JP2012127311A - Diffuser for reducing agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To propose a diffuser for a reducing agent having a structure that hardly causes generation of deposits in comparison with a conventional one.SOLUTION: In a diffuser 10, a reduction catalyst is arranged in an exhaust system of an engine, and the diffuser is used in an exhaust emission control device injecting the reducing agent from a nozzle into exhaust in an upstream side than the reduction catalyst. The diffuser includes a tube part 11 with an outer diameter smaller than an inner diameter of an exhaust pipe 4 in an upstream side of the reduction catalyst, using one of both end openings as an exhaust inlet 11in, and using the other as an exhaust outlet 11out; and a diffusion part 12 provided in the tube part 11 away from the inlet 11in, and stirring up the exhaust flowing in the tube part. The diffuser is installed in the exhaust pipe by connecting an inlet side end portion 11a of the tube part 11 to the exhaust pipe 4.

Description

  The present invention relates to an exhaust emission control device for an engine, and relates to an exhaust emission control device that injects a reducing agent (including a precursor thereof) into exhaust gas upstream of a reduction catalyst.

  An SCR type exhaust purification device is used as an exhaust purification device that removes NOx (nitrogen oxides) contained in engine exhaust. In this exhaust purification device, a reduction catalyst is disposed in the exhaust system, and a reducing agent is injected into the exhaust gas upstream of the reduction catalyst and added to the catalyst, thereby causing a catalytic reduction reaction between NOx and the reducing agent in the exhaust gas. Thus, NOx is purified to harmless components. The reduction reaction mainly uses ammonia having good reactivity with NOx. As a reducing agent for this, an aqueous urea solution that easily generates ammonia by hydrolysis with exhaust heat and water vapor in the exhaust, A liquid reducing agent such as an aqueous ammonia solution is used.

  In this type of exhaust purification device, in order to uniformly diffuse the reducing agent in the exhaust, as disclosed in Patent Document 1, a diffusion plate called a mixer is provided in the exhaust pipe upstream of the reduction catalyst to stir the exhaust, and from the nozzle A technique for promoting the diffusion of the injected reducing agent has been proposed. The diffusion plate is a metal plate having many punching holes as in Patent Document 1, a metal plate formed in a lattice shape, or a metal plate having many fins as disclosed in Patent Document 2.

JP 2007-077957 A JP 2009-024654 A

  When a diffusion plate is provided in the exhaust pipe upstream of the reduction catalyst as in the above background art, the reducing agent injected from the nozzle hits the diffusion plate before it is sufficiently dispersed (reduction of the reducing agent concentration). (Such as urea crystals) may adhere to the diffusion plate and the wall of the exhaust passage in front of the diffusion plate. Although this precipitate can be dissolved by increasing the exhaust temperature, it is feared that the exhaust pipe is narrowed to cause a pressure loss or the like, so that it is preferable to suppress the precipitation as much as possible.

  The present invention pays attention to this point, and proposes a reducing agent diffuser having a structure in which precipitates are less likely to occur than in the prior art.

The reducing agent diffuser proposed to solve the above problems is
A diffuser used in an exhaust purification device in which a reduction catalyst is disposed in an exhaust system of an engine, and a reducing agent is injected from a nozzle into the exhaust upstream of the reduction catalyst,
A cylindrical portion having an outer diameter smaller than the inner diameter of the exhaust pipe upstream of the reduction catalyst, one of both end openings serving as an exhaust inlet and the other serving as an exhaust outlet; And a diffusion part that stirs the exhaust gas flowing in the cylinder part.
The end portion on the inlet side of the cylindrical portion is connected to the exhaust pipe so as to be installed in the exhaust pipe.

  In the reducing agent diffuser according to the above proposal, a diffusion portion is provided in the cylindrical portion that is thinner than the exhaust pipe upstream of the reduction catalyst, away from the inlet. The cylinder part is installed in the exhaust pipe with the inlet side end portion connected to the exhaust pipe, and the exhaust flow after reducing agent injection flows into the cylinder part from the inlet to reduce the flow diameter. Can be increased at the inlet portion of the cylinder portion, and the exhaust gas having the increased flow velocity can be sent to the diffusion portion away from the inlet port. Since the dispersion of the reducing agent is promoted by increasing the flow velocity, the dispersion of the reducing agent proceeds when reaching the diffusion portion, and precipitates generated in the cylindrical portion are suppressed as compared with the conventional case.

Schematic which shows the structural example of the exhaust gas purification apparatus to which a diffuser is applied. Sectional drawing which shows 1st Embodiment of a diffuser. Sectional drawing which shows 2nd Embodiment of a diffuser. Sectional drawing which shows 3rd Embodiment of a diffuser.

  FIG. 1 shows two configuration examples of an exhaust purification device incorporated in an engine exhaust system. FIG. 1A is a type in which a PM collection filter and a reduction catalyst are arranged in a straight line, and FIG. 1B is an exhaust purification device in which a PM collection filter and a reduction catalyst are arranged in an S shape by folding the exhaust passage.

  The exhaust purification device is an SCR type exhaust purification device that has a PM trapping function in addition to NOx removal. In the exhaust system of the engine, an oxidation catalyst (DOC) and PM trapping are performed from upstream to downstream of the exhaust flow. A collecting filter (DPF), a reduction catalyst (SCR), and an ammonia slip catalyst (ASC) are arranged in series (the order is not limited to this). Among these, the oxidation catalyst and the PM collection filter are accommodated in the first casing 1 on the upstream side, and the reduction catalyst and the ammonia slip catalyst are accommodated in the second casing 2 on the downstream side. For example, an aqueous urea solution is used as the reducing agent (including the precursor), and the nozzle 3 that injects the reducing agent into the exhaust serves as a communication pipe that connects the first and second casings 1 and 2. 4 is provided.

  In the exhaust pipe 4 upstream of the reduction catalyst, a reducing agent diffuser 10 is installed on the downstream side of the nozzle 3. The diffuser 10 includes a cylindrical portion 11 and a diffusing portion 12, and is installed in the exhaust pipe 4 with the inlet of the cylindrical portion 11 being the upstream side and the outlet being the downstream side. The details of the first embodiment of the diffuser 10 are shown in FIG.

  The diffuser 10 according to the first embodiment is a cylindrical tube having a straight cylindrical portion 11, one of the openings at both ends is used as an inlet 11 in and the other as an outlet 11 out, and the outer diameter of the cylindrical portion 11 is the exhaust pipe 4. Smaller than the inner diameter. The cylindrical portion 11 has an inflow side end portion 11a connected to the exhaust pipe 4 via a circumferential flange 11b, and the exhaust gas containing the reducing agent flowing through the exhaust pipe 4 is entirely exhausted from the inflow port 11in. It flows into the part 11. Since the inner diameter of the cylindrical portion 11 is smaller than the inner diameter of the exhaust pipe 4, the flow diameter of the exhaust gas flowing from the exhaust pipe 4 into the cylindrical portion 11 is narrowed, and therefore the exhaust flow velocity is increased in the cylindrical portion 11.

  A diffusion portion 12 is provided in the cylindrical portion 11 so as to close the outflow port 11out at the outflow port side end portion 11c that is separated from the inflow port 11in, that is, in the case of this embodiment, that is farthest from the inflow port 11in. ing. The diffusing unit 12 is formed using a diffusing plate having a large number of fins as disclosed in Patent Document 2, for example. The diffusing unit 12 stirs the exhaust gas flowing through the cylindrical unit 11 to reduce the reducing agent. Has the function of diffusing. The position of the diffusing portion 12 may be in the middle of the cylindrical portion 11 as indicated by a dotted line in the figure, but it is preferable to keep it as far as possible from the inflow port 11in in terms of suppressing precipitates. For this purpose, the axial length of the cylindrical portion 11 should be as long as possible. When the diffusion portion 12 is provided at the outlet side end portion 11c as shown in the drawing, the exhaust purification device of FIG. The length is such that the diffusing portion 12 can be positioned immediately before the tube 4 is bent toward the reduction catalyst.

  The flange 11b that connects the cylinder part 11 to the exhaust pipe 4 is provided around the entire circumference of the peripheral edge of the inlet side end portion 11a of the cylinder part 11, and is provided around the outer periphery of the exhaust pipe 4. The gasket 4b is interposed between the flange 4a and the bolt is fixed with a bolt or the like. That is, the exhaust pipe 4 is divided into two pieces by the flange portion 4a, and is connected to each other by fastening the flange portion 4a with the flange 11b and the gasket 4b of the cylindrical portion 11 interposed therebetween.

  By fixing the flange 11b surrounding the inflow port 11in to the exhaust pipe 4, the heat insulating layer 13 is formed so as to surround the cylindrical portion 11 downstream of the flange 11b. That is, since the flange 11 b protruding from the outer periphery of the cylinder part 11 is fixed to the exhaust pipe 4, there is a gap between the outer peripheral surface of the cylinder part 11 and the inner peripheral surface of the exhaust pipe 4 so as to surround the cylinder part 11. Is formed. Since this gap becomes a space (air layer) with no flow, a layer with low heat conduction surrounding the cylindrical portion 11 is formed and functions as the heat insulating layer 13. Although the exhaust pipe 4 is cooled by being exposed to the traveling wind, the heat flowing through the cylindrical portion 11 is kept warm because the heat insulating layer 13 surrounds the cylindrical portion 11. Since the exhaust gas is kept warm, the temperature drop of the catalyst bed temperature can be suppressed, so that the purification efficiency in the reduction catalyst is improved.

  According to the diffuser 10 according to the first embodiment described above, the cylindrical portion 11 is installed in the pipe by connecting the inlet side end portion 11a to the exhaust pipe 4, and the exhaust after the reducing agent injection by the nozzle 3 is supplied to the inlet. Since the flow amount is reduced by flowing the entire amount from 11 in to the inside, the exhaust flow velocity can be increased at the inlet portion of the cylinder portion 11, and the exhaust gas having the increased flow velocity is sent to the diffusion portion 12 away from the inflow port 11 in. be able to. Since the dispersion of the reducing agent is promoted by increasing the flow velocity, the dispersion of the reducing agent proceeds when reaching the diffusion unit 12. It is possible to increase the distance from the reducing agent injection position by the nozzle 3 to the diffusing unit 12 and increase the exhaust flow velocity so that the reducing agent can be sufficiently dispersed and diffused by the diffusing unit 12 after the dense portion disappears in the exhaust. Therefore, the precipitate generated inside the cylinder portion 11 is suppressed as compared with the conventional case. In addition, even if precipitates are generated and accumulated in the cylindrical portion 11, it can be handled by replacing the diffuser 10 as a whole, so that maintenance is easy.

  FIG. 3 shows a second embodiment of the diffuser 10. The diffuser 10 according to the second embodiment has a configuration in which the inlet side end portion 11a 'of the cylindrical portion 11 extends in a trumpet shape. Others are the same as the first embodiment. The inflow-port side end portion 11a 'expands in a trumpet shape, thereby forming a funnel-shaped inflow port 11in that guides exhaust gas smoothly into the cylindrical portion 11. In the case of the first embodiment, since the inlet side end portion 11a provided with the flange 11b is an exit corner, the flow of exhaust gas in this portion is deteriorated, but in the second embodiment, this flow is improved. The

  FIG. 4 shows a third embodiment of the diffuser 10. In the diffuser 10 of the third embodiment, the inlet side end portion 11a ′ of the cylindrical portion 11 is expanded in a trumpet shape as in the second embodiment, and the outlet side end portion 11c of the cylindrical portion 11 is the diffusion portion 12. It is extended further downstream and drawn. That is, the inner diameter of the cylindrical portion 11 is reduced in the downstream portion of the diffusion portion 12, and the reduced diameter portion 11 d is formed on the downstream side of the diffusion portion 12. Since the flow rate of the exhaust gas increases when passing through the reduced diameter portion 11d, the reducing agent diffusion in the exhaust gas is further promoted. Except for the reduced diameter portion 11d, the second embodiment is the same as the first and second embodiments.

DESCRIPTION OF SYMBOLS 10 Diffuser 11 Cylindrical part 11a, 11a 'Inlet side end part 11b Flange 11c Outlet side end part 11d Reduced diameter part 11in Inlet 11out Outlet 12 Diffusion part 13 Heat insulation layer

Claims (4)

A reducing agent diffuser for use in an exhaust purification device in which a reducing catalyst is disposed in an exhaust system of an engine and a reducing agent is injected from a nozzle into exhaust upstream of the reducing catalyst,
A cylindrical portion having an outer diameter smaller than the inner diameter of the exhaust pipe upstream of the reduction catalyst, one of both end openings serving as an exhaust inlet and the other serving as an exhaust outlet;
A diffusion part that is provided in the cylinder part apart from the inlet and stirs the exhaust gas flowing in the cylinder part;
Comprising
A diffuser installed in the exhaust pipe by connecting an end portion on the inlet side of the cylindrical portion to the exhaust pipe.   A flange is provided around the outer periphery of the end portion on the inlet side of the cylindrical portion, and the flange is fixed to the exhaust pipe, so that the outer peripheral surface of the cylindrical portion and the inner peripheral surface of the exhaust pipe are downstream of the flange. The diffuser of Claim 1 in which the heat insulation layer surrounding the said cylinder part is formed in between.   The diffuser according to claim 1 or 2, wherein an end portion on the inlet side of the cylindrical portion extends in a trumpet shape.   The diffuser according to claim 1, wherein an inner diameter of a downstream portion of the cylindrical portion is smaller than that of the diffusing portion.

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