JP4217407B2 - Exhaust purification equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device.
[0002]
[Prior art]
PM (Particulate Matter, particulate matter) discharged from diesel engines is mainly composed of soot made of carbon and soluble organic components composed of high-boiling hydrocarbon components, and a trace amount of mist-like sulfate compound as a minor component. Including. A PM filter is used as a measure for reducing this type of PM. The PM filter is a ceramic filter equipped in an exhaust purification device mounted in the middle of an exhaust pipe of a diesel engine or the like. In FIG. 3, the detailed structure is shown.
[0003]
FIG. 3A shows a cross section of the PM filter 12. The PM filter 12 is composed of a large number of passages 32, and the passages 32 form a lattice in the cross section.
[0004]
FIG. 3B shows a longitudinal section of the PM filter. The partition walls 34 separating the passages 32 are formed in a honeycomb shape, and there are innumerable minute holes through which exhaust gas can pass but PM cannot pass. Since each passage 32 is alternately closed at only one of the inlet and the outlet, the gas entering from the inlet 36 always passes through the partition wall 34 and exits from the outlet 38 once. When the exhaust gas passes through the partition wall 34, PM in the exhaust gas is trapped in the partition hole and deposited there.
[0005]
[Problems to be solved by the invention]
At the normal diesel engine operating temperature, the self-combustion temperature of the accumulated PM is not reached. Therefore, such a PM filter has a problem that the filter is clogged by soot. In order to prevent this filter clogging, a soot combustion regeneration system has been devised by active heating with an electric heater or a combustion burner. However, in the soot burning regeneration method by heating, an electric system and a fuel system have to be laid, which causes a problem that the system becomes complicated and the cost increases.
[0006]
Thus, a soot oxidation continuous regeneration system using a catalytic oxidation reaction, that is, a system for promoting the oxidation reaction of carbon in soot using a catalyst has been devised. However, the oxidation reaction of carbon is not complete, harmful carbon monoxide is generated due to incomplete oxidation, and the filter is clogged relatively early.
[0007]
The present invention solves the above-described problem. In the PM filter, a catalyst for promoting the oxidation reaction of CO is supported on both sides of the catalyst for promoting the oxidation reaction of carbon, so that the soot oxidation continuous by the catalytic oxidation reaction is supported. An object of the present invention is to provide an apparatus capable of suppressing generation of harmful carbon monoxide even in the regeneration method. Also, by constructing the PM filter symmetrically, even if it is clogged with the flow of exhaust gas from one direction, the exhaust gas purification device is equipped with the PM filter in the reverse direction and flowing the exhaust gas from the reverse direction. The purpose is to extend the usable period.
[0008]
[Means for Solving the Invention]
In order to achieve the above object, an exhaust purification apparatus of the present invention is an exhaust purification apparatus equipped with a PM filter in the middle of an exhaust pipe, and a catalyst that promotes an oxidation reaction of carbon in exhaust gas inside the PM filter. And a compartment carrying a catalyst for promoting an oxidation reaction of CO in the exhaust gas is provided on both sides of the compartment. Therefore, in the present invention, even in the soot oxidation continuous regeneration system based on the catalytic oxidation reaction, after passing through the oxidation reaction of carbon in the exhaust gas, it passes through a filter carrying a catalyst that promotes the oxidation reaction of CO. Carbon oxide generation is suppressed. Moreover, even if clogging occurs due to the inflow of exhaust gas from one direction, the usable period can be extended by performing exhaust gas inflow from the other direction.
[0009]
In addition, the central part of the PM filter is provided with a section that supports a catalyst that promotes the oxidation reaction of carbon in the exhaust gas, and the oxidation reaction of CO in the exhaust gas is performed symmetrically on both sides of the section. By providing the section for supporting the catalyst to be promoted, even if clogging occurs due to the inflow of exhaust gas from one direction, the exhaust gas inflow from the other direction can be efficiently performed.
[0010]
The catalyst that promotes the oxidation reaction of CO in the exhaust gas is a single catalyst selected from the group consisting of platinum, palladium, alumina, chromium, and manganese, or a combination of a plurality of catalysts selected from the above group. As a result, the oxidation reaction of CO can be promoted efficiently.
[0011]
Further, the catalyst that promotes the oxidation reaction of carbon in the exhaust gas is a single catalyst selected from the group consisting of platinum, palladium, alumina, serina, lanthanum, and barium, or a plurality of catalysts selected from the above group. By being a combination, it becomes possible to efficiently promote the oxidation reaction of carbon.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0013]
FIG. 1 is a schematic diagram of an exhaust purification device in which a PM filter 12 is mounted in the middle of an exhaust pipe 10. The PM filter 12 is held by a case 14 and attached with front and rear cases 16 and bolts 18. Thus, while having a structure that is robust but easily dismantled, the catalyst case is periodically removed for easy ash removal of fuel and oil and can be easily washed with water or compressed air. Also, when the exhaust gas is caused to flow backward when the filter is clogged, it is only necessary to attach the PM filter 12 in the reverse direction inside the case 14. Further, by providing the front and rear case 16, a silencer for silencer may be incorporated therein and used as a catalyst muffler.
[0014]
In FIG. 2, the catalyst loading mode in the PM filter 12 will be described. In the PM filter 12, the first catalyst having a function of promoting both the NO ₂ generation reaction and the CO oxidation reaction is supported on the portions A 20 and C 21 that are about one fifth from both ends. As the first catalyst, it is desirable to use a catalyst such as platinum, palladium, alumina, chromium, manganese or the like alone or in combination.
[0015]
The second catalyst for promoting the carbon oxidation reaction is supported on the central part B22 of about three-fifths. As the second catalyst, it is desirable to use a catalyst such as platinum, palladium, alumina, ceria, lanthanum, and barium alone or in combination.
[0016]
Since the first catalyst is supported symmetrically on both sides of the second catalyst, it is not necessary to worry about the front-rear direction of the PM filter 12 when mounting the PM filter 12 after cleaning. There is no need to indicate the direction or mounting direction.
[0017]
Exhaust gas sucked from the suction port comprises a soot made of carbon, the NO _X. Among them, when nitric oxide NO passes through the portion A20 on the inlet side, it is oxidized by the supported catalyst according to the formula 1 to generate nitrogen dioxide NO2.
<Chemical Formula 1> NO + 1 / 2O ₂ → NO ₂
[0018]
Next, when the exhaust gas that has passed through the portion A20 passes through the portion B22, the carbon in the soot is oxidized according to Equation 2 or Equation 3.
<Chemical Formula 2> NO ₂ + C → CO ₂ + NO
<Chemical Formula 3> C + O ₂ → CO ₂ + CO
[0019]
Further, when passing through the first filter again at the rear end portion C21, the supported catalyst oxidizes nitrogen monoxide and carbon monoxide according to the formulas 1 and 4 to generate nitrogen dioxide and carbon dioxide, respectively.
<Chemical Formula 4> CO + 1 / 2O ₂ → CO ₂
[0020]
As described above, when carbon in the soot is oxidized in the portion B22, even if carbon monoxide is generated due to incomplete oxidation, the carbon monoxide is brought into contact with the first catalyst again in the rear end portion C21. Carbon monoxide in the exhaust gas that is oxidized and exhausted is reduced.
[0021]
When this PM filter 12 is used for a certain period, it becomes unusable due to clogging, but the soot in the exhaust gas is decomposed as it passes through the PM filter 12, so the front half is more clogged than the latter half. In the PM filter 12 according to this embodiment, since the catalyst is supported symmetrically in the front-rear direction, the PM filter 12 can be mounted with the front-rear direction reversed, and by doing so, it is relatively clogged. You can bring the missing part to the first half. In this way, even the PM filter 12 that has become unusable from one direction can be used from the reverse direction, and the life of the PM filter 12 can be extended by mounting in the reverse direction.
[0022]
In this embodiment, the catalyst that promotes the oxidation reaction of CO is supported symmetrically on both sides of the catalyst that promotes the oxidation reaction of carbon. However, the catalyst is not necessarily symmetrical.
[0023]
In this embodiment, the catalyst that directly promotes the oxidation reaction of CO is supported on both sides of the catalyst that promotes the oxidation reaction of carbon. However, another catalyst may be supported therebetween. Further, another catalyst may be supported before and after the catalyst that promotes the oxidation reaction of CO.
[0024]
【The invention's effect】
As is apparent from the above description, in the exhaust gas purification apparatus equipped with the PM filter in the middle of the exhaust pipe according to the present invention, the compartment carrying the catalyst for promoting the oxidation reaction of carbon in the exhaust gas inside the PM filter. And a section for supporting a catalyst that promotes the oxidation reaction of CO is provided on both sides thereof, thereby providing an apparatus in which harmful carbon monoxide generation is suppressed in the continuous oxidation regeneration system using the catalytic oxidation reaction.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an exhaust emission control device according to an embodiment of the present invention.
FIG. 2 is a configuration diagram of a PM filter according to an embodiment of the present invention.
FIG. 3A is a cross-sectional view of a conventional PM filter.
(B) is a longitudinal cross-sectional view of a conventional PM filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Exhaust pipe 12 PM filter 20 Compartment which carries the catalyst which accelerates | stimulates CO oxidation reaction 21 Compartment which carries the catalyst which promotes CO oxidation reaction 22 Compartment which carries the catalyst which promotes carbon oxidation reaction

Claims (2)

An exhaust purification device equipped with a PM filter in the middle of the exhaust pipe,
The PM filter includes a first compartment supporting a single catalyst selected from the group consisting of ceria, lanthanum, and barium, or a combination of a plurality of catalysts selected from the group ,
Provided on both sides of the compartment is a second compartment carrying a single catalyst selected from the group consisting of platinum, palladium, alumina, chromium, and manganese or a combination of a plurality of catalysts selected from the group. A featured exhaust purification device. 2. The exhaust emission control device according to claim 1, further comprising a second compartment on both sides of the first compartment so as to be bilaterally symmetric.

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