Methane purification system

Abstract

The reaction between methane and ozone is carried out while suppressing the adhesion of water to the catalyst. [Solution] The methane purification device 1 includes a pipeline 10 through which a first gas containing methane flows, an ozone supply unit 22 that supplies ozone to the first gas, a heating unit 23 that heats a second gas containing the first gas flowing through the pipeline 10 and the ozone supplied by the ozone supply unit 22, a catalyst 25 provided downstream of the heating unit 23 in the pipeline 10 for decomposing methane contained in the second gas, and a temperature control unit 423 that causes the heating unit 23 to heat the second gas so that the temperature of the second gas falls within a range R1 that indicates a temperature at which ozone does not decompose in a predetermined time and a range R1 that indicates a temperature at which condensation of water vapor contained in the second gas is suppressed.

Description

Technical Field

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

Background Art

[0002] The pollutant treatment method of Patent Document 1 includes methane and ozone, and by bringing a gas having a temperature within a predetermined range into contact with a catalyst, methane contained in the gas is oxidized and removed by ozone.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Methane is more likely to react on the catalyst as the temperature increases, but ozone is more likely to decompose itself as the temperature increases, making it difficult to oxidize methane. Therefore, a strategy of raising the temperature to a temperature at which ozone is difficult to decompose and reacting methane with ozone can be considered. In this case, however, water condensed from the water vapor contained in the gas adheres to the catalyst, making it difficult for methane and ozone to react on the catalyst.

[0005] Therefore, the present invention has been made in view of these points, and an object thereof is to react methane with ozone while suppressing the adhesion of water to the catalyst.

Means for Solving the Problems

[0006] A methane purification apparatus according to an aspect of the present invention comprises: a pipeline through which a first gas containing methane flows; an ozone supply unit for supplying ozone to the first gas; a heating unit for heating a second gas containing the first gas flowing through the pipeline and the ozone supplied by the ozone supply unit; a catalyst provided downstream of the heating unit in the pipeline for decomposing the methane contained in the second gas; and a temperature control unit that causes the heating unit to heat the second gas such that the temperature of the second gas falls within a first temperature range that indicates a temperature at which the ozone does not decompose in a predetermined time and a first temperature range that indicates a temperature that suppresses the condensation of water vapor contained in the second gas.

[0007] The temperature control unit may further include a detection unit for detecting the temperature of the catalyst, and the temperature control unit may cause the heating unit to heat the second gas so that the temperature detected by the detection unit falls within the first temperature range.

[0008] The catalyst may include zeolite, iron ion exchange zeolite, or cobalt ion exchange zeolite.

[0009] The heating element may have a carrier on its surface bearing Teflon®, silica, or titania.

[0010] The temperature control unit may heat the second gas in the heating unit for a predetermined period of time at a predetermined interval so that the temperature of the second gas falls within the first temperature range, and after the predetermined time has elapsed, the heating unit may heat the second gas in the heating unit so that the temperature of the second gas falls within a second temperature range that is lower than the temperature in the first temperature range and is a second temperature range in which the ozone does not decompose within a predetermined time.

[0011] The temperature control unit further includes a calculation unit that calculates the amount of water vapor contained in the first gas based on the absolute humidity of the first gas, which is determined by the temperature and humidity of the first gas detected upstream of the ozone supply unit in the pipeline, and the flow rate of the first gas in the pipeline, and calculates the amount of water vapor per unit weight of the catalyst based on the amount of water vapor and the weight of the catalyst. The temperature control unit may, if the amount of water vapor per unit weight exceeds a threshold, cause the heating unit to heat the second gas so that the temperature of the second gas falls within the first temperature range, and if the amount of water vapor per unit weight is below the threshold, cause the heating unit to heat the second gas so that the temperature of the second gas falls within a second temperature range that is lower than the temperature included in the first temperature range and is a second temperature range that does not cause the ozone to decompose in a predetermined time.

[0012] The temperature control unit further includes a detection unit for detecting the color of the catalyst, and if the color of the catalyst detected by the detection unit is a color indicating that water has adhered to the catalyst, the temperature control unit may cause the heating unit to heat the second gas so that the temperature of the second gas falls within the first temperature range, and if the color of the catalyst detected by the detection unit is a color indicating that water has not adhered to the catalyst, the heating unit may cause the heating unit to heat the second gas so that the temperature of the second gas falls within a second temperature range that is lower than the temperature included in the first temperature range and is a second temperature range that indicates that the ozone does not decompose in a predetermined time.

[0013] The system further includes a storage unit that stores a methane decomposition rate map for each type of catalyst, which shows the methane decomposition rate corresponding to the temperature of the catalyst. The temperature control unit may, by referring to the methane decomposition rate map, identify a temperature range in which the methane decomposition rate for each type of catalyst is equal to or greater than a predetermined decomposition rate, and determine the temperature range to be the first temperature range. [Effects of the Invention]

[0014] According to the present invention, the effect of reacting methane and ozone while suppressing the adhesion of water to the catalyst is achieved. [Brief explanation of the drawing]

[0015] [Figure 1] This diagram shows an overview of the methane purification device 1 according to this embodiment. [Figure 2] This figure shows an example of the temperature of catalyst 25. [Figure 3] This figure shows an example of the temperature of catalyst 25. [Figure 4] This figure shows an example of a methane decomposition rate map. [Figure 5] This figure shows an example of the processing sequence in methane purification device 1. [Modes for carrying out the invention]

[0016] <Overview of Methane Purification System 1> Figure 1 is a diagram showing an overview of the methane purification device 1 according to this embodiment. The methane purification device 1 shown in Figure 1 comprises a pipeline 10, an intake section 11, an ozone supply section 22, a heating section 23, a methane decomposition section 24, a temperature sensor 31, a color sensor 32, a temperature sensor 33, a humidity sensor 34, a memory section 41, and a control section 42. The methane purification device 1 is a device that has the function of decomposing methane contained in the air to produce water and carbon dioxide.

[0017] The conduit 10 is a conduit through which methane-containing air (hereinafter referred to as "first gas") flows. The intake section 11 is, for example, an intake fan that draws the first gas into the conduit 10.

[0018] The ozone supply unit 22 is provided in the pipeline 10 downstream of the intake unit 11 and upstream of the heating unit 23, and supplies ozone to the first gas inhaled by the intake unit 11. The ozone supply unit 22 has, for example, an AC power supply 22a and an electrode 22b coated with a dielectric such as glass, and performs a process of generating ozone (so-called silent discharge method) by applying an AC voltage from the AC power supply 22a to the electrode 22b. The ozone supply unit 22 may generate ozone by performing a process of discharging 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 rays to the first gas (so-called ultraviolet lamp method). The ozone supply unit 22 generates a second gas containing the first gas and ozone by supplying the generated ozone to the first gas.

[0019] The heating unit 23 is provided in the pipeline 10 downstream of the ozone supply unit 22 and upstream of the methane decomposition unit 24, and heats the second gas containing the first gas flowing through the pipeline 10 and the ozone supplied by the ozone supply unit 22. The heating unit 23 has, for example, a heating wire such as a nichrome wire that converts electrical energy into thermal energy by receiving electrical supply, and heats the second gas by heat exchange between the heated heating wire and the second gas.

[0020] Ozone contained in the second gas undergoes thermal decomposition when the second gas exceeds a predetermined temperature (for example, 150°C). However, when it comes into contact with a metal, thermal decomposition is likely to occur even if the temperature of the metal is below the predetermined temperature. Therefore, the heating unit 23 has a carrier having a substance that is difficult to decompose ozone as a coating layer supported on the surface. The heating unit 23 has, for example, a carrier having a coating layer of Teflon, silica, or titania supported on the surface. With such a configuration, the heating unit 23 can heat the second gas while making it difficult for ozone decomposition to occur due to the contact of ozone with the heating unit 23. Note that the material of the carrier of the heating unit 23 may be the same as the material of the coating layer of the heating unit 23.

[0021] The methane decomposition unit 24 is provided downstream of the heating unit 23 in the pipeline 10, contains a catalyst 25 for decomposing methane contained in the second gas, and reacts ozone and methane contained in the second gas on the catalyst 25 to decompose methane and generate water and carbon dioxide. The catalyst 25 has a carrier with a predetermined structure and a coating layer supported 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 material of the carrier is, for example, cordierite, silicon carbide, aluminum titanate, stainless steel, an iron-chromium-aluminum alloy, glass wool, glass fiber or titanium. The coating layer contains, for example, zeolite, iron ion-exchanged zeolite or cobalt ion-exchanged zeolite. Note that the surface area of the carrier may include a region that does not support the coating layer.

[0022] The temperature sensor 31 is a sensor provided on the inner wall surface of the methane decomposition unit 24 for detecting the temperature of the second gas flowing through the methane decomposition unit 24, and is, for example, a thermistor or a thermocouple. The color sensor 32 is a sensor provided downstream of the methane decomposition unit 24 in the pipeline 10 for detecting the color of the coating layer of the catalyst 25, and detects the color of the coating layer of the catalyst 25 based on, for example, the reflected light of the light irradiated on the catalyst 25.

[0023] The temperature sensor 33 is a sensor provided upstream of the intake unit 11 in the pipeline 10 for detecting the temperature of the first gas, and is, for example, a thermistor or a thermocouple. The humidity sensor 34 is a sensor provided upstream of the intake unit 11 in the pipeline 10 for detecting the humidity of the first gas, and includes, for example, a humidity-sensitive agent sandwiched between electrodes. Note that the temperature sensor 33 and the humidity sensor 34 may be provided downstream of the intake unit 11 and upstream of the ozone supply unit 22 in the pipeline 10.

[0024] The memory unit 41 has a storage medium such as ROM (Read Only Memory), RAM (Random Access Memory), HDD (Hard Disk Drive), or SSD (Solid State Drive). The memory unit 41 stores the program executed by the control unit 42 and various information for decomposing the methane containing the second gas.

[0025] The control unit 42 includes a processor such as a CPU (Central Processing Unit). The control unit 42 supplies electricity to the heating unit 23, causing the heating unit 23 to heat the second gas, and the heating unit 23 reacts the ozone and methane contained in the heated second gas on the catalyst 25, thereby decomposing the methane contained in the second gas. The control unit 42 may consist of one processor, or it may consist of multiple processors or a combination of one or more processors and electronic circuits.

[0026] Methane decomposes more easily on catalyst 25 at higher temperatures, but ozone reacts less with methane due to thermal decomposition above a certain temperature. In response to this, the control unit 42 heats the second gas to a temperature at which ozone is less likely to decompose (for example, 50°C), thereby suppressing the thermal decomposition of ozone and allowing ozone and methane to react on catalyst 25. On the other hand, the lower the temperature of the heated second gas, the more water vapor contained in the second gas condenses and adheres to catalyst 25, blocking the reaction sites (so-called reaction sites) where methane and ozone come into contact and react on catalyst 25, thus making it difficult for ozone and methane to react on catalyst 25.

[0027] Therefore, the control unit 42 instructs the heating unit 23 to heat the second gas so that its temperature is lower than the temperature at which ozone thermal decomposition occurs and higher than the temperature at which water is generated by the condensation of water vapor. In this way, by the control unit 42 instructing the heating unit 23 to heat the second gas, the methane purification device 1 can decompose methane by reacting the methane contained in the second gas with ozone on the catalyst 25 while suppressing the adhesion of water to the catalyst 25. The configuration and operation of the control unit 42 will be described in detail below.

[0028] <Configuration of control unit 42> As shown in Figure 1, the control unit 42 includes a detection unit 421, a calculation unit 422, and a temperature control unit 423. The control unit 42 functions as the detection unit 421, the calculation unit 422, and the temperature control unit 423 by executing a program stored in the storage unit 41.

[0029] The detection unit 421 detects the temperature of the catalyst 25. For example, the detection unit 421 acquires 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 also detects the color of the catalyst 25 by acquiring the color of the coating layer of the catalyst 25, which is detected by the color sensor 32.

[0030] The detection unit 421 detects the temperature of the first gas upstream of the ozone supply unit 22 in the pipeline 10 by acquiring the temperature of the first gas detected by the temperature sensor 33. The detection unit 421 also detects the humidity of the first gas upstream of the ozone supply unit 22 in the pipeline 10 by acquiring the humidity of the first gas detected by the humidity sensor 34.

[0031] The calculation unit 422 calculates the amount of water vapor contained in the first gas. For example, the calculation unit 422 calculates the amount of water vapor contained in the first gas based on the absolute humidity of the first gas, which is determined by the temperature and humidity of the first gas detected upstream of the ozone supply unit 22 in the pipeline 10, and the flow rate of the first gas in the pipeline 10.

[0032] Specifically, the calculation unit 422 identifies the absolute humidity of the first gas corresponding to the temperature and humidity of the first gas detected by the detection unit 421 by referring to a humidity map stored in the memory unit 41 that shows the absolute humidity corresponding to the temperature and humidity of the first gas. The calculation unit 422 identifies the intake volume of the intake unit 11 stored in the memory unit 41 as the flow rate of the first gas. The calculation unit 422 calculates the amount of water vapor contained in the first gas by multiplying the identified absolute humidity of the first gas by the flow rate of the first gas.

[0033] The calculation unit 422 calculates the amount of water vapor per unit weight of catalyst 25 based on the amount of water vapor and the weight of catalyst 25. Specifically, the calculation unit 422 calculates the amount of water vapor per unit weight of catalyst 25 by dividing the calculated amount of water vapor by the weight of catalyst 25 stored in the storage unit 41. By operating in this manner, the calculation unit 422 can cause the temperature control unit 423 to heat the second gas in the heating unit 23 based on the amount of water vapor contained in the first gas.

[0034] The temperature control unit 423 supplies electricity to the heating unit 23, causing the heating unit 23 to heat the second gas. The temperature control unit 423 heats the second gas in the heating unit 23 so that its temperature falls within the first temperature range. The first temperature range is a temperature range that indicates a temperature at which ozone does not decompose in a predetermined time (e.g., less than 150°C) and a temperature range that indicates a temperature at which condensation of water vapor contained in the second gas is suppressed (e.g., 100°C or higher), for example, 100°C or more and less than 150°C. The predetermined time is a time longer than the time from when the first gas is drawn into the pipeline 10 until it is discharged from the pipeline 10, for example, 3 minutes or more.

[0035] The temperature control unit 423, for example, causes the heating unit 23 to heat the second gas so that the temperature of the catalyst 25 detected by the detection unit 421 (i.e., the temperature of the second gas flowing through the methane decomposition unit 24) falls within the first temperature range. Figure 2 shows an example of the temperature of the catalyst 25. The horizontal axis in Figure 2 represents time, and the vertical axis represents the temperature of the catalyst 25. The range R1 shown in Figure 2 is the first temperature range. As shown in Figure 2, the temperature control unit 423, for example, causes the heating unit 23 to heat the second gas so that the temperature of the catalyst 25 falls within the range R1. The temperature control unit 423 has, for example, a feedback controller that sets the temperature E1 included in the range R1 as a target value, and starts or stops the heating of the second gas by the heating unit 23 to reduce the difference between the temperature of the catalyst 25 and the target value.

[0036] As described above, by controlling the temperature of the second gas, the temperature control unit 423 can suppress the reduction of ozone in the second gas due to thermal decomposition and suppress the condensation of water vapor in the second gas. As a result, the temperature control unit 423 can suppress a shortage of ozone for reaction with methane and suppress the blocking of reaction sites by water condensed from water vapor in the second gas, thereby enabling the reaction of methane and ozone on the catalyst 25.

[0037] The temperature control unit 423 may cause the heating unit 23 to heat the second gas so that the temperature of the second gas (i.e., the temperature of the catalyst 25) temporarily falls within the first temperature range, in order to remove water that has condensed from water vapor contained in the second gas and is attached to the catalyst 25. For example, the temperature control unit 423 may cause the heating unit 23 to heat the second gas so that the temperature of the second gas falls within the first temperature range for a predetermined period of time in a predetermined cycle, and after the predetermined time has elapsed, cause the heating unit 23 to heat the second gas so that the temperature of the second gas falls within the second temperature range. The predetermined cycle is, for example, 1 hour, and the predetermined time is, for example, 1 minute. The second temperature range is a temperature range that is lower than the temperature included in the first temperature range and is a temperature range that does not decompose ozone in a predetermined time, for example, 50°C or more and less than 100°C.

[0038] Figure 3 shows an example of the temperature of the catalyst 25. The vertical and horizontal axes of Figure 3, and the range R1 and temperature E1 shown in Figure 3, are the same as in Figure 2. In Figure 3, the range R2 representing the second temperature range, the temperature E2 included in the range R2, the time P1 representing a predetermined period, and the time P2 representing a predetermined time are shown. For example, at time T1, the temperature control unit 423 heats the second gas in the heating unit 23 so that the temperature of the second gas (i.e., the temperature of the catalyst 25) rises from temperature E2 to temperature E1 as time P1 has elapsed. Then, at time T2, the temperature control unit 423 heats the second gas in the heating unit 23 so that the temperature of the second gas falls from temperature E2 to temperature E1 as time P2 has elapsed since time T1.

[0039] The temperature control unit 423 sets the target value of its feedback controller to temperature E2 at time P1 and to temperature E1 at time P2. The temperature control unit 423 then starts or stops heating the second gas by the heating unit 23 so that the difference between the temperature of the catalyst 25 detected by the detection unit 421 and the target value becomes small.

[0040] As described above, by controlling the temperature of the second gas, the temperature control unit 423 can react ozone and methane at a temperature at which ozone is less likely to decompose thermally at time P1, and evaporate the water adhering to the catalyst 25 at time P2. As a result, after removing the water adhering to the catalyst 25, the temperature control unit 423 can decompose methane while suppressing the thermal decomposition of ozone.

[0041] The temperature control unit 423 may determine whether or not to heat the temperature of the second gas from a temperature within range R2 to a temperature within range R1 based on the amount of water vapor contained in the first gas, and may cause the heating unit 23 to heat the second gas. For example, if the amount of water vapor per unit weight calculated by the calculation unit 422 exceeds a threshold, the temperature control unit 423 will cause the heating unit 23 to heat the second gas so that its temperature falls within range R1. The threshold is a fixed value between 0.1 and 10 (for example, 1.0) and is stored in the storage unit 41. For example, if the amount of water vapor per unit weight calculated by the calculation unit 422 is below the threshold, the temperature control unit 423 will cause the heating unit 23 to heat the second gas so that its temperature falls within range R2.

[0042] As described above, the temperature control unit 423 operates in such a way that, if the amount of water vapor in the first gas is large, the temperature control unit 423 can heat the second gas in the heating unit 23 so that the temperature of the second gas falls within the range R1. As a result, the temperature control unit 423 can evaporate the water even if the water vapor condensed in the first gas is likely to adhere to the catalyst 25. On the other hand, if the amount of water vapor in the first gas is small, the temperature control unit 423 can heat the second gas in the heating unit 23 so that the temperature of the second gas falls within the range R2. As a result, if the water vapor condensed in the first gas is unlikely to adhere to the catalyst 25, the temperature control unit 423 can react ozone and methane at a temperature at which ozone is unlikely to decompose.

[0043] The zeolite, iron ion exchange zeolite, or cobalt ion exchange zeolite contained in the coating layer of catalyst 25 changes color from blue to pink when it absorbs moisture. Therefore, the temperature control unit 423 may decide whether or not to heat the temperature of the second gas from a temperature included in range R2 to a temperature included in range R1 based on the color of the coating layer of catalyst 25, and may heat the second gas in the heating unit 23.

[0044] For example, if the color of the catalyst 25 detected by the detection unit 421 indicates that water has adhered to the catalyst 25, the temperature control unit 423 will heat the second gas in the heating unit 23 so that the temperature of the second gas falls within the range R1. The color indicating that water has adhered is a color that contains the most red (R) among RGB (Red, Green, Blue), for example, pink. For example, if the color of the catalyst 25 detected by the detection unit 421 indicates that water has not adhered to the catalyst 25, the temperature control unit 423 will heat the second gas in the heating unit 23 so that the temperature of the second gas falls within the range R2. The color indicating that water has not adhered is a color that contains the most blue (B) among RGB, for example, blue.

[0045] As described above, the temperature control unit 423 operates in such a way that if the catalyst 25 has absorbed moisture, it can heat the second gas in the heating unit 23 so that the temperature of the second gas falls within the range R1, thereby evaporating the water contained in the catalyst 25. On the other hand, if the catalyst 25 has not absorbed moisture, the temperature control unit 423 can heat the second gas in the heating unit 23 so that the temperature of the second gas falls within the range R2, thereby allowing the ozone and methane to react on the catalyst 25 in a state where ozone is less likely to decompose under heat.

[0046] The methane decomposition rate corresponding to the temperature of the catalyst 25 (the ratio of the amount of methane decomposed by the catalyst 25 to the amount of methane contained in the second gas flowing into the methane decomposition unit 24) differs depending on the type of coating layer of the catalyst 25. Therefore, the temperature control unit 423 may refer to the methane decomposition rate map stored in the memory unit 41 to identify a temperature range in which the methane decomposition rate is equal to or greater than a predetermined decomposition rate for each type of coating layer of the catalyst 25, and determine the identified temperature range as range R1. The methane decomposition rate map is a map that shows the methane decomposition rate corresponding to the temperature of the catalyst 25 for each type of coating layer of the catalyst 25.

[0047] Figure 4 shows an example of a methane decomposition rate map. The horizontal axis of Figure 4 represents the temperature of catalyst 25 (temperature of the second gas), and the vertical axis represents the methane decomposition rate. In Figure 4, catalysts M1, M2, and M3 are shown as types of catalyst 25. The coating layer of catalyst M1 is cobalt ion exchange zeolite (Co-BEA), in which cobalt is supported on a β-type skeletal structure zeolite. The coating layer of catalyst M2 is iron ion exchange zeolite (Fe-BEA), in which iron is supported on a β-type skeletal structure zeolite. The coating layer of catalyst M3 is β-type skeletal structure zeolite (BEA).

[0048] As shown in Figure 4, for catalyst M1, when the temperature is below 150°C, the methane decomposition rate increases with increasing temperature. However, when the temperature is 150°C or higher, the methane decomposition rate decreases with increasing temperature due to ozone decomposition by the cobalt contained in catalyst M1 and the thermal decomposition of ozone. For catalyst M3, when the temperature is below 200°C, the methane decomposition rate increases with increasing temperature. However, when the temperature is 200°C or higher, the methane decomposition rate decreases with increasing temperature due to the thermal decomposition of ozone. As described above, the methane decomposition rate differs depending on the type of coating layer of catalyst 25.

[0049] The temperature control unit 423 identifies the type of coating layer of the catalyst 25 by referring to information indicating the type of coating layer of the catalyst 25 stored in the memory unit 41, and determines range R1 as the temperature range in which the methane decomposition rate for the identified coating layer is equal to or greater than a predetermined decomposition rate. Specifically, the temperature control unit 423 identifies that the type of coating layer of the catalyst 25 is the coating layer of catalyst M1 (cobalt ion exchange zeolite). Then, in the methane decomposition rate map shown in Figure 4, the temperature control unit 423 determines range R1 as the temperature range "temperature T10°C or higher and temperature T20°C or lower" in which the methane decomposition rate of catalyst M1 is equal to or greater than decomposition rate C, and determines range R2 as the temperature range "50°C or higher and temperature T10°C or lower". By operating in this way, the temperature control unit 423 can determine the optimal ranges R1 and R2 for methane decomposition according to the type of coating layer of the catalyst 25.

[0050] As shown in Figure 4, catalyst M2 has a smaller range R1 (temperature T30°C or higher and less than T40°C) in which its methane decomposition rate is greater than or equal to decomposition rate C, and it cannot decompose methane at temperatures included in the range R2 of catalyst M1. Therefore, the range of target temperatures for catalyst M2 when heating the second gas in the heating unit 23 is narrower than that of catalyst M1. Accordingly, the temperature control unit 423 may switch between heating the second gas using range R1 as shown in Figure 2, or heating the second gas using ranges R1 and R2 as shown in Figure 3, depending on the type of coating layer of catalyst 25.

[0051] For example, if catalyst 25 is catalyst M1, the temperature control unit 423 determines ranges R1 and R2 by referring to the methane decomposition rate map. Then, as shown in Figure 3, the temperature control unit 423 heats the second gas in the heating unit 23 so that the difference between temperature E1 and the temperature of the second gas is small at time P1, and heats the second gas in the heating unit 23 so that the difference between temperature E2 and the temperature of the second gas is small at time P2.

[0052] On the other hand, if catalyst 25 is catalyst M2, the temperature control unit 423 determines the range R1 by referring to the methane decomposition rate map. Then, as shown in Figure 2, the temperature control unit 423 heats the second gas in the heating unit 23 so that the difference between temperature E1 and the temperature of the second gas becomes small.

[0053] By operating as described above, the temperature control unit 423 can heat the second gas using only range R1 if the range of target temperatures for heating the second gas is smaller than a predetermined range. On the other hand, if the range of target temperatures for heating the second gas is larger than a predetermined range, the temperature control unit 423 can heat the second gas using both range R1 and range R2. As a result, the temperature control unit 423 can heat the second gas in a manner suitable for the type of coating layer of the catalyst 25.

[0054] <Processing sequence in methane purification device 1> Figure 5 shows an example of a processing sequence in the methane purification device 1. The processing sequence shown in Figure 5 is a sequence in which the temperature control unit 423 heats the second gas in the heating unit 23 based on the amount of water vapor contained in the first gas.

[0055] The temperature control unit 423 identifies the type of coating layer of the catalyst 25 by referring to the memory unit 41 (step S11). The temperature control unit 423 determines ranges R1 and R2 corresponding to the identified type of coating layer of the catalyst 25 by referring to the methane decomposition rate map stored in the memory unit 41 (step S12). For example, if the type of coating layer of the catalyst 25 identified in step S11 is the coating layer of catalyst M1, the temperature control unit 423 refers to the methane decomposition rate map shown in Figure 4 and determines range R1 to be "temperature T10°C or higher and temperature T20°C or lower," where the methane decomposition rate of catalyst M1 is greater than or equal to decomposition rate C. Then, the temperature control unit 423 determines range R2 to be "50°C or higher and temperature T10°C or lower."

[0056] The detection unit 421 detects the temperature and humidity of the first gas flowing upstream of the ozone supply unit 22 (step S13). For example, the detection unit 421 detects the temperature of the first gas flowing upstream of the ozone supply unit 22 by acquiring the temperature detected by the temperature sensor 33, and detects the humidity of the first gas flowing upstream of the ozone supply unit 22 by acquiring the humidity detected by the humidity sensor 34.

[0057] The calculation unit 422 obtains the intake volume of the intake unit 11 stored in the memory unit 41 as the flow rate of the first gas (step S14). The calculation unit 422 identifies the absolute humidity corresponding to the temperature and humidity of the first gas detected by the detection unit 421 by referring to the humidity map stored in the memory unit 41, and calculates the amount of water vapor contained in the first gas by multiplying the absolute humidity by the flow rate of the first gas (step S15). The calculation unit 422 calculates the amount of water vapor per unit weight of the catalyst 25 by dividing the calculated amount of water vapor by the weight of the catalyst 25 stored in the memory unit 41 (step S16).

[0058] The detection unit 421 detects the temperature of the catalyst 25 (i.e., the temperature of the second gas flowing through the methane decomposition unit 24) by acquiring the temperature detected by the temperature sensor 31 (step S17). If the amount of water vapor per unit weight of the catalyst 25 exceeds a threshold (YES in step S18), the temperature control unit 423 heats the second gas in the heating unit 23 to a target temperature within the range R1 (step S19). For example, the temperature control unit 423 heats the second gas in the heating unit 23 so that the difference between the temperature E1 shown in Figure 3 and the temperature of the catalyst 25 becomes small.

[0059] On the other hand, if the amount of water vapor per unit weight of the catalyst 25 is below a threshold (NO in step S18), the temperature control unit 423 heats the second gas in the heating unit 23, with a target temperature within the range R2 (step S20). The temperature control unit 423 heats the second gas in the heating unit 23 so that, for example, the difference between the temperature E2 shown in Figure 3 and the temperature of the catalyst 25 becomes small.

[0060] If the methane purification device 1 does not accept the operation to terminate processing (NO in step S21), the methane purification device 1 repeats the operations from step S13 to step S20. If the methane purification device 1 accepts the operation to terminate processing (YES in step S21), the methane purification device 1 terminates processing.

[0061] <Variation> In the above description, the operation of the methane purification device 1 in which it decomposes methane contained in air has been illustrated, but it is not limited to this. The methane purification device 1 may also decompose methane contained in exhaust gas emitted by equipment or vehicles installed in the plant. For example, the methane purification device 1 may be installed in the exhaust passage downstream of the engine of a vehicle and decompose methane contained in the engine's exhaust gas.

[0062] <Effects of Methane Purification Device 1> As described above, the methane purification device 1 includes a pipeline 10 through which a first gas containing methane flows, an ozone supply unit 22 that supplies ozone to the first gas, a heating unit 23 that heats a second gas containing the first gas flowing through the pipeline 10 and the ozone supplied by the ozone supply unit 22, a catalyst 25 provided downstream of the heating unit 23 in the pipeline 10 for decomposing methane contained in the second gas, and a temperature control unit 423 that causes the heating unit 23 to heat the second gas so that the temperature of the second gas falls within a range R1 that indicates a temperature at which ozone does not decompose in a predetermined time and a range R1 that indicates a temperature at which condensation of water vapor contained in the second gas is suppressed.

[0063] With the methane purification device 1 configured in this way, the methane purification device 1 can control the temperature of the second gas (temperature of the catalyst 25) to a temperature at which ozone is difficult to decompose thermally and water vapor contained in the second gas is difficult to condense. Therefore, the methane purification device 1 can suppress the blockage of reaction sites due to water adhering to the catalyst 25, while also suppressing the reduction of ozone, which is necessary to react with methane contained in the second gas, due to thermal decomposition. As a result, the methane purification device 1 can supply a sufficient amount of ozone to decompose the methane contained in the second gas and decompose the methane by reacting methane and ozone on the catalyst 25.

[0064] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of its gist. For example, all or part of the apparatus can be configured by functionally or physically distributing and integrating in any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of the new embodiments resulting from the combinations are combined with the effects of the original embodiments. [Explanation of Symbols]

[0065] 1. Methane purification system 10 conduit 11 Intake section 22 Ozone Supply Department 22a AC power supply 22b electrode 23 Heating section 24 Methane decomposition section 25 Catalyst 31 Temperature sensor 32-color sensor 33 Temperature Sensor 34 Humidity Sensor 41 Storage section 42 Control Unit 421 Detection Unit 422 Calculation Unit 423 Temperature Control Unit

Claims

1. A pipeline through which the first gas containing methane flows, An ozone supply unit that supplies ozone to the first gas, A heating unit that heats a second gas containing the first gas flowing through the pipeline and the ozone supplied by the ozone supply unit, A catalyst is provided downstream of the heating section in the aforementioned pipeline to decompose the methane contained in the second gas, A temperature control unit is provided that causes the heating unit to heat the second gas such that the temperature of the second gas falls within a first temperature range that indicates a temperature at which the ozone does not decompose in a predetermined time, and a first temperature range that indicates a temperature at which condensation of water vapor contained in the second gas is suppressed. A methane purification device having the following features.

2. The system further includes a detection unit for detecting the temperature of the catalyst, The temperature control unit causes the heating unit to heat the second gas so that the temperature detected by the detection unit falls within the first temperature range. The methane purification apparatus according to claim 1.

3. The catalyst includes zeolite, iron ion exchange zeolite, or cobalt ion exchange zeolite. The methane purification apparatus according to claim 1.

4. The heating section has a carrier on which Teflon (registered trademark), silica, or titania is supported on its surface. The methane purification apparatus according to claim 1.

5. The temperature control unit causes the heating unit to heat the second gas for a predetermined period of time at a predetermined interval so that the temperature of the second gas falls within the first temperature range, and after the predetermined time has elapsed, the heating unit causes the second gas to heat the second gas so that the temperature of the second gas falls within a second temperature range that is lower than the temperature within the first temperature range and is a second temperature range at which the ozone does not decompose within a predetermined time. The methane purification apparatus according to claim 1.

6. The system further includes a calculation unit that calculates the amount of water vapor contained in the first gas based on the absolute humidity of the first gas, which is determined by the temperature and humidity of the first gas detected upstream of the ozone supply unit in the pipeline, and the flow rate of the first gas in the pipeline, and calculates the amount of water vapor per unit weight of the catalyst based on the amount of water vapor and the weight of the catalyst. The temperature control unit, when the amount of water vapor per unit weight exceeds a threshold, causes the heating unit to heat the second gas so that the temperature of the second gas falls within the first temperature range, and when the amount of water vapor per unit weight is below the threshold, causes the heating unit to heat the second gas so that the temperature of the second gas falls within a second temperature range that is lower than the temperature included in the first temperature range and is a second temperature range that does not cause the ozone to decompose in a predetermined time. The methane purification apparatus according to claim 1.

7. The system further includes a detection unit for detecting the color of the catalyst, If the color of the catalyst detected by the detection unit indicates that water has adhered to the catalyst, the temperature control unit causes the heating unit to heat the second gas so that the temperature of the second gas falls within the first temperature range. If the color of the catalyst detected by the detection unit indicates that water has not adhered to the catalyst, the heating unit causes the heating unit to heat the second gas so that the temperature of the second gas falls within a second temperature range that is lower than the temperature included in the first temperature range and is a second temperature range that indicates that the ozone does not decompose within a predetermined time. The methane purification apparatus according to claim 1.

8. The system further includes a storage unit that stores a methane decomposition rate map showing the methane decomposition rate corresponding to the temperature of the catalyst for each type of catalyst. The temperature control unit, by referring to the methane decomposition rate map, identifies a temperature range in which the methane decomposition rate is equal to or greater than a predetermined decomposition rate for the type of catalyst, and determines the temperature range to be the first temperature range. The methane purification apparatus according to claim 1.

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