JP2016188579A - Exhaust purification unit - Google Patents

Abstract

An exhaust gas purification capability of an SCR catalyst is improved by increasing the efficiency of hydrolysis of urea water. A connecting pipe 24 that sends exhaust gas to an SCR catalyst 41, a urea water injection valve 30 that is disposed opposite to an exhaust upstream end of the connecting pipe 24 and injects urea water into the connecting pipe 24, and a front casing. A mixer chamber 23 that forms a flow path in which exhaust gas is folded and flows from the exhaust gas downstream end 20 to the exhaust gas upstream end of the connection pipe 24, and is provided in the mixer chamber 23 and connected from the vicinity of the injection port of the urea water injection valve 30. A frustum-shaped member that gradually expands toward the pipe 24 and has a plurality of small holes 50C, and a claw 50D that guides exhaust gas to the exhaust downstream side is provided for each small hole 50C. And a flow regulating member 50. [Selection] Figure 4

Description

  The present invention relates to an exhaust purification unit including an SCR catalyst.

  As an exhaust gas purification unit for reducing and purifying nitrogen compounds (NOx) in exhaust gas discharged from an internal combustion engine, a front stage portion including an oxidation catalyst and a filter for collecting particulate matter (hereinafter referred to as PM) in exhaust gas, and urea water And a rear stage portion that includes a selective reduction catalyst (hereinafter referred to as SCR catalyst) that purifies nitrogen compounds (hereinafter referred to as NOx) in exhaust gas using ammonia generated from the reducing agent as a reducing agent (for example, Patent Documents) 1 and 2).

  In the exhaust purification unit described in Patent Document 1, a front casing that houses an oxidation catalyst and a filter and a rear casing that houses an SCR catalyst are juxtaposed, and an upstream end and a downstream of a linear pipe disposed therebetween. The ends are respectively connected to the outlet of the front casing and the inlet of the rear casing. A urea water injection device is disposed at the upstream end of the pipe, and urea water is added to the exhaust gas introduced from the front casing to the rear casing, and the urea water is hydrolyzed in the exhaust gas to generate ammonia. The ammonia is supplied as a reducing agent to the SCR catalyst, whereby NOx in the exhaust gas is reduced and purified.

  In the exhaust gas purification unit described in Patent Document 2, a swirl flow generating fin that swirls exhaust gas is provided upstream of the urea water injection position, and the exhaust gas that is swirling flow and the urea that is injected Water is mixed in the pipe.

JP 2009-36109 A JP 2006-29233 A

  The urea water is injected from the vicinity of the upstream end of the pipe toward the downstream side, while the exhaust gas is introduced from the front casing to the upstream end of the pipe so as to intersect the flow of the exhaust gas. Therefore, a part of the injected urea water is caused to flow and adhere to the upstream wall surface of the pipe by the exhaust gas before diffusing. Therefore, the efficiency of hydrolysis of urea water is deteriorated, and the diffusibility of ammonia in the exhaust gas supplied to the SCR catalyst is lowered, so that the exhaust gas purification ability of the SCR catalyst is lowered.

  An object of the disclosed exhaust purification unit is to improve the exhaust gas purification ability of a catalyst by increasing the efficiency of hydrolysis of urea water and increasing the diffusibility of ammonia in the exhaust gas.

  The disclosed exhaust purification unit is provided in an exhaust system of an internal combustion engine and selectively reduces a nitrogen oxide in exhaust using ammonia as a reducing agent, and an exhaust pipe that sends exhaust gas to the selective reduction catalyst The urea water injection device that is disposed to face the exhaust upstream end of the exhaust pipe and injects urea water into the exhaust pipe, and connects the exhaust downstream end of the casing housing the catalyst and the exhaust upstream end of the exhaust pipe And a chamber that forms a flow path in which exhaust gas is folded back from the casing to the exhaust pipe, and the diameter of the exhaust gas gradually increases from the vicinity of the injection port of the urea water injection device toward the exhaust pipe. It is a pipe material having a truncated cone shape that extends while being provided with a plurality of vent holes, and a rectifying member provided with a guide for guiding exhaust gas to the exhaust downstream side for each vent hole.

  According to the disclosed exhaust purification unit, the exhaust gas purification ability of the catalyst can be improved by increasing the hydrolysis efficiency of urea water and increasing the diffusibility of ammonia in the exhaust gas.

It is a perspective view which shows the exhaust gas purification unit which concerns on one Embodiment. It is sectional drawing which shows the inside of a mixer chamber and connection piping. It is a figure which shows the flow of the exhaust gas in a mixer chamber. It is a figure which shows the flow of the exhaust gas in a mixer chamber. It is sectional drawing which shows the rectification | straightening part which concerns on other embodiment. It is sectional drawing which shows the rectification | straightening part which concerns on other embodiment. It is sectional drawing which shows the rectification | straightening part which concerns on other embodiment. It is sectional drawing which shows the rectification | straightening part which concerns on other embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing an exhaust purification unit 1 according to an embodiment. As shown in the figure, the exhaust purification unit 1 includes a front casing 20, a mixer chamber 23, a urea water injection valve 30, a connection pipe 24, and a rear casing 40 in order from the exhaust upstream side.

  The front-stage casing 20 and the rear-stage casing 40 have a cylindrical shape, are arranged in parallel so that their axes are parallel to each other, and are connected by a connection pipe 24 arranged therebetween. The connection pipe 24 includes a cylindrical first pipe 24 </ b> A, and is arranged so that the axis of the pipe 24 </ b> A is parallel to the axes of the front casing 20 and the rear casing 40.

  The front-stage casing 20 includes a first casing 20A and a second casing 20B arranged coaxially on the exhaust downstream side of the first casing 20A. An annular flange is provided at the exhaust downstream end of the first casing 20A and the exhaust upstream end of the second casing 20B, and both flanges are fastened by bolts and nuts. Further, the first casing 20A contains the first oxidation catalyst 21, and the second casing 20B contains the filter 22.

  The first oxidation catalyst 21 is, for example, a catalyst component or the like supported on the surface of a ceramic carrier such as a cordierite honeycomb structure. The first oxidation catalyst 21 oxidizes unburned hydrocarbons (HC) supplied by post injection or exhaust pipe injection to raise the exhaust temperature.

  In the filter 22, for example, a large number of cells partitioned by porous partition walls are arranged along the flow direction of the exhaust gas, and the upstream side and the downstream side of these cells are alternately plugged. The filter 22 collects particulate matter (hereinafter referred to as PM) in the exhaust gas in the pores and surfaces of the partition walls, and burns PM when the estimated amount of PM deposition reaches a predetermined amount and so-called forced filter regeneration is performed. Remove. Here, the forced filter regeneration is by supplying unburned hydrocarbons to the first oxidation catalyst 21 on the exhaust upstream side by exhaust pipe injection or post injection, and raising the exhaust temperature flowing into the filter 22 to the PM combustion temperature. Done.

  The mixer chamber 23 is disposed at the exhaust downstream end of the second casing 20B, and has a first chamber 23A having an arc-shaped side surface, and a second chamber 23B having an arc-shaped side surface extending from the side surface of the first chamber 23A to the rear casing 40 side. It has. The first chamber 23A is arranged coaxially with the second casing 20B. The diameter of the second chamber 23B is smaller than the diameter of the first chamber 23A, and the boundary between both is curved in an arc shape.

  An annular flange is provided at the exhaust downstream end of the second casing 20B and the exhaust upstream end of the first chamber 23A, and both flanges are fastened by bolts and nuts.

  The connection pipe 24 includes a cylindrical first pipe 24A connected to the second chamber 23B, and a second pipe 24B that connects the first pipe 24A and the exhaust upstream end of the rear casing 40. The first pipe 24 </ b> A is arranged coaxially with the injection shaft of the urea water injection valve 30.

  The second pipe 24B is an elbow pipe, and the exhaust downstream end is formed in a disk shape. The straight portion of the second pipe 24B is arranged coaxially with the first pipe 24A, and an annular flange is provided at the exhaust downstream end of the first pipe 24A and the exhaust upstream end of the second pipe 24B. Are fastened with bolts and nuts. An annular flange is provided at the exhaust downstream end of the second pipe 24B and the exhaust upstream end of the rear casing 40, and both flanges are fastened with bolts and nuts.

  The urea water injection valve 30 is provided in the second chamber 23B. The injection axis of the urea water injection valve 30 is aligned with the axis of the connection pipe 24, and urea water is injected (sprayed) from the urea water injection valve 30 to the exhaust downstream side of the connection pipe 24.

In the connection pipe 24, urea water injected from the urea water injection valve 30 and exhaust gas flowing from the mixer chamber 23 to the rear casing 40 are mixed, and the urea water is hydrolyzed by the exhaust heat to be ammonia (NH ₃ ). Is generated. The produced ammonia is supplied to the SCR catalyst 41 on the exhaust downstream side by the flow of the exhaust gas.

  The rear casing 40 contains an SCR catalyst 41 and a second oxidation catalyst 42 disposed on the exhaust downstream side of the SCR catalyst 41.

  The SCR catalyst 41 is, for example, one in which zeolite or the like is supported on a porous ceramic carrier. The SCR catalyst 41 adsorbs ammonia supplied as a reducing agent from the urea water injection valve 30 and selectively reduces and purifies NOx from the exhaust gas passing through the adsorbed ammonia.

  The second oxidation catalyst 42 is, for example, a catalyst component or the like supported on the surface of a ceramic carrier such as a cordierite honeycomb structure, and has a function of oxidizing ammonia slipped from the SCR catalyst 41 to the exhaust downstream side. doing.

  FIG. 2 is a cross-sectional view showing the inside of the mixer chamber 23 and the connection pipe 24. As shown in this figure, a rectifying unit 51 is provided in the second chamber 23 </ b> B of the mixer chamber 23, and a rectifying member 50 is provided in the rectifying unit 51. The rectifying member 50 is a truncated cone-shaped tube having both ends opened, and is arranged coaxially with the urea water injection valve 30.

  The small-diameter opening 50A of the rectifying member 50 is arranged to face the injection port of the urea water injection valve 30, and the large-diameter opening 50B of the rectifying member 50 is partially inserted into the upstream end of the connection pipe 24. Has been. Between the outer peripheral surface of the edge of the opening 50 </ b> B of the rectifying member 50 and the inner peripheral surface of the upstream end of the connection pipe 24, there is a gap through which exhaust gas passes.

  The rectifying member 50 is a porous member, and rectangular small holes 50C are formed at narrow intervals in the circumferential direction and the axial direction. Here, the small hole 50C is formed by cutting and bending, and the claw 50D is bent inside the rectifying member 50 from the upstream side of the small hole 50C. The claw 50D is bent and raised at an acute angle, and the claw 50D functions as a guide for guiding the exhaust gas that has passed through the small hole 50C to the exhaust downstream side.

  3 and 4 are diagrams illustrating the flow of exhaust gas in the mixer chamber 23. FIG. As shown in FIG. 3, the width of the flow path becomes narrower from the first chamber 23A to the second chamber 23B, and one (left side in the figure) side wall is curved and recessed, so that the first chamber 23A is A swirling flow is generated in the exhaust gas flowing through the two chambers 23B.

  As shown in FIG. 4, the exhaust gas that has turned into a swirling flow flows into the connection pipe 24 through the outside of the rectifying member 50, or passes through the small holes 50 </ b> C and the inside of the rectifying member 50. It flows in. In the connection pipe 24, the exhaust gas flows downstream while turning around the axis of the connection pipe 24.

  Here, the urea water injection valve 30 injects urea water into the rectifying member 50. The urea water that has been injected (sprayed) is expanded in diameter from the upstream side to the downstream side of the rectifying member 50, and the exhaust gas that has flowed in through the small holes 50C is guided to the exhaust downstream side by the claws 50D. Is diffused. Then, the diffused urea water and the exhaust gas that has turned into a swirl flow are mixed in the connection pipe 24.

  As a result, the urea water sprayed (sprayed) in the connection pipe 24 can be mixed with the exhaust gas that has turned into a swirl flow, and the urea water can be mixed with the second chamber 23B and the connection pipe by the flow of the exhaust gas. It can prevent adhering to the wall surface of 24. Therefore, the efficiency of hydrolysis of urea water can be improved.

  Here, when urea water adheres to the wall surface, the urea water is also hydrolyzed by the exhaust gas and the heat of the wall surface, but the diffusibility of ammonia in the connection pipe 24 is lowered. In contrast, in the rectifying unit 51 according to the present embodiment, it is possible to prevent the urea water from adhering to the wall surfaces of the second chamber 23B and the connection pipe 24, so that swirling exhaust gas in which ammonia is uniformly diffused can be generated. By being able to supply to the SCR catalyst 41, the exhaust gas purification ability of the SCR catalyst 41 can be improved.

  FIG. 5 is a cross-sectional view showing a rectifying unit 151 according to another embodiment. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned embodiment, and description is abbreviate | omitted. As shown in FIG. 5, the rectifying unit 151 includes a rectifying member 50 and a collision plate mixer 152 disposed on the exhaust downstream side of the rectifying member 50. The collision plate mixer 152 is an annular frame provided with a wire mesh (not shown) and a diffusion plate 152A. The collision plate mixer 152 is disposed near the downstream end of the rectifying member 50 so as to face the opening 50B.

  In the rectifying unit 151 having such a configuration, urea water injected from the urea water injection valve 30 and diffused by the rectifying member 50 collides with the wire mesh of the collision plate mixer 152. Thereby, hydrolysis of urea water is accelerated | stimulated. Then, urea water and ammonia generated by hydrolysis are further diffused by the diffusion plate 152 </ b> A and flow to the connection pipe 24.

  Therefore, compared with the exhaust purification unit provided with the above-mentioned rectification unit 51, the efficiency of the hydrolysis of urea water can be further increased, and thus the exhaust gas purification capability of the SCR catalyst 41 can be further improved.

  FIG. 6 is a cross-sectional view showing a rectifying unit 251 according to another embodiment. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned embodiment, and description is abbreviate | omitted. As shown in FIG. 6, the rectifying unit 251 includes a rectifying member 50 and a hydrolysis catalyst 252 disposed on the exhaust downstream side of the rectifying member 50. As the hydrolysis catalyst 252, for example, a honeycomb made of silicon nitride or a metal honeycomb having titanium oxide supported thereon, a cordierite honeycomb having aluminum oxide supported on the wall, or the like can be used. The hydrolysis catalyst 252 is disposed in the vicinity of the downstream end of the rectifying member 50 so as to face the opening 50B.

  In the rectifying unit 251 having such a configuration, urea water injected from the urea water injection valve 30 and diffused by the rectifying member 50 passes through the hydrolysis catalyst 252. At this time, hydrolysis of urea water is promoted. Then, urea water and ammonia generated by hydrolysis are sent to the exhaust downstream side of the connection pipe 24 by the exhaust gas that has turned into a swirling flow.

  Therefore, compared with the exhaust purification unit provided with the above-mentioned rectification unit 51, the efficiency of the hydrolysis of urea water can be further increased, and thus the exhaust gas purification capability of the SCR catalyst 41 can be further improved.

  FIG. 7 is a cross-sectional view showing a rectifying unit 351 according to another embodiment. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned embodiment, and description is abbreviate | omitted. As shown in FIG. 7, the rectifying member 351 is provided with a rectifying member 350. The rectifying member 350 is a truncated conical tube material having both ends opened, and is arranged coaxially with the urea water injection valve 30.

  The small-diameter opening 350A of the rectifying member 350 is disposed to face the injection port of the urea water injection valve 30, and the large-diameter opening 350B of the rectifying member 350 is disposed to face the upstream end of the connection pipe 24. . Between the edge of the opening 350B of the rectifying member 350, the upstream end of the connection pipe 24, and the second chamber 23B, a gap through which exhaust gas passes is provided.

  The rectifying member 350 is a porous member, which is formed by molding a metal honeycomb into a truncated cone shape, and rectangular small holes 350C are formed at narrow intervals in the circumferential direction and the axial direction. Here, the partition walls 350 </ b> D of the metal honeycomb are inclined with respect to the thickness direction of the metal honeycomb and are arranged in parallel to the axial center of the rectifying member 350. Accordingly, the partition wall 350D functions as a guide for guiding the exhaust gas that has passed through the small hole 350C to the exhaust downstream side.

  In the rectifying unit 351 having such a configuration, the sprayed (sprayed) urea water is expanded in diameter from the upstream side to the downstream side as in the above-described rectifying unit 51, and the small holes The exhaust gas flowing in from 350C is diffused by being guided to the exhaust downstream side by the partition wall 350D. Then, the diffused urea water and the exhaust gas that has turned into a swirl flow are mixed in the connection pipe 24.

  FIG. 8 is a cross-sectional view showing a rectifying unit 451 according to another embodiment. In addition, the same code | symbol is attached | subjected to the structure similar to the above-mentioned embodiment, and description is abbreviate | omitted. As shown in FIG. 8, the rectifying unit 451 includes a rectifying member 350 and a hydrolysis catalyst 252 disposed on the exhaust downstream side of the rectifying member 350.

  In the rectifying unit 451 having such a configuration, the urea water injected from the urea water injection valve 30 and diffused by the rectifying member 350 passes through the hydrolysis catalyst 252 as in the above-described rectifying unit 251. At this time, hydrolysis of urea water is promoted. Then, urea water and ammonia generated by hydrolysis are sent to the exhaust downstream side of the connection pipe 24 by the exhaust gas that has turned into a swirling flow.

  In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

DESCRIPTION OF SYMBOLS 1 Exhaust purification unit, 20 Front casing, 20A 1st casing, 20B 2nd casing, 21 1st oxidation catalyst, 22 Filter, 23 Mixer chamber, 23A 1st chamber, 23B 2nd chamber, 24 Connection piping, 24A 1st piping , 24B second piping, 30 urea water injection valve, 40 latter casing, 41 SCR catalyst, 42 second oxidation catalyst, 50 rectifying member, 50A opening, 50B opening, 50C small hole, 50D claw, 51 rectifying unit, 151 rectifying unit , 152 Collision plate mixer, 152A diffusion plate, 251 rectifier, 252 hydrolysis catalyst, 350 rectifier, 350A opening, 350B opening, 350C small hole, 350D partition, 351 rectifier, 451 rectifier

Claims (3)

A selective reduction catalyst that is provided in an exhaust system of an internal combustion engine and selectively reduces nitrogen oxides in the exhaust gas using ammonia as a reducing agent;
An exhaust pipe for sending exhaust gas to the selective catalytic reduction catalyst;
A urea water injection device arranged to face the exhaust upstream end of the exhaust pipe and injecting urea water into the exhaust pipe;
A chamber that connects an exhaust downstream end of a casing containing a catalyst and an exhaust upstream end of the exhaust pipe, and forms a flow path in which exhaust gas is folded back from the casing to the exhaust pipe;
A frustoconical tube provided in the chamber and extending gradually from the vicinity of the injection port of the urea water injection device toward the exhaust pipe, and a plurality of vents are formed, and each vent is formed. An exhaust purification unit comprising: a rectifying member provided with a guide for guiding exhaust gas to the exhaust downstream side.   The exhaust purification unit according to claim 1, further comprising a porous material disposed at an exhaust downstream end of the rectifying member.   The exhaust purification unit according to claim 1, further comprising a hydrolysis catalyst disposed at an exhaust downstream end of the rectifying member.

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