JP2014202192A - Exhaust emission cleaning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optionally select an element such as copper, which cannot be conventionally used as metal active species, as the metal active species of a selective reduction type catalyst.SOLUTION: An exhaust emission cleaning device includes a selective reduction type catalyst 4 selectively reacting NOx with ammonia even under the coexistence of oxygen, in the terminal part of an exhaust tube 2 (an exhaust flow passage), and can add urea water as reductant on the upstream side with respect to the selective reduction type catalyst 4. On the downstream side with respect to the selective reduction type catalyst 4, a wall-through type filter 11 capable of catching a metal active species separated from the selective reduction type catalyst 4 is arranged.

Description

  The present invention relates to an exhaust emission control device.

  2. Description of the Related Art In recent years, a selective reduction catalyst that includes a particulate filter that collects particulates in exhaust gas in the middle of an exhaust pipe, and that can selectively react NOx with ammonia even in the presence of oxygen on the downstream side of the particulate filter. It is considered that urea water is added as a reducing agent between the selective reduction catalyst and the particulate filter to simultaneously reduce particulates and NOx.

  In this case, since urea water is added to the selective reduction catalyst between the particulate filter and the selective reduction catalyst, the urea water added to the exhaust gas is ammonia and carbon dioxide. In order to secure a sufficient reaction time until thermal decomposition, it is necessary to increase the distance from the urea water addition position to the selective catalytic reduction catalyst. If they are spaced apart from each other by a large distance, there is a problem that the mountability on the vehicle is significantly impaired.

  Therefore, as shown in FIG. 3, a particulate filter 3 for collecting particulates in the exhaust gas 1 at the end of an exhaust pipe 2 (exhaust flow path) through which the exhaust gas 1 from the engine flows, and the particulates The selective reduction catalyst 4 having the property of allowing NOx to react selectively with ammonia even in the presence of oxygen is disposed downstream of the filter 3 by the casings 5 and 6 and arranged in parallel. Is connected to the inlet end of the selective catalytic reduction catalyst 4 by an S-shaped connecting flow path 7 so that the exhaust gas 1 discharged from the outlet end of the particulate filter 3 is reversed. An exhaust purification device has been devised that is folded back and introduced into the inlet end of the adjacent selective catalytic reduction catalyst 4.

  Here, the communication channel 7 surrounds the outlet side end of the particulate filter 3 and collects the exhaust gas 1 immediately after exiting from the outlet side end while changing the direction in a substantially perpendicular direction. A chamber 7A, a mixing pipe 7B for extracting the exhaust gas 1 collected in the gas collecting chamber 7A in a direction opposite to the exhaust flow of the particulate filter 3, and a direction in which the exhaust gas 1 guided by the mixing pipe 7B is substantially perpendicular The S-shaped structure is formed by the gas dispersion chamber 7C surrounding the inlet side end so that the dispersed exhaust gas 1 can be introduced into the inlet side end of the selective catalytic reduction catalyst 4 while being dispersed. In the center position of the inlet end of the mixing pipe 7B, a urea water addition injector 8 (urea water addition means) for adding urea water into the mixing pipe 7B There is equipped toward the outlet end side of the mixing pipe 7B.

  In the example shown here, an oxidation catalyst 9 that oxidizes unburned fuel in the exhaust gas 1 is provided in the front stage in the casing 5 in which the particulate filter 3 is held, In addition, an ammonia reduction catalyst 10 that oxidizes surplus ammonia is provided at the rear stage in the casing 6 in which the selective catalytic reduction catalyst 4 is held.

  If such a configuration is adopted, particulates in the exhaust gas 1 are collected by the particulate filter 3, and urea water is supplied from the urea water addition injector 8 in the middle of the mixing pipe 7B on the downstream side thereof. As a result of being added to the exhaust gas 1 and thermally decomposed into ammonia and carbon dioxide gas, the NOx in the exhaust gas 1 is reduced and purified well by ammonia on the selective catalytic reduction catalyst 4, so that the particulates and NOx in the exhaust gas 1 are reduced. Are simultaneously reduced.

  At this time, the exhaust gas 1 discharged from the outlet end portion of the particulate filter 3 is folded in the reverse direction by the connecting flow path 7 and then introduced into the inlet end portion of the adjacent selective catalytic reduction catalyst 4. Therefore, a long distance from the urea water addition position to the selective catalytic reduction catalyst 4 is secured, and a sufficient reaction time is secured for ammonia to be generated from the urea water.

  In addition, the particulate filter 3 and the selective catalytic reduction catalyst 4 are arranged in parallel, and the communication flow path 7 is arranged between the particulate filter 3 and the selective catalytic reduction catalyst 4, so that the whole The configuration becomes compact, and the mountability to the vehicle is greatly improved.

  Prior art document information relating to an exhaust gas purification apparatus in which this type of particulate filter 3 and selective reduction catalyst 4 are arranged in parallel and connected by an S-shaped connecting flow path 7 is disclosed in Patent Document 1 below. Etc.

JP 2008-196328 A

  However, it is known that the performance of the selective catalytic reduction catalyst 4 used in the exhaust gas purification apparatus as shown in FIG. 3 varies greatly depending on the metal active species. Is a NOx purification rate and the horizontal axis is the amount of Pt / Pd in the oxidation catalyst 9 in the previous stage, as compared with the case of iron (Fe-based catalyst) and the case of copper (Cu-based catalyst), It is already known that the performance (NOx purification rate) is higher when copper is used as the metal active species than the iron used as a general metal active species. For automobiles equipped with a system that performs exhaust purification using a selective catalytic reduction catalyst, it is stipulated that the specified six elements of vanadium, chromium, manganese, cobalt, nickel, and copper are not released into the atmosphere, and high performance is obtained. The known copper has a problem that it can not be used as a metal active species.

  The present invention has been made in view of the above circumstances, and an object thereof is to allow an element such as copper that could not be used as a metal active species so far to be arbitrarily selected as a metal active species of a selective catalytic reduction catalyst. And

  The present invention is equipped with a selective catalytic reduction catalyst that selectively reacts NOx with ammonia even in the presence of oxygen in the middle of the exhaust flow path, so that urea water can be added as a reducing agent upstream of the selective catalytic reduction catalyst. An exhaust purification device configured as described above, wherein a wall-through type filter capable of capturing active metal species desorbed from the selective catalytic reduction catalyst is disposed downstream of the selective catalytic reduction catalyst. It is what.

  Thus, even if a situation occurs in which the active metal species are desorbed from the selective catalytic reduction catalyst and scattered downstream, the scattered active metal species pass through the wall-through filter. Since it is trapped in the middle and the release of the active metal species into the atmosphere is prevented, the active metal species of the selective catalytic reduction catalyst can be arbitrarily selected.

  Further, in the present invention, it is preferable that copper is employed as the metal active species of the selective catalytic reduction catalyst. In this way, compared with the case of iron generally used as the metal active species so far. As a result, significant performance improvement can be achieved.

  In more specific implementation of the present invention, the wall-through type filter may be loaded with an ammonia reducing catalyst for oxidizing excess ammonia, or the selective reduction type catalyst and the wall-through type filter may be supported. You may make it arrange | position the ammonia reduction catalyst which oxidizes surplus ammonia between filters.

  According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the first and second aspects of the present invention, since the release of the active metal species separated from the selective catalytic reduction catalyst into the atmosphere can be prevented, it has not been possible to use as the active metal species until now. An element such as copper can be arbitrarily selected as the metal active species of the selective catalytic reduction, and the performance of the selective catalytic reduction can be greatly improved.

  (II) According to the invention described in claims 3 and 4 of the present invention, surplus ammonia that has passed through the selective catalytic reduction catalyst without being reacted can be oxidized by the ammonia reducing catalyst. Release to the atmosphere can be remarkably suppressed. In particular, when an ammonia reduction catalyst is supported on a wall-through filter, a compact arrangement can be achieved by eliminating the need for separate arrangement spaces for the filter and the ammonia reduction catalyst. Can be realized.

It is the schematic which shows an example of the form which implements this invention. It is the schematic which shows another form example of this invention. It is the schematic which shows a prior art example. It is the graph which compared the performance in case the metal active species is iron and copper.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment for carrying out the present invention, and the parts denoted by the same reference numerals as those in FIG. 3 represent the same items.

  As shown in FIG. 1, in this embodiment, copper is employed as the metal active species of the selective catalytic reduction catalyst 4 in the exhaust purification apparatus configured in the same manner as described above with reference to FIG. 3, and this selective catalytic reduction catalyst 4 A wall-through type filter 11 capable of capturing copper as a metal active species separated from the selective catalytic reduction catalyst 4 is disposed in the exhaust pipe 2 further downstream.

  Here, the wall-through type filter 11 has substantially the same structure as the particulate filter 3 disposed on the upstream side. More specifically, the wall-through type filter 11 is a porous material made of a ceramic such as cordierite. It has a quality honeycomb structure, and the inlets of each flow path partitioned in a lattice pattern are alternately sealed, and the outlets of the flow paths that are not sealed are sealed. Only the exhaust gas 1 that has permeated through the porous thin wall partitioning each flow path is discharged to the downstream side, and the copper released from the selective catalytic reduction catalyst 4 is captured by the porous thin wall. .

  Particularly in this embodiment, the wall-through type filter 11 is loaded with an ammonia reducing catalyst that oxidizes surplus ammonia, and the wall flow type (each channel partitioned in a grid pattern is straightened). The filter 11 is arranged using the arrangement space of the existing ammonia reduction catalyst 10 (see FIG. 3) as it is.

  Thus, in this way, even if a situation occurs in which copper is desorbed from the selective catalytic reduction catalyst 4 and scattered downstream, the scattered copper passes through the wall-through type filter 11. Since it is captured and the release of the copper into the atmosphere is prevented, it becomes possible to select copper that could not be used as the metal active species of the selective catalytic reduction catalyst 4 and used as a general metal active species. The performance can be greatly improved compared with the case of iron.

  In addition, since the ammonia reduction catalyst that oxidizes excess ammonia is supported on the wall-through filter 11, excess ammonia that has passed through the selective reduction catalyst 4 without being reacted is oxidized by the ammonia reduction catalyst. It can be processed, and the release of surplus ammonia into the atmosphere can be remarkably suppressed, and a compact arrangement can be achieved by eliminating the need for separate arrangement spaces for the filter 11 and the ammonia reduction catalyst 10 (see FIG. 3). Can be realized.

  FIG. 2 shows another embodiment of the present invention. In place of the ammonia reduction catalyst supported on the wall-through filter 11 in the embodiment of FIG. 1, the selective reduction catalyst 4 and Between the wall-through type filter 11, an ammonia reducing catalyst 10 for oxidizing excess ammonia is separately arranged.

  Even in this case, the copper desorbed from the selective catalytic reduction catalyst 4 and scattered downstream can be captured by the wall-through filter 11 to prevent the copper from being released into the atmosphere. Copper that could not be used so far can be selected as the metal active species of the type catalyst 4, and a significant performance improvement can be achieved compared to the case of iron that has been used as a general metal active species. .

  In addition, since the ammonia reduction catalyst 10 is disposed separately between the selective reduction catalyst 4 and the wall-through type filter 11, the excess ammonia that has passed through the selective reduction catalyst 4 while remaining unreacted is removed from the ammonia reduction catalyst. 10 can be oxidized, and the release of excess ammonia into the atmosphere can be remarkably suppressed.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment example, but a case where copper is employed as a metal active species of the selective catalytic reduction catalyst is described as a preferred example. The element that can be adopted as the metal active species of the type catalyst is not limited to copper, it is possible to select any element, and the combination with the particulate filter may be arbitrarily selected Of course, the arrangement form is not limited to the parallel arrangement as shown in the drawings, and various changes can be made without departing from the scope of the present invention.

1 Exhaust gas 2 Exhaust pipe (exhaust flow path)
4 Selective reduction catalyst 8 Injector for urea solution addition 10 Ammonia reduction catalyst 11 Wall-through filter

Claims (4)

  Equipped with a selective reduction catalyst that selectively reacts NOx with ammonia even in the presence of oxygen in the middle of the exhaust flow path, and configured to be able to add urea water as a reducing agent upstream of the selective reduction catalyst An exhaust gas purification apparatus comprising a wall-through type filter capable of capturing active metal species desorbed from a selective reduction catalyst downstream of the selective reduction catalyst. apparatus.   The exhaust emission control device according to claim 1, wherein copper is adopted as a metal active species of the selective catalytic reduction catalyst.   The exhaust purification apparatus according to claim 1 or 2, wherein an ammonia reduction catalyst for oxidizing surplus ammonia is supported on the wall-through type filter.   The exhaust emission control device according to claim 1 or 2, wherein an ammonia reduction catalyst that oxidizes excess ammonia is disposed between the selective reduction catalyst and the wall-through type filter.

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