JP2016205188A - Exhaust emission control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control unit for suppressing a temperature drop in a connection pipe thereby to enhance the efficiency of the hydrolysis of urea water thereby to improve the exhaust gas emission control capacity of a catalyst.SOLUTION: An exhaust emission control unit comprises: a connection pipe 24 for feeding an exhaust gas to an SCR catalyst 41; and a urea water injection valve 30 for injecting urea water into the connection pipe 24. The connection pipe 24 includes an inner pipe 24B, into which urea water is injected from the urea water injection valve 30, and an outer pipe 24A for forming a double pipe structure together with said inner pipe 24B. A passage for the exhaust gas is formed on the inner side of the inner pipe 24B and between the inner pipe 24B and the outer pipe 24A.SELECTED DRAWING: 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 arranged in parallel, and an upstream end of a straight exhaust pipe disposed between them and The downstream ends are respectively curved and connected to the outlet of the front casing and the inlet of the rear casing. A urea water injection device is disposed near the upstream end of the exhaust 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 generated ammonia is supplied to the SCR catalyst as a reducing agent, whereby NOx in the exhaust gas is reduced and purified.

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

JP 2009-36109 A JP 2006-29233 A

  In the exhaust pipe, the temperature of the exhaust gas decreases due to the latent heat when the urea water is hydrolyzed. Thereby, the conversion efficiency from urea water to ammonia decreases, and the NOx purification rate in the SCR catalyst decreases.

  An object of the disclosed exhaust purification unit is to increase the efficiency of hydrolysis of urea water and improve the exhaust gas purification ability of a catalyst by suppressing the temperature drop of the exhaust gas in the exhaust pipe.

  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 A urea water injection device that injects urea water into the exhaust pipe, and the exhaust pipe forms an inner pipe into which urea water is injected from the urea water injection apparatus and a double pipe structure together with the inner pipe An outer pipe is provided, and an exhaust gas flow path is formed inside the inner pipe and between the inner pipe and the outer pipe.

  According to the disclosed exhaust purification unit, it is possible to increase the efficiency of hydrolysis of urea water and improve the exhaust gas purification capability of the catalyst by suppressing the temperature drop of the exhaust gas in the connection pipe.

It is a perspective view which shows the exhaust gas purification unit which concerns on one Embodiment of this invention. It is sectional drawing which shows the inside of the mixer chamber and connection piping which concern on one Embodiment of this invention. It is a figure which shows the flow of the exhaust gas in the mixer chamber which concerns on one Embodiment of this invention. It is a figure which shows the flow of the exhaust gas in the mixer chamber which concerns on one Embodiment of this invention, and connection piping. It is sectional drawing which shows the inside of the mixer chamber and connection piping which concern on other embodiment. It is a figure which shows the flow of the exhaust gas in the mixer chamber and connection piping which concern 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 is a straight pipe and is arranged so that its axis 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 24D connected to the second chamber 23B, and a second pipe 24E that connects the first pipe 24D and the exhaust upstream end of the rear casing 40. The first pipe 24 </ b> D is arranged coaxially with the injection shaft of the urea water injection valve 30.

  The second pipe 24E is an elbow pipe, and the exhaust downstream end is formed in a disc shape. The straight line portion of the second pipe 24E is arranged coaxially with the first pipe 24D, and an annular flange is provided at the exhaust downstream end of the first pipe 24D and the exhaust upstream end of the second pipe 24E. Are fastened with bolts and nuts. An annular flange is provided at the exhaust downstream end of the second pipe 24E 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 first pipe 24D 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 50 </ b> A of the rectifying member 50 is disposed to face the injection port of the urea water injection valve 30, and the large-diameter opening 50 </ b> B of the rectifying member 50 is disposed to face the upstream end of the connection pipe 24. . Between the edge of the opening 50B of the flow regulating member 50, 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 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.

  The first pipe 24D of the connection pipe 24 has a double pipe structure, and a cylindrical outer pipe 24A extending linearly from the exhaust upstream end to the exhaust downstream end of the first pipe 24D and the exhaust of the first pipe 24D. And a cylindrical inner pipe 24B extending linearly from the upstream end to the exhaust downstream side. The exhaust upstream end of the inner pipe 24B and the exhaust downstream end of the rectifying member 50 have the same diameter, and these are joined. Thereby, the exhaust gas flowing outside the rectifying member 50 flows between the outer tube 24A and the inner tube 24B to the exhaust downstream side.

  An opening is not provided in a portion of the inner pipe 24B on the exhaust upstream side, and no exhaust gas enters and leaves the inside and outside of the inner tube 24B in this portion. On the other hand, a large number of small holes 24C are formed at narrow intervals in the circumferential direction and the axial direction in the portion of the inner pipe 24B on the exhaust downstream side, and the exhaust gas enters and exits the inside and outside of the inner pipe 24B.

  FIG. 3 is a view showing the flow of exhaust gas in the mixer chamber 23. 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.

  FIG. 4 is a view showing the flow of exhaust gas in the mixer chamber 23 and the connection pipe 24. As shown in this figure, the exhaust gas that has turned into a swirl flow flows between the outer pipe 24A and the inner pipe 24B of the connection pipe 24 through the outside of the rectifying member 50, or the small hole 50C and the rectifying member 50. It flows into the connection pipe 24 through the inside. In the connection pipe 24, the exhaust gas flows downstream while turning around the axis of the connection pipe 24. The exhaust gas flowing between the outer tube 24A and the inner tube 24B flows into the inner tube 24B through the small hole 24C on the exhaust downstream side in the double tube structure portion.

  By the way, 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. It is spread by. 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, it is possible to mix the exhaust gas that has been swirled after the urea water injected (sprayed) into the connection pipe 24 is diffused.

  Here, in the connection pipe 24, the exhaust gas flows between the outer tube 24A and the inner tube 24B, whereby the exhaust gas flowing in the inner tube 24B is heated. As a result, the temperature reduction of the exhaust gas due to the latent heat when the urea water is hydrolyzed can be suppressed, the conversion efficiency from urea water to ammonia can be improved, and thereby the NOx purification rate in the SCR catalyst 41 can be improved. it can.

  Further, the urea water can be prevented from adhering to the wall of the second chamber 23A and the connection pipe 24 due to the flow of the exhaust gas, so that the efficiency of hydrolysis of the urea water can be increased. The diffusibility of ammonia can be improved.

  Further, the exhaust gas flowing between the outer tube 24A and the inner tube 24B on the exhaust downstream side in the double tube structure portion flows into the inner tube 24B and is mixed with the exhaust gas in which ammonia or urea water is diffused. Thus, the diffusibility of ammonia in the exhaust gas can be further enhanced.

  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.

  For example, in the above-described embodiment, it has been described that the frustum-shaped rectifying member 50 is provided in the second chamber 23B of the mixer chamber 23. However, as shown in FIG. 5, the inner tube 24B extends to the second chamber 23B. The rectifying member 50 may be omitted and configured by providing a small hole 24C (punching hole) by extending the same. Also in this case, as shown in FIG. 6, the same effect as the above-described embodiment can be obtained.

  In the above-described embodiment, the small hole 24C (vent hole) is provided in a predetermined range on the exhaust upstream side of the inner tube 24B. However, the inner tube 24B may be shortened by the predetermined range.

  In the above-described embodiment, the introduction portion for introducing the exhaust gas into the inner pipe 24B is configured by the rectifying member 50 that gradually increases in diameter from the upstream side to the downstream side, but the diameter of the introduction portion may be constant. .

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 Outer pipe, 24B inner pipe, 24C small hole, 24D first pipe, 24E second pipe, 30 urea water injection valve, 40 rear casing, 41 SCR catalyst, 42 second oxidation catalyst, 50 rectifying member, 50A opening, 50B opening, 50C small Hole, 50D claw, 51 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 for injecting urea water into the exhaust pipe,
The exhaust pipe includes an inner pipe into which urea water is injected from the urea water injection device, and an outer pipe that forms a double pipe structure together with the inner pipe, and the inside of the inner pipe, the inner pipe, and the An exhaust gas purification unit in which an exhaust gas flow path is formed between the outer pipe and the outer pipe.   The exhaust purification unit according to claim 1, wherein a vent is formed in a predetermined range on the exhaust downstream side of the inner pipe.   Connected to the exhaust upstream end of the inner pipe, formed in a truncated cone shape so as to extend gradually from the vicinity of the injection port of the urea water injection device to the exhaust upstream end of the inner pipe, and a plurality of vent holes The exhaust purification unit according to claim 1 or 2, further comprising an exhaust introduction portion formed.

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