JP5533190B2 - Particulate filter and its regeneration method - Google Patents

Description

  The present invention relates to a particulate filter that is disposed in an exhaust passage of an engine and collects PM in exhaust gas, and more particularly to a particulate filter with improved regeneration efficiency after PM collection and a regeneration method thereof. is there.

  PM (particulate matter; particulate matter) purification device discharged from a diesel engine connects a DPF (diesel particulate filter) to the exhaust pipe of the diesel engine, collects PM with the DPF, and collects exhaust gas. Purify and discharge to the atmosphere.

  Since the PM collected by this DPF causes clogging of the filter, it is necessary to periodically oxidize, remove and regenerate the collected PM.

  As a method for forcibly regenerating PM, there is known a method (Patent Documents 1 and 2) of increasing exhaust temperature by spraying HC (for example, light oil) on an exhaust pipe and burning it with an oxidation catalyst (DOC). Yes.

  However, when exhaust gas moves from the DOC to the DPF, the temperature decreases, or the HC cannot completely burn and reaches the DPF to adversely affect the stability of PM regeneration.

  In order to reduce the PM regeneration temperature, a method of coating a catalyst from the DPF collection surface to the inside has been proposed (Patent Documents 3 and 4).

In this method, since the DPF is coated with a catalyst of a noble metal or OSC (oxygen storage capacity material, etc.), active oxygen and NO ₂ are generated during PM regeneration, so the oxidation temperature of PM decreases and PM regeneration occurs. Becomes better.

JP 2006-77675 A JP 2008-19820 A JP-A-2005-818 JP 2002-276339 A

  However, the cake-like PM collected on the surface is only partly in contact with the catalyst, and after the PM in contact with the catalyst is oxidized, the oxidation effect of the catalyst becomes limited, and thereafter the exhaust gas and HC There is a problem that only the regeneration of PM by oxidation results in a decrease in regeneration efficiency.

  Accordingly, an object of the present invention is to provide a particulate filter that can solve the above-described problems and improve the regeneration efficiency, and a regeneration method thereof.

In order to achieve the above object, the invention of claim 1 is a wall flow type particulate filter in which a cell is formed of a honeycomb-like porous body having a polygonal cross section and the inflow side and the outflow side are sealed. A cell having an open side and sealing the outflow side includes a first partition wall through which exhaust gas cannot pass, and a second partition wall through which exhaust gas can pass, wherein the first partition wall supports a catalyst, and The second partition wall is a particulate filter characterized in that no catalyst is supported .

In the invention of claim 2, the cell cross section is formed in a quadrangular shape, and two cells arranged alternately on the inflow side and the outflow side of the porous body are alternately sealed and opened on the inflow side. 2. The particulate filter according to claim 1, wherein a catalyst is supported on each inner surface of the first partition wall.

A third aspect of the present invention is the particulate filter according to the second aspect, wherein the catalyst is supported on the inner surfaces of the first partition walls of the two cells opened on the outflow side.

A fourth aspect of the present invention is the particulate filter according to any one of the first to third aspects, wherein the supported catalyst is composed of any of a noble metal, an oxide having OSC, or an HC adsorbent.

According to a fifth aspect of the present invention, in the method for regenerating PM collected by the particulate filter according to any one of the first to fourth aspects, HC is injected upstream of the particulate filter and is carried on the first partition wall. The particulate filter regeneration method is characterized in that HC is oxidized by the catalyst thus prepared to raise the temperature of the exhaust gas in the cell, and the PM collected in the second partition wall is combusted by the exhaust gas.

  According to the present invention, by coating the partition wall on one side of the cell, it is possible to perform HC adsorption, desorption, and oxidation with the coated catalyst in the vicinity of the PM at the time of regeneration. It can be transmitted to exhaust gas and exhibits an excellent effect that PM can be efficiently regenerated.

It is a figure which shows one embodiment of this invention. It is a sectional side view of the D section of FIG. It is sectional drawing explaining the flow of the waste gas of the D section in FIG. It is a figure which shows other embodiment of this invention. It is a sectional side view of the D section of FIG. It is sectional drawing explaining the flow of the waste gas of the D section in FIG. It is the schematic which shows the reproduction | regeneration system using the particulate filter of this invention. It is the schematic which shows the other reproduction | regeneration system using the particulate filter of this invention. It is a figure which shows the temperature rising characteristic at the time of reproduction | regeneration of the particulate filter in this invention and a prior art example. It is a figure explaining PM reproduction | regeneration of the particulate filter of this invention. It is a figure explaining PM regeneration of the conventional particulate filter.

  A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

  1 to 3 show an embodiment of the present invention.

  In the figure, a particulate filter (DPF) 10 is made of porous ceramics and is formed of a honeycomb porous body 12 having a large number of cross-sectional polygonal shapes, in the figure, quadrangular cells 11, and the inflow side and the outflow side are alternately plugged. Sealed with 13i and 13o to be wall flow type.

  In the present invention, the catalyst 14 is coated on the partition wall 12f on one surface of the cell 11 formed in a square shape of the particulate filter 10, and the other three partition walls 12t are made porous so that the exhaust gas can pass therethrough. It is a thing. Further, when the cell cross section has a quadrangular shape or more, the catalyst may be coated on at least one partition wall.

  When sealing the cells 11, as shown in FIGS. 1 and 2, the cells 11 are alternately closed with the sealing materials 13i and 13o on the inflow side and the outflow side every two cells arranged vertically (or left and right). The catalyst 14 is coated on the inner surface of the partition wall 12f between the two cells 11i, 11i that are sealed and formed on the outflow side and open on the inflow side, and the other three-surface partition walls in the cells 11i, 11i. 12t is made porous as it is so that exhaust gas can pass through.

  In addition, the two cells 11o, 11o that are sealed on the inflow side and opened on the outflow side remain porous partition walls 12f on all four surfaces.

By forming the particulate filter 10 in this way, at the time of PM collection, as shown in FIG. 3, exhaust gas flows from the other three partition walls 12t of the inflow side cell 11i to the adjacent outflow side cell 11o, and PM is Can be collected. At the time of regeneration, HC injected on the upstream side of the particulate filter 10 can be oxidized by the catalyst 14 coated on the inner surface of the partition wall 12f of the cell 11i, and the exhaust gas can be heated to a high temperature. In addition to being able to burn, the production of NO ₂ adsorbed on the catalyst 14 and the active oxygen from the OSC can be supplied to the surface of the PM, so that regeneration (oxidation) of PM can be performed efficiently.

  4 to 6 show another embodiment of the present invention, which is basically the same as the embodiment of FIGS. 1 to 3, but is sealed on the inflow side and opened on the outflow side. The inner surface of the partition wall 12f between the two outflow cells 11o, 11o is also coated with the catalyst 14, respectively, and the other three surfaces of both the cells 11o, 11o are made to be porous partition walls 12t so that the exhaust gas can pass. .

  In this embodiment, since the catalyst 14 is coated on the partition wall 12f of the outflow side cell 11o, the exhaust gas temperature can be raised, and the entire particulate filter 10 can be kept at the regeneration temperature or higher.

  As described above, the present invention collects PM by using a wall-through structure in which exhaust gas can pass through the three partition walls 12t of the partition walls 12 of the cells 11 of the particulate filter 10 made of a honeycomb-shaped porous body, and collecting the remaining PM. The partition wall 12f on one side has a wall flow that cannot pass exhaust gas, and the catalyst 14 is coated on the partition wall 12f on that surface.

As the catalyst 14 to be coated, a catalyst containing a noble metal (Pt, Pd, Rh, etc.), an OSC-containing oxide (CeO ₂ , Zr—Ce—O composite material, etc.), and an HC adsorbent (zeolite, etc.) is used. be able to.

  The catalyst 14 is coated on the partition wall 12f of the cell 11 of the particulate filter 10 and then baked and supported, and then the inflow side and the outflow side of the cell 11 are sealed to form a wall flow type.

  Thus, in the present invention, by using the particulate filter 10 in which the partition wall 12f on one surface of the cell 11 is coated with the catalyst 14, the HC adsorption → desorption → in the vicinity of the PM collected by the particulate filter 10 → It becomes possible to oxidize, and heat energy and HC can be used efficiently.

Further, since NO ₂ is generated and active oxygen from OSC can be supplied to the surface of the collected PM, regeneration (oxidation) of PM can be performed efficiently.

  In the above-described embodiment, the cell cross section has been described as a quadrilateral shape. However, the cell cross section is formed in a triangular shape or a hexagonal shape, and is formed so that the catalyst is coated on one surface, and the gas passes through the remaining surface. It may be a road. Further, when the cells are formed in a hexagonal shape, the catalyst may be coated on two surfaces facing in the radial direction, and the gas may pass on the other four surfaces.

  Examples of the present invention will be described below.

Example 1:
As described in FIGS. 1 to 3, the partition wall 12f of the inflow side cell 11i is coated with the oxidation catalyst 14 to form a partition wall (wall flow portion) through which the exhaust gas does not flow, and the other three surface partition walls 12t and the outflow side cell 11o. The four surfaces were wall-through through which exhaust gas flows, and the particulate filter 10 was formed by alternately sealing the honeycomb-shaped porous body 12 in the front and rear direction every two cells.

The coated catalyst 14 was obtained by using a Pt—Pd / Al ₂ O ₃ catalyst as a basic catalyst (catalyst 1) and containing the Zr—Ce—O composite material having OSC in the basic catalyst (catalyst 2), HC adsorption Four types were used: a catalyst containing zeolite (catalyst 3) and a mixture of catalyst 2 and catalyst 3 (catalyst 4).

Example 2:
As described with reference to FIGS. 4 to 6, the partition wall 12f of the inflow side cell 11i and the outflow side cell 11o is coated with the oxidation catalyst 14 to form the partition wall 12f (wall flow part) through which the exhaust gas does not flow, and the other three surface partition walls 12t. Is a wall filter through which exhaust gas flows, and a particulate filter 10 in which honeycomb-shaped porous bodies 12 are alternately sealed front and rear every two cells.

  Catalyst 14 was coated using Catalysts 1 to 4 as in Example 1.

Conventional example:
While the four surfaces of the partition walls of the inflow side cell and the outflow side cell were wall-through, catalyst 1 (oxidation catalyst) was coated from the collection surface to the inside to form a particulate filter.

  The particulate filters of Examples 1 and 2 and the conventional example were incorporated into the exhaust gas treatment apparatus shown in FIGS. 7 and 8, and the characteristics were evaluated in two ways.

  FIG. 7 shows an exhaust gas treatment system A in which a DPF device 23 including a DOC 22 and a particulate filter is incorporated in an exhaust gas passage 21 of the engine 20 and a nozzle 24 for injecting HC (light oil) is provided upstream of the DOC (oxidation catalyst) 22. FIG. 8 shows an exhaust gas treatment system B in which only the DPF device 23 is incorporated without incorporating the DOC.

  FIG. 9 shows the temperature rise characteristics of the particulate filter of the present invention and the conventional example.

  As shown in FIG. 9, the present invention was able to increase the temperature to 700 ° C. or more in 80 seconds after HC injection, whereas the conventional example was found to take about 130 seconds or more to reach 700 ° C. .

  Next, the particulate filter using each of the catalysts 1 to 4 of Examples 1 and 2 and the particulate filter of the conventional example were incorporated in the exhaust gas treatment system A of FIG. 7 and the exhaust gas treatment system B of FIG. Table 1 shows the results of comparison of the conventional example with respect to the temperature rise time, the temperature rise time during HC injection, the PM regeneration rate, and the HC / CO slip during regeneration.

  In Table 1, Examples 1 and 2 exceeded the characteristics of the conventional example no matter which catalyst 1 to 4 was used.

  In Table 1, Example 1 in which the catalyst was coated only on the inflow side was slightly inferior to Example 2 in which the catalyst was coated on the inflow side and the outflow side, but the other characteristics were the same as Example 2. there were.

  FIG. 10 is a diagram for explaining PM regeneration when regenerating PM deposited on the partition 12t of the particulate filter 10 of the present invention. FIG. 11 regenerates PM deposited on the partition 32t of the conventional particulate filter 30. It is a figure explaining PM reproduction at the time.

In the conventional example of FIG. 11, when PM is deposited as shown in FIG. 11A and HC and exhaust gas are supplied to regenerate the PM, the particles are oxidized from the surface of the PM deposition layer and at the same time, ceramic particles in the partition wall 32t. NO ₂ and active oxygen are generated on the surface of the catalyst 34 supported on 32S, and oxidation occurs from the surface side and the catalyst 34 side as shown in FIG. 11 (b). At this time, the oxidation rate by the catalyst 34 is higher than the oxidation rate from the surface side by the exhaust gas. However, as shown in FIG. 11B, the PM in contact with the catalyst 34 is oxidized rapidly. The oxidation rate decreases, and as shown in FIG. 11 (c), PM that is not in contact with the catalyst 34 partially remains unburned, and this is scattered in islands, per unit time. Reproduction efficiency will deteriorate.

On the other hand, in the present invention, when PM is deposited as shown in FIG. 10A and HC and exhaust gas are flowed to regenerate the PM, no catalyst is supported on the ceramic particles 12S of the partition wall 12t. without catalyst and HC and the exhaust gas contacts provided on the wall-flow one side of the partition wall to be in the cell, produces active oxygen NO ₂ is produced on that plane, and NO ₂ as shown in FIG. 10 (b) PM is oxidized from the surface with the exhaust gas whose temperature is increased by active oxygen, and the regeneration direction is unidirectional and there is no change in the oxidation rate. As a result, as shown in FIG. It can be played back.

  Thus, the present invention has the following effects.

  (1) By arranging the oxidation catalyst in the wall flow part close to the wall through surface where PM is deposited, the temperature increase rate during HC injection can be improved.

  (2) By arranging an oxidation catalyst in the wall flow part of the cell through which the wall-through gas has flowed out, it is possible to suppress HC / CO slip that occurs during PM regeneration.

(3) Since the PM collected by the partition walls is oxidized in the same direction by oxidation with NO ₂ and active O ₂ produced by the catalyst coated on the partition walls of the wall flow part and oxidation with heat, the oxidation rate is constant and short. PM regeneration progresses uniformly over time. Therefore, the reproduction rate can be increased as compared with the conventional example.

10 particulate filter 11 cell 11i inflow side cell 11o outflow side cell 12 porous body 12f partition wall (wall flow)
12t partition wall (wall through)
13i, 13o Sealant 14 Catalyst

Claims (5)

In a wall flow type particulate filter in which cells are made of a honeycomb-like porous body having a polygonal cross section and the inflow side and the outflow side are plugged ,
The cell that opens the inflow side and seals the outflow side includes a first partition wall through which the exhaust gas cannot pass, and a second partition wall through which the exhaust gas can pass,
The particulate filter , wherein the first partition wall carries a catalyst, and the second partition wall does not carry a catalyst . The cell cross-section is formed in a quadrangular shape, and every two cells arranged side by side on the inflow side and the outflow side of the porous body, alternately sealed, and on the inner surface of the first partition wall between the two cells opened on the inflow side, particulate filter according to claim 1, wherein the catalyst is supported. The particulate filter according to claim 2, wherein a catalyst is supported on the inner surfaces of the first partition walls of the two cells opened on the outflow side. The particulate filter according to any one of claims 1 to 3, wherein the catalyst to be supported is made of either a noble metal or an oxide having OSC, or an HC adsorbent. 5. The method for regenerating PM collected by the particulate filter according to claim 1, wherein HC is injected upstream of the particulate filter, and HC is oxidized by the catalyst supported on the first partition wall. The particulate filter regeneration method is characterized in that the temperature of the exhaust gas in the cell is raised and the PM collected in the second partition wall is combusted with the exhaust gas.

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