JP2001164924A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust purifying device to prevent the local increase of temperature at a surface layer part during regeneration and have high durability. SOLUTION: In an exhaust emission control device situated in the middle of an exhaust pipe 3 and removing particulate in exhaust gas 2, a number of vent holes are drilled in the peripheral surface of a metallic cylinder having one end part being opened and ceramic non-woven cloth is wound around the outer peripheral surface of the metallic cylinder to form a filter layer. The proper number of so formed filter bodies 8 is contained in a filter case 7 in the middle of the exhaust pipe 3. Exhaust gas 2 introduced from a spot situated upper stream from the filter case 7 is all introduced in the metallic cylinder of the filter body 8 and only the exhaust gas 2 passing through the vent holes of the metallic cylinder and the filter layer is discharged to a spot situated downstream from the filter case 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device applied to an internal combustion engine such as a diesel engine.

[0002]

2. Description of the Related Art Particulate matter (particulate matter) emitted from a diesel engine is:
Soot composed of carbonaceous material and SO composed of high-boiling hydrocarbon component
F (Soluble Organic Fraction: Soluble Organic Component) as a main component, and also contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, FIG. As shown in FIG. 1, an exhaust pipe 3 through which exhaust gas 2 from a diesel engine 1 flows
It is considered that a particulate filter 4 is provided in the middle of the process.

As shown in FIG. 7, the particulate filter 4 has a porous honeycomb structure made of ceramic, and the openings of the flow paths 5 partitioned in a lattice are alternately plugged. The outlet of the unsealed flow path 5 is plugged, and only the exhaust gas 2 that has passed through the porous thin wall 6 defining each flow path 5 is discharged to the downstream side. It is like that.

Since the particulates in the exhaust gas 2 are collected and deposited on the inner surface of the porous thin wall 6, the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. Although it is necessary to regenerate the particulate filter 4 in the normal operation state of the diesel engine 1, since there is little opportunity to obtain a high exhaust gas temperature such that the particulate self-combustes, in general, electric It has been considered to perform active heating by attaching a heater or the like.

[0005] Incidentally, the particulate filter 4 proposed in the prior art has a porous honeycomb structure in which carbon particles are mixed with cordierite clay and burned in air to burn off the carbon particles. Manufactured products are well known.

[0006]

However, in the conventional particulate filter 4, the particulates are collected on the inner surface of the porous thin wall 6 defining each flow path 5, and the exhaust gas 2 is filtered. In addition to the surface filtration as described above, particulates are aggregated in the surface layer by such surface filtration, and the aggregated particulates burn in the surface layer during regeneration of the particulate filter 4, causing local high temperature, As a result, there is a problem that erosion and cracks are easily generated and the durability of the particulate filter 4 is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a highly durable exhaust gas purifying apparatus capable of avoiding a local high temperature in a surface layer during regeneration.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an exhaust gas purifying apparatus provided in the middle of an exhaust pipe for removing particulates in exhaust gas, wherein the peripheral surface of a metal cylinder having only one end opened. A large number of ventilation holes are provided in the filter case, and a ceramic non-woven fabric is wound around the outer periphery of the metal tube, and a suitable number of filter bodies each serving as a filter layer are accommodated in the filter case in the middle of the exhaust pipe. It is configured such that all the introduced exhaust gas is guided into the metal cylinder of the filter body, and only the exhaust gas that has passed through the ventilation hole and the filter layer of the metal cylinder can be discharged to the downstream side of the filter case. Is what you do.

With this configuration, the exhaust gas introduced from the upstream side of the filter case is guided into the metal cylinder of the filter body, passes through the ventilation holes of the metal cylinder and the filter layer, and the exhaust gas flows into the filter body. When exiting to the outside, particulates in the exhaust gas are collected by the ceramic nonwoven fabric forming the filter layer, and the particulates enter not only the surface portion but also the deep portion of the ceramic nonwoven fabric and are collected. Therefore, according to such deep-layer filtration, the particulates are collected in a dispersed state and do not agglomerate in the surface layer, and even if the particulates are burned during regeneration of the filter body, local high temperature is avoided. Will be done.

Further, in the present invention, it is preferable that the metal cylinder is configured as an electric heater, so that when the exhaust gas does not flow strongly, such as when the engine is idling or when the engine is stopped. By selectively energizing the metal cylinder, the metal cylinder generates heat as an electric heater, so that particulates can be appropriately burned and removed before the exhaust resistance increases due to clogging, and the filter layer can be regenerated.

In an operation state in which the exhaust gas temperature is sufficiently high, the particulates self-burn and the filter body can be regenerated even if the metal cylinder is not heated as an electric heater.

Further, in the present invention, it is preferable that an oxidation catalyst is accommodated in the filter case on the upstream side of the filter main body. In this case, NO _{2 having} strong oxidizing power is contained in the exhaust gas by the oxidation catalyst. And active oxygen are generated, and the strong oxidizing NO ₂ and active oxygen efficiently contact the particulates collected in a state of being dispersed in the deep portion of the ceramic nonwoven fabric forming the filter layer to assist combustion. Therefore, the particulates are satisfactorily burned at a relatively low ignition temperature.

The ceramic non-woven fabric forming the filter layer may support the particles of the oxidation catalyst. In such a case, the efficiency of contact between the exhaust gas and the particles of the oxidation catalyst is high, so that NO ₂ and the activity of the catalyst are increased. In addition to the efficient generation of oxygen, NO ₂ and active oxygen generated in the filter layer immediately react with the particulates dispersed in the filter layer. It will be further supported. In particular, when combined with a configuration in which an oxidation catalyst is arranged on the upstream side of the filter main body, HC and CO in the exhaust gas are increased by the oxidation catalyst on the upstream side.
Is also oxidized, and thus HC,
If CO is oxidized first on the upstream side, the amount of HC and CO in the exhaust gas reaching the filter body on the downstream side is reduced, and the surface of the oxidation catalyst particles in the filter layer is protected against NO and the like. The selectivity of the oxidation reaction is enhanced, and the generation of NO ₂ and active oxygen in the filter layer is further promoted.

[0014]

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

FIGS. 1 to 5 show an embodiment of the present invention. As shown in FIG. 1, in an exhaust gas purifying apparatus according to the embodiment, as shown in FIG.
A filter case 7 is interposed in the middle of the exhaust pipe 3 through which the air flows, and a plurality of (six in the illustrated example) filter bodies 8 as described in detail below are collected inside the filter case 7. Housed.

As shown in FIG. 2, this filter body 8
A filter layer 12 is formed by forming a large number of ventilation holes 11 on the peripheral surface of a metal cylinder 10 opened only at one end as an inlet 9 and wrapping a ceramic non-woven fabric around the outer periphery of the metal cylinder 10. I have.

The metal tube 10 is made of, for example, Kanthal,
It is made of an electrothermal metal material such as nichrome. A flange 13 is formed around the entrance 9 and an electrode 14 protrudes from an end opposite to the entrance 9.

The ceramic non-woven fabric wound around the outer periphery of the metal tube 10 is a non-woven fabric made of long fibers of about 0.1 to 10 μm made of alumina, silicon carbide, silicon nitride or the like.

As shown in FIG. 3, each filter body 8 is accommodated in parallel at the rear side of the filter case 7 with the inlet 9 of the metal tube 10 facing upstream in the flow direction of the exhaust gas 2. The periphery of the inlet 9 of the metal tube 10 is sealed by a partition plate 15, and all the exhaust gas 2 introduced from the upstream side of the filter case 7 is removed from each filter body 8.
Into the metal cylinder 10 and the ventilation hole 11 of the metal cylinder 10
In addition, only the exhaust gas 2 that has passed through the filter layer 12 can be collected and discharged to the downstream side of the filter case 7.

Here, the flange 13 of each metal cylinder 10 is
The partition plate 15 is fastened by bolts or the like, and the electrode 14 of each metal tube 10 is insulated 18 (FIG.
), And the substantial housing portion of the filter body 8 sandwiched between the partition plate 15 and the holding plate 17 can be appropriately replaced as a cartridge. ing.

As shown in FIG. 1, the flange 13 of each metal tube 10 is grounded through a partition plate 15, and the electrode 14 of each metal tube 10
Is connected to a power supply 20 (battery) via a current controller 19, and each metal tube 10 is appropriately energized by a command signal 22 from a control device 21 so that it can function as an electric heater. is there.

Further, in the present embodiment, an upstream side of each filter body 8 in the filter case 7 is formed by adding an appropriate amount of a rare earth element such as cerium to alumina carrying platinum. As shown in FIG. 5, the oxidation catalyst 23 is formed as a flow-through type honeycomb structure or the like.

Further, as shown in FIG.
Oxidation catalyst particles 24 of substantially the same material as 3 are carried on the ceramic nonwoven fabric forming the filter layer 12 of each filter body 8.

When the particles 24 of the oxidation catalyst are carried on the ceramic non-woven fabric, the filter bodies 8 are immersed in a powder of alumina and platinum dissolved in water, dried, fired and oxidized. The catalyst particles 24 may be fixed by sintering.

In the drawing, reference numeral 25 denotes a muffler provided on the exhaust pipe 3 on the downstream side of the filter case 7.

In this way, the exhaust gas 2 introduced from the upstream side of the filter case 7 is distributed into the metal tubes 10 of each filter body 8, and particularly, as shown in FIG. When the exhaust gas 2 passes through the ventilation holes 11 and the filter layer 12 of the filter 10 and escapes to the outside of each filter body 8, the particulates in the exhaust gas 2 are collected by the ceramic nonwoven fabric forming the filter layer 12.

At this time, the particulates enter not only the surface layer portion of the ceramic nonwoven fabric but also the deep layer portion and are collected. Therefore, according to such deep layer filtration, the particulates are collected in a dispersed state. Aggregation at the surface layer is eliminated, and local high temperature is avoided even if particulates burn during regeneration of each filter body 8.

The current controller 19 is controlled by a command signal 22 from the control unit 21 when there is no strong flow of the exhaust gas 2 such as when the engine is idling or when the engine is stopped. When the metal tube 10 is heated as an electric heater by applying a current to the metal tube 10, the particulates are burned and removed by the heat generated by the metal tube 10, and the filter layer 12 can be regenerated.

In the operating state where the exhaust gas temperature is sufficiently high, the particulates self-burn and the filter body 8 does not generate heat even when the metal tube 10 is used as an electric heater.
Will be reproduced.

Further, in the present embodiment, in particular, since the oxidation catalyst 23 is accommodated in the filter case 7 on the upstream side of each filter main body 8, the oxidation catalyst 23 causes the NO 2 having a strong oxidizing power in the exhaust gas 2. ₂ and active oxygen are produced,
The above-mentioned NO ₂ and active oxygen efficiently contact the particulates collected in a state of being dispersed in the deep portion of the ceramic nonwoven fabric to support combustion, so that the particulates can be favorably formed at a relatively low ignition temperature. It will be burned.

Since the catalyst non-woven fabric forming the filter layer 12 also carries the oxidation catalyst particles 24, NO ₂ and active oxygen are reduced due to the high contact efficiency between the exhaust gas 2 and the oxidation catalyst particles 24. Is efficiently generated, and NO ₂ and active oxygen generated in the filter layer 12 immediately react with the particulates dispersed in the filter layer 12, and the combustion of the particulates becomes more difficult. It will be further supported. In particular, when combined with a configuration in which the oxidation catalyst 23 is arranged on the upstream side of the filter body 8 as in the present embodiment, the oxidation catalyst 2 on the upstream side is used.
Since HC and CO in the exhaust gas 2 are also oxidized by 3,
HC and C in the exhaust gas 2 reaching the filter body 8 on the downstream side
The amount of O decreases, the selectivity of the oxidation reaction to NO or the like at the surface of the oxidation catalyst particles 24 in the filter layer 12 increases, and the generation of NO ₂ and active oxygen in the filter layer 12 is further promoted. .

Therefore, according to the above-described embodiment, even if the particulates burn during regeneration of each filter main body 8, it is possible to avoid a local increase in temperature at the surface layer portion of the filter main body 8. Thus, it is possible to prevent the occurrence of erosion, cracks, and the like in the exhaust gas purifier 8 and to realize a highly durable exhaust gas purification apparatus.

Further, since the metal cylinder 10 can be energized to generate heat as an electric heater, the particulates can be appropriately burned and removed even in an operating state in which the exhaust temperature is not high enough to self-burn the particulates. Thus, the filter layer 12 can be regenerated before the exhaust resistance increases due to clogging.

Further, since the oxidizing catalyst 23 can generate strong oxidizing NO ₂ and active oxygen in the exhaust gas 2 before the filter main body 8, the oxidizing catalyst 23 is dispersed in the deep portion of the ceramic nonwoven fabric forming the filter layer 12. It is possible to efficiently combust the particulates collected in a state of contact with highly oxidizing NO ₂ and active oxygen to support combustion, and to burn the particulates well at a relatively low ignition temperature. Thus, the regeneration efficiency of the filter body 8 can be greatly improved.

Further, by supporting the oxidation catalyst particles 24 on the ceramic non-woven fabric forming the filter layer 12, the contact efficiency between the exhaust gas 2 and the oxidation catalyst particles 24 is increased, and the NO.
₂ and active oxygen can be efficiently generated in the filter layer 12, and the generated NO ₂ and active oxygen can be immediately reacted with the particulates, thereby further supporting the burning of the particulates. Therefore, the regeneration efficiency of the filter body 8 can be further improved.

The exhaust gas purifying apparatus of the present invention is not limited to the above-described embodiment. For example, only one filter body may be accommodated in a filter case. It may be configured so that it can be reproduced alternately by arranging itself in parallel,
It goes without saying that various changes can be made without departing from the spirit of the present invention.

[0037]

According to the exhaust gas purifying apparatus of the present invention described above, the following various excellent effects can be obtained.

(I) According to the first aspect of the present invention, even if the particulates burn during regeneration of the filter main body, it is possible to avoid local high temperature at the surface layer portion of the filter main body. Therefore, it is possible to prevent the occurrence of erosion, cracks, and the like in the filter main body, and to realize a highly durable exhaust gas purification apparatus.

(II) According to the second aspect of the present invention, since the metal cylinder can be energized to generate heat as an electric heater, it is not possible to obtain an exhaust temperature high enough to cause the particulates to self-burn. Even in the operating state, the particulates can be appropriately removed by burning, and the filter layer can be regenerated before the exhaust resistance increases due to clogging.

(III) According to the third aspect of the present invention, a strong oxidizing NO ₂ or active oxygen can be generated in the exhaust gas by the oxidation catalyst at a stage preceding the filter body. Relatively low ignition temperature, with efficient contact of NO ₂ or active oxygen with strong oxidizing power to particulates collected in a state of being dispersed in the deep part of the ceramic non-woven fabric forming the layer. Thus, the particulates can be satisfactorily burned, and the regeneration efficiency of the filter body can be greatly improved.

(IV) According to the invention as set forth in claim 4 of the present invention, since the particles of the oxidation catalyst are supported on the ceramic nonwoven fabric forming the filter layer, the contact efficiency between the exhaust gas and the particles of the oxidation catalyst can be improved. NO ₂ and active oxygen can be efficiently generated in the filter layer by increasing the amount of NO ₂ and active oxygen, and the generated NO ₂ and active oxygen can be immediately reacted with the particulates. It is possible to further assist and further improve the regeneration efficiency of the filter body.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment for implementing the present invention.

FIG. 2 is a perspective view showing details of a filter main body of FIG. 1;

FIG. 3 is a perspective view showing a housed state of each filter main body of FIG. 1;

FIG. 4 is a sectional view of the filter body of FIG. 3;

FIG. 5 is a perspective view showing details of the oxidation catalyst of FIG. 1;

FIG. 6 is a schematic diagram showing a conventional example.

FIG. 7 is a sectional view showing details of the particulate filter of FIG. 6;

[Explanation of symbols]

 2 Exhaust gas 3 Exhaust pipe 7 Filter case 8 Filter body 10 Metal cylinder 11 Vent hole 12 Filter layer 23 Oxidation catalyst 24 Oxidation catalyst particles

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 53/86 ZAB F01N 3/24 E 53/94 B01D 53/36 ZAB F01N 3/24 103B F-term (reference 3G090 AA03 AA04 BA01 BA04 CA04 CB15 DB03 DB04 DB05 EA02 3G091 AA18 AA28 AB02 AB13 BA08 BA10 BA15 BA19 CA03 FB16 FC02 GA05 GA06 GA21 GB01X GB04W GB06W GB10X GB13X GB15X GB17X HA08 HA15 4D048 AB01A18A18

Claims (4)

[Claims] 1. An exhaust gas purifying device provided in the middle of an exhaust pipe for removing particulates in exhaust gas, wherein a number of ventilation holes are formed in a peripheral surface of a metal cylinder having only one end opened. A suitable number of filter bodies each having a filter layer formed by winding a ceramic non-woven fabric around the outer periphery of the metal tube are accommodated in a filter case in the middle of the exhaust pipe, and all exhaust gas introduced from the upstream side of the filter case is filtered. An exhaust gas purification apparatus characterized in that only exhaust gas guided into a metal cylinder of a main body and passing through a ventilation hole and a filter layer of the metal cylinder can be discharged to a downstream side of the filter case. 2. The exhaust gas purifying apparatus according to claim 1, wherein the metal cylinder is configured as an electric heater. 3. The exhaust gas purification apparatus according to claim 1, wherein an oxidation catalyst is accommodated in the filter case upstream of the filter body. 4. The exhaust gas purification apparatus according to claim 1, wherein particles of an oxidation catalyst are carried on a ceramic nonwoven fabric forming a filter layer.