Honeycomb unit and catalytic converter

Abstract

This design enables radial exhaust gas flow without compromising the effect of the offset section (turbulence generation), thereby improving the purification performance of the catalytic converter in the presence of flow deviations. [Solution] A honeycomb unit for supporting a catalyst used in exhaust gas purification, comprising a honeycomb body formed by laminating a metal flat foil and a corrugated foil, and an outer cylinder positioned to surround the outer surface of the honeycomb body, wherein the corrugated foil has offset portions in which the phases of the fins are different at the front and rear in the axial direction of the honeycomb body, and the flat foil has a plurality of holes formed therein.

Description

Technical Field

[0001] The present invention relates to a catalytic converter, and particularly to a honeycomb unit for supporting a catalyst used in a catalytic converter for purifying exhaust gas of an internal combustion engine such as an automobile.

Background Art

[0002] As a device for purifying exhaust gas of an internal combustion engine such as an automobile, a catalytic converter in which a catalyst is supported on a honeycomb unit configured by fitting a honeycomb body made of a heat-resistant alloy into an outer cylinder made of the same alloy is used. <00000I3> In recent years, regulations on emissions of harmful substances such as carbon monoxide, hydrocarbons, and nitrogen oxides contained in exhaust gas of automobiles and the like have become extremely strict. As the honeycomb body constituting the catalytic converter, those formed by alternately laminating a metal flat foil having a thickness of about 50 μm and a corrugated foil obtained by corrugating the flat foil, or those formed by winding a strip-shaped flat foil and a corrugated foil in a spiral shape after overlapping them are used. In recent years, for the purpose of further improving the purification performance, catalytic converters capable of controlling the flow of exhaust gas by processing the metal foil constituting the honeycomb body have been increasingly used.

[0004] For example, Patent Document 1 discloses a catalytic converter in which an offset portion where the phases of fins are different from each other in the front and rear in the axial direction is provided on a corrugated foil. This offset structure is effective in generating turbulent flow, which facilitates mass transfer by the turbulent flow and can improve the purification performance.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] According to the catalytic converter disclosed in Patent Document 1, since it has a corrugated foil with an offset portion in which the phase of the fins differs at the front and rear in the axial direction, it enables exhaust gas flow not only in the axial direction but also in the circumferential direction. However, with this structure, it is not possible to flow the exhaust gas in the radial direction.

[0007] Therefore, if there is a flow bias in the exhaust gas, in the region with a high exhaust gas flow rate, the flow velocity is too high, making it easier for untreated exhaust gas to be discharged from the catalytic converter 1. Here, if there are regions with a high exhaust gas flow rate and regions with a low exhaust gas flow rate in the radial direction of the catalytic converter, and the difference in exhaust gas flow rates between these regions is approximately twice or more, then it can be considered that there is a "flow bias."

[0008] If turbulence occurs, allowing the exhaust gas to flow radially can mitigate the turbulence and suppress the outflow of untreated exhaust gas. Therefore, the present invention aims to improve the purification performance of a catalytic converter in the presence of turbulence by enabling radial exhaust gas flow without impairing the effect of the offset section (turbulence generation). [Means for solving the problem]

[0009] The present invention relates to a honeycomb unit for supporting a catalyst used in exhaust gas purification, comprising (1) a honeycomb body formed by laminating a flat metal foil and a corrugated metal foil, and an outer cylinder positioned to surround the outer circumferential surface of the honeycomb body, wherein the corrugated metal foil has offset portions in which the phases of the fins are different at the front and rear in the axial direction of the honeycomb body, and the flat metal foil has a plurality of holes formed therein.

[0010] (2) The honeycomb unit according to (1) above, characterized in that the fins are formed in a trapezoidal or rectangular shape when viewed in the axial direction of the honeycomb body.

[0011] (3) The honeycomb unit according to (1) above, characterized in that the fins are formed in a trapezoidal shape, and when viewed in the axial direction of the honeycomb body, the width of the top surface of the fins is W1, the maximum distance between the left and right sides of the fins is W2, and the height of the fins is H, the widths W1, W2, and H are each in the range of 0.5 mm to 10 mm.

[0012] (4) The honeycomb unit according to (3) above, characterized in that when the length of the fin is L and the average value of the widths W1 and W2 is taken as the average width W, the length L is 1 to 10 times the average value of the average width W and the height H.

[0013] (5) The honeycomb unit according to any one of (1) to (4) above, characterized in that the holes formed in the flat foil have a diameter or hydraulic diameter of 0.2 mm or more and 8.0 mm or less.

[0014] (6) The honeycomb unit according to any one of (1) to (5) above, characterized in that the porosity of the holes formed in the flat foil is 20% or more and 60% or less.

[0015] (7) A catalytic converter comprising a catalyst supported on a honeycomb unit as described in any one of (1) to (6) above. [Effects of the Invention]

[0016] According to the present invention, in a catalytic converter composed of a honeycomb body having an offset structure, when there is a flow bias in the exhaust gas flowing into the catalytic converter, the exhaust gas can also flow radially through the catalytic converter, thereby improving the purification performance. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram of catalytic converter 1. [Figure 2] This is a diagram of a portion of the wave foil 2 (with offset). [Figure 3]It is a perspective view of fins adjacent in the axial direction and the circumferential direction. [Figure 4] It is a perspective view showing the definition of the dimensions of the fins. [Figure 5] It is a development view of the flat foil 2. [Figure 6] It is an enlarged view of the development view of the flat foil 2.

Embodiments for Carrying out the Invention

[0018] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[0019] FIG. 1 is a schematic view of a catalytic converter viewed from the axial direction. The normal direction to the paper surface corresponds to the axial direction, and the direction along the paper surface corresponds to the radial direction. The catalytic converter 1 is configured by supporting a catalyst on a honeycomb body 4 formed by winding a flat foil 2 and a corrugated foil 3 around an axis, and an outer cylinder 5 surrounding the outer peripheral surface of the honeycomb body 4.

[0020] The cross-section of the honeycomb body 4 in the radial direction is formed in a circular shape. However, the honeycomb body 4 may be a laminate in which the flat foil 2 and the corrugated foil 3 are alternately stacked. Whether it is a wound body or a laminate, the flat foil 2 and the corrugated foil 3 are laminated in the cross-section. Stainless foil for catalyst support can be used for the flat foil 2 and the corrugated foil 3. The component system of this stainless foil will be described later.

[0021] <00=00099>FIG. 2 is a development view of a part of the corrugated foil. The white arrow corresponds to the exhaust gas conduction direction (corresponding to the above-mentioned axial direction), and the portion indicated by the hatching corresponds to the top surface of the fin F of the corrugated foil. FIG. 3 is a perspective view of the fins F adjacent to each other in the axial direction.

[0022] Referring to the unfolded view in Figure 2, the corrugated foil 3 is formed in an offset structure. Here, an offset structure is a structure in which the phases of adjacent fins F in the axial direction are different from each other, and in this embodiment, the fins F aligned in the axial direction are arranged in a staggered pattern so that they are alternating. However, the offset structure is not limited to a staggered pattern and may be other structures. Other structures will be described later. Furthermore, the offset structure may be formed on the entire corrugated foil 3 or on only a part of the corrugated foil 3. By forming the corrugated foil 3 in an offset structure in this way, the amount of exhaust gas in contact with the corrugated foil 3 is increased, and the purification performance of the catalytic converter 1 can be improved.

[0023] Each fin F has a top surface 101, a bottom surface 104, a left side surface 102, and a right side surface 103. These left side surface 102 and right side surface 103 may be perpendicular to the top surface 101, or they may be inclined in a direction that widens as they move away from the top surface 101. In other words, the fin F is formed in a rectangular or trapezoidal shape in an axial view. Figure 4, which will be described later, shows a trapezoidal fin F.

[0024] The top surfaces 101 of adjacent fins F in the axial direction are partially connected to each other. Similarly, the bottom surfaces 104 of adjacent fins F in the axial direction are partially connected to each other. Furthermore, by connecting the top surfaces 101 and bottom surfaces 104 via the left side surface 102 and the right side surface 103, adjacent fins F in the circumferential direction are also connected to each other. This allows a corrugated foil 3 containing staggered fins F to be formed from a single sheet of material.

[0025] Referring to Figure 4, for each fin F, when the width of the top surface 101 is W1, the width on the opposite side (in other words, the maximum distance between the left side surface 102 and the right side surface 103) is W2, the height of the fin F (in other words, the height of the trapezoid) is H, and the length of the fin is L, it is preferable to set the values ​​of W1, W2, and H to be between 0.5 mm and 10 mm, respectively. This numerical range can also be applied to the rectangular fin F (W1=W2) shown in Figure 3. If it is less than 0.5 mm, the cells are too fine and the pressure drop becomes too high. On the other hand, if it is 10 mm or more, the turbulence generation effect is insufficient. In other words, the values ​​of W1, W2, and H can be, for example, 0.5mm, 1.0mm, 1.5mm, 2.0mm, 2.5mm, 3.0mm, 3.5mm, 4.0mm, 4.5mm, 5.0mm, 5.5mm, 6.0mm, 6.5mm, 7.0mm, 7.5mm, 8.0mm, 8.5mm, 9.0mm, 9.5mm, 10.0mm, etc., and are not limited to these; values ​​between each of the dimensions exemplified here are also acceptable.

[0026] Regarding the value of L, it is preferable to take a value equal to or greater than the average value of W and H, with W being the average of W1 and W2. If the value is smaller than that, the number of fins F relative to the axial length of the honeycomb body 4 will be too large, resulting in excessive pressure loss. Furthermore, it is preferable to take a value of 10 times or less the average value of W and H. In the corrugated foil 3, exhaust gas can flow radially through the offset connection portion OC shown in Figures 3 and 4, so if the number of offset connection portions OC is too small, the radial flow of exhaust gas will be insufficient, even if the flat foil 2 has openings. In summary, a desirable value for L is between 1 and 10 times the average values ​​of W and H.

[0027] Figure 5 is an unfolded view of a portion of the flat foil 2. In the figure, the X-axis direction corresponds to the exhaust gas conduction direction in the honeycomb body 4 (i.e., the axial direction of the honeycomb body 4), and the Y-axis direction is perpendicular to the X-axis and corresponds to the longitudinal direction of the flat foil 2. Referring to the figure, the flat foil 2 has multiple holes 8 that penetrate in the thickness direction to allow the exhaust gas to flow radially.

[0028] The holes 8 can be formed in a staggered pattern along the X-axis in the region of the flat foil 2 excluding the gas inlet end T in the exhaust gas conduction direction. Here, "staggered pattern" means that the next row of holes 8 is arranged on an imaginary line extending in the X-axis direction, passing through the intermediate position of adjacent holes 8 in the Y-axis direction, and this arrangement is continuous in the Y-axis direction. Note that the arrangement of the holes 8 is not limited to a staggered arrangement along the X-axis direction; for example, a matrix arrangement in which the holes 8 are arranged linearly along the X-axis and Y-axis directions is also possible.

[0029] The reason for arranging the holes 8 in the region excluding the gas inlet end T in the exhaust gas flow direction is that the gas end region is susceptible to damage during exhaust gas purification, and forming holes 8 there may weaken the structure and reduce its lifespan. The range of the gas inlet end T is preferably 5 mm from the gas inlet end.

[0030] In this embodiment, the hole 8 is formed in a circular shape. The diameter of the hole 8 is preferably 0.2 mm or more. If the diameter of the hole 8 is less than 0.2 mm, the hole 8 may be blocked by the catalyst, preventing the exhaust gas in the catalytic converter 1 from flowing radially. There is no particular upper limit to the diameter of the hole 8, but it is preferably 8.0 mm or less. That is, the hole diameter can be, for example, 0.2 mm, 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 7.5 mm, 8.0 mm, etc., and is not limited to these, but may be a value between the diameters exemplified here. The shape of the hole 8 may be other than circular (for example, square or elliptical), but a circular shape is preferred considering the machinability of the hole drilling process. If the hole 8 is not circular in shape, it is preferable that the diameter of a circle with the same area as the hole 8 (i.e., the hydraulic diameter) be 0.2 mm or larger.

[0031] In this embodiment, the porosity of the holes 8 is preferably 20% or more and 60% or less. If the porosity is less than 20%, the amount of exhaust gas flowing radially through the catalytic converter 1 will be insufficient. On the other hand, if the porosity is greater than 60%, the strength of the honeycomb body 4 itself may decrease. In other words, the porosity of the holes 8 can be set to, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc., and is not limited to these values; it may be a value between the porosity approximations shown here.

[0032] Here, the open area ratio will be explained with reference to Figure 6. Figure 6 is an enlarged view of the area A enclosed by the dashed line in Figure 5. Referring to Figure 6, a triangle is drawn with the centroids of the three adjacent holes 8 (in this embodiment, the center C of hole 8) as its vertices, and the area of ​​this triangle is defined as the total area, and the area of ​​the part where the triangle and the holes 8 overlap is defined as the hole area. In this case, the open area ratio is calculated as the "ratio of the hole area to the total area". Even if the holes 8 have a shape other than a circle, the open area ratio can be similarly defined using the centroids of the holes 8. Furthermore, even if the arrangement of the holes 8 is not a staggered arrangement along the X-axis direction as shown in Figure 4 (for example, the matrix arrangement described above), the open area ratio can be calculated according to the above definition.

[0033] In the catalytic converter 1 having the above configuration, exhaust gas can also flow radially through the portions of the corrugated foil 3 that lack a top surface 103 or bottom surface 104, and through the holes 8 arranged in the flat foil 2, within the honeycomb body 4 that constitutes the catalytic converter 1. Therefore, even if there is a flow deviation in the exhaust gas flowing into the catalytic converter 1, the flow deviation is mitigated by the radial flow of the exhaust gas inside the catalytic converter 1, thereby improving the purification performance.

[0034] Metal foils made of heat-resistant alloys can be used for the flat foil 2 and corrugated foil 3. The thickness of the metal foil is preferably 20 μm to 100 μm. The width of the metal foil is preferably 10 mm to 500 mm. The size of the metal foil can be appropriately changed depending on the application of the catalytic converter 1.

[0035] Here, the most suitable heat-resistant alloy for use as the flat foil 2 and corrugated foil 3 is a ferritic stainless steel (in other words, Fe-20Cr-5Al alloy) consisting of Cr: 20 mass%, Al: 5 mass%, and the remainder being Fe and unavoidable impurities. However, the heat-resistant alloy applicable to the present invention is not limited to the aforementioned ferritic stainless steel, and various heat-resistant stainless steels containing Al in their alloy composition can be widely used. That is, the metal foil typically used in the honeycomb body 4 is a heat-resistant alloy containing 15-25 mass% Cr and 2-8 mass% Al, and Fe-18Cr-3Al alloy and Fr-20Cr-8Al alloy can also be suitably used.

[0036] For the outer cylinder 5, a ferritic stainless steel containing 13% to 20% by mass of Cr, such as SUS436L, SUS430, or EN standard 1.4509, can be used. However, it is not limited to ferritic stainless steel; austenitic stainless steel such as SUS315J1 can also be used. The thickness of the outer cylinder 2 is preferably set to 0.5 mm to 3 mm, more preferably to 1 mm to 2 mm.

[0037] The flat foil 2 and corrugated foil 3 that make up the honeycomb body 4, or the honeycomb body 4 and the outer cylinder 5, are joined using methods such as brazing or mechanical methods such as crimping. When joining by brazing, a method is used in which a highly heat-resistant Ni-based brazing material (e.g., BNi-5) is used, the brazing material is placed at the joint to be joined, and vacuum heat treatment is performed. In this way, the honeycomb unit is manufactured.

[0038] A catalytic converter 1 is manufactured by supporting a catalyst on a honeycomb unit. The catalyst can be supported on the metal foil of the honeycomb body 4 by applying a predetermined wash coat liquid to the surface of the metal foil, drying it, and firing it. For example, the wash coat liquid can be a slurry made by stirring γ-alumina powder, lanthanum oxide, zirconium oxide, and cerium oxide in an aqueous solution of palladium nitrate.

[0039] The catalytic converter 1 manufactured in this manner can be installed in the exhaust gas path of a vehicle. Vehicles include motorcycles, automobiles, and off-road vehicles. When exhaust gas flowing into the gas passage of the honeycomb structure comes into contact with the catalyst, CO, hydrocarbons, and NO contained in the exhaust gas are removed. X The gas is rendered harmless, and clean gas can be released outside the vehicle.

[0040] (Examples) Each of the embodiments described above will be explained in more detail by illustrating the examples. First, a flat foil 2 was manufactured by drilling holes in a ferritic stainless steel foil (Fe-20Cr-5Al alloy) with a thickness of 50 μm and a width of 100 mm, thereby forming circular holes in a staggered pattern. The hole diameter was 1.0 mm, and the porosity ratio was 40%. At this time, the holes were formed in positions that avoided the position up to 5 mm from the gas inlet side end (corresponding to the gas inlet side end T in the above embodiment). The definition of porosity ratio has been described above, so the explanation will be omitted. Furthermore, a ferritic stainless steel foil (Fe-20Cr-5Al alloy) with a thickness of 50 μm and a width of 100 mm was used to form fins F that satisfied the dimensional conditions of W1=4 mm, W2=4.5 mm, H=1 mm, and L=6 mm, thereby creating a corrugated foil 3.

[0041] After creating a coiled body (honeycomb body 4) with a diameter of 100 mm and a length of 100 mm by overlapping the corrugated foil 3 and flat foil 2 produced in this manner and winding them around the axial direction, an outer cylinder 5 with an outer diameter of 103 mm, a thickness of 1.5 mm, and a length of 100 mm was prepared, and the honeycomb body 4 was inserted into this outer cylinder 5. The outer cylinder 5 was made of ferritic stainless steel (SUS436L). Powdered brazing material was pre-applied to the planned joining locations of the corrugated foil 3 and flat foil 2 that constitute the honeycomb body 4, and foil brazing material was pre-applied to the outer surface of the honeycomb body 4 corresponding to the planned joining position between the honeycomb body 4 and the outer cylinder 5. Subsequently, the honeycomb body 4 inserted into the outer cylinder 5 was heat-treated at 1200°C in a vacuum atmosphere to manufacture the honeycomb unit.

[0042] Subsequently, a wash coat solution containing ceria-zirconia-lantana-alumina as the main component and 1.25 g of palladium per 100 g was passed through the honeycomb body 4 of the manufactured honeycomb unit. After removing the excess wash coat solution, the honeycomb body was dried at 180°C for 1 hour, followed by firing at 500°C for 4 hours to produce the catalytic converter 1. A predetermined weight of wash coat layer was supported on the corrugated foil 3 and flat foil 2 of this catalytic converter 1. The predetermined weight was 200 g / L per volume of the honeycomb body 4 after drying.

[0043] Next, 1 Nm of catalytic converter 1 is supplied under standard conditions. 3 Room temperature air was flowed at a rate of / min. At this time, the average flow velocity at the inlet end face was 2.12 m / s. However, to intentionally create a flow deviation, the flow velocity distribution was controlled so that the flow velocity near the center of the inlet end face was 10 m / s (i.e., the gas flow rate at the outer periphery was minimized). In this case, the UI value, expressed by the following formula to represent the velocity distribution at the inlet end face, was 0.49.

number

[0044] As described above, according to the present invention, in a catalytic converter having a honeycomb body with an offset structure, when there is a flow bias in the exhaust gas flowing into the catalytic converter, the exhaust gas can also flow radially through the catalytic converter, thereby improving the purification performance. [Explanation of Symbols]

[0045] 1. Catalytic converter 2 Flat foil 3 wave foil 4 Honeycomb 5. Outer cylinder 8 holes 101 Tianmian 102 Left side 103 Right side view 104 Bottom

Claims

1. A honeycomb unit for supporting a catalyst used in exhaust gas purification, comprising a honeycomb body formed by laminating flat metal foil and corrugated metal foil, and an outer cylinder positioned to surround the outer surface of the honeycomb body, The aforementioned wave foil has offset portions in which the phases of the fins are different at the front and rear in the axial direction of the honeycomb body. Multiple holes are formed in the aforementioned flat foil. A honeycomb unit characterized by the following:

2. The fins are formed in a trapezoidal or rectangular shape when viewed in the axial direction of the honeycomb body. The honeycomb unit according to feature 1.

3. The fin is formed in a trapezoidal shape, In an axial view of the honeycomb body, when the width of the top surface of the fin is W1, the maximum distance between the left and right sides of the fin is W2, and the height of the fin is H, The widths W1, W2, and H are each within the range of 0.5 mm to 10 mm. The honeycomb unit according to feature 1.

4. When the length of the fin is L, and the average width W is the average value of the widths W1 and W2, The length L is between 1 and 10 times the average value of the average width W and height H. The honeycomb unit according to feature 3.

5. The holes formed in the flat foil have a diameter or hydraulic diameter of 0.2 mm or more and 8.0 mm or less. A honeycomb unit according to any one of features 1 to 4.

6. The porosity of the holes formed in the flat foil is 20% or more and 60% or less. A honeycomb unit according to any one of features 1 to 5.

7. A catalytic converter comprising a catalyst supported on a honeycomb unit according to any one of claims 1 to 6.

Images