JPH045414A - Exhaust gas purifying device - Google Patents

Abstract

PURPOSE:To recondition a filter efficiently without being blinded by providing a filter which catches minute particles floating in exhaust gas, and holding catalyser on the surface of the filter having minute undulations formed thereon. CONSTITUTION:Electrodes 2 having conductivity and porous filters 1 are piled up alternately and held inside a housing 5 through an insulator 4 in the way of an exhaust passage 3. Many minute projections 15 are formed on the surface of each filter 1. Catalyser 17 is stuck on the projections 15. Thus, it is possible to catch and burn minute combustible particles such as particulate and the like in the exhaust gas at any time, and to recondition the filter efficiently without being blinded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an exhaust gas purification device that captures particulates in exhaust gas that pose an environmental problem, and more specifically to nitrogen oxide 1Fl (NOx) in exhaust gas from diesel engines. And fine particulate carbon substances! This invention relates to an exhaust gas purification device equipped with a filter that captures particulate matter or soot in the exhaust gas of a boiler.

[Prior art and problems to be solved by the invention] NOx and particulates contained in the exhaust gas of diesel engines, soot in the exhaust gas of boilers, etc. are environmental problems and are often removed using filters. . In this case, a filter that has become clogged due to trapping more particles than its limit must be replaced with a new one, or the filter must be regenerated by removing the trapped particles by some method.

For example, when using a filter made of a highly heat-resistant ceramic such as cordierite or a metal mesh, deposited fine particles are conventionally incinerated using a heat source such as a burner or an electric heater. However, in that case, the filter is likely to be damaged or melted due to combustion, so the amount of deposited particulates and the amount of oxygen in the exhaust gas must be limited.

In order to control the amount of accumulated particulates and automatically incinerate them for the purpose of purifying diesel engine exhaust gas, it was necessary to detect changes in exhaust pressure due to accumulation and activate the heat source. However, according to this method, if the detection level is adjusted so that the heat source operates at high pressures associated with high-speed operation, the heat source will not operate when low-speed operation continues and the filter will easily become clogged, and conversely, the low pressure If the detection levels are sometimes matched, the heat source will often operate in vain. Particularly in the former case, fuel efficiency deteriorates.

To solve this problem, one way to regenerate the filter is to attach electrodes to the filter made of insulating material.
There is a method in which when an electrode is electrically connected through conductive particles, the particles are incinerated by using the heat generated by energization (Japanese Patent Application Laid-Open No. 57-203812).

FIG. 5 shows an example of a conventional exhaust gas purification device using this principle, in which electrode rods 2 are embedded in a filter 1 made of an insulating material made entirely of porous material. In this exhaust gas purification device, it is difficult to completely incinerate particulates accumulated over a wide area by electrical conduction, and therefore it is virtually impossible to completely eliminate clogging (shaded area).

FIG. 6 shows another conventional exhaust gas purification device, in which electrodes 2 and 2 are attached to both end faces of a filter 1 made of an insulating material.
is arranged. In this case, fine particles tend to accumulate near the end face on the inlet side of the filter, which tends to cause clogging (shaded area) before the electrodes are electrically connected. In an attempt to solve this problem, if the voltage between the electrodes is increased, an excessive current flows locally, damaging the filter.

Furthermore, in the case of a conventional exhaust gas purification device as shown in FIG. Furthermore, an electrode wire 13 is provided on the inner wall of the through hole 11 . In this filter, when the electrodes are electrically connected, almost the entire area of the filter 1 can be incinerated, so that clogging as described above is unlikely to occur. However, the electrode wire 13 obstructs exhaust air, and it is difficult to insert the electrode wire 13 into the through hole 11 and bring it into close contact with the filter.

Therefore, an object of the present invention is to enable a filter to capture environmentally harmful particulates contained in exhaust gas and to efficiently regenerate the filter, and in particular to efficiently remove particulates contained in exhaust gas from diesel engines, etc. An object of the present invention is to provide an exhaust gas purification device that has the function of combusting unburned hydrocarbons (hereinafter referred to as HC), CO, NOx, etc., which are other harmful gas components.

[Means for Solving the Problems] In view of the above problems, as a result of intensive research, the present inventor has developed an exhaust gas purification device having a structure in which electrically insulating filters and electrodes are alternately laminated, and the captured particulates are incinerated by passing electricity. In,
The present invention was completed based on the discovery that a good exhaust gas purifying effect can be achieved by supporting a catalyst on the surface of the filter, which has been etched to form irregularities.

That is, the exhaust gas purification device of the present invention includes a filter made of a nonflammable and electrically insulating material that captures particulates floating in the exhaust gas, and electrodes that are stacked alternately with the filter, so that there is a gap between adjacent electrodes. By applying a voltage to the filter, when electrically conductive and combustible particles are captured by the filter, they are heated by the electricity and incinerated at any time within the filter, and fine irregularities are formed by the etching process. A catalyst is supported on the surface of the filter.

〔Example〕

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

FIG. 1 is a sectional view of an exhaust gas purification device according to an embodiment of the present invention. To explain its structure, conductive electrodes 2 and porous filters 1 are alternately stacked in the middle of an exhaust passage 3 with an insulator 4 interposed therebetween, and are held in a housing 5.

The filter 1 and the electrode 2 have a hollow disk shape, as shown in FIG. The thinner the filter 1 is, the lower the voltage applied to the electrode 2 will be, but in order to improve particulate collection efficiency and reduce manufacturing costs, II
It is desirable to have a thickness of W1 or more. Preferred forms of the electrode include gold plate 142a, punched metal plate 2b, and flat plate 20 as shown in FIG. The hollow lower surface of the laminate made of these filters and electrodes is closed with an insulating shielding plate 6 and fixed to the housing 5 with bolts.

Returning to FIG. 1, each electrode 2 is connected to every other end of the filter 1, with one set serving as a ground electrode 7 and the other set serving as a non-ground electrode 8, across the filter. A voltage is applied between adjacent electrodes. The filter 1 is made of a material with high insulation properties and heat resistance, such as ceramics such as cordierite and mullite, quartz, and glass wool. It is desirable that the material of the electrode 2 is low in energy loss, has heat resistance and corrosion resistance, and is inexpensive. Since the insulator 4 is constantly exposed to the exhaust gas flow, it needs to be made of a material that has heat resistance, corrosion resistance, and low expansion properties, and ceramics such as cordierite and mullite are preferable. The housing 5 is preferably made of a material that has heat resistance, corrosion resistance, and strength; for example, stainless steel is used. As shown in FIG. 3, on the surface of the filter 1,
A large number of fine protrusions 15 are formed, and a catalyst 17 is attached to the protrusions 15. To form the protrusions 15, etch bits are formed by sputter etching including plasma etching, or chemical etching with acid or alkali, before depositing the catalyst 17.

The parts where these etch pits are not formed remain and the protrusion 1
It becomes 5. The size of the projections 15 is preferably such that the average diameter is on the order of submicrons and the aspect ratio (length/diameter) is 10 or less, particularly 8 to 4.

The formation of fine irregularities by the protrusions I5 increases the surface area of the filter and increases the amount of catalyst supported. Furthermore, the degree of dispersion and fixation of the catalyst is also reduced, resulting in better catalytic action.

The catalyst I7 is supported on the filter 1 by being attached to the projections 15 by sputtering, electroplating, electroless plating, or the like. As a catalyst, it promotes the ignition and combustion of particulates, oxidizes and removes CO and HC,
It is also preferable to use a catalyst having catalytic properties that promotes the reduction of NOx by HC and particulates at a relatively low temperature. In particular, Pt, Pd, I? pt of h etc.
Group elements are preferred, and a mixture of them may be used. Moreover, in addition to those elements, Au or Ag can also be supported. Furthermore, according to the electroless Menki method, Co-
Fe, Co-Ni-Mn-Re, N1-Co-P
, N1-Fe-P and other alloys and amorphous alloys can also be supported as catalysts.

Next, the effect will be explained. As shown by the arrow in FIG. 1, when gas containing particulates such as particulates and harmful gas components such as HC, NOx, and GO flows from the upstream side to the downstream side of the exhaust passage, the gas flows inside the filter 1. Fine particles are captured by the filter while passing from the inner circumferential side to the outer circumferential side. As the particles gradually accumulate, the adjacent electrodes 2.
By applying a voltage between the two, conduction occurs through the particles, and the heat generated by the current incinerates the particles. After this, the conduction is cut off due to the incineration of the fine particles,
The generation of heat due to the electric current also stops. At the same time as the above action, the combustion of particulates is promoted by the catalyst supported on the filter 1, and HC, NOx, and Co are also purified.

In the present invention, the filters 1 and electrodes 2 are stacked alternately, so that the electrodes 2 penetrate the filter 1 from the inlet face to the outlet face, so that no matter where particulates accumulate on the filter, no particulate matter is deposited through the particulates. conduction, thereby incinerating fine particles.

At the same time, fine irregularities are formed on the contact supporting surface of each filter by etching, so that the contact area with exhaust gas is large and the exhaust gas purification characteristics are improved.

In addition, in FIG. 1, the exhaust passage may be oriented in the opposite direction to that in the above embodiment. In that case, the gas passes through the filter l from the outer circumferential side to the inner circumferential side, but the effect is the same as that described above.

FIG. 4 shows an exhaust gas purification device according to another embodiment of the present invention. In this case, the filter 1 and the electrode 2 are stacked on top of each other, centering around a heat-resistant ceramic tube 9 with one end sealed and a small hole 10 formed in the side wall at a position corresponding to the filter. By doing so, higher temperature exhaust gas can be applied. It also increases the strength of the entire device.

The present invention will be explained in further detail by the following examples.

In the apparatus shown in FIG. 4, a filter 1 made of mullite formed into a donut shape with a thickness of 11II11 was used. After molding, the filter is set as a substrate in a sputtering device, and 1. Plasma etching treatment was performed for 30 minutes using high frequency power with an output of 200 - in an atmosphere having a partial pressure of 0□ of OX 102 Torr. After treatment, the average diameter is about 0.1uH on the inner and outer surfaces of the filter.
A protrusion of I was formed.

Next, sputtering of PT was performed while rotating the filter at a speed of about 3.5 rpm, so that PT with an average thickness of 20 to 30 was supported on the protrusions on the filter surface.

The electrode 2 has a wire mesh shape and is made of copper as shown by 23 in FIG. 2 as a ground electrode, and a flat plate shape and made of stainless steel as shown as 20 in FIG. 2 as a non-ground electrode, both of which have a thickness of 1 m++.
It was used as Ceramic tube 9 was made from cordierite.

The exhaust gas purification device assembled using these parts is
■It was installed in the middle of the exhaust passage of a diesel engine that generates particulates per minute.

During operation of the engine, a DC voltage of 35 V was applied in pulses between the electrodes, and the pressure difference (pressure loss) of the exhaust gas at the inlet and outlet of the housing 5 was measured. Combustion of particulates occurred at the same time as the current reached a certain maximum value, and the current value dropped immediately after that, so the maximum pressure loss at that time was detected. The results are shown in Table 1.

At the same time, when the exhaust gas temperature was 250°C, the concentration of CO in the exhaust gas and the exhaust gas at the inlet and outlet of the purifier were continuously analyzed. The results are also shown in Table 1.

Twisting I After the filter was subjected to plasma etching treatment in the same manner as in Example 1, Pd with an average thickness of 20 mm was supported on the protrusions on the filter surface by electroless plating.

Using a purifier using this filter, the pressure loss of the exhaust gas and the concentrations of CO and IC in the exhaust gas were analyzed in the same manner as in Example 1. The results are also shown in Table 1.

Comparative Example 1: A filter made of mullite similar to Example 1, but without catalyst support.

Comparative Example 2: A mullite filter similar to Example 1, but with PT supported on the surface by sputtering without etching.

Comparative Example 3: A filter made of mullite similar to that of Example 1, but without etching, Pd was coated with an electroless method.
A filter supported on the surface using the Ki method.

Purifiers using the filters of Comparative Examples 1 to 3 above were assembled, and the pressure loss of the exhaust gas and the concentrations of CO and HC in the exhaust gas were analyzed in the same manner as in Example 1. The results are also shown in Table 1.

Table 1 As shown in Table 1, it can be seen that when the exhaust gas purification devices of Examples 1 and 2 were used, the pressure loss was smaller than that of the comparative example, and particulates were effectively incinerated.

In addition, CO and HC purification was performed with high efficiency.

〔Effect of the invention〕

As explained above, the exhaust gas purification device of the present invention captures and incinerates combustible particulates such as particulates in the exhaust gas at any time, and incineration of particulates is possible over the entire filter area, so it is efficient without clogging the filter. It can be played well.

In addition, since the catalyst is supported in the filter at a high concentration,
The ignitability of particulates increases, reducing NOx and HC.
, Co and other harmful gas components are also purified at the same time.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an exhaust gas purification device according to an embodiment of the present invention, FIG. 2 is a perspective view showing an example of a filter and an electrode used in the exhaust gas purification device of the present invention, and FIG. FIG. 4 is an enlarged cross-sectional view showing the state of the filter surface supporting the present invention; FIG. 4 is a cross-sectional view showing an exhaust gas purification device according to another embodiment of the present invention; FIGS. 5, 6, and 7 are respectively FIG. 2 is a sectional view showing a conventional exhaust gas purification device. 1. Filter 2... Electrode 3... Exhaust passage 5... Housing 7... Grounded electrode 8... Non-grounded electrode 9... Ceramic tube 15... Protrusion 17... Catalyst Applicant: Director of the Agency of Industrial Science and Technology Ken Sugiura Sub-agent of Riken Co., Ltd. Patent attorney Takaishi Tachibana Ma To Figure 5 Power Supply Figure 4 @ Present

Claims (4)

[Claims] (1) It has a filter made of a nonflammable and electrically insulating material that captures particulates floating in exhaust gas, and electrodes stacked alternately with the filter, and a voltage is applied between adjacent electrodes. When electrically conductive and combustible particulates are captured by the filter, they are heated by electricity and incinerated at any time within the filter. An exhaust gas purification device characterized by having a catalyst supported on it. (2) The exhaust gas purification device according to claim 1, wherein the flow direction of the exhaust gas within the filter is parallel to a laminated surface of the filter and the electrode. (3) The exhaust gas purification device according to claim 1 or 2, wherein both the filter and the electrode have a hollow disk shape. (4) The exhaust gas purification device according to claim 3, wherein a ceramic tube is inserted into the hollow portion.