Exhaust gas purification system

Abstract

The present invention provides an exhaust gas purification device that can prevent or suppress the peeling of the catalyst layer from the substrate. [Solution] An exhaust gas purification device in which a catalyst carrier 5, on which a catalyst 7 is supported on a base material 6, is housed inside a casing 4, and a number of flow channels 8 for guiding and circulating incoming exhaust gas G are provided dispersed on the catalyst carrier 5 within a plane intersecting the streamlines of the incoming exhaust gas, wherein the amount or thickness of the catalyst coating in the flow channels in a predetermined first region, which includes a predetermined area centered on the location with the largest amount of incoming exhaust gas and is prone to temperature rise, is less or thinner than the amount or thickness of the catalyst coating in the flow channels in a second region other than the first region.

Description

Technical Field

[0001] The present invention relates to an apparatus for purifying exhaust gas by removing substances that pollute the atmosphere, such as hydrocarbons, from the exhaust gas generated by combustion.

Background Art

[0002] Purification of exhaust gas is a process of oxidizing or reducing carbon monoxide, hydrocarbons, or nitrogen oxides in the exhaust gas to render them harmless by bringing the exhaust gas into contact with a catalyst. In order to perform this process efficiently, an exhaust gas purification apparatus is configured to pass the exhaust gas through a gas flow path formed by the catalyst. The catalyst contains a catalytic active substance such as a noble metal, and since it itself has low rigidity or strength to maintain a predetermined structure, generally, the catalyst is supported on a heat-resistant substrate and configured as an exhaust gas purification apparatus. An example thereof is described in Patent Document 1.

[0003] The apparatus described in Patent Document 1 is an apparatus configured to purify, for example, exhaust gas discharged from an automobile engine, and is configured by disposing a honeycomb carrier having a catalyst supported thereon in an exhaust gas flow path. The honeycomb carrier has a large number of through passages with a hexagonal cross section, and the surface thereof is covered with a catalyst layer. Therefore, while the exhaust gas flows through the through passages, the exhaust gas comes into contact with the catalyst, and reactions such as oxidation and reduction occur, thereby purifying the exhaust gas. The flow velocity of the exhaust gas flowing through the exhaust gas flow path, similar to a general fluid, is fast at the central portion of the flow path cross section and slow at the peripheral portion close to the flow path wall surface. Similarly, in the honeycomb carrier, the exhaust gas is concentrated at the central portion, and the flow velocity of the exhaust gas becomes slow at the peripheral portion and the amount of exhaust gas decreases. In order to correct such a bias in the amount of exhaust gas and improve the purification performance, in the apparatus of Patent Document 1, the thickness of the catalyst layer at the central portion of the honeycomb carrier is made thicker than the thickness at the peripheral portion. By doing so, in the apparatus described in Patent Document 1, the aperture ratio at the central portion of the honeycomb carrier becomes smaller than the aperture ratio at the peripheral portion, so that the exhaust gas is dispersed to the peripheral portion, and the flow rate of the exhaust gas is made uniform as a whole for the honeycomb carrier.

Prior Art Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-022873 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] As described in Patent Document 1, the catalyst is supported on a substrate such as a honeycomb structure and exposed to exhaust gas in that state, causing its temperature to rise due to the heat of the exhaust gas and the heat of reaction from oxidation reactions. Such temperature changes cause thermal expansion and contraction of the substrate and the catalyst layer, but since the thermal expansion coefficients of the substrate and the catalyst layer are different, the difference in the amount of thermal deformation between the substrate and the catalyst layer due to temperature changes becomes the force (strength) that peels the catalyst layer from the substrate. The resulting so-called peeling force increases with larger temperature changes and with thicker catalyst layers (or with a larger amount of catalyst coating). Therefore, as described in Patent Document 1, if the thickness of the catalyst layer is increased in the central part of the honeycomb support where exhaust gas tends to concentrate, the combination of large temperature changes (rises) and a thick catalyst layer can lead to accelerated peeling of the catalyst layer in the central part of the honeycomb support, potentially causing a premature decline in the purification performance of the catalyst support or exhaust gas purification device and shortening its service life.

[0006] This invention has been made in view of the above technical problems, and aims to provide an exhaust gas purification device that can prevent or suppress the peeling of the catalyst layer from the substrate. [Means for solving the problem]

[0007] To achieve the above objective, the present invention provides an exhaust gas purification device in which a catalyst carrier, on which a catalyst is supported on a substrate, is housed inside a casing, and a number of channels for guiding and circulating incoming exhaust gas are provided on the carrier, dispersed within a plane intersecting the streamlines of the incoming exhaust gas, characterized in that, among the number of channels, the amount or thickness of the catalyst coating in the channels in a predetermined first region, which includes a predetermined area centered on a large amount of incoming exhaust gas and is prone to temperature rise, is less or thinner than the amount or thickness of the catalyst coating in the channels in a second region other than the first region.

[0008] In the present invention, the first region may include the central part of the surface.

[0009] In the present invention, the carrier has an electrode to which a voltage is applied for heating the carrier, and the first region may include a predetermined range centered on the electrode. [Effects of the Invention]

[0010] In this invention, the temperature in the first region tends to become higher than the temperature in the second region due to factors such as the concentration of exhaust gas. Consequently, thermal deformation occurs in the catalyst in response to the temperature change in the first region. However, because the amount or thickness of the catalyst coating in the first region is less or thinner than in the second region other than the first region, the strength associated with thermal deformation is reduced, and as a result, peeling of the catalyst from the substrate is prevented or suppressed. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view showing one embodiment of the present invention. [Figure 2] The following are partial cross-sectional views showing an enlarged portion of the flow path: (a) is a partial cross-sectional view of section A in Figure 1, and (b) is a partial cross-sectional view of section B in Figure 1. [Figure 3]An embodiment of the present invention, an S / C catalyst, is shown, where (a) is an external view and (b) is a temperature distribution diagram when the catalyst is cross-sectioned along line bb in (a). [Figure 4] An electrothermal catalyst as an embodiment of the present invention is shown, where (a) is a perspective view of the catalyst support and (b) is a cross-sectional view of the catalyst support. [Modes for carrying out the invention]

[0012] Next, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the embodiments described below are merely examples of how the present invention can be implemented and do not limit the invention.

[0013] Figure 1 shows a schematic cross-sectional view of one embodiment of the present invention. The catalyst device 1 shown in Figure 1 is an example of an under-floor (U / F) catalyst and is located in the middle of the exhaust system of an engine (not shown), connected between an inlet pipe 2 that introduces exhaust gas and an outlet pipe 3 that discharges purified exhaust gas. The basic configuration of the catalyst device 1 may be the same as that of conventionally known automotive catalyst devices, in which a catalyst carrier 5 is housed inside a cylindrical casing 4, and the exhaust gas G introduced from the inlet pipe 2 is passed through the catalyst carrier 5. The outer diameter of the catalyst carrier 5 is larger than the inner diameter of the inlet pipe 2 and the outlet pipe 3, and therefore the casing 4 is provided with a tapered inlet section 4a and an outlet section 4b.

[0014] The catalyst support 5 is constructed by supporting a coating material 7 containing a catalytically active substance on a predetermined substrate 6. The substrate 6 may be a conventionally known substrate such as a honeycomb structure or mesh material as described in the aforementioned Patent Document 1, and its material may be a heat-resistant material such as ceramic or metal. Therefore, numerous through passages are formed in the substrate 6, and the coating material 7 covers the surface of the substrate 6, so that the inner surface of the through passages is covered by the coating material 7, which forms a flow path 8 for the exhaust gas G. Figure 2 shows an enlarged cross-sectional view of the flow path 8. Therefore, numerous flow paths 8 are provided, dispersed in a plane perpendicular or orthogonal to the streamlines L of the exhaust gas G. The coating layer (catalyst layer) made of the coating material 7 may be a BF coat (black fluoro compound coating).

[0015] In the configuration shown in Figure 1, the exhaust gas G flows towards the center of the catalyst support 5 and is diffused to the periphery of the catalyst support 5 by the inlet 4a. In this case, the flow rate of the exhaust gas G is higher in the center of the catalyst support 5 (i.e., the center of the exhaust gas G) and lower in the periphery. Therefore, the amount of heat carried to the catalyst support 5 by the exhaust gas G is also higher in the center of the catalyst support 5 and lower in the periphery, similar to the flow rate of the exhaust gas G. As a result, the temperature distribution in the catalyst support 5 is high in the center and gradually decreases towards the periphery, as shown by line T in Figure 1.

[0016] Since the coefficients of thermal expansion of the base material 6 and the coating material 7 are different, the amounts of expansion or contraction (i.e., thermal deformation) when the temperature rises are different, and a stress (a force for peeling) acts between the two. In the embodiment of the present invention, the following configuration is adopted to suppress the peeling of the coating material 7 from the base material 6 due to the stress. FIG. 2 is a cross-sectional view showing an enlarged part of the flow path 8, (a) shows the cross-sectional shape at part A in FIG. 1, and (b) shows the cross-sectional shape at part B in FIG. 1. Part A in FIG. 1 is the central part of the catalyst carrier 5 (particularly the central part on the inflow side), and as described above, it is a part where the temperature tends to be high. Further, part B in FIG. 1 is the peripheral part of the catalyst carrier 5, and it is a part where the temperature tends to be lower than the central part. Considering such ease of temperature increase, the thickness ta of the coating material (catalyst layer) 7 in part A is thinner than the thickness tb of the coating material (catalyst layer) 7 in part B (ta < tb). Alternatively, the coating amount is less in part A than in part B. Note that part A corresponds to the first region in the embodiment of the present invention, and part B corresponds to the second region in the embodiment of the present invention.

[0017] Here, we will further explain the section A (or first region) where the thickness ta of the coating material 7 is reduced, and the section B (or second region) where the thickness tb of the coating material 7 is thicker than that of section A. Section A is essentially the part where it is expected that the temperature will easily rise, and its location and size can be predetermined through experiments or simulations using the actual equipment. Section B can be predetermined as the part other than section A. Furthermore, since the temperature distribution is continuous, the entire part other than section A does not have to be treated as a single section B (second region), but may be further divided according to how easily the temperature rises. Moreover, the thickness or amount of coating material 7 in sections A and B, or in the first region and the second region, should be different as described above, and their boundaries do not need to be clear. In other words, the change in the thickness or amount of coating material 7 does not need to be stepwise, but can change continuously. Furthermore, in the case of catalyst supports where the length of the flow path 8 is long and the temperature can be easily made uniform on the downstream side, the so-called regional division by varying the thickness or amount of such coating material 7 may be limited to a predetermined range on the upstream side in the direction of exhaust gas G flow.

[0018] In the embodiments of the present invention described above, the thickness or amount of the coating material 7 in areas where the temperature rises due to the introduction of exhaust gas G is made thinner or less than in other areas where the temperature does not particularly rise. Therefore, the peeling force due to the rise in temperature is avoided or suppressed in the aforementioned area A (or first region), and the peeling of the coating material 7 from the substrate is prevented or suppressed, thereby maintaining good purification performance and durability.

[0019] The location where temperature rise is likely to occur in the present invention is not limited to the central part of the catalyst carrier 5, and depending on the configuration of the exhaust gas purification device or the shape of the casing and the catalyst carrier, it may be a location deviated from the central part of the catalyst carrier. FIG. 3 shows an example of an S / C catalyst (Start Converter) 10 provided following an exhaust manifold (not shown), where (a) is an external view and (b) is a diagram showing the temperature distribution in a cross-section along line b-b in (a).

[0020] In this S / C catalyst 10, since the inflow pipe 11 is connected to a location offset from the center to the outer peripheral side of the casing 12, there is a bent portion 13 that bends significantly at the location from the inflow pipe 11 to the catalyst carrier 14 inside the casing 12. Since the exhaust gas is bent and flows at the bent portion 13, the exhaust gas concentrates at the offset location on the outer peripheral side of the catalyst carrier 14. That is, the location surrounded by a line in (b) of FIG. 3 is the first region R1 where temperature rise is likely to occur, and the outside thereof is the second region R2. Therefore, in the S / C catalyst 10 shown in FIG. 3, the thickness or amount of the coating material in the first region R1 that is offset to the outer peripheral side of the catalyst carrier 14 is thinner or less than that in the second region R2. As a result, peeling of the coating material at the location where the temperature becomes high can be prevented or suppressed.

[0021] FIG. 4 shows an example of an electric heating catalyst (EHC). FIG. 4 shows the catalyst carrier 21 of the EHC, where (a) is a perspective view and (b) is a cross-sectional view. In the example shown here, positive and negative electrodes 22a, 22b for passing an electric current for heating are provided at two opposing locations on the outer peripheral portion of the catalyst carrier 21. The temperature distribution when an electric current is passed for heating is shown in (b) of FIG. 4. The current density becomes high and the temperature is likely to rise in the vicinity of the positive electrode 22a. This portion is defined as the first region R1, and the other portion is defined as the second region R2. And the thickness or amount of the coating material in the first region R1 is thinner or less than that in the second region R2. As a result, peeling of the coating material at the location where the temperature becomes high can be prevented or suppressed.

[0022] The embodiments of the present invention have been described above. However, the present invention is not limited to the configurations shown in the embodiments described above, and the shape of the catalyst carrier and the casing that houses it may be an appropriate shape as needed. Also, the amount and thickness of the coating material may be set to an amount or thickness that does not impair the purification performance. Therefore, the amount and thickness of the coating material in a region where the temperature is likely to rise may also be appropriately set within a range of an amount or thickness that does not impair the purification performance.

Explanation of Signs

[0023] 1 Catalyst device 2 Inflow pipe 3 Outflow pipe 4 Casing 4a Introduction part 4b Derivation part 5 Catalyst carrier 6 Base material 7 Coating material 8 Flow path 10 Catalyst 11 Inflow pipe 12 Casing 13 Bend part 14 Catalyst carrier 21 Catalyst carrier 22a Positive electrode 22a, 22b Electrodes G Exhaust gas L Streamline R1 First region R2 Second region ta, tb (Thickness of the) coating material

Claims

1. An exhaust gas purification device is provided in which a catalyst carrier, on which a catalyst is supported on a substrate, is housed inside a casing, and numerous flow channels for guiding and circulating incoming exhaust gas are provided on the carrier, dispersed within a plane that intersects the streamlines of the incoming exhaust gas, Of the numerous flow paths, the amount or thickness of the catalyst coating in a flow path located in a predetermined first region where temperature rise is likely to occur, including a predetermined area centered on the location where the amount of exhaust gas flowing in is greatest, is less or thinner than the amount or thickness of the catalyst coating in a flow path located in a second region other than the first region. An exhaust gas purification device characterized by the following features.

2. An exhaust gas purification device according to claim 1, The first region includes the central part of the surface. An exhaust gas purification device characterized by the following features.

3. An exhaust gas purification device according to claim 1, The carrier has electrodes to which a voltage is applied for heating the carrier. The first region includes a predetermined range centered on the electrode. An exhaust gas purification device characterized by the following features.

Images