JPS59186623A - Filter for purifying waste gas - Google Patents

Abstract

PURPOSE:To reduce the pressure loss and to make the filter small-sized without reducing the fine particle collecting efficiency of the waste gas filter by forming a cell of a ceramic porous body appearing in the cross section at right angles to the flow direction of a waste gas, into an elliptic shape. CONSTITUTION:The waste gas purifying filter 1 consists of a ceramic porous body 2 having a three-dimensional network skeleton structure and an internal communicated space therein, and the meshes 3 (cells of the ceramic porous body), appearing in a cross section 4 at right angles to the flow direction of the waste gas, are formed into an elliptic shape whereof the size ratio of the major axis to the minor axis is regulated to >=1.2. The 50-100cells/in., 0.25-0.7 bulk density, and 74-91% void ratio are desirable.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas purification filter that purifies the exhaust gas by collecting fine particles such as carbon in the exhaust gas discharged from a diesel engine or the like.

Recently, soot, benzpyrene, etc. emitted by diesel engines have been viewed as a pollution problem, and in the United States, for example, legislation is being enacted to regulate particulates in automobile diesel engine exhaust gas.

As a means for collecting such fine particles, it has been proposed to use a ceramic porous body having a three-dimensional network skeleton structure having an internal communication space serving as an exhaust gas passage as an exhaust gas purification filter discharged from an engine or the like. This ceramic porous body is obtained by attaching ceramic slurry to an organic 7-ohm structure having a large number of communicating pores and firing it. This type of ceramic porous body was used as an exhaust gas purification filter. In this case, turbulence occurs when the exhaust gas from the engine passes through the internal communication space, so there is sufficient collision and contact between the exhaust gas and the ceramic porous lattice, which can efficiently collect particulates. It is.

In this case, it is desirable that the exhaust gas purification filter made of the above-mentioned ceramic porous body has as high a collection efficiency as possible for fine particles such as carbon, has as low a pressure loss as possible, and is small in size. By using such a filter, it can be installed in a narrow space and can efficiently purify exhaust gas without affecting engine output.

However, increasing the collection efficiency of carbon and other particulates in the exhaust gas by an exhaust gas purification filter and reducing the pressure loss by the filter are in a contradictory relationship, and it is difficult to improve If a fine filter is used, the particle collection efficiency will be improved, but the pressure loss will increase.On the other hand, if a soft filter made of a foam with a large cell size is used, the pressure loss will be reduced, but the particle capture efficiency will be increased. Collection efficiency decreases.

In addition, if a filter with a long exhaust gas passage is used, the efficiency of collecting particulates will improve, but the pressure loss will increase; on the other hand, if a filter with a short exhaust gas passage is used, the pressure loss will be reduced, but the The collection efficiency of fine particles decreases. For this reason, conventionally, the car? In order to maintain both the collection efficiency of fine particles and the pressure loss due to the filter within an appropriate range, we selected the cell size of the foam, which is the base material for filter production, and adjusted the coarseness of the filter as appropriate. At the same time, efforts have been made to optimize the shape, dimensions, etc. of the filter, but it is quite difficult to satisfy the contradictory demands of reducing output loss without reducing the collection efficiency of the filter.

Furthermore, since engine back pressure generally increases when an exhaust gas purification filter is installed, it is desirable to keep the pressure loss through the filter as low as possible. Although it is advantageous to make the filter wider, in reality it is required to make the filter as small as possible due to constraints on the filter mounting space. Although it is necessary to fully optimize the design, it is also difficult to downsize the filter while suppressing an increase in pressure loss.

In view of the above circumstances, the present inventors have been working hard to reduce the pressure loss and downsize the exhaust gas purification filter made of the ceramic porous body without reducing the particulate collection efficiency. Even with the same filter, there are some differences in p pressure drop and particulate collection efficiency due to the anisotropy of the cell shape of the porous ceramic material and, therefore, the anisotropy of the resulting filter mesh. I thought about this and did a lot of research. That is, the present inventors
First, a flexible polyurethane foam having approximately elliptic spherical cell spaces was manufactured, and thereby a ceramic porous body having an elliptic spherical cell shape (internal communication space) was manufactured. An exhaust gas purification filter using this ceramic porous body in which the long axis direction of the sled cell is 1n angle with the exhaust gas flow direction (the shape of the mesh that appears in the cross section perpendicular to the exhaust gas flow direction is approximately An elliptical filter) and an exhaust gas purification filter with the cell length direction parallel to the exhaust gas flow direction (the mesh shape that appears in the cross section perpendicular to the exhaust gas flow direction is approximately circular) Two types of filters of the same size were manufactured, and the pressure loss and particulate collection efficiency of these two filters under the same conditions were measured and compared. As a result, although the exhaust gas purification filter is made of ceramic porous bodies of the same size and cells of the same shape, the former filter has an elliptical mesh that appears in the cross section perpendicular to the flow direction of the exhaust gas. In particular, when the length/breadth dimension ratio of the mesh (ceramic porous material cells) is 1.2 or more, compared to a filter in which the mesh that appears in the cross section perpendicular to the flow direction of the exhaust gas is circular. The pressure loss of the former filter is 60 to 8 times lower than that of the latter filter.
Surprisingly, it was found that there was almost no significant difference in particle collection efficiency between the two filters. In other words, in a filter in which the major diameter force of the mesh is perpendicular to the exhaust gas flow direction, the mesh size on the surface perpendicular to the exhaust gas flow direction is large, which may have led to a reduction in pressure loss, but carbon black Contrary to the prediction that the collection efficiency of such fine particles would similarly decrease, there was no decrease in the collection efficiency, and the collection efficiency was the same and only the pressure loss was reduced to a level of 60 to 80%. This fact was completely unknown until now, and was discovered by the present inventors for the first time. The present inventors have developed an engine exhaust gas purification filter made of a ceramic porous body by forming the cell shape, which appears in the cross section perpendicular to the exhaust gas flow direction, into an elliptical shape. A cell structure in which a large number of substantially elliptic spherical cell spaces are arranged in a certain direction is used, and the elliptical cell spaces of this ceramic porous body are arranged so that the major axis direction thereof is perpendicular to the flow direction of engine exhaust gas. By constructing a filter in which the cell shape that appears in the cross section perpendicular to the direction of flow of exhaust gas is elliptical, the above objectives are effectively achieved, and the particle collection efficiency is high and the pressure loss is reduced. The present invention was based on the full knowledge that it is possible to obtain a low-cost and compact exhaust gas purification filter.

The present invention provides an exhaust gas purification filter made of a ceramic porous body with a three-dimensional network skeleton structure having internal communication spaces, in which the shape of the cells of the ceramic porous body that appears in a cross section perpendicular to the flow direction of exhaust gas is elliptical. According to the exhaust gas purification filter of the present invention, compared to conventional filters, the efficiency of collecting fine particles such as carden in the exhaust gas of diesel engines was maintained at the same level even with the same size filter. 1. In addition, pressure loss can be reduced, and since pressure loss can be reduced in this way, engine back pressure does not increase, and it can contribute to improving the fuel efficiency of diesel engines. If it is made equal to , the filter can be made smaller and it is also useful for resource saving.

The present invention will be explained in more detail below.

The exhaust gas purification filter 1 according to the present invention, as shown in FIG. The shape of the mesh (cells of the ceramic porous body) 3 that appears in the cross section 4 in the perpendicular direction is formed into an elliptical shape.

Here, as the ceramic porous body 2, one having a cell structure in which a large number of elliptical spherical cell spaces are arranged in a fixed direction can be suitably used. By manufacturing an engine exhaust gas purification filter by arranging the long diameter direction to be perpendicular to the flow direction of engine exhaust gas, the mesh of the filter 1 that appears in the cross section perpendicular to the flow direction of engine exhaust gas (Cells of porous body 2) 3 can be formed into an elliptical shape.

Further, it is preferable that most or all of the elliptical meshes (cells) 3 have an elliptical shape with a dimension ratio of the major axis to the minor axis of 1.2 or more, more preferably 1.25 or more; It is possible to reliably collect particulates such as carden in exhaust gas without increasing pressure loss.

Here, the exhaust gas is introduced into the purification filter from any appropriate direction, such as horizontally or diagonally upward, but in this case, it is more preferable that the cross section in the direction perpendicular to the exhaust gas introduction direction also has the aforementioned elliptical shape. .

Note that the ceramic porous body has cells of pl per inch.
Preferably, the number is 0 to 50. If the number of cells is less than 10 cells/inch, particulates in the engine exhaust gas are likely to escape easily, the internal reception effect will not be sufficiently exhibited, and fine particulates may not be reliably removed. Furthermore, if the number of cells is 51 cells/inch or more, the pressure loss will be large and the strength will be weakened, which is not preferable for use in vibrating applications such as automobiles. The preferred number of cells is 15 to 30 cells/inch; within this range, excellent internal filtration action can be achieved, even fine particulate matter can be reliably removed, and the pressure loss can be minimized. can be made smaller to achieve efficient processing.

Further, the above ceramic porous body has a bulk specific gravity of 0.25
It is preferable to set it in the range of ~0.7, and the bulk specific gravity is sail 25
If the bulk specific gravity is smaller than 0.7, the strength may be insufficient and there may be a problem in usability for removing particulates from exhaust gas, and if the bulk specific gravity is larger than 0.7, clogging will easily occur and the efficiency will be reduced. There may be cases where the desired processing is not achieved.

Note that the most preferable bulk specific gravity range for capturing particulate rate is 0.3 to 0.5.

Furthermore, the ceramic porous body has a porosity of 74 to 91%.
It is preferable that the pressure loss of air is 0.1 to 75 mm in water column when passing through a thickness of 1 cm at a wind speed of 1 m/s.

In the present invention, the ceramic porous body having the substantially ellipsoidal cell spaces is produced by attaching a ceramic slurry to an organic foam structure without a cell membrane and sintering this to carbonize and remove the organic foam. It can be suitably manufactured. In this case, the organic heptadome structure is
In the manufacturing process, it is preferable that the PL is manufactured so as to form a substantially elliptical spherical cell space by sufficiently raising the gas generated in the foaming process from the organic foam to desorb and dissipate. By using Maki's organic foam structure as a substrate for producing PL, it is possible to easily obtain a ceramic porous body having approximately elliptic spherical cell spaces. By forming the exhaust gas filter so that the long axis direction of the elliptical spherical cells is perpendicular to the exhaust gas flow direction, the mesh shape that appears in the cross section perpendicular to the exhaust gas flow direction can be improved. It is possible to obtain an elliptical filter.

Note that a flexible polyurethane foam without a cell membrane can be preferably used as the organic foam structure, and by forming a porous ceramic body from a flexible polyurethane foam without a cell membrane, the dodecahedral ridges can be formed. A cage-shaped porous ceramic body is obtained, which has a large porosity and can treat engine exhaust gas with little pressure loss. When passing through the internal communication space, particulate matter in engine exhaust gas can be reliably collected and removed by internal filtration.

Furthermore, when producing a ceramic porous body using an organic foam structure as a base material as described above, it is impregnated with a slurry obtained by mixing and stirring the foam all-ceramic fine powder raw material, water, an organic binder, etc., and the excess slurry is removed. is removed by centrifugation or other separation methods, thoroughly dried, and if necessary, after performing minor processing such as partial sound cleaning except for exhaust gas passages, the product is manufactured by firing under appropriate firing conditions. In this case, the material of the ceramic porous body is not particularly limited, but if it is used in a place where temperature changes are severe, it is preferable to use one containing 20% by weight or more of cordierite phase, which improves thermal shock resistance. Moreover, when used in a place where the temperature exceeds 1250° C., it is preferable to use a material with high heat resistance, especially a material containing 87% by weight or more of alumina.

EXAMPLES Hereinafter, the effects of the present invention will be specifically explained with reference to Examples and Comparative Examples.

[Example, comparative example]

Various ceramic porous bodies were manufactured using a flexible polyurethane foam without a cell membrane as a base, having a racetrack-shaped cross section of 80 cm in short axis, 17 m in long axis (1 m in length), and an elliptical spherical cell space with a length of 125 mm, using the following method. .in this case,
As the flexible polyurethane foam without a cell membrane, those having various cell numbers are used, and the A type is cut so that the major axis direction of the elliptical spherical cells is perpendicular to the longitudinal direction of the base, and the A type is cut so that the major axis direction of the elliptical spherical cells is perpendicular to the longitudinal direction of the base. Two types of B type were prepared, which were cut parallel to the length direction.

In addition, as the ceramic slurry, cordierite fine powder; l o o parts, polyvinyl alcohol 6.7 parts, )y
- A low-viscosity corsolite slurry fi was prepared by mixing 0.2 parts of sodium icate and about 150 parts of water. In addition,
The viscosity of the slurry was adjusted by adjusting the amount of water added depending on the cell size of the polyurethane foam.

Manufacturing method of ceramic porous body The above A type and B type foams are respectively impregnated into the above slurry, and the excess slurry is removed by centrifugation, air blowing, etc., and then heated with a hot air dryer or high frequency dryer. The operation of sufficiently drying was repeated until an appropriate amount of fine cordierite powder was attached to the foam skeleton.

Note that the slurry was applied to the lengthwise peripheral portion of the foam to seal it. Thereafter, the foam to which the fine cordierite powder had adhered was fired at 1200 to 1400°C for 3 hours to remove carbonization. A ceramic porous body (exhaust gas filter (example)) with a nearly elliptical shape and a ceramic porous body (exhaust gas filter (comparative example)) with a nearly circular cell shape that appears in a similar cross section from the B type foam. Obtained. Note that none of the ceramic porous bodies (filters) were clogged and had a uniform network skeleton structure.

Next, the following experiment 1.2 was conducted using the filter obtained by the above method.

Experiment 1 Using some of the above exhaust gas filters, a cube of 5 cIrL on each side was cut from these filters into a plane parallel to the major axis direction of the cell (X plane) and a plane perpendicular to the major axis direction of the cell (Y plane).
Cut out so that each side (surface) is exposed, and cut out the sample / 1
61-6 were produced. Next, the gas was allowed to flow perpendicularly from the X or Y plane of each sample at a total wind speed of 3 m/sec, and the gas was allowed to flow out from the opposite surface, and the pressure loss at this time was measured. The results are shown in Table 1. . Here, when gas is introduced from a plane parallel to the long axis direction of the cell (X plane), the shape of the cell that appears in the cross section perpendicular to the gas flow direction becomes elliptical, and When gas is introduced from a perpendicular plane (Y plane), the shape of the cell that appears in a cross section perpendicular to the gas flow direction is approximately circular. In Table 1, the average cell major axis/breadth axis ratio is the average of the ratio of the major axis to the minor axis of 20 cells appearing in a cross section perpendicular to the gas inflow direction.

Table 1 Experiment 2 In the above filter production, Example filters and Comparative Example filters were manufactured using A type and B type polyurethane foam substrates having ellipsoidal cell spaces of the same shape and the same shape, respectively. All of these were housed in cylindrical containers of appropriate size with heat-resistant sealing material sealed sufficiently to prevent exhaust gas from leaking from the gap between the container and the filter. The container is provided with an inlet and an outlet for exhaust gas, and the exhaust gas inlet is connected to the exhaust Jt.
Connected to the manifold of a 1800cc, 4-cylinder diesel engine. Next, this diesel engine was operated at a rotation speed of 1500 rpm 10 and a load of 96 m (7), and the pressure loss and particulate collection efficiency at this time were measured. The results are shown in Table 2. In Table 2, the average cell length/breadth ratio was determined in the same manner as in Table 1.

Table 2 From the results in Table 1.2, it is clear that filters in which the shape of the cells appearing in the direction perpendicular to the exhaust gas flow direction are elliptical, and in particular, the ratio of the major axis to the minor axis is 1.2 or more, have a low pressure loss. It was observed that the particle capture efficiency was low and the particle capture efficiency was high.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an exhaust gas purification filter according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of the same filter taken along the line ■-■. DESCRIPTION OF SYMBOLS 1... Exhaust gas purification filter, 2... Ceramic porous body, 3... Cell, 4... Surface perpendicular to the exhaust gas flow direction. Applicant Brideston Tire Co., Ltd. Agent Patent Attorney Takashi Kojima

Claims (1)

[Scope of Claims] 1. In an exhaust gas purifying filter made of a ceramic porous body with a three-dimensional network-like structure having an internal communication space, cells of the ceramic porous body that appear in a cross section perpendicular to the flow direction of the exhaust gas. An exhaust gas purification filter characterized by having an elliptical shape. 2. The ceramic porous body has a cell structure in which a large number of substantially elliptical spherical cell spaces are arranged in a certain direction, and the major axis direction of the elliptic spherical cell spaces of this ceramic porous body is perpendicular to the flow direction of exhaust gas. 2. The exhaust gas purification filter according to claim 1, wherein the cells are arranged in such a manner that the shape of the cells appearing in the cross section in the plane angle direction with respect to the flow direction of the exhaust gas is formed into an elliptical shape. 3. A patent claim in which the shape of most or all of the cells of the ceramic porous body appearing in a cross section perpendicular to the direction of flow of engine exhaust gas is an ellipse with a dimension ratio of the major axis to the minor axis of 1.2 or more The exhaust gas purification filter according to item 1 or 2.