JP2005120964A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for well reducing particulates in exhaust gas down to a nano particle level. <P>SOLUTION: The exhaust emission control device comprises a catalyst regenerative particulate filter 10 mounted on the midway of an exhaust pipe 9. At the rear stage of the particulate filter 10, a nano particle treatment filter 12 is provided which has a precious metal catalyst carried on a metal non-woven cloth or a wire meshed filter. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust emission control device.

  Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of soot composed of carbonaceous matter and SOF content (Soluble Organic Fraction) composed of high-boiling hydrocarbon components. The composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which the exhaust gas flows. It has been done conventionally.

  This type of particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the flow paths partitioned in a lattice pattern are alternately sealed, and the inlets are not sealed. About the flow path, the exit is sealed, and only the exhaust gas which permeate | transmitted the porous thin wall which divides each flow path is discharged | emitted downstream.

  Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. Although it is necessary to regenerate, in normal diesel engine operation conditions, there are few opportunities to obtain exhaust temperatures that are high enough to cause the particulates to self-combust. It has been studied to adopt a catalyst regeneration type particulate filter that is integrally supported on the catalyst.

That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature lower than the conventional one. This is possible (for example, see Patent Document 1).
JP 2001-73748 A

  The adoption of such a catalyst regeneration type particulate filter has already achieved a reduction rate as high as about 95%, and particularly excellent results have been obtained with respect to removal of soot in the particulate. However, since the nanoparticles of 50 nm (0.05 μm) or less in the particulates will rub through the particulate filter as described above, the reduction of this kind of extremely fine nanoparticles will be a big issue in the future. It has become a challenge.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an exhaust emission control device that can satisfactorily reduce particulates contained in exhaust gas to a nanoparticle level.

  The present invention relates to an exhaust gas purification apparatus equipped with a catalyst regeneration type particulate filter in the middle of an exhaust pipe, the nanoparticle formed by supporting a noble metal catalyst on a metal non-woven fabric or a wire mesh filter at the subsequent stage of the particulate filter A processing filter is provided.

  Thus, in this way, the soot in the exhaust gas is almost removed when passing through the catalyst regeneration type particulate filter, and the exhaust gas, in which only the nanoparticles remain, is introduced into the downstream nanoparticle processing filter. Therefore, the nanoparticles in the exhaust gas repeatedly collide with the pillar part forming the pores in the nanoparticle treatment filter repeatedly and are collected in any pillar part. For example, the nanoparticles in the first half Even if it can pass through the processing filter, it will be collected while passing through the latter nanoparticle processing filter.

  At this time, the nanoparticles collected by the nanoparticle treatment filter are in a relatively flammable state released from the soot, and no retention time is required as in the case of burning and removing soot. Immediately after being collected in the filter, it is immediately burned and removed by the aid of the noble metal catalyst.

  In addition, the nanoparticle processing filter disposed in the latter stage of the particulate filter is heated by the heat generated when the collected particulate (soot) and SOF are burned (oxidation reaction) on the catalyst surface of the preceding particulate filter. Since warm exhaust gas is introduced, there are more opportunities to be exposed to exhaust gas having a higher temperature than the particulate filter in the previous stage, and the nanoparticles can be efficiently burned and removed under relatively advantageous temperature conditions. Is possible.

  Furthermore, in the present invention, instead of the nanoparticle treatment filter in which a noble metal catalyst is supported on a metal nonwoven fabric or wire mesh filter as described above, a nanoparticle treatment filter in which a zeolite catalyst is supported on a flow-through type honeycomb carrier. Alternatively, it is possible to employ a nanoparticle processing filter in which zeolite pellets are filled between a pair of ventilation plates.

  That is, when a nanoparticle treatment filter in which a zeolite catalyst is supported on the former flow-through type honeycomb carrier is adopted, while the exhaust gas flows separately for each flow path of the honeycomb carrier, The nanoparticles are adsorbed and collected on the surface of the porous zeolite catalyst, and immediately after that, the oxidation reaction is promoted by the catalytic action and immediately burned and removed.

  On the other hand, when a nanoparticle treatment filter is used in which zeolite pellets are filled between the latter pair of ventilation plates, the exhaust gas flows in a twisted manner so as to sew gaps between the zeolite pellets. In addition, the nanoparticles in the exhaust gas are adsorbed and collected on the surface of the porous zeolite pellet, and immediately after that, the oxidation reaction is promoted by the catalytic action and immediately burned and removed.

  Furthermore, in the present invention, an SOF partial oxidation catalyst comprising a flow-through type honeycomb carrier and an oxidation catalyst having an oxidizing power that can oxidize and purify the SOF content in the exhaust gas is supported before the particulate filter. It is preferable to provide it.

  In this way, when the exhaust gas passes through the SOF partial oxidation catalyst in the preceding stage of the particulate filter, the exhaust gas flows separately for each flow path of the honeycomb carrier, and the oxidation catalyst supported on the honeycomb carrier causes the exhaust gas to flow. The SOF component that is relatively easy to remove by combustion is promoted by the oxidation reaction and burned.

  That is, the particulate filter located at the latter stage of the SOF partial oxidation catalyst collects the soot that has been removed by the previous SOF partial oxidation catalyst to remove the mucous SOF fraction in advance. Compared with the case of a wet soot having a SOF content, the soot combustibility is greatly improved, and the trapped soot is removed by combustion relatively easily.

Incidentally, in the SOF partial oxidation catalyst in the previous stage of the particulate filter, CO and HC in the exhaust gas are oxidized to harmless CO ₂ and H ₂ O.

  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, second, and third aspects of the present invention, the exhaust gas from which most of the soot has been removed in advance by the catalyst regeneration type particulate filter is guided to the nanoparticle processing filter, so that the soot is removed from the soot. It is possible to reliably collect liberated nanoparticles that are relatively flammable, and to efficiently burn and remove nanoparticles using the heat of oxidation reaction of particulates in the previous particulate filter. Therefore, the particulates contained in the exhaust gas can be satisfactorily reduced to the nanoparticle level.

(II) According to the invention described in claim 4 of the present invention, the mucous SOF content can be removed in advance by the SOF oxidation catalyst, so that the dry-stage flammable soot can be used as a particulate filter in the subsequent stage. It can be collected and burned well, and CO and HC in the exhaust gas can be oxidized to harmless CO ₂ and H ₂ O by the SOF partial oxidation catalyst.

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

  1 to 3 show an example of an embodiment for carrying out the present invention. Reference numeral 1 in FIG. 1 denotes a diesel engine equipped with a turbocharger 2, and an intake 4 led from an air cleaner 3 is connected to an intake pipe. 5 is introduced to the compressor 2a of the turbocharger 2 and pressurized, and the pressurized intake air 4 is distributed and introduced to each cylinder of the diesel engine 1 via the intercooler 6.

  The exhaust gas 8 discharged from each cylinder of the diesel engine 1 through the exhaust manifold 7 is sent to the turbine 2b of the turbocharger 2, and the exhaust gas 8 driving the turbine 2b is sent to the catalyst regeneration type particulate filter 10. The particulates are collected through and discharged.

Here, the particulate filter 10 is a filter case in the middle of the exhaust pipe 9 that integrally carries a soot oxidation catalyst having a composition of alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), platinum (Pt), or the like. 11 and the particulate filter 10 in the filter case 11 has a metal non-woven fabric made of stainless steel wool or the like, a wire mesh filter or a wire mesh filter with a noble metal catalyst such as platinum or palladium. The nanoparticle processing filter 12 which carries | supports is accommodated.

  Further, particularly in the present embodiment, a flow-through type honeycomb carrier (having a large number of flow passages penetrating in the flow direction of the exhaust gas 8 in a lattice shape in the preceding stage of the particulate filter 10 in the filter case 11. ) Shows an example in which the SOF component oxidation catalyst 13 that carries an oxidation catalyst having an oxidizing power enough to oxidize and purify the SOF component in the exhaust gas 8 is accommodated.

The SOF partial oxidation catalyst 13 may be iron oxide (Fe ₂ O ₃ ) / alumina (Al ₂ O ₃ ) / ceria (CeO ₂ ) catalyst, or 0.005 to 0.5 g / L (liter). An oxidation catalyst having a relatively weak oxidizing power, such as a catalyst to which a very small amount of platinum (Pt) is added.

In other words, this SOF oxidation catalyst 13 is not intended to actively generate NO ₂ with strong oxidizing power to improve the oxidizing atmosphere or to burn soot, but to relatively remove combustion. It is possible to use an inexpensive one that hardly contains noble metal components and is intended only for oxidation purification of the SOF content that is easy to perform.

  Thus, in this way, the exhaust gas 8 introduced into the filter case 11 is first introduced into the SOF partial oxidation catalyst 13 and flows separately for each flow path of the honeycomb carrier, and is supported on this honeycomb carrier. By the oxidized catalyst, the SOF component that is relatively easy to burn and remove is promoted by the oxidation reaction and burned.

Incidentally, in the SOF partial oxidation catalyst 13 in the preceding stage of the particulate filter 10, CO, HC and the like in the exhaust gas 8 are oxidized to harmless CO ₂ and H ₂ O.

  Next, when the exhaust gas 8 from which the SOF content has been removed in advance is introduced into the particulate filter 10 immediately after, the soot in the exhaust gas 8 is almost removed when passing through the particulate filter 10.

  Here, the particulate filter 10 collects the soot that has been removed from the mucous SOF in advance by the SOF oxidation catalyst 13 in the previous stage, and thus has a SOF content on the surface. Compared with the case of wet soot, soot combustibility is greatly improved, and combustion removal of the collected soot is relatively easy.

  As a result of most of the soot in the exhaust gas 8 being removed by the particulate filter 10, the exhaust gas 8 in which only nanoparticles remain is led to the subsequent nanoparticle processing filter 12. In the nanoparticle treatment filter 12, the nanoparticles in the exhaust gas 8 repeatedly collide with the pillar portion forming the pores in the nanoparticle treatment filter 12 and are collected in any pillar portion. . For example, even if it can pass through the first nanoparticle processing filter 12, it will be collected while passing through the second nanoparticle processing filter 12.

  At this time, the nanoparticles collected by the nanoparticle treatment filter 12 are in a relatively flammable state released from the soot, and no holding time is required as in the case where the soot is burned and removed by the particulate filter 10. Therefore, immediately after being collected in the nanoparticle processing filter 12, it is immediately burned and removed by the assistance of the noble metal catalyst.

  In addition, the nanoparticle treatment filter 12 introduces exhaust gas 8 that has been heated by heat generated when particulates (soot) collected on the catalyst surface of the particulate filter 10 in the previous stage or SOF combusts (oxidation reaction). As a result, the opportunity to be exposed to the exhaust gas 8 having a temperature higher than that of the particulate filter 10 in the previous stage is increased, and the nanoparticles can be efficiently burned and removed under a relatively advantageous temperature condition. .

  Therefore, according to the above embodiment, the exhaust gas 8 from which the soot is almost removed by the catalyst regeneration type particulate filter 10 is guided to the nanoparticle processing filter 12, so that the exhaust gas 8 released from the soot is relatively inflammable. Since the nanoparticles can be reliably collected, and the nanoparticles can be efficiently burned and removed by utilizing the oxidation reaction heat of the particulates in the particulate filter 10 in the previous stage, they are included in the exhaust gas 8. The particulates can be reduced well to the nanoparticle level.

  In fact, according to a verification experiment by the present inventors, as shown by a graph (horizontal axis: particle size [nm] of particulates, vertical axis: number of particles contained in exhaust gas per 1 cc) in FIG. The distribution curve A for each particle size of the particles remaining in the exhaust gas 8 finally discharged in the present embodiment can obtain a good reduction effect even for nanoparticles of 50 nm (0.05 μm) or less. Compared with the distribution curve B in the case of using a single particulate filter alone, a remarkable improvement regarding the reduction of nanoparticles as shown by cross hatching in FIG. 3 was confirmed. A distribution curve C in the graph in FIG. 3 shows a comparative example in the case of discharging without passing through any post-processing device such as a particulate filter.

In addition, since the SOF component oxidation catalyst 13 can remove the mucous SOF component in advance, the soot with good flammability in the dry state can be collected in the particulate filter 10 and burned well. Further, CO and HC in the exhaust gas 8 can be oxidized to harmless CO ₂ and H ₂ O by the SOF partial oxidation catalyst 13.

  Furthermore, in the embodiment described above, the case where the nanoparticle processing filter 12 formed by supporting a noble metal catalyst on a metal nonwoven fabric has been described, but instead of the nanoparticle processing filter 12, as shown in FIG. Alternatively, a nanoparticle treatment filter 14 in which a zeolite catalyst is supported on a flow-through type honeycomb carrier may be employed.

  That is, in this case, the nanoparticles in the exhaust gas 8 are adsorbed and collected on the surface of the porous zeolite catalyst while the exhaust gas 8 flows separately for each flow path of the honeycomb carrier. Immediately thereafter, the oxidation reaction is promoted by the catalytic action, and the combustion is immediately removed. In addition, a noble metal catalyst such as platinum can be appropriately added to the zeolite catalyst.

  Further, in place of the nanoparticle processing filter 12 of FIG. 1, it is also possible to employ a nanoparticle processing filter 17 in which a zeolite pellet 16 is filled between a pair of ventilation plates 15 and 15 as shown in FIG. It is.

  That is, in this case, while the exhaust gas 8 flows while being bent so as to sew the gaps between the zeolite pellets 16, the nanoparticles in the exhaust gas 8 are on the surface of the porous zeolite pellets 16. Immediately thereafter, the oxidation reaction is promoted by the catalytic action and the combustion is immediately removed.

  Here, the zeolite pellets 16 may be formed by molding the zeolite itself into pellets, or may be those in which zeolite is supported on a pellet-like carrier, and further, a noble metal catalyst such as platinum is appropriately added. May be.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment. The SOF component oxidation catalyst does not necessarily have to be disposed in front of the particulate filter. Of course, various changes can be made without departing from the scope of the invention.

It is the schematic which shows an example of the form which implements this invention. It is a perspective view which expands and shows the nanoparticle processing filter of FIG. It is a graph which shows the relationship between the particle size of a particulate and the number of particles which remain in exhaust gas. It is a perspective view which shows another example of a form of this invention. It is a perspective view which shows another example of a form of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 8 Exhaust gas 9 Exhaust pipe 10 Particulate filter 12 Nanoparticle processing filter 13 SOF oxidation catalyst 14 Nanoparticle processing filter 15 Ventilation plate 16 Zeolite pellet 17 Nanoparticle processing filter

Claims (4)

  An exhaust purification apparatus equipped with a catalyst regeneration type particulate filter in the middle of an exhaust pipe, and a nanoparticle treatment filter comprising a metal nonwoven fabric or a wire mesh filter supporting a noble metal catalyst is provided downstream of the particulate filter. An exhaust purification device characterized by that.   An exhaust gas purification apparatus equipped with a catalyst regeneration type particulate filter in the middle of an exhaust pipe, and a nanoparticle processing filter comprising a zeolite catalyst supported on a flow-through type honeycomb carrier is provided downstream of the particulate filter. An exhaust purification device characterized by that.   An exhaust gas purification apparatus equipped with a catalyst regeneration type particulate filter in the middle of an exhaust pipe, and a nanoparticle treatment filter formed by filling zeolite pellets between a pair of ventilation plates at a subsequent stage of the particulate filter. An exhaust emission control device characterized by being provided.   An SOF component oxidation catalyst comprising an oxidation catalyst having an oxidizing power capable of oxidizing and purifying an SOF component in exhaust gas on a flow-through type honeycomb carrier is provided in a preceding stage of the particulate filter. The exhaust emission control device according to claim 1, 2 or 3.

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