A method and device for exhaust aftertreatment of a rail vehicle

Abstract

The application provides a tail gas aftertreatment method and device for a track locomotive, and relates to the field of tail gas treatment.The tail gas aftertreatment device comprises a DOC catalyst, an SCR catalyst and an ASC catalyst arranged in sequence, and is connected with an engine exhaust pipe and an atmosphere outlet, and the DOC catalyst is arranged close to the engine exhaust pipe; when the tail gas passes through the DOC catalyst, nitrogen monoxide, hydrocarbons and carbon monoxide are oxidized, and ammonia is oxidized to generate nitrogen monoxide and water under high-temperature conditions; the nitrogen monoxide generated from the ammonia is used as new nitrogen oxides, and the rest is original nitrogen oxides; when the tail gas passes through the SCR catalyst, the new nitrogen oxides and the original nitrogen oxides are reacted with the ammonia remaining after passing through the DOC catalyst to generate nitrogen and water; when the tail gas passes through the ASC catalyst, the ammonia remaining after passing through the SCR catalyst is oxidized to generate nitrogen and water, and is discharged from the atmosphere outlet.The application can solve the problem of equivalent ratio imbalance between ammonia and nitrogen oxides in tail gas when an ammonia engine is used.

Description

Technical Field

[0001] This invention relates to the field of exhaust gas treatment, and more particularly to a method and apparatus for exhaust gas after-treatment for rail locomotives. Background Technology

[0002] Rail locomotives, also known as diesel locomotives, use diesel fuel for power. During operation, rail locomotives often produce a large amount of exhaust gas, which contains a large amount of substances harmful to the atmosphere and organisms, such as nitric oxide (NO), nitrogen dioxide (NO2), hydrocarbons (HC), and carbon monoxide (CO). In particular, there is an existing ammonia engine that uses ammonia (NH3) and diesel fuel. However, when using ammonia as fuel, due to incomplete combustion, a large amount of ammonia is often left in the exhaust gas, with ammonia concentration reaching 17,000 ppm. Under the same operating conditions, the concentration of nitrogen oxides (NOx) is about 700 ppm. To avoid environmental pollution caused by exhaust gas emissions, it is necessary to treat the exhaust gas containing the high concentration of ammonia.

[0003] Exhaust gas aftertreatment technologies typically employ catalysts such as DOC, SCR, and ASC to convert the aforementioned harmful substances into harmless substances like CO2 and H2O. For instance, under the action of DOC, NO, HC, and CO are oxidized to produce NO2, CO2, and H2O; under the action of SCR, NO, NO2, and NH3 react to produce N2 and H2O; and under the action of ASC, NH3 is oxidized to N2.

[0004] In existing technologies, to reduce ammonia in exhaust gas, SCR catalysts and ASC catalysts are typically used to react the ammonia to generate nitrogen, which is then emitted in a harmless manner. However, when the SCR catalyst converts ammonia into nitrogen, NOx is required. NOx can react with ammonia in a 1:1 ratio, but under the same operating conditions, the NOx concentration is much lower than the ammonia concentration, making it impossible to handle the aforementioned high concentration of ammonia. In this case, even if an ASC catalyst is placed after the SCR catalyst, it still cannot handle the excess ammonia due to the limited efficiency of the ASC catalyst in catalyzing the conversion of ammonia, resulting in excessive ammonia emissions. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method and apparatus for exhaust gas aftertreatment for rail locomotives, which can solve the problem that when using ammonia engines in the prior art, the imbalance in the equivalence ratio of ammonia to nitrogen oxides in the exhaust gas means that even with the use of an ASC catalyst, it is still impossible to treat the excess ammonia, resulting in excessive ammonia emissions; and achieves control and adjustment of the equivalence ratio of ammonia to nitrogen oxides.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention provides a method for after-treatment of exhaust gas from rail locomotives, comprising the following steps: S101: In the exhaust aftertreatment device, DOC catalyst, SCR catalyst and ASC catalyst are arranged in sequence. The two ends of the exhaust aftertreatment device are connected to the engine exhaust pipe and the atmospheric outlet, respectively. The DOC catalyst is placed close to the engine exhaust pipe. S102: Exhaust gas enters through the engine exhaust pipe. When it passes through the DOC catalyst, nitric oxide, hydrocarbons and carbon monoxide are oxidized to produce nitrogen dioxide, carbon dioxide and water. Ammonia is oxidized under high temperature conditions to produce nitric oxide and water. Among them, the nitric oxide generated by ammonia is regarded as a new nitrogen oxide compound, and the rest are the original nitrogen oxide compounds. S103: When the exhaust gas passes through the SCR catalyst, both the new nitrogen oxides and the original nitrogen oxides react with the ammonia remaining after passing through the DOC catalyst to produce nitrogen and water. S104: When the exhaust gas passes through the ASC catalyst, the remaining ammonia gas after passing through the SCR catalyst will be oxidized to produce nitrogen gas and water gas, which will be discharged from the atmospheric outlet.

[0007] The exhaust gas aftertreatment method for rail locomotives provided by the present invention preferably includes, before "passing through DOC catalyst" in step S102: monitoring the ammonia concentration and nitrogen oxide concentration in the space between DOC catalyst and SCR catalyst by using an ammonia sensor and a nitrogen oxide sensor respectively; if the ammonia concentration is lower than the nitrogen oxide concentration, then controlling and discharging part of the exhaust gas from the engine exhaust pipe into the space between DOC catalyst and SCR catalyst through a metering valve.

[0008] The exhaust gas aftertreatment method for rail locomotives provided by the present invention preferably includes step S101 further comprising: monitoring the oxygen concentration in the space between the engine exhaust pipe and the DOC catalyst by means of an oxygen sensor; if the oxygen concentration is insufficient, controlling the introduction of compressed air into the space between the engine exhaust pipe and the DOC catalyst by means of a metering valve.

[0009] The present invention provides an exhaust gas aftertreatment device for rail locomotives, comprising a housing, a DOC catalyst, a first SCR catalyst, a second SCR catalyst, and an ASC catalyst; The DOC catalyst, the first SCR catalyst, the second SCR catalyst, and the ASC catalyst are sequentially disposed within the housing; gaps are provided between each pair of the DOC catalyst, the first SCR catalyst, the second SCR catalyst, and the ASC catalyst; exhaust gas inlets and exhaust gas outlets are provided on both sides of the housing; the DOC catalyst is adjacent to the exhaust gas inlet; the ASC catalyst is adjacent to the exhaust gas outlet; the exhaust gas inlet is connected to the engine exhaust port; and the exhaust gas outlet is connected to the atmosphere.

[0010] The exhaust gas aftertreatment device for rail locomotives provided by the present invention preferably further includes a bypass pipe and a controller; The two ends of the bypass pipe are respectively connected to the exhaust gas inlet and the space between the DOC catalyst and the first SCR catalyst; the bypass pipe is also equipped with a first metering valve; An ammonia sensor and a nitrogen-oxygen sensor are also provided in the space between the DOC catalyst and the first SCR catalyst; both the ammonia sensor and the nitrogen-oxygen sensor are electrically connected to the controller; the controller is electrically connected to the first metering valve.

[0011] The exhaust gas aftertreatment device for rail locomotives provided by the present invention preferably further includes a supply pipe; the two ends of the supply pipe are respectively connected to an exhaust gas inlet and a compressed air source; the supply pipe is also provided with a second metering valve; The exhaust gas inlet is also equipped with an oxygen sensor; the oxygen sensor is electrically connected to the controller; the controller is electrically connected to the second metering valve.

[0012] The above technical solution has the following advantages or beneficial effects: The exhaust gas aftertreatment method for rail locomotives provided by this invention includes, in step S101, a DOC catalyst, an SCR catalyst, and an ASC catalyst sequentially arranged in the exhaust gas aftertreatment device. The DOC catalyst treats NO, HC, and CO in the exhaust gas, oxidizing them into NO2, CO2, and H2O. The SCR catalyst reacts NO and NO2 with NH3 to generate N2 and H2O. The ASC catalyst oxidizes NH3 into N2. By sequentially arranging the above series of catalysts, harmful substances in the exhaust gas are converted into N2, CO2, and H2O, and the treated exhaust gas is then released into the atmosphere to reduce environmental pollution. In step S102, exhaust gas enters through the engine exhaust pipe. As it passes through the DOC catalyst, nitric oxide, hydrocarbons, and carbon monoxide are catalytically oxidized to nitrogen dioxide, carbon dioxide, and water. The conversion of nitric oxide to nitrogen dioxide improves the reaction efficiency of nitrogen oxides with ammonia under the subsequent action of the SCR catalyst. Specifically, because the DOC catalyst contains precious metals such as Pt and Pd, it possesses extremely strong broad-spectrum oxidation capabilities. When the DOC catalyst is close to the engine exhaust pipe, it is easily affected by the high temperature generated by the engine, causing the passing ammonia to oxidize. Nitric oxide and water are generated. Furthermore, since the conversion rate of ammonia and nitric oxide is 1:1, excess ammonia can be converted into nitrogen oxides for the SCR catalyst reaction, and the DOC catalyst has an efficiency of 40% in converting ammonia into nitric oxide. If the ammonia concentration is 17000 ppm and the nitrogen oxide concentration is 700 ppm, then the concentration of nitric oxide converted from ammonia is 6800 ppm, and the remaining ammonia concentration is 10200 ppm. For ease of explanation, the nitric oxide generated from ammonia is referred to as the new nitrogen oxide, and the rest are the original nitrogen oxides. In step S103, when the exhaust gas passes through the SCR catalyst, both the new nitrogen oxides (6800 ppm) and the original nitrogen oxides (700 ppm) react in a 1:1 ratio with the ammonia remaining after passing through the DOC catalyst (10200 ppm) to produce nitrogen and water. The ammonia concentration after the reaction is only 2700 ppm, which significantly reduces the ammonia concentration compared to not using the DOC catalyst to adjust the equivalence ratio of ammonia to nitrogen oxides, thus facilitating the subsequent treatment of ammonia by the ASC catalyst. In step S104, when the exhaust gas passes through the ASC catalyst, the remaining ammonia gas after passing through the SCR catalyst is oxidized to generate nitrogen gas and water gas, which are then discharged from the atmospheric outlet. This process treats the excess ammonia gas and prevents environmental pollution caused by excessive ammonia emissions. Attached Figure Description

[0013] The invention, its features, shape, and advantages will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings. Like reference numerals denote like parts throughout the drawings. The drawings are not intentionally drawn to scale; the focus is on illustrating the spirit of the invention.

[0014] Figure 1 This is a wireframe flowchart of the exhaust gas aftertreatment method for rail locomotives provided in Embodiment 1 of the present invention.

[0015] Figure 2 This is a cross-sectional structural schematic diagram of the exhaust gas aftertreatment device for rail locomotives provided in Embodiment 2 of the present invention.

[0016] Figure 3This is a schematic diagram of the electrical connection structure of the exhaust gas aftertreatment device for rail locomotives provided in Embodiment 2 of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the invention.

[0018] Example 1: like Figure 1 As shown, Embodiment 1 of the present invention provides a method for after-treatment of exhaust gas from rail locomotives, comprising the following steps: S101: In the exhaust aftertreatment device, DOC catalyst, SCR catalyst and ASC catalyst are arranged in sequence. The two ends of the exhaust aftertreatment device are connected to the engine exhaust pipe and the atmospheric outlet, respectively. The DOC catalyst is placed close to the engine exhaust pipe. S102: Exhaust gas enters through the engine exhaust pipe. When it passes through the DOC catalyst, nitric oxide, hydrocarbons and carbon monoxide are oxidized to produce nitrogen dioxide, carbon dioxide and water. Ammonia is oxidized under high temperature conditions to produce nitric oxide and water. Among them, the nitric oxide generated by ammonia is regarded as a new nitrogen oxide compound, and the rest are the original nitrogen oxide compounds. S103: When the exhaust gas passes through the SCR catalyst, both the new nitrogen oxides and the original nitrogen oxides react with the ammonia remaining after passing through the DOC catalyst to produce nitrogen and water. S104: When the exhaust gas passes through the ASC catalyst, the remaining ammonia gas after passing through the SCR catalyst will be oxidized to produce nitrogen gas and water gas, which will be discharged from the atmospheric outlet.

[0019] The exhaust gas aftertreatment method for rail locomotives provided in Embodiment 1 of the present invention includes, in step S101, a DOC catalyst, an SCR catalyst, and an ASC catalyst sequentially arranged in the exhaust gas aftertreatment device. The DOC catalyst treats NO, HC, and CO in the exhaust gas, oxidizing them into NO2, CO2, and H2O. The SCR catalyst reacts NO and NO2 with NH3 to generate N2 and H2O. The ASC catalyst oxidizes NH3 into N2. By sequentially arranging the above series of catalysts, harmful substances in the exhaust gas are converted into N2, CO2, and H2O, and the treated exhaust gas is discharged into the atmosphere to reduce environmental pollution. In step S102, exhaust gas enters through the engine exhaust pipe. As it passes through the DOC catalyst, nitric oxide, hydrocarbons, and carbon monoxide are catalytically oxidized to nitrogen dioxide, carbon dioxide, and water. The conversion of nitric oxide to nitrogen dioxide improves the reaction efficiency of nitrogen oxides with ammonia under the subsequent action of the SCR catalyst. Specifically, because the DOC catalyst contains precious metals such as Pt and Pd, it possesses extremely strong broad-spectrum oxidation capabilities. When the DOC catalyst is close to the engine exhaust pipe, it is easily affected by the high temperature generated by the engine, causing the passing ammonia to oxidize. Nitric oxide and water are generated. Furthermore, since the conversion rate of ammonia and nitric oxide is 1:1, excess ammonia can be converted into nitrogen oxides for the SCR catalyst reaction, and the DOC catalyst has an efficiency of 40% in converting ammonia into nitric oxide. If the ammonia concentration is 17000 ppm and the nitrogen oxide concentration is 700 ppm, then the concentration of nitric oxide converted from ammonia is 6800 ppm, and the remaining ammonia concentration is 10200 ppm. For ease of explanation, the nitric oxide generated from ammonia is referred to as the new nitrogen oxide, and the rest are the original nitrogen oxides. In step S103, when the exhaust gas passes through the SCR catalyst, both the new nitrogen oxides (6800 ppm) and the original nitrogen oxides (700 ppm) react in a 1:1 ratio with the ammonia remaining after passing through the DOC catalyst (10200 ppm) to produce nitrogen and water. The ammonia concentration after the reaction is only 2700 ppm, which significantly reduces the ammonia concentration compared to not using the DOC catalyst to adjust the equivalence ratio of ammonia to nitrogen oxides, thus facilitating the subsequent treatment of ammonia by the ASC catalyst. In step S104, when the exhaust gas passes through the ASC catalyst, the remaining ammonia gas after passing through the SCR catalyst is oxidized to generate nitrogen gas and water gas, which are then discharged from the atmospheric outlet. This process treats the excess ammonia gas and prevents environmental pollution caused by excessive ammonia emissions.

[0020] The exhaust gas aftertreatment method for rail locomotives provided in Embodiment 1 of the present invention preferably addresses the issue that, under certain engine operating conditions, the concentration of ammonia in the exhaust gas is low. If the above-mentioned method is still used to treat ammonia, the DOC catalyst will consume ammonia while generating a large amount of nitrogen oxides, resulting in a nitrogen oxide concentration greater than the ammonia concentration. Consequently, the subsequent ammonia is insufficient to completely react the nitrogen oxides. To solve this problem, in step S102, before "passing through the DOC catalyst," the method further includes: monitoring the ammonia concentration and nitrogen oxide concentration in the space between the DOC catalyst and the SCR catalyst using an ammonia sensor and a nitrogen oxide sensor, respectively. If the ammonia concentration is lower than the nitrogen oxide concentration, a portion of the exhaust gas from the engine exhaust pipe is controlled and discharged into the space between the DOC catalyst and the SCR catalyst through a metering valve. By drawing ammonia that has not yet been oxidized by the DOC catalyst to the area behind the DOC catalyst, the ammonia concentration at the SCR catalyst is increased, and the generation of nitrogen oxides is suppressed, thereby maintaining the ammonia concentration slightly higher than the nitrogen oxide concentration. If the ammonia concentration is detected to be slightly higher than the nitrogen oxide concentration, the metering valve is closed.

[0021] The exhaust gas aftertreatment method for rail locomotives provided in Embodiment 1 of the present invention preferably includes the following steps: Since the DOC catalyst requires a large amount of oxygen to oxidize nitric oxide, carbon monoxide, hydrocarbons and ammonia, which can easily lead to insufficient oxygen concentration, in order to solve the above problem, step S101 further includes: monitoring the oxygen concentration in the space between the engine exhaust pipe and the DOC catalyst through an oxygen sensor; if the oxygen concentration is insufficient, compressed air is introduced into the space between the engine exhaust pipe and the DOC catalyst through a metering valve.

[0022] Example 2: like Figures 2-3 As shown, Embodiment 2 of the present invention provides an exhaust gas aftertreatment device for rail locomotives, comprising a housing 1, a DOC catalyst 2, a first SCR catalyst 3, a second SCR catalyst 4, and an ASC catalyst 5; DOC catalyst 2, first SCR catalyst 3, second SCR catalyst 4 and ASC catalyst 5 are sequentially arranged inside housing 1; gaps are provided between each pair of DOC catalyst 2, first SCR catalyst 3, second SCR catalyst 4 and ASC catalyst 5; exhaust gas inlet 11 and exhaust gas outlet 12 are provided on both sides of housing 1; DOC catalyst 2 is adjacent to exhaust gas inlet 11; ASC catalyst 5 is adjacent to exhaust gas outlet 12; exhaust gas inlet 11 is connected to engine exhaust port; exhaust gas outlet 12 is connected to atmosphere.

[0023] The exhaust gas aftertreatment device for rail locomotives provided in Embodiment 2 of the present invention discharges exhaust gas from the engine exhaust pipe, enters the housing 1 through exhaust gas inlet 11, passes through DOC catalyst 2, first SCR catalyst 3, second SCR catalyst 4 and ASC catalyst 5 in sequence, and is then discharged into the atmosphere through exhaust gas outlet 12. Specifically, nitric oxide, hydrocarbons, and carbon monoxide in the exhaust gas can be oxidized by DOC catalyst 2 to produce nitrogen dioxide, carbon dioxide, and water. Nitrogen dioxide, generated from nitric oxide, is converted into nitrogen and water under the action of the first SCR catalyst 3 and the second SCR catalyst 4. In particular, under high temperature, DOC catalyst 2 can oxidize ammonia to nitric oxide and water, thereby increasing the concentration of nitrogen oxides and decreasing the concentration of ammonia, making the ammonia concentration slightly higher than the nitrogen oxide concentration. This allows ammonia to react with nitrogen oxides in a 1:1 ratio under the action of the first SCR catalyst 3 and the second SCR catalyst 4, thus removing nitrogen oxides while consuming a large amount of ammonia. The remaining ammonia can be oxidized by ASC catalyst 5 to produce nitrogen and water. By sequentially setting DOC catalyst 2, first SCR catalyst 3, second SCR catalyst 4 and ASC catalyst 5, a portion of ammonia is converted into nitrogen oxides, thereby making the equivalence ratio of ammonia to nitrogen oxides close to 1, thus avoiding excessive ammonia emissions due to excessively high ammonia concentration.

[0024] The exhaust gas aftertreatment device for rail locomotives provided in Embodiment 2 of the present invention is preferably designed to address the issue that, under certain operating conditions of the engine, the concentration of ammonia in the exhaust gas is low. If the above-mentioned device is used to treat the ammonia, the DOC catalyst 2 will produce more nitrogen oxides while consuming the ammonia, resulting in a higher concentration of nitrogen oxides than the concentration of ammonia. Consequently, the subsequent ammonia is insufficient to completely react the nitrogen oxides. To solve the above problem, a bypass pipe 6 and a controller 7 are also included. The two ends of the bypass pipe 6 are respectively connected to the exhaust gas inlet 11 and the space between the DOC catalyst 2 and the first SCR catalyst 3. Since the exhaust gas is continuously discharged from the engine exhaust pipe to the exhaust gas inlet 11, the exhaust gas inlet 11 is under high pressure, which makes it easy to guide some of the exhaust gas into the low-pressure bypass pipe 6. The ammonia gas that has not yet been oxidized by the DOC catalyst is drawn to the back of the DOC catalyst through the bypass pipe 6 to increase the ammonia gas concentration at the SCR catalyst and suppress the generation of nitrogen oxides, thereby maintaining the ammonia gas concentration slightly higher than the nitrogen oxides concentration, and thus avoiding excessive emission of nitrogen oxides. Furthermore, in order to selectively use the above structure, a first metering valve 61 is also provided in the bypass pipe 6, and an ammonia sensor 2301 and a nitrogen oxide sensor 2302 are also provided in the space between the DOC catalyst 2 and the first SCR catalyst 3. The ammonia concentration and nitrogen oxide concentration in the space between the DOC catalyst 2 and the first SCR catalyst 3 are monitored by the ammonia sensor 2301 and the nitrogen oxide sensor 2302, respectively. If the ammonia concentration is lower than the nitrogen oxide concentration, the first metering valve 61 is opened until the ammonia concentration is slightly higher than the nitrogen oxide concentration. It should be noted that, in order to control the opening and closing of the first metering valve 61 through the ammonia sensor 2301 and the nitrogen-oxygen sensor 2302, both the ammonia sensor 2301 and the nitrogen-oxygen sensor 2302 are electrically connected to the controller 7, and the controller 7 is electrically connected to the first metering valve 61.

[0025] The exhaust gas aftertreatment device for rail locomotives provided in Embodiment 2 of the present invention preferably includes a supply pipeline 8, since the DOC catalyst 2 requires a large amount of oxygen to oxidize nitric oxide, carbon monoxide, hydrocarbons and ammonia, which can easily lead to insufficient oxygen concentration. The two ends of the supply pipeline 8 are connected to the exhaust gas inlet 11 and the compressed air source, respectively, and the required oxygen is supplied to the exhaust gas inlet 11 through compressed air. Furthermore, in order to selectively use the above structure, the supply pipe 8 is also equipped with a second metering valve 81, and the exhaust gas inlet 11 is also equipped with an oxygen sensor 1101. The oxygen concentration of the exhaust gas inlet 11 is monitored by the oxygen sensor 1101. If the oxygen concentration is insufficient, the second metering valve 81 is opened until the oxygen concentration is sufficient. It should be noted that, in order to control the opening and closing of the second metering valve 81 through the oxygen sensor 1101, the oxygen sensor 1101 is electrically connected to the controller 7, and the controller 7 is electrically connected to the second metering valve 81.

[0026] In summary, the exhaust gas aftertreatment method and apparatus for rail locomotives provided by this invention can solve the problem of excessive ammonia emissions caused by the imbalance of the equivalence ratio of ammonia to nitrogen oxides in the exhaust gas when using ammonia engines in the prior art, even with the use of an ASC catalyst. This problem allows for the control and adjustment of the equivalence ratio of ammonia to nitrogen oxides.

[0027] Those skilled in the art should understand that variations can be implemented by combining existing technology and the above embodiments, and will not be elaborated here. Such variations do not affect the essence of the present invention, and will not be elaborated here.

[0028] The preferred embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and the devices and structures not described in detail should be understood as being implemented in a manner common to the art; any possible variations and modifications made by those skilled in the art without departing from the technical solution of the present invention, or equivalent embodiments with equivalent changes, do not affect the essential content of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for after-treatment of exhaust gas from rail locomotives, characterized in that, Includes the following steps: S101: In the exhaust aftertreatment device, DOC catalyst, SCR catalyst and ASC catalyst are arranged in sequence. The two ends of the exhaust aftertreatment device are connected to the engine exhaust pipe and the atmospheric outlet, respectively. The DOC catalyst is placed close to the engine exhaust pipe. S102: Exhaust gas enters through the engine exhaust pipe. When it passes through the DOC catalyst, nitric oxide, hydrocarbons and carbon monoxide are oxidized to produce nitrogen dioxide, carbon dioxide and water. Ammonia is oxidized under high temperature conditions to produce nitric oxide and water. Among them, the nitric oxide generated by ammonia is regarded as a new nitrogen oxide compound, and the rest are the original nitrogen oxide compounds. S103: When the exhaust gas passes through the SCR catalyst, both the new nitrogen oxides and the original nitrogen oxides react with the ammonia remaining after passing through the DOC catalyst to produce nitrogen and water. S104: When the exhaust gas passes through the ASC catalyst, the remaining ammonia gas after passing through the SCR catalyst will be oxidized to produce nitrogen gas and water gas, which will be discharged from the atmospheric outlet. In step S102, before "passing through the DOC catalyst", the following steps are also included: monitoring the ammonia concentration and nitrogen oxide concentration in the space between the DOC catalyst and the SCR catalyst by using an ammonia sensor and a nitrogen oxide sensor, respectively. If the ammonia concentration is lower than the nitrogen oxide concentration, a portion of the exhaust gas from the engine exhaust pipe is controlled and discharged into the space between the DOC catalyst and the SCR catalyst through a metering valve.

2. The exhaust gas aftertreatment method for rail locomotives as described in claim 1, characterized in that, Step S101 further includes: monitoring the oxygen concentration in the space between the engine exhaust pipe and the DOC catalyst using an oxygen sensor; if the oxygen concentration is insufficient, controlling the introduction of compressed air into the space between the engine exhaust pipe and the DOC catalyst using a metering valve.

3. A track locomotive exhaust gas aftertreatment device applying the exhaust gas aftertreatment method for track locomotives as described in any one of claims 1 to 2, characterized in that, Includes a shell, DOC catalyst, first SCR catalyst, second SCR catalyst, and ASC catalyst; The DOC catalyst, the first SCR catalyst, the second SCR catalyst, and the ASC catalyst are sequentially disposed within the housing; gaps are provided between each pair of the DOC catalyst, the first SCR catalyst, the second SCR catalyst, and the ASC catalyst; exhaust gas inlets and exhaust gas outlets are provided on both sides of the housing; the DOC catalyst is adjacent to the exhaust gas inlet; the ASC catalyst is adjacent to the exhaust gas outlet; the exhaust gas inlet is connected to the engine exhaust port; the exhaust gas outlet is connected to the atmosphere; It also includes bypass pipes and controllers; The two ends of the bypass pipe are respectively connected to the exhaust gas inlet and the space between the DOC catalyst and the first SCR catalyst; the bypass pipe is also equipped with a first metering valve; An ammonia sensor and a nitrogen-oxygen sensor are also provided in the space between the DOC catalyst and the first SCR catalyst; both the ammonia sensor and the nitrogen-oxygen sensor are electrically connected to the controller; the controller is electrically connected to the first metering valve.

4. The exhaust gas aftertreatment device for rail locomotives as described in claim 3, characterized in that, It also includes a supply pipeline; the two ends of the supply pipeline are respectively connected to the exhaust gas inlet and the compressed air source; the supply pipeline is also equipped with a second metering valve; The exhaust gas inlet is also equipped with an oxygen sensor; the oxygen sensor is electrically connected to the controller; the controller is electrically connected to the second metering valve.

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