode threshold.

[0044] The output of the ammonia combustion engine is, in particular, 560 kW or more. This type of ammonia combustion engine is suitable for use in the ocean, for example, as a ship's engine.

[0045] In the present invention, the above object is further achieved by a method for post-treatment of exhaust gas in an exhaust gas post-treatment system for an exhaust gas flow generated by an ammonia combustion engine, wherein nitrous oxide present in the exhaust gas flow is at least partially converted by an N2O decomposition catalyst.

[0046] The method according to the present invention reliably prevents nitrous oxide from being released into the environment, or at least enables minimizing the amount of nitrous oxide released into the environment, regardless of the amount of nitrous oxide present in the exhaust gas of the ammonia combustion engine.

[0047] The exhaust gas post-treatment system is, in particular, the above-described exhaust gas post-treatment system. The features and properties of the exhaust gas post-treatment system according to the present invention also apply equally to the method according to the present invention, and vice versa.

[0048] Furthermore, the above object is achieved by using an N2O decomposition catalyst in the exhaust gas post-treatment system of the ammonia combustion engine.

[0049] The exhaust gas post-treatment system is, in particular, the above-described exhaust gas post-treatment system. The features and properties of the exhaust gas post-treatment system according to the present invention also apply equally to the use according to the present invention, and vice versa.

Brief Description of the Drawings

[0050] Further features and characteristics of the present invention will be described based on the following description of exemplary embodiments (which should not be understood in a limiting sense) and the following drawings.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0051] FIG. 1 schematically shows a first embodiment of an exhaust gas aftertreatment system 10 for an ammonia combustion engine 12 according to the present invention.

[0052] The ammonia combustion engine 12 uses ammonia as fuel and converts the ammonia to generate an exhaust gas flow (shown as arrow P in FIG. 1).

[0053] The ammonia combustion engine 12 is fluidly connected to the exhaust gas aftertreatment system 10, and the direction of the exhaust gas flow is as indicated by arrow P in FIG. 1. That is, each component of the exhaust gas aftertreatment system 10 shown on the right side of the reference point in FIG. 1 is located downstream of that reference point, and each component of the exhaust gas aftertreatment system 10 shown on the left side of the reference point in FIG. 1 is located upstream of that reference point.

[0054] The exhaust gas aftertreatment system 10 of FIG. 1 includes a passive SCR catalyst 14, an oxidation catalyst 16, a metering supply unit 18 for supplying ammonia to the exhaust gas flow, a mixing module 20, a control SCR catalyst 22, and an N2O decomposition catalyst 24, along the direction of the exhaust gas flow. These are connected to each other as a flow, and each forms a component of the exhaust gas aftertreatment system 10.

[0055] The exhaust gas aftertreatment system 10 is used to purify the exhaust gas generated by the ammonia combustion engine 12 by chemically converting undesirable components of the exhaust gas stream.

[0056] Its purpose is to convert nitrogen oxides (NO x ), ammonia (NH3), and nitrous oxide (N2O) contained in the exhaust gas stream into nitrogen (N2), oxygen (O2), and water (H2O) as thoroughly as possible. This is made possible by each component of the exhaust gas aftertreatment system 10 arranged to function in conjunction. Details will be described below.

[0057] Before treatment by the exhaust gas aftertreatment system, the exhaust gas stream contains, among other things, up to 10,000 ppm of ammonia, up to 5,000 ppm of nitrogen oxides, up to 500 ppm of nitrous oxide, and water in a proportion of 5 - 25 volume percent. It will be understood that the exact composition of the exhaust gas stream depends on the ammonia combustion engine 12 used and its load state at that time.

[0058] Figure 6 shows a schematic flow diagram of the content of certain constituents of the exhaust gas stream, namely nitrogen oxides (NO x ), nitrous oxide (N2O), and ammonia (NH3). These concentrations are as low as possible at the end of the exhaust gas aftertreatment system 10 located downstream of the exhaust gas stream, i.e., after the exhaust gas stream has flowed through each component of the exhaust gas aftertreatment system 10.

[0059] In Figure 6, only the relative content of each constituent of the exhaust gas stream is graphed to show the functions of the various catalysts of the exhaust gas aftertreatment system 10. It will be understood that depending on the design and load situation of the ammonia combustion engine 12, the various components in the exhaust gas stream can be present in various ratios.

[0060] First, the exhaust gas stream contacts the passive SCR catalyst 14. The passive SCR catalyst 14 removes nitrogen oxides from the exhaust gas stream, and ammonia present in the exhaust gas stream is partially consumed for the chemical conversion of nitrogen oxides. However, the passive SCR catalyst 14 is inert, i.e., resistant, to dinitrogen monoxide.

[0061] As shown in FIG. 6, the passive SCR catalyst 14 can be designed such that the exhaust gas stream 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 only slightly decreases as compared to the composition of the exhaust gas stream upstream of the passive SCR catalyst 14.

[0062] Thereby, each component of the exhaust gas aftertreatment system 10 arranged along the exhaust gas stream downstream of the passive SCR catalyst 14 is prevented from being adversely affected by an overly high concentration of nitrogen oxides present in the exhaust gas stream. In particular, the concentration of nitrogen oxides in the exhaust gas stream downstream of the passive SCR catalyst 14 can be made substantially independent of the concentration of nitrogen oxides in the exhaust gas stream upstream of the passive SCR catalyst 14.

[0063] The oxidation catalyst 16 is disposed in the exhaust gas stream downstream of the passive SCR catalyst 14 in the exhaust gas stream. The oxidation catalyst 16 selectively oxidizes ammonia present in the exhaust gas stream so that the exhaust gas stream is substantially free of ammonia downstream of the oxidation catalyst 16.

[0064] Depending on the achievable selectivity of such an oxidation catalyst, nitrogen oxides and dinitrogen monoxide may be produced as undesirable by-products of the oxidation of ammonia, as shown by the increase in content in FIG. 6.

[0065] The oxidation catalyst 16 preferably operates passively, i.e., without being controlled based on a measurement probe assigned to the oxidation catalyst 16.

[0066] The newly generated nitrogen oxide typically has a lower concentration compared to the nitrogen oxide contained in the exhaust gas flow before being processed by the exhaust gas aftertreatment system 10. However, in order to remove this nitrogen oxide, a controlled SCR catalyst 22 is provided in the exhaust gas flow downstream of the oxidation catalyst 16.

[0067] The operation of the controlled SCR catalyst 22 is controlled via a measurement sensor (not shown) that measures the concentration of nitrogen oxide in the exhaust gas flow.

[0068] For the controlled operation of the controlled SCR catalyst 22, ammonia is supplied by a metering supply unit 18 downstream of the oxidation catalyst 16 and upstream of the controlled SCR catalyst 22. This ammonia is dispersed into the exhaust gas flow passing through the mixing module 20. The mixing module 20 is designed as a connecting pipe, for example.

[0069] A relatively small amount of ammonia metered and supplied in such an intended manner via the metering supply unit 18 is then decomposed in the controlled SCR catalyst 22.

[0070] As is apparent from FIG. 6, dinitrogen monoxide in the exhaust gas flow is not decomposed via the passive SCR catalyst 14, the oxidation catalyst 16, or the controlled SCR catalyst 22.

[0071] Therefore, in the present invention, at least one N2O decomposition catalyst 24 for oxidizing or reducing dinitrogen monoxide contained in the exhaust gas flow is additionally provided. In this way, the content of dinitrogen monoxide can be reduced and minimized compared to the composition of the exhaust gas flow before being processed by the exhaust gas aftertreatment system 10 according to the present invention.

[0072] In the first embodiment, the N2O decomposition catalyst 24 is located in the exhaust gas flow downstream of the passive SCR catalyst 14, the oxidation catalyst 16, and the controlled SCR catalyst 22. In this way, an N2O decomposition catalyst that is not compatible with nitrogen oxide and ammonia can be used.

[0073] Instead, all components located in the exhaust gas stream upstream of the N2O decomposition catalyst 24 are preferably resistant to nitrous oxide.

[0074] In this context, the expression "not compatible with" the constituents of the exhaust gas stream means the following. That is, the desired chemical conversion by each component cannot occur, or at least, if it does occur, the yield and / or selectivity decreases when the corresponding constituent of the exhaust gas stream is present at a concentration exceeding a threshold value, for example, a concentration exceeding 10 ppm.

[0075] In contrast, the expression "resistant to" the components of the exhaust gas stream is used to mean the following. That is, the desired chemical conversion by each component can proceed substantially without change even if the corresponding component of the exhaust gas stream is present or is present at a concentration exceeding another threshold value, for example, a concentration exceeding 100 ppm.

[0076] Optionally, the exhaust gas aftertreatment system 10 may include an exhaust gas turbocharger (not shown) disposed in the exhaust gas stream upstream of the passive SCR catalyst 14 or between two of the aforementioned components of the exhaust gas aftertreatment system 10. In this case, the position of the exhaust gas turbocharger is selected so that the operating conditions are optimal for the components used in the exhaust gas aftertreatment system 10.

[0077] FIG. 2 shows a second embodiment of the exhaust gas aftertreatment system 10 according to the present invention.

[0078] Since the second embodiment is substantially equivalent to the first embodiment, only the differences will be described below. The same reference numerals mean the same or functionally identical components, and refer to the above description.

[0079] In the second embodiment, the N2O decomposition catalyst 24 is disposed in the exhaust gas stream downstream of the passive SCR catalyst 14 and upstream of the oxidation catalyst 16.

[0080] Therefore, in this embodiment, the passive SCR catalyst 14 is resistant to nitrous oxide, and the N2O decomposition catalyst 24 is resistant to ammonia. This is because ammonia is first decomposed in the oxidation catalyst 16. It is also possible to design the N2O decomposition catalyst 24 such that the amount of ammonia and / or nitrogen oxides still contained in the exhaust gas stream supports the function of the N2O decomposition catalyst 24.

[0081] On the other hand, the oxidation catalyst 16 and the controlled SCR catalyst 22 either do not have resistance to nitrous oxide, or the threshold values of these components for nitrous oxide can be selected to be lower. This is because the content of nitrous oxide in the exhaust gas stream has already been at least reduced by the N2O decomposition catalyst 24 before the exhaust gas stream reaches the oxidation catalyst 16.

[0082] Optionally, as in the first embodiment, a further N2O decomposition catalyst 24 can be arranged in the exhaust gas stream downstream of the controlled SCR catalyst 22. This further catalyst decomposes the remaining nitrous oxide or the nitrous oxide generated in the oxidation catalyst 16.

[0083] In principle, the passive SCR catalyst 14 and the N2O decomposition catalyst 24 may exist in the form of a composite catalyst, which, as described above, not only converts nitrogen oxides by the excess ammonia in the exhaust gas stream, but also at the same time at least partially converts the nitrous oxide contained in the exhaust gas stream.

[0084] FIG. 3 shows a third embodiment of the exhaust gas aftertreatment system 10 according to the present invention.

[0085] Since the third embodiment is substantially equivalent to the above-described embodiment, only the differences will be described below. The same reference numerals mean the same or functionally identical components, and reference is made to the above description.

[0086] In the third embodiment, the N2O decomposition catalyst 24 is arranged in the exhaust gas stream upstream of the passive SCR catalyst 14.

[0087] Thus, in the third embodiment, the N2O decomposition catalyst 24 is a component of the exhaust gas aftertreatment system 10 that is first exposed to the exhaust gas stream generated by the ammonia combustion engine 12.

[0088] Therefore, in this case, the N2O decomposition catalyst 24 is designed to be resistant to all of the components of the exhaust gas stream that are expected to be present due to the use of the ammonia combustion engine 12, particularly resistant to nitrogen oxides and ammonia.

[0089] Instead, both the passive SCR catalyst 14 and the oxidation catalyst 16, and the controlled SCR catalyst 22 may not be compatible with dinitrogen monoxide, or at least, their thresholds for dinitrogen monoxide can be made lower.

[0090] FIG. 4 shows a fourth embodiment of the exhaust gas aftertreatment system 10 according to the present invention.

[0091] Since the fourth embodiment is substantially equivalent to the above embodiment, only the differences will be described below. The same reference numerals denote the same or functionally identical components, and reference is made to the above description.

[0092] In the fourth embodiment, the N2O decomposition catalyst 24 is disposed in the exhaust gas stream downstream of the passive SCR catalyst 14 and the oxidation catalyst 16 and upstream of the metering supply unit 18, and thus upstream of the controlled SCR catalyst 22.

[0093] In this embodiment, the N2O decomposition catalyst 24 need not be designed to be resistant to ammonia, and may not be resistant to nitrogen oxides, or at least, can be designed such that its threshold for nitrogen oxides is lower than that in the case of the third embodiment.

[0094] In addition, the controlled SCR catalyst 22 may not be compatible with dinitrogen monoxide, or at least, its threshold for dinitrogen monoxide can be made lower.

[0095] On the other hand, in this embodiment, both the passive SCR catalyst 14 and the oxidation catalyst 16 are resistant to nitrous oxide.

[0096] FIG. 5 shows a fifth embodiment of the exhaust gas aftertreatment system 10 according to the present invention.

[0097] Since the fifth embodiment is substantially equivalent to the above-described embodiment, only the differences will be described below. The same reference numerals denote the same or functionally identical components, and reference is made to the above description.

[0098] In the fifth embodiment, the N2O decomposition catalyst 24 is disposed in the exhaust gas stream downstream of the passive SCR catalyst 14, the oxidation catalyst 16, and the metering supply unit 18 and upstream of the control SCR catalyst 22.

[0099] In this embodiment, the necessary design of the components of the exhaust gas aftertreatment system 10 used is approximately equivalent to that in the fourth embodiment. However, the N2O decomposition catalyst 24 is at least resistant to ammonia in the sense that the amount of ammonia in the exhaust gas stream required for the operation of the control SCR catalyst 22 must not exceed the threshold value of the N2O decomposition catalyst 24.

[0100] Disposing the N2O decomposition catalyst 24 at various positions in the exhaust gas stream is similarly included in the spirit of the present invention. Therefore, each of the above-described embodiments can be arbitrarily combined with each other.

[0101] Overall, the feature of the exhaust gas aftertreatment system 10 according to the present invention is that a series of components of the exhaust gas aftertreatment system 10 are related to each component expected in the exhaust gas stream of the ammonia combustion engine, their ratios, and in addition, their compatibility with those components.

Claims

1. An exhaust gas aftertreatment system (10) in an exhaust gas system of an ammonia combustion engine (12), the exhaust gas aftertreatment system (10) being in an exhaust gas system through which the exhaust gas flow of the ammonia combustion engine (12) can pass, a passive SCR catalyst (14), an oxidation catalyst (16) capable of oxidizing ammonia contained in the exhaust gas flow, and a controlled SCR catalyst (22), wherein the oxidation catalyst (16) is disposed in the exhaust gas system downstream of the passive SCR catalyst (14), and the controlled SCR catalyst (22) is disposed in the exhaust gas system downstream of the oxidation catalyst (16). At least one N ２ O decomposition catalyst (24), which is disposed in the exhaust gas system upstream of the passive SCR catalyst (14) or downstream of the passive SCR catalyst (14), the oxidation catalyst (16), and / or the control SCR catalyst (22). ２ An exhaust gas aftertreatment system (10) further comprising an O decomposition catalyst (24).

2. A metering supply unit (18) for supplying ammonia to the exhaust gas flow is present upstream of the controlled SCR catalyst (22). said at least one N ２ The exhaust gas aftertreatment system according to claim 1, wherein the at least one NO decomposition catalyst (24) is disposed in the exhaust gas system upstream or downstream of the metering supply unit (18).

3. One of the components of the exhaust gas aftertreatment system (10) is a composite catalyst that combines two or more functions of each of the catalysts (14, 16, 22, 24) included in the exhaust gas aftertreatment system (10) into one component. The exhaust gas aftertreatment system according to claim 1 or 2.

4. Before treatment by the exhaust gas aftertreatment system (10), the temperature of the exhaust gas flow is in the range of 250°C to 550°C. The exhaust gas aftertreatment system according to any one of claims 1 to 3.

5. Before treatment by the exhaust gas aftertreatment system (10), the exhaust gas flow contains ammonia at a maximum of 10,000 ppm and nitrogen oxides at a maximum of 5,000 ppm. The exhaust gas aftertreatment system according to any one of claims 1 to 4.

6. Before treatment by the exhaust gas aftertreatment system (10), the exhaust gas flow contains nitrous oxide at a maximum of 500 ppm. The exhaust gas aftertreatment system according to any one of claims 1 to 5.

7. Before treatment by the exhaust gas aftertreatment system (10), the exhaust gas flow contains water at a ratio of 5 to 25 volume percent. The exhaust gas aftertreatment system according to any one of claims 1 to 6.

8. The output of the ammonia combustion engine (12) is 560 kW or more. The exhaust gas aftertreatment system according to any one of claims 1 to 7.

9. A method for exhaust gas aftertreatment in an exhaust gas aftertreatment system (10) for an exhaust gas flow generated by an ammonia combustion engine (12), A method in which nitrous oxide present in the exhaust gas stream is at least partially converted by an N ２ O decomposition catalyst (24).

10. Use of an NO decomposition catalyst (24) in an exhaust gas aftertreatment system (10) of an ammonia combustion engine (12). ２ ​

Images