System for treatment of ammonia combustion exhaust gas

Abstract

This invention provides a treatment system for ammonia combustion exhaust gas that can simultaneously reduce leaked NH3 and suppress the byproduct N2O. The system treats the combustion exhaust gas from marine engines that use ammonia as the main fuel. It includes an SCR catalyst (3) for treating NOx in the combustion exhaust gas, and an ASC (5) for treating leaked NH3 downstream of the SCR catalyst (3). The ratio of the volume of the SCR catalyst (3) in contact with the exhaust gas to the volume of the ASC (5) is adjusted so that the NH3 concentration after treating the leaked NH3 and the N2O concentration generated during the treatment of the leaked NH3 are below a specified concentration.

Description

Technical Field

[0001] This invention relates to a treatment system for ammonia combustion exhaust gas, specifically, to a treatment system for ammonia combustion exhaust gas capable of suppressing N2O generation and reducing the volume of ASC. Background Technology

[0002] Patent Document 1 discloses that NH3 leakage in exhaust gas can be suppressed by using an ammonia leakage catalyst (ASC), and NOx can be reduced using a selective catalytic reduction (SCR) catalyst. Patent Document 1 further describes that the ASC is positioned downstream of the SCR catalyst, and that NOx is removed by reacting with NH3 in the SCR catalyst. It further describes that if NH3 is present after the SCR catalyst for some reason, it is oxidized by the ASC, which removes NH3. The ASC processes all gases in the same way as the SCR. Therefore, when the ASC is installed in a large two-stroke engine, since all exhaust gases need to be processed, the size of the ASC is the same as that of the SCR catalyst.

[0003] Therefore, Patent Document 1 points out that since SCR catalysis is a very large device, adding an excessively large ASC device would be a problem.

[0004] Furthermore, Patent Document 1 points out that N2O becoming a byproduct of NH3 oxidation in ASCs is also a problem. It discloses that a temperature exceeding 400°C is required to achieve effective N2O removal, which is an exhaust gas temperature that is not easily achievable in high-efficiency marine engines.

[0005] Based on this viewpoint, Patent Document 1 discloses the following method: highly adjusting the molar ratio so that NH3 and NOx in the exhaust gas treated by the SCR catalyst become equivalent molar reactions, thereby reducing the presence of excess or unreacted NH3 after the reaction and suppressing ammonia leakage.

[0006] However, although the idea behind this method is considered excellent, there are problems with the increased size of the device structure in order to succeed in practical applications, such as in cases where NOx is loaded on a ship or manufactured at sea. Furthermore, there are various issues that need to be studied, such as improving the accuracy of various gas sensors and eliminating time delays in the control sequence.

[0007] [Existing Technical Documents]

[0008] [Patent Literature]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2024-52583

[0010] [Patent Document 2] Japanese Patent Application Publication No. 2023-182938 Summary of the Invention

[0011] The problem the invention aims to solve

[0012] Patent Document 2 confirms the following: considering that the activation of the N2O decomposition catalyst requires about 500°C, a first processing unit is arranged upstream of the exhaust receiver, and the N2O decomposition rate is increased to 60% to 73% at a temperature of 600°C to 800°C (see Table 1 of the Examples).

[0013] This technology is valuable in achieving N2O treatment in the exhaust gas treatment of ammonia fuel.

[0014] Without strictly controlling the molar ratio of NH3 to NOx in the exhaust gas as described in Patent Document 1, and without setting high-temperature conditions during N2O decomposition, the inventors investigated the reduction of leaked ammonia (hereinafter, as needed, "leaked NH3"). The results showed that the N2O concentration in the exhaust gas was not at a level requiring treatment. However, since there is a trade-off between reducing leaked ammonia and N2O byproducts, a method was developed to reduce emitted ammonia by decreasing leaked NH3 while simultaneously suppressing N2O byproducts, thus minimizing emitted N2O. As a result, this invention was completed.

[0015] Therefore, the purpose of this invention is to provide a treatment system for ammonia combustion exhaust gas that can simultaneously reduce NH3 leakage and suppress N2O byproducts.

[0016] Furthermore, other aspects of the present invention become clear from the following description.

[0017] Technical means to solve the problem

[0018] The above-mentioned problems are solved by the following inventions.

[0019] 1. A system for treating ammonia combustion exhaust gas from marine engines that use ammonia as the main fuel, wherein,

[0020] It is equipped with an SCR catalyst for treating NOx in the combustion exhaust gas.

[0021] An ASC (Anti-Synthetic Filter) is installed downstream of the SCR catalyst to treat leaked NH3.

[0022] The ratio of the volume of the SCR catalyst in contact with the exhaust gas to the volume of the ASC is adjusted so that the NH3 concentration after treating the leaked NH3 and the N2O concentration generated during the treatment of the leaked NH3 are below a specified concentration.

[0023] The ratio of the volume of the SCR catalyst to the volume of the ASC is such that, when the sum of the volumes of the SCR catalyst and the ASC is set to 1,

[0024] The lower limit of the volume of the ASC is a value calculated based on the NH3 concentration of the combustion exhaust gas, the target value of the NH3 concentration after treating the leaked NH3, the catalytic performance of the ASC, the catalytic performance of the SCR catalyst, and the space velocity SV (1 / h) of the exhaust gas relative to the SCR catalyst and the ASC.

[0025] The upper limit of the volume of the ASC is a value calculated based on the NH3 concentration of the combustion exhaust gas, the target value of the NH3 concentration after treating the leaked NH3, the catalytic performance of the ASC, the catalytic performance of the SCR catalyst, and the space velocity SV (1 / h) of the exhaust gas relative to the SCR catalyst and the ASC.

[0026] 2. A system for treating ammonia combustion exhaust gas from marine engines that use ammonia as the main fuel, wherein...

[0027] It is equipped with an SCR catalyst for treating NOx in the combustion exhaust gas.

[0028] An ASC (Anti-Synthetic Filter) is installed downstream of the SCR catalyst to treat leaked NH3.

[0029] The ratio of the volume of the SCR catalyst in contact with the exhaust gas to the volume of the ASC is adjusted so that the NH3 concentration after treating the leaked NH3 and the N2O concentration generated during the treatment of the leaked NH3 are below a specified concentration.

[0030] The ratio of the volume of the SCR catalyst to the volume of the ASC is such that, when the sum of the volumes of the SCR catalyst and the ASC is set to 1,

[0031] The volume ratio (r) of the ASC satisfies the following formula, which uses the NH3 concentration of the combustion exhaust gas ([NH3]in_scr), the target value of the NH3 concentration after treating the leaked NH3 ([NH3]_target), the target value of the N2O concentration after treating the leaked NH3 ([N2O]_target), the proportionality constant (α) related to N2O generation of the ASC, the reaction rate constant (ka) related to NH3 decomposition of the ASC, the reaction rate constant (ks) related to NH3 decomposition of the SCR catalyst, and the space velocity SV (1 / h) of the exhaust gas relative to the SCR catalyst and the ASC.

[0032] [Formula 1]

[0033] SV / (ka-ks)·LN([NH3]in_scr / [NH3]_target)<r<1-SV / ks·LN(α·[NH3]in_scr / [N2O]_target).

[0034] 3. In the ammonia combustion exhaust gas treatment system described in 1 or 2 above, the ratio of the volume of the SCR catalyst to the volume of the ASC is such that, when the sum of the volumes of the SCR catalyst and the ASC is set to 1, the volume of the ASC is 0.1 or more and less than 0.6.

[0035] 4. In the ammonia combustion exhaust gas treatment system described in 1 or 2 above, the space velocity SV (1 / h) of the exhaust gas relative to the SCR catalyst and ASC is above 5000.

[0036] 5. In the ammonia combustion exhaust gas treatment system described in 1 or 2 above, the ASC includes an SCR catalyst in the leaked NH3 oxidation catalyst.

[0037] 6. In the ammonia combustion exhaust gas treatment system described in 1 or 2 above, there is a structure for adjusting the gas flow path so as to achieve a desired catalyst ratio relative to the gas composition when the gas composition of the exhaust gas changes.

[0038] The effects of the invention

[0039] According to the present invention, a treatment system for ammonia combustion exhaust gas that can simultaneously reduce NH3 leakage and suppress N2O byproducts can be provided. Attached Figure Description

[0040] Figure 1 (A) is a block diagram illustrating an example of an ammonia combustion exhaust gas treatment system for treating the combustion exhaust gas of a marine engine that uses ammonia as its main fuel. Figure 1 (B) is a block diagram representing another example.

[0041] Figure 2 It is a graph representing the experimental results.

[0042] [Symbol Marking Explanation]

[0043] 1. Engine

[0044] 2 First exhaust pipe

[0045] 3 SCR catalysts

[0046] 4 Second exhaust pipe

[0047] 5ASC

[0048] 6 Third Piping Detailed Implementation

[0049] The preferred embodiments of the present invention will be described below.

[0050] Figure 1 (A) is a block diagram illustrating an example of an ammonia combustion exhaust gas treatment system for treating the combustion exhaust gas of a marine engine that uses ammonia as its main fuel.

[0051] exist Figure 1 In, for example, a turbocharged large low-speed two-stroke diesel engine 1 (hereinafter referred to as the "engine mechanism" or "engine") uses ammonia (NH3) as the main fuel. NH3 can be supplied to the engine in the form of liquid NH3 and / or gaseous NH3.

[0052] The engine 1 only needs to have at least one ammonia mode, and may also have conventional fuel modes in addition to ammonia mode. In ammonia mode, the engine 1 operates using ammonia fuel, or uses an ignition fuel in addition to ammonia-based fuel to increase ignition and combustion temperature. In conventional fuel mode, it operates with conventional fuels, such as fuel oil (marine diesel fuel) or heavy oil.

[0053] The engine in this embodiment is a two-stroke (2st) engine. For each cylinder of the engine, for example, a scavenging port can be provided in the lower region of the cylinder liner, and an exhaust valve can be provided in the center of the top of the cylinder liner.

[0054] In this embodiment, a 4-stroke (4st) engine can also be used, but since the 2st engine has a lower speed and longer combustion time compared to the 4st engine, and the fuel is sprayed after the compressed air, there is a tendency for leakage of ammonia or a lower concentration of N2O in the exhaust. Therefore, the 2st engine is preferred.

[0055] Exhaust gas from engine 1 is sent to selective catalytic reduction (SCR) catalyst 3 via first exhaust pipe 2, and then to leak ammonia catalyst (ASC) 5 via second exhaust pipe 4. The treated exhaust gas is discharged outside the system through third pipe 6.

[0056] In this embodiment, such as Figure 1 As shown in (B), the second exhaust pipe 4 can also be omitted, and the SCR catalyst 3 and ASC5 can be housed in the same housing for processing, but it is not limited to this.

[0057] In NH3 combustion, the exhaust gas from engine 1 may contain both NOx and NH3. Exhaust gas from fossil fuel combustion typically does not contain NH3. In contrast, in NH3 combustion, it is possible to contain more NH3 in the exhaust gas compared to conventional fuels. That is, the amount of leaked NH3 may become greater.

[0058] SCR catalyst 3 acts as a NOx removal catalyst to remove both NO and NO2, which are NOx components, from the exhaust gas.

[0059] In addition, SCR catalyst 3 functions as both a NOx removal catalyst and an NH3 removal catalyst.

[0060] If NH3 is in excess, it must be considered that all NOx will react with NH3, and the excess NH3 will be discharged from the SCR catalyst as leaked NH3.

[0061] The permissible leakage of NH3 in the exhaust gas discharged into the outside is low. In this invention, an upper limit of 25 ppm is considered acceptable.

[0062] There are no particular limitations on the SCR catalyst. For example, the following catalysts can be used: those with a honeycomb structure formed by loading active components such as V, Cr, Mo, Mn, Fe, Ni, Cu, Ag, Au, Pd, Y, Ce, Nd, W, In, Ir, and Nb onto a support such as TiO2 or SiO2-TiO2, WO3-TiO2, Al2O3-SiO2, or ternary composite oxides such as WO3-SiO2-TiO2 and Mo3-SiO2-TiO2, and which reduce NOx and convert it into nitrogen for purification in the presence of NH3 (reducing agent).

[0063] For leaking ammonia catalysts (ASC), such as those in the form of catalysts with active components loaded on a honeycomb support, metals such as Pt, Fe, Cu or Pd can be used as active components.

[0064] In this embodiment, to ensure the suppression of secondary NOx formation, the ASC can be configured as an NH3 oxidation catalyst that functions as an oxidizing catalyst to remove leaked NH3, in addition to its function as an ASC itself. In this case, the ASC material preferably includes an SCR catalyst containing at least one of titanium oxide and vanadium oxide, and any one of Pt, Fe, and Cu, which are highly active ammonia oxidizing agents.

[0065] In cases where ASC contains precious metals, increasing the catalyst volume also increases the environmental impact; therefore, it is preferable to minimize the volume of ASC. Thus, by adjusting and optimizing the volume ratio of the catalyst in this invention, the amount of precious metals used in the overall catalyst can be reduced.

[0066] In this embodiment, such as Figure 1As shown, the SCR catalyst 3, which treats NOx in the exhaust gas from the first exhaust pipe 2, is positioned upstream of the ASC 5. That is, an ASC for treating leaked NH3 is positioned downstream of the SCR catalyst.

[0067] In this embodiment, the ratio of the volume of the SCR catalyst in contact with the exhaust gas to the volume of the ASC is adjusted so that the N2O concentration after suppressing N2O generation is below a specified concentration (e.g., 25 ppm).

[0068] Here, the volumes of the SCR catalyst and ASC are assumed to be the volumes of the shell when the SCR catalyst and ASC are filled into a specified shell. This is because, even if the amount of catalyst itself varies due to the shape of the catalyst, the density of the packing, etc., as long as they are filled into the same shell (space), the volume of each catalyst is considered constant.

[0069] By adjusting this volume ratio, experiments confirmed that it helps to balance reducing the concentration of leaked NH3 and suppressing the N2O generated during the treatment of leaked NH3.

[0070] In the experiment, using Figure 1 The apparatus shown, under the condition that the volume of SCR catalyst 3 + the volume of ASC 5 = the total volume of the catalyst, makes the total volume of the catalyst a change in the ratio of the volume of the SCR catalyst to the volume of ASC in contact with the exhaust gas under condition 1.

[0071] In this experiment, the volume ratio is calculated as ASC ratio = ASC / (SCR + ASC).

[0072] The volume ratio changes in five ways, as shown in (1) to (5).

[0073] (1) Volume ratio with an ASC rate of 0

[0074] The volume of SCR catalyst 3 + the volume of ASC 5 = the total volume of the catalyst. When the total volume of the catalyst is 1, since the volume of ASC is 0, the volume of SCR is 1.0.

[0075] (2) ASC ratio of 0.4 for volume ratio

[0076] Since the volume of ASC is 0.4, the volume of SCR is 0.6.

[0077] (3) Volume ratio with an ASC rate of 0.5

[0078] Since the volume of ASC is 0.5, the volume of SCR is also 0.5.

[0079] (4) Volume ratio with an ASC rate of 0.6

[0080] Since the volume of ASC is 0.6, the volume of SCR is 0.4.

[0081] (5) Volume ratio with an ASC rate of 1.0

[0082] Since the volume of ASC is 1.0, the volume of SCR is 0.

[0083] In a preferred embodiment of the present invention, when the total volume of the catalyst (volume of SCR catalyst 3 + volume of ASC5) is set to 1, the volume of ASC5 is preferably 0.1 or more and less than 0.6. More preferably, when the total volume of the catalyst (volume of SCR catalyst 3 + volume of ASC5) is set to 1, the volume of ASC5 is 0.1 or more and less than 0.55. This reduces NH3 leakage and suppresses N2O formation.

[0084] Furthermore, the space velocity (SV) of the exhaust gas relative to SCR catalyst 3 and ASC 5 is preferably above 5000. This allows for the reduction of leaked NH3 while maintaining the space velocity, and also suppresses the N2O generated accompanying the reduction of leaked NH3.

[0085] As an experimental method, under the conditions of NH3 concentration of 1000 ppm and NO concentration of 600 ppm in the exhaust gas, Figure 1 The catalyst configuration shown is used to treat NH3 combustion exhaust gas. The exhaust gas is flowed at the space velocity shown in the table below to obtain the concentration of NH3 leaking at the outlet of ASC 5 (in the table below, when the ASC rate is 0, it is SCR catalyst 3), and then the amount of N2O generated is determined.

[0086] At this point, the volume ratio of the SCR catalyst to the ASC was changed. The results of the above experiments are shown in Table 1.

[0087] [Table 1]

[0088]

[0089] Next, in Table 1, the maximum values ​​of the concentration of NH3 and the amount of N2O generated during leakage were extracted when the catalyst temperature was above 250°C for the space velocity, and the SV was calculated when the concentration of NH3 and the amount of N2O generated during leakage were both 25 ppm.

[0090] The results are shown in Table 2.

[0091] [Table 2]

[0092] Volume ratio <![CDATA[SV / NH3(=25ppm)]]> <![CDATA[SV / N2O(=25ppm)]]> ASC rate 0 2003.1 1759.9 ASC rate 0.4 16492.9| 16038.4 ASC rate 0.5 15382.8 10094.7 ASC rate 0.6 18409.6 -12635.4 ASC rate 1 35519.7 -

[0093] In addition, based on the data in Table 2, the following charts were created: Figure 2 The curve.

[0094] exist Figure 2 In the diagram, a curve depicting the ASC ratio from 0 to 1 represents the boundary line for achieving NH3 levels below 25 ppm. That is, if the space velocity (SV) is lower than this curve, it indicates that NH3 levels below 25 ppm are achievable.

[0095] In addition, Figure 2 In the diagram, the region enclosed by a parabola-like curve within the ASC ratio range of 0 to 0.6 represents the region where N2O is below 25 ppm. That is, if the space velocity (SV) is within this region, it indicates that N2O can be kept below 25 ppm.

[0096] The overlapping region between one curve and another is defined as the area where, when the total volume of the catalyst (the volume of SCR catalyst 3 + the volume of ASC 5) is set to 1, the volume of ASC 5 is 0.1 or more and less than 0.6. If it falls within this region, both the reduction of leaked NH3 and the suppression of N2O byproducts can be achieved. Furthermore, in this embodiment, a space velocity SV (1 / h) of 5000 or more is preferred.

[0097] In this invention, it is preferable to have a structure for adjusting the gas flow path so that when the gas composition of the exhaust gas changes, it becomes the desired catalyst ratio corresponding to the above-mentioned gas composition.

[0098] Next, in this invention, the following formula can be used to express the relationship of N2O generation after ASC.

[0099] [Equation 2]

[0100] [N2O]=α·Δ[NH3]_asc

[0101] In Equation 2, [N2O] represents the amount of N2O generated after passing through ASC (ppm), α is the inherent proportionality constant of ASC, and is a parameter representing the catalytic performance of ASC. Δ[NH3]_asc represents the amount of NH3 decomposed during the passage of ASC (ppm).

[0102] In addition, the relationship between the amount of NH3 decomposed by ASC can be expressed by the following formula.

[0103] [Formula 3]

[0104] Δ[NH3]_asc=[NH3]in_asc·(1-EXP(·(ka·r) / SV))

[0105] In Equation 3, [NH3]in_asc is the NH3 concentration (ppm) before ASC, SV is the space velocity (1 / h), EXP is an exponential function with the Napier number as the base, ka is the intrinsic reaction rate constant of ASC, and is a parameter representing the catalytic performance of ASC. Additionally, r is the volume ratio of ASC when the sum of the volumes of the SCR catalyst and ASC is set to 1.

[0106] Secondly, the relationship between the amount of NH3 decomposition when passing through an SCR catalyst can be expressed by the following formula.

[0107] [Formula 4]

[0108] Δ[NH3]_scr=[NH3]in_scr·(1-EXP(-(ks·(1-r)) / SV))

[0109] In Equation 4, Δ[NH3]_scr represents the amount of NH3 decomposed during SCR, and [NH3]in_scr represents the NH3 concentration (ppm) before SCR. Additionally, ks is the inherent reaction rate constant of the SCR catalyst and depends on the NH3 and NOx concentrations before SCR. The catalyst-inherent reaction rate constant ks, involved in the NH3 decomposition due to the reaction of NH3 and NOx with the SCR catalyst, is a parameter representing the inherent performance of the SCR catalyst and therefore varies for each catalyst. However, by determining the exhaust gas conditions ([NH3]in_scr, [NOXin_scr, exhaust gas temperature), the corresponding ks can be calculated.

[0110] According to these formulas, when an SCR catalyst is configured on the upstream side and an ASC is configured on the downstream side, the NH3 concentration and N2O concentration after treating the leaked NH3 can be expressed as Equation 5 below.

[0111] [Formula 5]

[0112] [NH3]=[NH3]in_scr·EXP(·(ks·(1·r)) / SV)·EXP(-(ka·r) / SV)

[0113] [N2O]=α·[NH3]in_scr·EXP(-(ks·(1-r)) / SV)·(1·EXP(-(ka·r) / SV))

[0114] If the target value of NH3 concentration after treating the leaked NH3 is set as [NH3]_target and the target value of N2O is set as [N2O]_target, then the volume ratio r of ASCs that can achieve the target value can be expressed by the following formula 6.

[0115] [Formula 6]

[0116] [NH3]_target>[NH3]in_scr·EXP(-(ks·(1-r)) / SV)·EXP(-(ka·r) / SV)

[0117] [N2O]_target>α·[NH3]in_scr·EXP(-(ks·(1-r)) / SV)·(1-EXP(-(ka·r) / SV))

[0118] Rearranging r in equation 6 above, we obtain the following equation.

[0119] [Formula 7]

[0120] SV / (ka-ks)·LN([NH3]in_scr / [NH3]_target)<r<1-SV / ks·LN(α·[NH3]in_scr / [N2O]_target)

[0121] In Equation 7, LN is the natural logarithm function.

[0122] In this experiment, the data shown in Table 3 below were used to calculate the range of ASC based on Equation 7 above.

[0123] [Table 3]

[0124] <![CDATA[[NH3]in_scr(ppm)]]> 1000 [NOx]in_scr(ppm) 600 <![CDATA[[NH3]_target(ppm)]]> 25 <![CDATA[[N2O]_target(ppm)]]> 25 <![CDATA[SV(h -1 )]]> 20000 <![CDATA[ka(s -1 )]]> 126 <![CDATA[ks(s -1 )]]> 18 α 0.12

[0125] If the data shown in Table 3 is used, then in Equation 7, since ka >> ks during the derivation process, it can be approximated as ks / (ka-ks) → 0, and approximated as (1-EXP(-(ka·r) / SV)) → 1.

[0126] Furthermore, α, ka, and ks are temperature-dependent values; for example, it is preferable to use the values ​​at the temperature that produces the most N2O within the envisioned combustion exhaust temperature range. By using the temperature data that produces the most N2O, safety can be further ensured.

[0127] In addition, ks depends on the values ​​of [NH3]in_scr and the NOx concentration [NOx]in_scr before passing through SCR. For example, it is preferable to select the maximum NH3 concentration in the envisioned combustion exhaust gas as [NH3]in_scr, and it is preferable to select the minimum NOx concentration in the envisioned combustion exhaust gas as [NOx]in_scr.

[0128] For example, using the data in Table 3 above, according to Formula 7, the volume ratio r of ASC can be calculated to be in the range of 0.19 < r < 0.52.

[0129] Next, using the data shown in Table 4 below, the range of ASC is calculated based on Equation 7 above.

[0130] [Table 4]

[0131] <![CDATA[[NH3]in_scr(ppm)]]> 1000 [NOx]in_scr(ppm) 0 <![CDATA[[NH3]_target(ppm)]]> 25 <![CDATA[[N2O]_target(ppm)]]> 25 <![CDATA[SV(h -1 )]]> 5000 <![CDATA[ka(s -1 )]]> 126 <![CDATA[ks(s -1 )]]> 3 α 0.12

[0132] If the data shown in Table 4 is used, then in Equation 7, the situation is the same as in Table 3. During the derivation process, since ka >> ks, it can be approximated as ks / (ka-ks) → 0, and approximated as (1-EXP(-(ka·r) / SV)) → 1.

[0133] Furthermore, similar to Table 3, α, ka, and ks are temperature-dependent values, but for example, it is preferable to use the values ​​at the temperature that produces the most N2O within the envisioned combustion exhaust temperature range. By using the temperature data that produces the most N2O, safety can be further ensured.

[0134] In addition, ks depends on the values ​​of [NH3]in_scr and the NOx concentration [NOx]in_scr before passing through SCR. For example, it is preferable to select the maximum NH3 concentration in the envisioned combustion exhaust gas as [NH3]in_scr, and it is preferable to select the minimum NOx concentration in the envisioned combustion exhaust gas as [NOx]in_scr.

[0135] For example, using the data in Table 4, based on Formula 7, the volume ratio r of ASC can be calculated to be in the range of 0.04 < r < 0.27.

[0136] Based on the data in Tables 3 and 4 above, it can be seen that when only the NOx concentration differs under exhaust gas conditions, the inherent reaction rate constant ks of the SCR catalyst, which depends on the NOx concentration, changes, resulting in a change in the range of the volume ratio r of ASC.

[0137] The experimental results show that the lower limit of r can be calculated based on the NH3 concentration in the combustion exhaust gas, the target NH3 concentration after treating the leaked NH3, the catalytic performance of ASC, the catalytic performance of SCR catalyst, and the space velocity SV. In addition, the upper limit of r can be calculated based on the NH3 concentration in the combustion exhaust gas, the target N2O concentration after treating the leaked NH3, the catalytic performance of ASC, the catalytic performance of SCR catalyst, and the space velocity SV.

Claims

1. A system for treating ammonia combustion exhaust gas from marine engines that use ammonia as the main fuel, characterized in that, It is equipped with an SCR catalyst for treating NOx in the combustion exhaust gas. An ASC (Anti-Synthetic Filter) is installed downstream of the SCR catalyst to treat leaked NH3. The volume of the SCR catalyst plus the volume of the ASC equals the total volume of the catalyst. When the total volume of the catalyst is considered 1, the volume ratio of the ASC is equal to the volume of the ASC divided by (the volume of the SCR catalyst plus the volume of the ASC). The volume ratio of the SCR catalyst is also equal to the volume of the SCR catalyst divided by (the volume of the SCR catalyst plus the volume of the ASC). The ratio of the volume of the SCR catalyst in contact with the exhaust gas to the volume of the ASC is adjusted so that the NH3 concentration after treating the leaked NH3 and the N2O concentration generated during the treatment of the leaked NH3 are below a specified concentration. The lower limit of the volume ratio of the ASC is a value calculated based on the NH3 concentration in the combustion exhaust gas, the target value of the NH3 concentration after treating the leaked NH3, the catalytic performance of the ASC, the catalytic performance of the SCR catalyst, and the space velocity SV of the exhaust gas relative to the SCR catalyst and the ASC. The unit of the space velocity SV is 1 / h. The upper limit of the volume ratio of the ASC is a value calculated based on the NH3 concentration of the combustion exhaust gas, the target value of the NH3 concentration after treating the leaked NH3, the catalytic performance of the ASC, the catalytic performance of the SCR catalyst, and the space velocity SV of the exhaust gas relative to the SCR catalyst and the ASC, with the unit of space velocity SV being 1 / h.

2. A system for treating ammonia combustion exhaust gas from marine engines that use ammonia as the main fuel, characterized in that, It is equipped with an SCR catalyst for treating NOx in the combustion exhaust gas. An ASC (Anti-Synthetic Filter) is installed downstream of the SCR catalyst to treat leaked NH3. The volume of the SCR catalyst plus the volume of the ASC equals the total volume of the catalyst. When the total volume of the catalyst is considered 1, the volume ratio of the ASC is equal to the volume of the ASC divided by (the volume of the SCR catalyst plus the volume of the ASC). The volume ratio of the SCR catalyst is also equal to the volume of the SCR catalyst divided by (the volume of the SCR catalyst plus the volume of the ASC). The ratio of the volume of the SCR catalyst in contact with the exhaust gas to the volume of the ASC is adjusted so that the NH3 concentration after treating the leaked NH3 and the N2O concentration generated during the treatment of the leaked NH3 are below a specified concentration. The volume ratio r of the ASC satisfies the following formula, which uses the NH3 concentration [NH3]in_scr of the combustion exhaust gas, the target value of the NH3 concentration [NH3]_target after treating the leaked NH3, the target value of the N2O concentration [N2O]_target after treating the leaked NH3, the proportionality constant α related to N2O generation of the ASC, the reaction rate constant ka related to NH3 decomposition of the ASC, the reaction rate constant ks related to NH3 decomposition of the SCR catalyst, and the space velocity SV of the exhaust gas relative to the SCR catalyst and the ASC, where the unit of space velocity SV is 1 / h. LN is the natural logarithm function. [Formula 1] 。 3. The ammonia combustion waste gas treatment system according to claim 1 or 2, characterized in that... , The ratio of the volume of the SCR catalyst to the volume of the ASC is such that, when the sum of the volumes of the SCR catalyst and the ASC is set to 1, the volume of the ASC is greater than 0.1 and less than 0.

6.

4. The ammonia combustion waste gas treatment system according to claim 1 or 2, characterized in that, The space velocity (SV) of the exhaust gas relative to the SCR catalyst and ASC is above 5000, and the unit of space velocity (SV) is 1 / h.

5. The ammonia combustion waste gas treatment system according to claim 1 or 2, characterized in that, The ASC includes an additional SCR catalyst in the leaked NH3 oxidation catalyst.

6. The ammonia combustion waste gas treatment system according to claim 1 or 2, characterized in that, It has a structure for adjusting the gas flow path so as to achieve a desired catalyst ratio relative to the gas composition when the gas composition of the exhaust gas changes.

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