JPH0364611A - Exhaust gas purifying device - Google Patents

Abstract

PURPOSE:To enhance ignition properties as well as to reduce harmful components in exhaust gas by supporting catalysts by filters in a device wherein the filters which arrest fine particles in exhaust gas, and electrodes which burn the fine particles, are alternately piled up. CONSTITUTION:Conductive electrodes 2 and porous filters 1 are alternately piled up via insulators 4 on the way of an exhaust passage 3 so as to be held in a housing 5. Each electrode 2 is alternately connected with each end section of the filters 1, and one group of these connected electrodes, and the other group of them are concurrently set on an earthing electrode 7 and a non- earthing electrode 8 respectively. In addition, the lower surface of the center section of the piled-up bodies 1 and 2 is blocked by an insulation shielding plate 6. In this case, catalysts (not shown) are supported within the filters 1. As catalysts, a compound composed of, for example, alkalimetal shall be used in order that HC and particulates can be burnt or ignited while an reduction of NOx is thereby accelerated at low temperatures.

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, the present invention relates to an exhaust gas purification device that captures fine particles in exhaust gas that pose an environmental problem. The present invention relates to an exhaust gas purification device equipped with a filter that captures particulate carbon materials (particulates) and soot in the exhaust gas of a boiler.

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

For example, when using a filter with a honeycomb structure made of highly heat-resistant ceramic such as cordierite, deposited fine particles are conventionally incinerated using a heat source such as a burner or an electric heater. However, in that case, the honeycomb structure is likely to be damaged due to combustion.
The amount of particulate deposits 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 is activated when the pressure is high due to high-speed operation, the filter is likely to become clogged when low-speed operation continues, and conversely, the detection level is adjusted when the pressure is low. This increases the amount of wasteful operation of the heat source. Particularly in the former case, fuel efficiency deteriorates.

To solve this problem, one way to regenerate filters is to attach electrodes to a filter made of insulating material and use the heat generated by direct conduction when the electrodes conduct through conductive particles. There is a method of incinerating fine particles (Japanese Unexamined Patent Publication No. 57-203812).

Figure 4 shows an example of the prior art based on this principle, in which an electrode rod 2 is embedded in a filter 1 made entirely of an insulating material, which should not be porous. It is impossible to incinerate the particles through electrical conduction, making it difficult to eliminate clogging (shaded area).

FIG. 5 also shows another embodiment of the prior art, in which electrodes 2.2 are arranged on both end faces of a filter 1 made of an insulating material, but in this case, electrodes 2.2 are arranged near the popular end face of the filter. Because fine particles tend to accumulate on the electrodes, clogging (shaded area) tends to occur before the electrodes become electrically connected. In an attempt to solve this problem, increasing the voltage between the electrodes causes excessive current to flow locally, damaging the filter.

Further, in the case of FIG. 6, a large number of through holes 11 are provided in the cylindrical filter 1, one opening of each through hole 11 is closed with an electrode plate 12, and an electrode wire 13 is further provided on the inner wall of the through hole 11. When electrical conduction occurs between the electrodes, 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. To provide an exhaust gas purification device which has a function of simultaneously purifying particulates and NOx while burning them, and a function of purifying unburned hydrocarbons (hereinafter referred to as HC) and CD, which are other harmful gas components. It is.

[Means to solve the problem]

As a result of intensive research in view of the above problems, the present inventors have discovered that by alternately stacking electrically insulating filters and electrodes, and by making the filter support a catalyst for removing harmful gas components,
The inventors have discovered that it is possible to provide a device that exhibits a good exhaust gas purification effect, and have completed the present invention.

That is, the exhaust gas purification device of the present invention includes at least one filter that is made of a nonflammable and electrically insulating material and that captures particulates floating in the exhaust gas, and at least one electrode that is alternately stacked with the filter. By applying a voltage between adjacent electrodes, the electrically conductive and combustible particulates captured by the filter are heated by electricity and incinerated within the filter at any time. is supported, and the catalyst reduces harmful gas components in exhaust gas.

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 the 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, the better the electrode 2.
However, in order to improve particulate collection efficiency and reduce manufacturing costs,
It is desirable to have a thickness of 11IllI1 or more. As for the form of the electrode, a wire mesh 2as, a bunch metal plate 2b, a flat plate 2c, etc. as shown in FIG. 2 are preferable. The hollow lower surface of the laminate made of these filters and electrodes is closed with an insulating shielding plate 6, and is fixed to the housing 5 with bolts.

Each electrode 2 is connected to every other end of the filter 1, one set is connected to the ground electrode 7, and the other set is connected to the non-grounded electrode 8, so that a voltage is applied between the adjacent electrodes across the filter. It is supposed to take a while.

The filter 1 is made of a material with high insulation properties and heat resistance, such as ceramics such as cordierite, 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 are preferable. The housing 5 is preferably made of a material having heat resistance, corrosion resistance, and strength, such as stainless steel.

A catalyst is supported in the filter 1.

As a catalyst, it burns or ignites HC and particulates, and also produces NOx by HC and particulates.
For the purpose of promoting the reduction of (a) an alkali metal and (b) groups rB, group IIA, and nB of the periodic table at relatively low temperatures,
1 selected from the group consisting of transition metals including group members and Sn
A material consisting of a species or two or more kinds of elements and (c) a rare earth element is used. Due to the presence of these catalysts, HC and particulates in the exhaust gas act as reducing agents even at relatively low temperatures, effectively reducing NOx. This is considered to be because NOX in the exhaust gas is effectively reduced due to the synergistic effect caused by the coexistence of alkali metals, transition metals, and rare earth elements with particulates.

Further, as a catalyst for purifying residual hydrocarbons and CD, a catalyst containing a platinum group element or Rh having high oxidizing ability can be used. This may be a pt-based catalyst, a Pd-based catalyst, or a Rh-based catalyst, a mixed catalyst of pt-based, Pd-based, or Rh-based, or a mixed catalyst of pt-based, Pd-based, and Rh-based. Moreover, gold or silver can be further supported on the above-mentioned platinum group catalyst.

In the present invention, the above two types of catalysts may be used alone or at the same time, but if they are used at the same time, they are supported separately in two parts of the filter. is desirable.

In that case, NOX using IIc and particulates
The reduction catalyst is set on the exhaust gas inlet side of the filter, that is, on the inner peripheral side in FIG. Further, a platinum group catalyst for purifying residual hydrocarbons and CO is set on the exhaust gas outlet side of the filter, that is, on the outer peripheral side.

When the filter and catalyst are installed in this way, the purification effect of exhaust gas will be further improved.

That is, LTC and particulates are effectively combusted or ignited by reaction with oxygen on the surface of the catalyst supported on the exhaust gas inlet side. At the same time, HC and particulates act as reducing agents to reduce NDX, and particulates and NOx are effectively removed simultaneously. Then, on the outlet side, the CO and still remaining HC in the exhaust gas are effectively purified by the residual oxygen. Further, since the exhaust gas is purified efficiently, no sudden pressure loss occurs.

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 CO 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 fine particles gradually accumulate, conduction occurs through the fine particles by applying a voltage between adjacent electrodes 2.2, and the fine particles are incinerated by the heat generated by the current. After this, the conduction is cut off due to the incineration of the particles, and the generation of heat due to the 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 H['5NOX and CO are also purified.

In the present invention, since the filter 1 and the electrode 2 are alternately stacked, the electrode 2 penetrates through the filter 1 from the inlet side to the exhaust side, so that no matter where particulates accumulate on the filter, they will not pass through the particulates. conduction, thereby incinerating fine particles.

In FIG. 1, the exhaust passage may be directed in the opposite direction to that of the previous embodiment. That is, the direction is from the bottom to the top of the figure. In that case, the gas passes through the filter 1 from the outer circumferential side to the inner circumferential side, but the action and effect are the same as those described above.

FIG. 3 shows another embodiment. In this case, instead of the insulator 4 in FIG. 1, the filter 1 and the electrode 2 are stacked around a heat-resistant ceramic tube 9 with one end sealed and a small hole IO made in the side wall corresponding to the filter. It was made into a state. By doing so, higher temperature exhaust gas can be used. It also increases the strength of the entire device.

〔Example〕

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

Example 1 The device shown in FIG. 3 was installed in the middle of the exhaust passage of a diesel engine. Filter 1 uses glass wool with a thickness of 1
A plate molded into a mm-thick plate was used.

The electrode 2 has a wire mesh shape made of copper as shown in 2a in Fig. 2 for the ground electrode, and a flat stainless steel am electrode shown as 2C in Fig. 2 as the non-ground electrode, both of which have a thickness of 1 mm. Using. The ceramic tube 9 was made from cordierite.

A DC voltage of 24 V was continuously applied between the electrodes while flowing exhaust gas. As a result of detecting the pressure difference (pressure loss) of the exhaust gas at the inlet and outlet of the housing 5 and the magnitude of the current flowing between the electrodes, the pressure difference became small immediately after the maximum current of 3 A flowed. This confirmed that combustion of particulates occurs when the amount of particulates trapped in the filter reaches a level that allows conduction of electric current.

Example 2 A mullite filter was coated with 10% by weight of alumina by an impregnation method, and 0.5% by weight of PT was supported on the alumina as a catalyst. Using the apparatus shown in FIG. 3 using this filter, the same voltage as in Example 1 was applied to detect the pressure difference and current.

At the same time, NOx and CO2 are generated at the entrance and exit of the housing.
The concentration of 1HC was analyzed continuously.

As a result, the pressure difference became small immediately after the maximum current of 2.5 A flowed. Also, the analysis value of the gas concentration at that time is the first
As shown in the table, CD and ) IC are significantly reduced, and NOx
It was also confirmed that there was a slight decrease in

Table 1 Table 1 Example 3 A mullite filter was coated with 10% by weight of alumina by an impregnation method, and 2% by weight of Cu and Ce were each supported on the alumina as catalysts.

Using the apparatus shown in FIG. 3 using this filter, pressure loss and exhaust gas purification characteristics were evaluated in the same manner as in Example 2.

As a result, the pressure difference became small immediately after the maximum current of 2.2 A flowed. Also, the analysis value of the gas concentration at that time is the second
As shown in the table, it was confirmed that NOX and HC were reduced.

〔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 since incineration of particulates is possible over the entire filter area, it maintains high performance for a long period of time. be able to.

In addition, since a catalyst is supported within the filter, the ignitability of particulates is increased, resulting in NOxSHC.

Harmful gas components such as CD 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. 6 is a cross-sectional view showing an exhaust gas purification device according to another embodiment of the invention, and FIGS. 4, 5, and 6 are cross-sectional views showing conventional devices. 1... Filter 2... Electrode 3... Exhaust passage 5... Housing 7... Grounded electrode 8... Non-grounded electrode 9... Ceramic tube

Claims (7)

[Claims] (1) It is made of a nonflammable and electrically insulating material and has at least one filter that captures particulates floating in exhaust gas, and at least one electrode that is stacked alternately with the filter, and has a gap between adjacent electrodes. In an exhaust gas purification device, the electrically conductive and combustible particulates captured by the filter are heated by electricity and incinerated at any time in the filter by applying a voltage to the filter, and the filter supports a catalyst. . An exhaust gas purification device, wherein harmful gas components in exhaust gas are reduced by the catalyst. (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. (5) In the exhaust gas purification device according to any one of claims 1 to 4, the catalyst includes (a) an alkali metal element;
(b) one or more elements selected from the group consisting of Group IB, Group IIA, Group IIB of the periodic table, transition metals, and Sn; and (c) one element selected from rare earth elements. Or an exhaust gas purification device characterized by comprising two or more types of elements. (6) The exhaust gas purification device according to any one of claims 1 to 4, wherein the catalyst is made of one or more elements selected from the group consisting of platinum group elements and Rh. Purification device. (7) In the exhaust gas purification device according to claim 5, the catalyst is selected from the group consisting of platinum metal elements and Rh in addition to those selected from (a), (b), and (c). An exhaust gas purification device comprising one or more elements.