An ammonia engine exhaust aftertreatment system and method of controlling the same

Abstract

An ammonia engine emission aftertreatment system and a control method thereof, the aftertreatment system comprising an SCR catalyst, an ASC catalyst, a gas mixer, a DNC catalyst, a main path throttle valve arranged on an exhaust pipe of the ammonia engine, a bypass pipeline connected to the front of an inlet of the DNC catalyst and the gas mixer respectively and provided with a bypass switch valve, a primary NOx sensor and a primary HN3 sensor arranged on the exhaust pipe, a first temperature sensor arranged at an inlet of the SCR catalyst, a second temperature sensor arranged at an inlet of the ASC catalyst and a third temperature sensor arranged at an outlet of the ASC catalyst, a tail NOx sensor and a tail HN3 sensor arranged at an outlet of the DNC catalyst; all the sensors, the main path throttle valve and the bypass switch valve are electrically connected to an ECU. X The present application utilizes the primary NH3 of the engine to reduce the ASC to generate by-products NO X , N2O, improves the aftertreatment effect without increasing the NH3 injection system, reduces the pollutant emission and realizes the ammonia engine ultra-low emission target. x ​

Description

Technical Field

[0001] This invention belongs to the field of ammonia engine exhaust gas purification technology, specifically relating to an after-treatment device and control method for pollutants emitted by ammonia engines. Background Technology

[0002] In the context of global efforts to reduce carbon emissions, new engines using ammonia as fuel can achieve zero carbon emissions and have promising application prospects in fields such as ships, non-road machinery, and heavy trucks.

[0003] Ammonia engines emit almost no carbon, but ammonia is inert during combustion, making it difficult to ignite and resulting in a slow flame propagation speed. Unignited NH3 is emitted with the exhaust gas, leading to a high concentration of NH3 in the original engine emissions—approximately 2 to 30 times higher than the NH3 concentration after urea decomposition in a diesel engine's aftertreatment system. Furthermore, because NH3 contains nitrogen (N), its combustion inevitably produces NO. x Byproducts such as nitrogen dioxide (N2O) are produced by ammonia engines, which, compared to traditional fossil fuel engines, produce less NO. x N2O emissions are even higher. The greenhouse effect of N2O is approximately 265-298 times stronger than that of CO2. If it cannot be eliminated through aftertreatment, it will significantly reduce the carbon emission benefits of ammonia engines. Precisely because of N2O's strong greenhouse effect, major economies worldwide have listed it as a key target for control in the next phase of emission regulations. Heavy-duty vehicle regulations will restrict N2O from two dimensions: first, by directly setting emission limits to restrict N2O specific emissions (mg / kWh); second, by setting greenhouse gas specific emission limits for engines of different power ranges, multiplying the N2O specific emissions by 273 to convert it into equivalent CO2 specific emissions for restriction. Heavy-duty vehicle regulations also require NO... x Emission limits have been reduced by 63%. Therefore, the issue of pollutant emissions must be addressed before ammonia engines can be used on a large scale.

[0004] To address the high NH3 emissions from ammonia engines, ascorbic acid catalytic converters (ASCs) are typically used to remove unburned NH3 from the emissions. During the catalytic oxidation of NH3 by ASCs, NO is generated. x Current post-treatment technologies lack the ability to eliminate NO byproducts such as ASC and N2O. x The methods used to remove N2O and NH3 make it difficult for both to meet the requirements of newer emission regulations. For example, the aftertreatment system disclosed in CN120798499A adopts the EHC+NDC+SCR+ASC route, which uses EHC to increase the aftertreatment temperature, NDC catalyst to eliminate N2O and reduce NH3 concentration, and SCR catalyst to eliminate NO. x Further reduce the NH3 concentration. The remaining untreated NH3 is eliminated by oxidation using an ASC catalyst. During the catalytic oxidation of NH3 by ASC, a side reaction occurs to generate NO. xWhen the concentration of NH3 in the engine exhaust is high, ASC generates NO. x There are no means to eliminate N2O, leading to NO... x There is a risk that N2O emissions will exceed the emission limits for the next stage. For example, CN121593877A discloses an aftertreatment device that uses the EHC+SCR+ASC+NDC route, which eliminates NO through SCR. x The process involves reducing NH3, eliminating NH3 with ASC, decomposing engine exhaust gases with NDC, and oxidizing NH3 with ASC to produce N2O. ASC also produces NO. x The lack of a reducing agent prevents its elimination; similarly, when the original NH3 concentration is high, NO will also be present. x Risk of exceeding standards. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing aftertreatment technologies for ammonia engines, specifically targeting the high levels of NH3, N2O, and NO in ammonia engines. x This paper addresses the emission characteristics of ammonia engines by providing a highly adaptable and efficient after-treatment system and control method, thus overcoming the shortcomings of existing after-treatment technologies in eliminating ASC-generated NO. x The method of using N2O can achieve synergistic purification of the three pollutants.

[0006] The technical solution adopted in this invention is as follows: An ammonia engine aftertreatment system includes an SCR catalyst mounted on the exhaust pipe of the ammonia engine, an ASC catalyst connected downstream of the SCR catalyst, a gas mixer connected downstream of the ASC catalyst, a DNC catalyst connected downstream of the gas mixer, a main throttle valve mounted on the exhaust pipe, a bypass pipe with its two ends connected to the inlet of the DNC catalyst and the gas mixer respectively, a bypass switch valve mounted on the bypass pipe, and a primary NOx emission control system mounted on the exhaust pipe. X The sensors include the primary HN3 sensor, the first temperature sensor located at the SCR catalyst inlet, the second temperature sensor located at the ASC catalyst inlet, the third temperature sensor located at the ASC catalyst outlet, and the tail NO sensor located at the DNC catalyst outlet. X Sensors and exhaust HN3 sensor; The original NO X Sensors, primary exhaust HN3 sensor, first temperature sensor, second temperature sensor, third temperature sensor, exhaust NO X The sensors, exhaust HN3 sensor, main throttle valve, and bypass switch valve are all electrically connected to the ECU of the ammonia engine.

[0007] Preferably, through holes are uniformly formed on the pipe section of the bypass pipe that extends into the mixer.

[0008] The control method for the ammonia engine aftertreatment system described in this invention is stored in the ECU. The ECU controls the valve opening in a closed loop by reading sensor signals, employing the following control strategy: (1) Set the system to the initial state. In the initial state, the main throttle valve is fully open and the bypass switch valve is closed. At the same time, set the main throttle valve and the bypass switch valve to the linkage state. That is, when the bypass switch valve is closed, the main throttle valve can only be fully open, and when the bypass switch valve is open, the main throttle valve can adjust the opening and closing angle. (2) After the ammonia engine starts, the aftertreatment system performs a self-test, and the ECU collects the original NO emissions. x Sensors, primary exhaust NH3 sensor, main throttle valve status, bypass switch valve status, first temperature sensor, second temperature sensor, third temperature sensor, exhaust NO x Data signals from the sensor and the exhaust NH3 sensor are used by the ECU to detect NO in the exhaust. x Sensors, primary exhaust NH3 sensor, exhaust NO x Before the sensor and exhaust NH3 sensor dew point signal, the system is in an initial state; if the ECU reads the original exhaust NO... x Sensors, primary exhaust NH3 sensor, exhaust NO x If one or more signals from the sensor or the exhaust NH3 sensor are abnormal, it indicates a malfunction in the aftertreatment system. (3) NO x After the NH3 sensor signal indicates that the dew point has been exceeded, the NO3 discharge will proceed through the original discharge channel. x The concentration signal of NH3 is used to calculate the original ammonia nitrogen ratio. When the original NH3 / NO3 ratio is... x When ≤1, the original NH3 emission preferentially ensures the SCR catalytic reduction of NO in the original emission. x The system maintains its initial state; when NH3 / NO x If the value is greater than 1, proceed to the next step; (4) Determine whether the aftertreatment system has reached the ignition temperature (T). 50 When the SCR inlet temperature displayed by the first temperature sensor is greater than the SCR ignition temperature, and the ASC inlet temperature displayed by the second temperature sensor is less than or equal to the ASC outlet temperature displayed by the third temperature sensor, the aftertreatment system is considered to have reached its operating temperature and proceeds to the next step; otherwise, it maintains the initial state. The SCR ignition temperature is the temperature at which the SCR catalyst NO... x The temperature at which the conversion efficiency reaches 50% is stored in the engine ECU; (5) Determine whether there is excessive NH3 before DNC based on the NH3 concentration signal detected by the tail discharge NH3 sensor, and eliminate the risk of NH3 leakage. If the NH3 concentration in the tail discharge is <10ppm, it is considered that there is no excessive NH3 and proceed to the next step; otherwise, maintain the initial state. (6) Based on the last NOx NO detected by the sensor in the tail exhaust x The concentration signal determines whether a reducing agent needs to be introduced into the DNC catalyst. When NO is emitted from the tail end... x When the concentration is >10 ppm, ASC oxidizes NH3 to produce NO. x NH3 needs to be introduced before DNC to reduce NO. x Proceed to the next step; otherwise, maintain the initial state. (7) Open the bypass switch valve, and the main throttle valve passes through the tail NO. x The concentration signal is used for closed-loop control, which employs the industry-standard PID algorithm, as follows: Calculate control values : ,

[0009] Calculate the opening of the main throttle valve:

[0010]

[0011] This invention sequentially sets up an SCR catalyst, an ASC catalyst, and a DNC catalyst, and adds a bypass line to the aftertreatment system to direct the exhaust NH3 to the DNC catalyst inlet, utilizing the exhaust NH3 to reduce ASC and generate the byproduct NO. x The use of N2O improves after-treatment efficiency and reduces pollutant emissions without adding an NH3 injection system, thus achieving the ultra-low emission target of ammonia engines.

[0012] This invention addresses the high levels of NH3, N2O, and NO in ammonia engines. x Based on the emission characteristics of ammonia engines, this paper presents a highly adaptable and efficient after-treatment system and control method for ammonia engines, which overcomes the lack of existing after-treatment technologies in eliminating ASC and generating NO. x The method of using N2O achieves synergistic purification of the three pollutants and has good application prospects. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the post-processing system of the present invention; Figure 2 This is the control strategy logic diagram of the post-processing system control method of the present invention; Figure 3 The difference between the NO values ​​in the embodiments and the comparative examples is that they are located at different positions. x Concentration change; Figure 4 The examples and comparative examples show the changes in N2O concentration at different locations; Figure 5 The variations in NH3 concentration at different locations are shown in the examples and comparative examples. Detailed Implementation

[0014] The present invention will be further described below with reference to specific embodiments and accompanying drawings. Example 1

[0015] like Figure 1 As shown, an ammonia engine aftertreatment system includes an SCR catalyst (selective reduction catalyst) 9 installed on the exhaust pipe 2 of the ammonia engine 1, an ASC catalyst (ammonia oxidation catalyst) 11 connected after the SCR catalyst, a gas mixer 13 connected after the ASC catalyst, a DNC catalyst (nitrous oxide removal catalyst) 14 connected after the gas mixer, a main throttle valve 6 installed on the exhaust pipe 2, a bypass pipe 5 with its two ends connected to the inlet of the DNC catalyst and the gas mixer respectively, a bypass switch valve 7 installed on the bypass pipe, and a primary NO emission control valve installed on the exhaust pipe. X Sensor 3 and original HN3 sensor 4, first temperature sensor 8 at the SCR catalyst inlet, second temperature sensor 10 at the ASC catalyst inlet, and third temperature sensor 12 at the ASC catalyst outlet, and tail NO at the DNC catalyst outlet. X Sensor 15 and tailpipe HN3 sensor 16.

[0016] The original NO X Sensor 3, Primary exhaust HN3 sensor 4, First temperature sensor 8, Second temperature sensor 9, Third temperature sensor 12, Exhaust NO X Sensor 15, exhaust HN3 sensor 16, main throttle valve 6, and bypass switch valve 7 are all electrically connected to the ECU (electronic control unit) of the ammonia engine 1.

[0017] The aftertreatment system of this invention is connected to the engine via an exhaust pipe and arranged sequentially along the airflow direction. The SCR catalyst is a Cu-Fe based molecular sieve catalyst and serves as the first-stage catalyst in the aftertreatment system, utilizing NH3 in the exhaust gas of the ammonia engine to catalytically reduce NO emissions. x The ASC catalyst is a Pt or Pt / Pd catalyst, installed after the SCR, for the catalytic oxidation of NH3 in emissions. A bypass line is used to divert the engine's exhaust gases into the mixer before flowing to the DNC for NO reduction. xN2O. The rear end of the bypass line is inserted into the mixer, and through holes are evenly distributed on the section of the pipe extending into the mixer to allow the incoming gas to flow into the mixer uniformly. The mixer is used to mix the bypass gas and the main gas evenly to improve the performance of the downstream DNC. The DNC catalyst is an Fe-based small-pore molecular sieve catalyst. When the bypass line is closed, the DNC utilizes the exhaust waste heat from the engine and the heat released from the oxidation of NH3 by Ascorbic Acid (ASC) to catalytically decompose N2O in the exhaust. When the bypass line is open, it utilizes the NH3 introduced from the exhaust to catalytically reduce the N2O in the exhaust and the NO generated by the oxidation of NH3 by ASC. x N2O. The flow rate of the main exhaust pipe and bypass pipe can be changed by controlling the opening of the main throttle valve, and the connection and disconnection of the bypass pipe can be achieved by controlling the bypass switch valve.

[0018] The original NO x The sensor and the primary exhaust NH3 sensor are used to collect NO in the primary exhaust of the ammonia engine. x Concentration, NH3 concentration. NO emissions x The sensor and the exhaust NH3 sensor are used to collect NO in the after-treatment purified exhaust gas. x Concentration, NH3 concentration.

[0019] To verify the effectiveness of the aftertreatment system and control method, three engine steady-state operating conditions were selected for performance verification of the aftertreatment system. Based on the engine speed and output power, the three operating conditions were defined as: high operating condition, medium operating condition, and low operating condition.

[0020] The control method of the ammonia engine aftertreatment system described in this invention employs, as follows: Figure 2 The control logic shown is as follows: (1) Initial state setting of the post-processing system: In the initial state, the main pipeline throttle valve is fully open and the bypass switch valve is closed; at the same time, the linkage setting of the main pipeline throttle valve and the bypass switch valve is completed. When the bypass switch valve is closed, the main pipeline throttle valve can only be fully open. When the bypass switch valve is open, the main pipeline throttle valve can adjust the opening and closing angle.

[0021] (2) After the engine starts, the aftertreatment system performs a self-test, and the ECU collects the original NO emissions. x Sensors, primary exhaust NH3 sensor, main throttle valve status, bypass switch valve status, first temperature sensor, second temperature sensor, third temperature sensor, exhaust NO x Data signals from the sensor and the exhaust NH3 sensor are used by the ECU to detect NO in the exhaust. x Sensors, primary exhaust NH3 sensor, exhaust NO x Before the sensor and exhaust NH3 sensor dew point signal, the system is in an initial state; if the ECU reads the original exhaust NO... x Sensors, primary exhaust NH3 sensor, exhaust NOx If one or more signals from the sensor or the exhaust NH3 sensor are abnormal, it indicates a malfunction in the aftertreatment system.

[0022] After the aftertreatment system completes its self-test, the ECU reads normal signals from all sensors and valves. When the engine is running at high operating conditions, the speed is 1500 r / min and the power is 295 kW; When the engine is running under medium operating conditions, the speed is 1200 r / min and the power is 120 kW; When the engine is running at low operating conditions, the speed is 1200 r / min and the power is 25 kW.

[0023] (3) NO x After the NH3 sensor signal indicates that the dew point has been exceeded, the NO3 discharge will proceed through the original discharge channel. x The concentration signal of NH3 is used to calculate the original ammonia nitrogen ratio. When the original NH3 / NO3 ratio is... x When ≤1, the original NH3 emission preferentially ensures the SCR catalytic reduction of NO in the original emission. x The system maintains its initial state; when NH3 / NO x If the result is greater than 1, proceed to the next step.

[0024] Confirm the ammonia-nitrogen ratio: Under high operating conditions: NO x After the NH3 sensor receives the dew point signal, NO... x NH3 concentration readings are normal, original NO emissions x Sensor (NO) x -1) The signal is 3078 ppm, and the signal of the primary exhaust NH3 sensor (NH3-1) is 7211 ppm. Primary exhaust NH3 / NO x =2.34>1, proceed to the next step; Under medium operating conditions: NO x The -1 signal was 3065 ppm, and the NH3-1 signal was 5029 ppm. The original discharge NH3 / NO... x =1.64>1, proceed to the next step; At low operating conditions: NO x The -1 signal was 2174 ppm, and the NH3-1 signal was 6101 ppm. The original discharge NH3 / NO... x =2.81>1, proceed to the next step.

[0025] (4) Determine whether the aftertreatment system has reached the ignition temperature (T). 50When the SCR inlet temperature displayed by the first temperature sensor is greater than the SCR ignition temperature, and the ASC inlet temperature displayed by the second temperature sensor is less than or equal to the ASC outlet temperature displayed by the third temperature sensor, the aftertreatment system is considered to have reached its operating temperature and proceeds to the next step; otherwise, it maintains the initial state. The SCR ignition temperature is the temperature at which the SCR catalyst NO... x The temperature at which the conversion efficiency reaches 50% was obtained through catalyst sample test bench or engine bench test and stored in the engine ECU.

[0026] Under high operating conditions: the signal from the first temperature sensor (T1) at the SCR inlet is 448℃, the signal from the second temperature sensor (T2) at the ASC inlet is 484℃, and the signal from the third temperature sensor (T3) at the ASC outlet is 635℃. The ignition temperature of the SCR catalyst sample experiment is 183℃. If T1 > 183℃ and T2 < T3, proceed to the next step. Under medium operating conditions: T1 = 438℃, T1 > 183℃; T2 = 477℃, T3 = 589℃, T2 < T3; Proceed to the next step; Under low operating conditions: T1=349℃, T1>183℃; T2=377℃, T3=475℃, T2<T3; Proceed to the next step.

[0027] (5) NH3 leakage check: Based on the NH3 concentration signal detected by the NH3 sensor in the tail discharge, determine whether there is excessive NH3 before DNC and eliminate the risk of NH3 leakage. If the NH3 concentration in the tail discharge is <10ppm, it is considered that there is no excessive NH3 and proceed to the next step; otherwise, maintain the initial state.

[0028] Under high operating conditions: Exhaust NH3 sensor (NO x -2) The concentration signal is 0 ppm, and the concentration of NH3 sensor (NH3-2) in the tail exhaust is <10 ppm. Proceed to the next step. Under medium operating conditions: NO x -2=0ppm, NH3-2<10ppm, proceed to the next step; At low operating conditions: NO x -2=1.2ppm, NH3-2<10ppm, proceed to the next step.

[0029] (6) Exhaust NO x Leakage inspection: based on tailpipe NO x NO detected by the sensor in the tail exhaust x The concentration signal determines whether a reducing agent needs to be introduced into the DNC catalyst. When NO is emitted from the tail end... x When the concentration is >10 ppm, ASC oxidizes NH3 to produce NO. x NH3 needs to be introduced before DNC to reduce NO. xProceed to the next step; otherwise, maintain the initial state.

[0030] Under high operating conditions: NO x -2=263ppm, NO in exhaust gas x When the concentration is greater than 10 ppm, ASC generates NO. x The concentration is high, so it is necessary to introduce NH3 from the original discharge to reduce NO. x Proceed to the next step; Under medium operating conditions: NO x -2 = 1096 ppm, NO x -2 > 10 ppm, proceed to the next step; At low operating conditions: NO x -2=76ppm, NO x -2 > 10 ppm, proceed to the next step.

[0031] (7) Open the bypass switch valve 7, and the main throttle valve 6 passes through NO x The -2 concentration signal is used for closed-loop control, which employs an industry-standard PID algorithm. The specific algorithm for the main throttle valve opening is as follows: Calculate control values ​​under high operating conditions : ,

[0032] Calculate the main circuit throttle valve opening under low operating conditions: ,

[0033] The results of treating the exhaust gases from the ammonia engine using the aftertreatment system and control method of this embodiment are shown in Table 1.

[0034] As shown in Table 1, under high operating conditions, the exhaust gas from the aftertreatment outlet was sampled and analyzed using a gas analyzer, and the test results were: NO x Concentration 7 ppm, NH3 concentration 2 ppm, N2O concentration 0 ppm; Under medium operating conditions, NO x The concentrations are 4 ppm, NH3 concentration is 1 ppm, and N2O concentration is 2 ppm; At low operating conditions, NO x The concentrations are 1 ppm, NH3 concentration is 3 ppm, and N2O concentration is 11 ppm.

[0035] The conversion efficiency of major pollutants is greater than 90% under all three operating conditions, achieving the ultra-low emission target of ammonia engine.

[0036] Comparative Example 1 The same catalyst and SCR+ASC+DNC integration method as in Example 1 were used. Unlike Example 1, Comparative Example 1 did not have a bypass pipe to introduce the exhaust gas into the DNC. The experiment was conducted on the exhaust end of the same engine, using the same high, medium, and low operating conditions for verification. The experimental conditions were kept as consistent as possible with those in Example 1. The exhaust test results are as follows, and a comparison with the examples is shown in Table 1.

[0037] Under high operating conditions, NO x The concentration was 1089 ppm, the NH3 concentration was 1 ppm, and the N2O concentration was 3 ppm; Under medium operating conditions, NO x The concentration was 913 ppm, the NH3 concentration was 0 ppm, and the N2O concentration was 2 ppm; Under medium operating conditions, NO x The concentration was 129 ppm, the NH3 concentration was 0 ppm, and the N2O concentration was 48 ppm.

[0038] NO under three operating conditions x High concentrations of NH3 in the exhaust, especially under high and medium operating conditions where the ASC inlet temperature exceeds 450℃, lead to the oxidation of NH3 into NO. x The NOx concentration in the tailpipes increased, exceeding 900 ppm, leading to increased NOx emissions in the aftertreatment system. x The conversion efficiency is less than 70%, far lower than that of the China VI emission standard aftertreatment system. Under low operating conditions, the ASC inlet temperature is 377℃, the N2O concentration generated by NH3 oxidation reaches 48ppm, and the N2O treatment efficiency of the aftertreatment system is only 62%.

[0039] Comparative Example 2 The same SCR catalyst, ASC catalyst, and DNC catalyst as in Example 1 were used, the difference being that they were integrated in a DNC+SCR+ASC manner (DNC catalyst, SCR catalyst, and ASC catalyst were arranged in sequence), and no bypass pipeline was installed. The DNC+SCR+ASC catalyst was installed on the exhaust end of the same engine for testing, and the same high, medium, and low operating conditions were used for verification. The experimental conditions were kept as consistent as possible with those in Example 1. The exhaust test results are as follows, and a comparison with Example 1 is shown in Table 1.

[0040] Under high operating conditions, NO x The concentration was 431 ppm, the NH3 concentration was 1 ppm, and the N2O concentration was 48 ppm; Under medium operating conditions, NO x The concentration was 290 ppm, the NH3 concentration was 1 ppm, and the N2O concentration was 63 ppm; At low operating conditions, NO x The concentration was 176 ppm, the NH3 concentration was 2 ppm, and the N2O concentration was 99 ppm.

[0041] NO under three operating conditions x The processing efficiency decreased compared to ratio 1, and the post-processing system NO under high operating conditions x The conversion efficiency is 86%. N2O emissions are all above 45 ppm under all three operating conditions, and the N2O conversion efficiency of the aftertreatment system is <30%.

[0042] Table 1: NO under different operating conditions in the examples and comparative examples x Comparison of N2O and NH3 treatment capacities

[0043] Examples and comparative examples show different NO positions in post-processing under high operating conditions. x Concentration changes such as Figure 3 As shown, post-processing entry NO x With similar concentrations, the first-stage catalyst SCR in Example 1 and Comparative Example 1 utilized the original NH3 to reduce NO in the original exhaust. x At SCR export NO x With a concentration close to 0 ppm, when the exhaust gas passes through the second-stage catalyst ASC, some of the original NH3 is catalytically oxidized to NO. x ASC Export NO x When the concentration exceeds 800 ppm, the exhaust gas passes through the third-stage DNC catalyst. In Example 1, NH3 from the original discharge is introduced through a bypass pipeline. The DNC uses this portion of NH3 to catalytically reduce ASC to NO. x NO at the post-processing system outlet x The concentration was only 7 ppm. In Comparative Example 1, NO was present at the post-treatment outlet in the absence of reducing agent in DNC. x The concentration was equivalent to 1089 ppm at the ASC outlet. In Comparative Example 2, the first-stage catalyst DNC ​​utilized the emitted NH3 to reduce part of the NO. x , make NO x The NO concentration decreased to 1903 ppm at the DNC catalyst outlet, after passing through the second-stage catalyst SCR. x When the concentration drops to 0 ppm, the remaining NH3 is oxidized by a third-stage ASC catalyst to produce NO as a byproduct. x Post-processing export NO x The concentration was 431 ppm.

[0044] Changes in N2O concentration at different locations, such as Figure 4 As shown, the first-stage catalyst SCR catalyst in Example 1 and Comparative Example 1 reduces NO. xA small amount of byproduct N2O is generated. Upon passing through ASC, NH3 oxidizes to generate a small amount of byproduct N2O. After passing through DNC, N2O is catalytically decomposed. In Example 1, the N2O concentration in the tail-end emission is 0 ppm, and in Comparative Example 1, the N2O concentration in the tail-end emission is 3 ppm. In Comparative Example 2, the first-stage catalyst DNC ​​almost completely eliminates N2O from the original tail-end emission. After passing through SCR, a small amount of N2O is generated at a concentration of 9 ppm. Upon passing through ASC, byproduct N2O is generated, increasing the N2O tail-end emission concentration to 48 ppm.

[0045] Changes in NH3 concentration at different locations, such as Figure 5 As shown, in Example 1 and Comparative Example 1, the first-stage SCR catalyst consumes part of the NH3 to reduce NO. x After ASC treatment, NH3 is essentially oxidized and eliminated. In Example 1, because the bypass line introduces NH3 into the engine exhaust, the concentration is maintained at 1233 ppm. After DNC treatment, NH3 is used to reduce NO. x And N2O, the tail gas concentration is 0 ppm. Comparative Example 2 exhaust gas, after passing through SCR and DNC, consumes part of the NH3 to reduce NO. x The remaining NH3 is eliminated by oxidation with N2O and ASC catalyst, and the NH3 concentration in the tail is 1 ppm.

Claims

1. An ammonia engine emission aftertreatment system, characterized in that, This includes an SCR catalyst (9) installed on the exhaust pipe (2) of the ammonia engine (1), an ASC catalyst (11) connected to the SCR catalyst, a gas mixer (13) connected to the ASC catalyst, a DNC catalyst (14) connected to the gas mixer, a main throttle valve (6) installed on the exhaust pipe (2), a bypass pipe (5) with its two ends connected to the DNC catalyst inlet and the gas mixer respectively, a bypass switch valve (7) installed on the bypass pipe, and a primary NO emission valve installed on the exhaust pipe. X Sensor (3) and original HN3 sensor (4), first temperature sensor (8) installed at the SCR catalyst inlet and second temperature sensor (10) installed at the ASC catalyst inlet and third temperature sensor (12) installed at the ASC catalyst outlet, and tail NO installed at the DNC catalyst outlet X Sensor (15) and tail exhaust HN3 sensor (16); The original NO X Sensor (3), primary exhaust HN3 sensor (4), first temperature sensor (8), second temperature sensor (9), third temperature sensor (12), exhaust NO X Sensor (15), exhaust HN3 sensor (16), main throttle valve (6), and bypass switch valve (7) are all electrically connected to the ECU of the ammonia engine (1).

2. The ammonia engine emission aftertreatment system according to claim 1, characterized in that, The bypass pipe (5) has through holes evenly opened on the pipe section that extends into the mixer.

3. The control method for the ammonia engine aftertreatment system as described in claim 1 or 2, characterized in that, The following control strategy is adopted: (1) Set the system to the initial state. In the initial state, the main throttle valve is fully open and the bypass switch valve is closed. At the same time, set the main throttle valve and the bypass switch valve to the linkage state. That is, when the bypass switch valve is closed, the main throttle valve can only be fully open, and when the bypass switch valve is open, the main throttle valve can adjust the opening and closing angle. (2) After the ammonia engine starts, the aftertreatment system performs a self-test, and the ECU collects the original NO emissions. x Sensors, primary exhaust NH3 sensor, main throttle valve status, bypass switch valve status, first temperature sensor, second temperature sensor, third temperature sensor, exhaust NO x Data signals from the sensor and the exhaust NH3 sensor are used by the ECU to detect NO in the exhaust. x Sensors, primary exhaust NH3 sensor, exhaust NO x Before the sensor and exhaust NH3 sensor dew point signal, the system is in an initial state; if the ECU reads the original exhaust NO... x Sensors, primary exhaust NH3 sensor, exhaust NO x If one or more signals from the sensor or the exhaust NH3 sensor are abnormal, it indicates a malfunction in the aftertreatment system. (3) NO x After the NH3 sensor signal indicates that the dew point has been exceeded, the NO3 discharge will proceed through the original discharge channel. x The concentration signal of NH3 is used to calculate the original ammonia nitrogen ratio. When the original NH3 / NO3 ratio is... x When ≤1, the original NH3 emission preferentially ensures the SCR catalytic reduction of NO in the original emission. x The system maintains its initial state; when NH3 / NO x If the value is greater than 1, proceed to the next step; (4) Determine whether the aftertreatment system has reached the ignition temperature. When the SCR inlet temperature displayed by the first temperature sensor is greater than the SCR ignition temperature, and the ASC inlet temperature displayed by the second temperature sensor is less than or equal to the ASC outlet temperature displayed by the third temperature sensor, the aftertreatment system is considered to have reached the operating temperature and proceeds to the next step; otherwise, maintain the initial state. The SCR ignition temperature is the temperature at which the SCR catalyst NO... x The temperature at which the conversion efficiency reaches 50% is stored in the engine ECU; (5) Determine whether there is excessive NH3 before DNC based on the NH3 concentration signal detected by the tail discharge NH3 sensor, and eliminate the risk of NH3 leakage. If the NH3 concentration in the tail discharge is <10ppm, it is considered that there is no excessive NH3 and proceed to the next step; otherwise, maintain the initial state. (6) Based on the last NO x NO detected by the sensor in the tail exhaust x The concentration signal determines whether a reducing agent needs to be introduced into the DNC catalyst. When NO is emitted from the tail end... x When the concentration is >10 ppm, ASC oxidizes NH3 to produce NO. x NH3 needs to be introduced before DNC to reduce NO. x Proceed to the next step; otherwise, maintain the initial state. (7) Open the bypass switch valve, and the main throttle valve passes through the tail NO. x The concentration signal is used for closed-loop control, which employs the industry-standard PID algorithm, as follows: Calculate control values : , ； Calculate the opening of the main throttle valve:

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