Exhaust aftertreatment A-SCR system and method for ammonia fuel low-speed engine

Abstract

The invention belongs to the technical field of marine engines, and particularly relates to an exhaust aftertreatment A-SCR system and method of an ammonia fuel low-speed engine. The system comprises an SCR controller, an SCR reactor, an ammonia supply system and an exhaust collecting pipe, wherein the exhaust collecting pipe is connected with the exhaust end of the low-speed engine and the SCR reactor; the SCR controller is used for calculating the amount of ammonia gas needing to be additionally injected according to a gas concentration signal in the exhaust header and controlling the ammonia supply system to supply the ammonia gas into the exhaust header; the additionally injected ammonia gas and the exhaust gas of the low-speed engine are mixed in the exhaust gas collecting pipe and then enter the SCR reactor. Existing ammonia fuel in a shipyard is used as a supplementary reducing agent, the temperature of ammonia gas is adjusted by arranging the heating device, the heated ammonia gas is mixed with exhaust gas of a low-speed engine in the exhaust gas collecting pipe and then enters the SCR reactor, and the problem of crystallization caused by low temperature is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of marine engines, and in particular relates to an exhaust gas aftertreatment A-SCR system and method for an ammonia fuel low-speed engine. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The shipping industry is the backbone of global trade. Currently, most global freight is transported by sea, and the proportion of global carbon dioxide emissions caused by shipping is increasing year by year. In order to curb greenhouse gas emissions from shipping, the International Maritime Organization (IMO) has continuously issued new mandatory conventions and indicators to control greenhouse gas emissions from ships, and revised and issued greenhouse gas emission reduction targets. However, reducing greenhouse gas emissions from ships by increasing the size of ships and improving propulsion systems has great limitations; ammonia (Ammonia) is the most promising carbon-free energy, with obvious capacity density advantages and high fuel economy advantages, and can be used as a carbon-free power fuel for the shipping sector.

[0004] After ammonia fuel is burned in a marine engine, it only produces nitrogen dioxide (NOx), nitrous oxide (N2O) and unburned NH3; toxic and harmful nitrogen oxide gases can be treated by selective catalytic reduction (SCR); however, unlike diesel, the exhaust gas temperature produced by ammonia combustion is lower than that of diesel engines, which puts higher requirements on the reduction reaction;

[0005] In addition, ammonia combustion will also produce N2O, and the greenhouse effect of N2O is nearly 300 times stronger than that of NO2, and the current conventional SCR system cannot effectively treat N2O. In addition, due to the incomplete combustion of ammonia, a large amount of NH3 will escape; NH3 is toxic, and classification societies and other organizations have set limits on its emission concentration.

[0006] Generally speaking, conventional SCR systems use 40% urea solution as a reducing agent, and spray the urea solution into the mixing tube through a urea spray gun. Under the action of high-temperature exhaust gas, the urea solution thermally generates NH3, which reacts with NOx in the exhaust gas to generate N2 and water.

[0007] However, in actual use, especially under low load conditions, the exhaust temperature of the engine is low, and the urea thermal decomposition speed is slow; and when it hits the cold inner wall of the mixing tube, it is very easy to deposit in the low temperature area and form crystals, affecting the final emission effect. In addition, as a special chemical medium, urea solution also needs to be equipped with a special urea solution storage device, which occupies a lot of space and affects the equipment layout and installation on the ship. Summary of the invention

[0008] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides an exhaust aftertreatment A-SCR system and method for an ammonia fuel low-speed engine.

[0009] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions:

[0010] A first aspect of the present invention provides an exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine, comprising an SCR controller, an SCR reactor, an ammonia supply system and an exhaust manifold, wherein the exhaust manifold is connected to the exhaust end of the low-speed engine and the SCR reactor respectively;

[0011] A gas concentration sensor electrically connected to the SCR controller is provided in the exhaust manifold, and the SCR controller is used to calculate the amount of ammonia gas that needs to be additionally injected into the exhaust manifold according to the gas concentration signal, and control the ammonia supply system to supply ammonia gas into the exhaust manifold;

[0012] The ammonia supply system includes an ammonia tank, a heating device, an ammonia supply pump, a proportional valve and a spray gun which are connected in sequence through a supply pipeline; the liquid ammonia provided by the ammonia tank changes from liquid to gas under the action of the heating device, and the ammonia gas enters the spray gun after being regulated by the ammonia supply pump and the proportional valve in sequence; the spray gun is installed at one end of the exhaust manifold connected to the low-speed engine, and is used to spray ammonia gas into the exhaust manifold.

[0013] The second aspect of the present invention provides an exhaust aftertreatment method for an ammonia fuel low-speed engine, based on an exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine provided by the first aspect of the present invention, comprising:

[0014] The operation mode of the low-speed engine is obtained. If the low-speed engine operates in the ammonia Tier II mode, the SCR controller controls the ammonia supply system to be closed; the exhaust gas of the low-speed engine enters the SCR reactor through the exhaust manifold to react;

[0015] If the low-speed engine operates in ammonia Tier III mode, the SCR controller calculates the amount of additional ammonia that needs to be injected into the exhaust manifold based on the gas concentration signal in the exhaust manifold, and controls the ammonia supply system to supply ammonia into the exhaust manifold; the exhaust gas of the low-speed engine and the ammonia supplied by the ammonia supply system are mixed in the exhaust manifold and then enter the SCR reactor to react.

[0016] One or more of the above technical solutions have the following beneficial effects:

[0017] (1) The ammonia supply system provided by the present invention utilizes the existing ammonia fuel in the shipyard as a supplementary reducing agent for the SCR system, thereby eliminating the thermal decomposition process of the urea solution and avoiding the problem of the urea solution being difficult to thermally decompose and easy to crystallize under low load conditions. At the same time, a heating device is provided to adjust the temperature of the ammonia gas. The heated ammonia gas is mixed with the exhaust gas of the low-speed engine in the exhaust manifold and then enters the SCR reactor, thereby ensuring the smooth progress of the reaction and avoiding the crystallization problem caused by low temperature.

[0018] (2) The present invention utilizes the unburned NH3 of ammonia fuel as a reducing agent on the one hand, and utilizes the NH3 provided by the ammonia supply system as a supplementary reducing agent on the other hand; the control logic of the SCR control system calculates the ammonia that needs to be additionally injected, and controls the ammonia supply system to inject ammonia into the exhaust manifold, so that the ammonia and the exhaust gas are mixed in the exhaust pipe; this method not only reduces the design of the urea tank, but also reduces the setting of the mixer, saving the shipyard space, and reducing the thermal decomposition process of the urea solution, effectively solving the crystallization problem of the urea solution under low temperature conditions.

[0019] (3) The SCR reactor provided by the present invention is provided with three different types of catalysts, which can simultaneously treat NOx, N2O and escaped NH3 in the exhaust gas under various conditions, so that its emissions meet the requirements of relevant regulations.

[0020] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0022] Figure 1 This is a system structure diagram of the first embodiment.

[0023] Figure 2 This is the ammonia supply amount PID adjustment flow chart of the first embodiment.

[0024] In the figure, 1. ammonia tank, 2. ammonia gas supply system, 3. control valve group, 4. heating device, 5. filter, 6. ammonia supply pump, 7. flow meter, 8. proportional valve, 9. spray gun, 10. exhaust manifold, 11. N2O sensor, 12. NOx sensor, 13. NH3 sensor, 14. SCR controller, 15. low-speed engine, 16. RSV valve, 17. SCR reactor, 18. denitrification catalyst, 19. conventional catalyst, 20. deamination catalyst, 21. RTV valve, 22. RBV valve, 23. turbocharger, 24. overflow valve, 25. cooling and pressurizing device. DETAILED DESCRIPTION

[0025] Embodiment 1

[0026] like Figure 1 As shown, this embodiment discloses an exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine, comprising an SCR controller 14, an SCR reactor 17, an ammonia supply system and an exhaust manifold 10; the exhaust manifold 10 is respectively connected to the exhaust end of the low-speed engine and the SCR reactor 17;

[0027] The exhaust gas discharged by the low-speed engine 15 first enters the exhaust manifold 10. When the ammonia supply system is started, the ammonia supply system supplies ammonia to the exhaust manifold 10. The exhaust gas of the low-speed engine 15 and the ammonia additionally supplied by the ammonia supply system are mixed in the exhaust manifold 10. The mixed gas enters the SCR reactor 17 to react and is then discharged.

[0028] The exhaust gas discharged by the low-speed engine 15 contains not only a large amount of NOx generated after the combustion of NH3, but also a large amount of incompletely burned NH3 and a small amount of N2O. Therefore, this part of incompletely burned NH3 can be used as a reducing agent to carry out subsequent selective catalytic reduction reaction, thereby reducing the supply and consumption of ammonia.

[0029] The ammonia supply system includes an ammonia tank 1, an ammonia gas supply system 2, a control valve group 3, a heating device 4, an ammonia supply pump 6, a proportional valve 8 and a spray gun 9 which are connected in sequence through a supply pipeline; the supply of ammonia is controlled by the control valve group 3. After the control valve group 3 is opened, the liquid ammonia provided by the ammonia tank 1 changes from liquid to gas under the action of the heating device 4. After the ammonia passes through the ammonia supply pump 6, the supply flow rate of the ammonia is adjusted in real time by controlling the opening of the proportional valve 8; the spray gun 9 is installed at one end of the exhaust manifold 10 connected to the low-speed engine, and the spray gun 9 is used to spray ammonia into the exhaust manifold 10.

[0030] In this embodiment, the ammonia tank 1 is used to provide an ammonia reducing agent. A control valve group 3 is provided on the ammonia tank. The control valve group 3 is used to control the on and off supply of the ammonia reducing agent. If the low-speed engine 15 is in a shutdown state or there is no need to additionally supply NH3 to the exhaust manifold 10, the control valve group 3 is cut off to ensure the safety of the system.

[0031] When the SCR system is started, the control valve group 3 is opened, and the liquid ammonia enters the heating device 4 through the supply pipeline. The heating device 4 is used to heat the liquid ammonia to a suitable temperature, so that the ammonia is converted from liquid to gas.

[0032] The spray gun 9 is installed at the end of the exhaust manifold 10 to spray gaseous ammonia into the exhaust manifold 10 and achieve full mixing of ammonia and exhaust gas by means of the complex exhaust gas flow field in the exhaust manifold to facilitate the next reaction.

[0033] The present invention does not use conventional 40% urea solution as a reducing agent, but uses ammonia fuel of an ammonia fuel engine and NH3 escaped from exhaust gas as a reducing agent, thereby eliminating the thermal decomposition process of the urea solution and avoiding the difficult problem of thermal decomposition and easy crystallization of the urea solution under low load conditions. At the same time, the selection of ammonia reducing agent reduces the design of the urea cabin, greatly saves space, and reduces workload.

[0034] As a further embodiment, the ammonia supply pump 6 is a fixed frequency pump, and a filter 5 is provided on the supply pipeline between the heating device 4 and the ammonia supply pump 6. The filter 5 is used to filter impurities in the ammonia gas to avoid clogging of the pipeline.

[0035] As a further implementation, a flow meter 7 is provided on the supply pipeline between the ammonia supply pump 6 and the proportional valve 8, and the flow meter 7 is electrically connected to the SCR controller; the flow meter 7 is used to detect the supply amount of ammonia in the supply pipeline in real time and transmit it to the SCR controller.

[0036] As a further embodiment, the ammonia supply system further includes an overflow valve 24 and a cooling and pressurizing device 25 connected in sequence through a recovery pipeline; the overflow valve 24 is connected to the supply pipeline between the ammonia supply pump 6 and the flow meter 7 through the recovery pipeline, and the cooling and pressurizing device 25 is connected to the ammonia tank 1 through the recovery pipeline;

[0037] The ammonia gas flowing through the ammonia supply pump 6 is sprayed into the exhaust manifold 10 through the flow meter 7, the proportional valve 8 and the spray gun 9; the excess ammonia gas passes through the overflow valve 24 and enters the cooling and pressurizing device 25. The cooling and pressurizing device 25 is used to convert the excess ammonia gas into liquid ammonia and then flow back to the ammonia tank 1.

[0038] The ammonia supply pump 6 is used to provide a quantitative amount of ammonia to the SCR system. The SCR controller 14 adjusts the opening of the proportional valve 8 in real time according to the required ammonia supply, thereby achieving precise control of the ammonia supply; the excess ammonia flows into the ammonia tank 1 again after passing through the overflow valve 24 and the cooling and pressurizing device 25.

[0039] As a further embodiment, a gas concentration sensor is provided in the exhaust manifold 10, and the gas concentration sensor includes an NH3 sensor 11, a NOx sensor 12, and an N2O sensor 13. The gas concentration sensor is electrically connected to the SCR controller 14, and is used to feed back the collected signal to the SCR controller 14;

[0040] The SCR controller 14 calculates the amount of ammonia that the ammonia supply system needs to inject into the exhaust manifold 10 through the fed-back concentration signal, and adjusts the actual ammonia supply amount by adjusting the opening of the proportional valve 6 to inject a specified amount of ammonia; Figure 2 As shown, PID regulation is adopted to monitor and compare the deviation between the feedback value and the set value of the ammonia supply, so as to realize precise control of the ammonia supply.

[0041] As a further embodiment, the SCR reactor 17 is a multifunctional reactor having an inlet end at the top and an outlet end at the bottom. A denitration catalyst 18, a conventional catalyst 19 and a deamination catalyst 20 are sequentially arranged in the SCR reactor from the inlet end to the outlet end.

[0042] In order to remove N2O from the exhaust gas, the present invention adds a denitration catalyst in the SCR reactor 17 to convert N2O in the exhaust gas into NOx, thereby reducing the emission of N2O. The generated NOx can also be removed by subsequent conventional catalysts.

[0043] The number of layers of the denitrification catalyst 18, the conventional catalyst 19 and the deamination catalyst 20 can be selected as required. In this embodiment, one layer of denitrification catalyst, three layers of conventional catalyst and one layer of deamination catalyst are arranged. The present invention can simultaneously treat multiple components in the exhaust gas, such as NOx and N2O and escaped ammonia, by arranging three different catalysts in the SCR reactor 17, so that the exhaust gas emissions meet the requirements of relevant regulations and the system functions are more comprehensive.

[0044] As a further embodiment, a RSV valve 16 is provided on the pipeline between the exhaust manifold 10 and the inlet end of the SCR reactor, and a RTV valve 21, a turbocharger 23 and a RBV valve 22 are provided in sequence on the pipeline between the exhaust manifold 10 and the outlet end of the SCR reactor.

[0045] When the low-speed engine 15 operates in the ammonia Tier II mode, the emission of NOx in the exhaust gas of the low-speed engine meets the requirements, and only NH3 and N2O in the exhaust gas need to be processed to meet the regulatory requirements.

[0046] The exhaust gas of the low-speed engine enters the exhaust manifold 10. Since the exhaust gas contains a large amount of unburned NH3, in order to ensure that the emission of NH3 meets the requirements, the ammonia supply system and the RBV valve 22 are controlled to be closed, and the RSV valve 16 and the RTV valve 21 are controlled to be opened, so that the exhaust gas enters the SCR reactor through the SCR pipeline to react, and the A-SCR system starts the passive operation mode.

[0047] The exhaust gas of the low-speed engine flows out of the exhaust manifold 10 and enters the SCR reactor 17 through the SCR pipeline and the RSV valve 16; in the SCR reactor 17, the exhaust gas first passes through the denitration catalyst 18, and the N2O in the exhaust gas generates NOx under the action of the denitration catalyst 18, and is fully mixed with other NOx in the exhaust gas, and then flows through the conventional catalyst 19. At this time, the NOx and NH3 in the exhaust gas undergo a reduction reaction under the action of the conventional catalyst 19 to generate N2 and water; since the concentration of escaping NH3 is greater than that of NOx, the excess NH3 is removed by the deamination catalyst 20 in the SCR reactor 17, so that the emissions of NOx and NH3 meet the requirements; finally, the exhaust gas is discharged through the RTV valve 21 and the turbocharger 23.

[0048] When the low-speed engine operates in the ammonia Tier III mode, the SCR controller 14 calculates the amount of ammonia that needs to be additionally injected into the exhaust manifold according to the gas concentration signal, and controls the ammonia supply system to supply ammonia into the exhaust manifold 10;

[0049] The ammonia additionally injected by the ammonia supply system is fully mixed with NH 3 and NOx in the exhaust gas of the low-speed engine in the exhaust manifold 10 , and the mixed gas enters the SCR reactor 17 to react.

[0050] Specifically: the mixed exhaust gas first reaches the first layer catalyst denitrification catalyst 18 in the SCR reactor 17, and under the catalytic action of the denitrification catalyst 18, the N2O in the exhaust gas is oxidized into NOx, and after mixing with the original NOx and NH3 in the exhaust gas, under the action of the conventional catalyst 19 arranged after the denitrification catalyst 18, a reduction reaction occurs, thereby removing NOx from the exhaust gas.

[0051] If too much NH3 is produced after the combustion of ammonia, after calculation by the SCR controller 14, no additional ammonia injection is required, and the opening of the regulating valve 8 is controlled to be 0, and no ammonia is sprayed into the exhaust manifold 10; the exhaust gas enters the SCR reactor 17 after passing through the RSV valve 16, and under the action of the denitrification catalyst 18, the N2O in the exhaust gas is oxidized into NOx, and the NOx and NH3 in the exhaust gas undergo a reduction reaction under the action of the conventional catalyst 19, and the excess NH3 can be removed by the denitrification catalyst 20 arranged after the conventional catalyst 19 to meet the emission requirements.

[0052] When the low-speed engine runs in the diesel Tier II mode, the NOx in the exhaust of the low-speed engine meets the emission requirements, the SCR controller controls the ammonia supply system to be closed, and the A-SCR system does not run; at this time, the RSV valve 16 and the RTV valve 21 are controlled to be closed, and the RBV valve 22 is opened, and the exhaust gas directly enters the turbocharger 23 through the RBV valve 22 and is then discharged.

[0053] If the low-speed engine runs in the diesel Tier III mode, the SCR controller calculates the amount of ammonia that needs to be additionally injected into the exhaust manifold according to the gas concentration signal in the exhaust manifold, and controls the ammonia supply system to supply ammonia into the exhaust manifold 10; the exhaust gas of the low-speed engine and the ammonia supplied by the ammonia supply system are mixed in the exhaust manifold and then enter the SCR reactor 17 to react. In this mode, the exhaust gas does not contain N2O and NH3. Therefore, after the exhaust gas reaches the SCR reactor 17, only under the action of the conventional catalyst 19, NOx and NH3 undergo a reduction reaction, thereby removing NOx from the exhaust gas.

[0054] Embodiment 2

[0055] This embodiment discloses an exhaust aftertreatment method for an ammonia fuel low-speed engine, based on an exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine disclosed in Embodiment 1, comprising:

[0056] The operation mode of the low-speed engine is obtained. If the low-speed engine operates in the ammonia Tier II mode, the SCR controller controls the ammonia supply system to be closed; the exhaust gas of the low-speed engine enters the SCR reactor through the exhaust manifold to react;

[0057] If the low-speed engine runs in the ammonia Tier III mode, the SCR controller calculates the amount of additional ammonia that needs to be injected into the exhaust manifold based on the gas concentration signal in the exhaust manifold, and controls the ammonia supply system to supply ammonia into the exhaust manifold; the exhaust gas of the low-speed engine and the ammonia supplied by the ammonia supply system are mixed in the exhaust manifold and then enter the SCR reactor to react;

[0058] If the low-speed engine runs in diesel Tier Ⅱ mode, the SCR controller controls the ammonia supply system to be closed, and controls the RSV valve and RTV valve to be closed, and the RBV valve to be opened, so that the exhaust gas enters the turbocharger and is discharged;

[0059] If the low-speed engine runs in diesel Tier III mode, the SCR controller calculates the amount of additional ammonia that needs to be injected into the exhaust manifold based on the gas concentration signal in the exhaust manifold, and controls the ammonia supply system to supply ammonia into the exhaust manifold; the exhaust gas of the low-speed engine and the ammonia supplied by the ammonia supply system are mixed in the exhaust manifold and then enter the SCR reactor to react; the reacted gas passes through the RTV valve and turbocharger in sequence and is discharged.

[0060] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0061] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. An exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine, characterized in that: It includes an SCR controller, an SCR reactor, an ammonia supply system and an exhaust manifold, wherein the exhaust manifold is connected to the exhaust end of the low-speed engine and the SCR reactor respectively; A gas concentration sensor electrically connected to the SCR controller is provided in the exhaust manifold, and the SCR controller is used to calculate the amount of ammonia gas that needs to be additionally injected into the exhaust manifold according to the gas concentration signal, and control the ammonia supply system to supply ammonia gas into the exhaust manifold; The ammonia supply system includes an ammonia tank, a heating device, an ammonia supply pump, a proportional valve and a spray gun which are connected in sequence through a supply pipeline; the liquid ammonia provided by the ammonia tank changes from liquid to gas under the action of the heating device, and the ammonia gas enters the spray gun after being regulated by the ammonia supply pump and the proportional valve in sequence; the spray gun is installed at one end of the exhaust manifold connected to the low-speed engine, and is used to spray ammonia gas into the exhaust manifold.

2. The exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine as claimed in claim 1, characterized in that: The ammonia tank is provided with a control valve group, and the opening and closing of the ammonia tank is controlled by the control valve group.

3. The exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine as claimed in claim 1, characterized in that: A filter is provided on the supply pipeline between the heating device and the ammonia supply pump, and the filter is used to filter impurities in the ammonia gas.

4. The exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine as claimed in claim 1, characterized in that: A flow meter is provided on the supply pipeline between the ammonia supply pump and the proportional valve, and the flow meter is electrically connected to the SCR controller; the flow meter is used to detect the supply amount of ammonia in the supply pipeline and transmit it to the SCR controller.

5. The exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine as claimed in claim 4, characterized in that: The ammonia supply system further comprises an overflow valve and a cooling and pressurizing device which are connected in sequence through a recovery pipeline, wherein the overflow valve is connected to the supply pipeline between the ammonia supply pump and the flow meter through the recovery pipeline, and the cooling and pressurizing device is connected to the ammonia tank through the recovery pipeline; The ammonia gas flowing through the ammonia supply pump enters the cooling and pressurizing device through the overflow valve, and the cooling and pressurizing device is used to convert the excess ammonia gas into liquid ammonia and then flow back to the ammonia tank.

6. The exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine as claimed in claim 1, characterized in that: An RSV valve is arranged on the pipeline between the exhaust manifold and the inlet end of the SCR reactor, and an RTV valve, a turbocharger and an RBV valve are arranged in sequence on the pipeline between the exhaust manifold and the outlet end of the SCR reactor.

7. The exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine as claimed in claim 1, characterized in that: The gas concentration signal includes N2O concentration, NOx concentration and NH3 concentration.

8. The exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine as claimed in claim 1, characterized in that: The SCR reactor is provided with a denitration catalyst, a conventional catalyst and a deamination catalyst in sequence from the inlet end to the outlet end.

9. An exhaust aftertreatment method for an ammonia fuel low-speed engine, based on an exhaust aftertreatment A-SCR system for an ammonia fuel low-speed engine according to any one of claims 1 to 8, characterized in that: include: The operation mode of the low-speed engine is obtained. If the low-speed engine operates in the ammonia Tier II mode, the SCR controller controls the ammonia supply system to be closed; the exhaust gas of the low-speed engine enters the SCR reactor through the exhaust manifold to react; If the low-speed engine operates in ammonia Tier III mode, the SCR controller calculates the amount of additional ammonia that needs to be injected into the exhaust manifold based on the gas concentration signal in the exhaust manifold, and controls the ammonia supply system to supply ammonia into the exhaust manifold; the exhaust gas of the low-speed engine and the ammonia supplied by the ammonia supply system are mixed in the exhaust manifold and then enter the SCR reactor to react.

10. The method according to claim 9, characterized in that include: If the low-speed engine runs in the diesel Tier II mode, the SCR controller controls the ammonia supply system to be closed, and controls the RSV valve and the RTV valve to be closed, and the RBV valve to be opened, so that the exhaust gas enters the turbocharger and is then discharged; If the low-speed engine operates in the diesel Tier III mode, the SCR controller calculates the amount of additional ammonia that needs to be injected into the exhaust manifold based on the gas concentration signal in the exhaust manifold, and controls the ammonia supply system to supply ammonia into the exhaust manifold; the exhaust gas of the low-speed engine and the ammonia supplied by the ammonia supply system are mixed in the exhaust manifold and then enter the SCR reactor to react; the reacted gas is discharged after passing through the RTV valve and the turbocharger in sequence.

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