Exhaust treatment device, engine system, and exhaust treatment method

Abstract

An exhaust treatment apparatus (6) includes a treatment case (61) and a catalyst section (62). The exhaust gas of an engine (1) that uses a gas containing methane as fuel is introduced into the treatment case (61). The catalyst section (62) is housed in the treatment case (61) and oxidizes unburned methane contained in the exhaust gas. In a case where the temperature of the catalyst section (62) is lower than a prescribed normal temperature, the catalyst section (62) oxidizes carbon monoxide contained in the exhaust gas and is warmed to a temperature above the normal temperature by the heat of reaction of the oxidation of carbon monoxide. Thus, even in a case where the temperature of the exhaust gas supplied to the catalyst section (62) is lower than the normal temperature, the catalyst section (62) can be rapidly warmed to a temperature above the normal temperature. Therefore, methane in the exhaust gas can be preferably oxidized. An engine system and an exhaust treatment method are also provided.

Description

[0001] Reference to relevant applications

[0002] This application claims the benefit of priority to Japanese Patent Application JP2021-081912, filed on May 13, 2021, and incorporates the entire disclosure of that application. Technical Field

[0003] This invention relates to a technology for treating exhaust gas, and more particularly to an exhaust gas treatment device, an engine system, and an exhaust gas treatment method. Background Technology

[0004] Previously, in LNG carriers transporting liquefied natural gas (LNG), the boil-off gas (BOG) inevitably generated from the LNG as cargo was used as fuel gas. Furthermore, in recent years, the number of ships using LNG as fuel gas, even those other than LNG carriers, has been increasing.

[0005] In ships that use LNG as fuel gas, when the combustion temperature of the fuel gas in the engine is low, some of the methane (CH4) in the fuel gas remains unburned in the exhaust gas and may be released into the atmosphere along with the exhaust. Since methane has a high warming effect, it is necessary to treat the methane in the exhaust gas using catalysts or the like to prevent its release into the atmosphere. For example, in the exhaust gas purification device disclosed in Japanese Patent Application Publication No. 2018-135808 (Document 1), a catalyst is used to oxidize the hydrocarbons and carbon monoxide contained in the exhaust gas of a gas engine.

[0006] However, the catalyst in Reference 1 can oxidize methane at temperatures above 350°C and below 500°C. Therefore, when the exhaust gas temperature introduced into the exhaust gas purification equipment is below 350°C, it is difficult to preferably oxidize the methane in the exhaust gas. Summary of the Invention

[0007] The present invention relates to an exhaust gas treatment device, the purpose of which is to preferably oxidize methane in exhaust gas even at low exhaust gas temperatures.

[0008] A preferred embodiment of the exhaust gas treatment apparatus of the present invention includes: a treatment frame for introducing exhaust gas from an engine that uses methane-containing gas as fuel; and a catalyst section housed in the treatment frame for oxidizing unburned methane contained in the exhaust gas. When the temperature of the catalyst section is lower than a predetermined operating temperature, the catalyst section oxidizes carbon monoxide contained in the exhaust gas and raises the temperature to above the operating temperature using the heat of oxidation of carbon monoxide.

[0009] According to the present invention, methane in the exhaust gas can be preferably oxidized even at low exhaust temperatures.

[0010] Preferably, when the temperature of the catalyst section is lower than the normal operating temperature, the engine is adjusted to a predetermined state in which the concentration of carbon monoxide in the exhaust is higher than that during stable operation.

[0011] Preferably, when the engine is in the specified adjustment state, the concentration of carbon monoxide in the exhaust is 0.04% by volume or more and 2.5% by volume or less.

[0012] Preferably, when the temperature of the catalyst section is lower than a first switching temperature which is lower than the normal operating temperature, the engine is adjusted to a first adjustment state in which the concentration of carbon monoxide in the exhaust is higher than that during stable operation. When the temperature of the catalyst section rises to the first switching temperature, the engine is adjusted to a second adjustment state in which the concentration of carbon monoxide in the exhaust is higher than that during stable operation and lower than that of the first adjustment state.

[0013] Preferably, the exhaust gas treatment device further includes an inlet temperature sensor, which measures the temperature of the exhaust gas introduced into the treatment frame.

[0014] Preferably, the processing frame is positioned upstream of the turbine that rotates through the exhaust gas in the direction of exhaust flow.

[0015] Preferably, the processing frame is positioned further downstream of the turbine that rotates through the exhaust gas in the direction of exhaust flow.

[0016] This invention also relates to an engine system. A preferred embodiment of the engine system includes: an engine that uses a gas containing methane as fuel; and an exhaust treatment apparatus for treating the exhaust gas from said engine.

[0017] Preferably, the engine is a two-stroke engine.

[0018] This invention also relates to an exhaust gas treatment method for oxidizing unburned methane in the exhaust gas of an engine that uses a gas containing methane as fuel. A preferred embodiment of the exhaust gas treatment method includes: a) a step of supplying exhaust gas at a temperature below a predetermined operating temperature to a catalyst section; b) a step of oxidizing carbon monoxide contained in the exhaust gas in the catalyst section and using the heat of oxidation of carbon monoxide to raise the temperature of the catalyst section to above the operating temperature; and c) a step of oxidizing the methane in the exhaust gas by passing it through the catalyst section at the temperature above the operating temperature after step b).

[0019] The stated objectives and other objectives, features, methods, and advantages will become clear from the following detailed description of the invention with reference to the accompanying drawings. Attached Figure Description

[0020] Figure 1 This is a diagram showing the structure of an engine system according to one embodiment.

[0021] Figure 2 It is a diagram showing the exhaust gas processing flow.

[0022] Figure 3 This is a diagram showing the structure of another engine system.

[0023] [Explanation of Symbols]

[0024] 1: Engine

[0025] 6: Exhaust treatment equipment

[0026] 10: Engine System

[0027] 51: Turbo

[0028] 61: Processing the frame

[0029] 62: Catalyst Section

[0030] S11~S18: Steps Detailed Implementation

[0031] Figure 1 This is a diagram illustrating the structure of an engine system 10 according to one embodiment of the present invention. The engine system 10 is, for example, mounted on an LNG carrier transporting liquefied natural gas (LNG). The engine system 10 serves, for example, as the main engine of the LNG carrier.

[0032] Engine system 10 includes engine 1 and exhaust treatment equipment 6. Engine 1 is a gas-fired engine that uses gas containing methane (CH4) as fuel. Engine 1 is, for example, a two-stroke engine. Engine 1 is, for example, a reciprocating internal combustion engine with combustion methods such as Otto cycle, premixed combustion, Diesel cycle, or Sabathe cycle. Engine 1 is, for example, a low-pressure engine. Engine 1 may also use liquefied natural gas (LNG) volatile gas (BOG) as fuel. BOG is, for example, the gas produced by vaporizing LNG as cargo in LNG carriers, containing methane.

[0033] Engine 1 includes: cylinder 2, piston 3, scavenging air passage 41, exhaust air passage 42, air cooler 43, turbocharger 5, engine control unit 7, and exhaust duct 81. Cylinder 2 is a cylinder with a piston 3. Figure 1 The cylinder 2 has a covered, generally cylindrical member centered on a central axis extending vertically. The piston 3 is a generally cylindrical member centered on the central axis, with its upper part disposed inside the cylinder 2. The piston 3 is capable of moving vertically. Furthermore, Figure 1 The vertical direction in the equation does not necessarily need to be parallel to the direction of gravity.

[0034] Cylinder 2 includes a cylinder liner 21, a cylinder head 22, and an exhaust valve 25. The cylinder liner 21 is a generally cylindrical component centered on the central axis. The cylinder head 22 is a covered, generally cylindrical component mounted on the upper part of the cylinder liner 21. An exhaust port 24 is formed in the top cover portion of the cylinder head 22. The exhaust port 24 is connected to an exhaust flow path 42. The exhaust port 24 is opened and closed by the exhaust valve 25. Figure 1 As shown by the solid line, the exhaust valve 25 moves downward from the exhaust port 24, thus opening the exhaust port 24. Additionally, as... Figure 1 As shown by the two-point chain, the exhaust valve 25 contacts the cylinder head 22 and overlaps with the exhaust port 24, thereby closing the exhaust port 24. A scavenging port 23 is provided near the lower end of the cylinder liner 21. The scavenging port 23 is a collection of multiple through holes arranged circumferentially on the side of the cylinder liner 21. The scavenging port 23 is connected to the scavenging flow path 41.

[0035] The piston 3 includes a piston crown 31 and a piston rod 32. The piston crown 31 is a thick, generally circular plate-shaped portion centered on the central axis. The piston crown 31 is disposed inside the cylinder liner 21. The piston rod 32 is a generally cylindrical portion extending downward from the lower surface of the piston crown 31. The lower end of the piston rod 32 is connected to a crank mechanism (not shown). Through this crank mechanism, the piston 3 reciprocates in the vertical direction. Figure 1In the diagram, the piston 3 located at the bottom dead center of the reciprocating motion is depicted using a solid line, and the piston 3 located at the top dead center is depicted using a two-point chain line.

[0036] In engine 1, the space enclosed by cylinder liner 21, cylinder head 22, exhaust valve 25, and the upper surface of piston top 31 (i.e., the upper surface of piston 3) is a combustion chamber 20 for burning fuel and air.

[0037] Scavenging air is supplied to the combustion chamber 20 via the scavenging port 23 and the scavenging flow path 41. The scavenging flow path 41 includes a scavenging chamber 411 and a scavenging receiver 412. The scavenging chamber 411 is the space (i.e., the scavenging pipe) disposed around the scavenging port 23 of the cylinder liner 21. The scavenging port 23 communicates with the scavenging receiver 412 via the scavenging chamber 411. The scavenging receiver 412 is a generally cylindrical large container that supplies scavenging air to the scavenging chamber 411.

[0038] The gases generated by the combustion of fuel and air in the combustion chamber 20 (i.e., combustion gases) are discharged through the exhaust port 24 to the exhaust flow path 42. The exhaust flow path 42 is a conduit for the flow of gases discharged from the combustion chamber 20 (hereinafter referred to as "exhaust gas"). The exhaust flow path 42 includes an exhaust pipe 421 and an exhaust receiver 422. The exhaust pipe 421 is a pipe connecting the exhaust port 24 to the exhaust receiver 422. The exhaust receiver 422 is a generally cylindrical large container that receives the exhaust gas from the combustion chamber 20.

[0039] Although the illustrations are omitted, the engine 1 includes multiple sets of cylinders 2 and pistons 3, and multiple combustion chambers 20 connected to a scavenging receiver 412 and an exhaust receiver 422. Specifically, the scavenging receiver 412 is a scavenging manifold used to distribute scavenging air to the multiple combustion chambers 20. Additionally, the exhaust receiver 422 is an exhaust manifold (also called an exhaust manifold) that collects the exhaust gas discharged from the multiple combustion chambers 20.

[0040] The exhaust gas collected at the exhaust receiver 422 is treated by the exhaust treatment device 6. In the exhaust treatment device 6, unburned (i.e., unreacted) methane contained in the exhaust gas from the combustion chamber 20 is oxidized to produce carbon dioxide (CO2) and water (H2O). As a result, the concentration of unburned methane in the exhaust gas discharged from the engine system 10 into the atmosphere (hereinafter also referred to as "slip methane concentration") is below a predetermined value. The exhaust treatment device 6 includes: a treatment housing 61, a catalyst unit 62, a catalyst temperature sensor 63, and an inlet temperature sensor 64.

[0041] In the exhaust gas treatment device 6, exhaust gas from the combustion chamber 20 is introduced into the internal space of the treatment frame 61. The treatment frame 61 is, for example, a generally cylindrical reaction vessel. A catalyst section 62 is housed (i.e., filled) within the internal space of the treatment frame 61. The catalyst section 62 is, for example, an oxidation catalyst with a honeycomb structure. Specifically, the catalyst section 62 has the following structure: an oxidation catalyst, such as a catalyst metal, is supported on charge carriers with a honeycomb structure. The catalyst metal includes, for example, noble metals such as palladium (Pd) or platinum (Pt). In the exhaust gas treatment device 6, when the exhaust gas introduced into the treatment frame 61 passes through the catalyst section 62, the unburned methane contained in the exhaust gas is oxidized by the catalyst section 62. Additionally, the catalyst section 62 also oxidizes carbon monoxide (CO) contained in the exhaust gas. Furthermore, the structure and shape of the treatment frame 61 and the catalyst section 62 can be varied. For example, the charge carriers of the catalyst section 62 can also have other shapes such as cylindrical or plate-like.

[0042] Catalyst temperature sensor 63 measures the temperature of catalyst section 62 and outputs the result to engine control unit 7. Catalyst temperature sensor 63 can also measure the temperature of the internal space of the processing housing 61 and output the measurement result as the temperature of catalyst section 62 to engine control unit 7. Inlet temperature sensor 64 measures the temperature of exhaust gas at the moment it is introduced into processing housing 61 and outputs the result to engine control unit 7. Inlet temperature sensor 64 is, for example, installed in the piping connecting exhaust receiver 422 to processing housing 61, directly in front of the inlet of processing housing 61. Thermocouples can be used as catalyst temperature sensor 63 and inlet temperature sensor 64, for example.

[0043] In the exhaust gas treatment device 6, a predetermined operating temperature is set. When the temperature of the catalyst section 62 is above this operating temperature, the oxidation of methane in the exhaust gas proceeds sufficiently, and the escape methane concentration falls below the predetermined value. This operating temperature can be, for example, the temperature of the catalyst section 62 when the escape methane concentration becomes equal to the predetermined value, or it can be a temperature with a predetermined margin (e.g., 10°C to 50°C) added to the predetermined temperature. The operating temperature is set, for example, by the manufacturer of the exhaust gas treatment device 6 or the engine system 10. The operating temperature varies depending on the type of catalyst section 62, and is, for example, 400°C when the exhaust gas supply flow rate to the catalyst section 62 is 0.1 m / sec to 3.0 m / sec. Furthermore, when the temperature of the catalyst section 62 is below the operating temperature, the escape methane concentration may exceed the predetermined value.

[0044] The turbocharger 5 is a turbocharger including a turbine 51 and a compressor 52. In the turbocharger 5, exhaust gas is used to pressurize the intake air, generating scavenging air. Specifically, the turbine 51 rotates due to exhaust gas from the combustion chamber 20, and the compressor 52 uses the rotational force generated by the turbine 51 (i.e., using the rotation of the turbine 51 as power) to compress the intake air (air) taken in from outside the engine 1 via the intake path 82. The pressurized air (i.e., the scavenging air) is cooled by the air cooler 43 and supplied to the scavenging air receiver 412, and from the scavenging air receiver 412 is supplied to the combustion chamber 20. The exhaust gas used for the rotation of the turbine 51 is directed to the flue 81 and discharged from the flue 81 to the outside of the engine 1. Figure 1 In the example shown, the turbine 51 is positioned between the flue 81 and the treatment frame 61 of the exhaust treatment device 6. In other words, the treatment frame 61 is positioned upstream of the turbine 51, which rotates through the exhaust gas, in the flow direction of the exhaust gas discharged from the combustion chamber 20. The exhaust gas, after being treated by the catalyst section 62 within the treatment frame 61, is introduced into the turbine 51.

[0045] The engine control unit 7 controls the adjustment state of the engine 1 based on the output of the catalyst temperature sensor 63 from the exhaust treatment device 6 (i.e., the temperature of the catalyst section 62). The engine control unit 7 is, for example, a Programmable Logic Controller (PLC). The PLC includes a processor, a memory, an input / output unit, and a bus. The bus is a signal circuit connecting the processor, the memory, and the input / output unit. The memory stores programs and various information. The processor performs various processes (e.g., numerical calculations) while utilizing the memory, according to the programs stored in the memory. The input / output unit receives signal inputs from other devices (e.g., the exhaust treatment device 6) or from the operator, and outputs signals to other devices. The PLC processes according to a predetermined program, thereby realizing the function of the engine control unit 7. The engine control unit 7 can be a general computer system including a keyboard or display, or it can be a circuit board.

[0046] In engine system 10, during engine 1 startup or low-output operation, the temperature of the exhaust gas delivered from combustion chamber 20 to exhaust treatment device 6 is sometimes relatively low. For example, sometimes the temperature output from the inlet temperature sensor 64 to engine control unit 7 (i.e., the exhaust gas temperature at the time of inlet to treatment housing 61) is lower than the commonly used temperature. Thus, when the exhaust gas temperature delivered to treatment housing 61 is relatively low, in conventional exhaust treatment devices, the catalyst section 62 hardly oxidizes methane, and the heat of oxidation generated by the oxidation is also small. Therefore, the temperature of catalyst section 62 may not reach the commonly used temperature.

[0047] Figure 2 This diagram illustrates the exhaust gas processing flow in the engine system 10 of the present invention. In the engine system 10, exhaust gas from the combustion chamber 20 is supplied to the catalyst section 62 while the temperature of the catalyst section 62 is measured by the catalyst temperature sensor 63 (step S11). As described above, if the temperature of the exhaust gas introduced into the processing housing 61 (i.e., the temperature of the exhaust gas supplied to the catalyst section 62) is lower than the normal operating temperature, the temperature of the catalyst section 62 may also be lower than the normal operating temperature. During engine 1 startup or low-output operation, the temperature of the exhaust gas introduced into the processing housing 61 (hereinafter also referred to as the "introduced exhaust gas temperature") is, for example, lower than 250°C, and the difference between the normal operating temperature and the introduced exhaust gas temperature (i.e., the value obtained by subtracting the introduced exhaust gas temperature from the normal operating temperature) is, for example, 90°C or higher. The introduced exhaust gas temperature is higher than or equal to the oxidation start temperature of carbon monoxide through the catalyst section 62 (i.e., the temperature at which the exothermic reaction caused by the oxidation of carbon monoxide begins). The introduced exhaust gas temperature is, for example, 150°C to 350°C.

[0048] If the temperature of the catalyst section 62, transmitted from the catalyst temperature sensor 63 to the engine control unit 7, is lower than a predetermined first switching temperature (step S12), the engine control unit 7 controls the adjustment state of the engine 1 to be set to a first adjustment state different from the adjustment state during stable operation (hereinafter also referred to as the "reference adjustment state") (step S13). Specifically, if the adjustment state of the engine 1 is either the reference adjustment state or the first adjustment state, the engine control unit 7 switches the adjustment state to the first adjustment state. Furthermore, if the adjustment state of the engine 1 is the first adjustment state, the first adjustment state is maintained. The first switching temperature is a temperature lower than the normal operating temperature, for example, a temperature above the methane oxidation start temperature (i.e., the temperature at which the exothermic reaction caused by the methane oxidation begins). The first switching temperature is appropriately preset according to the usage mode of the engine system 10, etc.

[0049] In the first adjustment state, the concentration of carbon monoxide in the exhaust gas discharged from the combustion chamber 20 is higher than that in the reference adjustment state. The carbon monoxide concentration in the exhaust gas in the first adjustment state is, for example, 0.05 vol% or more, preferably 0.5 vol% or more. The carbon monoxide concentration in the exhaust gas in the first adjustment state is, for example, 5 vol% or less, preferably 4 vol% or less, more preferably 2.5 vol% or less, and even more preferably 1 vol% or less. In this embodiment, the carbon monoxide concentration in the exhaust gas in the first adjustment state is set to be 0.05 vol% or more and 2.5 vol% or less. Furthermore, stable operation refers to the predetermined operating state during normal navigation of a ship equipped with the engine system 10. The reference adjustment state is set to make the fuel consumption rate or environmental load approximately optimal during stable operation of the engine 1. The carbon monoxide concentration in the exhaust gas in the reference adjustment state is, for example, 0.005 vol% or more and less than 0.04 vol%.

[0050] Furthermore, the methane concentration in the exhaust gas under the reference adjustment state is, for example, 0.5 vol% to 1.5 vol%. The methane concentration in the exhaust gas under the first adjustment state may be the same as or different from the methane concentration in the exhaust gas under the reference adjustment state. In this embodiment, the methane concentration in the exhaust gas under the first adjustment state is approximately the same as the methane concentration in the exhaust gas under the reference adjustment state, for example, 0.5 vol% to 1.5 vol%. By setting the methane concentration in the exhaust gas to 0.5 vol% or more, the oxidation of methane in the catalyst section 62 can be carried out efficiently. In addition, by setting the methane concentration in the exhaust gas to 1.5 vol% or less, excessive heating of the catalyst section 62 caused by the heat of oxidation of methane in the catalyst section 62 can be prevented.

[0051] Switching the adjustment state of engine 1 can be achieved, for example, by changing one or more of the following: the amount of fuel supplied to combustion chamber 20, the amount of air sealed into combustion chamber 20, and the maximum pressure of combustion chamber 20 (also known as maximum combustion pressure). Specifically, for example, when the amount of fuel supplied to combustion chamber 20 (hereinafter also referred to as "fuel supply amount") is increased, the amount of air in combustion chamber 20 is relatively reduced, and the concentration of carbon monoxide in the exhaust gas discharged from combustion chamber 20 increases. The fuel supply amount can be changed by controlling the operation of the fuel supply pump in the fuel supply unit (not shown in the figure).

[0052] Furthermore, for example, when the amount of air sealed into the combustion chamber 20 (hereinafter also referred to as "sealed air amount") is reduced, the carbon monoxide concentration in the exhaust gas discharged from the combustion chamber 20 increases. By reducing the maximum pressure of the combustion chamber 20, the carbon monoxide concentration in the exhaust gas discharged from the combustion chamber 20 also increases. The sealed air amount and the maximum pressure of the combustion chamber 20 can be changed by controlling the closing timing of the exhaust valve 25 when the piston 3 rises from bottom dead center. Specifically, for example, by delaying the closing timing of the exhaust valve 25, the sealed air amount is reduced, and the maximum pressure of the combustion chamber 20 becomes lower.

[0053] Furthermore, during the switching of the adjustment state of engine 1, the engine control unit 7 can control other structures, and can also change any one or more of the following: fuel supply, air intake, and maximum pressure of combustion chamber 20. Alternatively, the adjustment state of engine 1 can be switched by adjusting factors other than fuel supply, air intake, and maximum pressure of combustion chamber 20.

[0054] The oxidation start temperature of carbon monoxide through catalyst section 62 is lower than the normal operating temperature and the oxidation start temperature of methane through catalyst section 62, being below the temperature of the exhaust gas supplied to catalyst section 62 (i.e., the inlet exhaust gas temperature). Therefore, the carbon monoxide in the exhaust gas is oxidized by catalyst section 62. Catalyst section 62 is heated by the heat of carbon monoxide oxidation (step S14). Furthermore, the oxidation start temperature of carbon monoxide through catalyst section 62 varies depending on the type of catalyst section 62, etc., and is, for example, 200°C under the condition that the exhaust gas supply flow rate to catalyst section 62 is 0.1 m / sec to 3.0 m / sec.

[0055] In engine system 10, as described above, engine 1 is in a first adjustment state, where the concentration of carbon monoxide in the exhaust increases, resulting in more heat generated during the oxidation reaction of carbon monoxide by catalyst section 62. Consequently, catalyst section 62 rapidly heats up and reaches the oxidation start temperature of methane.

[0056] When the catalyst section 62 is heated to the oxidation start temperature of methane, the oxidation of methane in the exhaust gas substantially begins in the catalyst section 62. The catalyst section 62 is heated to a temperature above the commonly used temperature by the heat of oxidation of carbon monoxide and the heat of oxidation of methane. Then, the oxidation of carbon monoxide and methane in the exhaust gas continues through the catalyst section 62 at the temperature above the commonly used temperature.

[0057] In the exhaust treatment device 6, the temperature of the catalyst section 62 is continuously measured by the catalyst temperature sensor 63. When the temperature of the catalyst section 62 sent from the catalyst temperature sensor 63 to the engine control unit 7 reaches the first switching temperature (step S12), the engine control unit 7 controls the adjustment state of the engine 1 to switch from the first adjustment state to the second adjustment state (step S15). Furthermore, even during low-output operation, if the temperature of the catalyst section 62 sent from the catalyst temperature sensor 63 to the engine control unit 7 is above the first switching temperature but below the normal operating temperature from the beginning (step S12), the adjustment state of the engine 1 can be set to the second adjustment state without going through the first adjustment state (step S15).

[0058] In the second adjustment state, the concentration of carbon monoxide in the exhaust gas discharged from the combustion chamber 20 is lower than that in the first adjustment state. Furthermore, the carbon monoxide concentration in the exhaust gas in the second adjustment state is higher than that in the exhaust gas in the reference adjustment state. The carbon monoxide concentration in the exhaust gas in the second adjustment state is, for example, 0.04 vol% or more, preferably 0.4 vol% or more. The carbon monoxide concentration in the exhaust gas in the second adjustment state is, for example, 4 vol% or less, preferably 2 vol% or less, more preferably 0.75 vol% or less. In this embodiment, the carbon monoxide concentration in the exhaust gas in the second adjustment state is set to 0.04 vol% or more and 2 vol% or less. That is, in this embodiment, the carbon monoxide concentration in the exhaust gas in both the first and second adjustment states is 0.04 vol% or more and 2.5 vol% or less. Furthermore, the carbon monoxide concentration in the exhaust gas in the first and second adjustment states is not limited to the aforementioned range and can be varied in various ways. The methane concentration in the exhaust gas in the second adjustment state may be the same as or different from the methane concentration in the exhaust gas in the reference adjustment state. In this embodiment, the methane concentration in the exhaust gas under the second adjustment state is approximately the same as the methane concentration in the exhaust gas under the reference adjustment state, for example, 0.5 vol% to 1.5 vol%.

[0059] As described above, in the second adjustment state, the carbon monoxide concentration in the exhaust is reduced compared to the first adjustment state, and the heat of oxidation of carbon monoxide in the catalyst section 62 is also reduced. On the other hand, in the heated catalyst section 62, in addition to carbon monoxide, methane oxidation also occurs. Since the heat of oxidation per unit mass of methane (i.e., heat of combustion) is greater than that of carbon monoxide per unit mass, the temperature of the catalyst section 62 is raised to a predetermined second switching temperature above the first switching temperature and above the normal operating temperature due to the heat of oxidation of carbon monoxide and methane (steps S16 and S17). The second switching temperature, like the first switching temperature, is also appropriately preset according to the usage mode of the engine system 10.

[0060] Then, when the temperature of the catalyst section 62 reaches the second switching temperature (step S16), the engine control unit 7 controls the adjustment state of the engine 1 to switch from the second adjustment state to the reference adjustment state (step S18). In the exhaust treatment device 6, the temperature of the catalyst section 62 is raised to above the normal operating temperature, so even in the reference adjustment state, the methane in the exhaust gas discharged from the combustion chamber 20 can be preferably oxidized by the catalyst section 62. As a result, the emission of methane from the engine system 10 into the atmosphere (i.e., methane escape) can be suppressed. Furthermore, when the temperature of the catalyst section 62 sent from the catalyst temperature sensor 63 to the engine control unit 7 is above the second switching temperature from the beginning, the adjustment state of the engine 1 can also be adjusted accordingly. Figure 2 The situation shown is different; it becomes the base state without going through the first and second adjustment states.

[0061] As explained above, the exhaust gas treatment device 6 includes a treatment housing 61 and a catalyst unit 62. Exhaust gas from an engine 1, which uses methane-containing gas as fuel, is introduced into the treatment housing 61. The catalyst unit 62, housed in the treatment housing 61, oxidizes the unburned methane contained in the exhaust gas. When the temperature of the catalyst unit 62 is below a predetermined operating temperature, the catalyst unit 62 oxidizes the carbon monoxide contained in the exhaust gas and raises the temperature to above the operating temperature using the heat of oxidation of carbon monoxide. Therefore, even when the temperature of the exhaust gas supplied to the catalyst unit 62 is below the operating temperature, the catalyst unit 62 can be rapidly heated to above the operating temperature. Thus, the methane in the exhaust gas can preferably be oxidized, thereby preferably suppressing methane escape. As a result, the concentration of escaped methane can be kept below the predetermined value.

[0062] As described above, it is preferable that when the temperature of the catalyst section 62 is lower than the normal operating temperature, the engine 1 is adjusted to a predetermined adjustment state (i.e., the first adjustment state and / or the second adjustment state) where the concentration of carbon monoxide in the exhaust is higher than that during stable operation. This increases the heat of oxidation of carbon monoxide in the catalyst section 62, thereby rapidly raising the temperature of the catalyst section 62 to the normal operating temperature.

[0063] As described above, preferably, when the engine 1 is in the specified adjustment state, the carbon monoxide concentration in the exhaust is 0.04% by volume or more and 2.5% by volume or less. By setting the carbon monoxide concentration to 0.04% by volume or more, the heat of oxidation of carbon monoxide in the catalyst section 62 can be further increased, causing the temperature of the catalyst section 62 to rise to the normal operating temperature more rapidly (for example, within 120 minutes from the start of supplying exhaust gas to the catalyst section 62). In addition, by setting the carbon monoxide concentration to 2.5% by volume or less, the deterioration of fuel consumption rate under the adjustment state (i.e., the first adjustment state and / or the second adjustment state) compared with stable operation at a high fuel consumption rate can be suppressed.

[0064] As described above, it is preferable that when the temperature of the catalyst section 62 is lower than the first switching temperature (which is less than the commonly used temperature), the engine 1 is adjusted to a first adjustment state where the concentration of carbon monoxide in the exhaust is higher than that during stable operation (i.e., the reference adjustment state). Furthermore, it is preferable that when the temperature of the catalyst section 62 rises to the first switching temperature, the engine 1 is adjusted to a second adjustment state where the concentration of carbon monoxide in the exhaust is higher than that during stable operation but lower than that of the first adjustment state. Thus, when the temperature of the catalyst section 62 is above the first switching temperature, the heat of oxidation of carbon monoxide in the catalyst section 62 can be reduced, preventing excessive heating of the catalyst section 62. In addition, since the engine 1's adjustment state is closer to the reference adjustment state than the first adjustment state, the deterioration of fuel consumption rate compared to stable operation can be further suppressed. As a result, from a low exhaust temperature state such as at the start of operation to reaching stable operation, the deterioration of fuel consumption rate can be suppressed, and methane escape is preferably suppressed.

[0065] As described above, even when the temperature of the exhaust gas supplied to the catalyst section 62 is lower than the normal operating temperature, the exhaust gas treatment device 6 can preferably oxidize the methane contained in the exhaust gas. Therefore, the exhaust gas treatment device 6 is particularly suitable for situations where the temperature of the exhaust gas introduced into the treatment housing 61 (i.e., the inlet exhaust gas temperature) is low and the catalyst section 62 is not easily heated to the normal operating temperature. For example, the exhaust gas treatment device 6 is particularly suitable for situations where the temperature difference between the exhaust gas introduced into the treatment housing 61 and the normal operating temperature is 90°C or more.

[0066] As described above, the exhaust gas treatment device 6 preferably further includes an inlet temperature sensor 64 for measuring the temperature of the exhaust gas introduced into the treatment housing 61 (i.e., the inlet exhaust temperature). This allows for easy detection of states where the inlet exhaust temperature is low and a switching of the aforementioned adjustment state is required.

[0067] As described above, the processing housing 61 is preferably positioned upstream of the turbine 51, which rotates through the exhaust gas, in the exhaust flow direction. This allows the high-temperature exhaust gas to be introduced into the processing housing 61 compared to when it passes through the turbine 51. Consequently, the catalyst section 62 can be rapidly heated to its operating temperature, enabling efficient oxidation of methane by the catalyst section 62.

[0068] Furthermore, such as Figure 3 As shown, the treatment housing 61 is preferably positioned downstream of the turbine 51, which rotates through the exhaust gas, in the exhaust flow direction. This allows lower-pressure exhaust gas to be introduced into the treatment housing 61 compared to before passing through the turbine 51. Consequently, the structure of the treatment housing 61 is simplified. Furthermore, since there is no need to change the main structure of the engine 1 when installing the exhaust treatment device 6, it can be easily installed on existing ships. Moreover, as described above, even when the temperature of the exhaust gas supplied to the catalyst section 62 is low, the exhaust treatment device 6 can preferably oxidize methane, thus preferably oxidizing the methane in the exhaust gas cooled by passing through the turbine 51. Furthermore, in Figure 3 In the example shown, the processing housing 61 is disposed between the flue 81 and the turbine 51, and the exhaust gas for the rotation of the turbine 51 is introduced into the processing housing 61.

[0069] Figure 1 and Figure 3 The illustrated engine system 10 includes an engine 1 that uses a gas containing methane as fuel, and an exhaust treatment device 6 that treats the exhaust gas from the engine 1. Therefore, even at low exhaust temperatures, methane escape from the engine system 10 can be suppressed. Thus, the engine system 10 is particularly suitable for situations where a two-stroke engine with a relatively low exhaust temperature is used as the engine 1. Furthermore, the engine system 10 is particularly suitable for situations where a low-pressure two-stroke engine, which tends to have more methane escape compared to a high-pressure two-stroke engine, is used as the engine 1.

[0070] The exhaust treatment method described above is a method for oxidizing unburned methane in the exhaust of an engine 1 that uses methane-containing gas as fuel. The exhaust treatment method includes: a step of supplying exhaust gas at a temperature below a predetermined operating temperature to a catalyst section 62 (step S11); a step of oxidizing carbon monoxide contained in the exhaust gas in the catalyst section 62 and using the heat of oxidation of carbon monoxide to raise the temperature of the catalyst section 62 to above the operating temperature (step S14); and a step of oxidizing the methane in the exhaust gas through the catalyst section 62 at a temperature above the operating temperature after step S14 (step S15). Thus, similarly, even when the temperature of the exhaust gas supplied to the catalyst section 62 is lower than the operating temperature, the catalyst section 62 can be rapidly heated to the operating temperature, thereby preferably oxidizing the methane contained in the exhaust gas.

[0071] Various modifications can be made to the exhaust treatment equipment 6, the engine system 10, and the exhaust treatment method.

[0072] For example, the temperature difference between the exhaust gas introduced into the processing frame 61 and the normal operating temperature can be less than 90°C.

[0073] Furthermore, in cases where the temperature of the exhaust gas discharged from the combustion chamber 20 is lower than the oxidation start temperature of carbon monoxide, in order to promote the oxidation of carbon monoxide by the catalyst section 62, the exhaust gas from the combustion chamber 20 to the processing frame 61 and / or the catalyst section 62 can be heated by supplying boiler steam or a heater. This heating continues, for example, until the temperature of the catalyst section 62 reaches or exceeds the oxidation start temperature of carbon monoxide.

[0074] In the exhaust treatment device 6, it is not necessarily necessary to switch the adjustment state of the engine 1 based on the temperature measurement results obtained by the catalyst temperature sensor 63. For example, a table showing the relationship between the operating conditions such as the elapsed time or output (speed) since the start of the engine 1 and the exhaust temperature and the temperature of the catalyst section 62 can be prepared in advance, and the exhaust temperature and the temperature of the catalyst section 62 can be inferred based on the actual operating conditions and the table. In this case, the catalyst temperature sensor 63 can be omitted. In addition, the inlet temperature sensor 64 can also be omitted in the exhaust treatment device 6.

[0075] The control of the adjustment state of engine 1 by engine control unit 7 is not limited to the example described above, and various changes can be made. For example, after the adjustment state of engine 1 switches from the first adjustment state to the second adjustment state, if the temperature of catalyst section 62 drops below the first switching temperature for some reason, the adjustment state of engine 1 can switch back from the second adjustment state to the first adjustment state. Alternatively, the adjustment state of engine 1 can also switch from the second adjustment state to a third adjustment state where the carbon monoxide concentration in the exhaust is between the first and second adjustment states. Furthermore, in controlling the adjustment state of engine 1, it is not necessarily necessary to switch from the first adjustment state to the second adjustment state. Specifically, for example, if the second adjustment state is not set in engine 1, and the temperature of catalyst section 62 is below the second switching temperature, the adjustment state of engine 1 remains in the first adjustment state; when the temperature of catalyst section 62 reaches the second switching temperature, it directly switches from the first adjustment state to the reference adjustment state. In this case, the carbon monoxide concentration in the exhaust in the first adjustment state is preferably 0.04% by volume or more and 2.5% by volume or less. Furthermore, the switching of the adjustment state of engine 1 does not necessarily need to be performed automatically by the engine control unit 7; it can also be performed manually by the operator.

[0076] When increasing the carbon monoxide concentration in the exhaust gas compared to stable operation, it is not necessarily necessary to switch the engine 1's adjustment state from the baseline adjustment state during stable operation to the first adjustment state. For example, a gas separation device or the like can be installed between the combustion chamber 20 and the treatment housing 61 to increase the carbon monoxide concentration in the exhaust gas introduced into the treatment housing 61. Alternatively, exhaust gas recirculation (EGR) can be performed to reduce the oxygen concentration in the scavenging air, thereby increasing the carbon monoxide concentration in the exhaust gas.

[0077] In the example described, catalyst section 62 includes an oxidation catalyst for the oxidation of carbon monoxide and methane, but as mentioned above, the structure and shape of catalyst section 62 can be varied. For example, catalyst section 62 may include a first oxidation catalyst for the oxidation of carbon monoxide and a second oxidation catalyst for the oxidation of methane. The first oxidation catalyst and the second oxidation catalyst are different types of oxidation catalysts. In this case, the first oxidation catalyst is disposed upstream of the exhaust flow inside the processing frame 61, and the second oxidation catalyst is disposed downstream of the first oxidation catalyst. The exhaust gas that has passed through the first oxidation catalyst is supplied to the second oxidation catalyst. In catalyst section 62, when the exhaust gas flowing into the processing frame 61 passes through the first oxidation catalyst, the carbon monoxide in the exhaust gas is oxidized, and the exhaust gas heated by the heat of the carbon monoxide oxidation reaction is supplied to the second oxidation catalyst. In this case, also substantially the same as described above, the second oxidation catalyst in catalyst section 62 can be rapidly heated to above the normal operating temperature. Therefore, the methane in the exhaust gas can preferably be oxidized, and methane escape can preferably be suppressed. Furthermore, the oxidation of both carbon monoxide and methane can also be performed in the second oxidation catalyst.

[0078] Engine 1 may not use BOG (Bottle-Off Gas), but instead use LNG (LNG prepared as fuel for engine 1). Alternatively, engine 1 may be a binary fuel engine capable of switching between using fuel gas containing methane and heavy oil fuel.

[0079] Engine 1 can also be a four-stroke engine. Alternatively, engine 1 can also be a high-pressure engine using the Diesel cycle or diffusion combustion method.

[0080] The engine system 10 can be used as the main engine of a vessel other than an LNG carrier, or for purposes other than the main engine of a vessel.

[0081] The structures in the described embodiments and variations can be appropriately combined as long as they do not contradict each other.

[0082] The invention has been described and illustrated in detail, but the description is illustrative and not limiting. Therefore, various modifications or methods are possible without departing from the scope of the invention.

Claims

1. An exhaust gas treatment device, comprising: A processing frame for introducing exhaust gas from an engine that uses methane-containing gas as fuel; as well as A catalyst section, housed within the processing frame, oxidizes unburned methane contained in the exhaust gas. in, When the temperature of the catalyst section is lower than the specified operating temperature, the engine is adjusted to a specified state where the concentration of carbon monoxide in the exhaust is higher than that during stable operation. The catalyst section oxidizes the carbon monoxide in the exhaust and uses the heat of oxidation to raise the temperature above the specified operating temperature. When the temperature of the catalyst section is lower than a first switching temperature which is lower than the normal operating temperature, the engine is adjusted to a first adjustment state in which the concentration of carbon monoxide in the exhaust is higher than that during stable operation. When the temperature of the catalyst section rises to the first switching temperature, the engine is adjusted to a second adjustment state in which the concentration of carbon monoxide in the exhaust is higher than that during stable operation and lower than that during the first adjustment state.

2. The exhaust gas treatment equipment according to claim 1, wherein... When the engine is in the specified adjustment state, the concentration of carbon monoxide in the exhaust is 0.04% by volume or more and 2.5% by volume or less.

3. The exhaust gas treatment equipment according to claim 1, wherein... It also includes an inlet temperature sensor that measures the temperature of the exhaust gas introduced into the processing frame.

4. The exhaust gas treatment device according to any one of claims 1 to 3, wherein The processing frame is positioned upstream of the turbine that rotates through the exhaust gas in the direction of exhaust flow.

5. The exhaust gas treatment device according to any one of claims 1 to 3, wherein The processing frame is positioned downstream of the turbine that rotates through the exhaust gas in the direction of exhaust flow.

6. An engine system comprising: An engine that uses gas containing methane as fuel; as well as An exhaust treatment apparatus as described in any one of claims 1 to 5 for treating the exhaust of the engine.

7. The engine system according to claim 6, wherein The engine is a two-stroke engine.

8. An exhaust treatment method for oxidizing unburned methane in the exhaust of an engine that uses a gas containing methane as fuel, wherein the exhaust treatment method comprises: a) The process of supplying exhaust gas at a temperature lower than the specified operating temperature to the catalyst section; b) When the temperature of the catalyst section is lower than the normal operating temperature, the engine is adjusted to a predetermined state where the concentration of carbon monoxide in the exhaust is higher than that during stable operation, and the carbon monoxide in the exhaust is oxidized in the catalyst section, and the heat of the carbon monoxide oxidation reaction is used to raise the temperature of the catalyst section to above the normal operating temperature; and c) A step following step b) in which methane in the exhaust gas is oxidized by passing it through a catalyst section at a temperature above the normal operating temperature. in, When the temperature of the catalyst section is lower than a first switching temperature which is lower than the normal operating temperature, the engine is adjusted to a first adjustment state in which the concentration of carbon monoxide in the exhaust is higher than that during stable operation. When the temperature of the catalyst section rises to the first switching temperature, the engine is adjusted to a second adjustment state in which the concentration of carbon monoxide in the exhaust is higher than that during stable operation and lower than that during the first adjustment state.

Images