Exhaust gas treatment system and exhaust gas treatment method

Abstract

This invention provides an exhaust gas treatment system and exhaust gas treatment method that can improve the oxidation efficiency of methane. [Solution] The exhaust gas treatment system treats exhaust gas emitted from an internal combustion engine, which contains methane, sulfur oxides, and carbon monoxide. The exhaust gas treatment system comprises a sulfur oxide adsorption section having a sulfur oxide adsorbent for adsorbing sulfur oxides, and a methane oxidation catalyst section located downstream of the sulfur oxide adsorption section in the direction of exhaust gas flow, which has a methane oxidation catalyst for oxidizing components including methane. Furthermore, the sulfur oxide adsorbent also oxidizes components including carbon monoxide.

Description

[Technical Field]

[0001] This disclosure relates to an exhaust gas treatment system and an exhaust gas treatment method. [Background technology]

[0002] Harmful substances (e.g., hydrocarbons, nitrogen oxides, etc.) contained in exhaust gases emitted from internal combustion engines and other sources cause air pollution. Therefore, to treat these harmful substances in exhaust gases, a technology is known that involves placing a catalyst (exhaust gas treatment catalyst) in the exhaust passage through which the exhaust gas flows to treat these harmful substances. Furthermore, if the exhaust gas emitted from internal combustion engines and other sources contains sulfur oxides, contact between the sulfur oxides and the exhaust gas treatment catalyst may reduce the performance of the exhaust gas treatment catalyst (e.g., exhaust gas treatment capacity). For this reason, it has been proposed to place a sulfur-absorbing material upstream of the exhaust gas treatment catalyst in the direction of exhaust gas flow (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2007-222833 [Overview of the project] [Problems that the invention aims to solve]

[0004] On the other hand, when using a methane oxidation catalyst as an exhaust gas treatment catalyst, the methane oxidation efficiency may be low depending on the exhaust gas temperature.

[0005] The present disclosure aims to provide an exhaust gas treatment system and an exhaust gas treatment method that can improve the oxidation efficiency of methane. [Means for solving the problem]

[0006] This disclosure [1] provides an exhaust gas treatment system for treating exhaust gas discharged from an internal combustion engine, which contains methane, sulfur oxides, and carbon monoxide, comprising: a sulfur oxide adsorption section equipped with a sulfur oxide adsorbent for adsorbing sulfur oxides; and a methane oxidation catalyst section disposed downstream of the sulfur oxide adsorption section in the flow direction of the exhaust gas and equipped with a methane oxidation catalyst for oxidizing components including methane, wherein the sulfur oxide adsorbent further oxidizes components including carbon monoxide.

[0007] Such an exhaust gas treatment system includes a sulfur oxide adsorption section equipped with a sulfur oxide adsorbent for adsorbing sulfur oxides, and a methane oxidation catalyst section located downstream of the sulfur oxide adsorption section in the direction of exhaust gas flow, equipped with a methane oxidation catalyst for oxidizing components including methane, wherein the sulfur oxide adsorption section oxidizes components including carbon monoxide.

[0008] The reaction in the sulfur oxide adsorption section to oxidize components, including carbon monoxide, in the exhaust gas is an exothermic reaction. Therefore, a relatively high-temperature exhaust gas is supplied to the methane oxidation catalyst section, which is located downstream of the sulfur oxide adsorption section in the direction of exhaust gas flow. In the methane oxidation catalyst, a relatively high exhaust gas temperature results in higher oxidation efficiency in oxidizing components, including methane.

[0009] In other words, in an exhaust gas treatment system, sulfur oxides are adsorbed by the sulfur oxide adsorption section, suppressing the performance degradation of the methane oxidation catalyst section. Furthermore, the sulfur oxide adsorption section oxidizes the components to be oxidized, including carbon monoxide, and increases the temperature of the exhaust gas supplied to the methane oxidation catalyst section. As a result, the oxidation efficiency of methane can be improved.

[0010] This disclosure [2] includes the exhaust gas treatment system described in [1] above, wherein the sulfur oxide adsorption unit and the methane oxidation catalyst unit are spaced apart in the direction of the exhaust gas flow.

[0011] In such an exhaust gas treatment system, the sulfur oxide adsorption section and the methane oxidation catalyst section are arranged at an interval in the flow direction of the exhaust gas. Therefore, the exhaust gas whose temperature has been raised by the sulfur oxide adsorption section is supplied to the methane oxidation catalyst section without causing a temperature drop due to contact with other members. As a result, the oxidation efficiency of methane can be improved.

[0012] The present disclosure [3] includes the exhaust gas treatment system according to the above [1] or [2], wherein at least a part of the methane oxidation catalyst has an active metal that oxidizes the to-be-oxidized component containing methane in the exhaust gas, and the content of the active metal per unit area of the methane oxidation catalyst decreases from the upstream side to the downstream side in the flow direction of the exhaust gas.

[0013] In such an exhaust gas treatment system, at least a part of the methane oxidation catalyst has an active metal that oxidizes the to-be-oxidized component containing methane in the exhaust gas, and the content of the active metal per unit area of the methane oxidation catalyst decreases from the upstream side to the downstream side in the flow direction of the exhaust gas.

[0014] The reaction of oxidizing the to-be-oxidized component containing methane in exhaust gas by the methane oxidation catalyst is an exothermic reaction. Therefore, in the methane oxidation catalyst section, the temperature of the exhaust gas rises from the upstream side to the downstream side in the flow direction of the exhaust gas. For the methane oxidation catalyst, the relatively higher the temperature of the exhaust gas, the higher the oxidation efficiency of oxidizing the to-be-oxidized component containing methane.

[0015] That is, in the methane oxidation catalyst section, since the temperature of the exhaust gas rises from the upstream side to the downstream side in the flow direction of the exhaust gas, the desired methane oxidation efficiency can be maintained even if the content of the active metal per unit area of the methane oxidation catalyst decreases from the upstream side to the downstream side in the flow direction of the exhaust gas. In other words, the content of the active metal can be reduced while maintaining the desired methane oxidation efficiency.

[0016] This disclosure [4] includes the exhaust gas treatment system described in [3] above, wherein the methane oxidation catalyst section comprises a plurality of methane oxidation catalyst units along the exhaust gas flow direction, each methane oxidation catalyst unit having a methane oxidation catalyst with substantially uniform content of the active metal per unit area in the exhaust gas flow direction, and in adjacent methane oxidation catalyst units in the exhaust gas flow direction, the content of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located upstream in the exhaust gas flow direction is greater than the content of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located downstream in the exhaust gas flow direction.

[0017] In such an exhaust gas treatment system, the methane oxidation catalyst section comprises multiple methane oxidation catalyst units arranged along the direction of exhaust gas flow. Each methane oxidation catalyst unit has a methane oxidation catalyst with a substantially uniform active metal content per unit area in the direction of exhaust gas flow. In adjacent methane oxidation catalyst units in the direction of exhaust gas flow, the active metal content per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located upstream in the direction of exhaust gas flow is greater than the active metal content per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located downstream in the direction of exhaust gas flow. Therefore, each of the multiple methane oxidation catalyst units can be easily manufactured, and as a result, the exhaust gas treatment system can be easily manufactured.

[0018] This disclosure [5] includes an exhaust gas treatment system according to [3] above, wherein the methane oxidation catalyst section comprises a plurality of methane oxidation catalyst units along the flow direction of the exhaust gas, each methane oxidation catalyst unit having a methane oxidation catalyst in which the content of the active metal per unit area decreases from the upstream side to the downstream side in the flow direction of the exhaust gas, and in adjacent methane oxidation catalyst units in the flow direction of the exhaust gas, the minimum content of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located on the upstream side in the flow direction of the exhaust gas is greater than the maximum content of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located on the downstream side in the flow direction of the exhaust gas.

[0019] In such an exhaust gas treatment system, the methane oxidation catalyst section comprises multiple methane oxidation catalyst units arranged along the direction of exhaust gas flow. Each methane oxidation catalyst unit has a methane oxidation catalyst in which the active metal content per unit area decreases from the upstream to the downstream side in the direction of exhaust gas flow. In adjacent methane oxidation catalyst units in the direction of exhaust gas flow, the minimum active metal content per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located upstream is greater than the maximum active metal content per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located downstream. Therefore, in the methane oxidation catalyst section, the exhaust gas temperature increases from the upstream to the downstream side in the direction of exhaust gas flow. As a result, even if the active metal content per unit area of ​​the methane oxidation catalyst decreases from the upstream to the downstream side in the direction of exhaust gas flow, the desired methane oxidation efficiency can be maintained. In other words, the active metal content can be further reduced while maintaining the desired methane oxidation efficiency.

[0020] The present disclosure [6] includes an exhaust gas treatment system according to [3] above, wherein the methane oxidation catalyst section comprises a plurality of methane oxidation catalyst units along the exhaust gas flow direction, at least one of the methane oxidation catalyst units having a methane oxidation catalyst with substantially uniform active metal content per unit area in the exhaust gas flow direction, at least one of the methane oxidation catalyst units having a methane oxidation catalyst with decreasing active metal content per unit area from upstream to downstream in the exhaust gas flow direction, and in adjacent methane oxidation catalyst units in the exhaust gas flow direction, the minimum active metal content per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located upstream in the exhaust gas flow direction is greater than the maximum active metal content per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located downstream in the exhaust gas flow direction.

[0021] In such an exhaust gas treatment system, the methane oxidation catalyst section comprises a plurality of methane oxidation catalyst units arranged along the direction of exhaust gas flow, at least one of the methane oxidation catalyst units has a methane oxidation catalyst with substantially uniform active metal content per unit area in the direction of exhaust gas flow, at least one of the methane oxidation catalyst units has a methane oxidation catalyst with decreasing active metal content per unit area from upstream to downstream in the direction of exhaust gas flow, and among methane oxidation catalyst units adjacent to each other in the direction of exhaust gas flow, the minimum active metal content per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located upstream in the direction of exhaust gas flow is greater than the maximum active metal content per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located downstream in the direction of exhaust gas flow. Therefore, in the methane oxidation catalyst section, the exhaust gas temperature increases from the upstream to the downstream side in the direction of exhaust gas flow. As a result, even if the active metal content per unit area of ​​the methane oxidation catalyst decreases from the upstream to the downstream side in the direction of exhaust gas flow, the desired methane oxidation efficiency can be maintained. In other words, the active metal content can be further reduced while maintaining the desired methane oxidation efficiency.

[0022] This disclosure [7] includes an exhaust gas treatment method for supplying the exhaust gas to an exhaust gas treatment system described in any one of the above [1] to [6] and treating the exhaust gas, comprising the steps of supplying the exhaust gas to a sulfur oxide adsorption unit to oxidize the oxidizable components including carbon monoxide and adsorb the sulfur oxides, and supplying the exhaust gas that has passed through the sulfur oxide adsorption unit to a methane oxidation catalyst unit to oxidize the oxidizable components including methane, wherein the temperature of the exhaust gas supplied to the sulfur oxide adsorption unit is 300°C or higher and 600°C or lower.

[0023] This exhaust gas treatment method includes a step of supplying exhaust gas to a sulfur oxide adsorption section to oxidize the oxidizable components, including carbon monoxide, and adsorb sulfur oxides, and a step of supplying the exhaust gas that has passed through the sulfur oxide adsorption section to a methane oxidation catalyst section to oxidize the oxidizable components, including methane, wherein the temperature of the exhaust gas supplied to the sulfur oxide adsorption section is 300°C or higher and 600°C or lower.

[0024] Therefore, the sulfur oxide adsorption section can adequately adsorb sulfur oxides, while simultaneously suppressing the desorption of the adsorbed sulfur oxides. Furthermore, the sulfur oxide adsorption section oxidizes the oxidizable components, including carbon monoxide, and the resulting increase in exhaust gas temperature allows the exhaust gas to be supplied to the methane oxidation catalyst section at a temperature suitable for methane oxidation, thereby improving the methane oxidation efficiency.

[0025] This disclosure [8] includes the exhaust gas treatment method described in [7] above, wherein the temperature of the exhaust gas supplied to the methane oxidation catalyst is higher than the temperature of the exhaust gas supplied to the sulfur oxide adsorption section.

[0026] In this type of exhaust gas treatment method, the temperature of the exhaust gas supplied to the methane oxidation catalyst is higher than the temperature of the exhaust gas supplied to the sulfur oxide adsorption section. Therefore, carbon monoxide is properly oxidized in the sulfur oxide adsorption section, and the exhaust gas can be supplied to the methane oxidation catalyst at a temperature suitable for methane oxidation, thereby improving the methane oxidation efficiency.

[0027] This disclosure [9] includes the exhaust gas treatment method described in [8] above, wherein the difference between the temperature of the exhaust gas supplied to the methane oxidation catalyst and the temperature of the exhaust gas supplied to the sulfur oxide adsorption unit is 10°C or more and 200°C or less.

[0028] In this type of exhaust gas treatment method, the temperature difference between the exhaust gas supplied to the methane oxidation catalyst and the exhaust gas supplied to the sulfur oxide adsorption section is between 10°C and 200°C. Therefore, even if the temperature of the exhaust gas supplied to the sulfur oxide adsorption section is relatively low, the exhaust gas can be supplied to the methane oxidation catalyst at a temperature suitable for methane oxidation, thereby improving the methane oxidation efficiency. [Effects of the Invention]

[0029] The exhaust gas treatment system of this disclosure comprises a sulfur oxide adsorption section equipped with a sulfur oxide adsorbent for adsorbing sulfur oxides, and a methane oxidation catalyst section located downstream of the sulfur oxide adsorption section in the direction of exhaust gas flow and equipped with a methane oxidation catalyst for oxidizing methane. The sulfur oxide adsorption section oxidizes carbon monoxide. When carbon monoxide is oxidized in the sulfur oxide adsorption section, heat is generated, and the temperature of the exhaust gas rises. Therefore, the exhaust gas is supplied to the methane oxidation catalyst section at a relatively high temperature, and the methane oxidation efficiency can be improved.

[0030] The exhaust gas treatment method of this disclosure comprises the steps of supplying exhaust gas to the above-mentioned sulfur oxide adsorption section, oxidizing carbon monoxide and adsorbing sulfur oxides, and supplying the exhaust gas that has passed through the sulfur oxide adsorption section to the above-mentioned methane oxidation catalyst section, and oxidizing methane, wherein the temperature of the exhaust gas supplied to the sulfur oxide adsorption section is 300°C or higher and 600°C or lower. Because the temperature of the exhaust gas supplied to the sulfur oxide adsorption section is 300°C or higher and 600°C or lower, the oxidation of carbon monoxide in the sulfur oxide adsorption section generates heat, causing the temperature of the exhaust gas to rise. Therefore, the exhaust gas can be supplied to the methane oxidation catalyst section at a temperature suitable for methane oxidation, and the methane oxidation efficiency can be improved. [Brief explanation of the drawing]

[0031] [Figure 1] Figure 1 is a schematic diagram of a first embodiment of the exhaust gas treatment system of the present disclosure. [Figure 2] Figure 2 is a plan view of the sulfur oxide adsorption section and the methane oxidation catalyst section in the exhaust gas treatment system shown in Figure 1. [Figure 3] Figures 3A and 3B are perspective views of the sulfur oxide adsorption section in the exhaust gas treatment system shown in Figure 2. [Figure 4] Figures 4A and 4B are perspective views of the methane oxidation catalyst section in the exhaust gas treatment system shown in Figure 2. [Figure 5] Figure 5 is a schematic graph showing the relationship between the active metal content per unit area of ​​the methane oxidation catalyst and the distance from the upstream side in the exhaust gas flow direction, as shown in Figure 4. [Figure 6] Figure 6 is a schematic diagram of a second embodiment of the exhaust gas treatment system of the present disclosure. [Figure 7] Figure 7 is a plan view of the sulfur oxide adsorption section and the methane oxidation catalyst section in the exhaust gas treatment system shown in Figure 6. [Modes for carrying out the invention]

[0032] 1. First embodiment of an exhaust gas treatment system A first embodiment of the exhaust gas treatment system 1 will be described with reference to Figures 1 and 2.

[0033] The exhaust gas treatment system 1 treats exhaust gas containing methane, sulfur oxides, and carbon monoxide emitted from an internal combustion engine. For example, the exhaust gas treatment system 1 treats exhaust gas containing methane, sulfur oxides, and carbon monoxide emitted from an LNG-fueled ship. The exhaust gas treatment system 1 also treats exhaust gas containing methane, sulfur oxides, and carbon monoxide generated in processes such as gas-phase reactions in a chemical plant. Examples of internal combustion engines include onshore engines and marine engines.

[0034] The exhaust gas is not particularly limited as long as it contains methane, sulfur oxides, and carbon monoxide. Specifically, the concentrations of methane, sulfur oxides, and carbon monoxide in the exhaust gas are not particularly limited. As will be described in more detail later, the configuration of the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 can be adjusted according to the concentrations of methane, sulfur oxides, and carbon monoxide in the exhaust gas.

[0035] The exhaust gas treatment system 1 comprises an exhaust passage 2, a sulfur oxide adsorption section 3, and a methane oxidation catalyst section 4. Specifically, the exhaust gas treatment system 1 comprises an exhaust passage 2, a sulfur oxide adsorption section 3 interposed in the exhaust passage 2, and a methane oxidation catalyst section 4 interposed in the exhaust passage 2 and positioned downstream of the sulfur oxide adsorption section 3 in the direction of exhaust gas flow. The exhaust gas treatment system 1 may also include other components as needed.

[0036] In the exhaust gas treatment system 1, the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 are preferably arranged at a distance from each other in the direction of exhaust gas flow. Arrangement at a distance from each other in the direction of exhaust gas flow means that the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 do not come into contact, and that no other components for treating harmful substances in the exhaust gas (for example, other adsorption units other than the sulfur oxide adsorption unit 3 and other exhaust gas treatment catalyst units other than the methane oxidation catalyst unit 4) are placed between the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4. Other components that do not affect the treatment of harmful substances in the exhaust gas (for example, an exhaust passage 2, a flow straightener, and a concentration sensor) may be placed between the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4.

[0037] In the exhaust gas treatment system 1, the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 are more preferably arranged with a space between them in the direction of exhaust gas flow. The arrangement of the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 with a space between them in the direction of exhaust gas flow means that the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 do not come into contact, and that no other components for treating harmful substances in the exhaust gas (for example, other adsorption units other than the sulfur oxide adsorption unit 3 and other exhaust gas treatment catalyst units other than the methane oxidation catalyst unit 4) are placed between the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4. Furthermore, there is no exhaust passage 2 between the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4. A flow straightening device, a concentration sensor (described later), etc., that do not affect the treatment of harmful substances in the exhaust gas may be placed between the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4.

[0038] As shown in Figure 2, in the exhaust gas treatment system 1 of this embodiment, the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 are arranged with space between them in the direction of exhaust gas flow, and are also arranged in a single reactor. In the exhaust gas treatment system 1 of this embodiment, since the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 are arranged in a single reactor, an exhaust passage 2 is not arranged between them, however, a flow straightening device, a concentration sensor, etc. (not shown) can be arranged as appropriate.

[0039] The distance between the sulfur oxide adsorption section 3 and the methane oxidation catalyst section 4 in the direction of exhaust gas flow is not particularly limited. The distance between the sulfur oxide adsorption section 3 and the methane oxidation catalyst section 4 in the direction of exhaust gas flow is, for example, 10 mm to 1000 mm, preferably 10 mm to 500 mm, and more preferably 50 mm to 300 mm. Alternatively, the above distance may be, for example, 10 mm or more, preferably 50 mm or more, and also, for example, 1000 mm or less, preferably 500 mm or less, and more preferably 300 mm or less.

[0040] If the distance between the sulfur oxide adsorption section 3 and the methane oxidation catalyst section 4 in the direction of exhaust gas flow is below the above upper limit, it is possible to suppress the excessive decrease in the temperature of the exhaust gas, which has risen due to the sulfur oxide adsorption section 3, before it reaches the methane oxidation catalyst section 4.

[0041] 1.1. Exhaust passage In the direction of exhaust gas flow, the upstream end (inlet) of the exhaust passage 2 is connected to the outlet of the exhaust gas discharged from the internal combustion engine. The exhaust gas discharged from the internal combustion engine flows through the exhaust passage 2. Also in the direction of exhaust gas flow, the downstream end of the exhaust passage 2 is open to the outside air or connected to a known aftertreatment device (for example, another exhaust gas treatment device equipped with a denitrification catalyst, ammonia decomposition catalyst, N2O decomposition catalyst, etc.).

[0042] 1.2.Sulfur oxide adsorption section The sulfur oxide adsorption unit 3 is interposed in the exhaust passage 2 and is positioned upstream of the methane oxidation catalyst unit 4 (described later) in the direction of exhaust gas flow. One embodiment of the sulfur oxide adsorption unit 3 will be described with reference to Figures 2, 3A, and 3B.

[0043] As shown in Figure 2, the sulfur oxide adsorption unit 3 of this embodiment includes a sulfur oxide adsorbent unit 31 along the direction of exhaust gas flow. Furthermore, as shown in Figure 3B, the sulfur oxide adsorbent unit 31 includes a sulfur oxide adsorbent 32. The sulfur oxide adsorbent 32 adsorbs sulfur oxides and further oxidizes oxidizable components, including carbon monoxide. In other words, the sulfur oxide adsorption unit 3 includes a sulfur oxide adsorbent 32 that adsorbs sulfur oxides and further oxidizes oxidizable components, including carbon monoxide. Examples of oxidizable components include carbon monoxide, methane, and hydrocarbons (excluding methane).

[0044] As shown in Figure 1, the methane oxidation catalyst section 4 of this embodiment comprises a plurality of methane oxidation catalyst units 41 arranged along the direction of exhaust gas flow.

[0045] (1) Sulfur oxide adsorbent The sulfur oxide adsorbent 32 adsorbs sulfur oxides and further oxidizes the oxidizable components, including carbon monoxide.

[0046] The sulfur oxide adsorbent 32 comprises a sulfur oxide adsorption component. As shown in Figure 3B, the sulfur oxide adsorbent 32 preferably comprises a sulfur oxide adsorption component and a substrate supporting the sulfur oxide adsorption component. Furthermore, the sulfur oxide adsorbent may contain additives as needed.

[0047] (Sulfur oxide adsorption component) The sulfur oxide adsorbent adsorbs sulfur oxides (e.g., sulfur dioxide) contained in exhaust gas. Furthermore, the sulfur oxide adsorbent adsorbent oxidizes oxidizable components, including carbon monoxide. The sulfur oxide adsorbent adsorbent is supported on a substrate.

[0048] The sulfur oxide adsorbent is not particularly limited as long as it adsorbs sulfur oxides and oxidizes the oxidizable component, including carbon monoxide. Examples of sulfur oxide adsorbent components include metals and metal oxides. Preferably, metal oxides are used.

[0049] Examples of sulfur oxide adsorption components include iron (Fe), manganese (Mn), cerium (Ce), copper (Cu), magnesium (Mg), aluminum (Al), titanium (Ti), zirconium (Zr), nickel (Ni), and cobalt (Co). Other examples of sulfur oxide adsorption components include iron oxide, manganese oxide, copper oxide, magnesium oxide, zirconia, nickel oxide, and cobalt oxide. Manganese oxide is more preferably included. Note that the sulfur oxide adsorption components do not include platinum group metals or oxides of platinum group metals, which are included as active metals in the methane oxidation catalyst 42 described later.

[0050] The sulfur oxide adsorption components may be used alone or in combination of two or more. When two or more are used in combination, the sulfur oxide adsorption components include, for example, manganese oxide and at least one selected from the group consisting of iron oxide (Fe2O3), copper oxide (CuO), magnesium oxide (MgO), zirconia (ZrO2), nickel oxide (NiO), and cobalt oxide (CoO, Co2O3, Co3O4). The sulfur oxide adsorption components may also be composite oxides of multiple metals. Preferably, they do not contain composite oxides of multiple metals.

[0051] Examples of manganese oxide include divalent manganese oxide (MnO), trivalent manganese oxide (Mn2O3), and tetravalent manganese oxide (MnO2). Preferably, trivalent manganese oxide (Mn2O3) and tetravalent manganese oxide (MnO2) are used. The manganese oxide may consist of manganese oxide of a single valency, or manganese oxides of different valencies may be used in combination. The valency of the manganese oxide can be detected by X-ray photoelectron spectroscopy (XPS) analysis.

[0052] If the sulfur oxide adsorbent component includes manganese oxide, it exhibits high sulfur oxide adsorption and high oxidation performance against oxidizable components, including carbon monoxide, in relatively high-temperature environments. In particular, if the manganese oxide consists of trivalent manganese oxide (Mn2O3) and / or tetravalent manganese oxide (MnO2), it exhibits high sulfur oxide adsorption in relatively high-temperature environments.

[0053] Furthermore, sulfur oxide adsorption capacity is an indicator of the adsorption rate of sulfur oxides, and it indicates the adsorption of sulfur oxides and the suppression of desorption of adsorbed sulfur oxides. In other words, high sulfur oxide adsorption capacity means that the adsorption rate of sulfur oxides is high, or to put it another way, that sulfur oxides are adsorbed with high efficiency while the desorption of adsorbed sulfur oxides is suppressed.

[0054] When the sulfur oxide adsorbent contains manganese oxide, the ratio of manganese oxide content to the total amount of sulfur oxide adsorbent (= manganese oxide content (moles) / total amount of sulfur oxide adsorbent (total moles) × 100) is 20 moles or more, preferably 30 moles or more, more preferably 40 moles or more, even more preferably 50 moles or more, particularly preferably 60 moles or more, and 100 moles or less, preferably 95 moles or less, more preferably 90 moles or less.

[0055] If the sulfur oxide adsorbent contains manganese oxide, and the ratio of manganese oxide content to the total amount of sulfur oxide adsorbent (= manganese oxide content (moles) / total amount of sulfur oxide adsorbent (total moles) × 100) is within the above range, then it exhibits high sulfur oxide adsorption and high oxidation performance against oxidizable components including carbon monoxide in relatively high-temperature environments.

[0056] When the sulfur oxide adsorbent component contains manganese oxide, the ratio of metals and metal oxides other than manganese oxide to the total amount of sulfur oxide adsorbent component (= content of metals and metal oxides other than manganese oxide (moles) / total amount of sulfur oxide adsorbent component (total moles) × 100) is, for example, 0 moles or more, preferably 5 moles or more, more preferably 10 moles or more, and also, for example, 80 moles or less, preferably 70 moles or less, more preferably 60 moles or less, even more preferably 50 moles or less, and particularly preferably 40 moles or less.

[0057] The specific surface area of ​​the sulfur oxide adsorbent is, for example, 10 m². 2 / g or more, preferably 30m 2 / g or more, comfortable, 50m 2 It is 1 / g or more.

[0058] The average particle size of the sulfur oxide adsorbent is, for example, 50 μm or less, preferably 30 μm or less, and more preferably 10 μm or less.

[0059] If the sulfur oxide adsorbent contains multiple metals and / or metal oxides, the specific surface area and average particle size of the sulfur oxide adsorbent are the overall average values.

[0060] (base material) Examples of substrates include inorganic fiber sheets. Examples of inorganic fiber sheets include glass paper and ceramic paper. Glass paper is preferred.

[0061] Commercially available glass paper containing an organic binder can also be used. Examples of organic binders used in commercially available glass paper include acrylic resin, polyvinyl alcohol (PVA)-polyvinyl acetate copolymer, unsaturated polyester resin, and epoxy resin.

[0062] The base material has thickness in the height direction and extends in the surface direction (the direction of exhaust gas flow and the width direction). The shape of the base material is, for example, a flat plate and / or corrugated plate that extends in the direction of exhaust gas flow and the width direction. Preferably, the base material is a flat plate of glass paper and / or corrugated glass paper that extends in the direction of exhaust gas flow and the width direction. The direction perpendicular to the height direction is the surface direction, and in the surface direction, the direction perpendicular to the direction of exhaust gas flow is the width direction.

[0063] Since the external shape of the substrate is the same as the external shape of the sulfur oxide adsorbent 32, the shape of the substrate and the shape of the sulfur oxide adsorbent 32 are the same. In other words, the shape of the sulfur oxide adsorbent 32 is, for example, a flat plate and / or corrugated plate that extends in the direction of exhaust gas flow and width.

[0064] The dimensions of the base material are adjusted as appropriate according to the application. Specifically, the length in the exhaust gas flow direction and the width direction of the base material are not particularly limited. The length in the exhaust gas flow direction of the base material is, for example, 100 mm to 1000 mm. The width direction of the base material is, for example, 100 mm to 500 mm. The length in the exhaust gas flow direction of the base material is preferably longer than the width direction of the base material. The thickness (height direction) of the base material is, for example, 0.2 mm to 1.0 mm.

[0065] The amount of sulfur oxide adsorbent components supported per unit area of ​​the substrate is, for example, 150 g / m². 2 Preferably, 200 g / m² 2 More comfortably, 250g / m² 2 In addition, for example, 300g / m 2 The following applies. Note that the amount of sulfur oxide adsorbent components supported per unit area of ​​the substrate is the amount of sulfur oxide adsorbent components supported per unit area on the surface extending in the planar direction of the substrate (the direction of exhaust gas flow and the width direction).

[0066] The substrate is not particularly limited as long as it can support sulfur oxide adsorbent components and can be commonly used as a sulfur oxide adsorbent; for example, it may be a monolithic substrate having a cross-sectional network structure (honeycomb structure).

[0067] (Additives) The sulfur oxide adsorbent 32 may contain additives as needed.

[0068] The additives are not particularly limited as long as they are additives commonly used in sulfur oxide adsorbents 32, and examples include diluents and binders. The sulfur oxide adsorbent 32 preferably contains a binder.

[0069] The diluent is a substance that is inert to the methane oxidation reaction, and by adding the diluent to the sulfur oxide adsorbent 32, temperature control can be easily achieved.

[0070] Examples of diluents include alumina (e.g., α-alumina, θ-alumina, γ-alumina) and titania (e.g., rutile titania, anatase titania). Diluents may be used individually or in combination of two or more.

[0071] The binder, for example, increases the strength of the substrate. In other words, it can improve the strength of the sulfur oxide adsorbent 32. The binder also, for example, binds the sulfur oxide adsorbents 32 together.

[0072] Examples of binders include inorganic binders. Examples of inorganic binders include metal oxides, metalloid oxides, and metal hydroxides.

[0073] Examples of metal oxides include titania, alumina, and ceria. Examples of metalloid oxides include silica. Examples of metal hydroxides include iron hydroxide, aluminum hydroxide, and cerium hydroxide.

[0074] Binders can be used individually or in combination of two or more types.

[0075] The proportions of diluent components and binders in the sulfur oxide adsorbent 32 can be arbitrarily selected depending on the specific application of the sulfur oxide adsorbent 32.

[0076] (2) Sulfur oxide adsorbent unit The sulfur oxide adsorbent unit 31 has a sulfur oxide adsorbent 32. More specifically, as shown in Figure 3B, the sulfur oxide adsorbent unit 31 has a casing 33 and a sulfur oxide adsorbent 32 filled inside the casing 33.

[0077] The shape of the casing 33 is not particularly limited, but examples include a rectangular tube shape and a cylindrical shape extending in the direction of exhaust gas flow. Preferably, a rectangular tube shape extending in the direction of exhaust gas flow is used. Specifically, the casing 33 may consist of a casing body with a substantially U-shape in cross-section and a flat plate-shaped cover that covers its opening, a casing body with a substantially square shape in cross-section only, and a casing body with a substantially L-shape in cross-section and a cover with a substantially inverted L-shape in cross-section that fits thereto.

[0078] The dimensions of the casing 33 are adjusted as appropriate depending on the application. Specifically, the width and height of the casing 33 are not particularly limited, as long as they can accommodate the sulfur oxide adsorbent 32.

[0079] An inorganic fiber blanket 44 may be laid over the entire inner surface of the casing 33. By laying an inorganic fiber blanket 44 on the inner surface of the casing 33, vibrations can be suppressed. Examples of inorganic fibers in the inorganic fiber blanket 44 include ceramic fibers, glass fibers, silica sol fibers, alumina fibers, and rock wool. Ceramic fibers are preferred.

[0080] In the sulfur oxide adsorbent unit 31, the sulfur oxide adsorbent 32 is packed within the casing 33 in a height direction perpendicular to the exhaust gas flow direction. Specifically, in the sulfur oxide adsorbent unit 31, flat plate-shaped sulfur oxide adsorbent 32 and corrugated plate-shaped sulfur oxide adsorbent 32 are stacked alternately within the casing 33 without being bonded together. This stacking causes the sulfur oxide adsorbent 32 to form a cross-sectional network structure (honeycomb structure). In other words, the sulfur oxide adsorbent unit 31 comprises multiple stacked sulfur oxide adsorbent 32. The number of stacked flat plate-shaped sulfur oxide adsorbent 32 and corrugated plate-shaped sulfur oxide adsorbent 32 is not particularly limited.

[0081] As described above, the sulfur oxide adsorption unit 3 of this embodiment includes a sulfur oxide adsorbent unit 31 having a sulfur oxide adsorbent. The sulfur oxide adsorbent unit 31 has a sulfur oxide adsorbent. In other words, the sulfur oxide adsorption unit 3 includes a sulfur oxide adsorbent for adsorbing sulfur oxides contained in exhaust gas and oxidizing carbon monoxide.

[0082] As shown in Figures 2 and 3A, in the sulfur oxide adsorption section 3 of this embodiment, the sulfur oxide adsorbent units 31 are arranged along the direction of exhaust gas flow. In addition, in the sulfur oxide adsorption section 3 of this embodiment, a plurality of (12 in Figure 3A) sulfur oxide adsorbent units 31 are aligned in the width direction and height direction perpendicular to the direction of exhaust gas flow. Although not shown, a plurality of sulfur oxide adsorbent units 31 may also be aligned in the direction of exhaust gas flow.

[0083] The number and arrangement of the sulfur oxide adsorbent units 31 in the sulfur oxide adsorption unit 3 are not particularly limited and can be adjusted as appropriate depending on the installation space and other factors.

[0084] In the sulfur oxide adsorption section 3, the content of sulfur oxide adsorbent components per unit area of ​​sulfur oxide adsorbent units 31 adjacent to each other in the planar direction is not particularly limited and may be the same or different. Preferably, they are the same.

[0085] When the sulfur oxide adsorption section 3 is used for exhaust gas discharged from an LNG-fueled ship, the total amount of sulfur oxide adsorbent packed in the sulfur oxide adsorption section 3 is, for example, 0.1 kg or more, preferably 0.5 kg or more, more preferably 1.0 kg or more, even more preferably 5.0 kg or more, and particularly preferably 10 kg or more.

[0086] 1.3. Methane Oxidation Catalyst Section The methane oxidation catalyst section 4 is interposed in the exhaust passage 2 and is positioned downstream of the sulfur oxide adsorption section 3 in the direction of exhaust gas flow. One embodiment of the methane oxidation catalyst section 4 will be described with reference to Figures 2, 4A, and 4B.

[0087] As shown in FIG. 2, the methane oxidation catalyst unit 4 of the present embodiment includes a methane oxidation catalyst unit 41 along the flow direction of exhaust gas. Further, as shown in FIG. 4B, the methane oxidation catalyst unit 41 has a methane oxidation catalyst 42. The methane oxidation catalyst 42 oxidizes components to be oxidized including methane. In other words, the methane oxidation catalyst unit 4 is provided with the methane oxidation catalyst 42 that oxidizes components to be oxidized including methane.

[0088] (1) Methane oxidation catalyst The methane oxidation catalyst 42 oxidizes components to be oxidized including methane in exhaust gas.

[0089] The methane oxidation catalyst 42 is not particularly limited as long as it can oxidize components to be oxidized including methane in exhaust gas, but at least a part of the methane oxidation catalyst 42 has an active metal that oxidizes components to be oxidized including methane in exhaust gas. Preferably, the entire methane oxidation catalyst 42 has the active metal.

[0090] As shown in FIG. 4B, the methane oxidation catalyst 42 preferably has an active metal and a base material supporting the active metal. Furthermore, the methane oxidation catalyst 42 may optionally contain additives as needed.

[0091] The methane oxidation catalyst 42 is, for example, in the form of a flat plate and / or a corrugated plate extending in the flow direction of exhaust gas.

[0092] The content of the active metal per unit area of the methane oxidation catalyst 42 is, for example, 0.5g / m 2 ~50g / m 2 , preferably 1g / m 2 ~25g / m 2 .

[0093] The content of the active metal per unit area of the methane oxidation catalyst 42 is, for example, 0.5g / m 2 or more, preferably 1g / m 2 or more, and for example, 50g / m 2 or less, preferably 25g / m 2The following applies. Note that the active metal content per unit area of ​​the methane oxidation catalyst 42 is the active metal content per unit area on the surface in contact with the exhaust gas. In other words, it is the active metal content per unit area on the surface of the methane oxidation catalyst 42 that extends in the surface direction (the direction of exhaust gas flow and the width direction) (the same applies hereafter).

[0094] (active metal) The activated metal is supported on a substrate, for example. Specifically, the activated metal is supported on the substrate together with the particulate components described later.

[0095] The active metal comprises platinum group metals and / or oxides of platinum group metals. Preferably, it comprises platinum group metals and / or oxides of platinum group metals as its main component. More preferably, it consists of platinum group metals and / or oxides of platinum group metals. In other words, the active metal preferably does not contain other metals and other metal oxides other than platinum group metals and / or oxides of platinum group metals.

[0096] Furthermore, when an active metal is described as containing platinum group metals and / or oxides of platinum group metals as its main component, it means that if the active metal contains other metals and other metal oxides in addition to platinum group metals and / or oxides of platinum group metals, the proportion of platinum group metals in the active metal (= platinum group metal content / total amount of active metal × 100) is greater than 50% by mass. In addition, even if the active metal consists of platinum group metals and / or oxides of platinum group metals, the inclusion of unavoidable impurities is permissible. The proportion of unavoidable impurities in the active metal is, for example, 1.0% by mass or less, preferably 0.5% by mass or less, and more preferably 0.1% by mass or less.

[0097] Examples of platinum group metals include palladium (Pd), platinum (Pt), iridium (Ir), rhodium (Rh), and ruthenium (Ru). Examples of platinum group metal oxides include palladium oxide, platinum oxide, iridium oxide, rhodium oxide, and ruthenium oxide. Active metals may be used individually or in combination of two or more.

[0098] The active metal comprises platinum group metals and / or oxides of platinum group metals. More preferably, it comprises at least one selected from the group consisting of Pd, Pt, Ru, and their oxides. Even more preferably, it comprises at least one selected from the group consisting of Pd, Pt, and Ru. Even more preferably, it comprises Pd and Pt, or Pd and Ru (Pd-Pt composite support, Pd-Ru composite support).

[0099] The active metal consists of platinum group metals and / or oxides of platinum group metals. More preferably, it consists of at least one selected from the group consisting of Pd, Pt, Ru, and their oxides. Even more preferably, it consists of at least one selected from the group consisting of Pd, Pt, and Ru. Even more preferably, it consists of Pd and Pt, or Pd and Ru (Pd-Pt composite support, Pd-Ru composite support).

[0100] If the active metal includes metals and other metal oxides other than platinum group metals and / or oxides of platinum group metals, examples of other metals and other metal oxides include nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), copper (Cu), and oxides thereof.

[0101] If the active metal contains other metals and other metal oxides other than platinum group metals and / or oxides of platinum group metals, the content of platinum group metals in the active metal (= platinum group metal content / total amount of active metal × 100) is, for example, more than 50% by mass, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0102] When the active metal contains Pd, the Pd content in the active metal (= Pd content / total amount of active metal × 100) is, from the viewpoint of ensuring catalytic activity, for example, 30% by mass or more, preferably 50% by mass or more, more preferably 70% by mass or more, and also, for example, less than 100% by mass, preferably 95% by mass or less, more preferably 90% by mass or less.

[0103] When the active metal contains Pt and / or Ru, the proportion of Pt and Ru in the active metal (= Pt and Ru content / total amount of active metal × 100) is, for example, 1.0% by mass or more, preferably 5.0% by mass or more, more preferably 10% by mass or more, and also, for example, 60% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less.

[0104] (Particle component) The particulate components increase the strength of the substrate. In other words, the strength of the methane oxidation catalyst 42 can be improved.

[0105] The particulate components are supported on the substrate together with the active metal. Alternatively, the particulate components may support the active metal; in this case, the active metal is supported on the particulate components and then supported on the substrate.

[0106] Examples of particulate components include metals and metal oxides other than platinum group metals and platinum group metal oxides. Metalloid oxides can also be used as particulate components. Examples of particulate components include zirconia, ceria, silica, alumina, titania, and zeolites.

[0107] The particulate components may be used individually or in combination of two or more. Furthermore, the particulate components may be composite oxides such as zirconia, ceria, silica, alumina, titania, and zeolite. Examples of composite oxides include ceria-zirconia composite oxide. X Zr 1-XO2) is, for example, a solid solution of ceria (CeO2) and zirconia (ZrO2). Note that X is greater than 0 and less than 1.

[0108] The particulate components preferably include zirconia and / or ceria-zirconia composite oxides. The zirconia includes, for example, a monoclinic zirconia (m-ZrO2) phase and / or a tetragonal zirconia (t-ZrO2) phase. The ceria-zirconia composite oxide includes, for example, tetragonal ceria-zirconia (t-Ce X Zr 1-X Contains the O2 phase.

[0109] Furthermore, zirconia contains a monoclinic zirconia (m-ZrO2) phase and / or a tetragonal zirconia (t-ZrO2) phase, and ceria-zirconia composite oxide is tetragonal ceria-zirconia (t-Ce X Zr 1-X The presence of the O2 phase can be confirmed by measuring the X-ray diffraction (XRD) pattern.

[0110] The zirconia content percentages listed below include both zirconia present individually in the particle components and zirconia forming ceria-zirconia composite oxides.

[0111] When the particulate component contains zirconia, the zirconia content in the particulate component is, for example, 50% by mass or more, preferably 70% by mass or more, and more preferably 80% by mass or more.

[0112] (Additives) The methane oxidation catalyst 42 may contain additives as needed. Examples of additives include those listed for the sulfur oxide adsorbent 32 above.

[0113] (base material) The substrate is the same as the substrate described for the sulfur oxide adsorbent 32 above. Since the external shape of the substrate is the same as the external shape of the methane oxidation catalyst 42, the shape of the substrate and the shape of the methane oxidation catalyst 42 are identical. That is, the shape of the methane oxidation catalyst 42 is, for example, a flat plate and / or corrugated plate extending in the exhaust gas flow direction and width direction.

[0114] The amount of active metal supported per unit area of ​​the substrate is, for example, 0.5 g / m². 2 Preferably, 1 g / m 2 In addition, for example, 50g / m 2 Preferably, 25 g / m 2 The following applies. In this embodiment, the amount of active metal supported on the substrate is substantially uniform in the direction of exhaust gas flow. The amount of active metal supported per unit area of ​​the substrate is the same as the amount of active metal per unit area of ​​each methane oxidation catalyst 42. The amount of active metal supported per unit area of ​​the substrate is the amount of active metal supported per unit area on the surface of the substrate that extends in the surface direction (direction of exhaust gas flow and width direction).

[0115] The amount of particulate matter supported per unit area of ​​the substrate is, for example, 10 g / m². 2 Preferably, 20 g / m 2 In addition, for example, 500g / m 2 Preferably, 450 g / m 2 The following applies: In this embodiment, the amount of particulate matter on the substrate is substantially uniform in the direction of exhaust gas flow. The amount of particulate matter per unit area of ​​the substrate is the amount of particulate matter per unit area on the surface of the substrate that extends in the surface direction (direction of exhaust gas flow and width direction).

[0116] (2) Methane oxidation catalyst unit The methane oxidation catalyst unit 41 has a methane oxidation catalyst 42. More specifically, as shown in Figure 4B, the methane oxidation catalyst unit 41 has a casing 43 and a methane oxidation catalyst 42 filled inside the casing 43. In addition, an inorganic fiber blanket 44 may be laid over the entire inner surface of the casing 43.

[0117] The casing 43 and inorganic fiber blanket 44 are the same as the casing 33 described above in the sulfur oxide adsorbent unit 31.

[0118] In the methane oxidation catalyst unit 41, the methane oxidation catalyst 42 is packed within the casing 43 in a height direction perpendicular to the exhaust gas flow direction. Specifically, in the methane oxidation catalyst unit 41, flat methane oxidation catalysts 42 and corrugated methane oxidation catalysts 42 are stacked alternately within the casing 43 without being bonded together. This stacking arrangement causes the methane oxidation catalysts 42 to form a cross-sectional network structure (honeycomb structure). In other words, the methane oxidation catalyst unit 41 comprises multiple stacked methane oxidation catalysts 42. The number of stacked flat methane oxidation catalysts 42 and corrugated methane oxidation catalysts 42 is not particularly limited.

[0119] In this embodiment, the amount of active metal per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 is substantially uniform in the direction of exhaust gas flow. In other words, the methane oxidation catalyst unit 41 has a methane oxidation catalyst with substantially uniform active metal content per unit area in the direction of exhaust gas flow.

[0120] Furthermore, when we say that the active metal content per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 is substantially uniform in the direction of exhaust gas flow, we mean that the active metal content per unit area of ​​each individual methane oxidation catalyst 42 is substantially uniform, and that the methane oxidation catalyst unit 41 is formed using only such methane oxidation catalysts 42.

[0121] As described above, the methane oxidation catalyst unit 4 of this embodiment comprises a plurality of methane oxidation catalyst units 41, each having a methane oxidation catalyst 42, arranged along the direction of exhaust gas flow. Each of the plurality of methane oxidation catalyst units 41 has a methane oxidation catalyst 42. In other words, the methane oxidation catalyst unit 4 comprises a methane oxidation catalyst 42 for oxidizing methane contained in the exhaust gas. Therefore, when exhaust gas containing methane is supplied to the methane oxidation catalyst unit 4, the methane in the exhaust gas is oxidized to CO2 and H2O.

[0122] In the methane oxidation catalyst section 4 of this embodiment, a plurality of methane oxidation catalyst units 41 are arranged in alignment along the direction of exhaust gas flow. In the methane oxidation catalyst section 4 shown in Figure 4A, three methane oxidation catalyst units 41a, 41b, and 41c are arranged in alignment along the direction of exhaust gas flow. In addition, in the methane oxidation catalyst section 4, a plurality of methane oxidation catalyst units 41 may be arranged in a planar direction (both width and height directions) perpendicular to the direction of exhaust gas flow. In the methane oxidation catalyst section 4 shown in Figure 4A, a plurality (12 in Figure 4A) of methane oxidation catalyst units 41 are arranged in alignment in the width and height directions.

[0123] In other words, in the methane oxidation catalyst section 4 shown in Figure 4A, multiple (36 in Figure 1) methane oxidation catalyst units 41 are arranged in alignment in the direction of exhaust gas flow, width, and height.

[0124] The number and arrangement of the methane oxidation catalyst units 41 in the methane oxidation catalyst section 4 are not particularly limited and can be adjusted as appropriate depending on the installation space and other factors.

[0125] In the methane oxidation catalyst section 4 of this embodiment, in methane oxidation catalyst units 41 adjacent to each other in the exhaust gas flow direction, the amount of active metal per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 located upstream in the exhaust gas flow direction is greater than the amount of active metal per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 located downstream in the exhaust gas flow direction.

[0126] In other words, in Figure 4B, among the methane oxidation catalyst units 41a, 41b, and 41c, which are arranged linearly in the direction of exhaust gas flow, the amount of active metal per unit area of ​​the methane oxidation catalyst in methane oxidation catalyst unit 41a is greater than the amount of active metal per unit area of ​​the methane oxidation catalyst in methane oxidation catalyst unit 41b. Furthermore, the amount of active metal per unit area of ​​the methane oxidation catalyst in methane oxidation catalyst unit 41b is greater than the amount of active metal per unit area of ​​the methane oxidation catalyst in methane oxidation catalyst unit 41c.

[0127] As described above, in this embodiment, the amount of active metal per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 is substantially uniform in the direction of exhaust gas flow. Therefore, in such a methane oxidation catalyst section 4, as shown in Figure 5, the amount of active metal per unit area of ​​the methane oxidation catalyst 42 decreases in stages from the upstream side to the downstream side in the direction of exhaust gas flow. In other words, in the methane oxidation catalyst section 4, the amount of active metal per unit area of ​​the methane oxidation catalyst 42 decreases from the upstream side to the downstream side in the direction of exhaust gas flow.

[0128] Figure 5 is an example of a schematic graph showing the relationship between the active metal content per unit area of ​​the methane oxidation catalyst and the distance from the upstream side in the exhaust gas flow direction in the methane oxidation catalyst section 4 of this embodiment. In the graph of Figure 5, the upstream side in the exhaust gas flow direction indicates the first position in the methane oxidation catalyst section 4 where the exhaust gas comes into contact with the methane oxidation catalyst.

[0129] In this embodiment, the content of active metal per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 is substantially uniform in the direction of exhaust gas flow, but is not limited thereto. Specifically, the methane oxidation catalyst unit 41 may have a methane oxidation catalyst 42 in which the content of active metal per unit area decreases from the upstream side to the downstream side in the direction of exhaust gas flow.

[0130] In this case, among methane oxidation catalyst units 41 adjacent to each other in the exhaust gas flow direction, the minimum amount of active metal per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 located upstream in the exhaust gas flow direction is greater than the maximum amount of active metal per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 located downstream in the exhaust gas flow direction.

[0131] The minimum active metal content per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 located upstream in the exhaust gas flow direction refers to the active metal content per unit area of ​​the methane oxidation catalyst 42 at the downstream end of the methane oxidation catalyst unit 41 located upstream in the exhaust gas flow direction. Conversely, the maximum active metal content per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 located downstream in the exhaust gas flow direction refers to the active metal content per unit area of ​​the methane oxidation catalyst 42 at the upstream end of the methane oxidation catalyst unit 41 located downstream in the exhaust gas flow direction.

[0132] Furthermore, a methane oxidation catalyst unit 41 having a methane oxidation catalyst 42 in which the active metal content per unit area is substantially uniform in the exhaust gas flow direction, and a methane oxidation catalyst unit 41 having a methane oxidation catalyst 42 in which the active metal content per unit area decreases from the upstream side to the downstream side in the exhaust gas flow direction, may be used in combination. In other words, at least one of the methane oxidation catalyst units 41 has a methane oxidation catalyst 42 in which the active metal content per unit area is substantially uniform in the exhaust gas flow direction, and at least one of the methane oxidation catalyst units 41 has a methane oxidation catalyst 42 in which the active metal content per unit area decreases from the upstream side to the downstream side in the exhaust gas flow direction.

[0133] In this case as well, among the methane oxidation catalyst units 41 adjacent to each other in the exhaust gas flow direction, the minimum amount of active metal per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 located upstream in the exhaust gas flow direction is greater than the maximum amount of active metal per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 located downstream in the exhaust gas flow direction.

[0134] In methane oxidation catalyst units 41 adjacent to each other in the exhaust gas flow direction, the ratio of the active metal content per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 located downstream in the exhaust gas flow direction to the active metal content per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 located upstream in the exhaust gas flow direction (active metal content per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 located downstream in the exhaust gas flow direction / active metal content per unit area of ​​the methane oxidation catalyst 42 in the methane oxidation catalyst unit 41 located upstream in the exhaust gas flow direction) is, for example, 0.1 to 1.0, preferably 0.2 to 0.9, more preferably 0.3 to 0.8, and even more preferably 0.4 to 0.7. Furthermore, the above ratios are, for example, less than 1.0, preferably 0.9 or less, more preferably 0.8 or less, even more preferably 0.7 or less, and also, for example, 0.1 or more, preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.4 or more.

[0135] The above ratio may be the same or different for all methane oxidation catalyst units 41 adjacent to each other in the exhaust gas flow direction. From the viewpoint of ease of manufacture, the above ratio is preferably the same for all methane oxidation catalyst units 41 adjacent to each other in the exhaust gas flow direction.

[0136] In the methane oxidation catalyst section 4, the amount of active metal per unit area of ​​the methane oxidation catalyst 42 in methane oxidation catalyst units 41 adjacent to each other in the planar direction is not particularly limited and may be the same or different.

[0137] When the methane oxidation catalyst section 4 is used for exhaust gas containing methane discharged from an LNG-fueled ship, the total amount of methane oxidation catalyst 42 packed into the methane oxidation catalyst section 4 is, for example, 0.5 kg or more, preferably 5 kg or more, more preferably 10 kg or more, even more preferably 50 kg or more, particularly preferably 100 kg or more, and most preferably 150 kg or more.

[0138] 1.4. Other Configurations The exhaust gas treatment system 1, although not shown in the diagram, may include other components such as a concentration sensor and a control unit, as needed.

[0139] (1) Concentration sensor Examples of concentration sensors include non-contact gas concentration meters that detect sulfur oxide concentrations, methane concentrations, carbon monoxide concentrations, oxygen concentrations, etc., in exhaust gas. The placement of the concentration sensors is not particularly limited. The concentration sensors may be placed in the exhaust passage 2 upstream of the sulfur oxide adsorption unit 3 in the direction of exhaust gas flow, between the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4, or in the exhaust passage 2 downstream of the methane oxidation catalyst unit 4 in the direction of exhaust gas flow. Furthermore, the concentration sensors may be electrically connected to a control unit described later.

[0140] When the concentration sensor detects the sulfur oxide concentration, the sulfur oxide adsorption performance in the sulfur oxide adsorption section 3 can be confirmed over time. Similarly, when the concentration sensor detects the carbon monoxide concentration, the oxidation efficiency of carbon monoxide in the sulfur oxide adsorption section 3 can be confirmed over time. When the concentration sensor detects the methane concentration, the oxidation efficiency of methane in the sulfur oxide adsorption section 3 can be confirmed over time.

[0141] Furthermore, when oxygen concentration is detected by a concentration sensor, the control unit can appropriately change the combustion conditions in the internal combustion engine according to the oxygen concentration.

[0142] (2) Control Unit The control unit is a unit that performs electrical control of the exhaust gas treatment system 1. The control unit consists of a microcomputer equipped with an arithmetic processing unit (CPU) and a memory unit. The control unit controls the exhaust gas treatment system 1 based on a control program stored in the memory unit.

[0143] Furthermore, the control unit is electrically connected to the concentration sensor, as described above.

[0144] The control unit can appropriately adjust the operation of the exhaust gas treatment system 1 based on the sulfur oxide concentration, methane concentration, carbon monoxide concentration, oxygen concentration, etc., in the exhaust gas detected by the concentration sensor.

[0145] 1.5. Effects (1) The exhaust gas treatment system 1 of this disclosure includes a sulfur oxide adsorption unit 3 equipped with a sulfur oxide adsorbent 32 for adsorbing sulfur oxides, and a methane oxidation catalyst unit 4 positioned downstream of the sulfur oxide adsorption unit 3 in the direction of exhaust gas flow and equipped with a methane oxidation catalyst 42 for oxidizing components to be oxidized, including methane. The sulfur oxide adsorption unit 3 oxidizes components to be oxidized, including carbon monoxide. In such an exhaust gas treatment system 1, sulfur oxides are adsorbed by the sulfur oxide adsorption unit 3, suppressing a decrease in the performance of the methane oxidation catalyst unit 4. Furthermore, the sulfur oxide adsorption unit 3 oxidizes components to be oxidized, including carbon monoxide, and increases the temperature of the exhaust gas supplied to the methane oxidation catalyst unit 4. As a result, the oxidation efficiency of methane can be improved.

[0146] (2) In the exhaust gas treatment system 1 of this disclosure, the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 are arranged with a gap between them in the direction of exhaust gas flow. Therefore, the exhaust gas whose temperature has risen due to the sulfur oxide adsorption unit is supplied to the methane oxidation catalyst unit without a decrease in temperature due to contact with other components. As a result, the methane oxidation efficiency can be improved.

[0147] (3) In the exhaust gas treatment system 1 of this disclosure, at least a portion of the methane oxidation catalyst 42 has an active metal that oxidizes methane and other oxidizable components in the exhaust gas, and the content of the active metal per unit area of ​​the methane oxidation catalyst 42 decreases from the upstream to the downstream side in the direction of exhaust gas flow. In the methane oxidation catalyst section 4, the temperature of the exhaust gas increases from the upstream to the downstream side in the direction of exhaust gas flow, so even if the content of the active metal per unit area of ​​the methane oxidation catalyst 42 decreases from the upstream to the downstream side in the direction of exhaust gas flow, the desired methane oxidation efficiency can be maintained. In other words, the content of the active metal can be reduced while maintaining the desired methane oxidation efficiency.

[0148] (4) The exhaust gas treatment system 1 of the present disclosure has a methane oxidation catalyst section 4 which has a plurality of methane oxidation catalyst units 41 along the direction of exhaust gas flow, and each methane oxidation catalyst unit 41 has a methane oxidation catalyst 42 in which the active metal content per unit area is substantially uniform in the direction of exhaust gas flow, and in methane oxidation catalyst units 41 adjacent to each other in the direction of exhaust gas flow, the active metal content per unit area of ​​the methane oxidation catalyst 42 of the methane oxidation catalyst unit 41 located on the upstream side in the direction of exhaust gas flow is greater than the active metal content per unit area of ​​the methane oxidation catalyst 42 of the methane oxidation catalyst unit 41 located on the downstream side in the direction of exhaust gas flow. Therefore, each of the plurality of methane oxidation catalyst units 41 can be easily manufactured, and as a result, the exhaust gas treatment system 1 can be easily manufactured.

[0149] (5) The exhaust gas treatment system 1 of the present disclosure comprises a methane oxidation catalyst section comprising a plurality of methane oxidation catalyst units along the direction of exhaust gas flow, each methane oxidation catalyst unit having a methane oxidation catalyst in which the active metal content per unit area decreases from the upstream side to the downstream side in the direction of exhaust gas flow, and in methane oxidation catalyst units adjacent to each other in the direction of exhaust gas flow, the minimum active metal content per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located on the upstream side in the direction of exhaust gas flow is greater than the maximum active metal content per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located on the downstream side in the direction of exhaust gas flow. Therefore, in the methane oxidation catalyst section, the temperature of the exhaust gas increases from the upstream side to the downstream side in the direction of exhaust gas flow, so even if the active metal content per unit area of ​​the methane oxidation catalyst decreases from the upstream side to the downstream side in the direction of exhaust gas flow, the desired methane oxidation efficiency can be maintained. In other words, the active metal content can be further reduced while maintaining the desired methane oxidation efficiency.

[0150] (6) The exhaust gas treatment system 1 of the present disclosure comprises a methane oxidation catalyst section comprising a plurality of methane oxidation catalyst units along the direction of exhaust gas flow, at least one of the methane oxidation catalyst units having a methane oxidation catalyst with substantially uniform active metal content per unit area in the direction of exhaust gas flow, at least one of the methane oxidation catalyst units having a methane oxidation catalyst with decreasing active metal content per unit area from upstream to downstream in the direction of exhaust gas flow, and in methane oxidation catalyst units adjacent to each other in the direction of exhaust gas flow, the minimum active metal content per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located upstream in the direction of exhaust gas flow is greater than the maximum active metal content per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit located downstream in the direction of exhaust gas flow. Therefore, in the methane oxidation catalyst section, the exhaust gas temperature increases from the upstream to the downstream side in the direction of exhaust gas flow. As a result, even if the active metal content per unit area of ​​the methane oxidation catalyst decreases from the upstream to the downstream side in the direction of exhaust gas flow, the desired methane oxidation efficiency can be maintained. In other words, the active metal content can be further reduced while maintaining the desired methane oxidation efficiency.

[0151] 1.6. Variations of Exhaust Gas Treatment Systems In the modified exhaust gas treatment system, the same reference numerals are used for components and processes as in the above-described embodiment of the exhaust gas treatment system, and their detailed descriptions are omitted. Furthermore, the modified versions can achieve the same effects and advantages as the above-described embodiment of the exhaust gas treatment system, unless otherwise specified. Moreover, the above-described embodiment and modified versions of the exhaust gas treatment system can be combined as appropriate.

[0152] In the exhaust gas treatment system 1 described above, the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 are spaced apart in the direction of exhaust gas flow and are located in a single reactor. In other words, in the exhaust gas treatment system 1 of this embodiment, there is no exhaust passage 2 between the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4. However, the system is not limited to this.

[0153] In the exhaust gas treatment system 1, the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 are arranged at an interval in the direction of exhaust gas flow, and the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 may be placed in their respective reactors. In other words, an exhaust passage 2 may be provided between the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4.

[0154] Specifically, as shown in Figures 5 and 6, a modified example of the exhaust gas treatment system 1 includes an exhaust passage 2, a sulfur oxide adsorption unit 3 interposed in the exhaust passage 2, and a methane oxidation catalyst unit 4 interposed in the exhaust passage 2 and positioned downstream of the sulfur oxide adsorption unit 3 in the exhaust gas flow direction. The sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4 are spaced apart in the exhaust gas flow direction, with the exhaust passage 2 located between the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4. A flow straightener, concentration sensor, etc., which do not affect the treatment of harmful substances in the exhaust gas, may be placed between the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4. The flow straightener, concentration sensor, etc., may be placed in the exhaust passage 2 between the sulfur oxide adsorption unit 3 and the methane oxidation catalyst unit 4, between the downstream side of the sulfur oxide adsorption unit 3 in the exhaust gas flow direction and the exhaust passage 2, or between the exhaust passage 2 and the upstream side of the methane oxidation catalyst unit 4 in the exhaust gas flow direction.

[0155] The distance between the sulfur oxide adsorption section 3 and the methane oxidation catalyst section 4 in the direction of exhaust gas flow (including the exhaust passage 2 between the sulfur oxide adsorption section 3 and the methane oxidation catalyst section 4) is not particularly limited. The distance between the sulfur oxide adsorption section 3 and the methane oxidation catalyst section 4 in the direction of exhaust gas flow is, for example, 100 mm to 10,000 mm, preferably 100 mm to 8,000 mm, and more preferably 300 mm to 5,000 mm. Alternatively, the above distance may be, for example, 100 mm or more, preferably 300 mm or more, and also, for example, 10,000 mm or less, preferably 8,000 mm or less, and more preferably 5,000 mm or less.

[0156] Furthermore, although not shown in the figures, the exhaust passage 2 between the sulfur oxide adsorption section 3 and the methane oxidation catalyst section 4 may have branching. When sulfur oxides are desorbed from the sulfur oxide adsorbent in the sulfur oxide adsorption section 3, the branching of the exhaust passage 2 between the sulfur oxide adsorption section 3 and the methane oxidation catalyst section 4 allows the desorbed sulfur oxides to be recovered without coming into contact with the methane oxidation catalyst section 4.

[0157] 2. Manufacturing method of exhaust gas treatment system One embodiment of a method for manufacturing an exhaust gas treatment system will be described.

[0158] A method for manufacturing an exhaust gas treatment system includes, for example, an adsorbent manufacturing step for manufacturing a sulfur oxide adsorbent unit 31, a catalyst manufacturing step for manufacturing a methane oxidation catalyst unit 41, and an arrangement step for arranging the sulfur oxide adsorbent unit 31 and the methane oxidation catalyst unit 41.

[0159] 2.1. Adsorbent Preparation Process The adsorbent preparation process includes, for example, a step of preparing a slurry containing a sulfur oxide adsorbent component (preparation step), a step of applying or immersing the slurry on a substrate (application step), a step of firing the substrate to which the slurry has been applied or immersed (firing step), and a step of filling the casing 33 with the sulfur oxide adsorbent 32 (filling step).

[0160] (preparation process) In the preparation step, a slurry containing sulfur oxide adsorbent components is prepared. Specifically, the sulfur oxide adsorbent components and additives as needed are added to a dispersion and stirred to obtain the slurry.

[0161] The dispersion medium is not particularly limited as long as it can disperse the sulfur oxide adsorbent component and particulate component. Examples of dispersion mediums include water (e.g., deionized water and ultrapure water) and organic solvents (e.g., alcohols and carboxylic acids). Water is preferred. Furthermore, if the dispersion medium is water, it may also contain alcohols, carboxylic acids, etc.

[0162] The stirring temperature is, for example, 5°C or higher, and for example, 35°C or lower. The stirring time can be set appropriately according to the amount to be prepared, for example, 15 hours or more, and for example, 21 hours or less.

[0163] (Coating process) In the coating process, the slurry obtained in the preparation process described above is applied to or impregnated onto the substrate.

[0164] In the coating process, the substrate is preferably flat. The substrate is, for example, flat glass paper.

[0165] Methods for application or impregnation include, for example, the so-called dipping method, brush application method, spray application method, and drop application method. Preferably, the dipping method and brush application method are mentioned.

[0166] Specifically, when impregnating a substrate with slurry using the dipping method, the substrate is impregnated with the slurry obtained in the preparation step. Alternatively, when applying slurry to a substrate using the brush application method, the slurry obtained in the preparation step is dropped onto the substrate and then spread over the substrate using a brush.

[0167] (Firing process) In the firing process, the substrate coated with slurry is fired. More specifically, the substrate coated with slurry is dried, and then fired.

[0168] One drying method involves placing a substrate coated with slurry onto a heated mold and drying the slurry.

[0169] The drying temperature (mold heating temperature) is, for example, between 70°C and 150°C. The drying time is, for example, between 0.5 hours and 50 hours.

[0170] When the substrate coated with the dried slurry is to be flat, a flat mold is used for drying. When the substrate coated with the dried slurry is to be corrugated, it is molded into a corrugated shape during drying. Specifically, the substrate coated with the slurry is placed in a heated corrugated mold, and the mold is applied using a jig.

[0171] Next, the substrate coated with the dried slurry is fired.

[0172] The firing method is not particularly limited, and known methods can be used. The substrate coated with the dried slurry can be fired in a stacked state. Specifically, a flat substrate coated with the dried slurry and a corrugated flat substrate coated with the dried slurry can be stacked alternately and fired.

[0173] The firing temperature is, for example, 300°C to 800°C. The firing time is, for example, 1 minute to 10 hours.

[0174] In this way, the sulfur oxide adsorbent 32 can be obtained.

[0175] (filling process) In the filling process, the sulfur oxide adsorbent 32 is filled into the casing 33 to produce a sulfur oxide adsorbent unit 31.

[0176] Specifically, a casing 33 is prepared with an inorganic fiber blanket 34 laid on its inner surface, and flat sulfur oxide adsorbents 32 and corrugated sulfur oxide adsorbents 32 are alternately layered inside the casing 33 without being bonded together. This layering causes the sulfur oxide adsorbents 32 to form a cross-sectional network structure (honeycomb structure).

[0177] In this way, a sulfur oxide adsorbent unit 31 is manufactured in which a laminate of sulfur oxide adsorbents 32 is filled into a casing 33.

[0178] 2.2. Catalyst Preparation Process The catalyst preparation process includes, for example, a step of preparing a slurry containing an active metal (preparation step), a step of applying or immersing the slurry on a substrate (application step), a step of firing the substrate to which the slurry has been applied or immersed (firing step), and a step of filling the casing 43 with the methane oxidation catalyst 42 (filling step).

[0179] In the catalyst preparation process, the preparation, coating, calcination, and filling steps are the same as those in the adsorbent preparation process described above, except that an active metal is used instead of a sulfur oxide adsorbing component.

[0180] The manufactured methane oxidation catalyst units 41 have a substantially uniform active metal content per unit area of ​​the methane oxidation catalyst 42 in each methane oxidation catalyst unit 41. However, the active metal content per unit area of ​​the methane oxidation catalyst 42 in each manufactured methane oxidation catalyst unit 41 differs.

[0181] Furthermore, when a methane oxidation catalyst 42 is formed on a substrate using a slurry containing an active metal at a certain concentration (for example, when a slurry containing an active metal at a certain concentration is applied to or immersed in the substrate to form the methane oxidation catalyst 42), it is determined that the active metal content per unit area of ​​the methane oxidation catalyst 42 is substantially uniform. In addition, if slurries containing multiple different concentrations of active metals are prepared and applied to the substrate in order from the slurry with the highest concentration of active metal to the slurry from the upstream side to the downstream side in the direction of exhaust gas flow, a methane oxidation catalyst 42 can be formed in which the active metal content per unit area decreases from the upstream side to the downstream side in the direction of exhaust gas flow.

[0182] 2.3. Placement process In the arrangement process, the sulfur oxide adsorbent unit 31 and the methane oxidation catalyst unit 41 are arranged to manufacture the exhaust gas treatment system 1. Specifically, the sulfur oxide adsorbent unit 31 and the methane oxidation catalyst unit 41 manufactured in the adsorbent production process and catalyst production process described above are arranged in alignment in the direction of exhaust gas flow, the width direction, and the height direction, as shown in Figures 2, 3A, and 4A.

[0183] Specifically, in the methane oxidation catalyst section 4, the methane oxidation catalyst units 41 are arranged in descending order from those with a large active metal content per unit area of ​​the methane oxidation catalyst 42 in the exhaust gas flow direction, from upstream to downstream.

[0184] In other words, in the methane oxidation catalyst section 4, the methane oxidation catalyst units 41 are arranged such that the amount of active metal per unit area of ​​the methane oxidation catalyst 42 decreases in stages from the upstream side to the downstream side in the direction of exhaust gas flow.

[0185] In this way, the exhaust gas treatment system 1 is manufactured.

[0186] 3. Exhaust gas treatment method One embodiment of an exhaust gas treatment method using the exhaust gas treatment system 1 described above will be explained.

[0187] The exhaust gas treatment method of this embodiment involves supplying exhaust gas containing methane, sulfur oxides, and carbon monoxide to the exhaust gas treatment system 1 described above, and treating the exhaust gas.

[0188] Furthermore, the exhaust gas is not particularly limited as long as it contains methane, sulfur oxides, and carbon monoxide. In other words, the exhaust gas may contain, for example, hydrocarbons (excluding methane), nitrous oxide, nitrogen oxides, ammonia, oxygen, nitrogen, and water (water vapor) in addition to methane, sulfur oxides, and carbon monoxide. Examples of exhaust gas include exhaust gas emitted from internal combustion engines that use LNG (liquefied natural gas) fuel, fossil fuels (e.g., gasoline, heavy oil), etc.

[0189] The methane concentration in the exhaust gas supplied to the exhaust gas treatment system 1 is not particularly limited, and is, for example, 500 ppm or more, preferably 1000 ppm or more, and also, for example, 30000 ppm or less, preferably 20000 ppm or less.

[0190] The sulfur oxide concentration in the exhaust gas supplied to the exhaust gas treatment system 1 is, for example, 100 ppm or less, preferably 10 ppm or less, from the viewpoint of sufficiently adsorbing sulfur oxides by the sulfur oxide adsorbent 32 and suppressing the effect on the methane oxidation catalyst 42. Furthermore, there is no particular lower limit to the sulfur oxide concentration in the exhaust gas supplied to the exhaust gas treatment system 1. With the sulfur oxide adsorbent 32 of this disclosure, sulfur oxides can be sufficiently adsorbed even if the sulfur oxide concentration in the exhaust gas supplied to the exhaust gas treatment system 1 is, for example, 0.01 ppm or more, or 0.1 ppm or more.

[0191] The carbon monoxide concentration in the exhaust gas supplied to the exhaust gas treatment system 1 is not particularly limited, and is, for example, 100 ppm or more, preferably 200 ppm or more, and also, for example, 5000 ppm or less, preferably 4000 ppm or less.

[0192] The exhaust gas treatment method of this embodiment includes, for example, an oxidation and adsorption step in which exhaust gas is supplied to a sulfur oxide adsorption unit 3 to oxidize components to be oxidized, including carbon monoxide, and to adsorb sulfur oxides, and a methane oxidation step in which exhaust gas that has passed through the sulfur oxide adsorption unit 3 is supplied to a methane oxidation catalyst unit 4 to oxidize components to be oxidized, including methane.

[0193] 3.1. Oxidation / adsorption process In the oxidation and adsorption process, exhaust gas is supplied to the sulfur oxide adsorption unit 3. Specifically, the sulfur oxide adsorbent in the sulfur oxide adsorption unit 3 is brought into contact with the exhaust gas.

[0194] The temperature of the exhaust gas supplied to the sulfur oxide adsorption section 3 (the contact temperature between the sulfur oxide adsorbent and the exhaust gas in the sulfur oxide adsorption section 3) is, for example, 200°C or higher, preferably 250°C or higher, more preferably 300°C or higher, and also, for example, 600°C or lower, preferably 550°C or lower, more preferably 500°C or lower.

[0195] Furthermore, the sulfur oxide adsorption temperature of the sulfur oxide adsorbent is above the lower limit, and the sulfur oxide desorption temperature of the sulfur oxide adsorbent is above the upper limit. In other words, if the temperature of the exhaust gas supplied to the sulfur oxide adsorption unit 3 is within the above range, the sulfur oxide adsorbent can sufficiently adsorb sulfur oxides while suppressing desorption.

[0196] If the sulfur oxide adsorption capacity decreases, desulfur oxides are removed from the sulfur oxide adsorbent. Removing sulfur oxides from the sulfur oxide adsorbent restores its adsorption capacity. The desulfur oxide adsorbent's desulfurization temperature is, for example, 650°C or higher, preferably 680°C or higher, and for example, 1000°C or lower.

[0197] The temperature of the exhaust gas discharged from the sulfur oxide adsorption unit 3 is higher than the temperature of the exhaust gas supplied to the sulfur oxide adsorption unit 3.

[0198] The temperature difference between the exhaust gas discharged from the sulfur oxide adsorption section 3 and the temperature of the exhaust gas supplied to the sulfur oxide adsorption section 3 (the temperature rise of the exhaust gas in the sulfur oxide adsorption section 3) is, for example, 5°C or higher, preferably 8°C or higher, more preferably 10°C or higher, even more preferably 15°C or higher, particularly preferably 20°C or higher, and also, for example, 200°C or lower.

[0199] The sulfur oxide adsorption rate (%) in the sulfur oxide adsorption section 3, according to the following formula, is, for example, 60% or more, preferably 70% or more, more preferably 80% or more, even more preferably 85% or more, and particularly preferably 90% or more.

[0200] Sulfur oxide adsorption rate (%) = (Sulfur oxide concentration of exhaust gas supplied to sulfur oxide adsorption unit 3 - Sulfur oxide concentration that has passed through sulfur oxide adsorption unit 3) / (Sulfur oxide concentration of exhaust gas supplied to sulfur oxide adsorption unit 3) × 100

[0201] The sulfur oxide concentration of the exhaust gas supplied to the sulfur oxide adsorption unit 3 is the sulfur oxide concentration before contact with the sulfur oxide adsorbent, and the sulfur oxide concentration of the exhaust gas that has passed through the sulfur oxide adsorption unit 3 is the sulfur oxide concentration after contact with the sulfur oxide adsorbent.

[0202] 3.2. Methane Oxidation Process In the methane oxidation process, exhaust gas that has passed through the sulfur oxide adsorption unit 3 is supplied to the methane oxidation catalyst unit 4. Specifically, the exhaust gas that has passed through the sulfur oxide adsorption unit 3 is brought into contact with the methane oxidation catalyst in the methane oxidation catalyst unit 4.

[0203] The temperature of the exhaust gas supplied to the methane oxidation catalyst section 4 (the contact temperature between the methane oxidation catalyst and the exhaust gas in the methane oxidation catalyst section 4) is, for example, 250°C or higher, preferably 300°C or higher, more preferably 350°C or higher, even more preferably 380°C or higher, and also, for example, 700°C or lower, preferably 650°C or lower, more preferably 600°C or lower.

[0204] Furthermore, the oxidation temperature of methane in the methane oxidation catalyst is within the above range.

[0205] The temperature of the exhaust gas discharged from the methane oxidation catalyst unit 4 is higher than the temperature of the exhaust gas supplied to the methane oxidation catalyst unit 4.

[0206] The temperature difference between the exhaust gas discharged from the methane oxidation catalyst section 4 and the temperature of the exhaust gas supplied to the methane oxidation catalyst section 4 (the temperature rise of the exhaust gas in the methane oxidation catalyst section 4) is, for example, 5°C or more, preferably 10°C or more, more preferably 15°C or more, even more preferably 20°C or more, particularly preferably 30°C or more, and also, for example, 200°C or less.

[0207] Furthermore, the temperature of the exhaust gas supplied to the methane oxidation catalyst section 4 is higher than the temperature of the exhaust gas supplied to the sulfur oxide adsorption section 3.

[0208] The temperature difference between the exhaust gas supplied to the methane oxidation catalyst section 4 and the exhaust gas supplied to the sulfur oxide adsorption section 3 is, for example, 5°C or more, preferably 8°C or more, more preferably 10°C or more, even more preferably 15°C or more, particularly preferably 20°C or more, and also, for example, 200°C or less.

[0209] Furthermore, when the sulfur oxide adsorption section 3 and the methane oxidation catalyst section 4 are arranged with space between them in the direction of exhaust gas flow, the temperature difference between the exhaust gas supplied to the methane oxidation catalyst section 4 and the exhaust gas supplied to the sulfur oxide adsorption section 3 is almost the same as the temperature difference between the exhaust gas discharged from the sulfur oxide adsorption section 3 and the exhaust gas supplied to the sulfur oxide adsorption section 3 (the temperature rise of the exhaust gas in the sulfur oxide adsorption section 3).

[0210] In the methane oxidation catalyst section 4, the oxidation rate (%) of methane according to the following formula is, for example, 60% or more, preferably 70% or more, more preferably 80% or more, even more preferably 85% or more, and particularly preferably 90% or more.

[0211] Methane oxidation rate (%) = (Methane concentration of exhaust gas supplied to methane oxidation catalyst unit 4 - Methane concentration of exhaust gas that has passed through methane oxidation catalyst unit 4) / (Methane concentration of exhaust gas supplied to methane oxidation catalyst unit 4) × 100

[0212] The methane concentration of the exhaust gas supplied to the methane oxidation catalyst section 4 is the methane concentration before contact with the methane oxidation catalyst 42, and the methane concentration of the exhaust gas that has passed through the methane oxidation catalyst section 4 is the methane concentration after contact with the methane oxidation catalyst 42.

[0213] The flow rate of exhaust gas supplied to the exhaust gas treatment system 1 is, for example, 300 Nm³. 3 / h or more, preferably 500 Nm 3 / h or more, more preferably 700Nm 3 / h or more, and for example, 10,000 Nm 3 / h or less, preferably 9000Nm 3 / h or less, more preferably 8000Nm 3 It is less than or equal to / h.

[0214] The space velocity, defined as the amount of exhaust gas supplied to the exhaust gas treatment system 1 per unit time relative to the volume of the methane oxidation catalyst, is, for example, 1000 h. -1 Preferably, 2000h -1 Above, more comfortable, 3000h -1 The above, and also, for example, 30,000h -1 Preferably, 25,000h -1 Below, more comfortably, 20,000h -1 The following applies:

[0215] The temperature rise of the exhaust gas in the exhaust gas treatment system 1 (the difference between the temperature of the exhaust gas discharged from the methane oxidation catalyst section 4 and the temperature of the exhaust gas supplied to the sulfur oxide adsorption section 3) is, for example, 10°C or higher, preferably 20°C or higher, more preferably 30°C or higher, even more preferably 40°C or higher, particularly preferably 50°C or higher, and also, for example, 400°C or lower.

[0216] In the exhaust gas treatment system 1, the carbon monoxide oxidation rate (%) according to the following formula is, for example, 70% or more, preferably 80% or more, more preferably 85% or more, even more preferably 90% or more, and particularly preferably 95% or more.

[0217] Carbon monoxide oxidation rate (%) = (carbon monoxide concentration of exhaust gas supplied to sulfur oxide adsorption unit 3 - carbon monoxide concentration of exhaust gas that has passed through methane oxidation catalyst unit 4) / (carbon monoxide concentration of exhaust gas supplied to sulfur oxide adsorption unit 3) × 100

[0218] The carbon monoxide concentration of the exhaust gas supplied to the sulfur oxide adsorption section 3 is the carbon monoxide concentration before contact with the sulfur oxide adsorbent and the methane oxidation catalyst, while the carbon monoxide concentration of the exhaust gas that has passed through the methane oxidation catalyst section 4 is the carbon monoxide concentration after contact with the sulfur oxide adsorbent and the methane oxidation catalyst.

[0219] 3.3. Effects (1) The exhaust gas treatment method of the present disclosure comprises the steps of supplying exhaust gas to a sulfur oxide adsorption unit 3 to oxidize components to be oxidized, including carbon monoxide, and adsorbing sulfur oxides, and supplying exhaust gas that has passed through the sulfur oxide adsorption unit 3 to a methane oxidation catalyst unit 4 to oxidize components to be oxidized, including methane, wherein the temperature of the exhaust gas supplied to the sulfur oxide adsorption unit is 300°C or higher and 600°C or lower. Therefore, sulfur oxides can be sufficiently adsorbed in the sulfur oxide adsorption unit, and the desorption of adsorbed sulfur oxides can be suppressed. Furthermore, by oxidizing components to be oxidized, including carbon monoxide, in the sulfur oxide adsorption unit and raising the temperature of the exhaust gas, the exhaust gas can be supplied to the methane oxidation catalyst unit at a temperature suitable for methane oxidation, thereby improving the methane oxidation efficiency.

[0220] (2) In the exhaust gas treatment method of this disclosure, the temperature of the exhaust gas supplied to the methane oxidation catalyst section 4 is higher than the temperature of the exhaust gas supplied to the sulfur oxide adsorption section 3. Therefore, carbon monoxide is properly oxidized in the sulfur oxide adsorption section 3, and the exhaust gas can be supplied to the methane oxidation catalyst section 4 at a temperature suitable for methane oxidation, thereby improving the methane oxidation efficiency.

[0221] (3) In the exhaust gas treatment method of this disclosure, the temperature difference between the exhaust gas supplied to the methane oxidation catalyst section 4 and the exhaust gas supplied to the sulfur oxide adsorption section 3 is 10°C or more and 200°C or less. Therefore, even if the temperature of the exhaust gas supplied to the sulfur oxide adsorption section 3 is relatively low, the exhaust gas can be supplied to the methane oxidation catalyst section 4 at a temperature suitable for methane oxidation, thereby improving the methane oxidation efficiency. [Explanation of Symbols]

[0222] 1. Exhaust gas treatment system 2 Exhaust passage 3 Sulfur oxide adsorption section 4. Methane oxidation catalyst section

Claims

1. An exhaust gas treatment system for treating exhaust gas emitted from an internal combustion engine, which contains methane, sulfur oxides, and carbon monoxide, A sulfur oxide adsorption section comprising a sulfur oxide adsorbent that adsorbs the aforementioned sulfur oxides, A methane oxidation catalyst section is provided, which is located downstream of the sulfur oxide adsorption section in the direction of exhaust gas flow and includes a methane oxidation catalyst that oxidizes the oxidizable components, including methane. Equipped with, The exhaust gas treatment system further comprises a sulfur oxide adsorbent that oxidizes the oxidizable components, including the carbon monoxide.

2. The exhaust gas treatment system according to claim 1, wherein the sulfur oxide adsorption unit and the methane oxidation catalyst unit are arranged at an interval in the direction of the exhaust gas flow.

3. At least a portion of the methane oxidation catalyst has an active metal that oxidizes the methane and other components to be oxidized in the exhaust gas, The exhaust gas treatment system according to claim 1, wherein the content of the active metal per unit area of ​​the methane oxidation catalyst decreases from the upstream side to the downstream side in the flow direction of the exhaust gas.

4. The methane oxidation catalyst section comprises a plurality of methane oxidation catalyst units arranged along the flow direction of the exhaust gas, The methane oxidation catalyst unit has a methane oxidation catalyst in which the content of the active metal per unit area is substantially uniform in the flow direction of the exhaust gas, The exhaust gas treatment system according to claim 3, wherein, in the methane oxidation catalyst units adjacent to each other in the direction of exhaust gas flow, the amount of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit arranged on the upstream side in the direction of exhaust gas flow is greater than the amount of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit arranged on the downstream side in the direction of exhaust gas flow.

5. The methane oxidation catalyst section comprises a plurality of methane oxidation catalyst units arranged along the flow direction of the exhaust gas, The methane oxidation catalyst unit has a methane oxidation catalyst in which the content of the active metal per unit area decreases from the upstream side to the downstream side in the flow direction of the exhaust gas, The exhaust gas treatment system according to claim 3, wherein, in the methane oxidation catalyst units adjacent to each other in the direction of exhaust gas flow, the minimum content of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit arranged on the upstream side in the direction of exhaust gas flow is greater than the maximum content of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit arranged on the downstream side in the direction of exhaust gas flow.

6. The methane oxidation catalyst section comprises a plurality of methane oxidation catalyst units arranged along the flow direction of the exhaust gas, At least one of the methane oxidation catalyst units has a methane oxidation catalyst in which the content of the active metal per unit area is substantially uniform in the flow direction of the exhaust gas, At least one of the methane oxidation catalyst units has a methane oxidation catalyst in which the content of the active metal per unit area decreases from the upstream side to the downstream side in the flow direction of the exhaust gas, The exhaust gas treatment system according to claim 3, wherein, in the methane oxidation catalyst units adjacent to each other in the direction of exhaust gas flow, the minimum content of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit arranged on the upstream side in the direction of exhaust gas flow is greater than the maximum content of the active metal per unit area of ​​the methane oxidation catalyst in the methane oxidation catalyst unit arranged on the downstream side in the direction of exhaust gas flow.

7. An exhaust gas treatment method comprising supplying the exhaust gas to an exhaust gas treatment system according to any one of claims 1 to 6 and treating the exhaust gas, The process involves supplying the exhaust gas to the sulfur oxide adsorption unit, oxidizing the oxidizable components including carbon monoxide, and adsorbing the sulfur oxides. The process involves supplying the exhaust gas, which has passed through the sulfur oxide adsorption section, to the methane oxidation catalyst section to oxidize the components to be oxidized, including the methane. Equipped with, An exhaust gas treatment method wherein the temperature of the exhaust gas supplied to the sulfur oxide adsorption unit is 300°C or higher and 600°C or lower.

8. The exhaust gas treatment method according to claim 7, wherein the temperature of the exhaust gas supplied to the methane oxidation catalyst is higher than the temperature of the exhaust gas supplied to the sulfur oxide adsorption unit.

9. The exhaust gas treatment method according to claim 8, wherein the difference between the temperature of the exhaust gas supplied to the methane oxidation catalyst and the temperature of the exhaust gas supplied to the sulfur oxide adsorption unit is 10°C or more and 200°C or less.

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