Methane oxidation catalyst device

Abstract

This methane oxidation catalyst device is provided with: a catalyst casing that internally forms an exhaust gas flow path through which exhaust gas discharged from an internal combustion engine flows; a partition part that divides the exhaust gas flow path formed inside the catalyst casing into a plurality of parallel flow paths; a plurality of methane oxidation catalyst reactors that include a methane oxidation catalyst for promoting oxidation of methane contained in the exhaust gas, and that are respectively disposed in the plurality of parallel flow paths; and a flow rate control device that is configured so as to control the flow rate of the exhaust gas flowing through the plurality of parallel flow paths, the flow rate control device being configured such that, during low-load operation of the internal combustion engine, the number of parallel flow paths through which the exhaust gas is allowed to flow is reduced as compared to during high-load operation of the internal combustion engine.

Description

Methane oxidation catalyst device

[0001] This application claims priority to Japanese Patent Application No. 2024-056014, filed with the Japan Patent Office on March 29, 2024, the contents of which are incorporated herein by reference.

[0002] Exhaust gas discharged from an internal combustion engine that burns a fuel gas containing methane as a fuel may contain unburned methane (methane slip). A catalyst casing (methane oxidation catalyst device) containing a methane oxidation catalyst capable of oxidizing methane may be provided in the path of the exhaust gas discharged from the internal combustion engine (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2018-135809

[0004] The heat generated during methane oxidation causes a rapid rise in the exhaust gas temperature inside the methane oxidation catalyst, which can lead to thermal degradation of the catalyst. This is particularly problematic when the internal combustion engine is running at low load, as the methane content in the exhaust gas is higher than when it is running at high load, accelerating the oxidation reaction and causing a rapid rise in the exhaust gas temperature.

[0005] One possible solution to the rise in exhaust gas temperature is to bypass the methane oxidation catalyst, but this is undesirable because exhaust gas containing slip methane would be discharged outside the system. Another possible solution would be to install a heat exchanger or similar device upstream of the methane oxidation catalyst to lower the temperature of the exhaust gas being introduced to the catalyst, but this would require additional equipment to lower the exhaust gas temperature, and there would also be the issue of installation space, making this difficult to adopt.

[0006] In view of the above circumstances, an object of at least one embodiment of the present disclosure is to provide a methane oxidation catalyst device that can suppress thermal degradation of a methane oxidation catalyst during low load operation of an internal combustion engine.

[0007] A methane oxidation catalyst device according to at least one embodiment of the present disclosure comprises: a catalyst casing forming an exhaust gas flow path therein through which exhaust gas emitted from an internal combustion engine flows; a partition section dividing the exhaust gas flow path formed inside the catalyst casing into a plurality of parallel flow paths; a plurality of methane oxidation catalyst reactors each containing a methane oxidation catalyst for promoting the oxidation of methane contained in the exhaust gas, the plurality of parallel flow paths being respectively arranged; and a flow control device configured to control the flow rate of the exhaust gas flowing through the plurality of parallel flow paths, the flow control device being configured to reduce the number of parallel flow paths through which the exhaust gas can flow when the internal combustion engine is operating at a low load compared to when the internal combustion engine is operating at a high load.

[0008] According to at least one embodiment of the present disclosure, there is provided a methane oxidation catalyst device that can suppress thermal degradation of the methane oxidation catalyst during low load operation of an internal combustion engine.

[0009] 1 is a schematic diagram of an internal combustion engine system equipped with a methane oxidation catalyst device according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram of an internal combustion engine system equipped with a methane oxidation catalyst device according to an embodiment of the present disclosure. FIG. 3 is a schematic perspective view of a methane oxidation catalyst device according to an embodiment of the present disclosure. FIG. 4 is a schematic cross-sectional view taken along the arrows AB shown in FIG. 1. FIG. 5 is an explanatory diagram illustrating the relationship between the load of an internal combustion engine, the methane oxidation rate, and the number of damper opening and closing operations. FIG. 6 is an explanatory diagram illustrating the relationship between the exhaust gas amount per catalyst volume of a methane oxidation catalyst, the methane oxidation rate, and the catalyst volume of a methane oxidation catalyst. FIG. 7 is an explanatory diagram illustrating the relationship between the load of an internal combustion engine, the exhaust gas temperature, the methane content, and the number of damper opening and closing operations. FIG. 8 is a control flow diagram of a damper opening and closing control device according to an embodiment of the present disclosure. FIG. 9 is an explanatory diagram illustrating a method for selecting a damper to close a parallel flow path.

[0010] Hereinafter, several embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present disclosure.

[0011] In the following description, when simply referring to the upstream side, it refers to the upstream side along the main flow direction of the fluid in the part or area described in the direction. Similarly, in the following description, when simply referring to the downstream side, it refers to the downstream side along the main flow direction of the fluid in the part or area described in the direction.

[0012] (Internal combustion engine system) Figures 1 and 2 are each a schematic diagram of an internal combustion engine system 11 including a methane oxidation catalyst device 1 according to an embodiment of the present disclosure. Figure 3 is a schematic perspective view of the methane oxidation catalyst device 1 according to an embodiment of the present disclosure. In Figure 3, a part of the catalyst casing 3 of the methane oxidation catalyst device 1 is omitted to show the internal structure of the catalyst casing 3. As shown in Figures 1 and 2, the methane oxidation catalyst device 1 according to some embodiments is mounted in an internal combustion engine system 11 including an internal combustion engine 12.

[0013] The methane oxidation catalyst device 1 is provided in an exhaust gas exhaust system through which exhaust gas discharged from an internal combustion engine 12 flows. As shown in Figures 1 and 2, an internal combustion engine system 11 includes the methane oxidation catalyst device 1, an internal combustion engine 12, an exhaust gas inlet line 13, and an exhaust gas outlet line 14. The methane oxidation catalyst device 1 includes a plurality of methane oxidation catalyst reactors 2, a catalyst casing 3 that houses the plurality of methane oxidation catalyst reactors 2, a partition section 4 provided inside the catalyst casing 3, and a flow rate control device 5.

[0014] (Internal Combustion Engine) The internal combustion engine 12 is configured to be able to burn fuel gas containing methane as a fuel. Specific examples of the fuel gas include liquefied natural gas. When the internal combustion engine 12 uses fuel gas containing methane as a fuel, the exhaust gas emitted from the internal combustion engine 12 may contain slip methane, which is unburned methane.

[0015] (Exhaust Gas Introduction Line) The exhaust gas introduction line 13 forms a flow path for guiding exhaust gas from the internal combustion engine 12 to the catalyst casing 3, and is formed, for example, by a pipe through which exhaust gas can flow. One end (upstream end) of the exhaust gas introduction line 13 is connected to an outlet for discharging exhaust gas from the internal combustion engine 12, and the other end (downstream end) is connected to the exhaust gas introduction port 361 of the catalyst casing 3.

[0016] (Exhaust Gas Discharge Line) The exhaust gas discharge line 14 forms a flow path for discharging exhaust gas from the catalyst casing 3, and is formed, for example, by a pipe through which exhaust gas can flow. One end (upstream end) of the exhaust gas discharge line 14 is connected to the exhaust gas discharge port 371 of the catalyst casing 3. Note that the internal combustion engine system 11 may also include a bypass line (not shown) that forms a flow path for guiding exhaust gas from the exhaust gas introduction line 13 to the exhaust gas discharge line 14, bypassing the catalyst casing 3.

[0017] 1 and 2 show a cross section taken along a first direction D1, which is the flow direction of exhaust gas flowing inside the catalyst casing 3. The catalyst casing 3 has an internal space 30 formed therein, which is an exhaust gas flow path through which exhaust gas discharged from the internal combustion engine 12 and guided into the catalyst casing 3 flows. In the illustrated embodiment, the catalyst casing 3 includes a cylindrical portion 31 having the internal space 30.

[0018] The exhaust gas flowing inside the catalyst casing 3 (internal space 30) flows from the upstream side to the downstream side in a first direction D1. The catalyst casing 3 may be disposed vertically so that the exhaust gas flows vertically inside the catalyst casing 3, or may be disposed horizontally so that the exhaust gas flows horizontally inside the catalyst casing 3. The first direction D1 may be a direction along the vertical direction or a direction along the horizontal direction.

[0019] The cylindrical portion 31 is formed in a rectangular cylindrical shape extending along the first direction D1. Specifically, the cylindrical portion 31 has four walls 32, 33, 34, and 35 that surround the outer periphery of the internal space 30 and the four sides of a rectangular cross section that intersects with the first direction D1, and these four walls 32, 33, 34, and 35 form the rectangular cylindrical shape that has the internal space 30.

[0020] FIG. 4 is a schematic cross-sectional view taken along the arrows A-B in FIG. 1 . The partition 4 divides the internal space 30 into multiple parallel flow paths 40 (40A-40H). The internal space 30 includes two spaces 30A and 30B partitioned by the methane oxidation catalytic reactor 2. That is, the internal space 30 includes an upstream internal space 30A located upstream of the partition 4 in the first direction D1, and a downstream internal space 30B located downstream of the partition 4 in the first direction D1. The upstream internal space 30A and the downstream internal space 30B are connected to all of the multiple parallel flow paths 40. Note that in the illustrated embodiment, the internal space 30 is divided into eight parallel flow paths 40 by the partition 4, but the number of divided parallel flow paths 40 is not limited to eight. In the illustrated embodiment, the cross-section of the parallel flow paths 40 is rectangular, but the cross-section may be other than rectangular.

[0021] In the illustrated embodiment, the partition 4 includes at least one (three in the illustrated example) first partition plate 41 extending along the third direction D3 and at least one second partition plate 42 extending along the second direction D2. The second direction D2 and the third direction D3 are each perpendicular to the first direction D1. The third direction D3 is perpendicular to the second direction D2. The multiple first partition plates 41 are arranged at intervals in the second direction D2. The first partition plate 41 divides the internal space 30 into multiple sections in the second direction D2. The second partition plate 42 divides the internal space 30 into multiple sections in the third direction D3. The partition 4 may be formed integrally with the catalyst casing 3 or may be separate from the catalyst casing 3.

[0022] The catalyst casing 3 has a plate-shaped one-side lid portion 36 whose outer peripheral end is connected to one end (upstream side in the first direction D1) of the cylindrical portion 31 and which extends radially inward. The one-side lid portion 36 is the upstream end of the catalyst casing 3 in the first direction D1, and has the above-mentioned exhaust gas inlet 361 formed in the center thereof for introducing exhaust gas from outside the catalyst casing 3 into the upstream internal space 30A.

[0023] The catalyst casing 3 has an other-side lid portion 37 formed in a plate shape that extends radially inward and whose outer peripheral end is connected to the other end (downstream side in the first direction D1) of the cylindrical portion 31. The other-side lid portion 37 is the downstream end of the catalyst casing 3 in the first direction D1, and has an exhaust gas outlet 371 formed in its center for discharging exhaust gas from the downstream-side internal space 30B to the outside of the catalyst casing 3.

[0024] The internal space 30 is a space defined by the inner wall surfaces of the four walls 32, 33, 34, and 35, the one side lid portion 36, and the other side lid portion 37. In the illustrated embodiment, the first direction D1 is the direction from the one side lid portion 36 toward the other side lid portion 37, which faces the one side lid portion 36 across the internal space 30. The walls 32 and 33 extend along a third direction D3 from the wall 34 toward the wall 35, which faces the wall 34 across the internal space 30. The walls 34 and 35 extend along a second direction D2 from the wall 32 toward the wall 33, which faces the wall 32 across the internal space 30.

[0025] (Methane Oxidation Catalytic Reactor) Each of the multiple methane oxidation catalytic reactors 2 includes a methane oxidation catalyst for promoting the oxidation of methane (slip methane), and is configured to oxidize at least a portion of the methane (slip methane) in the exhaust gas using the methane oxidation catalyst and remove it from the exhaust gas. As the methane oxidation catalyst, for example, a catalyst containing a precious metal such as Pt (platinum) or Ir (iridium) can be used. Note that the methane oxidation catalytic reactor 2 may include not only the methane oxidation catalyst but also a catalyst carrier that supports the methane oxidation catalyst.

[0026] Each of the multiple methane oxidation catalytic reactors 2 is arranged in a corresponding parallel flow path 40 among the multiple parallel flow paths 40, and extends along a direction intersecting (orthogonal to) the first direction D1.

[0027] Exhaust gas emitted from the internal combustion engine 12 flows through the exhaust gas introduction line 13 and the upstream internal space 30A and is introduced into the parallel flow path 40. As the exhaust gas introduced into the parallel flow path 40 passes through the methane oxidation catalytic reactor 2, the methane oxidation catalyst provided in the methane oxidation catalytic reactor 2 promotes the oxidation of unburned methane that may be contained in the exhaust gas. The exhaust gas that has passed through the methane oxidation catalytic reactor 2 is discharged from the exhaust gas discharge port 371 to the outside of the catalyst casing 3, specifically, into the exhaust gas discharge line 14. As the exhaust gas passes through the methane oxidation catalytic reactor 2, its temperature is increased by an oxidation reaction caused by the methane oxidation catalyst provided in the methane oxidation catalytic reactor 2.

[0028] 1 and 2 , the flow control device 5 includes at least one damper 6 (in the illustrated example, multiple dampers) configured to control the flow rate of exhaust gas flowing through the multiple parallel flow paths 40. The at least one damper 6 is configured to be able to open and close at least one of the multiple parallel flow paths 40. The flow control device 5 includes a damper opening and closing control device 7 configured to control the opening and closing of the parallel flow paths 40 by the damper 6 so as to reduce the number of parallel flow paths 40 through which exhaust gas can flow when the internal combustion engine 12 is operating at a low load compared to when the internal combustion engine 12 is operating at a high load.

[0029] In the illustrated embodiment, each of the multiple dampers 6 (6A to 6H, see FIG. 3 ) is arranged in a corresponding parallel flow path 40 of the multiple parallel flow paths 40 (40A to 40H), and is capable of opening and closing the corresponding parallel flow path 40. Each of the multiple dampers 6 may be an on-off valve whose opening degree can be adjusted between fully closed and fully open, or an opening adjustment valve whose opening degree can be adjusted to fully closed, fully open, and at least one intermediate opening degree therebetween. Note that in other embodiments, no damper 6 may be arranged in some of the multiple parallel flow paths 40 (some parallel flow paths 40 may be normally open), or a single damper 6 may be configured to open and close two or more parallel flow paths 40.

[0030] In the illustrated embodiment, each of the multiple dampers 6 includes a valve stem 61 having a central axis LA extending in a direction intersecting the first direction D1 (in the illustrated example, the third direction D3), and two rectangular plate-shaped valve bodies 62, 63 that protrude radially outward from the valve stem 61 and have valve seat surfaces on their outer peripheries. Note that the dampers 6 are not limited to the shape shown in the drawings as long as they are configured to be able to open and close the parallel flow paths 40.

[0031] (Damper opening and closing control device) The damper opening and closing control device (controller) 7 is an electronic control unit for controlling the opening and closing operation of the damper 6. The damper opening and closing control device 7 may be configured as a microcomputer including memories such as ROM and RAM, a storage device 701 such as an external storage device, input / output devices 702 and 703 such as an I / O interface and a communication interface, and an arithmetic device 704 such as a CPU (processor). The damper opening and closing control device 7 may also be configured as a hard relay circuit that can be manufactured relatively inexpensively. When the damper opening and closing control device 7 is configured as a microcomputer, the processor (arithmetic device 704) operates (performs calculations, etc.) in accordance with the instructions of a program loaded into the memory, thereby controlling the operation of the damper 6.

[0032] 1 and 2, the methane oxidation catalyst device 1 includes an inlet-side exhaust gas temperature acquisition device (temperature sensor) 15 and an outlet-side exhaust gas temperature acquisition device (temperature sensor) 16. The inlet-side exhaust gas temperature acquisition device 15 is configured to acquire (measure) the temperature of the exhaust gas at the inlet of the catalyst casing 3 (e.g., the upstream internal space 30A). The outlet-side exhaust gas temperature acquisition device 16 is configured to acquire (measure) the temperature of the exhaust gas at the outlet of the catalyst casing 3 (e.g., the downstream internal space 30B). Measurement results (signals) from the inlet-side exhaust gas temperature acquisition device 15 and the outlet-side exhaust gas temperature acquisition device 16 are sent to the damper opening / closing control device 7. Information (signals) related to the load of the internal combustion engine 12 is also sent to the damper opening / closing control device 7.

[0033] FIG. 5 is an explanatory diagram illustrating the relationship between the load of the internal combustion engine 12, the methane oxidation rate, and the number of damper openings and closings (opening rate of the parallel flow paths 40). FIG. 5 shows a graph with the load of the internal combustion engine 12 on the horizontal axis and the methane oxidation rate on the vertical axis. The solid line L1 in FIG. 5 shows the relationship between the load of the internal combustion engine 12 and the methane oxidation rate when the damper 6 is not in use. The dotted line L2 in FIG. 5 shows the relationship between the load of the internal combustion engine 12 and the methane oxidation rate when the damper 6 is in use. Here, "when the damper 6 is in use" means that at least one parallel flow path 40 is closed by the damper 6. "When the damper 6 is not in use" means that none of the parallel flow paths 40 are closed by the damper 6. As shown by the solid line L1, when the load of the internal combustion engine 12 is relatively low, the methane oxidation rate tends to be high due to the relationship between the flow rate of exhaust gas passing through the methane oxidation catalyst and the amount of methane oxidation catalyst installed.

[0034] FIG. 5 shows multiple regions LR1, LR2, LR3, and LR4 divided according to the load of the internal combustion engine 12. The first region LR1 is a region where the load of the internal combustion engine 12 is higher than the second region LR2. The third region LR3 is a region where the load of the internal combustion engine 12 is lower than the second region LR2 and is a region where the load of the internal combustion engine 12 is higher than the fourth region LR4. In the illustrated embodiment, the lower the load of the internal combustion engine 12, the more closed dampers 6 (dampers 6 that close the parallel flow paths 40) are. In the first region LR1, no dampers 6 are closed, i.e., no dampers 6 are used. As shown by the dotted line L2, in the regions LR2, LR3, and LR4 where the load of the internal combustion engine 12 is relatively low, closing some of the parallel flow paths 40 using dampers 6 reduces the methane oxidation rate compared to when no dampers 6 are used.

[0035] FIG. 6 is an explanatory diagram illustrating the relationship between the amount of exhaust gas per catalyst volume (space velocity SV), the methane oxidation rate, and the catalyst volume of the methane oxidation catalyst. In FIG. 6, the horizontal axis represents the amount of exhaust gas per catalyst volume (space velocity SV) of the methane oxidation catalyst, and the vertical axis represents the methane oxidation rate and catalyst volume. The solid line L3 in FIG. 6 shows the relationship between the space velocity SV and the methane oxidation rate. The solid line L4 in FIG. 6 shows the relationship between the space velocity SV and the catalyst volume of the methane oxidation catalyst. The catalyst volume V1 when the damper 6 is used is smaller than the catalyst volume V2 when the damper 6 is not used, because the parallel flow path 40 is closed. Furthermore, when the damper 6 is used, the space velocity SV1 is higher than the space velocity SV2 when the damper 6 is not used, i.e., the amount of exhaust gas per catalyst volume increases. As a result, the methane oxidation rate R1 when the damper 6 is used can be lower than the methane oxidation rate R2 when the damper 6 is not used.

[0036] Fig. 7 is an explanatory diagram illustrating the relationship between the load of the internal combustion engine 12, the exhaust gas temperature, the methane content, and the number of damper openings and closings. Fig. 7 shows a graph with the load of the internal combustion engine 12 on the horizontal axis and the exhaust gas temperature at the outlet of the catalyst casing 3 (e.g., the downstream inner space 30B) and the methane content at the outlet of the catalyst casing 3 (e.g., the downstream inner space 30B) on the vertical axis. The solid line L5 in Fig. 7 shows the relationship between the load of the internal combustion engine 12 and the exhaust gas temperature at the outlet of the catalyst casing 3 when the damper 6 is not used. As shown by the solid line L5, when the internal combustion engine 12 is operating at a low load, the exhaust gas temperature at the outlet of the catalyst casing 3 exceeds the heat resistance temperature HT of the methane oxidation catalyst, which may cause thermal degradation of the methane oxidation catalyst.

[0037] The dotted line L6 in Fig. 7 shows the relationship between the load on the internal combustion engine 12 and the exhaust gas temperature at the outlet of the catalyst casing 3 when the damper 6 is in use. By using the damper 6 to reduce the methane oxidation rate when the internal combustion engine 12 is under low load, an excessive increase in the exhaust gas temperature inside the methane oxidation catalyst can be suppressed (see the dotted line L6 in Fig. 7), and thermal degradation of the methane oxidation catalyst can be suppressed.

[0038] The dotted line L7 in Fig. 7 shows the relationship between the load on the internal combustion engine 12 and the methane content of the exhaust gas at the outlet of the catalyst casing 3 when the damper 6 is in use. The solid line L8 in Fig. 7 shows the relationship between the methane content of the exhaust gas that is passed through the bypass line to avoid thermal degradation of the methane oxidation catalyst and the load on the internal combustion engine 12. By suppressing thermal degradation of the methane oxidation catalyst, the methane oxidation catalyst device 1 can be used even in the expanded area EA (low load range) that exists between the dotted line L7 and the solid line L8, thereby reducing slip methane emissions in the low load range.

[0039] In some embodiments, the damper opening / closing control device 7 (flow rate control device 5) described above is configured to reduce the number of parallel flow paths 40 through which exhaust gas can flow when the load on the internal combustion engine 12 reaches a predetermined load at which the exhaust gas temperature at the outlet of the catalyst casing 3 exceeds the heat resistance temperature HT of the methane oxidation catalyst when the dampers 6 are not in use, i.e., when all of the multiple dampers 6 are in the open state. In other words, when the load on the internal combustion engine 12 reaches the predetermined load, the damper opening / closing control device 7 is configured to issue an opening instruction to the dampers 6 so that at least one of the multiple dampers 6 changes from an open state to a closed state.

[0040] If the load on the internal combustion engine 12 reaches a predetermined load at which the exhaust gas temperature at the outlet of the catalyst casing 3 when the damper 6 is not in use exceeds the heat resistance temperature HT of the methane oxidation catalyst, there is a high possibility that the methane oxidation catalyst will thermally deteriorate. In this case, by reducing the number of parallel flow paths 40 through which exhaust gas can flow, thermal deterioration of the methane oxidation catalyst can be effectively suppressed.

[0041] In the illustrated embodiment, each of the multiple dampers 6 is disposed upstream of the methane oxidation catalytic reactor 2 in the parallel flow path 40 in the exhaust gas flow direction. In this case, by disposing the damper 6 capable of closing the parallel flow path 40 upstream of the methane oxidation catalytic reactor 2 in the parallel flow path 40 in the exhaust gas flow direction, it is possible to prevent exhaust gas from flowing into the methane oxidation catalytic reactor 2 from upstream of the parallel flow path 40, thereby effectively suppressing thermal degradation of the methane oxidation catalyst. Note that in some other embodiments, each of the multiple dampers 6 may be disposed downstream of the methane oxidation catalytic reactor 2 in the parallel flow path 40 in the exhaust gas flow direction. In this case as well, the damper 6 obstructs the flow of exhaust gas in the parallel flow path 40, making it difficult for exhaust gas to flow into the methane oxidation catalytic reactor 2 from upstream of the parallel flow path 40.

[0042] (Opening / Closing Number Determination Unit) Figure 8 is a control flow diagram of the damper opening / closing control device 7 in one embodiment of the present disclosure. In the embodiment shown in Figure 8, the above-mentioned damper opening / closing control device 7 (flow rate control device 5) includes an opening / closing number determination unit 71 configured to determine the opening / closing number of the multiple dampers 6 from the load of the internal combustion engine 12, based on association information that associates the load of the internal combustion engine 12 with the opening / closing number of the multiple dampers 6. The association information is configured so that the number of dampers 6 that are closed increases as the load of the internal combustion engine 12 decreases. By using such association information, it is possible to appropriate the opening / closing number of the dampers 6 in response to fluctuations in the load of the internal combustion engine 12.

[0043] (First Correction Unit) In the embodiment shown in FIG. 8 , the damper opening / closing control device 7 (flow rate control device 5) described above includes a first correction unit 72 configured to correct the opening / closing number of the damper 6 determined by the opening / closing number determination unit 71, taking into account the exhaust gas temperature at the outlet of the catalyst casing 3. The first correction unit 72 may be configured to calculate the correction number from the temperature acquired by the outlet-side exhaust gas temperature acquisition device 16, based on association information that associates the exhaust gas temperature at the outlet of the catalyst casing 3 with a correction number for the opening / closing number of the damper 6. The correction value preferably increases the number of dampers 6 that are closed. In addition, in the embodiment shown in FIG. 8 , when the first correction unit 72 corrects the opening / closing number of the damper 6, information regarding the upper limit of the exhaust gas temperature at the outlet of the catalyst casing 3 corresponding to the load of the internal combustion engine 12 is used. For example, the first correction unit 72 may be configured to calculate the correction number from the temperature acquired by the outlet-side exhaust gas temperature acquisition device 16 and information related to the upper limit value, based on association information that associates the exhaust gas temperature at the outlet of the catalyst casing 3, information related to the upper limit value, and a correction number for the number of openings and closings of the damper 6. Furthermore, the first correction unit 72 may not calculate the correction number until the temperature acquired by the outlet-side exhaust gas temperature acquisition device 16 reaches a predetermined value (for example, the upper limit value).

[0044] When the exhaust gas temperature at the outlet of the catalyst casing 3 is high, it is highly likely that the exhaust gas temperature inside the methane oxidation catalyst is also high. Therefore, by correcting the number of times the damper 6 is opened and closed and reducing the number of parallel flow paths 40 through which exhaust gas can flow, thermal degradation of the methane oxidation catalyst can be effectively suppressed.

[0045] (Second Correction Unit) In the embodiment shown in FIG. 8 , the damper opening / closing control device 7 (flow rate control device 5) described above includes a second correction unit 73 configured to correct the opening / closing number of the damper 6 determined by the opening / closing number determination unit 71, taking into account the exhaust gas temperature at the inlet of the catalyst casing 3. The second correction unit 73 may be configured to calculate the correction number from the temperature acquired by the inlet-side exhaust gas temperature acquisition device 15, based on association information that associates the exhaust gas temperature at the inlet of the catalyst casing 3 with a correction number for the opening / closing number of the damper 6. The correction value is preferably one that increases the number of dampers 6 that are closed. Furthermore, in the embodiment shown in FIG. 8 , when the second correction unit 73 corrects the opening / closing number of the damper 6, information related to the planned value of the exhaust gas temperature at the inlet of the catalyst casing 3 corresponding to the load of the internal combustion engine 12 is used. For example, the second correction unit 73 may be configured to calculate the correction number from the temperature acquired by the inlet-side exhaust gas temperature acquisition device 15 and information related to the planned value, based on association information that associates the exhaust gas temperature at the inlet of the catalyst casing 3, information related to the planned value, and a correction number for the number of openings and closings of the damper 6. Furthermore, the second correction unit 73 may not calculate the correction number until the temperature acquired by the inlet-side exhaust gas temperature acquisition device 15 reaches a predetermined value (for example, the planned value).

[0046] If the exhaust gas temperature at the inlet of the catalyst casing 3 is high, there is a high possibility that the exhaust gas temperature inside the methane oxidation catalyst will rise in the future. Therefore, by correcting the number of times the damper 6 is opened and closed in advance and reducing the number of parallel flow paths 40 through which exhaust gas can flow, thermal degradation of the methane oxidation catalyst can be effectively suppressed.

[0047] In the embodiment shown in Figure 8, the damper opening / closing control device 7 (flow control device 5) includes both the first correction unit 72 and the second correction unit 73, but it may be configured to include either the first correction unit 72 or the second correction unit 73, or it may be configured to not include both the first correction unit 72 and the second correction unit 73.

[0048] FIG. 9 is an explanatory diagram illustrating a method for selecting a damper 6 to close the parallel flow path 40. The damper opening / closing control device 7 (flow control device 5) stores the total operating time for each damper 6 while it is open in the storage device 701. The total operating time includes not only the operating time for the most recent open state but also the operating time for previous open states including the closed state. The damper opening / closing control device 7 (flow control device 5) described above includes an opening / closing determination unit 74 configured to determine the opening / closing state of each of the multiple dampers 6 based on the number of opening / closing states of the dampers 6 determined by the opening / closing number determination unit 71 and the total operating time WT for each damper 6 while it is open. The opening / closing number of the dampers 6 determined by the opening / closing number determination unit 71 includes the corrected opening / closing number corrected by the first correction unit 72 and the second correction unit 73.

[0049] For example, when the number of dampers 6 to be closed determined by the opening / closing number determination unit 71 is three, the damper opening / closing control device 7 selects the dampers 6 (6H, 6G, 6F) to be closed in order of the longest total operating time WT, and issues opening / closing instructions to each of the multiple dampers 6 so that the remaining dampers 6 are opened.

[0050] In this case, the total operating time for each damper 6 when open can be made uniform. This makes it possible to standardize the usage time of the methane oxidation catalyst and suppress continuous use of a specific methane oxidation catalyst, thereby extending the life of the methane oxidation catalyst. In some other embodiments, the opening / closing determination unit 74 may be configured to determine the opening / closing of each of the multiple dampers 6 based not only on the number of dampers 6 to be opened / closed and the total operating time WT for each damper 6 when open determined by the opening / closing number determination unit 71, but also on the exhaust gas temperature. When determining which dampers 6 to open / close, the opening / closing determination unit 74 may use at least one of information regarding the exhaust gas temperature at the inlet of the catalyst casing 3 acquired by the inlet-side exhaust gas temperature acquisition device 15 and information regarding the exhaust gas temperature at the outlet of the catalyst casing 3 acquired by the outlet-side exhaust gas temperature acquisition device 16. In some other embodiments, the opening / closing determination unit 74 may determine the opening / closing of each of the multiple dampers 6 without taking into account the total operating time WT for each damper 6 when open, the exhaust gas temperature, etc.

[0051] In this specification, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0052] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0053] The contents of the above-described embodiments can be understood, for example, as follows.

[0054] 1) A methane oxidation catalyst device (1) according to at least one embodiment of the present disclosure comprises: a catalyst casing (3) that forms an exhaust gas flow path (internal space 30) therein through which exhaust gas discharged from an internal combustion engine (12) flows; a partition section (4) that divides the exhaust gas flow path formed inside the catalyst casing (3) into a plurality of parallel flow paths (40); a plurality of methane oxidation catalyst reactors (2) that contain a methane oxidation catalyst for promoting the oxidation of methane contained in the exhaust gas and are arranged in the plurality of parallel flow paths (40), respectively; and a flow control device (5) configured to control the flow rate of the exhaust gas flowing through the plurality of parallel flow paths (40), and configured to reduce the number of the parallel flow paths (40) through which the exhaust gas can flow during low-load operation of the internal combustion engine (12) compared to during high-load operation of the internal combustion engine (12).

[0055] According to the above configuration 1), the amount of exhaust gas per catalyst volume of the methane oxidation catalyst can be increased by reducing the number of parallel flow paths (40) through which exhaust gas can flow during low-load operation of the internal combustion engine (12). This reduces the methane oxidation rate, thereby suppressing a rapid increase in exhaust gas temperature and suppressing thermal degradation of the methane oxidation catalyst.

[0056] 2) In some embodiments, in the methane oxidation catalyst device (1) described in 1) above, the flow rate control device (5) includes a plurality of dampers (6) capable of opening and closing the parallel flow paths (40), and is configured to reduce the number of the parallel flow paths (40) through which the exhaust gas can flow when the load of the internal combustion engine (12) reaches a predetermined load at which the exhaust gas temperature at the outlet of the catalyst casing (3) when the dampers (6) are not in use exceeds the heat resistance temperature (HT) of the methane oxidation catalyst.

[0057] According to the configuration of 2) above, when the load on the internal combustion engine (12) reaches a predetermined load at which the exhaust gas temperature at the outlet of the catalyst casing (3) when the damper (6) is not in use exceeds the heat resistance temperature (HT) of the methane oxidation catalyst, there is a high possibility that the methane oxidation catalyst will undergo thermal degradation. In this case, by reducing the number of parallel flow paths (40) through which exhaust gas can flow, it is possible to effectively suppress thermal degradation of the methane oxidation catalyst.

[0058] 3) In some embodiments, in the methane oxidation catalyst device (1) described in 1) or 2) above, the flow rate control device (5) includes a plurality of dampers (6) that are arranged upstream of the methane oxidation catalyst reactor (2) in the plurality of parallel flow paths (40) in the flow direction of the exhaust gas and that are capable of opening and closing the parallel flow paths (40).

[0059] According to the above configuration 3), by arranging the damper (6) capable of closing the parallel flow path (40) on the parallel flow path (40) upstream of the methane oxidation catalytic reactor (2) in the flow direction of the exhaust gas, it is possible to prevent the exhaust gas from flowing into the methane oxidation catalytic reactor (2) from upstream of the parallel flow path (40), and therefore it is possible to effectively suppress thermal deterioration of the methane oxidation catalyst.

[0060] 4) In some embodiments, in the methane oxidation catalyst device (1) described in 2) or 3) above, the flow control device (5) includes an opening / closing number determination unit (71) configured to determine the opening / closing numbers of the plurality of dampers (6) from the load of the internal combustion engine (12) based on association information that associates the load of the internal combustion engine (12) with the opening / closing numbers of the plurality of dampers (6).

[0061] According to the above configuration 4), by using the association information, the number of times the damper (6) is opened and closed can be set to an appropriate value in accordance with the fluctuation of the load on the internal combustion engine (12).

[0062] 5) In some embodiments, in the methane oxidation catalyst device (1) described in 4) above, the flow rate control device (5) includes a first correction unit (72) configured to correct the opening and closing number of the damper (6) determined by the opening and closing number determination unit (71) in consideration of the exhaust gas temperature at the outlet of the catalyst casing (3).

[0063] According to the configuration of 5) above, when the exhaust gas temperature at the outlet of the catalyst casing (3) is high, it is highly likely that the exhaust gas temperature inside the methane oxidation catalyst is also high. Therefore, by correcting the number of times the damper (6) is opened and closed and reducing the number of parallel flow paths (40) through which exhaust gas can flow, thermal deterioration of the methane oxidation catalyst can be effectively suppressed.

[0064] 6) In some embodiments, in the methane oxidation catalyst device (1) described in 4) or 5) above, the flow rate control device (5) includes a second correction unit (73) configured to correct the opening and closing number of the damper (6) determined by the opening and closing number determination unit (71) in consideration of the exhaust gas temperature at the inlet of the catalyst casing (3).

[0065] According to the above-described configuration 6), when the exhaust gas temperature at the inlet of the catalyst casing (3) is high, there is a high possibility that the exhaust gas temperature inside the methane oxidation catalyst will rise in the future. Therefore, by correcting the number of times the damper (6) is opened and closed in advance and reducing the number of parallel flow paths (40) through which exhaust gas can flow, thermal deterioration of the methane oxidation catalyst can be effectively suppressed.

[0066] 7) In some embodiments, in the methane oxidation catalyst device (1) described in any one of 4) to 6) above, the flow rate control device (5) includes an opening / closing determination unit (74) configured to determine opening / closing of each of the plurality of dampers (6) based on the number of openings / closings of the dampers (6) determined in the opening / closing number determination unit (71) and the total operating time when each damper (6) is open.

[0067] According to the configuration of 7) above, the total operating time when each damper (6) is open can be made uniform, which makes it possible to standardize the usage time of the methane oxidation catalyst and suppress continuous use of a specific methane oxidation catalyst, thereby extending the life of the methane oxidation catalyst.

[0068] DESCRIPTION OF SYMBOLS 1 Methane oxidation catalyst device 2 Methane oxidation catalyst reactor 3 Catalyst casing 4 Partition 5 Flow rate control device 6 Damper 7 Damper opening / closing control device 11 Internal combustion engine system 12 Internal combustion engine 13 Exhaust gas introduction line 14 Exhaust gas discharge line 15 Inlet-side exhaust gas temperature acquisition device 16 Outlet-side exhaust gas temperature acquisition device 30 Internal space 30A Upstream-side internal space 30B Downstream-side internal space 40 Parallel flow path 41 First partition plate 42 Second partition plate 61 Valve stem 62 Valve body 71 Opening / closing number determination unit 72 First correction unit 73 Second correction unit 74 Opening / closing determination unit D1 First direction D2 Second direction D3 Third direction EA Expansion region HT Heat-resistant temperature WT Total operating time

Claims

1. A methane oxidation catalyst device comprising: a catalyst casing forming an exhaust gas flow path therein through which exhaust gas emitted from an internal combustion engine flows; partitions dividing the exhaust gas flow path formed inside the catalyst casing into a plurality of parallel flow paths; a plurality of methane oxidation catalyst reactors each containing a methane oxidation catalyst for promoting the oxidation of methane contained in the exhaust gas, the methane oxidation catalyst reactors being disposed in each of the plurality of parallel flow paths; and a flow control device configured to control the flow rate of the exhaust gas flowing through the plurality of parallel flow paths, the flow control device being configured to reduce the number of parallel flow paths through which the exhaust gas can flow when the internal combustion engine is operating at a low load compared to when the internal combustion engine is operating at a high load.

2. A methane oxidation catalyst device according to claim 1, wherein the flow rate control device includes a plurality of dampers capable of opening and closing the parallel flow paths, and is configured to reduce the number of parallel flow paths through which the exhaust gas can flow when the load on the internal combustion engine reaches a predetermined load at which the exhaust gas temperature at the outlet of the catalyst casing when the dampers are not in use exceeds the heat resistance temperature of the methane oxidation catalyst.

3. A methane oxidation catalyst device according to claim 1 or 2, wherein the flow rate control device includes a plurality of dampers that are arranged in each of the plurality of parallel flow paths upstream of the methane oxidation catalyst reactor in the flow direction of the exhaust gas and that are capable of opening and closing the parallel flow paths.

4. The methane oxidation catalyst device according to claim 2, wherein the flow control device includes an opening / closing number determination unit configured to determine the opening / closing numbers of the plurality of dampers from the load of the internal combustion engine based on association information that associates the load of the internal combustion engine with the opening / closing numbers of the plurality of dampers.

5. A methane oxidation catalyst device as described in claim 4, wherein the flow rate control device includes a first correction unit configured to correct the opening and closing number of the damper determined by the opening and closing number determination unit, taking into account the exhaust gas temperature at the outlet of the catalyst casing.

6. A methane oxidation catalyst device according to claim 4, wherein the flow rate control device includes a second correction unit configured to correct the opening and closing number of the damper determined by the opening and closing number determination unit, taking into account the exhaust gas temperature at the inlet of the catalyst casing.

7. The methane oxidation catalyst device according to claim 4, wherein the flow control device includes an opening / closing determination unit configured to determine opening / closing of each of the plurality of dampers based on the number of openings / closings of the dampers determined by the opening / closing number determination unit and the total operating time when each damper is open.

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