JPH0153083B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a filter device for removing combustible particulates contained in gas, particularly combustible particulates such as carbon contained in automobile exhaust gas. More specifically, the present invention relates to a filter device that efficiently burns and removes filtered combustible particulates while maintaining high filterability by applying electricity to the filter itself to generate heat.

[Prior art and its problems] Conventionally, it has been proposed to use a filter in the exhaust system or exhaust recirculation system in order to remove carbon particles contained in the exhaust gas of automobile engines, especially diesel engines, as a pollution control measure. However, when used for a long period of time, carbon builds up and causes clogging, resulting in pressure loss. To overcome this drawback, it is possible to heat the particulate trapping part of the filter by combining it with a nichrome wire heater or a heat-generating metal layer, by injecting fuel into the particulate trapping part and heating it with the combustion heat of the fuel, or by installing a high-voltage electrode. Methods have been used to prevent clogging by heating by spark discharge or by heating the filter by applying electricity to the carbon fiber to incinerate the carbon particles.

However, when using nichrome wire, the heat generating area is small, resulting in poor energy efficiency, and it is also time-consuming to attach it to the filter.If a heat generating metal layer is provided, it must be thin and small in area so as not to interfere with filtration. However, it is energy inefficient and requires a lot of effort to install.If the temperature cannot be raised properly due to exhaust gas, the engine must be stopped and the carbon particles that have accumulated in the filter must be burned off. Something unexpected happened. Additionally, fuel injection and high-pressure discharge methods require particularly complex equipment, consume large amounts of energy, and
Fire problems caused by the fuel and damage to the filter due to discharge occur, and those using carbon fibers have the disadvantage that the fibers themselves are destroyed by combustion.

On the other hand, ceramic honeycomb structure filters are known for similar applications.Compared to general filters, these filters have less pressure loss even when the mesh is finely woven, and are compact, so they can reduce the amount of carbon in automobile exhaust gas. Although the filter is suitable for removal, if it becomes clogged, the filter surface is spread over a wide area, so the filter must be removed from the area where it is used and the entire filter must be heated to burn off the carbon particles.

[Structure of the Invention] In view of the above-mentioned shortcomings in the prior art, the present inventors have devised a method to efficiently remove combustible particulates while the engine is running, without worsening pressure loss, and without requiring particularly complex equipment. As a result of intensive research, we discovered that combustible particles can be efficiently removed without making major changes to the current equipment by using a ceramic honeycomb structure filter itself as a current-carrying heating element. The present invention was completed.

The gist of the present invention is to form a wall structure that forms a plurality of passages extending from the inlet side to the outlet side, and the passages include a group of inlet passages whose outlet side is closed by an outlet closing wall and an inlet side which is closed by an inlet closing wall. a group of closed outlet passages, wherein any one inlet passage shares a wall with at least one outlet passage to form a filtration wall for trapping combustible particulates; An outer circumferential wall portion of the filter that is formed of ceramic and connects the end surfaces of the exhaust gas introduction end surface where the inlet is open and the exhaust gas discharge end surface where the outlet is open, in which the voltage application means for heating the wall structure is connected. A filter device for removing combustible particulates is provided.

Next, explanation will be given with reference to the drawings.

FIG. 1 is a front view of a cylindrical filter device that is an embodiment of the present invention, FIG. 2 is a cross-sectional view thereof, and FIG.
The figure shows a partially cutaway schematic perspective view thereof. In FIG. 1, reference numeral 1 denotes a group of inlet passages, the inlet ports 3 of which open in a checkered pattern on a circular end face 21.
The outlet 4 of the outlet passage group 2 is similarly opened at an end surface 22 opposite to this end surface 21, and the filter device forms a cylindrical body as a whole together with its cylindrical peripheral surface 20.

Next, referring to FIG. 2, inlet passage group 1
is closed by a closing wall 5 at the end of the passage opposite to the inlet 3 into which the gas flows, and its side surfaces are composed of four sides of a porous conductive ceramic filtration wall 7, and as a whole, it has a non-penetrating cross section. It forms a square hole.

The outlet passage group 2 is closed by a closing wall 6 at the passage end opposite to the outlet 4 through which the gas flows out;
Its side surfaces are made up of four sides of a porous conductive ceramic filter wall 7 similar to the above-mentioned inlet passage 1, forming a hole with a square cross section that does not pass through as a whole.

Each passage of the inlet passage group 1 and each passage of the outlet passage group 2 are arranged adjacent to each other while sharing one or more filter walls 7, and when the passages 1 and 2 have a square cross section, the passages Up to four sides per side are shared filtration walls between the inlet and outlet passages, and the overall arrangement is such that the square inlet 3 or outlet 4 on each end is closed, as shown in Figure 1. It forms a checkered pattern with wall 5 or 6.

Both end faces 21 include an end face (exhaust gas introduction end face) 21 where the inflow port (inlet) 3 is open and an end face (exhaust gas discharge end face) 22 where the outflow port (outlet) 4 is open,
22 are connected by a cylindrical side wall (outer peripheral wall) 20.

Further, on the outer surface of the cylindrical side wall 20, metal electrodes 8 and 9 for voltage application are formed in a band shape from the end face 21 to the end face 22, and are spaced apart from each other at a constant interval. The size of each electrode is as seen from the center line of the cylinder.
It is preferable to set the width to around 60°, particularly 50° to 80°, from the viewpoint of uniform heat generation in the cross section of the honeycomb. The reason why the metallic electrodes 8 and 9 are not provided on the inlet and outlet end faces of the filter is that the inlet 3 or outlet 4 is open at the end faces, which limits the shape of the electrodes 8 and 9, and the filter This is because it becomes extremely difficult to control the current to generate heat uniformly throughout. Furthermore, normally, the cylindrical side wall (outer peripheral wall portion) 20 can be freely selected in electrode shape according to the heating conditions according to the shape, structure, and application of the filter without any hindrance.

Here, the gas filtration effect of this embodiment will be explained.

First, the gas flowing from the direction of the end face 21
It enters the inlet passage group 1 through each inlet port 3 that is open to the rear, passes through the holes in the porous filter wall 7 as indicated by the dotted arrows in FIG. 2, and enters the adjacent outlet passage group 2. Leach. At that time, fine particles in the gas are captured by the filter wall 7, and only the gas exit passage group 2
It flows out from each outlet 4 through the outlet.

At this time, if a voltage is applied between both electrodes of the filter device and electricity is supplied, the filtration wall 7 of the filter generates heat, and the temperature rises above the combustion temperature of carbon, etc., so that the carbon trapped in the filtration wall is The combustible particulates such as these burn and disappear.

Here, the filter walls 7, 20 and the closing walls 5, 6 are made of porous conductive ceramic and have the function of filtering the gas that enters the inlet passage 1 from the inlet 3 and guiding it from the outlet passage 2 to the outlet 4. Normal pore size
If it is 2μ to 30μ, it is suitable for capturing combustible particles such as carbon. However, although the filter wall 20 or the closing walls 5 and 6 do not need to be particularly porous, it is preferable that they be made of a homogeneous material since they will not be damaged by distortion during heating or the like. If the closing walls 5 and 6 are also porous, a filtration action will occur in these portions as well, improving the overall filtration ability.

Here, the ceramic raw material used for the filter wall 7 and the closing walls 5, 6 is silicon carbide (chemical formula:
SiC) or molybdenum disilicide (chemical formula MoSi ₂ )
In particular, those containing molybdenum disilicide as the main component exhibit positive characteristics in the change in electrical resistance with respect to temperature over the entire temperature range in which they are used, making it easy to control the temperature.

In the above embodiment, the honeycomb structure of the filter wall can be manufactured, for example, as follows. In addition to the main ingredients such as silicon carbide or molybdenum disilicide, fine raw material powders such as alumina and silica, organic binders such as sodium alginate, ammonium alginate, and polyvinyl alcohol, and solvents such as water and ethyl alcohol are added and kneaded. An integrated structure is created by making a compound and extruding it through a die consisting of a large number of slits so that the cross-sectional shape of the through hole forms a polygon such as a triangle, square, or hexagon, or a predetermined shape such as a circle or an ellipse. A raw filter wall honeycomb structure can be obtained by obtaining a long product and cutting the long product to a required length.

Next, in order to manufacture a filter device from the honeycomb structure, for example, only the gas inlet 3 of the entire inlet passage group 1 is punched out on the outlet side end face of the inlet passage 1 and the outlet passage 2 of the structure. A raw ceramic sheet is pasted using a paste-like composition of raw ceramic as a binder to form the closing wall 6, and in the same manner, the gas outlet of all the outlet passages 2 is attached to the outlet side end. A raw ceramic sheet punched out only at the location 4 is pasted to form the closing wall 5, and then fired.

The outer shape of the filter can be selected from various forms such as a square prism, cylindrical body, etc., depending on the application area, and the shape of the passage can also be selected from various forms such as a square prism, hexagonal prism, triangular prism, etc. is possible.

Next, on the outer surface of the cylindrical side wall 20 of the cylindrical filter fired as described above, a metal powder paste such as platinum or a powder paste mixture of nickel, cobalt, etc. and silicon is applied in strips at intervals.
By baking, the metallic electrodes 8 and 9 can be laminated to obtain a filter device.

Further, in order to impart airtightness to the side wall 20 of the filter device, the glass-filled ceramic layer can be partially or entirely fired, thereby making the side wall 20 airtight.
It is possible to prevent the high-temperature exhaust gas leaking from the 0 from having an adverse effect on other parts.

The shape of the filter device may be not only cylindrical but also prismatic, for example. FIG. 5 shows a square prism-shaped filter device.

The metal electrodes 23 and 24 are provided on two opposing sides of the four sides of the filter device.

FIG. 4 shows an example of application of the present invention as a filter device for filtering automobile exhaust gas.

Here, 10 is a filter device for removing combustible particles of the present invention, which is fixed to an outer cylinder 18 by ceramic insulating support rings 14a and 14b. The outer cylinder 18 has a flange 1 on its inflow side.
It is joined to the flange 16a of the joint pipe 16 at 8a, and is connected to the exhaust manifold. On the opposite side, that is, the outflow side, the flange 18b is connected to the flange 17b of the joint pipe 17, and connected to the exhaust pipe.

A conducting wire 12a is connected to one electrode 8 of the filter device 10.
They are electrically connected by brazing or other means, and guided to the outside while being insulated from the vehicle body by an insulator 13a inserted through the outer cylinder 18, and connected to the negative side of the power source E and grounded.

A conductive wire 12b is electrically connected to the other electrode 9 by brazing or other means, and is led to the outside while maintaining insulation from the vehicle body by an insulator 13b penetrating the outer cylinder 18, and is switched to the positive side of the power source E. 15, and these power supply E, conductor 12
a, 12b, switch 15 and filter device 1
The entire 0 forms a heating circuit.

In the above configuration, the exhaust gas containing carbon particles from the engine passes through the exhaust manifold and the connecting pipe 16 as it is and is directed toward the upstream direction F.
Then, it flows into the inlet passage 1 of the filter device 10 for removing particulates. Then, as shown by the dotted line in FIG. 2, the exhaust gas passes through the filter wall 7, exits to the outlet passage 2, and is discharged to the outside of the filter device 10 from the outlet 4.
Head toward the downstream exhaust pipe direction B.

By passing through the filter wall 7, the carbon particulates in the exhaust gas are captured by the filter wall 7, and the exhaust gas containing almost no carbon particulates is discharged to the outside of the vehicle.

Therefore, by turning on the switch 15, electricity is passed between the electrodes 8 and 9, causing the filter device 10 to generate heat and heating the carbon particles to the ignition temperature.The carbon is burned out and the filter eyelids due to the carbon deposits are removed. This makes it possible to prevent clogging and pressure loss due to clogging.

In this heating circuit, conductors 12a and 12b
However, since the carbon particles are not exposed to the space where the carbon particles are flowing and the carbon particles are not deposited on the surface of the conductor, there is no fear of shoots, which is advantageous.

Further, it is advantageous to have a catalytic metal such as platinum supported in a distributed manner within the porous wall structure of the filter, since carbon can be incinerated at a lower temperature. This can be obtained, for example, by immersing the porous wall structure in a solution of the acid or salt of the catalytic metal and then heating it at a relatively high temperature.

[Effects of the Invention] As described above, the filter device for removing flammable particulates of the present invention simplifies the filter structure for carbon particulate filtration and heating without particularly changing the shape of the conventional honeycomb structure filter. Manufacturing becomes easier.

In addition, during use, the entire filter, especially the filter wall itself, generates heat, so all of the captured carbon is efficiently heated and incinerated, and the temperature rises quickly and is energy efficient. Moreover, pressure loss is small, and carbon fine particles are generated. It also maintains the inherent advantage of honeycomb structure filters, such as good trapping properties.

Note that since the exhaust gas is also heated, combustible particulates captured by the filter are efficiently burned and extinguished.

Furthermore, the outer circumferential wall only has to function as a partition wall and is simple in shape. Therefore, the shape of the electrodes provided on the outer peripheral wall can be arbitrarily selected depending on the shape, structure, and application of the filter so that voltage and current can be suitably controlled, so there is a high degree of freedom as a highly functional filter.

Next, a specific manufacturing example will be given and explained.

Production example 1 Silicon carbide powder, boron carbide (chemical formula B ₄ C) as a sintering aid, phenolic resin, and graphite powder (average particle size 25μ) as a pore size control agent,
A formulation prepared at a weight ratio of SiC: 100, B ₄ C: 0.25, phenolic resin: 5, and graphite powder: 15.
100, polyvinyl alcohol: 3, water: 25
The mixture was blended and kneaded in the following proportions and extruded through a mold to form a long article having a passageway extending through it, and cut into a required length to obtain a green wall structure.

Next, a green sheet with the same composition as above, with inlets or outlets punched out in advance, was applied to both cut surfaces of the cut green wall structure, with increasing proportions of solvent among the above components. It was attached using a blended paste. This product was fired at 1950°C for 3 hours in a nitrogen atmosphere, and then in the atmosphere at 1000°C to burn off excess combustible carbon components to produce a filter with the same shape as shown in Figure 3.

Next, a mixture of 50% by weight of silicon and 50% by weight of fine powders of nickel and cobalt was fired for 30 minutes at 1500°C in a non-oxidizing atmosphere to form an alloy, and a paste of the powder was further ground and applied to the above-mentioned fired filter. At opposite positions of the cylindrical side wall (outer peripheral wall) of the
After coating as shown in the figure, it was dried and baked for 10 minutes in a non-oxidizing atmosphere at 1500°C to obtain a cylindrical filter device for removing combustible particles having the properties shown in Table 1.

Table 1 Diameter: 100mm Length: 100mm Filtration wall thickness: 0.5mm Glue in the passage Square, 3.0mm on each side Filtration area: Approximately 8200mm ² /in ³ Average porosity: 55% Average pore diameter: 20μ Interelectrode resistance (at room temperature): 0.5Ω Manufacturing example 2 72 parts by weight of molybdenum disilicide powder, 8 parts by weight of alumina
Example 1: 20 parts by weight of graphite powder was mixed with 3 parts by weight of polyvinyl alcohol as an organic binder and 20 parts by weight of water and kneaded.
Molded and fired in the same shape and conditions as,
Excess combustible carbon components were burned off at 1000℃ in the atmosphere, and a filter with the same shape as shown in Figure 3 was made.

A paste of platinum powder was applied to the obtained filter in the same manner as in Production Example 1, and baked at 1200° C. in the atmosphere to obtain a cylindrical filter device for removing combustible particles.

Its properties were the same as those in Table 1 except that the interelectrode resistance value at room temperature was 0.3Ω.

Temperature rise test When a voltage of 26V was applied in the atmosphere between both electrodes of the filter device obtained in Production Example 1, the temperature rose from room temperature to
The temperature reached over 600℃ in 108 seconds.

On the other hand, when a voltage of 26 V was applied in the atmosphere between both electrodes of the filter device obtained in Production Example 2, the temperature reached from room temperature to over 600° C. in 103 seconds. Furthermore, since the molybdenum disilicide filter had positive characteristics, temperature control was easy.

[Brief explanation of drawings]

Fig. 1 is a front view of an embodiment of a filter device for removing combustible particulates according to the present invention, Fig. 2 is a sectional view thereof, Fig. 3 is a partially cutaway schematic perspective view thereof, and Fig. 4 is a filter device for automobile exhaust gas filtration. FIG. 5 is a schematic cross-sectional view of the filter device. FIG. 5 is a schematic perspective view of another embodiment. 1... Entrance passage group, 2... Exit passage group, 3...
Inflow port, 4...Outflow port, 5, 6...Closing wall, 7...
...filtering wall, 8,9,23,24...metallic electrode,
20...Cylindrical side wall (outer peripheral wall).

Claims (1)

[Scope of Claims] 1 A wall structure forming a plurality of passages extending from the inlet side to the outlet side, and the passages include an inlet passage group whose outlet side is closed by an outlet closing wall, and an inlet passage group whose inlet side is closed by an inlet closing wall. In the filter, at least one wall structure is made of porous conductive ceramic. A voltage applying means for heating the wall structure with electricity is provided on the outer peripheral wall portion of the filter that connects both end surfaces of the exhaust gas introduction end surface where the inlet is open and the exhaust gas discharge end surface where the outlet is open. A filter device for removing combustible particles. 2. The filter device for removing combustible particulates according to claim 1, wherein the porous conductive ceramic contains silicon carbide as a main component. 3. A filter device for removing combustible particulates according to claim 1, wherein the porous conductive ceramic contains molybdenum disilicide as a main component.