CN111005789A

CN111005789A - Urea SCR mixer, tail gas aftertreatment system and diesel vehicle

Info

Publication number: CN111005789A
Application number: CN201911380504.XA
Authority: CN
Inventors: 张秋实; 刘海涛; 赵庆良; 华伦; 朱君君
Original assignee: Suzhou Automotive Research Institute of Tsinghua University
Current assignee: Suzhou Automotive Research Institute of Tsinghua University
Priority date: 2019-12-27
Filing date: 2019-12-27
Publication date: 2020-04-14
Anticipated expiration: 2039-12-27
Also published as: CN111005789B

Abstract

The invention belongs to the technical field of diesel vehicles and discloses a urea SCR mixer, a tail gas aftertreatment system and a diesel vehicle. The urea SCR mixer comprises a first-stage mixer and a second-stage mixer, and comprises a support frame and a plurality of first guide vanes obliquely arranged on different parts of the support frame, wherein each first guide vane is obliquely arranged towards the center direction of the support frame, and the first guide vanes are configured to be capable of dropping urea liquid and NH₃Directing the flow to a central region of the first stage mixer; a second mixer located downstream of the first mixer and connected to the first mixer by a connecting shaft, the second mixer comprising a plurality of swirl vanes connected to the connecting shaft, the swirl vanes being configured to be able to mix urea droplets with NH₃And (4) performing rotational flow diffusion from inside to outside. So as to enter NH in front of the end face of the SCR₃Distribution in exhaust gas ductsThe method is more uniform, the efficiency and the utilization rate of SCR catalytic conversion are increased, and the risk of urea deposition is reduced, so that the risk of urea crystallization is reduced.

Description

Urea SCR mixer, tail gas aftertreatment system and diesel vehicle

Technical Field

The invention relates to the technical field of diesel vehicles, in particular to a urea SCR mixer, a tail gas aftertreatment system and a diesel vehicle.

Background

At present, with the increasing importance of the country on the environmental protection problem, higher requirements are put forward on the exhaust emission of diesel engines, wherein nitrogen oxide NO_XThe emission limit was reduced to 3.5 g/(kw.h). In a plurality of NO_XAmong the treatment technologies, the Selective Catalytic Reduction (SCR) technology is currently considered to be the most promising and widely used technology, and is mature. The mechanism is as follows: the high-temperature exhaust pipe is provided with a urea metering injection device for injecting urea aqueous solution into the high-temperature exhaust pipe, and the urea generates NH after hydrolysis and pyrolysis reaction at high temperature₃，NH₃Has reducibility, and can react with NO under the action of specific catalyst_XReduction to non-polluting N₂And H₂O, thereby reducing the emission of pollutants.

With the increasing maturity of the SCR technology and the limitation of the installation space of the whole vehicle aftertreatment system, the structure of the SCR system becomes more and more compact. The structural design imperfection can cause the problems of insufficient urea evaporation efficiency, uneven distribution and the like, crystals are easily formed on the inner wall of the SCR or the front end face of the carrier, and the performance of the engine is seriously affected even, so that the problems of urea distribution uniformity, evaporation efficiency, crystallization and the like must be paid attention to in the structural design of the SCR.

And urea is hydrolyzed to NH₃Can then react with NO_XThe reaction occurs, the hydrolysis of urea is mainly realized by a mixer at present, but the mixer adopted at present easily generates larger back pressure, influences the power of an engine, can not effectively reduce the concentration of urea due to insufficient hydrolysis of urea, and is easy to generate crystallization.

Of the current mixers, almost all single-stage mixers can only make NH under certain specific conditions₃The uniformity of the urea spraying device meets the requirement, and under some limit working conditions, such as low-load working conditions, the flow is low, and the urea is easy to spray in the mixerAnd the tail gas speed is high under the high-load working condition, urea is impacted by the high-speed tail gas, and urea liquid drops are concentrated on the upper part of the mixer. Thus, NH during lower or higher load conditions₃The concentration is higher in a certain part of a cross section, which results in NH entering the SCR₃Uneven distribution of NO_XThe transformation is not uniform and the efficiency is low.

Disclosure of Invention

It is an object of the present invention to provide a urea SCR mixer that improves NH₃The distribution uniformity improves the efficiency and the utilization rate of SCR catalytic conversion.

The invention also aims to provide the tail gas post-treatment system which is high in tail gas treatment efficiency, environment-friendly and energy-saving.

The invention also aims to provide a diesel vehicle which has high tail gas treatment efficiency and is environment-friendly and energy-saving.

In order to achieve the purpose, the invention adopts the following technical scheme:

a urea SCR mixer, comprising:

the first-stage mixer comprises a support frame and a plurality of first guide vanes obliquely arranged on different parts of the support frame, each first guide vane inclines towards the center direction of the support frame, and the first guide vanes are configured to be capable of mixing urea liquid drops and NH₃Directing flow to a central region of the primary mixer;

a secondary mixer located downstream of the primary mixer and connected thereto by a connecting shaft, the secondary mixer including a plurality of swirl vanes connected to the connecting shaft, the swirl vanes being configured to be able to mix the urea droplets and NH₃And (4) performing rotational flow diffusion from inside to outside.

As a preferable technical solution of the urea SCR mixer, the support frame includes a first ventilation area and a plurality of second ventilation areas that are defined by a partition plate, and the plurality of second ventilation areas are distributed at intervals in a circumferential direction of the first ventilation area; the partition plate on the outermost periphery of the first ventilation area and the partition plate on the outermost periphery of the second ventilation area are both provided with the first guide vanes.

As a preferable embodiment of the urea SCR mixer, the first ventilation area and the second ventilation area are each partitioned into a plurality of sub-ventilation areas by a sub-partition plate.

In a preferred embodiment of the urea SCR mixer, the sub-ventilation regions are the same size.

As a preferable technical solution of the urea SCR mixer, the cross section of the first ventilation area is square, the cross section of the second ventilation area is rectangular and four second ventilation areas are provided, the four second ventilation areas are respectively provided around the first ventilation area, the sides of the square and the long sides of the rectangle are overlapped, and the short side of the rectangle is equal to one-half of the long side.

As the preferable technical scheme of the urea SCR mixer, an extension partition plate is arranged between every two adjacent second ventilation areas, a second guide vane is obliquely arranged on the extension partition plate, and the second guide vane inclines towards the center direction of the support frame.

As a preferable technical scheme of the urea SCR mixer, the swirl vanes are fan-shaped.

As a preferable technical scheme of the urea SCR mixer, a plurality of swirl vanes are uniformly distributed on the connecting shaft along the circumferential direction.

An exhaust aftertreatment system comprises an exhaust pipe and the urea SCR mixer, wherein the urea SCR mixer is fixedly arranged in the exhaust pipe.

A diesel vehicle comprises the exhaust aftertreatment system.

Compared with the prior art, the invention has the advantages and beneficial effects that:

the invention provides a urea SCR (selective catalytic reduction) mixer which comprises a first-stage mixer and a second-stage mixer, wherein the first-stage mixer comprises a support frame and a plurality of first guide vanes obliquely arranged on different parts of the support frame, each first guide vane is obliquely arranged towards the center direction of the support frame, and the first guide vanes are configured to beCan drop urea and NH₃Directing the flow to a central region of the first stage mixer; then passing through a second-stage mixer with a swirl vane to mix the urea liquid drops and NH in the middle₃Uniformly and outwardly diffused to make NH before entering the end face of the SCR₃The distribution in the tail gas exhaust pipe is more uniform, the catalytic conversion efficiency and the utilization rate of the SCR are increased, the urea liquid drop quantity on the front end face of the SCR is reduced, and the risk of urea deposition is reduced, so that the risk of urea crystallization is reduced; and the urea SCR mixer has compact and simple structure and lower cost.

The invention provides an exhaust gas post-treatment system which comprises an exhaust gas exhaust pipe and the urea SCR mixer, wherein the urea SCR mixer is fixedly arranged in the exhaust gas exhaust pipe. The tail gas post-treatment system has high tail gas treatment efficiency, and is environment-friendly and energy-saving.

The diesel vehicle provided by the invention comprises the tail gas aftertreatment system, and is high in tail gas treatment efficiency, environment-friendly and energy-saving.

Drawings

FIG. 1 is a schematic diagram of a urea SCR mixer according to an embodiment of the present invention;

FIG. 2 is an exploded schematic view of a urea SCR mixer provided in accordance with an embodiment of the present invention;

fig. 3 is a front view of an end face of an exhaust pipe according to an embodiment of the present invention.

The figures are labeled as follows:

1. a first-stage mixer; 11. a support frame; 111. a first venting area; 112. a second venting area; 113. an extension spacer; 12. a first guide vane; 13. a second guide vane;

2. a secondary mixer; 21. a swirl vane;

3. a connecting shaft;

100. and a tail gas exhaust pipe.

Detailed Description

In order to make the technical problems solved, the technical solutions adopted and the technical effects achieved by the present invention clearer, the technical solutions of the present invention are further described below by way of specific embodiments with reference to the accompanying drawings.

In the description of the present invention, unless expressly stated or limited otherwise, the terms "connected," "connected," and "fixed" are to be construed broadly, e.g., as meaning permanently connected, removably connected, or integral to one another; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.

In the description of the present embodiment, the terms "upper", "lower", "left", "right", and the like are used based on the orientations and positional relationships shown in the drawings only for convenience of description and simplification of operation, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used only for descriptive purposes and are not intended to have a special meaning.

The present embodiment discloses a urea SCR mixer, as shown in fig. 1 and fig. 2, the urea SCR mixer includes two single-stage mixers, i.e., a first-stage mixer 1 and a second-stage mixer 2, and the second-stage mixer 2 is close to the front end surface of the SCR. The two mixers are structurally different and have different functions. Wherein, as shown in FIG. 2, the first-stage mixer 1 comprises a support frame 11 and an inclineA plurality of first guide vanes 12 disposed at different positions of the support frame 11, each of the first guide vanes 12 being inclined toward a center of the support frame 11, the first guide vanes 12 being configured to be able to mix urea droplets and NH₃The flow is guided to the central area of the first-stage mixer 1; a second mixer 2 located downstream of the first mixer 1 and connected to the first mixer 1 by a connecting shaft 3, the second mixer 2 comprising a plurality of swirl vanes 21 connected to the connecting shaft 3, the swirl vanes 21 being configured to be able to mix urea droplets with NH₃And (4) performing rotational flow diffusion from inside to outside.

The urea SCR mixer in the embodiment adopts two single-stage mixers with different functions, and the two mixers are combined together to make up the respective defects of the two mixers: the first mixer 1 divides urea liquid drops and NH into regions by the first guide vanes 12₃Leading to the middle zone and increasing the turbulence intensity, and passing through a swirl vane type two-stage mixer 2, the urea droplets and NH in the middle₃Uniformly and outwardly diffused to make NH before entering the end face of the SCR₃More uniform distribution in the exhaust pipe 100, increasing the efficiency and utilization rate of the SCR catalytic conversion. By arranging the two-stage mixer, the primary crushing degree and the secondary crushing of urea liquid drops are increased, the pyrolysis amount of the urea liquid drops when passing through the mixer is further increased, the urea liquid drop amount on the front end face of the SCR is reduced, the risk of urea deposition is reduced, and therefore the risk of urea crystallization is reduced; and the urea SCR mixer has compact and simple structure and lower cost.

Specifically, as shown in fig. 3, the supporting frame 11 includes a first ventilation area 111 and a plurality of second ventilation areas 112, which are defined by partitions, and the plurality of second ventilation areas 112 are distributed at intervals along the circumferential direction of the first ventilation area 111; the outermost partition of the first ventilation area 111 and the outermost partition of the second ventilation area 112 are provided with first guide vanes 12. As shown in fig. 1 to 3, the first ventilation area 111 is located in a central area of the supporting frame 11, the plurality of second ventilation areas 112 are respectively disposed at the periphery of the first ventilation area 111, and in this structure, the supporting frame 11 divides the exhaust gas exhaust pipe 100 into a plurality of areas, and each area is provided with the first guide vane 12 and the first guide vane 12The guide vanes 12 are inclined toward the center region to separate urea droplets and NH₃Leading to the middle area. And the baffle structure and the first guide vane 12 act together to increase the turbulence intensity, which is beneficial to the breaking and hydrolysis of urea liquid drops.

Further, the first and

second venting areas

111 and 112 are each divided by a sub-partition into a plurality of sub-venting areas to further increase the turbulence intensity. Preferably, the sub-aeration zones are the same size, so that urea droplets and NH may be made₃The distribution in the exhaust pipe 100 is more uniform, and the efficiency and the utilization rate of the SCR catalytic conversion are improved. Further preferably, the first guide vanes 12 are respectively disposed at the edges of the respective sub-ventilation areas.

In the present embodiment, as shown in fig. 3, the cross section of the first ventilation area 111 is square, the cross section of the second ventilation area 112 is rectangular and four second ventilation areas 112 are provided, the four second ventilation areas 112 are provided around the first ventilation area 111, the sides of the square and the long sides of the rectangle overlap, and the short side of the rectangle is equal to one-half of the long side. Under the structure, each sub-ventilation area is square and has the same size, and the peripheral edge of each sub-ventilation area is provided with a first guide vane 12. It is understood that the supporting frame 11 provided in this embodiment can be regarded as a frame structure formed by a sixteen-grid rack with four corners removed.

Specifically, the first ventilation area 111 may be set as a middle area, and the four second ventilation areas 112 may be an upper ventilation area, a lower ventilation area, a left ventilation area, and a right ventilation area, respectively, so that the support frame 11 composed of the partition plate divides the ventilation space of the exhaust gas exhaust pipe 100 into five areas, and the upper ventilation area and the lower ventilation area are disposed vertically symmetrically with respect to the middle area, and the left ventilation area and the right ventilation area are disposed horizontally symmetrically with respect to the middle area. The first guide vane 12 of the upper ventilation area bends downwards, under the high-load working condition, because the air flow velocity is very high, the momentum exchange between the air and urea liquid drops is large, the urea which is not pyrolyzed in time is blown to the upper half part of the first-stage mixer 1, and the urea liquid drops which fall on the upper half part are pyrolyzed and then are in the first areaNH can be avoided under the guiding action of the guide vane 12 to the middle area₃Concentrated in the upper half area. The first guide vane 12 of the lower ventilation area is bent upwards, urea liquid drops can be more concentrated on the lower half part of the first-stage mixer 1 under the low-load working condition, and NH can be avoided under the guide effect of the first guide vane 12 of the area to the middle area after the urea liquid drops dropping on the lower half part are pyrolyzed₃Concentrated in the lower half area. The first guide vane 12 of the left ventilation area is bent to the right, and the first guide vane 12 of the right ventilation area is bent to the left, so that urea droplets close to the pipe wall of the exhaust pipe 100 can be guided to the middle area. In the present embodiment, the up, down, left, and right directions are all directions in fig. 3.

Further preferably, an extending partition 113 is disposed between two adjacent second ventilation areas 112, a second guide vane 13 is disposed on the extending partition 113, and the second guide vane 13 inclines toward the center of the support frame 11. Specifically, the extension partition plate 113 located between the upper ventilation area and the left ventilation area, and the extension partition plate 113 located between the upper ventilation area and the right ventilation area are both horizontally connected to the partition plate of the upper ventilation area, and the second guide vanes 13 on the two extension partition plates 113 are both bent downward; the extension partition 113 between the lower ventilation area and the left ventilation area and the extension partition 113 between the lower ventilation area and the right ventilation area are horizontally connected to the partition of the lower ventilation area, and the second guide vanes 13 on the two extension partitions 113 are bent upwards. Alternatively, the length of the extension partition 113 is designed not to affect the installation of the support frame 11 into the exhaust stack 100, and the size of the second guide vane 13 on the extension partition 113 is different from the size of the first guide vane 12 in the first and

second ventilating areas

111 and 112. Illustratively, the width of the second guide vane 13 on the extension partition 113 is smaller than the width of the first guide vane 12, and the length of the second guide vane 13 on the extension partition 113 is greater than the length of the first guide vane 12. For the size design of each guide vane, the embodiment does not have too much limitation, and is suitable for better realizing the guide function.

With the above structure, the first-stage mixer 1 in the present embodiment includes sixteen guide vanes, and the bending angles of the guide vanes in the respective ventilating areas may be the same or different, and need to be designed according to actual conditions. Preferably, the bending angle of each first guide vane 12 disposed in the same ventilation area is kept consistent, and the bending angle of the second guide vane 13 on the extension partition 113 is kept consistent with the bending angle of the first guide vane 12 in the same ventilation area. The air current can greatly increase the turbulence in different directions and different sizes through the primary mixer 1, the turbulence intensity is increased, and the urea liquid drop crushing and decomposition are facilitated, so that the urea pyrolysis is promoted, and the urea is pyrolyzed into NH as much as possible before entering the SCR₃And H₂O。

In the present embodiment, the swirl vanes 21 of the secondary mixer 2 form a certain angle with the plane, and like the fan blades, the planar shape of the swirl vanes 21 is fan-shaped, which can achieve better swirl diffusion effect.

Furthermore, a plurality of swirl vanes 21 are uniformly arranged on the connecting shaft 3 along the circumferential direction, so that urea droplets and NH can be further improved₃Uniformity of diffusion. Optionally, eight swirl blades 21 are provided in the present embodiment, the eight swirl blades 21 are uniformly welded on the connecting shaft 3, and one end of the connecting shaft 3, at which no swirl blade 21 is provided, is welded on the support frame 11 of the first-stage mixer 1, so as to form an integrated two-stage SCR mixer. The structure of the connecting shaft 3 may be a cylindrical shape or a prismatic shape, and the present embodiment is not particularly limited.

Under the action of the first-stage mixer 1, under the working conditions of different loads of the diesel vehicle, urea liquid drops and NH₃Mainly concentrated in the middle area of the exhaust pipe 100, urea droplets and NH₃After impacting the downstream secondary mixer 2 from the middle area, the secondary mixer 2 starts to perform cyclone diffusion from the middle to the outside, and the secondary mixer 2 has better cyclone effect like a fan, so that urea liquid drops and NH are concentrated₃Become more uniform before entering the SCR and during the swirling, the urea droplets are further pyrolyzed, further reducing the urea droplets before entering the SCR, thus reducing the shapeRisk of urea formation crystallization. Experiments prove that the urea SCR mixer provided by the embodiment can meet the NH requirement of the front end face of the SCR₃The working condition range required by the uniformity index is greatly increased.

The embodiment further provides an exhaust gas aftertreatment system, which comprises an exhaust gas exhaust pipe 100 and the urea SCR mixer, wherein the urea SCR mixer is fixedly arranged in the exhaust gas exhaust pipe 100. The tail gas post-treatment system has high tail gas treatment efficiency, and is environment-friendly and energy-saving.

The invention also provides a diesel vehicle which comprises the tail gas after-treatment system, and the diesel vehicle is high in tail gas treatment efficiency, environment-friendly and energy-saving.

It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A urea SCR mixer, comprising:

the one-stage mixer (1) comprises a support frame (11) and a plurality of first guide vanes (12) obliquely arranged on different parts of the support frame (11), wherein each first guide vane (12) inclines towards the central direction of the support frame (11), and the first guide vanes (12) are configured to be capable of mixing urea liquid drops and NH₃Is guided to the central area of the primary mixer (1);

a secondary mixer (2) located downstream of the primary mixer (1) and connected with the primary mixer (1) by a connecting shaft (3), the secondary mixer (2) comprising a plurality of swirl vanes (21) connected to the connecting shaft (3), the swirl vanes (21) being configured to be able to mix urea droplets and NH₃And (4) performing rotational flow diffusion from inside to outside.

2. A urea SCR mixer as claimed in claim 1, wherein the support frame (11) comprises a first aeration zone (111) and a plurality of second aeration zones (112) defined by partitions, the plurality of second aeration zones (112) being circumferentially spaced apart along the first aeration zone (111); the first guide vane (12) is disposed on the partition plate at the outermost periphery of the first ventilation area (111) and the partition plate at the outermost periphery of the second ventilation area (112).

3. A urea SCR mixer as claimed in claim 2, wherein the first (111) and second (112) aeration zones are each divided by a sub-partition into a plurality of sub-aeration zones.

4. The urea SCR mixer of claim 3, wherein the sub-breathing zones are the same size.

5. A urea SCR mixer according to claim 4, characterized in that the cross section of the first aeration zone (111) is square, the cross section of the second aeration zone (112) is rectangular and is provided with four, four of the second aeration zones (112) being arranged respectively around the first aeration zone (111), the sides of the square coinciding with the long sides of the rectangle, the short sides of the rectangle being equal to half the long sides.

6. A urea SCR mixer according to claim 5, characterized in that an extension partition (113) is provided between two adjacent second aeration areas (112), and a second guide vane (13) is provided on the extension partition (113) and inclined towards the center of the support frame (11) in the second guide vane (13).

7. Urea SCR mixer according to claim 6, characterized in that the swirl vanes (21) are fan-shaped.

8. Urea SCR mixer according to claim 7, characterized in that a number of swirl vanes (21) are evenly distributed in circumferential direction on the connecting shaft (3).

9. An exhaust gas aftertreatment system, characterized in that it comprises an exhaust gas duct (100) and a urea SCR mixer according to any of claims 1-8, which is fixedly arranged in the exhaust gas duct (100).

10. A diesel vehicle comprising an exhaust aftertreatment system according to claim 9.