An exhaust gas treatment device and method for an ammonia diesel engine

Abstract

The present invention discloses an exhaust gas treatment device and method for an ammonia-diesel engine. The exhaust gas treatment device includes an SCR-ASC front assembly, a DOC, a DPF, and an SCR-ASC rear assembly arranged in sequence. In both the SCR-ASC front assembly and the SCR-ASC rear assembly, the SCR is arranged in front of the ASC; an electric heating device is arranged in front of the SCR in the SCR-ASC front assembly, and an ammonia nozzle is arranged in front of the SCR in the SCR-ASC rear assembly. The ammonia nozzle is connected to a liquid ammonia tank, and the liquid ammonia tank is the ammonia source configured for the ammonia-diesel engine. In the present invention, the ammonia source of the SCR borrows the NH3 used for engine combustion, eliminating the urea injection system and completely solving the problem of urea crystallization; the present invention also arranges the SCR-ASC front assembly in front of the DOC, enabling the unburned NH3 to be completely consumed in the SCR and ASC in the ammonia-diesel mode, and solving the problem of N2O generated by the high-concentration NH3 passing through the DOC.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle exhaust gas treatment devices, and in particular to an exhaust gas treatment device and method for an ammonia diesel engine. Background Art

[0002] In the vehicle field, the traditional diesel internal combustion engine exhaust treatment device is an oxidation catalyst (DOC) + particulate filter (DPF) + selective catalytic reducer (SCR) + ammonia slip catalyst (ASC) system, in which the DOC is used to purify carbon monoxide and hydrocarbons in the exhaust gas; the DPF is used to capture large particles (5um) in the exhaust gas by collision and interception, and to capture small particles less than 100nm by diffusion, which makes the particle capture efficiency of the DPF as high as 95% or more; the SCR injects urea into the exhaust pipe through the urea injection system, and under the action of the catalyst, the nitrogen oxides and urea undergo a reduction reaction, thereby achieving the purpose of removing nitrogen oxides. A urea injection system is required, including a urea tank, a urea injection pipeline, and a nozzle. ASC uses a catalyst coating such as precious metals on the inner wall of the carrier to catalytically oxidize the exhaust gas, which can be used to eliminate excess NH3 or unreacted NH3 in the SCR.

[0003] Most of the existing diesel engine exhaust treatment devices use urea aqueous solution to decompose NH3, which is used as the ammonia source of SCR for the reduction reaction of nitrogen oxides (NOX). This will cause a series of problems such as urea crystallization, low SCR conversion efficiency caused by inferior urea, nozzle clogging, catalyst clogging, etc. Solid ammonia is rarely used as an ammonia source; the durability of solid ammonia storage materials has not been solved, and carrying a large solid ammonia tank only as an ammonia source for the post-treatment system increases the weight of the vehicle and the cost.

[0004] Compared with pure diesel engines, ammonia-diesel engines have added NH3 as fuel, so the exhaust contains a large amount of unburned NH3. When high-concentration NH3 passes through DOC, a large amount of N2O is produced. The greenhouse effect of N2O is 300 times that of CO2, and it cannot be removed by post-treatment devices. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides an exhaust gas treatment device and method for an ammonia-diesel engine. In the present invention, the ammonia source of the SCR is the NH3 used for engine combustion, the urea injection system is eliminated, and the urea crystallization problem is completely solved. The present invention also arranges the SCR-ASC pre-assembly before the DOC, so that the unburned NH3 can be completely consumed in the SCR and ASC in the ammonia-diesel mode, solving the problem of high-concentration NH3 generating N2O through the DOC.

[0006] In order to solve the above technical problems, the present invention is implemented by the following technical solutions:

[0007] On the one hand, the present invention provides an exhaust gas treatment device for an ammonia-diesel engine, the exhaust gas treatment device comprising an SCR-ASC front assembly, a DOC, a DPF, and an SCR-ASC rear assembly which are arranged in sequence from front to back, wherein the SCR in the SCR-ASC front assembly and the SCR-ASC rear assembly is arranged at the front end of the ASC; an electric heating device is arranged at the front end of the SCR in the SCR-ASC front assembly, and the electric heating device is used to heat the exhaust gas; an ammonia nozzle is arranged at the front end of the SCR in the SCR-ASC rear assembly, and the ammonia nozzle is connected to a liquid ammonia tank, and the liquid ammonia tank is an ammonia source configured for the ammonia-diesel engine.

[0008] Preferably, an ammonia sensor is provided at the rear end of the SCR-ASC post-assembly, and the ammonia sensor is used to monitor the ammonia content in the exhaust gas.

[0009] Preferably, the exhaust outlet end of the ammonia diesel engine, the front end of the SCR-ASC pre-assembly and the front end of the SCR-ASC post-assembly are all provided with temperature sensors, and the temperature sensors are used to monitor the exhaust gas temperature.

[0010] Preferably, a hydrocarbon nozzle is provided at the front end of the DOC.

[0011] Preferably, pressure sensors are provided at the front and rear ends of the DPF.

[0012] Preferably, the front and rear ends of the SCR-ASC rear assembly are both provided with nitrogen oxide sensors, and the nitrogen oxide sensors are used to monitor the nitrogen oxide content in the exhaust gas.

[0013] On the other hand, the present invention also provides a method for treating tail gas of an ammonia diesel engine, comprising:

[0014] When the exhaust temperature of the ammonia-diesel engine is lower than the first preset temperature value, the ammonia-diesel engine enters the pure diesel mode. In the pure diesel mode, the supply of ammonia to the engine is suspended, and the exhaust gas is sequentially processed by the SCR-ASC pre-assembly, DOC, DPF, and SCR-ASC post-assembly before being discharged. The ammonia source required by the SCR in the SCR-ASC post-assembly is provided by the liquid ammonia tank;

[0015] When the exhaust temperature of the ammonia-diesel engine is greater than the first preset temperature value, the temperature of the front end of the SCR in the heated SCR-ASC front assembly is greater than the second preset temperature value, and the ammonia-diesel engine enters the ammonia-diesel mode. In the ammonia-diesel mode, ammonia is supplied to the engine and ammonia supply to the SCR-ASC rear assembly is suspended. The exhaust gas is processed by the SCR-ASC front assembly, DOC, DPF, and SCR-ASC rear assembly in sequence and then discharged; the first preset temperature value is less than the second preset temperature value.

[0016] Preferably, when the exhaust temperature of the ammonia diesel engine is greater than the first preset temperature value and the SCR front end temperature in the SCR-ASC pre-assembly is greater than the third preset temperature value, heating is stopped; the second preset temperature value is less than the third preset temperature value.

[0017] Preferably, the first preset temperature value is 250°C, and the second preset temperature value is 400°C.

[0018] Preferably, the third preset temperature value is 450°C.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0020] The exhaust gas treatment device of the present invention is compatible with the pure diesel mode and the ammonia diesel mode. The exhaust gas treatment method of the present invention can be divided into the pure diesel mode and the ammonia diesel mode according to the engine exhaust temperature as a dividing line, specifically:

[0021] When the engine exhaust temperature is below the first preset temperature value (250°C) (engine start-up phase), the engine runs in pure diesel mode. The ammonia source required for SCR in the SCR-ASC rear assembly is provided by a liquid ammonia tank. By using the liquid ammonia tank used for engine combustion, the urea injection system is eliminated, and the urea crystallization problem is completely solved. By using the liquid ammonia tank, only one injection line needs to be separated, which reduces the weight of the vehicle and the cost of the post-treatment system, while also improving the conversion efficiency of the SCR.

[0022] When the engine exhaust temperature is above a first preset temperature value (250°C), the temperature of the front end of the SCR in the SCR-ASC front assembly is made greater than a second preset temperature value (400°C) by heating, and the ammonia-diesel engine enters the ammonia-diesel mode (engine constant operation stage). In the ammonia-diesel mode, ammonia is supplied to the engine and ammonia supply to the SCR-ASC rear assembly is suspended. The present invention arranges the SCR-ASC front assembly before the DOC, and improves the conversion efficiency of the SCR-ASC to NH3 by heating, so that the unburned NH3 can be basically consumed in the SCR and ASC (conversion rate is above 99%), thereby solving the problem of high-concentration NH3 generating N2O through the DOC.

[0023] When the exhaust temperature of the ammonia-diesel engine is greater than the first preset temperature value (250°C) and the SCR front end temperature in the SCR-ASC pre-assembly is greater than the third preset temperature value (450°C), heating is stopped; this is because when the heating temperature is greater than 450°C, the SCR-ASC pre-assembly has little improvement in the conversion efficiency of NH3. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the system principle of the tail gas treatment device of the present invention.

[0025] Numbers in the figure: 1. SCR-ASC front assembly; 11. Electric heating device; 2. DOC; 21. Hydrocarbon nozzle; 3. DPF; 31. Pressure sensor; 4. SCR-ASC rear assembly; 41. Nitrogen oxide sensor; 5. Ammonia diesel engine; 6. Liquid ammonia tank; 7. Ammonia nozzle; 8. Ammonia sensor; 9. Temperature sensor. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention, the preferred implementation scheme of the present invention is described below in conjunction with specific embodiments. However, it should be understood that the drawings are only used for exemplary description and cannot be understood as a limitation on this patent. In order to better illustrate this embodiment, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted. The positional relationship described in the drawings is only for exemplary description and cannot be understood as a limitation on this patent.

[0027] like Figure 1 As shown, the present invention provides an exhaust gas treatment device for an ammonia diesel engine, the exhaust gas treatment device comprises an SCR-ASC pre-assembly 1, a DOC2, a DPF3, and an SCR-ASC post-assembly 4 which are arranged in sequence. Among them, a hydrocarbon nozzle 21 is arranged at the front end of the DOC2, and a pressure sensor 31 is arranged at the front and rear ends of the DPF3. The SCR-ASC pre-assembly 1 is arranged at the front end of the DOC2, and the unburned NH3 can be completely consumed in the SCR-ASC pre-assembly 1 by heating with an electric heating device 11, thereby solving the problem of high-concentration NH3 generating N2O through DOC2.

[0028] The SCR-ASC pre-assembly 1 is composed of an SCR and an ASC. The SCR is arranged at the front end of the ASC. An electric heating device 11 is arranged at the front end of the SCR. The electric heating device 11 is used to increase the temperature of the exhaust gas entering the SCR system, which can improve the conversion efficiency of the SCR-ASC pre-assembly 1 to NH3; a temperature sensor 9 is arranged at the front end of the SCR-ASC pre-assembly 1, and the temperature sensor 9 is used to monitor the temperature of the exhaust gas heated by the electric heating device 11; a temperature sensor 9 is arranged at the exhaust outlet end of the ammonia-diesel engine 5, which is used to monitor the exhaust temperature of the ammonia-diesel engine 5.

[0029] The SCR-ASC rear assembly 4 is composed of an SCR and an ASC, and the SCR is arranged at the front end of the ASC; an ammonia sensor 8 is arranged at the rear end of the SCR-ASC rear assembly 4, and the ammonia sensor 8 is used to monitor the ammonia content in the exhaust gas; a temperature sensor 9 is arranged at the front end of the SCR-ASC rear assembly 4; nitrogen oxide sensors 41 are arranged at the front and rear ends of the SCR-ASC rear assembly 4, and the nitrogen oxide sensors 41 are used to monitor the nitrogen oxide content in the exhaust gas.

[0030] Furthermore, an ammonia nozzle 7 is provided at the front end of the SCR in the SCR-ASC rear assembly 4, and the ammonia nozzle 7 is connected to a liquid ammonia tank 6, which is an ammonia source configured for the ammonia diesel engine 5. The ammonia source of the SCR uses the liquid ammonia tank 6 used for combustion of the ammonia diesel engine 5, eliminating the urea injection system and completely solving the urea crystallization problem; using the engine fuel ammonia tank, only one injection pipeline needs to be separated, reducing the weight of the whole vehicle, reducing the cost of the post-processing system, and also improving the conversion efficiency of the SCR.

[0031] Based on the above structure, the present invention provides an exhaust gas treatment method for an ammonia diesel engine, comprising:

[0032] When the exhaust temperature of the ammonia-diesel engine 5 is lower than the first preset temperature value (250°C), the ammonia-diesel engine 5 enters the pure diesel mode. In the pure diesel mode, the supply of ammonia to the engine is suspended, and the exhaust gas is sequentially processed by the SCR-ASC pre-assembly 1, DOC2, DPF3, and SCR-ASC post-assembly 4 before being discharged. The ammonia source required by the SCR in the SCR-ASC post-assembly 4 is provided by the liquid ammonia tank 6;

[0033] When the exhaust temperature of the ammonia-diesel engine 5 is greater than the first preset temperature value (250°C), the temperature of the front end of the SCR in the heated SCR-ASC front assembly 1 is greater than the second preset temperature value (400°C), and the ammonia-diesel engine 5 enters the ammonia-diesel mode. In the ammonia-diesel mode, ammonia is supplied to the engine and ammonia is supplied to the SCR-ASC rear assembly 4. The exhaust gas is sequentially processed by the SCR-ASC front assembly 1, DOC2, DPF3, and SCR-ASC rear assembly 4 before being discharged;

[0034] When the exhaust temperature of the ammonia diesel engine 5 is greater than the first preset temperature value (250° C.), and the SCR front end temperature in the SCR-ASC front assembly 1 is greater than the third preset temperature value (450° C.), the heating is stopped.

[0035] The reasons for selecting the first preset temperature value, the second preset temperature value and the third preset temperature value are as follows:

[0036] Table 1 DOC performance, inlet NH3 1000ppm; space velocity 200K h-1

[0037] DOC Performance 200℃ 250℃ 300℃ 350℃ 400℃ 450℃ 500℃ <![CDATA[NH3 conversion efficiency / %]]> 3 92 97 98 99 99 99 <![CDATA[Production capacity of N2O / ppm]]> 0 180 230 170 100 60 30 NOX generation capacity / ppm 0 40 240 510 660 820 900

[0038] Table 2 SCR performance, inlet NH3 600ppm; space velocity 60K h-1

[0039] SCR Performance 200℃ 250℃ 300℃ 350℃ 400℃ 450℃ 500℃ <![CDATA[NH3 conversion efficiency / %]]> 0 0 0 70 93 96 99 <![CDATA[The N2O generation capacity / ppm]]> 0 5 24 37 34 32 36 NOX generation capacity / ppm 0 0 40 66 68 69 100

[0040] Table 3 ASC performance, inlet NH3 1000ppm; space velocity 200K h-1

[0041] ASC Performance 200℃ 250℃ 300℃ 350℃ 400℃ 450℃ 500℃ <![CDATA[NH3 conversion efficiency / %]]> 2 55 75 78 81.5 83 86 <![CDATA[Production capacity of N2O / ppm]]> 0 70 90 60 40 25 15 NOX generation capacity / ppm 0 0 0 15 40 70 90

[0042] Combined with Table 1, it can be seen that when the exhaust temperature is ≥250℃, the ability of DOC2 to convert NH3 is greater than 92%, but a large amount of N2O is generated at the same time, with a maximum of 250ppm; therefore, the SCR-ASC pre-assembly 1 needs to be adjusted before DOC2, which can greatly reduce the amount of N2O generated to tens of ppm.

[0043] Combining Tables 2 and 3, it can be seen that when the SCR temperature is lower than 250°C, the NH3 conversion efficiency is 0; when the ASC temperature is lower than 250°C, the NH3 conversion efficiency is 55%; when the temperature is lower than 250°C, the conversion efficiency of SCR\ASC to NH3 is extremely low. Therefore, when the engine exhaust temperature is less than 250°C, the engine operates in pure diesel mode, and the exhaust gas treatment device operates in accordance with the pure diesel mode; in pure diesel mode, the reducing agent NH3 required by the SCR-ASC rear assembly 4 is provided by the engine fuel liquid ammonia tank 6 and enters the exhaust gas treatment device through the ammonia nozzle 7.

[0044] Combining Tables 2 and 3, it can be seen that the optimal window for SCR to convert NOX is 350-450℃, and the optimal window for SCR\ASC to convert NH3 is >400℃. SCR\ASC comprehensively considers three factors: NOX conversion capacity, NH3 conversion capacity, and low N2O generation. Therefore, the SCR\ASC temperature should be controlled at 400-450℃. Therefore, when the engine exhaust temperature is >250℃, the electric heating device 11 is started, so that when the exhaust gas temperature at the front end of the SCR-ASC pre-assembly 1 is >400℃, the engine enters the ammonia-diesel model and burns ammonia; when the exhaust gas temperature at the front end of the SCR-ASC pre-assembly 1 is >450℃, the heating stops; when the exhaust gas temperature at the front end of the SCR-ASC pre-assembly 1 is <400℃, the heating starts to keep the exhaust gas temperature at the front end of the SCR-ASC pre-assembly 1 in the range of 400-450℃.

[0045] In the 5th mode of the ammonia diesel engine, the exhaust gas temperature at the front end of the SCR-ASC front assembly 1 is maintained at ≥400℃, the NH3 conversion efficiency of the SCR is higher than 93%, and the NH3 conversion efficiency of the ASC is higher than 81.5%; when there is 2000ppm NH3 in the exhaust gas, accompanied by 800ppm NOX entering the exhaust gas treatment device, the following reactions are performed:

[0046] NO+NH3→N2+H2O

[0047] NO+NO2+NH3→N2+H2O

[0048] The NOX conversion efficiency at 400°C is close to 100%. The NOX reaction consumes 800ppm NH3, leaving 1200ppm NH3. After 93% conversion by SCR and 81.5% conversion by ASC, 15.5ppm remains.

[0049] The technical features of the pressure sensor, nitrogen oxide sensor, ammonia sensor, temperature sensor, etc. described in the present invention (constituent units / elements of the present invention), unless otherwise specified, are obtained from conventional commercial channels or prepared by conventional methods. Their specific structures, working principles, and possible control methods and spatial layout methods can be selected conventionally in the field and should not be regarded as the innovative points of the present invention. For those skilled in the art, it is understandable that the patent of the present invention will not be further elaborated.

[0050] According to the description and drawings of the present invention, those skilled in the art can easily manufacture or use the exhaust gas treatment device of an ammonia diesel engine of the present invention, and can produce the positive effects described in the present invention.

[0051] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. An exhaust gas treatment device for an ammonia diesel engine, characterized in that: The exhaust gas treatment device comprises an SCR-ASC front assembly (1), a DOC (2), a DPF (3), and an SCR-ASC rear assembly (4) which are arranged in sequence from front to back, wherein the SCR in the SCR-ASC front assembly (1) and the SCR-ASC rear assembly (4) are both arranged at the front end of the ASC; an electric heating device (11) is arranged at the front end of the SCR in the SCR-ASC front assembly (1), and the electric heating device (11) is used to heat the exhaust gas; an ammonia nozzle (7) is arranged at the front end of the SCR in the SCR-ASC rear assembly (4), and the ammonia nozzle (7) is connected to a liquid ammonia tank (6), and the liquid ammonia tank (6) is an ammonia source configured for the ammonia diesel engine (5); The exhaust gas treatment method of the ammonia diesel engine includes: When the exhaust temperature of the ammonia-diesel engine (5) is lower than a first preset temperature value, the ammonia-diesel engine (5) enters a pure diesel mode. In the pure diesel mode, the supply of ammonia to the engine is suspended, and the exhaust gas is sequentially processed by the SCR-ASC front assembly (1), the DOC (2), the DPF (3), and the SCR-ASC rear assembly (4) before being discharged. The ammonia source required by the SCR in the SCR-ASC rear assembly (4) is provided by the liquid ammonia tank (6); When the exhaust temperature of the ammonia-diesel engine (5) is greater than a first preset temperature value, the temperature of the front end of the SCR in the heated SCR-ASC front assembly (1) is greater than a second preset temperature value, and the ammonia-diesel engine (5) enters an ammonia-diesel mode. In the ammonia-diesel mode, ammonia is supplied to the engine and ammonia supply to the SCR-ASC rear assembly (4) is suspended. The exhaust gas is sequentially processed by the SCR-ASC front assembly (1), the DOC (2), the DPF (3), and the SCR-ASC rear assembly (4) before being discharged; The first preset temperature value is lower than the second preset temperature value.

2. The exhaust gas treatment device of an ammonia diesel engine according to claim 1, characterized in that: An ammonia sensor (8) is arranged at the rear end of the SCR-ASC rear assembly (4), and the ammonia sensor (8) is used to monitor the ammonia content in the exhaust gas.

3. The exhaust gas treatment device of an ammonia diesel engine according to claim 1, characterized in that: The exhaust outlet of the ammonia diesel engine, the front end of the SCR-ASC front assembly (1) and the front end of the SCR-ASC rear assembly (4) are all provided with temperature sensors (9), and the temperature sensors (9) are used to monitor the exhaust gas temperature.

4. The exhaust gas treatment device of an ammonia diesel engine according to claim 1, characterized in that: A hydrocarbon nozzle (21) is provided at the front end of the DOC (2).

5. The exhaust gas treatment device of an ammonia diesel engine according to claim 1, characterized in that: Pressure sensors (31) are provided at the front and rear ends of the DPF (3).

6. The exhaust gas treatment device of an ammonia diesel engine according to claim 1, characterized in that: The front and rear ends of the SCR-ASC rear assembly (4) are both provided with nitrogen oxide sensors (41), and the nitrogen oxide sensors (41) are used to monitor the nitrogen oxide content in the exhaust gas.

7. The exhaust gas treatment device of an ammonia diesel engine according to claim 1, characterized in that: When the exhaust temperature of the ammonia diesel engine (5) is greater than a first preset temperature value and the SCR front end temperature in the SCR-ASC front assembly (1) is greater than a third preset temperature value, heating is stopped; the second preset temperature value is less than the third preset temperature value.

8. The exhaust gas treatment device of an ammonia diesel engine according to claim 1, characterized in that: The first preset temperature value is 250°C, and the second preset temperature value is 400°C.

9. The exhaust gas treatment device of an ammonia diesel engine according to claim 7, characterized in that: The third preset temperature value is 450°C.

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