SCR (Selective Catalytic Reduction) mixer and tail gas after-treatment device
By coating the dehydrogenation catalyst on the steel wool of the SCR mixer and using the cyclone and rectifier tube structure, the problem of urea crystallization under low load conditions is solved, and the exhaust gas mixing uniformity and urea nozzle compatibility are improved. Reduced costs.
Patent Information
- Application Number
- CN202323671286.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-30
- Publication Date
- 2024-12-17
- Estimated Expiration
- 2033-12-30
AI Technical Summary
When existing SCR mixers run for a long time under low load conditions of the engine, they are prone to urea crystallization problems, which affects the exhaust gas treatment effect.
The dehydrogenation catalyst coating is applied on the steel wool of the SCR mixer, and the isocyanate catalytic decomposition isocyanate into isocyanogen and hydrogen ions is used to prevent the formation of urea crystals, and improve the exhaust gas through the cyclone and rectifier tube structures. Mixing uniformity.
It effectively reduces the occurrence of urea crystallization, improves the robustness and atomization effect of urea nozzles, increases the mixing uniformity of exhaust gas, and reduces the production cost of urea nozzles.
Smart Images
Figure CN222184900U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of tail gas post-processing, in particular to an SCR mixer and a tail gas post-processing device. Background Art
[0002] Selective catalytic reduction technology (SCR): urea is converted into ammonia as a reducing agent and nitrogen oxides undergo catalytic reduction reaction under the action of a catalyst to purify exhaust gas.
[0003] In actual use of existing SCR mixers, urea crystals are prone to occur in the mixer due to the wide variety of operating conditions of the entire vehicle, especially when the engine runs for a long time under low load conditions and there is a need to inject urea. Utility Model Content
[0004] In view of the deficiencies in the prior art, the purpose of the embodiments of the present utility model is to provide an SCR mixer to solve the problem of urea crystallization when the engine runs for a long time under low load conditions and there is a need to inject urea.
[0005] In order to achieve the above purpose, the embodiment of the utility model provides the following technical solutions:
[0006] An SCR mixer comprises: a conduit, steel wool, a swirl tube and a rectifier tube; the conduit has an air inlet and an air outlet, the steel wool is arranged at the air inlet, the rectifier tube is arranged at the air outlet, the swirl tube is arranged in the conduit and is located downstream of the steel wool; wherein the steel wool has a dehydrogenation catalyst coating.
[0007] Optionally, the conduit is a bent pipe, comprising an air inlet pipe section, a bent pipe section and an air outlet pipe section arranged in sequence, the steel wool is arranged at the air inlet of the air inlet pipe section, the swirl tube is arranged at the air inlet pipe section, and the rectifier tube is arranged at the air outlet of the air outlet pipe section.
[0008] Optionally, the end and side opening of the air inlet pipe section form the air inlet of the conduit, and the end opening of the air outlet pipe section forms the air outlet of the conduit.
[0009] Optionally, the swirl tube includes a tube body, a tube wall of the tube body is provided with swirl grooves in a circumferential array, a swirl fin is provided at the position of each swirl groove, and the swirl fin is arranged on the outer side of the tube body.
[0010] Optionally, the tube body is a conical tube, comprising a small end and a large end, the small end of the tube body faces the steel wool, and the large end of the tube body matches the inner diameter of the catheter.
[0011] Optionally, the rectifier tube includes a first sealing plate, a side plate and a second sealing plate, the first sealing plate and the second sealing plate are respectively located at both ends of the side plate, the first sealing plate, the second sealing plate and the side plate form a closed structure, and rectifying holes are opened on the first sealing plate and the second sealing plate.
[0012] Optionally, the side plate is a conical tube, which includes a small mouth end and a large mouth end, the small mouth end of the conical tube is located upstream of the airflow of the large mouth end, the first sealing plate is arranged at the small mouth end of the conical tube, the second sealing plate is arranged at the large mouth end of the conical tube, and the tube wall of the conical tube is also provided with a rectifying hole.
[0013] Optionally, the dehydrogenation catalyst coating is a tungsten carbide coating.
[0014] Optionally, the dehydrogenation catalyst coating has a thickness of 3 nm-5 nm.
[0015] The embodiment of the utility model further provides an exhaust gas post-treatment device, comprising the SCR mixer as described above.
[0016] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:
[0017] 1. The utility model coats the dehydrogenation catalyst onto the steel wool of the SCR mixer to form a dehydrogenation catalyst coating on the steel wool. If the engine is running at a low load, that is, when the exhaust temperature of the diesel engine is low, isocyanic acid will precipitate. At this time, isocyanic acid is decomposed into isocyanate and hydrogen ions under the catalytic action of the dehydrogenation catalyst tungsten carbide. Before the isocyanic acid forms urea crystals, it is cracked to form isocyanate and hydrogen ions that cannot be crystallized, effectively solving the urea crystallization problem when the engine runs for a long time under low load conditions and there is a need to inject urea. By coating the dehydrogenation catalyst on steel wool, the contact efficiency is higher and the dehydrogenation effect is better. Therefore, the atomization effect of the urea nozzle can be appropriately reduced, which is conducive to reducing the requirements for the performance of the urea nozzle, increasing the robustness of the urea nozzle, and reducing the production cost of the urea nozzle.
[0018] 2. In the mixer of the utility model, after urea is sprayed by the urea nozzle, it flows through the steel wool to mix with the engine exhaust gas, flows through the swirl tube, increases the turbulent disturbance of the exhaust gas, thereby achieving the mixing of urea and the diesel engine exhaust gas, and then flows through the rectifier tube downstream of the swirl tube, further increasing the mixing of the exhaust gas and improving the mixing uniformity of the exhaust gas.
[0019] Additional advantages of the present invention will be given in the following description, and some will become apparent from the following description or will be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation on the present invention.
[0021] Figure 1 It is an assembly diagram of the SCR mixer provided by the embodiment of the utility model;
[0022] Figure 2 It is an exploded diagram of the SCR mixer provided by the embodiment of the utility model;
[0023] Figure 3 It is a schematic diagram of a cyclone tube provided in an embodiment of the utility model;
[0024] Figure 4 This is a stereoscopic diagram of a rectifier tube provided in an embodiment of the utility model;
[0025] Figure 5 This is a top view of a rectifier tube provided in an embodiment of the utility model;
[0026] Figure 6 This is a bottom view of a rectifier tube provided by an embodiment of the utility model;
[0027] In the figure: 1, conduit; 2, steel wool; 3, swirl tube; 31, tube body; 32, swirl fin; 33, swirl groove; 4, rectifier tube; 41, first sealing plate; 42, rectifier hole; 43, side plate; 44, second sealing plate;
[0028] In order to show the positions of various parts, the distances or sizes between them are exaggerated and the schematic diagram is for reference only. DETAILED DESCRIPTION
[0029] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.
[0030] Urea nozzle: a device used to spray urea into the selective catalytic reduction unit. The urea nozzle is the simplest and most reliable mechanical device to achieve the atomization of liquid working fluid. It has two main functions: one is to spray the urea aqueous solution at a certain cone angle at high speed and atomize it into fine droplets; the other is the metering function, which is to spray a certain amount of urea according to the signal given by the ECU. The atomization performance and atomization cone angle of the urea nozzle are important indicators for evaluating the performance of the nozzle, and play an important role in the treatment of NOx in the engine exhaust. The motion state and evaporation of the droplets after the spray hits the wall will affect the formation of the liquid film. The formation and accumulation of the liquid film may cause the crystallization and deposition of urea. A large amount of sediment will affect the performance of the exhaust pipe and even block the exhaust pipe, seriously affecting the catalytic reduction performance, and will also cause waste of urea solution.
[0031] NOx: A general term for nitrogen oxides, usually including NO and NO2, which are common air pollutants.
[0032] In theory, urea aqueous solution will eventually generate NH3 after thermal decomposition in the SCR catalytic converter, but in the actual process, some other chemical reactions may be mixed, causing the urea aqueous solution to decompose and generate HNCO (isocyanate). At around 150-190, HNCO (isocyanate) can react with urea under certain conditions to generate biuret (N3H5 (CO) 2). As the temperature rises, it can react to generate ammeline (C3N3 (OH) 2NH2), ammeline (C3N3OH (NH2) 2), melamine (C3N3 (NH2) 3), etc. at around 250-300. As these by-products generated during the decomposition of urea continue to deposit on the inner wall of the SCR catalytic converter, crystals are generated. Therefore, the crystals are mainly a mixture of biuret and melamine, among which the decomposition temperature of the crystal components mainly composed of biuret is low, while the decomposition temperature of the crystal components mainly composed of melamine is relatively high.
[0033] As mentioned in the background technology, in the actual use process of the existing SCR mixer, when the engine runs for a long time under low-load conditions and there is a need to spray urea, urea crystals are particularly prone to occur in the mixer. In order to avoid the occurrence of such problems or the reduction of the amount of urea crystals, the urea spray beam sprayed by the urea nozzle is required to have a better atomization effect to reduce the risk of urea crystals. In order to prevent urea crystals from causing the post-processing function to fail or the engine fuel consumption to increase, thereby reducing economic performance, the utility model proposes an SCR mixer to eliminate or reduce the occurrence of urea crystals, while eliminating the problems caused by crystallization of the post-processing system.
[0034] like Figure 1 , Figure 2As shown, an SCR mixer is proposed in one embodiment of the utility model, comprising: a conduit 1, steel wool 2, a swirl tube 3 and a rectifier tube 4; the conduit 1 has an air inlet and an air outlet, the steel wool 2 is arranged at the air inlet, the rectifier tube 4 is arranged at the air outlet, and the swirl tube 3 is arranged in the conduit 1 and is located downstream of the steel wool 2;
[0035] The urea spray jet from the urea nozzle directly hits the steel wool 2 of the mixer, which increases the secondary atomization of the urea particles, making the urea particles finer, that is, the SMD (Sott mean particle diameter) is smaller and the atomization is better. When the atomized particle size is small, the decomposition efficiency of the urea particles is relatively good when the engine exhaust temperature is low.
[0036] Since isocyanic acid is a necessary reactant for the formation of urea crystals, it is necessary to inhibit isocyanic acid from continuing to react to form urea crystals. Based on this, a dehydrogenation catalyst coating is coated on the steel wool 2, wherein the dehydrogenation catalyst coating can be a tungsten carbide coating, and the thickness of the dehydrogenation catalyst coating is 3nm-5nm. If the engine is running at a low load, that is, when the exhaust temperature of the diesel engine is low, isocyanic acid will precipitate. At this time, isocyanic acid is decomposed into isocyanide and hydrogen ions under the catalytic action of the dehydrogenation catalyst tungsten carbide. Before the isocyanic acid forms urea crystals, it is cracked to form isocyanide and hydrogen ions (HNCO→NCO - +H + ), effectively solving the problem of urea crystallization in the mixer. When the engine exhaust temperature rises, the isocyanate will decompose to generate ammonia and water, which effectively solves the problem of urea crystallization in the mixer.
[0037] In addition, there is also a solution in the prior art to coat the nozzle with a dehydrogenation catalyst, which is mainly used to solve the problem of urea nozzle orifice clogging due to urea dehydration and crystallization when the urea nozzle is not working. However, the coating is mainly coated on the nozzle, and compared with the present application, there are still the following problems:
[0038] 1) When the dehydrogenation catalyst is coated on the orifice plate, there is a urea solution at the nozzle. At this time, the coating contacts the urea solution instead of isocyanic acid, so the dehydrogenation effect is very poor.
[0039] 2) Urea is sprayed out from the orifice plate of the nozzle. At this time, when the engine is running at low conditions, the exhaust temperature is not high, and the urea is basically not decomposed, and it is still a urea solution; and the contact time between the urea and the orifice plate is very short during injection; based on the above two points, it is difficult for the nozzle to achieve the dehydrogenation effect at this time.
[0040] 3) The orifice plate is relatively small, with a diameter of 10 to 20 mm, and a relatively small contact area, which is far smaller than the volume of steel wool 2, resulting in a poor dehydrogenation effect.
[0041] like Figure 1 , Figure 2 As shown, the conduit 1 in this embodiment is a curved pipe, and the conduit 1 includes an intake pipe section ( Figure 1 The vertical section in the middle), the bent section and the outlet section ( Figure 1 The steel wool 2 is arranged at the air inlet of the air inlet pipe section, the swirl pipe 3 is arranged at the air inlet pipe section, and the rectifier pipe 4 is arranged at the air outlet of the air outlet pipe section. The end and side openings of the air inlet pipe section form the air inlet of the conduit 1, and the end opening of the air outlet pipe section forms the air outlet of the conduit 1. In a limited space, by adopting the elbow setting, the running length of the exhaust gas and ammonia is increased, and the mixing uniformity is improved.
[0042] like Figure 1 , Figure 3 As shown, the cyclone tube 3 includes a tube body 31, and a cyclone groove 33 is provided on the tube wall of the tube body 31 in a circumferential array manner. A cyclone fin 32 is provided at the position of each cyclone groove 33, and the cyclone fin 32 is arranged on the outer surface of the tube body 31. The tube body 31 is a conical tube, and the tube body 31 includes a small end and a large end. The small end of the tube body 31 faces the steel wool 2, and the large end of the tube body 31 matches the inner diameter of the conduit 1. After the exhaust gas enters the cyclone tube 3, since the cyclone fin 32 has a certain angle, the exhaust gas will rotate along this angle, and the exhaust gas will be mixed more evenly with the ammonia decomposed by urea under the action of cyclone and turbulence.
[0043] like Figure 4 , Figure 5 , Figure 6 As shown, the rectifier tube 4 includes a first sealing plate 41, a side plate 43 and a second sealing plate 44, the first sealing plate 41 and the second sealing plate 44 are respectively located at the two ends of the side plate 43, the first sealing plate 41, the second sealing plate 44 and the side plate 43 form a closed structure, and the first sealing plate 41 and the second sealing plate 44 are provided with rectifying holes 42. Furthermore, the side plate 43 is a conical tube, the conical tube includes a small mouth end and a large mouth end, the small mouth end of the conical tube is located upstream of the large mouth end, the first sealing plate 41 is arranged at the small mouth end of the conical tube, the second sealing plate 44 is arranged at the large mouth end of the conical tube, and the tube wall of the conical tube is also provided with rectifying holes 42. At present, most rectifying structures are plate structures with fewer holes, and the degree of uniformity improvement is not high.
[0044] The rectifier tube 4 in this embodiment adopts a three-dimensional porous structure. The ammonia and exhaust gas pass through the rectifier holes of the first sealing plate 41 or the conical side plate 43 and then pass through the rectifier holes 42 of the second sealing plate 44, so that the ammonia and exhaust gas pass through the porous plate structure twice, which increases the disturbance of the airflow and improves the mixing uniformity of the exhaust gas.
[0045] In the mixer of the utility model, after urea is sprayed by the urea nozzle, it flows through the steel wool 2 to mix with the engine exhaust gas, flows through the swirl tube 3, increases the turbulent disturbance of the exhaust gas, thereby achieving the mixing of urea and the exhaust gas of the diesel engine, and then flows through the rectifying tube 4 downstream of the swirl tube 3, further increases the mixing of the exhaust gas and improves the mixing uniformity of the exhaust gas.
[0046] In summary, the utility model has the following technical effects:
[0047] (1) The structure is relatively simple and the processing difficulty is low. The turbulent disturbance of the mixed exhaust gas is increased by the swirl tube 3, and the rectifier tube 4 structure is added. The swirl disturbance and the rectifier tube 4 are used in a limited space to increase the mixing uniformity of the exhaust gas in the mixer;
[0048] (2) By adding a tungsten carbide coating to the steel wool 2, the formation of crystals by isocyanic acid is eliminated or at least greatly reduced.
[0049] (3) The tungsten carbide coating is provided on the steel wool 2, which increases the robustness of the system and the compatibility with the urea nozzle.
[0050] Based on the above-mentioned SCR mixer, an embodiment of the utility model further provides an exhaust gas after-treatment device, in which the SCR mixer described in the above-mentioned embodiment is arranged. After the exhaust gas passes through the DOC and the DPF at the tail pipe, it enters the mixer and mixes with urea to form a mixture of urea and exhaust gas. The urea is then hydrolyzed to generate ammonia, which reacts with the nitrogen oxides in the exhaust gas to generate nitrogen and water, so as to reduce the emission of nitrogen oxides.
[0051] Although the above describes the specific implementation methods of the utility model in combination with the accompanying drawings, it is not intended to limit the scope of protection of the utility model. Technical personnel in the relevant field should understand that on the basis of the technical solution of the utility model, various modifications or deformations that can be made by technical personnel in this field without creative work are still within the scope of protection of the utility model.
Claims
1. An SCR mixer, characterized in that: include: ducts, steel wool, swirl tubes and rectifier tubes; The conduit has an air inlet and an air outlet, the steel wool is arranged at the air inlet, the rectifier tube is arranged at the air outlet, and the swirl tube is arranged in the conduit and is located downstream of the steel wool; wherein the steel wool has a dehydrogenation catalyst coating.
2. The SCR mixer according to claim 1, characterized in that: The conduit is a curved pipe, comprising an air inlet pipe section, a bent pipe section and an air outlet pipe section arranged in sequence, the steel wool is arranged at the air inlet of the air inlet pipe section, the swirl pipe is arranged at the air inlet pipe section, and the rectifier pipe is arranged at the air outlet of the air outlet pipe section.
3. The SCR mixer according to claim 2, characterized in that: The end and the side opening of the air inlet pipe section form the air inlet of the conduit, and the end opening of the air outlet pipe section forms the air outlet of the conduit.
4. The SCR mixer according to claim 1, characterized in that: The swirl tube comprises a tube body, a tube wall of which is provided with swirl grooves in a circumferential array, and a swirl fin is arranged at each swirl groove, and the swirl fin is arranged on the outer side of the tube body.
5. The SCR mixer according to claim 4, characterized in that: The tube body is a conical tube, comprising a small end and a large end, the small end of the tube body faces the steel wool, and the large end of the tube body matches the inner diameter of the catheter.
6. The SCR mixer according to claim 1, characterized in that: The rectifier tube includes a first sealing plate, a side plate and a second sealing plate. The first sealing plate and the second sealing plate are respectively located at two ends of the side plate. The first sealing plate, the second sealing plate and the side plate form a closed structure, and rectifying holes are opened on the first sealing plate and the second sealing plate.
7. The SCR mixer according to claim 6, characterized in that The side plate is a conical tube, which includes a small end and a large end. The small end of the conical tube is located upstream of the large end in the airflow. The first sealing plate is arranged at the small end of the conical tube, and the second sealing plate is arranged at the large end of the conical tube. The tube wall of the conical tube is also provided with rectifying holes.
8. The SCR mixer according to claim 1, characterized in that: The dehydrogenation catalyst coating is a tungsten carbide coating.
9. The SCR mixer according to claim 1, characterized in that: The thickness of the dehydrogenation catalyst coating is 3nm-5nm.
10. An exhaust gas post-treatment device, characterized in that: Comprising the SCR mixer as described in any one of claims 1-9.