JPH0211289B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a filter 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 that efficiently burns and removes filtered combustible particulates while maintaining high filterability by applying electricity to the filter itself to generate heat.

[Prior Art] Conventionally, it has been proposed to use a filter in the exhaust system or exhaust recirculation system in order to remove carbon particulates contained in the exhaust gas of an automobile engine as a pollution control measure. However, there was a problem in that carbon accumulated and clogged, resulting in pressure loss. To solve this problem, it is possible to combine a heater such as a nichrome wire or a heat-generating metal layer in the particulate trapping part of the filter and heat it with electricity, inject fuel into the particulate part and heat it with the combustion heat of the fuel, or use a high-voltage electrode. Methods have been used to prevent clogging by providing a filter and heating it by spark discharge, or by using a filter made of carbon fiber and heating the carbon fiber by passing an electric current through the filter to incinerate the carbon fine particles.

[Problems to be solved by the invention] However, when using a nichrome wire, etc., the heat generating area is small and the energy efficiency is poor, and attachment to the filter is also time-consuming, and when a heat generating metal layer is provided. They had to be thin and placed in a small area so as not to interfere with filtration, which resulted in poor energy efficiency and time-consuming installation, and since they were thin metal wires, there was a risk of them breaking due to oxidative corrosion. In addition, if the temperature cannot be raised properly due to the cooling effect of the exhaust gas, it may be necessary to stop the engine and then burn off the carbon particles that have accumulated in the filter. Additionally, fuel injection and high pressure discharge methods require exceptionally complex equipment, consume large amounts of energy, create fuel fire problems, damage filters from discharge, and
Additionally, those using carbon fibers had the disadvantage that the fibers themselves were destroyed by combustion.

[Structure of the Invention] In view of the above problems, the present inventors have completed intensive research and have completed a filter that solves the above problems.

That is, the gist of the present invention is that a plurality of independent plate-shaped ceramic heating resistors are arranged approximately parallel to each other between ceramic skeleton filter bodies, and electrodes are attached to each end of the heating resistors. A ceramic filter for removing combustible particulates is provided. Here, the skeleton type filter body refers to a porous material having felt-like, woven-fabric, or spongy-like filtration performance.

[Example] Next, an example of the ceramic filter for removing combustible particulates according to the present invention will be described based on the drawings.

FIG. 1 is a front view of an embodiment of the filter of the present invention;
FIG. 2 is a sectional view thereof, and FIG. 3 is a perspective view thereof. Reference numeral 1 represents a skeleton type filter, 2 a plate-like heating resistor, and 3 and 4 electrodes. Here, the skeleton-type filter body 1 and the plate-shaped heating resistor 2 are stacked alternately so that the resistor 2 is sandwiched between the filter body 1 to form a rectangular parallelepiped, and the plate-shaped heating resistor is attached to the side surface of the rectangular parallelepiped. Electrodes 3 and 4 are provided to connect the ends of each resistor 2 at the exposed portions thereof. The material used for the filter body 1 is generally one whose main component is silicon carbide, molybdenum disilicide, alumina, aluminum titanate, mullite, cordierite, or a combination of two or more thereof. This filter body 3
It is advantageous if a catalytic metal such as platinum, rhodium, palladium, etc. is supported on the carbon, since the carbon can be incinerated at a lower temperature. The material of the resistor 2 can be used as long as it generates heat when electricity is applied and is heat resistant, but it is generally made of silicon carbide or molybdenum disilicide as the main component, with alumina, silica, etc. added as necessary. used. The material used for the electrodes 3 and 4 is one whose main component is metal powder such as platinum, nickel, or cobalt, with powder of silicon or the like added as necessary.

Here, when the filter of this embodiment is used to remove combustible particulates in gas, for example, the second
When gas to be filtered enters from the left direction F in the figure, the gas enters the porous filter body 1. As a result, fine particles in the gas are dispersed and captured in the filter body 1. When the electrodes 3 and 4 are energized, the fine particles captured in this way are heated to a temperature above the ignition point. It heats up and burns and disappears.

This energizing heat-generating incineration process can be performed simultaneously with the filtration process by simply passing electricity between the electrodes, so there is no need to remove the filter for incineration process, and no clogging occurs even after long-term use.

The filter of this embodiment having the structure as described above is manufactured, for example, by the following method.

First, in order to form the filter body 1, raw ceramic whose composition has been blended to form a skeleton-type filter body through a firing process may be heated and fired. A mixture of a dispersion medium and a binder is further added and mixed with a soft urethane foam stock solution such as polyol and polyisocyanate, which is injected into a mold, and a raw ceramic foam is formed by the foaming reaction of the resulting isocyanate. It may be formed by heating and baking after drying. In addition, the filter body 3 can be formed by impregnating a plastic foam that has already been formed into a plate shape with a slurry-like mixture containing ceramic raw materials, a dispersion medium, a binder, etc., and then heating and baking it after drying. You can also do it. In this case, by changing the size of the pores in the foam, the pores in the filter body 3 can be made smaller continuously in the gas flow direction, and as a result,
Fine particles can be more uniformly dispersed and captured in the filter, and the incineration process can be performed more efficiently.

Further, in order to manufacture the plate-shaped heating resistor, the following steps are performed, for example. 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. A mixture is made and extruded through a die with a through-hole having a rectangular slit cross-section to obtain a long piece with an integral structure, and the long piece is cut to the required length to produce a raw plate-like heat generating material. A resistor can be obtained. In addition, it can also be formed by press molding or the like.

The shape of the heating resistor may also take various other plate shapes such as a corrugated plate shape. If the skeleton filter body is made of an electrically conductive material, the electrical resistance value of the heating resistor should be set to be slightly lower than the resistance value of the filter body, depending on the material density and shape. The temperature difference between the filter body and the filter body becomes smaller, resulting in more uniform heat generation.

The plate-shaped filter bodies fired by the above method or the raw filter bodies before firing and the fired plate-shaped resistors or raw resistors before firing are stacked alternately to form silicon carbide. They are joined with or without a paste-like adhesive mainly composed of , and if necessary, they are heat-treated to eliminate the polymeric foam material, etc., and then baked at a predetermined temperature to be integrated.

To form the electrodes 4 and 5 on the end face of the filter,
This is done by applying a paste made by adding and blending the above-mentioned metal powder with a dispersion medium, binder, etc. to the end face of a raw filter by printing, etc., and then firing it at the same time as firing the entire filter. .

Although the filter of this embodiment described above has a rectangular parallelepiped shape, it is possible to adopt various shapes, such as a cylindrical shape, a triangular prism shape, a hexagonal prism shape, etc., depending on the application location of the filter of the present invention.

Since this embodiment is configured as described above, the basic configuration is simply to laminate the filter 1 and the heating resistor 2 and provide electrodes on the two exposed surfaces of the heating resistor 2. Thus, it is possible to manufacture a filter having a function of removing combustible particles very easily. During the manufacturing process, the heating resistor 2 is not made of nichrome wire but is made of ceramic material, so that no deterioration or embrittlement occurs during the firing treatment performed as appropriate, and the heating performance of the filter is not affected. Therefore, the yield is high, the productivity is high, and the durability during use is also high.

Furthermore, since the strong and hard heating resistor 2 and the weak and relatively flexible filter body 1 are alternately laminated to form a composite, it produces the effect of a composite material and can be heated simply by uniformly applying electricity. Not only is this possible, but also in terms of strength, the tensile and compressive strength of the heating resistor 2 and the flexibility of the filter body 1 synergistically overlap, resulting in a stronger filter.

Next, FIG. 4 shows an example in which the filter of this embodiment is applied to an exhaust pipe or an exhaust gas recirculation pipe of an automobile engine.

Here, 15 is a ceramic filter for removing combustible particles of the present invention, which is fixed to the outer cylinder 17 by ceramic insulating support rings 16a and 16b. On the inflow side of the outer cylinder 17,
Connected to the flange 18a of the joint pipe 18 at the flange 17a,
Connected to the exhaust manifold. On the opposite side, that is, the outflow side, the flange 17b is connected to the flange 19b of the joint pipe 19, and connected to the exhaust pipe.

A conductive wire 20 is electrically connected to one electrode 3 of the filter 15 by brazing or other means, and the outer cylinder 17
The insulator 22 installed through the insulator 22 leads the insulator to the outside while maintaining insulation from the vehicle body, and is connected to the negative side of the power source E and grounded.

A conductive wire 21 is electrically connected to the other electrode 4 by brazing or other means, and is led to the outside while maintaining insulation from the vehicle body by an insulator 23 penetrating the outer cylinder 17, and is switched to the positive side of the power source E. 23, and these power supply E, conductors 20, 2
1. The switch 23 and the filter 15 together form 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 18 as it is and is directed toward the upstream direction F.
Ceramic filter 1 for removing combustible particles
It flows into the inlet side of No.5. Then, the exhaust gas passes through filter body 1
, and is discharged from the outlet side to the outside of the filter 15, passes through the connecting pipe 19, and heads in the direction B toward the downstream exhaust pipe or the like.

By passing through the filter 1, the carbon particulates in the exhaust gas are captured by the filter 1, and the exhaust gas containing almost no carbon particulates is discharged to the outside of the vehicle.

Therefore, by turning on the switch 23, electricity is passed between the electrodes 3 and 4, causing the heating resistor 2 to generate heat, thereby heating the filter 15, and raising the temperature of the carbon particles to the ignition temperature, which causes the carbon to burn and disappear. This makes it possible to prevent filter clogging due to carbon deposition and pressure loss due to clogging.

In this heating circuit, conductors 12a and 12
B is not exposed to the space where the carbon fine particles are flowing, and the carbon fine particles are not deposited on the surface of the conductive wire, which is advantageous because there is no fear of shoots.

[Effects of the Invention] As described in detail above, the present invention arranges a plurality of mutually independent plate-shaped ceramic heat generating resistors approximately parallel to each other between ceramic skeleton filter bodies,
By providing electrodes at each end of the heating resistor, even when the filter is running, the heating resistor generates heat and the combustible particles are heated and burnt out, so that the filter can be heated. It prevents clogging and can be used for long periods of time. In addition, since the heating resistor existing between the filter bodies generates heat, the amount of heat generated can be freely adjusted by appropriately selecting the thickness of the resistor during extrusion molding, and uniform molding can be achieved. Since this is easy, quality control such as uniform heating performance is improved, and a filter of excellent quality that does not crack due to partial heat generation etc. can be manufactured at a high yield. Furthermore, since uniform heating is possible as described above, combustible particulates captured by the filter can be efficiently burned.

Furthermore, compared to a skeleton-type filter that itself generates heat, the filter of the present invention has a smaller surface area of the heat-generating portion relative to its volume, and thus can significantly improve oxidation resistance. In addition, since the filter body does not particularly require electrical conductivity, inexpensive materials such as alumina and cordierite can be used, and the filter itself has the advantage of being simple in structure, making it easy to manufacture and achieving high yields. have

Next, the method for manufacturing the filter of the present invention will be described with reference to manufacturing examples.

Production Example 1 β-SiC (average particle size 0.3μ) (parts by weight, same below)
100 parts B ₄ C 0.25 parts Phenol resin 6 parts Ethyl alcohol 100 parts The above components were mixed in a ball mill for 3 hours to obtain a slurry formulation with controlled viscosity.

The above formulation has an average pore diameter of approximately 0.8 mm and a porosity of 80%.
A green filter body was obtained by impregnating commercially available polyurethane foam and drying it. On the other hand, β-SiC (average particle size 0.3 μ) 100 parts B ₄ C 0.25 parts Methyl cellulose 5 parts Water 20 parts The above ingredients were kneaded, extruded, cut and dried to form a raw flat heating resistor. Obtained.

Seven raw filter bodies and six raw heating resistors obtained by the above method were alternately laminated with the above starch composition and bonded together, and then dried to obtain a raw filter. This was held in a vacuum at 800°C for 1 hour to blow off the resin component, and then sintered in an argon stream at 2030°C for 1 hour to perform primary firing, and then in a nitrogen gas atmosphere at 1950°C.
After secondary firing at ℃ for 3 hours, the thickness of each filter body part was 26
mm, average pore diameter approximately 0.8 mm, porosity 80%, and thickness of the flat heating resistor portion 3 mm.
An integrated filter of 200 mm, width 200 mm, and thickness 30 mm was obtained. Platinum paste was applied to both ends of this filter, and the electrodes were baked at 1200℃ for 0.5 hours in the air.
A ceramic filter for removing combustible particulates with an interelectrode resistance value (at room temperature) of 0.3Ω was obtained.

When 24V was applied in the atmosphere between both electrodes of the filter obtained in Manufacturing Example 1 above,
The temperature reached over 900℃ in about 60 seconds, and the heat was generated evenly.

Production Example 2 Molybdenum disilicide 100 parts Polyvinyl alcohol (PVA) 2 parts Water 100 parts The above ingredients were used as a slurry formulation, while the above ingredients mixture was made into a slurry preparation.Molybdenum disilicide 100 parts Polyvinyl alcohol (PVA) 5 parts Water 20 parts For use as a heating resistor, molded and fired under the same shape and conditions as Manufacturing Example 1,
Attach electrodes in the same way, and measure the interelectrode resistance (at room temperature).
A 0.3Ω filter was obtained.

When 24V was applied in the atmosphere between both electrodes of the filter obtained in Manufacturing Example 2 above,
It took 80 seconds to reach a temperature of over 900°C, and the heat was generated uniformly. Furthermore, since the main component is molybdenum disilicide, the resistance of the filter has a positive characteristic with respect to temperature, and temperature control is easy.

Production Example 3 The filter obtained in Production Example 1 was immersed in a platinum catalyst solution to impregnate the filter with platinum catalyst and then dried.The catalyst was then baked in the air at 700°C for 2 hours to reduce the volume. A filter carrying 2 g of platinum catalyst per 1000 c.c. was obtained.

The filter obtained in Manufacturing Example 3 above was 2000c.c.
When the device was installed in the middle of the exhaust pipe of a diesel engine and tested at an engine speed of 2000 rpm, it continued to capture carbon particles with a capture rate of over 50%, reaching near saturation after one hour. here
When a voltage of 24V was applied to the filter electrode,
Combustion started at a filter temperature of about 400°C and finished in 2 minutes. In the filter of Production Example 1 in which no combustion catalyst was supported, combustion started at a temperature of 550° C. or higher.

[Brief explanation of drawings]

FIG. 1 is a front view of an embodiment of the filter of the present invention;
FIG. 2 is a sectional view thereof, FIG. 3 is a perspective view thereof, and FIG. 4 is a partially cutaway view for explaining the case where the filter of the embodiment is applied to an exhaust pipe or an exhaust gas recirculation pipe of an automobile engine. 1...Ceramic skeleton type filter body, 2...
... Plate-shaped ceramic heating resistor, 3, 4... Electrode.

Claims (1)

[Scope of Claims] 1 A plurality of independent plate-shaped ceramic heat generating resistors are arranged approximately parallel to each other between ceramic skeleton filter bodies, and electrodes are provided at each end of the heat generating resistors. A ceramic filter for removing combustible particulates. 2. The ceramic filter for removing combustible particulates according to claim 1, wherein the heating resistor and the skeleton filter body contain silicon carbide or molybdenum disilicide as a main component. 3. The ceramic filter for removing combustible particulates according to claim 1 or 2, wherein the skeleton filter body supports a catalyst for combustion of combustible particulates.