JPH07127434A - Diesel particulate filter - Google Patents

Abstract

PURPOSE:To provide a diesel particulate filter regenerated in a short time while improving particulate collecting efficiency and realizing the uniform heating of platelike filters. CONSTITUTION:Cases 1 disposed at an exhaust passage 7 are formed of electrical insulating close SiC ceramics. Plate like filters 3 disposed between the cases 1 are formed of conductive porous SiC ceramics with Fe compound scattered in SiC base phase with open pores formed of large diameter pares 5 and small diameter pores 4, and electrode parts 2 are provided at both end parts of the plate like filters 3. Particulates contained in exhaust gas are collected into the large diameter pores 5, and each plate like filter 3 itself is made function as a heater. The collected particulates are thereby heated and incinerated, and the plate like filter 3 is regenerated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel particulate filter for collecting particulates contained in exhaust gas discharged from a diesel engine.

[0002]

2. Description of the Related Art Conventionally, as a material for an exhaust gas treatment filter which collects particulates such as carbon, soot, HC, etc. from exhaust gas of a diesel engine, a material for trapping when passing through a porous wall has been used. Diesel particulates such as a wall type filter for exhaust gas treatment aiming at a collection effect, that is, a filter for exhaust gas treatment that uses a three-dimensional meshed honeycomb-shaped or porous ceramics body A filter is disclosed.

Further, Japanese Utility Model Laid-Open No. 63-105714 discloses an exhaust particulate treatment device. The exhaust particulate treatment apparatus has a porous cylindrical SiC in which a plurality of ends are closed by an insulating porous body in a case having an inlet and an outlet.
A heating element is inserted, and a heat-generating filter body having an insulating porous body positioned in the center thereof is disposed so that the SiC heating element can be energized.

Further, Japanese Utility Model Laid-Open No. 31328/1993 discloses that
An exhaust gas aftertreatment device is disclosed. The exhaust gas post-treatment device, the trap filter is composed of a plurality of divided bodies arranged in parallel in the exhaust gas flow direction, the filter density of the divided body arranged on the downstream side in the exhaust gas flow direction,
The filter density is set to be higher than the filter density of the divided body arranged on the upstream side in the exhaust gas flow direction.

[0005]

The effect of the diesel particulate filter has been confirmed especially as a device for removing black smoke in the exhaust gas of a diesel engine. However, as a conventional diesel particulate filter material, porous cordierite is used, and its regeneration is carried out by collecting black smoke with a burner or electric heat and then igniting its collecting end. Non-uniformity occurs due to thermal stress, cracks easily occur, and a problem occurs in the durability of the filter. In order to eliminate the drawbacks of the filter regeneration method, a method of intermittently flowing a high-pressure gas in a direction opposite to the exhaust gas flow direction, cleaning it, and dropping the collected black smoke has also been studied.

In order to regenerate a diesel particulate filter that collects particulate matter in exhaust gas, there are roughly two methods.
One method is to burn black smoke, carbon, soot,
Particulate matter such as HC, that is, particulates, is burned and incinerated. Another method is to heat an electric heater to ignite the deposited particulate matter, and the ignition device ignites the deposited particulate matter,
It propagates combustion and regenerates it. Therefore, the exhaust gas treatment filter sometimes becomes too hot, and thermal stress may cause the filter to melt or break. In addition, the propagation of combustion becomes non-uniform, which causes clogging of the filter, the pressure loss gradually increases, the exhaust pressure of the engine increases, and the performance may deteriorate.

[0007] Usually, the particulates or smoke such as carbon and HC contained in the exhaust gas discharged from the diesel engine are said to have a diameter of about 200Å, but they are gradually aggregated to 10 µm to 20 µm.
Grows into soot with a diameter of. These soots are usually 60
If oxygen is present at a temperature of 0 ° C to 700 ° C, it burns into carbon dioxide.

As a filter for removing particulates in exhaust gas, a diesel particulate filter such as that disclosed in the above publication, in which the filter itself generates heat, the filter oxidizes during regeneration to change resistance or cause corrosion. Or Further, when the filter has a honeycomb shape or a tubular shape, it is difficult to uniformly heat the entire filter, and the volume of the filter becomes large, and cracks or breaks due to thermal stress occur.

Therefore, an object of the present invention is to solve the above-mentioned problems, and is used by being incorporated in an exhaust system to purify exhaust gas discharged from a diesel engine, and exhausted from the diesel engine. It collects particulate matter such as carbon, soot, and HC contained in the gas, that is, particulates, and has an opening made up of large pores and small pores in a case made of electrically insulating dense SiC ceramics. Conductive porous Si having pores
A plate-shaped filter made of C ceramics is arranged, the plate-shaped filter functions as a heater, the plate-shaped filter is uniformly heated, and the collected particulates are burned uniformly to shorten the plate-shaped filter. An object of the present invention is to provide a diesel particulate filter that is regenerated in time.

[0010]

In order to achieve the above object, the present invention is configured as follows. That is,
The present invention relates to a diesel particulate filter which is disposed in an exhaust system and collects particulates contained in exhaust gas to be incinerated and regenerated. A case made of electrically insulating dense SiC ceramics, and the case is disposed in the case. Plate filter made of conductive porous SiC ceramics in which a Fe compound is dispersed in a matrix of SiC having open pores composed of large pores and small pores, and both end portions of the plate filter The present invention relates to a diesel particulate filter, characterized in that it has electrode portions respectively provided on the.

Further, in this diesel particulate filter, the large pores in the open pores of the plate filter are 10 μm or more in terms of spherical diameter,
The small pores are 1/3 or less of the large pores.

In this diesel particulate filter, the Pd oxidation catalyst is carried in the small pores.

Further, in this diesel particulate filter, the electrode portion is made of conductive dense SiC ceramics.

Further, in this diesel particulate filter, a plurality of the plate-shaped filters are arranged at intervals in the longitudinal direction of the case. In addition, the plate-like filter arranged on the downstream side of the case has P
An oxidation catalyst for t and Rh is supported.

Further, in this diesel particulate filter, the Fe compound is an oxide, a silicide, a carbide, a nitride of Fe or a mixture thereof.

[0016]

The diesel particulate filter according to the present invention is constructed as described above and has the following actions. That is, in this diesel particulate filter, a plate filter is arranged in a case made of electrically insulating dense SiC ceramics, and the plate filter has open pores composed of large pores and small pores. Moreover, since it is composed of conductive porous SiC ceramics in which Fe compound is scattered in the mother phase of SiC, and the electrode portions are provided at both ends of the plate-like filter, respectively, it is possible to obtain particulates with large pores. It can be collected and the plate-shaped filter is regenerated by heating with electricity. That is, when the plate filter itself is heated by uniformly energizing both ends of the plate filter that collects particulates such as carbon in the exhaust gas, smoke, etc., it becomes uniform with respect to the plate filter. Heating can be realized,
It is possible to incinerate the particulates to regenerate the plate filter, prevent the plate filter from melting, and prevent the plate filter from melting due to thermal stress, improving durability, The particulates are burned uniformly and burned in a short time, the plate filter is regenerated, and unburned particulates do not remain in the plate filter.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the diesel particulate filter according to the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram for explaining an embodiment of a diesel particulate filter according to the present invention, and FIG. 2 is A of FIG.
It is a sectional view of a part.

This diesel particulate filter can be used, for example, by incorporating it in an exhaust gas purifying device of a diesel engine, and is arranged in an exhaust system to collect particulates contained in exhaust gas and regenerate by incineration. is there. In this exhaust gas purifying apparatus, a plate filter 3 is provided in a case 1 arranged in an exhaust passage 7 of an exhaust system that exhausts exhaust gas from a diesel engine.
The plate-like filter 3 collects particulates such as carbon, soot, HC, and black smoke in the exhaust gas in the case 1, and heats and incinerates the collected particulates.
As the means for energizing the plate filter 3 to heat and burn the particulates collected by the plate filter 3 for incineration, a heating circuit leading to a power source is provided in the controller 10.

This diesel particulate filter is mainly made of a case 1, which is made of electrically insulating dense SiC ceramics, and is made of SiC which is arranged in the case 1 and has open pores composed of large pores 5 and small pores 4. Conductive porous Si in which Fe compound is scattered in the mother phase 6
The plate-shaped filter 3 is made of C ceramics, and the electrode parts 2 are provided at both ends of the plate-shaped filter 3, respectively. The case 1 may be formed as a hollow case, or may be arranged so as to face both ends of the plate filter 3. The large pores 5 and the small pores 4 in the open pores of the plate-shaped filter 3 are dispersedly present in the matrix phase 6, and the small pores 4 are formed on the wall surface and the periphery of the large pores 5. . Further, the large pores 5 have a diameter of 10 μm or more in terms of spherical diameter, and the small pores 4 have large pores 5.
1/3 or less of the size.

In this diesel particulate filter, the Fe compound is an oxide, a silicide, a carbide, a nitride of Fe or a mixture thereof. Further, by supporting an oxidation catalyst such as palladium Pd in the small pores 4, it is possible to suppress the generation of CO. The electrode part 2 is made of conductive dense SiC ceramics and is connected to a heating circuit provided with a power source in the controller 10. The electrode portion 2 for energizing the plate-shaped filter 3 has a conductive and dense SiC spacer 8 interposed between the plate-shaped filter 3 and the case 1 to form the case 1
It can be fixed so as to be sandwiched in the hole 9 formed in the. When the plate filter 3 is fixed to the case 1 in this way, the electrode portion 2 is sealed with the non-conductive dense SiC ceramics and the conductive dense SiC ceramics, and the electrode portion 2 is exposed to the exhaust gas. Therefore, the electrode portion 2 is prevented from being corroded by the influence of the exhaust gas. Then, the plate filter 3 is energized through the electrode portion 2 according to a command from the controller 10.

In this diesel particulate filter, a plurality of plate-shaped filters 3 (four in the figure) are arranged at intervals in the longitudinal direction of the hollow case 1, and each is supported by the electrically insulating hollow case 1. Thus, the temperature of each plate filter 3 can be individually controlled by the controller 10. Further, by carrying an oxidation catalyst such as platinum Pt or rhodium Rh on the plate-like filter 3 installed on the outlet side of the exhaust passage 7, it is possible to purify HC, NO, etc. contained in the exhaust gas. .

This diesel particulate filter can be manufactured as follows. In this method for producing a diesel particulate filter, first, a predetermined amount of iron oxide (Fe ₃ O ₄ ) is added to a mixed powder of silicon carbide SiC and carbon C, and the mixture is mixed with methanol and a binder by a ball mill for about 24 hours, and then, Granulation was performed by a spray dryer to produce granules. This granular material was used as a raw material, preliminarily molded in a mold, and then a rectangular parallelepiped molded body was obtained by CIP with a pressing pressure of about 2000 kgf / cm ² . After degreasing this molded body, the degreased molded body was immersed in molten Si in a vacuum of 20 Pa and heated and fired to 1600 ° C. to obtain a sintered body. Then, it was heated up to 1700 ° C. in a vacuum of 20 Pa to remove residual Si in the sintered body to produce a sintered body of SiC ceramics.

When a test piece was cut out from the obtained sintered body of SiC ceramics and the surface thereof was observed, as shown in FIG. 2, macro pores of φ80 μm to φ100 μm, that is, φ10 μm to the wall surface and the periphery of the large pores 5, φ20 μm
It was confirmed that the micropores, that is, the small pores 4, were formed, and the large pores 5 and the small pores 4 formed continuous open pores. The porosity of this sintered body of SiC ceramics was 70%. Furthermore, this Si
It was also confirmed that the sintered body of C ceramics was electrically conductive. About this sintered body of SiC ceramics, XR
As a result of D analysis, SiC changed in the order of α → α + β → α + β, and the Fe oxide changed in the order of Fe ₃ O ₄ → FeSi → FeSi ₂ while progressing from the starting material → sintering → vacuum treatment.

The sintered body of SiC ceramics produced by the above-described manufacturing method was cut out as a plate of 150 × 250 × 10 mm, which was used as a plate-shaped filter 3 and incorporated in the case 1 to prepare a diesel particulate filter. That is, the plate-shaped filter 3 has the large pores 5 and the small pores 4.
It is composed of a conductive porous SiC ceramics having open pores composed of and Fe compounds interspersed in the SiC mother phase.

Using the diesel particulate filter produced as described above, the exhaust gas was caused to flow and the collection efficiency (%) due to the accumulation of particulates and the pressure loss (KPa) were measured. As a comparative example, a honeycomb-type diesel particulate filter having the same bulk volume was manufactured, and its collection efficiency (%) was measured in the same manner as above.
And the pressure loss (KPa) were measured. The result is shown in FIG. In FIG. 3, the horizontal axis represents the collection time (minutes), and the vertical axis represents the collection efficiency (%) and the pressure loss (KPa). As can be seen from FIG. 3, the product of the present invention and the conventional product of the honeycomb type have almost the same collection efficiency, but the conventional product of the honeycomb type has a large pressure loss of 1.5 times that of the product of the present invention. Is appearing. In other words, it can be seen that when the pressure losses of both are made equal, the product of the present invention exhibits a collection efficiency of 1.5 times that of the conventional honeycomb type product.

Further, in this diesel particulate filter, when the particulates collected by electrically heating the individual particulate filters 3 under the control of electric power feedback are heated and incinerated, the particulate particulate filters 5 are
Could be played in minutes. As a result of the collection test of the diesel particulate filter, the pores of the plate-like filter 3 have large pores 5 of 50 μm to 150 μm in size.
Further, it has been found that the size of the small-diameter pores 4 is 10 μm to 50 μm and the porosity is 50% or more is appropriate and preferable.

FIG. 4 is a graph showing changes in the pore size (μm) of the large pores 5 with respect to the amount of Fe oxide added (wt%). Further, FIG. 5 shows the addition amount of Fe oxide (wt.
3 is a graph showing changes in porosity (%) with respect to (%).
As can be seen from FIGS. 4 and 5, 40 to 55 wt% of Fe oxide is used to manufacture the material forming the plate filter 3 under the above conditions, that is, the conductive porous SiC ceramics.
The desired porosity and large pores 5 can be added and fired.
Can be obtained, which is desirable.
The pore size of the small pores 4 can also be controlled by adjusting the particle size of the starting SiC powder.

[0028]

The diesel particulate filter according to the present invention is constructed as described above and has the following effects. That is, in this diesel particulate filter, a plate filter is arranged in a case made of electrically insulating dense SiC ceramics, and the plate filter has open pores composed of large pores and small pores. Moreover, since it is composed of the conductive porous SiC ceramics in which Fe compound is scattered in the SiC mother phase, it is possible to reliably and satisfactorily collect the particulates in the large pores, that is, the macropores. Since the plate filter itself can function as a heater, when electricity is applied to the plate filter through the electrode portions provided at both ends of the plate filter, combustion due to flame propagation does not occur,
The plate filter can be uniformly heated in the entire area and can be heated in a short time, the particulates are immediately burned and incinerated, and the plate filter is regenerated in a short time. Moreover, it is possible to prevent the plate-shaped filter from being melted and damaged due to thermal stress, and to improve durability.

Therefore, when incinerating the particulates collected by the plate-shaped filter, the particulates should burn uniformly and remain locally in the plate-shaped filter in a state where the particulates are not burned. In addition, abnormal combustion does not occur, local heating does not occur, and melting and damage of the plate filter does not occur. Moreover, in the regeneration of the plate filter, it is possible to uniformly energize the plate filter, reduce the thermal stress applied to the plate filter, prevent damage to the plate filter itself, and improve durability. You can

The large pores in the open pores of the plate-like filter are 10 μm or more in terms of spherical diameter, and the small pores are 1/3 or less of the large pores. It is preferable from the viewpoints of increasing the collection efficiency and reducing the pressure loss.

Further, by supporting the Pd oxidation catalyst in the small pores of the plate-like filter, the generation of CO can be suppressed and the combustion temperature can be lowered. Further, P is provided in the small-diameter pores of the plate-like filter arranged on the downstream side of the case, that is, on the exhaust gas outlet side.
By supporting an oxidation catalyst of t, Rh, HC,
It is also possible to purify NO.

Further, since the electrode portion is made of conductive dense SiC ceramics, the electric connection portion is improved, and the electric heating process of the plate filter can be smoothly performed. Further, by arranging a plurality of the plate-shaped filters in the longitudinal direction of the case in a spaced-apart state, it is possible to perform control to sequentially energize the plate-shaped filters individually,
The particulates collected in the plate filter can be individually heated and incinerated to prevent abnormal combustion, and the plate filter can be uniformly regenerated. Also, F
As the e compound, Fe oxide, silicide, carbide, nitride or a mixture thereof can be used.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of an exhaust gas treatment device incorporating a diesel particulate filter according to the present invention.

FIG. 2 is an enlarged sectional view of a portion A of the plate filter shown in FIG.

FIG. 3 is a graph showing the relationship between the collection efficiency and the pressure loss with respect to the collection time of the product of the present invention and the conventional honeycomb type product.

FIG. 4 is a graph showing the relationship between the amount of Fe oxide added and the pore size of large pores.

FIG. 5 is a graph showing the relationship between the added amount of Fe oxide and the porosity.

[Explanation of symbols]

 1 Case 2 Electrode Section 3 Plate Filter 4 Small Diameter Pore 5 Large Diameter Pore 6 Mother Phase 7 Exhaust Passage 8 Spacer 9 Hole 10 Controller

Claims (7)

[Claims] 1. A diesel particulate filter which is disposed in an exhaust system and collects particulates contained in exhaust gas to be incinerated and regenerated. In the diesel particulate filter, a case made of electrically insulating dense SiC ceramics and a space between the cases are provided. A plate-like filter made of a conductive porous SiC ceramics in which Fe compounds are dispersed in a matrix of SiC having open pores which are arranged and have large pores and small pores,
A diesel particulate filter, comprising: an electrode portion provided on each end of the plate filter; 2. The large pores in the open pores of the plate filter are 10 μm or more in terms of spherical diameter, and the small pores are 1/3 or less of the large pores. The diesel particulate filter according to claim 1. 3. The diesel particulate filter according to claim 2, wherein a Pd oxidation catalyst is carried in the small pores. 4. The diesel particulate filter according to claim 1, wherein the electrode portion is made of a conductive dense SiC ceramics. 5. The diesel particulate filter according to claim 1, wherein a plurality of the plate-shaped filters are arranged at intervals in a longitudinal direction of the case. 6. The diesel particulate filter according to claim 5, wherein the plate-shaped filter disposed on the downstream side of the case carries an oxidation catalyst of Pt and Rh. 7. The diesel particulate filter according to claim 1, wherein the Fe compound is an oxide, a silicide, a carbide, a nitride of Fe or a mixture thereof.