WO2020019463A1

WO2020019463A1 - Spoiler structure applied to tail gas treatment and composite scr mixer

Info

Publication number: WO2020019463A1
Application number: PCT/CN2018/106921
Authority: WO
Inventors: 张超锋; 孙川; 候晓澄
Original assignee: 江南大学
Priority date: 2018-07-27
Filing date: 2018-09-21
Publication date: 2020-01-30
Also published as: CN108843432A

Abstract

Disclosed are a spoiler structure applied to a tail gas treatment and a composite SCR mixer. The spoiler structure (100) comprises: a first spoiler member (101), comprising a grid (101a), a baffle plate (101b) and a first peripheral wall (101c), with the baffle plate (101b) being arranged on the grid (101a), and the first peripheral wall (101c) being arranged at the outer periphery of the grid (101a); and a second spoiler member (102), the second spoiler member (102) comprising a rotating blade (102a) and a second peripheral wall (102b), with the second peripheral wall (102b) being arranged at the outer periphery of the first peripheral wall (101c), and the rotating blade (102a) being arranged between the second peripheral wall (102b) and the first peripheral wall (101c). The spoiler structure has a compact structure. With the rotating blade (102a) of the second spoiler member (102), the flowing speed of gas near a pipe wall can be effectively increased in order to improve the component homogenization effect; and at the same time, the temperature of the pipe wall is increased to reduce the risk of crystal substances forming on the pipe wall. In addition, the grid (101a) and the baffle plate (101b) of the first spoiler member (101) are densely arranged, so that the speed uniformity of the gas flow can be improved.

Description

Spoiler structure applied to exhaust gas treatment and composite SCR mixer

Technical field

The invention relates to the technical field of exhaust aftertreatment of diesel engines, in particular to a spoiler structure and a composite SCR mixer applied to exhaust gas treatment.

Background technique

Previous research results show that installing a proper mixer in the SCR mixer can significantly improve the flow field distribution. The mixer can fully mix the vapor phase and the liquid phase, accelerate the pyrolysis of the urea aqueous solution, thereby improving the conversion efficiency of the catalyst and reducing the risk of crystallization on the wall. The indicators for measuring the mixer mainly include: carrier velocity uniformity, ammonia uniformity, back pressure loss and anti-crystallization performance under low temperature operation of the engine. Generally, the static mixing unit fixed in the pipe is used to change the flow state of the exhaust gas, so that the fluid is in the pipeline. The flow impacts various types of plate elements, thereby breaking the spray droplets. Existing mixers are divided into two categories: grid baffle structure and spiral leaf structure.

The grid baffle structure mixer uses grid-shaped blades staggered up and down as a mixing unit, and the inclination angle of each blade is generally 45 degrees. Rotary blade structure mixers usually use several blades with a certain angle with the horizontal plane, which are divided into single-layer arrangement type and double-layer arrangement type. The former mixer structure can get better velocity uniformity of the front end of the carrier, but the ammonia uniformity is relatively low, and the latter is just the opposite. In terms of anti-crystallization performance, the grid baffle structure can effectively prevent the formation of block crystals in the middle of the mixer, while the rotary leaf structure mixer can effectively suppress the formation of crystals on the tube wall of the catalyst.

Summary of the Invention

The purpose of this section is to summarize some aspects of the embodiments of the invention and to briefly introduce some preferred embodiments. Simplifications or omissions may be made in this section and the abstract and title of the invention to avoid obscuring the purpose of this section, the abstract, and the title of the invention, and such simplifications or omissions cannot be used to limit the scope of the invention.

In view of the above-mentioned existing spoiler structure applied to exhaust gas treatment and the problems existing in the composite SCR mixer, the present invention is proposed.

Therefore, the object of the present invention is to provide a spoiler structure and a compound SCR mixer for tail gas treatment, and the rotary blade of the second spoiler can effectively increase the gas flow velocity near the tube wall and improve the component homogenization effect. At the same time, the temperature of the pipe wall is increased to reduce the risk of crystal formation on the pipe wall; and the grids and baffles of the first spoiler are densely arranged, which can improve the uniformity of the speed of the airflow; the structure of each part of the first spoiler and the second spoiler The functions can be mutually promoted to achieve the effect of maximizing the functions of the hybrid accessories in a limited space.

In order to solve the above technical problems, the present invention provides the following technical solution: a spoiler structure applied to exhaust gas treatment, the spoiler structure includes a first spoiler, including a grille, a baffle, and a first peripheral wall; The baffle is disposed on the grille, and the first peripheral wall is disposed on the periphery of the grille; and a second spoiler, the second spoiler includes a rotary blade and a second peripheral wall, The second peripheral wall is disposed on the periphery of the first peripheral wall, and the spiral leaf is interposed between the second peripheral wall and the first peripheral wall.

As a preferred solution of the spoiler structure and the compound SCR mixer used in the exhaust gas treatment according to the present invention, the grid includes a horizontal substrate and a vertical substrate, and the horizontal substrate and the vertical substrate are intersected.

As a preferred solution of the spoiler structure and the compound SCR mixer used in the exhaust gas treatment according to the present invention, the plane N formed by the horizontal substrate and the vertical substrate is arranged at a certain angle with the baffle.

As a preferred solution of the spoiler structure and composite SCR mixer according to the present invention applied to exhaust gas treatment, the baffle is divided into a first facing body and a second facing body, and the first facing body and The second facing bodies are arranged adjacently, and the adjacent first facing bodies and the second facing bodies are staggered in opposite directions.

As a preferred solution of the spoiler structure and the compound SCR mixer used in the exhaust gas treatment according to the present invention, the first facing body and the second facing body are both disposed on the vertical substrate.

As a preferred solution of the spoiler structure and the composite SCR mixer according to the present invention, the first peripheral wall and the second peripheral wall are both annular structures.

As a preferred solution of the spoiler structure and composite SCR mixer according to the present invention, the spiral blade includes a first end surface, a second end surface, a third end surface, and a fourth end surface. The first end face, the second end face, the third end face, and the fourth end face are connected end to end in sequence;

The second end surface and the fourth end surface are both arc-shaped structures, and the second end surface is disposed on the periphery of the fourth end surface.

As a preferred solution of the spoiler structure and composite SCR mixer according to the present invention, the connection points of the first end face, the second end face, the third end face, and the fourth end face are sequentially One intersection n, second intersection n, third intersection n and fourth intersection n;

Wherein, the first intersection edge n and the second intersection edge n are respectively connected to both ends of the first peripheral wall;

Wherein, the third intersection n and the fourth intersection n are respectively connected to both ends of the second peripheral wall.

As a preferred solution of the spoiler structure and the compound SCR mixer used in the exhaust gas treatment according to the present invention, a compound CSR mixer is based on the compound according to claims 1 to 8 Application of spoiler structure,

Wherein, the mixer further includes a mixing accessory, and the spoiler structure is disposed in the mixing accessory.

As a preferred solution of the spoiler structure and the compound SCR mixer used in the exhaust gas treatment of the present invention, the mixing accessories include a carrier and a spraying member, and the spraying member is embedded in and arranged at a certain angle. Inside the carrier

Wherein, the nozzle of the spraying member faces the grille of the spoiler structure.

Beneficial effects of the present invention: The present invention has reasonable design, compact spoiler structure, and the rotating blades of the second spoiler can effectively increase the gas flow velocity near the tube wall, increase the component homogenization effect, and simultaneously increase the tube wall temperature and reduce the tube. The risk of wall crystal formation; and the dense arrangement of the grille and baffle of the first spoiler can improve the uniformity of the velocity of the airflow; the structural functions of the first spoiler and the second spoiler can promote each other, achieving In the limited space, the effect of the maximum function of the hybrid accessories is exerted; at the same time, under the premise of ensuring high mixing uniformity, the back pressure loss is the lowest compared to traditional hybrid accessories, which meets the needs of use.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to explain the technical solution of the embodiment of the present invention more clearly, the drawings used in the description of the embodiments are briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. Those of ordinary skill in the art can obtain other drawings according to these drawings without paying creative labor. among them:

FIG. 1 is a schematic structural view of the spoiler structure applied to the exhaust gas treatment of the present invention and the front view of the spoiler structure of the first embodiment of the composite SCR mixer.

FIG. 2 is a schematic view of a rear view of a spoiler structure applied to exhaust gas treatment according to the present invention and a spoiler structure according to the first embodiment of the composite SCR mixer.

FIG. 3 is a schematic view of a spoiler structure applied to exhaust gas treatment according to the present invention and the structure of a rotary blade according to the first embodiment of the composite SCR mixer.

FIG. 4 is a schematic diagram of the structure of a spoiler structure applied to exhaust gas treatment according to the present invention and a compound SCR mixer according to a second embodiment of the compound SCR mixer.

FIG. 5 is a spoiler structure applied to exhaust gas treatment according to the present invention and a, b, c, and d of a third embodiment of the composite SCR mixer, which respectively represent four types of grid plate type, baffle type, rotary blade type, and composite type. Schematic diagram of the spoiler structure.

FIG. 6 is a velocity field cloud diagram of four spoiler structures a, b, c, and d of the third embodiment of the composite SCR mixer according to the spoiler structure applied to the exhaust gas treatment of the present invention.

FIG. 7 is a schematic diagram of the velocity distribution within 10 cm of the front surface of the four spoiler structures a, b, c, and d of the third embodiment of the composite SCR mixer according to the spoiler structure applied to the exhaust gas treatment of the present invention.

FIG. 8 is a schematic diagram of the front-end surface velocity distribution cloud diagram of the four spoiler structures a, b, c, and d of the third embodiment of the composite SCR mixer according to the spoiler structure applied to the exhaust gas treatment of the present invention.

FIG. 9 is a schematic diagram of the ammonia distribution within 10 cm of the front end surface of the four spoiler structures a, b, c, and d of the third embodiment of the composite SCR mixer according to the spoiler structure applied to the exhaust gas treatment of the present invention.

FIG. 10 is a schematic diagram of an ammonia distribution cloud at the front end surface of the four spoiler structures a, b, c, and d of the third embodiment of the composite SCR mixer according to the spoiler structure applied to the exhaust gas treatment of the present invention.

FIG. 11 is a schematic diagram of the liquid film temperature distribution of the agitator structure of four types of agitator structure a, b, c, and d of the composite SCR mixer according to the third embodiment of the present invention applied to exhaust gas treatment.

FIG. 12 is a liquid film thickness distribution diagram of a turbulent structure applied to exhaust gas treatment according to the present invention, and a, b, c, and d four turbulent structure mixers of the third embodiment of the composite SCR mixer.

FIG. 13 is a schematic diagram of a radial temperature distribution downstream of the four spoiler structures a, b, c, and d of the third embodiment of the composite SCR mixer according to the spoiler structure applied to the exhaust gas treatment of the present invention.

FIG. 14 is a spoiler structure applied to exhaust gas treatment according to the present invention, and a, b, c, and d four types of spoiler structures of the third embodiment of the composite SCR mixer. Distribution diagram.

FIG. 15 is a turbulent structure applied to the exhaust gas treatment of the present invention and a liquid film distribution diagram on the side of the tube wall of the four turbulent structures a, b, c, and d of the third embodiment of the composite SCR mixer.

FIG. 16 is a liquid film distribution diagram of the bottom surface of the tube wall of the four types of spoiler structures a, b, c, and d of the third embodiment of the composite SCR mixer according to the spoiler structure applied to the exhaust gas treatment of the present invention.

FIG. 17 is a schematic view of the turbulent structure applied to the exhaust gas treatment of the present invention and the distribution of crystals upstream of the four turbulent structure a, b, c, and d mixers of the third embodiment of the composite SCR mixer.

FIG. 18 is a schematic view of a crystalline structure downstream of four turbulent structures a, b, c, and d of the third embodiment of the composite SCR mixer according to the turbulent structure applied to the exhaust gas treatment of the present invention.

FIG. 19 is a schematic diagram showing the weighing quality of the four spoiler structures a, b, c, and d of the third embodiment of the compound SCR mixer according to the present invention, which is used for exhaust gas treatment.

FIG. 20 is a schematic diagram of the spoiler structure applied to the exhaust gas treatment of the present invention and the pressure loss of the four spoiler structures a, b, c, and d of the third embodiment of the composite SCR mixer.

detailed description

In order to make the foregoing objects, features, and advantages of the present invention more comprehensible, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In the following description, many specific details are set forth in order to fully understand the present invention, but the present invention can also be implemented in other ways than those described herein, and those skilled in the art can do this without violating the meaning of the present invention. Similar promotion, so the present invention is not limited by the specific embodiments disclosed below.

Secondly, "an embodiment" or "an embodiment" referred to herein refers to a particular feature, structure, or characteristic that can be included in at least one implementation of the present invention. The appearances of "in one embodiment" in various places in this specification do not all refer to the same embodiment, nor are they separate or selectively mutually exclusive embodiments.

Secondly, the present invention is described in detail with reference to schematic diagrams. In the detailed description of the embodiments of the present invention, for convenience of explanation, the cross-sectional view showing the structure of the device will not be partially enlarged according to general proportions, and the schematic diagrams are merely examples, which should not be used here Limit the scope of protection of the present invention. In addition, the actual production should include three-dimensional space dimensions of length, width and depth.

Referring to FIGS. 1 and 2, a first embodiment of the present invention provides a turbulent structure applied to exhaust gas treatment and a schematic diagram of the overall structure of a composite SCR mixer. As shown in FIG. 1, a turbulence applied to exhaust gas treatment is provided. The flow structure and the composite SCR mixer include a spoiler structure 100 including a first spoiler 101 including a grille 101a, a baffle 101b, and a first peripheral wall 101c. The baffle 101b is provided on the grille 101a, and the first periphery The wall 101c is provided on the periphery of the grille 101a; and, the second spoiler 102 includes a spiral blade 102a and a second peripheral wall 102b, and the second peripheral wall 102b is provided on the periphery of the first peripheral wall 101c. The rotary blade 102a is interposed between the second peripheral wall 102b and the first peripheral wall 101c.

Specifically, the main structure of the present invention includes a spoiler structure applied to exhaust gas treatment. The spoiler structure 100 includes a first spoiler 101 and a second spoiler 102. The structural functions of the two components can promote each other to achieve In the limited space, the effect of the maximum function of the mixing accessories is exerted. At the same time, under the premise of ensuring high mixing uniformity, the back pressure loss is the lowest compared to traditional mixing accessories. It should be noted that the first spoiler 101 includes the grille 101a. The baffle 101b and the first peripheral wall 101c cooperate with each other, so that under forced convection, vortex diffusion and molecular diffusion are achieved, so that the gas and liquid phases are fully mixed, and the speed and the uniformity of ammonia distribution are simultaneously improved. Purpose, further, the baffle 101b is disposed on the grille 101a, and the first peripheral wall 101c is wrapped around the periphery of the grille 101a. Preferably, the grille 101a, the baffle 101b, and the first peripheral wall 101c are integrated structures. The second spoiler 102 divides the airflow into a large-scale vortex, so that the airflow is rotated near the wall surface of the bearing member 201 to generate a vortex, which promotes mass transfer at the bearing member, and includes a rotating blade 102a and a second periphery. 102b, the second peripheral wall 102b is disposed on the periphery of the first peripheral wall 101c, and the two are connected by the rotary blade 102a, so the rotary blade 102a is interposed between the second peripheral wall 102b and the first peripheral wall 101c, and the rotary blade 102a is generated The near-wall surface swirls, which creates a surface coupling effect with the middle airflow, improves the wall heat distribution, reduces the risk of liquid film accumulation at the pipe wall, and can effectively reduce the probability of crystal formation. Better, the first spoiler 101 and the second The spoiler 102 is an integrated structure and is made of cast iron or stainless steel.

Further, the grid 101a includes a horizontal substrate 101a-1 and a vertical substrate 101a-2, and the horizontal substrate 101a-1 and the vertical substrate 101a-2 are intersected, wherein the number of the horizontal substrate 101a-1 and the vertical substrate 101a-2 is at least There are two (the number in the figure is for reference only), where the plane N formed by the horizontal substrate 101a-1 and the vertical substrate 101a-2 and the baffle 101b are arranged at a certain angle, and the angle and Yes, in this embodiment, the plane N formed by the horizontal substrate 101a-1 and the vertical substrate 101a-2 is arranged at an angle of 45 ° with the baffle plate 101b; and the horizontal substrate 101a-1 and the vertical substrate 101a-2 are perpendicular to each other. Settings.

Further, the baffle 101b is divided into a first facing body 101b-1 and a second facing body 101b-2, and the first facing body 101b-1 and the second facing body 101b-2 are disposed adjacent to each other, and adjacent to the first facing body 101b-1 and second orientation body 101b-2 are staggered in reverse, which can create turbulence on the exhaust gas and promote rapid pyrolysis of droplets. In the illustration, the first orientation body 101b-1 and the second orientation body 101b-2 Both are trapezoidal structures; it should be noted that the first facing body 101b-1 and the second facing body 101b-2 are both disposed on the vertical substrate 101a-2.

Further, the first peripheral wall 101c and the second peripheral wall 102b are both annular structures, and the two are concentric rings; the first peripheral wall 101c is disposed inside the second peripheral wall 102b.

Further, referring to FIG. 3, at least two rotary blades 102a are arranged, and the two rotary blades 102a are arranged clockwise (the number in the figure is for reference only). The rotary blade 102a includes a first end surface 102a-1 and a second end surface 102a. -2, the third end face 102a-3 and the fourth end face 102a-4, the first end face 102a-1, the second end face 102a-2, the third end face 102a-3, and the fourth end face 102a-4 are sequentially connected end to end; among them, Both the second end surface 102a-2 and the fourth end surface 102a-4 are arc-shaped structures, and the second end surface 102a-2 is disposed on the periphery of the fourth end surface 102a-4; it should be noted that the first end surface 102a-1, the second end surface The junctions of the end faces 102a-2, the third end face 102a-3, and the fourth end face 102a-4 are, in order, the first intersection n1, the second intersection n2, the third intersection n3, and the fourth intersection n4; A cross edge n1 and a second cross edge n2 are connected to both ends of the first peripheral wall 101c; wherein a third cross edge n3 and a fourth cross edge n4 are connected to both ends of the second peripheral wall 102b; specifically The fourth intersecting edge n4 is disposed below the adjacent rotary blade 102a, and the adjacent rotary blade 102a is partially stacked, that is, the spiral structure as a whole.

Referring to FIG. 4, a second embodiment of the present invention is different from the first embodiment in that the composite SCR mixer includes a spoiler structure 100, and further includes a mixing accessory 200, a spoiler structure 100 and a hybrid The fittings 200 cooperate with each other to achieve the maximum function of the mixed fittings 200 in a limited space and the process of discharging. At the same time, under the premise of ensuring high mixing uniformity, the back pressure loss is the lowest compared to the traditional mixing fittings 200, which meets Usage requirements. Specifically, referring to FIG. 1, the main structure includes a spoiler structure 100 including a first spoiler 101 and a second spoiler 102, and the structural functions of the two components can promote each other to achieve the maximum performance of the hybrid accessories in a limited space. The effect of function; At the same time, under the premise of ensuring high mixing uniformity, the back pressure loss is the lowest compared to traditional mixing accessories. It should be noted that the first spoiler 101 includes a grille 101a, a baffle 101b, and a first periphery. The wall 101c and the three cooperate with each other, so that they can be fully mixed by the vortex diffusion and molecular diffusion under forced convection, and the purpose of simultaneously improving the speed and the uniformity of ammonia distribution is achieved. Further, the baffle 101b It is arranged on the grille 101a, and the first peripheral wall 101c is wrapped around the periphery of the grille 101a. Preferably, the grille 101a, the baffle 101b, and the first peripheral wall 101c are an integrated structure; the second spoiler 102, The airflow is divided into large-scale vortices, so that the airflow rotating near the wall surface of the carrier 201 generates vortices, which promotes mass transfer at the carrier, and includes a rotating blade 102a and a second peripheral wall 102b. The second peripheral wall 102b is provided at The periphery of a peripheral wall 101c, the two are connected by a rotating blade 102a, so the rotating blade 102a is located between the second peripheral wall 102b and the first peripheral wall 101c. The near-wall surface swirl generated by the spiral blade 102a and the middle airflow Generate surface coupling effect, improve the wall heat distribution, reduce the risk of liquid film accumulation at the wall of the tube, and effectively reduce the probability of crystal formation. Preferably, the first spoiler 101 and the second spoiler 102 are integrated structures. Made of cast iron or stainless steel. The composite SCR mixer also includes a mixing part 200. The mixing part 200 includes a carrier 201 and a sprinkler 202. The sprinkler 202 is embedded in the carrier 201 by welding at a certain angle, and the spoiler structure 100 is disposed in the carrier 201 The two can be made by bolts or welding. Among them, the spraying part 202 uses a three-hole nozzle, the carrier 201 is a cylindrical shell and is made of cast iron, and the nozzle of the spraying part 202 faces the turbulence in the same direction as the exhaust gas flow direction. The grille 101a of the structure 100 provides such a better mixing.

Further, both ends of the bearing member 201 are provided with a first connection flange 201a and a second connection flange 201b. The first connection flange 201a is connected to the exhaust exhaust pipe by a bolt, and the second connection flange 201b is connected to the exhaust pipe by a bolt. Exhaust gas inlet pipe connection.

5 to 20, this is a third embodiment of the present invention. This embodiment is different from the above embodiment in that a series of comparative experiments are performed to prove the optimal performance of the present spoiler structure 100. It should be noted that the present interference The flow structure 100 is a composite structure. Specifically, the spoiler structure 100 is installed in a suitable mixing fitting 200, which can make the composite SCR mixer significantly improve the flow field distribution, make the vapor phase meet the liquid phase to be fully mixed, and accelerate the pyrolysis of the urea aqueous solution, thereby improving the composite SCR mixing. The conversion efficiency of the device reduces the risk of crystallization on the wall surface of the carrier 201. The indicators for measuring the compound SCR mixer mainly include: carrier velocity uniformity, ammonia uniformity, back pressure loss and anti-crystallization performance under low temperature operation of the engine.

The mixing process generally uses a static mixing unit fixed in the carrier tube to change the flow state of the exhaust gas, so that the fluid flows in the pipeline to impact various types of plate elements, so that the spray droplets are completely broken. (A) of FIG. 5 is a grid plate type spoiler structure, in which each baffle unit is at an angle of 45 ° to the horizontal plane, and 6 rows and 7 rows are staggered.

In order to eliminate (Fig. 5 (a)) grid plate-type spoiler structure, the dead corners of crystals may be generated at the reverse staggering of the blades, and improve the heat transfer efficiency on the wall surface; The large plate structure at 70 ° to the horizontal plane, with the outer blades facing down and the middle part facing up, can create turbulence for the exhaust gas division, and promote rapid pyrolysis of the droplets.

In order to further mix the fluid to achieve sufficient mixing with the atomized particles, the spoiler structure is designed as a double-layered spiral blade structure (Figure 5 (c)), which constitutes a spiral-blade-type spoiler structure. Specifically, each layer consists of 9 blades. Structure, the first layer is arranged counterclockwise, and the second layer is arranged counterclockwise; the droplets first hit the wall surface of the spoiler structure to complete the crushing, and then the swirl created by the blade is fully mixed with the exhaust gas, so that the droplets quickly Pyrolysis.

The traditional spoiler structure usually does not consider the crystallization of the wall surface. Therefore, based on the traditional grid plate spoiler structure (Figure 5 (a)), 8 blades with inclined angles are designed on the outside of the grid plate (Figure 5 (d) )), Which constitutes the preferred composite spoiler structure, which generates swirling near-wall surface through these blades, and generates a coupling effect with the middle airflow, thereby improving the uniformity of airflow while improving the heat distribution on the wall.

The following experiments and analysis are performed on the above four spoiler components:

The test bench mainly includes a VM28 (97KW) diesel engine (such as Table 1), an SCR aftertreatment system, an electric dynamometer and its control system, a fuel supply and fuel consumption measurement system, an intercooler, and a multi-component gas analyzer.

The above-mentioned four spoiler components are respectively welded to the flange, and then installed at a distance of 10 cm from the rear end of the spray member 202. In the case of urea injection, ESC (European Steady-State Cycle) and ETC (European Unsteady-State Cycle) cycles were performed. Then a crystallization test with a cycle of 340s and a total time of 20 hours was performed according to the crystallization specification. After the test is completed, the spoiler assembly is disassembled and weighed, and the front end of the SCR mixer is dissected to check the specific crystal distribution.

Table1 engine parameters

Results and discussion:

1.Uniformity

There are two main factors affecting the catalytic efficiency of the catalyst, one is the uniformity of the gas flow rate, and the other is the uniformity of the ammonia vapor distribution. The uneven flow velocity distribution for a long time will cause excessive air velocity and temperature at the higher flow velocity of the carrier, which will cause the radial temperature gradient of the catalyst to be too large, which will generate thermal stress gradients, cause thermal fatigue damage, accelerate the catalyst's degradation and reduce its Service life. The uneven distribution of reducing agent will cause local excessive or insufficient ammonia distribution, resulting in reduced SCR catalytic efficiency and ammonia gas leakage, uneven catalyst aging, and affecting the overall catalytic performance. In order to obtain the maximum denitration rate and minimum ammonia leakage in the SCR mixer, The performance of the rate must make the UWS distributed as evenly as possible on the front surface of the carrier. Its uniformity coefficient is expressed as follows:

In the formula, Vi is the normal velocity of the unit carrier, Vmean is the normal average velocity of the end face of the carrier air inlet, A is the cross-sectional area of the unit, and Ai is the total number of interface meshes.

1.1 Speed uniformity

The velocity field distribution of the four spoiler structures is shown in Figure 6. The airflow in the middle of the downstream of the inlet pipe with the grid channel plate spoiler structure is relatively smooth. The axial speed in the tube 201 is stable and the uniformity of the speed in the tube is better (Figure 6 (a)). Due to the large blade structure in the middle, As a result, two rows of low-speed regions are generated downstream of the spoiler structure, while the velocity downstream of the baffle gap is high, and the velocity distribution in the tube is extremely uneven (Figure 6 (b)); the double-layered rotating blade structure can effectively accelerate the circumferential rotation of the airflow to make the tube Strong swirling flow is generated at the wall, which promotes vapor-liquid mixing, but the gas velocity in the middle of the mixing pipe is relatively low (Figure 6 (c)); the first spoiler 101 installed in the middle of the composite spoiler structure has been significantly improved Simply using the speed uniformity of the rotating blade structure (Figure 6 (d)); not only a stronger swirl is produced near the wall surface of the spoiler structure, but also the air velocity at the pipe wall is significantly higher than the structure without the rotating blade . At the same time, the axial velocity intensity of the exhaust gas in the tube of the bearing member 201 also obtains good continuity.

The velocity uniformity of the UWS in the axial distance in front of the spoiler structure carrier is directly related to the utilization of the catalyst. The velocity uniformity of the axial cross sections in the range of 10 cm in length of the front surface of the carrier under different spoiler structures is shown in Figure 7; the velocity uniformity of Case1 and Case2 at 8 cm in the mixing cavity suddenly decreases, and the lowest values are respectively 0.64 and 0.72; the overall velocity uniformity is significantly lower than Case3 and Case4; although Case3 has the highest uniformity index at 0 to 8 cm away from the carrier, there is also a sudden decrease in velocity uniformity in Case 3 at 9 cm Compared with case1 and case2, the minimum value is increased to 0.79; Case4 is the only test piece that does not show a sudden decrease in velocity uniformity, which makes its uniformity index in the area 10cm in front of the carrier reaches more than 8.3, which significantly improves the velocity distribution in the mixing cavity. Uniformity can effectively eliminate dead angles in low-speed flow areas.

In order to further clarify the influence of the external airflow on the end face of the carrier on the stability of the carrier, we monitored the uniformity of the velocity distribution at 1 cm inside the carrier, as shown in Figure 8. As a whole, the difference in speed between the four structures is not obvious. When the spoiler structure is a grid structure (Figure 8 (a), (d)), the middle part of the spoiler structure has a small impact on the airflow disturbance, and the exhaust gas obtains a relatively strong turbulent kinetic energy through the spoiler structure, and its velocity is uniform. Sex is better. When the spoiler structure is of the baffle type and the double-layer rotary blade type, there is a large area of low speed, the radial velocity gradient is large, and the velocity uniformity of the end face of the carrier is deteriorated (Fig. 8 (b), (c)). This will cause uneven heating of the front end of the carrier, which will reduce its service life to a certain extent.

1.2 Ammonia uniformity

The reducing agent uniformity index in the mixing chamber is an important index to measure whether the mixer can continuously obtain the maximum denitration rate and the minimum ammonia leakage. Figure 9 shows the uniform exponential distribution of ammonia in the axial section at 10 cm in front of the carrier when different spoiler structures are loaded. The plate-like blade spoiler structure of case1 and case2 can produce axially stable laminar flow, but it cannot overcome the disturbance of the airflow by the mixing plate, which leads to a significant exponential drop near the mixing plate at 8cm in both scenarios. Zone, ammonia uniformity is lowest at 0.53 and 0.57. The case3 and case4 spoiler structure with spiral blade structure effectively eliminates the sudden decrease in the ammonia uniformity index caused by the mixing plate by manufacturing a circumferential rotating airflow, and at the same time ensures that the axial ammonia concentration distribution index in the mixing chamber is always Keep above 0.75, which is nearly 1.5 times that of case1 and case2.

Similarly, we also tested the ammonia uniformity distribution within 1 cm of the front surface of the carrier (Figure 10); the overall ammonia distribution of Case1 is relatively uniform, but a high concentration region can be observed in the lower left (Figure 10 (a)); Case2, Because most of the mixing baffles have an angle of 70 ° with the horizontal plane and the direction is downward, this makes the ammonia vapor distribution more and less, and there is a serious eccentricity (red area at the bottom left of the end face), which is not conducive to the overall catalytic performance (Figure 10 (b)); The double-layer spiral blade structure effectively solves the problem of concentration of high-concentration areas in the lower left of case1 and case2, but because the middle part of the case3 spoiler structure is a swirl energy concentration area, the high-concentration area moves up to the end face near the center (Figure 10 (c)). The coupling effect produced by the compound spoiler structure significantly improves the problem of locally high ammonia concentration in the other three schemes, and the uniformity of the reducing agent distribution is significantly better than the other three schemes (Figure 10 (d)).

Table 2 reflects the velocity uniformity and ammonia uniformity index at 1 cm inside the carrier. From the table we can see that traditional case1 has advantages in speed uniformity, while case3 has advantages in ammonia uniformity. The new composite spoiler structure designed in this paper not only combines the advantages of case1 and case3, but also improves the speed uniformity and ammonia uniformity to 0.993 and 0.924, respectively. For component homogenization and mass transfer, when the exhaust gas enters the intake pipe, the airflow passing through the outer blades of the spoiler structure is divided into large-scale vortices, so that the near-surface airflow rotates to generate vortices, which promotes mass transfer at the pipe wall. At the same time, the swirling flow at the wall of the tube drives the airflow stretched and sheared through the middle grid baffle to rotate, so that it can diffuse through the vortex and molecular diffusion under the force of convection, thereby achieving the purpose of sufficient mixing of gas and liquid phases. The purpose of simultaneously improving the speed and the uniformity of ammonia distribution is achieved.

Table 2 Carrier Uniformity Index at 1cm

2 Crystallization performance

During the urea injection process, a large number of droplets collide with the turbulent structure and the wall of the tube due to inertia. The temperature of the wall decreases with the intensity of the collision. When the temperature of the wall is lower than the Leidenfrost point, Later, the liquid droplets deposited on the wall will form a liquid film. Under the influence of air flow, the liquid film will continue to evaporate, peel, and detach. When this process is incomplete, crystals on the wall surface are formed.

According to the existing research, the temperature of the wall film is the main factor that determines the chemical properties of the relevant sediments. There are three main forms: easy to produce urea crystal (T≤133 ℃), slow pyrolysis of urea (133 ℃ <T <163 ℃) and rapid urea decomposition accompanied by secondary reaction (T≥163 ℃), high deposition risk area The temperature of the wall film is between about 160 ° C and 170 ° C. Once crystals are formed in low temperature conditions, not only will the exhaust pipe be blocked and the back pressure will be increased, but the flow field distribution will be changed and the working efficiency of the mixer will be reduced.

2.1 Liquid film temperature distribution of spoiler structure

The liquid film temperature distribution of the spoiler structure is shown in Figure 11. In case1, there is a large area of low temperature in the lower part of the blade (T <133 ℃), and the maximum temperature difference of the liquid film of the spoiler structure is 102 ~ 110 ℃ (Figure 11 (a)). In case2, there is a low temperature region (T <155 ° C) at the third and third row of baffles (Figure 11 (b)). The temperature distribution of the other baffles is uniform and the temperature is mostly above 200 ° C. It can be seen that the large blade structure can be used. Improve the temperature of the liquid film on the wall to a certain extent. The spiral leaf-like spoiler structure case3 is located at the tip of the blade where the nozzle is directly sprayed and there is an obvious low-temperature liquid film aggregation area at the second layer of spiral leaves (Figure 11 (c)). The temperature distribution of case4 is better than the other three schemes. The grid plate area in the middle of the spoiler structure is evenly heated. The low temperature area is mainly distributed on the three blades at the junction of the spoiler structure and the bottom of the pipe wall (Figure 11 (d)). There may be liquid film deposition on the leaves.

2.2 Spread structure liquid film thickness distribution

When the liquid film attached to the wall evaporates and decomposes continuously at a lower rate than the newly formed liquid film, a liquid film deposition phenomenon will occur. The liquid film thickness distribution of the four spoiler structures under urea injection is shown in Figure 12. In case 1, the liquid film is mainly concentrated at the bottom two rows of wall surfaces of the spoiler structure (Figure 12 (a)), and has a wide range and serious deposition. . In the third layer of case2, there are lamellar liquid film deposits on the outer and middle leaves (Figure 12 (b)), and there is a greater risk of crystallization in this part. A large band-shaped liquid film can be observed at the center of the spiral-shaped spoiler structure (Fig. 12 (c)). (Figure 12 (d)) In the thickness range of the spoiler liquid film in case 4, the reducing agent has no flake-like deposition zone on the wall surface, and only a few speckle-like deposition zones can be observed on the bottom spiral leaf.

By comparing FIG. 11 and FIG. 12, it is found that the liquid film temperature determines the liquid film thickness distribution of the spoiler structure and the location of the sediment to a certain extent. The probability of liquid film accumulation in regions with a temperature below 156 ° C is significantly higher than in other parts. At the same time, we can observe that although there is a large range of lower temperature areas in the case 3 and case 4 spiral leaves, the area where the liquid film is deposited is much smaller than the area of the low temperature area. This is because the high air velocity near the wall prevents the droplets from staying and gathering on the rotary blade for a long time, which reduces the risk of sediment formation.

2.3 Spoiler structure and tube wall temperature distribution

Figure 13 shows the radial temperature distribution in the downstream direction of the turbulent structure perpendicular to the tube wall (tube wall diameter 8cm). The abscissa axis 0 is the upper edge near the nozzle, 8 is the contact portion between the lower edge and the bottom of the tube wall, and the right end is the disturbance. The flow structure contacts the pipe wall. It can be observed from the figure that when the spray particles first came into contact with the wall of the spoiler structure, the temperature of the upper area of case1 was 172 ° C, which was about 30 ° C lower than the other three types, and the difference in the temperature distribution of the grid plate was small. A significant temperature decrease was observed at 6cm in the middle and lower part of case2. This phenomenon continued until the spoiler structure contacted the wall surface and finally decreased to 178 ° C. Case3 also began to occur at 7cm at the bottom, and the temperature dropped to 182 ° C, where a low temperature was formed. Areas will cause droplets to fail to pyrolyze quickly, increasing the risk of crystallization. This phenomenon has been significantly improved in case 4 to keep the downstream temperature of the spoiler structure above 195 ° C.

The highest temperature distribution is helpful to accelerate the pyrolysis of droplets and reduce the probability of deposits forming on the pipe wall downstream of the spoiler structure. Figure 14 shows the temperature distribution at the axial 14cm downstream of the contact point between the spoiler structure and the bottom of the wall. The left end of the abscissa axis is the contact point between the spoiler structure and the pipe wall, and the right end is 14cm away from this point. The temperature range of case1 is 195 ～ 207 ℃, the fluctuation range is small, and the temperature distribution is ideal. The average temperature of the wall area of case2 is the lowest of the four schemes, and there is a continuous low temperature region at 6-9cm, and the lowest temperature is reduced to 153 ° C, which is relatively easy to form crystals. Although the wall temperature of Case3 decreased significantly at 5-9 cm, the overall temperature range was 174-214 ° C, and the lowest value was still higher than the high sediment formation risk temperature (T <170 ° C). The temperature distribution of Case4 ranges from 189 to 211 ° C, and the overall temperature is maintained at a relatively high level. The heat transfer effect of the composite spoiler structure on the downstream pipe wall is significantly better than that of case2 and case3.

2.4 Tube wall liquid film distribution

Observing the following distribution map of the liquid wall of the tube wall, it can be seen that there is a large area of liquid film deposition in the case 1 on the side of the wall of the tube wall in Figure 15 (a) and Figure 16 (a). Case2 has a small area of liquid film deposition along the circumference of the tube wall (Figure 15 (a)), and most of the sediment is concentrated at the bottom of the tube wall (Figure 16 (a)). This part has a great risk of crystallization. The deposition area of case3 is mainly concentrated in the circumferential area (Figure 15 (c)) where the spoiler structure contacts the bottom of the tube wall, and no obvious liquid film aggregation area is observed at the bottom of the wall (Figure 16 (c)). In case 4, a little liquid film is observed at the bottom of the tube wall (Figure 16 (d)), and the area of the liquid film forming area in the circumferential direction of the tube wall is the smallest (Figure 15 (d)), which indicates that the outer spiral leaf structure makes the tube wall circumferential. The crystallization risk is significantly reduced, but there is a certain crystallization risk in the axial direction.

2.5 Experimental results

The crystallization test sediment distribution upstream and downstream of the spoiler structure is shown in Fig. 17 and Fig. 18, respectively. From these two figures, it can be seen that the crystalline sediments upstream and downstream of the spoiled structure are almost symmetrical.

The crystals of the Case1 mesh-like spoiler structure are mainly concentrated in the direct spraying part of the nozzle (Figure 17 (a)), which is roughly consistent with the results of the simulation analysis (Figure 11 (a)). The main reason is that the liquid film accumulates in this area due to the low temperature, and even crystals are formed. In the same way, due to the large amount of liquid film deposition in FIG. 15 (a), a large number of crystals are finally formed at the wall surface. FIG. 18 (a).

The liquid film deposition area of Case2 starting from the third row of baffles in the lower and middle spoiler structure begins to form crystals (Figure 12 (b)), and the agglomerates block the exhaust duct. Similarly, there is a large amount of crystals attached to the wall of Fig. 16 (b) at the liquid film distribution downstream of the spoiler structure (Fig. 18 (b)).

Case3 spiral-blade spoiler structure produces severe crystallization at the blade interlayer. Figure 17 (c). The formation of massive crystals is due to the larger liquid film area of the blade under the spoiler structure. Figure 12 (c), resulting in accumulation effects. The uneven heating of the blades at the bottom of the spoiler structure can't make the reducing agent pyrolyze quickly. There are fewer pipe wall parts downstream of the spoiler structure, and the wall surface is smooth and clean. Figure 18 (c).

Case4 has the least crystals on the composite spoiler structure, and the amount of crystals at the tube wall is significantly lower than that of case1. This is mainly because the outer blades make the airflow rotate to increase the airflow velocity near the wall, which improves the heat and mass transfer at the wall. The situation makes the liquid film hard to accumulate here, and effectively reduces the risk of crystallization on the wall surface. The spoiler structure only has a small amount of crystals attached in the middle and lower part of the grid baffle, the amount of crystals is significantly less than that of case 1, and no block crystals are generated to block the pipeline. Figure 17 (d). This is because the outer swirling flow causes the airflow at the central grid plate to move in a circumferential direction, reducing the residence time of the droplets on the wall surface, and effectively reducing the risk of forming a liquid film deposition area. 2.6 Crystal weight

The parts loaded with the four spoiler structures were disassembled and weighed, as shown in Figure 19, and the weight of the sediment was obtained by comparing the weight difference of the system before and after the experiment (the measurement accuracy is ± 0.01 g). It is found from the figure that the crystal weight of the spoiler structure gradually increases from case1 to case3, and the minimum crystal weight of case4 is 2.31g, which are respectively 34.7%, 22.6%, and 16.7% of case1, case2, and case3. The experimental data show that although the double-layer spiral leaf structure can obtain better ammonia uniformity, it is very easy to form large crystals at low temperature conditions. The spoiler structure with a grid channel plate can effectively improve the structure. Crystallization performance of the mixer under low temperature conditions.

3.Back pressure loss

Increased back pressure increases exhaust resistance, reducing engine power and fuel economy. When the structural optimization design of the mixer is performed, as much as possible, while obtaining a higher uniformity index, the mixer's back pressure loss to the exhaust system is reduced. Figure 20 shows the back pressure loss of the four spoiler structures. It can be seen from the figure that the back pressure loss of the case 4 composite spoiler structure is similar to the back pressure loss of case 1, but the ammonia uniformity of the former is 6.7% higher than that of the latter. . At the same time, when the ammonia uniformity of case4 and case3 is close, the pressure loss of the former is effectively reduced by 139Pa compared with the latter. In summary, the spoiler structure of case 4 has better comprehensive performance.

in conclusion

In this study, the homogeneity and crystallization performance of the reducing agent under low temperature conditions of the new designed spoiler structure were analyzed and verified by means of simulation and experiments. The main results are as follows:

(1) Based on improving the evaporation characteristics of urea droplets under low-temperature emissions, this study proposes a new composite spoiler structure in combination with the existing spoiler structure. Through spray simulation of four different spoiler structures, the spoiler structure and the wall crystal formation site were accurately predicted. The new spoiler structure significantly reduces the amount of crystals under low temperature conditions, which significantly improves the mixer's resistance to crystal formation under low temperature conditions.

(2) Through the structural optimization design, the ammonia uniformity index is increased by 6.7%, 3.1%, and 0.07% compared to case1, case2, and case3, respectively. Moreover, in the case of obtaining the same ammonia uniformity (compared to case 3), the exhaust back pressure is reduced by 7.8%.

(3) The installation of a rotating blade structure on the spoiler structure can effectively increase the gas flow velocity near the tube wall, improve the component homogenization effect, increase the tube wall temperature, and reduce the risk of crystal formation on the tube wall. The dense grid baffle structure can improve the velocity uniformity of the airflow.

It should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be carried out. Modifications or equivalent replacements without departing from the spirit and scope of the technical solutions of the present invention should all be covered by the claims of the present invention.

Claims

A spoiler structure applied to exhaust gas treatment, characterized in that the spoiler structure (100) includes:

The first spoiler (101) includes a grille (101a), a baffle (101b), and a first peripheral wall (101c). The baffle (101b) is disposed on the grille (101a). A first peripheral wall (101c) is provided on the periphery of the grille (101a); and,

A second spoiler (102), the second spoiler (102) comprising a spiral leaf (102a) and a second peripheral wall (102b), the second peripheral wall (102b) being disposed on the first peripheral wall ( 101c), the spiral leaf (102a) is interposed between the second peripheral wall (102b) and the first peripheral wall (101c).
The spoiler structure according to claim 1, wherein the grille (101a) comprises a horizontal substrate (101a-1) and a vertical substrate (101a-2), and the horizontal substrate (101a) -1) Crosswise with the vertical substrate (101a-2).
The spoiler structure for exhaust gas treatment according to claim 2, characterized in that: the plane (N) formed by the horizontal substrate (101a-1) and the vertical substrate (101a-2) and the baffle (101b) ) Arranged at a certain angle.
The spoiler structure according to any one of claims 1 to 3, wherein the baffle plate (101b) is divided into a first facing body (101b-1) and a second facing body (101b- 2), the first facing body (101b-1) and the second facing body (101b-2) are arranged adjacent to each other, and the adjacent first facing body (101b-1) and the second facing body (101b-2) ) Reverse stagger setting.
The spoiler structure according to claim 4, wherein the first facing body (101b-1) and the second facing body (101b-2) are both disposed on the vertical substrate (101a). -2).
The spoiler structure according to claim 4 or 5, wherein the first peripheral wall (101c) and the second peripheral wall (102b) are both annular structures.
The spoiler structure for exhaust gas treatment according to claim 6, wherein the spiral blade (102a) includes a first end surface (102a-1), a second end surface (102a-2), and a third end surface ( 102a-3) and a fourth end face (102a-4), the first end face (102a-1), the second end face (102a-2), the third end face (102a-3), and the fourth end face (102a-4) ) Connected end to end;

The second end surface (102a-2) and the fourth end surface (102a-4) are both arc-shaped structures, and the second end surface (102a-2) is disposed on the fourth end surface (102a-4). periphery.
The spoiler structure for exhaust gas treatment according to claim 7, wherein the first end face (102a-1), the second end face (102a-2), the third end face (102a-3), and the first end face The connection points of the four end faces (102a-4) are a first intersection edge (n1), a second intersection edge (n2), a third intersection edge (n3), and a fourth intersection edge (n4) in this order;

Wherein, the first intersection edge (n1) and the second intersection edge (n2) are connected to both ends of the first peripheral wall (101c), respectively;

Wherein, the third intersection edge (n3) and the fourth intersection edge (n4) are respectively connected to both ends of the second peripheral wall (102b).
A composite SCR mixer, characterized in that the mixer is based on the application of the spoiler structure (100) according to claims 1 to 8,

The mixer further includes a mixing accessory (200), and the spoiler structure (100) is disposed in the mixing accessory (200).
The composite SCR mixer according to claim 9, characterized in that the mixing accessory (200) comprises a carrier (201) and a spraying member (202), and the spraying member (202) is embedded in and arranged at a certain angle. Inside the carrier (201);

Wherein, the nozzle of the spraying member (202) faces the grille (101a) of the spoiler structure (100).