Methane purification device

Abstract

A methane purification device (1) is provided with: a flow path (10) through which a first gas containing methane flows; an ozone supply unit (22) that supplies ozone to the first gas; a catalyst (25) that decomposes methane contained in a second gas containing the first gas flowing through the flow path (10) and the ozone supplied by the ozone supply unit (22); and a microwave output means (29) that outputs microwaves in the flow path (10) in the vicinity of the catalyst (25).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a methane purification device. BACKGROUND

[0002] A conventional pollutant treatment method removes methane contained in a gas by bringing the gas containing methane and ozone and having a temperature within a predetermined range into contact with a catalyst and oxidizing the methane with ozone (for example, Japanese Unexamined Patent Application Publication No. 2021-505376). SUMMARY

[0003] Problem to be Solved by the Invention

[0004] When methane is decomposed on a catalyst by reacting with ozone, water is produced and the produced water adheres to the catalyst and blocks a region on the catalyst where methane and ozone come into contact and react, thereby making it difficult for methane and ozone to react on the catalyst.

[0005] The present disclosure is made in view of these points, and aims to allow methane and ozone to react while removing water adhering to a catalyst.

[0006] Means for Solving the Problem

[0007] A methane purification device according to one aspect of the present disclosure includes: a flow path through which a first gas containing methane flows; an ozone supply unit that supplies ozone to the first gas; a catalyst that decomposes methane contained in a second gas, the second gas including the first gas flowing through the flow path and ozone supplied by the ozone supply unit; and a microwave output unit that outputs microwaves in the flow path in the vicinity of the catalyst.

[0008] The methane purification device can further include: a first shield plate disposed upstream of the catalyst and the microwave output unit in the flow path, including one or a plurality of first through portions through which the second gas passes, and blocking microwaves; and a second shield plate disposed downstream of the catalyst and the microwave output unit in the flow path, including one or a plurality of second through portions through which the second gas passes, and blocking microwaves.

[0009] The first shield plate can include a first through portion whose length of a side or diameter is half or less of a wavelength of microwaves output by the microwave output unit, and the second shield plate can include a second through portion whose length of a side or diameter is equal to or less than half of the wavelength of microwaves output by the microwave output unit.

[0010] The methane purification device can further include: a purification control unit that controls a period in which the ozone supply unit supplies ozone and a period in which the microwave output unit outputs microwaves.

[0011] The purification control unit can cause the microwave output unit to output microwaves immediately after the start of the methane purifying device, and can cause the ozone supply unit to supply ozone after a lapse of a predetermined period of time from the time when the microwave output unit starts to output microwaves.

[0012] The methane purifying device can further include a detection unit that detects a first concentration of methane contained in the first gas at an inlet of the flow path and a second concentration of methane contained in a second gas flowing in the flow path downstream of the catalyst, wherein the purification control unit can cause the microwave output unit to output microwaves on a condition that (i) a methane purification rate based on the first concentration and the second concentration is less than a predetermined purification rate or (ii) the second concentration is equal to or greater than a predetermined concentration.

[0013] The methane purifying device can further include a detection unit that detects a temperature of the catalyst, wherein the purification control unit can cause the microwave output unit to stop output of microwaves when the temperature of the catalyst reaches a predetermined temperature after the purification control unit has caused the microwave output unit to start to output microwaves.

[0014] The purification control unit can alternately execute a process in which the ozone supply unit supplies ozone and a process in which the microwave output unit outputs microwaves.

[0015] The purification control unit can reduce the output of microwaves when the purification control unit causes the microwave output unit to output microwaves during a period of time in which the purification control unit causes the ozone supply unit to supply ozone.

[0016] The purification control unit can identify a temperature corresponding to the atmospheric pressure by referring to a table stored in the storage unit after acquiring the atmospheric pressure of the inside of the flow path, the table indicating atmospheric pressures corresponding to temperatures, and determine the temperature as the predetermined temperature.

[0017] The purification control unit can start to suck the first gas into the flow path by causing the microwave output unit, which starts to output microwaves after the power-on start of the methane purifying device, to stop output of microwaves.

[0018] Effects of the Invention

[0019] According to the present disclosure, an effect of allowing methane and ozone to react while removing water adhering to a catalyst can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a diagram showing an overview of a methane purifying device 1 according to the present embodiment.

[0021] Figure 2 is a diagram showing operations of the ozone supply unit 22 and the microwave output unit 29.

[0022] Figure 3is a diagram showing an example of a processing sequence in the methane purifying apparatus 1. DETAILED DESCRIPTION

[0023] <Overview of the Methane Purifying Apparatus 1>

[0024] Figure 1 is a diagram showing an overview of the methane purifying apparatus 1 according to the present embodiment. Figure 1 The methane purifying apparatus 1 shown includes a flow path 10, an intake unit 11, an ozone supply unit 22, a methane decomposition unit 24, a microwave output unit 29, a first shield plate 30a, a second shield plate 30b, a temperature sensor 31, a methane concentration sensor 37, a methane concentration sensor 38, a storage unit 41, and a control unit 42. The methane purifying apparatus 1 is an apparatus that decomposes methane contained in air to produce water and carbon dioxide.

[0025] The flow path 10 is a flow path through which air containing methane (hereinafter referred to as "first gas") flows. The intake unit 11 is, for example, an intake fan, and sucks the first gas from the outside of the flow path 10 into the flow path 10.

[0026] The ozone supply unit 22 is provided in the flow path 10 downstream of the intake unit 11 and upstream of the methane decomposition unit 24, and supplies ozone to the first gas sucked by the intake unit 11. The ozone supply unit 22 includes, for example, an AC power source 22a and an electrode 22b covered with a dielectric such as glass, and performs a process of generating ozone by applying an AC voltage to the electrode 22b by the AC power source 22a (so-called silent discharge method). The ozone supply unit 22 can generate ozone by performing a process in which discharge occurs on the surface of the dielectric covering the electrode (so-called surface discharge method), a process of electrolyzing water (so-called electrolysis method), or a process of irradiating ultraviolet light onto the first gas (so-called ultraviolet lamp method). By supplying the generated ozone to the first gas, the ozone supply unit 22 generates a second gas containing the first gas and ozone.

[0027] The methane decomposition unit 24 is provided in the flow path 10 downstream of the ozone supply unit 22, and houses a catalyst 25. The methane decomposition unit 24 decomposes methane by, for example, causing ozone and methane contained in the second gas to react on the catalyst 25 to produce water and carbon dioxide.

[0028] Catalyst 25 decomposes methane contained in a second gas, which includes a first gas flowing through flow path 10 and ozone supplied by ozone supply unit 22. Catalyst 25 includes a carrier with a predetermined structure and a coating loaded on the surface of the carrier. The predetermined structure is, for example, a honeycomb structure, a corrugated structure, a mesh structure, or a porous structure. The carrier material is, for example, cordierite, silicon carbide, glass wool, or glass fiber. The carrier material is preferably a microwave-permeable and non-conductive material, but is not limited to such materials. The coating includes, for example, zeolite, iron-ion-exchange zeolite, or cobalt-ion-exchange zeolite. Areas on the carrier surface may include areas where the coating is not supported.

[0029] A microwave output unit 29 is positioned downstream of the methane decomposition unit 24 in the flow path 10 and outputs microwaves near the catalyst 25 within the flow path 10. The frequency of the microwaves is a frequency capable of raising the temperature of the water adhering to the catalyst 25, and is, for example, 2.4 GHz. The microwave output unit 29 is, for example, a magnetron having a diode-type vacuum tube 29a and an antenna 29b. Electrons rotate around the cathode of the diode-type vacuum tube 29a due to the Lorentz force, and the energy obtained is output as radio waves (microwaves) from the antenna 29b. By operating in this way, the microwave output unit 29 can raise the temperature of the water produced by the decomposition of methane and adhering to the catalyst 25, causing the water to evaporate. As a result, the water on the catalyst 25 is removed.

[0030] The first shielding plate 30a is disposed upstream of the catalyst 25 and the microwave output unit 29 in the flow path 10, and includes one or more first through portions for the passage of the second gas, while blocking microwaves. The first shielding plate 30a is, for example, an expanded metal plate, a decorative metal plate, a perforated metal plate, or a metal mesh plate, and includes one or more first through portions having a circular, elliptical, or polygonal shape.

[0031] When the first through-section is circular, the first shielding plate 30a includes a first through-section with a diameter equal to or less than the length L1, which is half or less of the wavelength λ of the microwave output by the microwave output unit 29. When the first through-section is elliptical, the first shielding plate 30a includes a first through-section with a side length of L1. When the first through-section is polygonal, the first shielding plate 30a includes a first through-section with one side of length L1. With the above configuration, the first shielding plate 30a allows the second gas to pass through while preventing microwave leakage to the upstream side of the first shielding plate 30a in the flow path 10.

[0032] The second shielding plate 30b is disposed downstream of the catalyst 25 and the microwave output unit 29 in the flow path 10, including one or more second through portions for the passage of the second gas and blocking microwaves. The second shielding plate 30b is, for example, an expanded metal plate, a decorative metal plate, a perforated metal plate, or a metal mesh plate, and includes one or more second through portions having a circular, elliptical, or polygonal shape.

[0033] When the second through-section is circular, the second shielding plate 30b includes a second through-section with a diameter equal to or less than length L2, where length L2 is half the wavelength λ of the microwave output by microwave output unit 29. When the second through-section is elliptical, the second shielding plate 30b includes a second through-section with a side length of length L2. When the second through-section is polygonal, the second shielding plate 30b includes a second through-section with one side of length L2. Using the above configuration, the second shielding plate 30b allows the second gas to pass through while preventing microwave leakage to the downstream side of the second shielding plate 30b in the flow path 10. Lengths L1 and L2 can be the same or different.

[0034] Temperature sensor 31 is a sensor for detecting the temperature of the second gas flowing through the methane decomposition unit 24. Temperature sensor 31 is disposed on the inner wall surface of the methane decomposition unit 24 and is, for example, a thermistor or thermocouple. Methane concentration sensor 37 is a sensor for detecting the concentration of methane contained in the first gas. Methane concentration sensor 37 is disposed upstream of the inlet unit 11 in the flow path 10. Methane concentration sensor 38 is a sensor for detecting the concentration of methane contained in the second gas. Methane concentration sensor 38 is disposed downstream of the catalyst 25 in the flow path 10. For example, methane concentration sensors 37 and 38 detect methane concentration by: (i) irradiating the flow path 10 with light having a predetermined wavelength (e.g., 1653 nm); and (ii) detecting the 1f (10 kHz) component and the 2f (20 kHz) component, which are proportional to the light intensity.

[0035] Storage unit 41 includes a storage medium such as ROM (Read-Only Memory), RAM (Random Access Memory), hard disk drive (HDD), or solid-state drive (SSD). Storage unit 41 stores programs executed by control unit 42 and various types of information for decomposing the methane contained in the second gas.

[0036] The control unit 42 includes a processor such as a CPU (central processing unit). The control unit 42 applies voltage to the AC power supply 22a, thereby supplying ozone to the ozone supply unit 22. The control unit 42 causes the microwave output unit 29 to output microwaves, thereby increasing the temperature of the water attached to the catalyst 25. The control unit 42 can be configured with a single processor, or it can be configured with multiple processors or a combination of one or more processors and electronic circuitry.

[0037] Because the control unit 42 operates in this manner, the methane purification device 1 can evaporate the water adhering to the catalyst 25 by increasing the temperature of the microwaves output by the microwave output unit 29. As a result, since the water adhering to the catalyst 25 is reduced, the reaction between methane and ozone, which is unlikely to occur on the catalyst 25 due to the water-blocking zone (so-called reaction site) where methane and ozone contact and react on the catalyst 25, can be suppressed. The configuration and operation of the control unit 42 will be described in detail below.

[0038] Configuration of control unit 42.

[0039] like Figure 1 As shown, the control unit 42 includes a detection unit 421 and a purification control unit 424. The control unit 42 functions as both the detection unit 421 and the purification control unit 424 by executing a program stored in the storage unit 41.

[0040] The detection unit 421 detects the temperature of the catalyst 25. For example, the detection unit 421 detects the temperature of the catalyst 25 by acquiring the temperature of the second gas flowing through the methane decomposition unit 24, which is detected by the temperature sensor 31, as the temperature of the catalyst 25. The detection unit 421 detects a first concentration of methane contained in the first gas at the inlet of the flow path 10 and a second concentration of methane contained in the second gas flowing downstream of the catalyst 25 in the flow path 10. The detection unit 421 detects the first concentration and the second concentration, for example, by acquiring the methane concentration detected by the methane concentration sensor 37 as the first concentration and acquiring the methane concentration detected by the methane concentration sensor 38 as the second concentration.

[0041] The purification control unit 424 controls the time period during which the ozone supply unit 22 supplies ozone and the time period during which the microwave output unit 29 outputs microwaves. For example, the purification control unit 424 causes the ozone supply unit 22 to supply ozone by applying voltage to the AC power supply 22a, and stops the ozone supply unit 22 from supplying ozone by stopping the application of voltage to the AC power supply 22a. For example, the purification control unit 424 causes the antenna 29b to output microwaves by applying voltage to the diode-type vacuum tube 29a, and stops the output of microwaves from the antenna 29b by stopping the application of voltage to the diode-type vacuum tube 29a.

[0042] Figure 2 This is a diagram illustrating the operation of the ozone supply unit 22 and the microwave output unit 29. Figure 2 The horizontal axis in the diagram represents timing, while... Figure 2 The vertical axis represents "Power Supply", "Inlet Unit 11", "Ozone Supply Unit 22", "Microwave Output Unit 29", and "Second Concentration". "Power Supply" indicates whether the power supply to the methane purification device 1 is on. "Inlet Unit 11", "Ozone Supply Unit 22", and "Microwave Output Unit 29" each indicate whether they are in operation. "Second Concentration" represents the second concentration of methane detected by the detection unit 421. In "Power Supply", the power-off state "OFF" and the power-on state "ON" are shown. In "Inlet Unit 11", "Ozone Supply Unit 22", and "Microwave Output Unit 29", the stop state "OFF" and the operating state "ON" are shown.

[0043] exist Figure 2 At time T0, when the methane purification device 1 switches from a power-off state to a power-on state, the intake unit 11 switches from a stopped state to an operating state and begins to draw the first gas into the flow path 10. After the methane purification device 1 is activated (i.e., immediately after time T0), the purification control unit 424 causes the microwave output unit 29 to output microwaves. By operating in this way, the purification control unit 424 can raise the temperature of the moisture contained in the air that has adhered to the catalyst when the methane purification device 1 is turned off, and remove (evaporate) the moisture by causing the microwave output unit 29 to output microwaves. After removing moisture from the catalyst 25, the purification control unit 424 can cause methane and ozone to react on the catalyst 25.

[0044] Next, after a predetermined time period (i.e., time T1) elapses after the microwave output unit 29 begins outputting microwaves, the purification control unit 424 stops the microwave output unit 29 from outputting microwaves and starts the ozone supply unit 22 to supply ozone. After time T1, the purification control unit 424 alternately executes the process of the ozone supply unit 22 supplying ozone and the process of the microwave output unit 29 outputting microwaves.

[0045] Through the operation described above, the purification control unit 424 can supply power to one of the ozone supply unit 22 and the microwave output unit 29. As a result, the methane purification device 1 can reduce power consumption. Furthermore, the purification control unit 424 can enable the ozone supply unit 22 to start supplying ozone immediately after the microwave output unit 29 has removed the water adhering to the catalyst 25, thereby allowing methane and ozone to react more easily on the catalyst 25.

[0046] For example, at a time after time T1, the purification control unit 424 causes the ozone supply unit 22 to perform the process of supplying ozone at a predetermined period P for a predetermined time period P1. The predetermined period P and time period P1 are values ​​corresponding to the amount of water that can adhere to the catalyst 25, and are calculated based on, for example, the volume of the flow path 10, the volume of the catalyst 25, and a target value for the amount of methane purified by the methane purification device 1. These values ​​are stored in the storage unit 41. For example, as Figure 2 As shown, the purification control unit 424 causes the ozone supply unit 22 to supply ozone during the time period P1 from time T1 to time T2. Next, the purification control unit 424 causes the ozone supply unit 22 to supply ozone during the time period P1 from time T3 to time T5, where T3 is the time point after a predetermined period P from time T1.

[0047] Through the operation described above, the purification control unit 424 can cause the microwave output unit 29 to output microwaves during the period P2 when the ozone supply unit 22 has stopped supplying ozone. As a result, the purification control unit 424 can evaporate the water produced by the decomposition of methane and attached to the catalyst 25.

[0048] For example, the purification control unit 424 causes the microwave output unit 29 to perform a process of outputting microwaves at a predetermined period P for a predetermined time period P2. The predetermined time period P2 corresponds to the amount of water that can adhere to the catalyst 25 and is calculated based on, for example, the volume of the flow path 10, the volume of the catalyst 25, and a target value for the amount of methane purified by the methane purification device 1. These values ​​are stored in the storage unit 41. For example, as Figure 2 As shown, the purification control unit 424 causes the microwave output unit 29 to output microwaves during the time period P2 from time T2 to time T3. Next, the purification control unit 424 causes the microwave output unit 29 to output microwaves during the time period P2 from time T5 to time T6, where T5 is the time point after a predetermined period P from time T2.

[0049] Through the operation described above, the purification control unit 424 can... Figure 2 During the time period P2 shown, water adhering to catalyst 25 evaporates. As a result, immediately after time period P2, since the water adhering to the reaction site has been removed, methane and ozone can react more easily, and the purification control unit 424 can reduce the increased second concentration at regular intervals. Specifically, the second concentration indicating concentration M2 at times T2 and T5 can be reduced to concentration M1 at times T4 and T7.

[0050] The amount of water adhering to catalyst 25 increases rapidly with the increase in the amount of methane contained in the second gas. As a result, the greater the amount of methane in the second gas, the more difficult it becomes for methane and ozone to react on catalyst 25 in a short time, and thus the second concentration increases. Therefore, when the purification control unit 424 causes the microwave output unit 29 to output microwaves at a predetermined period P, the greater the amount of methane contained in the second gas, the higher the probability that the timing of microwave output will be inappropriate, and thus the second concentration is more likely to increase.

[0051] Therefore, the purification control unit 424 can cause the microwave output unit 29 to output microwaves under the following conditions: (i) the methane purification rate based on the first and second concentrations detected by the detection unit 421 is less than a predetermined purification rate; or (ii) the second concentration is equal to or greater than the predetermined concentration. The predetermined purification rate is, for example, a purification rate corresponding to a target value of the amount of methane purified by the methane purification device 1, and is stored in the storage unit 41. The predetermined concentration is, for example, a concentration corresponding to a target value of the amount of methane purified by the methane purification device 1, and is stored in the storage unit 41.

[0052] For example, the purification control unit 424 at a second concentration equal to or higher Figure 2 Under the condition of concentration M2 shown, microwave output unit 29 outputs microwaves. For example, purification control unit 424 calculates the methane purification rate by dividing the second concentration by the first concentration, and when this ratio is less than a predetermined purification rate, microwave output unit 29 outputs microwaves. By operating in this way, purification control unit 424 can remove (evaporate) water adhering to catalyst 25 by outputting microwaves in response to an increase in methane concentration, thereby allowing methane and ozone to react more easily on catalyst 25. As a result, purification control unit 424 can output microwaves at the appropriate time and suppress the increase in the second concentration.

[0053] Since water evaporates at approximately 100°C (99.974°C) at 1 atm, the amount of evaporated water is not easily increased even if microwaves corresponding to temperatures exceeding 100°C are output. Therefore, after the purification control unit 424 has started outputting microwaves to the microwave output unit 29, when the temperature of the catalyst 25 detected by the detection unit 421 reaches a predetermined temperature, the purification control unit 424 can stop the microwave output unit 29 from outputting microwaves. This predetermined temperature is, for example, 100°C. By operating in this way, the purification control unit 424 can appropriately control the duration of microwave output by the microwave output unit 29.

[0054] Furthermore, the purification control unit 424 can determine the predetermined temperature based on the atmospheric pressure within the flow path 10. The purification control unit 424 acquires, for example, the atmospheric pressure detected by an atmospheric pressure sensor (not shown) disposed inside the flow path 10. After acquiring the internal atmospheric pressure of the flow path 10, by referring to a table stored in the storage unit 41 indicating atmospheric pressure (vapor pressure) corresponding to temperature, the purification control unit 424 identifies the temperature corresponding to the internal atmospheric pressure acquired by the atmospheric pressure sensor and determines the identified temperature as the predetermined temperature. By operating in this manner, the purification control unit 424 can improve the accuracy of determining the predetermined temperature and therefore can more appropriately control the duration of microwave output by the microwave output unit 29.

[0055] When the purification control unit 424 determines the microwave output time based on the methane concentration or the microwave output duration based on the catalyst 25 temperature, there may be periods during which both the ozone supply unit 22 and the microwave output unit 29 operate. In this case, the methane purification device 1 consumes a large amount of power during the periods when both the ozone supply unit 22 and the microwave output unit 29 are operating. Therefore, when the purification control unit 424 causes the microwave output unit 29 to output microwaves during the periods when the purification control unit 424 also causes the ozone supply unit 22 to supply ozone, the purification control unit 424 can reduce the microwave output.

[0056] For example, when the purification control unit 424 causes the microwave output unit 29 to output microwaves when the ozone supply unit 22 is not supplying ozone (i.e., no voltage is applied to the AC power supply 22a), the purification control unit 424 applies a first voltage to the diode-type vacuum tube 29a. On the other hand, when the purification control unit 424 causes the microwave output unit 29 to output microwaves when the ozone supply unit 22 is supplying ozone (i.e., a voltage is applied to the AC power supply 22a), the purification control unit 424 applies a second voltage lower than the first voltage to the diode-type vacuum tube 29a. By operating in this way, the purification control unit 424 can prevent an increase in the power consumption of the methane purification device 1.

[0057] <Processing sequence in methane purification unit 1>

[0058] Figure 3 This is a diagram illustrating an example of the processing sequence in methane purification unit 1. Figure 3 The processing sequence shown is used to determine the timing and time period of microwave output by microwave output unit 29 based on methane concentration and catalyst 25 temperature. Figure 3 The processing sequence shown is at the moment when the methane purification unit 1 switches from a power-off state to a power-on state (e.g., Figure 2 The time shown is T0).

[0059] The purification control unit 424 activates the microwave output unit 29 to begin outputting microwaves to remove water adhering to the catalyst 25 when the methane purification device 1 is in a stopped state (step S11). If the predetermined time period has not yet elapsed ("No" in step S12), the purification control unit 424 keeps the microwave output unit 29 in an activated state. If the predetermined time period has elapsed ("Yes" in step S12), the purification control unit 424 causes the microwave output unit 29 to stop outputting microwaves and activates the ozone supply unit 22 to begin supplying ozone (step S13).

[0060] The purification control unit 424 acquires the first concentration and the second concentration detected by the detection unit 421, and calculates the methane purification rate R as the ratio obtained by dividing the second concentration by the first concentration (step S14). If the methane purification rate R is equal to or higher than the predetermined purification rate ("No" in step S15), the purification control unit 424 returns to the processing in step S14. If the methane purification rate R is less than the predetermined purification rate ("Yes" in step S15), the purification control unit 424 activates the microwave output unit 29 to start outputting microwaves, and at the same time, the ozone supply unit 22 stops supplying ozone (step S16).

[0061] The detection unit 421 detects the temperature E of the catalyst 25 (step S17). If the temperature E is lower than the predetermined temperature ("No" in step S18), the purification control unit 424 returns to the process in step S17. If the temperature E is equal to or higher than the predetermined temperature ("Yes" in step S18), the purification control unit 424 causes the microwave output unit 29 to stop outputting microwaves and activates the ozone supply unit 22 to start supplying ozone (step S19). If the methane purification device 1 does not receive an operation to end the process ("No" in step S20), the methane purification device 1 repeats the process from steps S14 to S19. If the methane purification device 1 receives an operation to end the process ("Yes" in step S20), the methane purification device 1 causes the purification control unit 424 to stop the ozone supply unit 22 and end the process.

[0062] <First Variation>

[0063] The above description illustrates the operation of methane purification device 1 in decomposing methane contained in the air, but the operation is not limited to this. Methane purification device 1 can decompose methane contained in exhaust gases emitted from equipment installed in a factory or from vehicles. As an example, methane purification device 1 can be installed in the exhaust passage downstream of an engine included in a vehicle, and can decompose methane contained in the engine's exhaust.

[0064] <Second Variation>

[0065] The above description illustrates an example of a configuration where the microwave output unit 29 is located downstream of the methane decomposition unit 24 in the flow path 10; however, this configuration is not limited to this. The microwave output unit 29 can also be located downstream of the first shielding plate 30a and upstream of the methane decomposition unit 24 in the flow path 10.

[0066] <Third Variation>

[0067] In the above description, the moment when the intake unit 11 is powered on by the methane purification device 1 is illustrated (e.g., Figure 2 The operation of drawing the first gas into the flow path 10 begins at time T0 (as shown), but this operation is not limited to this. The intake unit 11 can start from time (...). Figure 2 At time T1, the first gas is drawn into the flow path 10. At this time, the microwave output unit 29, which immediately begins outputting microwaves after the power to the methane purification device 1 is turned on, stops outputting microwaves. In other words, by stopping the microwave output unit 29, which begins outputting microwaves after the power to the methane purification device 1 is turned on, the purification control unit 424 begins to draw the first gas into the flow path 10. By operating in this way, the methane purification device 1 can prevent the first gas from being drawn into the flow path 10. Figure 2 The output gas has a high methane concentration during the time period from time T0 to time T1.

[0068] <Effects of Methane Purification Device 1>

[0069] As described above, the methane purification device 1 includes: a flow path 10 through which a first gas containing methane flows; an ozone supply unit 22 for supplying ozone to the first gas; a catalyst 25 for decomposing methane contained in a second gas, the second gas containing the first gas flowing through the flow path 10 and the ozone supplied by the ozone supply unit 22; and a microwave output unit 29 for outputting microwaves in the flow path 10 near the catalyst 25.

[0070] Using this configuration, the methane purification device 1 can evaporate the water produced by the decomposition of methane and attached to the catalyst 25 by raising its temperature using microwaves output from the microwave output unit 29. As a result, the methane purification device 1 can decompose methane by reacting it with ozone on the catalyst 25, while suppressing the reaction between methane and ozone, which is hindered by the water attached to the catalyst 25 blocking the reaction sites on the catalyst 25.

[0071] This disclosure has been described based on exemplary embodiments. The technical scope of this disclosure is not limited to the scope described in the above embodiments, and various changes and modifications can be made within the scope of this disclosure. For example, all or part of the apparatus can be configured using any functionally or physically distributed or integrated units. Furthermore, new exemplary embodiments resulting from any combination of embodiments are included in the exemplary embodiments. Moreover, the effects of the new exemplary embodiments resulting from the combination also have the effects of the original exemplary embodiments.

[0072] [Symbol Description]

[0073] 1. Methane purification unit

[0074] 10 flow path

[0075] 11. Intake Unit

[0076] 22 Ozone Supply Units

[0077] 22 AC power supply

[0078] 22b electrode

[0079] 24 Methane decomposition unit

[0080] 25 Catalysts

[0081] 29 Microwave Output Unit

[0082] 29A Diode-type Vacuum Tube

[0083] 29b antenna

[0084] 30a First shielding plate

[0085] 30b Second Shielding Plate

[0086] 31 Temperature sensor

[0087] 37 Methane Concentration Sensor

[0088] 38 Methane Concentration Sensor

[0089] 41 storage units

[0090] 42 Control Unit

[0091] 421 Detection Unit

[0092] 424 Purification Control Unit

Claims

1. A methane purification device comprising: a flow path through which a first gas containing methane flows; an ozone supply unit that supplies ozone to the first gas; a catalyst that decomposes the methane contained in a second gas that includes the first gas flowing through the flow path and the ozone supplied by the ozone supply unit; and a microwave output unit that outputs microwaves in the flow path in the vicinity of the catalyst.

2. The methane purification device according to claim 1, further comprising: a first shield plate that is provided in the flow path upstream of the catalyst and the microwave output unit, includes one or a plurality of first through portions through which the second gas passes, and blocks the microwaves; and a second shield plate that is provided in the flow path downstream of the catalyst and the microwave output unit, includes one or a plurality of second through portions through which the second gas passes, and blocks the microwaves. the first shield plate includes the first through portions whose length of side or diameter is half or less of the wavelength of the microwaves output by the microwave output unit, and the second shield plate includes the second through portions whose length of side or diameter is equal to or less than half of the wavelength of the microwaves output by the microwave output unit.

3. The methane purification device of claim 2, wherein, 4. The methane purification device according to claim 1, further comprising: a purification control unit that controls a period during which the ozone supply unit supplies the ozone and a period during which the microwave output unit outputs the microwaves. the purification control unit causes the microwave output unit to output the microwaves immediately after the methane purification device is started, and causes the ozone supply unit to supply the ozone after a predetermined period elapses from the time at which the microwave output unit starts outputting the microwaves.

6. The methane purification device according to claim 4, further comprising:

5. The methane purification device of claim 4, wherein, a detection unit that detects a first concentration of the methane contained in the first gas at an inlet of the flow path and a second concentration of the methane contained in the second gas flowing in the flow path downstream of the catalyst, wherein, on a condition that (i) a methane purification rate based on the first concentration and the second concentration is less than a predetermined purification rate or (ii) the second concentration is equal to or greater than a predetermined concentration, the purification control unit causes the microwave output unit to output the microwaves.

7. The methane purification device according to claim 4, further comprising: a detection unit that detects a temperature of the catalyst, wherein, after the purification control unit has caused the microwave output unit to start outputting the microwaves, when the temperature of the catalyst reaches a predetermined temperature, the purification control unit causes the microwave output unit to stop outputting the microwaves. the purification control unit alternately performs a process in which the ozone supply unit supplies the ozone and a process in which the microwave output unit outputs the microwaves. when the purification control unit causes the microwave output unit to output the microwaves during a period during which the purification control unit causes the ozone supply unit to supply the ozone, the purification control unit reduces the output of the microwaves.

8. The methane purification device of claim 4, wherein, ​ 9. The methane purification device of claim 4, wherein, ​ 10. The methane purification device of claim 7, wherein, After acquiring the atmospheric pressure of the inside of the flow path, the purification control unit identifies a temperature corresponding to the atmospheric pressure by referring to a table stored in a storage unit, the table indicating atmospheric pressures corresponding to temperatures, and determines the temperature as the predetermined temperature.

11. The methane purification device of claim 4, wherein, The purification control unit starts the suction of the first gas into the flow path by stopping the output of the microwaves by the microwave output unit that starts outputting the microwaves after the energization start of the methane purifying device.

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