Methane production device and methane production method

Abstract

The invention provides a methane production apparatus and a methane production method. When methane is produced, the wetted catalyst is recovered. When methane is produced using a reactor that generates methane using carbon dioxide and hydrogen as raw material gases, the raw material gases are caused to flow through a raw material gas flow path that spans a first region and a second region of the reactor. A catalyst for generating methane from a raw material gas is accommodated in the first region and the second region of the reactor so as to be in contact with the circulating raw material gas. Furthermore, a refrigerant is made to flow through a refrigerant flow path spanning a first region and a second region in the reactor, and after methane is produced for a predetermined period of time in a state in which the raw material gas and the refrigerant are made to flow through the first region and the second region in the reactor, the flow directions of the raw material gas and the refrigerant are changed. The temperature of the first region and the second region at a low temperature during the predetermined period is increased.

Description

Technical Field

[0001] This invention relates to a technique for manufacturing methane. Background Technology

[0002] An apparatus for producing methane using a methanation reaction with carbon dioxide and hydrogen as feedstock gases is known (see, for example, Patent Document 1). In the apparatus described in Patent Document 1, a medium (hereinafter also referred to as a refrigerant) for heat exchange with the catalyst is supplied to a reactor containing the catalyst for producing methane, and methane is stably produced by controlling the flow rate of the feedstock gas supplied to the reactor and the flow rate of the cooling medium.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2022-152517 Summary of the Invention

[0004] The methane manufacturing apparatus described in Patent Document 1 is excellent because the methanation reaction is a reaction that generates heat, and the heat of reaction is appropriately removed by controlling the flow rate of the heat exchange medium. However, since water is generated by the methanation reaction and becomes water vapor, the inventors have discovered the following problem: the water vapor condenses around the catalyst and sometimes hinders the production of methane.

[0005] The present invention can be implemented in the following manner or in the following application examples.

[0006] (1) The present invention enables the implementation of a methane manufacturing apparatus comprising a reactor for generating methane from carbon dioxide and hydrogen as feed gases. The methane manufacturing apparatus comprises: a feed gas flow path through which the feed gas flows between a first region and a second region of the reactor; a catalyst contained in the first and second regions of the reactor in contact with the flowing feed gas, and generating methane from the feed gas; a refrigerant flow path through which a refrigerant flows between the first and second regions of the reactor; and a control unit that, while the feed gas and the refrigerant are flowing between the first and second regions of the reactor, after a predetermined methane manufacturing period, raises the temperature of the side of the first and second regions that was at a low temperature during the predetermined period by changing the flow direction of the feed gas and the refrigerant. In this way, when generating methane from the feed gas, by changing the flow direction of the feed gas and the refrigerant, the temperature of the side of the catalyst that was at a low temperature during the predetermined period is raised, thus alleviating the wet state of the catalyst and suppressing the decline in methane production.

[0007] (2) In the above structure, the methane manufacturing apparatus can be configured such that the raw material gas flow path causes the raw material gas to flow from the first region of the reactor toward the second region, and the control unit performs the following control: During the specified period when the moisture accumulation in the reactor is less than a preset accumulation threshold, the refrigerant flows from the second region of the reactor toward the first region; and after the specified period, the refrigerant flows from the first region of the reactor toward the second region. In this way, after the period when the moisture accumulation is less than the preset accumulation threshold, the refrigerant flow direction from the first region to the second region easily raises the temperature of the second region, which has been at a low temperature until now.

[0008] (3) In the above structure, the methane manufacturing apparatus can be configured such that, during the specified period, the flow directions of the raw material gas and the refrigerant are opposite, and after the specified period, the flow directions of the raw material gas and the refrigerant are set to the same direction. In this way, the efficiency of heat exchange based on the refrigerant after the specified period is reduced, which allows the temperature of the low-temperature region to rise.

[0009] (4) In the structures (1) to (3) above, the methane manufacturing apparatus can be configured such that the raw material gas flow path and the refrigerant flow path extend from the upper part to the lower part of the reactor along the direction of gravity, with the first region located in the upper part and the second region located in the lower part. In this way, the generated water, which is the cause of the catalyst becoming wet, can easily flow along gravity, thus easily eliminating the wet state.

[0010] (5) In the structures described in (1) to (4) above, the methane production apparatus may be configured to include: a cooler for cooling the methane produced in the reactor; and a tank for recovering the discharge water discharged from the reactor via the cooler, wherein the control unit causes the refrigerant in the refrigerant flow path to flow from the upper part to the lower part of the reactor if the amount of generated water estimated based on the amount of methane produced is more than a predetermined amount than the amount of discharge water recovered into the tank. In this way, the amount of generated water adhering to the catalyst and making it wet can be estimated.

[0011] (6) In the structures described in (1) to (5) above, the methane production apparatus may be configured to include a temperature sensor that detects the temperature inside the reactor. After the control unit is configured to allow the refrigerant in the refrigerant flow path to flow from the top to the bottom of the reactor, if the detected temperature is above 100°C and the rate of temperature rise is less than a preset rate threshold, it maintains the state in which the refrigerant in the refrigerant flow path flows from the top to the bottom of the reactor. In this way, it can be easily determined that the wet state of the catalyst has not been eliminated.

[0012] (7) The present invention can also implement a methane production method that uses a reactor to produce methane by using carbon dioxide and hydrogen as feedstock gases. This methane production method includes the following steps: allowing the feedstock gas to flow through a feedstock gas flow path spanning a first region and a second region of the reactor; containing a catalyst for generating methane from the feedstock gas in contact with the flowing feedstock gas in the first and second regions of the reactor; allowing a refrigerant to flow through a refrigerant flow path spanning the first and second regions of the reactor; and, after a predetermined methane production period while the feedstock gas and the refrigerant are flowing through the first and second regions of the reactor, raising the temperature on the side of the first and second regions that was at a low temperature during the predetermined period by changing the flow direction of the feedstock gas and the refrigerant. In this way, by changing the flow direction of the feedstock gas and the refrigerant during methane production, the temperature on the side of the catalyst that was at a low temperature during the predetermined period can be raised, thus alleviating the wet state of the catalyst and suppressing the decline in methane production. Attached Figure Description

[0013] Figure 1 This is a schematic structural diagram showing the methane manufacturing apparatus of each embodiment with the refrigerant flow path as the initial state.

[0014] Figure 2 This is a flowchart illustrating the overview of the methane manufacturing process based on the control unit.

[0015] Figure 3 This is a simplified structural diagram showing the state of the refrigerant flow path after switching.

[0016] Figure 4 This is an illustrative diagram illustrating the amount of methanation reaction and water production within the reactor.

[0017] Figure 5 This is an explanatory diagram showing the difference in the peak position of heat generation caused by different flow directions of the refrigerant.

[0018] Figure 6This is a flowchart illustrating the outline of the methane manufacturing process in the second embodiment.

[0019] Figure 7 This is a flowchart illustrating the outline of the methane manufacturing process in the third embodiment.

[0020] Figure 8 This is an explanatory diagram illustrating an example of the temperature of various parts when determining the state of humidity. Detailed Implementation

[0021] A. Implementation Method 1:

[0022] (A1) Structure of a methane manufacturing unit:

[0023] Figure 1 This is a schematic structural diagram of the methane manufacturing apparatus 10 according to the first embodiment. The methane manufacturing apparatus 10 produces methane (CH4) as a product gas by causing a methanation reaction in a feed gas containing carbon dioxide gas (CO2) and hydrogen (H2) supplied from the feed gas supply unit 20. In this embodiment, the methanation reaction occurs in a first reactor 30 and a second reactor 60, but only one reactor is required. Unless otherwise specified, the first reactor 30 or the second reactor 60 is sometimes simply referred to as reactors 30 and 60. A refrigerant, such as oil, is supplied to reactors 30 and 60 for heat exchange with catalysts 50 and 70 that generate the methanation reaction. In the methane manufacturing apparatus 10 of this embodiment, the refrigerant flow rate is controlled according to the change in the flow rate of the feed gas supplied to reactors 30 and 60. This causes the amount of methane generated in reactors 30 and 60 to vary in accordance with the change in the flow rate of the feed gas.

[0024] As shown in the figure, the methane production apparatus 10 includes: a first reactor 30 and a second reactor 60, the first reactor 30 being upstream of the feed gas and the second reactor 60 being downstream of the feed gas to produce methane; a mass flow controller (hereinafter referred to as MFCH) 21, which adjusts the flow rate of hydrogen (hereinafter sometimes referred to as H2) supplied to the inlet (upper end) 31 of the first reactor 30; a mass flow controller (hereinafter referred to as MFCC) 22, which adjusts the flow rate of carbon dioxide gas (hereinafter sometimes referred to as CO2) supplied to the inlet 31 of the first reactor 30; a pump 40, which supplies refrigerant to the first reactor 30; and a first switching valve 41, which switches the flow rate through the first reactor 30. The apparatus includes: a refrigerant flow path for 0; a second switching valve 51 for selecting the refrigerant flow path from the first reactor 30; a first condenser 45, which is a cooler that cools and removes water (hereinafter, sometimes simply referred to as H2O) from a mixture of gases containing methane gas (hereinafter, sometimes simply referred to as CH4) discharged from the outlet 34 of the first reactor 30; a first storage tank 46 for storing the condensate discharged from the first condenser 45; a second condenser 75 for removing water from a mixture of gases containing CH4 discharged from the outlet 64 of the second reactor 60; a second storage tank 76 for storing the condensate from the second condenser 75; and a control unit 90 for controlling various parts of the methane manufacturing apparatus 10.

[0025] The first reactor 30 and the second reactor 60 are identical in shape except for the shape of the refrigerant inlet and outlet, and their internal structures are also identical. Therefore, the structure of the first reactor 30 will be described in detail below, and sometimes the symbols of the corresponding structures or parts of the second reactor 60 will be placed in parentheses for explanation. The reactor 30 (60) has a tubular shape that is arranged vertically along the direction of gravity and in which the raw material gas flows downward along the direction of gravity. Figure 1 As shown, reactor 30 (60) includes: catalyst 50 (70) for causing methanation of the feed gas; temperature sensor 35 (55) for detecting the temperature of catalyst 50 (70); and refrigerant flow path 33 (63). The refrigerant flow path 33 (63) is formed on the outside of the interior containing catalyst 50 (70) separated by a partition wall. The flow path of the refrigerant and the control of its flow will be described in detail later. In this embodiment, the upper part of catalyst 50 (70) in the direction of gravity is a first region, and the lower part is a second region. The first region and the second region of catalyst 50 (70) can be continuous or separate. Furthermore, reactor 30 (60) can be configured to be tilted relative to the direction of gravity, and as long as the generated water can be discharged, it can be configured such that the feed gas flows in the horizontal direction.

[0026] Examples of catalysts 50 (70) contained in reactor 30 (60) include ruthenium-containing complexes. In other embodiments, known methanation catalysts other than ruthenium, such as platinum, can be used. Temperature sensor 35 (65) is a thermocouple in this embodiment, but a thermistor or infrared thermometer can be used as long as the heat resistance temperature is met. The temperature of catalyst 50 (70) detected by temperature sensor 35 (65) is used for control by control unit 90 in the third embodiment described later. Multiple temperature sensors 35 (65) can be arranged along the flow direction from inlet 31 (61) to outlet 34 (64) within reactor 30 (60), or one or two can be arranged at locations where the average temperature of reactor 30 (60) can be measured.

[0027] In this embodiment, H2 is supplied to MFCH21 with adjusted flow rate from a hydrogen tank (not shown). CO2 is supplied to MFCC22 with adjusted flow rate from a carbon dioxide tank (not shown). CO2 can be gases contained in the exhaust gas of a factory or similar source. The H2 and CO2 supplied to the first reactor 30 via the feed gas flow path 25 from MFCH21 and MFCC22 undergo a methanation reaction in the catalyst 50 within the first reactor 30, as shown in formula (1), where a portion becomes CH4, while H2O is generated and heat is produced.

[0028] CO2+4H2=CH4+H2O+165kJ…(1)

[0029] The heat generated by the reaction and the heat from the refrigerant maintain the temperature inside the first reactor 30 above 100°C, thus producing water (H2O) as water vapor. This water vapor, mixed with the generated CH4 and unreacted residual H2 and CO2, is discharged from the outlet 34 of the first reactor 30. As the discharged gas passes through the first condenser 45, the water vapor drips as condensate (wt) and is stored in the first storage tank 46. The gas mixture with the water vapor removed as condensate flows into the second reactor 60 from the inlet 61 via the gas supply path 55. The H2 and CO2 remaining in the gas mixture undergo a methanation reaction in the catalyst 70 within the second reactor 60, becoming CH4 and H2O (water vapor), which are then discharged from the outlet 64. The water vapor in the discharged gas is removed as condensate (wt) through the second condenser 75. The resulting methane gas is then guided to the storage tank 80 via the gas discharge path 79 and stored. Additionally, in... Figure 1The diagram shows a first water level gauge 47 installed in the first condenser 45 or a second water level gauge 77 installed in the second condenser 75, but these are for the second embodiment, and their structure and function will be described in the second embodiment. These water level gauges may not be present in other embodiments besides the second embodiment.

[0030] (A2) The pathway and function of refrigerant:

[0031] In the methane production apparatus 10, a refrigerant flow path is provided to supply refrigerant to the first reactor 30 and the second reactor 60. Oil, serving as the refrigerant, is drawn from the refrigerant storage tank 42 by a pump 40 and, via a first switching valve 41 (a three-way valve with one input port and two output ports), is sent to either the upper supply path 43 or the first supply path 44. Figure 1 The diagram shows the state where the first switching valve 41 is set to its default position, i.e., position 1. In position 1, the input port of the first switching valve 41 is connected to the output port of the first supply path 44, while the output port of the upper supply path 43 is blocked. Therefore, refrigerant supplied from pump 40 flows into the first supply path 44. In the diagram, the flow path where the refrigerant does not flow is indicated by a dashed line. If the first switching valve 41 is switched to position 2, the input port of the first switching valve 41 is connected to the output port of the upper supply path 43, while the output port of the first supply path 44 is blocked.

[0032] When the first switching valve 41 is in the first position, the refrigerant supplied from the first switching valve 41 flows into the refrigerant flow path 33 of the first reactor 30 through the first supply passage 44 from the lower inlet 36 located at the bottom of the first reactor 30; or when the first switching valve 41 is in the second position, it flows into the refrigerant flow path 33 of the first reactor 30 through the upper supply passage 43 from the upper inlet 32 ​​located at the top of the first reactor 30. The refrigerant flow path 33 is formed over the entire circumference of the catalyst 50 through a partition wall, and the refrigerant in the refrigerant flow path 33 exchanges heat with the catalyst 50 in the first reactor 30. The refrigerant that has passed through the refrigerant flow path 33 is discharged from the upper outlet 37 located at the top of the first reactor 30 via the upper discharge passage 53 or from the lower outlet 38 located at the bottom of the first reactor 30 via the lower discharge passage 52 to the second switching valve 51, which is a three-way valve with two input ports and one output port.

[0033] exist Figure 1The diagram shows the second switching valve 51 in its default position, i.e., position 1. In position 1, of the two input ports of the second switching valve 51, the input port connected to the upper discharge path 53 is connected to the output port, while the input port connected to the lower discharge path 52 is blocked. If the second switching valve 51 is switched to position 2, the input port connected to the lower discharge path 52 of the first reactor 30 is connected to the output port, while the input port connected to the upper discharge path 53 is blocked. As a result, if the second switching valve 51 is in its default position, i.e., position 1, the refrigerant flowing from the upper outlet 37 of the first reactor 30 flows from the upper discharge path 53 through the second switching valve 51 into the second supply path 74. On the other hand, if the second switching valve 51 is switched to position 2, the refrigerant flowing from the lower outlet 38 of the first reactor 30 flows from the lower discharge path 52 through the second switching valve 51 into the second supply path 74.

[0034] The refrigerant supplied to the second supply path 74 flows into the refrigerant flow path 63 from the lower inlet 66 located at the bottom of the second reactor 60. Passing through the refrigerant flow path 63, which surrounds the catalyst 70 of the second reactor 60 via a partition wall, it is discharged from the upper outlet 67 located at the top of the second reactor 60 to the upper discharge path 73. The refrigerant discharged from the upper discharge path 73 returns to the refrigerant storage tank 42 via the circulation path 82. A throttle valve 85 is provided in the circulation path 82 to adjust the refrigerant flow rate. The opening degree of the throttle valve 85 adjusts the refrigerant flow rate. A cooling device (not shown) is provided in the refrigerant storage tank 42, where the refrigerant is recovered via the circulation path 82, and the refrigerant is stored in the refrigerant storage tank 42 at a cooled state of approximately 70°C. In this embodiment, the temperature of the refrigerant in the first reactor 30 during methane production by the methane production apparatus 10 rises to approximately 50-60°C, and the temperature in the second reactor rises to approximately 20°C. Therefore, the temperature of the refrigerant returning to the refrigerant storage tank 42 is approximately 150°C. The refrigerant absorbs heat from reactors 30 and 60 through heat exchange, thus functioning as a refrigerant. However, due to its high operating temperature, it is sometimes used, as described later, to heat catalyst 50 and remove its wetted state; therefore, it is sometimes referred to as a heat transfer medium. In this specification, the use for such heating purposes is also included, and is referred to as a refrigerant.

[0035] (A3) Control unit 90 and control:

[0036] The control unit 90 includes a CPU 91, a memory 92, and input / output interfaces (not shown). The control unit 90 is connected to actuators such as MFCH 21, MFCC 22, pump 40, first switching valve 41, second switching valve 51, and throttle valve 85, as well as sensors such as first temperature sensor 35, second temperature sensor 55, first water level gauge 47, and second water level gauge 77. In this embodiment, the control unit 90 executes a processing program stored in the memory 92 to determine the flow rates of the raw material gas and refrigerant supplied to reactors 30 and 60, respectively, and drives various actuators such as the first switching valve 41. Specifically, the control unit 90 controls the flow rates of the raw material gas supplied to the first reactor 30 and the second reactor 60 by controlling MFCH 21 and MFCC 22. Furthermore, the control unit 90 controls the flow rates of the refrigerant supplied to the first reactor 30 and the second reactor 60 by controlling the rotational speed of pump 40 and the opening degree of throttle valve 85. Furthermore, in this embodiment, the flow direction of the refrigerant in the first reactor 30 is controlled by switching the positions of the first switching valve 41 and the second switching valve 51.

[0037] Next, use Figure 2 The flowchart illustrates the methane manufacturing process performed by the control unit 90. If the control unit 90 begins methane manufacturing, the process shown in the diagram begins. First, the control unit 90 sets the entire methane manufacturing apparatus 10 to its initial state (step S101). The initial state means that the supply of H2 or CO2 from MFCH21 or MFCC22 to the first reactor 30 is set to a preset flow rate, and the valve body position of the first switching valve 41 or the second switching valve 51 is set to the default position. Figure 1 (as shown in the image), set the opening of the throttle valve 85 to the preset opening, and set the speed of the pump 40 to the preset speed.

[0038] In this state, the temperature of the refrigerant stored in the refrigerant storage tank 42 is 70°C. This refrigerant is drawn out by the pump 40 and supplied to the refrigerant flow path 33 from the lower inlet 36 of the first reactor 30 via the first switching valve 41. In this state, the refrigerant flows upward in the first reactor 30, becoming a flow opposite to the feed gas (H2 and CO2) flowing from the inlet 31 towards the outlet 34. In this state, the first reactor 30 operates in a countercurrent manner (step S111). In the catalyst 50 of the first reactor 30, a methanation reaction occurs, producing methane CH4 and water H2O by the previously described formula (1), and because it is an exothermic reaction, the temperature of the catalyst 50 itself rises due to its heat. This heat is exchanged with the refrigerant flowing countercurrently through the refrigerant flow path 33, so the temperature of the catalyst 50 is maintained below a constant temperature. In this embodiment, the temperature measured by the first temperature sensor 35 is not used for control, but the temperature inside the first reactor 30 rises to about 130°C. Therefore, the generated water becomes water vapor, which, along with the generated methane gas, is discharged from outlet 34 and cooled in the first condenser 45. Through cooling, the water vapor is liquefied into condensate and stored in the first storage tank 46. Additionally, the mixed gas discharged from outlet 34 and dehydrated as condensate is guided to inlet 61 of the second reactor 60. In the second reactor 60, similarly to the first reactor 30, methane gas and water are generated through a methanation reaction via catalyst 70. At this time, in the second reactor 60, the refrigerant flow path is fixed, and the feed gas and refrigerant flow counter-currently.

[0039] Thus, while the first reactor 30 or the second reactor 60 continues to operate in countercurrent mode, the control unit 90 determines whether to resume operation (step S121). Resuming operation refers to removing the water that has been generated by the methanation reaction and is adhering to the surface of the catalyst 50 in a liquid state, thus hindering the methanation reaction, thereby restoring the overall methanation reaction of the catalyst. In this embodiment, if the countercurrent operation has continued for a predetermined period in step S111, it is determined that resuming operation is necessary. The predetermined period can be a pre-measured time or the period until the mass flow rates of H2 and CO2 flowing in the first reactor 30 reach a predetermined flow rate.

[0040] If it is determined that operation needs to be resumed (step S121: "Yes"), the refrigerant flow path is switched (step S131). Specifically, both the first switching valve 41 and the second switching valve 51 are switched to the second position. The positions of the first switching valve 41 and the second switching valve 51 and the refrigerant flow at this time are shown in the figure. Figure 3 .

[0041] As shown in the figure, in the first switching valve 41, refrigerant from pump 40 flows into the upper supply path 43, which is connected to the upper inlet 32 ​​of the first reactor 30. Furthermore, refrigerant discharged from the first reactor 30 reaches the second switching valve 51 through the lower outlet 38 (not the upper outlet 37) of the first reactor 30 via the lower discharge path 52, and is then sent to the second reactor 60 via the second supply path 74. As a result, the refrigerant flow becomes a parallel flow consistent with the flow direction of the feed gas.

[0042] Therefore, in this state, i.e., when the refrigerant flow is parallel, the control unit 90 operates the first reactor 30 (step S141). The relationship between the amount of reaction in the methanation reaction and the amount of water adhering during countercurrent operation (step S141) is illustrated below. Figure 4 Furthermore, the difference in temperature distribution within the reactor when operating in a counter-current manner (step S111) and in a co-current manner (step S141) is illustrated in... Figure 5 .

[0043] like Figure 4 As shown, in the first reactor 30, since the feed gas is fed in from the inlet 31 side, the amount of CH4 reacted becomes greater at the inlet 31 side. This is the same in the initial, middle, and final stages of operation of the first reactor 30 accompanying the methanation reaction. As shown in equation (1), the methanation reaction is accompanied by heat generation, and the refrigerant is fed in from the bottom, so the temperature of the refrigerant rises when it reaches the top of the first reactor 30. Therefore, a high temperature is generated in the upper part of the first reactor 30. This situation is shown in... Figure 5 The diagram on the left shows the case where the feed gas and refrigerant flow in a countercurrent manner. In this case, the refrigerant at approximately 70°C enters from the lower inlet 36 and rises along the refrigerant flow path 33 to the upper outlet 37. Therefore, it is not affected by the heat generated by the methanation reaction in the lower part of the first reactor 30, or if it is affected, the impact is small. The heat generated by the methanation reaction is mainly generated in the upper part of the first reactor 30, and the temperature of the refrigerant exiting from the upper outlet 37 may rise to approximately 130°C, for example. However, the temperature of the catalyst 50 in the lower part of the first reactor 30 is kept low by the lower-temperature refrigerant (approximately 70°C) that is fed in.

[0044] On the other hand, the water generated by the methanation reaction is sent to the outlet 34 side as water vapor through the heat of reaction and discharged. However, as the reaction proceeds, as shown by the shaded line in the figure, it adheres to the surface of the catalyst 50 on the outlet 34 side. This is because if the water generated by the methanation reaction is sent into the first reactor 30 as water vapor (gas), causing the partial pressure of water vapor in the first reactor 30 to increase, condensation will occur and the water (liquid) will form when the temperature of the catalyst 50 surface on the outlet 34 side is less than 100°C. Moreover, as mentioned above, the refrigerant is fed into the refrigerant flow path 33 of the first reactor 30 from the lower inlet 36, and the temperature inside the first reactor 30 decreases as it gets lower. Therefore, as the methanation reaction in the first reactor 30 proceeds, the amount of water adhering to the surface of the catalyst 50 gradually increases. As a result, it can be seen that up to the middle of the reaction, water adheres to the vicinity of the CH4 generation site XA, which sometimes hinders the generation of CH4.

[0045] In the first embodiment, the running time of the first reactor 30 is measured, and if it is determined to be the end of the reaction, i.e. Figure 4 As shown, there is a risk of water adhering to the surface of catalyst 50. Therefore, the first switching valve 41 and the second switching valve 51 are switched to change the flow of refrigerant from a flow in the opposite direction to the flow direction of the feed gas to a parallel flow in the same direction as the flow direction of the feed gas. Figure 2 (Step S121). The result is as follows: Figure 3 As shown, the refrigerant flow in refrigerant path 33 in the first reactor 30 is from outlet 34 towards inlet 31. Therefore, the temperature of the upper part of the first reactor 30 decreases due to the refrigerant flow, and the location of the strongest heat generation caused by the methanation reaction shifts downwards. As a result, during countercurrent operation, the temperature of the lower part of the first reactor 30, which is at risk of water adhering to the catalyst 50, rises above 100°C. If the temperature of the catalyst 50 exceeds 100°C, assuming water temporarily adheres to the surface, the water becomes water vapor and is discharged from outlet 34 along with the CH4-containing gas mixture. Thus, by removing the water from the surface of the catalyst 50, the first reactor 30 can resume operation.

[0046] To ensure that the refrigerant flows in the same direction as the raw material gas, the control unit 90 determines whether the reset condition is met. Figure 3(Step S151). In the first embodiment, if the recovery operation to restore the catalyst 50 has been performed for a predetermined time, it is determined that the reset condition has been met. If the recovery operation has not been performed for the predetermined time (step S151: "No"), the process returns to step S141 and continues to operate in a parallel flow manner. On the other hand, if the recovery operation has been performed for the predetermined time (step S151: "Yes"), the process returns to step S101, that is, the methane production apparatus 10 is restored to its initial state, and the above process is repeated. Therefore, the refrigerant flow becomes countercurrent.

[0047] Subsequently, the above-described methane gas production process is repeated. However, when the operation of the methane production unit 10 is stopped through an interruption process, the supply of raw material gas is stopped, and methane gas is produced in a counter-current manner for a specified time. Then, pump 40 is stopped, and the supply and circulation of refrigerant are also stopped. This shutdown process is initiated under conditions such as running the methane production unit 10 for a specified operating time or producing a specified amount of methane gas. Alternatively, the operator of the methane production unit 10 may stop the operation of the methane production unit 10 by operating a "run stop button" (not shown).

[0048] (A4) Effects of the first embodiment:

[0049] According to the methane production apparatus 10 described above, when CH4 is generated from a feed gas containing H2 and CO2 via a methanation reaction, the formation of CH4 can be prevented by switching the refrigerant flow from a countercurrent flow opposite to the feed gas flow to a cocurrent flow in the same direction. This prevents water, which is generated along with CH4, from adhering to the catalyst 50 and hindering CH4 formation. Typically, by setting the refrigerant flow to countercurrent, the heat generated in the first reactor 30 through the methanation reaction can be effectively removed. Furthermore, when operation continues and water adheres to the catalyst 50, hindering CH4 formation in a portion of the catalyst 50, setting the refrigerant flow to cocurrent increases the temperature at the base of the first reactor 30, where water readily adheres, thus removing the water. Since the temperature rise at the bottom of the catalyst 50 caused by such cocurrent flow occurs only for a short time, it does not affect the durability of the first reactor 30 vessel or the lifespan of the catalyst 50, or it is sufficiently suppressed. Regarding the removal of water adhering to the catalyst 50, only the refrigerant flow direction needs to be changed, requiring almost no new equipment. Furthermore, in the first embodiment, the switching of the refrigerant flow direction is managed on a time-based basis, which can be achieved through simplified control based on the control unit 90.

[0050] B. Second Implementation Method:

[0051] The methane manufacturing apparatus 10 according to the second embodiment will be described. The methane manufacturing apparatus 10 of the second embodiment has the same hardware structure as that of the first embodiment. The difference from the first embodiment is that control is performed using a first level gauge 47 installed in the first storage tank 46 or a second level gauge 77 installed in the second storage tank 76. In the second embodiment, using... Figure 6 The methane manufacturing process performed by the control unit 90 will be described. Furthermore, for processes identical to those in the first embodiment, the same step numbers will be used, and descriptions will be omitted or simplified.

[0052] When the control unit 90 of the methane manufacturing apparatus 10 in the second embodiment starts operation and begins producing CH4, it performs an initialization process similar to that in the first embodiment, starting the supply of raw material gas and the supply of refrigerant in a counter-current manner (steps S101, S111). Next, it performs a process of setting a threshold Tw1, which is an accumulation threshold related to water level (step S112), a process of reading the water level of the condensate accumulated in the first storage tank 46 using the first water level gauge 47 of the first storage tank 46 (step S113), and a process of determining whether the read condensate water level is below the set threshold Tw1 (step S123). Here, the total amount of condensate, i.e., the amount of water accumulated, is compared with the threshold Tw1, but since the shape of the first storage tank 46 is known, the water level can be used instead.

[0053] The threshold Tw1 is set to determine whether the amount of condensate accumulated in the first storage tank 46 is commensurate with the amount of generated water produced in the first reactor 30. It can be set directly based on the amount of generated water, but since some of the generated water adheres to the catalyst 50, it is difficult to measure the amount of generated water directly. On the other hand, the production of methane gas is carried out according to the methanation reaction shown in formula (1), so as long as any of the other terms constituting formula (1), namely the consumption of H2 or CO2 or the production of CH4, and the heat generated, is known, the amount of generated water can be calculated. Moreover, if the flow rate of the raw material gas or refrigerant supplied to the first reactor 30 is kept constant, the amount of CH4 or H2O generated becomes constant, so the amount of water generated can be predicted based on the time from the start of production.

[0054] Thus, a threshold Tw1 is calculated based on the calculated amount of water generated (step S112), which serves as a parameter corresponding to the actual amount of condensate stored in the first storage tank 46. The water level is read from the first water level gauge 47 (step S113), and by comparing the two (step S123), the amount of water adhering to the catalyst 50 can be determined. If the determination in step S123 is "no," meaning the condensate level is higher than the threshold Tw1 and the water generated through the methanation reaction is almost completely recovered, the process returns to step S111 to continue processing, allowing the refrigerant to generate methane gas in a countercurrent manner relative to the raw material gas (steps S111 to S123).

[0055] If the determination in step S123 is "yes," meaning the condensate level is below the threshold Tw1, it is determined that a specified amount of water generated by the methanation reaction adheres to the catalyst 50 and may hinder the methanation reaction. Therefore, the refrigerant flow path is switched (step S131), causing the refrigerant to flow in parallel with the feed gas in the first reactor 30 (step S141). As a result, the temperature at the bottom of the first reactor 30 rises, and the water adhering to the catalyst 50 temporarily becomes water vapor and is discharged from the outlet 34, condensed by the first condenser 45, and stored in the first storage tank 46.

[0056] Therefore, the control unit 90 performs the following processes: setting a threshold Tw2 related to the water level (step S142); reading the water level of the condensate accumulated in the first storage tank 46 using the first water level gauge 47 of the first storage tank 46 (step S143); and determining whether the read condensate water level is greater than the set threshold Tw2 (step S153). This process corresponds to the process of causing the refrigerant to flow in a countercurrent manner (steps S112, S113, S123).

[0057] By making the refrigerant flow parallel to the feed gas, if the generated water adhering to the catalyst 50 is recovered, the water level of the condensate in the first storage tank 46 rises. As a result, initially, if the judgment in step S153 is "no", that is, the water level of the condensate is below the threshold Tw2, and the recovery of the generated water is insufficient, the process returns to step S141 to continue processing, so that the refrigerant continues to produce methane gas in a parallel flow with the feed gas (steps S141 to S153).

[0058] If the determination in step S153 is "yes," meaning the condensate level is higher than the threshold Tw2, then it is determined that a specified amount of water adhering to the catalyst 50 is recycled, and the process returns to step S101, restoring the first reactor 30 to its initial state. Specifically, the refrigerant flow path is switched, causing the refrigerant to flow counter-currently relative to the raw material gas in the first reactor 30, thereby continuing the production of methane gas.

[0059] The methane production apparatus 10 according to the second embodiment described above, in addition to performing the same effects as the first embodiment, can also determine the moment to switch the refrigerant flow from countercurrent to cocurrent flow relative to the feed gas based on the amount of water adhering to the catalyst 50. Therefore, the situation where the flow switches to cocurrent flow without water adhering to the catalyst 50 is avoided, and CH4 production can continue effectively in the first reactor 30. Furthermore, by reducing the period of operation when water adhering to the catalyst 50 reduces the surface area of ​​the catalyst 50 that facilitates the methanation reaction, the production rate of methane gas per unit time can be increased.

[0060] C. Third implementation method:

[0061] Next, the methane manufacturing apparatus 10 according to the third embodiment will be described. The methane manufacturing apparatus 10 of the third embodiment has the same hardware structure as that of the first embodiment. The difference from the first embodiment is that, during resumption of operation, control is performed using a first temperature sensor 35 installed in the first reactor 30. In the third embodiment, using... Figure 7 The methane manufacturing process performed by the control unit 90 will be described. Furthermore, for processes identical to those in the first embodiment, the same step numbers will be used, and descriptions will be omitted or simplified.

[0062] When the control unit 90 of the methane manufacturing apparatus 10 in the third embodiment starts operation and begins producing CH4, it performs initialization processing in the same manner as in the first embodiment, starting the supply of raw material gas and the supply of refrigerant in a counter-current manner (steps S101, S111). Next, in the same manner as in the first embodiment, it determines whether operation needs to be resumed (step S121). If operation does not need to be resumed, it returns to step S101 and continues to operate in a counter-current manner. On the other hand, if it is determined that operation needs to be resumed (step S121: "Yes"), it switches either the first switching valve 41 or the second switching valve 51 to switch the refrigerant flow path to parallel flow (step S131), operating in a parallel flow manner (step S141).

[0063] While operating in parallel flow mode, the temperature inside the reactor is read from the first temperature sensor 35 of the first reactor 30. Further processing is performed based on the continuously read temperature to calculate the temperature rise rate (step S145). Then, based on the temperature inside the first reactor 30 and its rise rate, it is determined whether at least a portion, particularly the lower portion, inside the first reactor 30 is in a humid state (step S155). The determination of the humid state can be based on whether the refrigerant temperature is above a preset temperature threshold and the temperature rise rate is below a preset rate threshold. If the humid state is maintained (step S155: "Yes"), the process returns to step S141, repeating the parallel flow operation and temperature detection and temperature rise rate calculation (step S145). If the process is determined not to be humid (step S155: "No"), the process returns to step S101, switching the refrigerant flow path to the initial state, i.e., counter-flow, and the processing from step S111 onwards is executed again.

[0064] use Figure 8 The principle of the control unit 90's judgment based on step S155, namely, judging whether the catalyst is in a wet state based on the temperature measured by the first temperature sensor 35 and the temperature rise rate calculated based on the measured temperature, will be explained. Figure 8 This is an explanatory diagram showing the temperature changes of various parts before and after the refrigerant flow path is switched. In the diagram, the dashed line OL illustrates the temperature change of the refrigerant flowing in the refrigerant flow path 33, the single-dotted line Wn illustrates the temperature change when the catalyst 50 is not wetted, and the solid line Wp illustrates the temperature change when the catalyst 50 is wetted. The horizontal axis of the diagram represents time. Up to time t0, the refrigerant flow is countercurrent relative to the feed gas. At time t0, the refrigerant flow switches to parallel flow. Furthermore, the refrigerant temperature is measured at the location in the refrigerant flow path 33 corresponding to the location of the first temperature sensor 35 that measures the temperature of the catalyst 50.

[0065] As shown in the figure, if the refrigerant flow switches to co-current, the heat generated by the methanation reaction in the upper part of the first reactor 30 is used to heat the refrigerant, causing its temperature to rise sharply as indicated by the dashed line OL. Consequently, the temperature of the catalyst 50 also rises. However, if the water generated by the methanation reaction wets the lower part of the catalyst 50, the heat of the refrigerant is used for the heat of vaporization of the attached water, thus the temperature rise temporarily stalls near the boiling point of water. Furthermore, while the boiling point of water is shown as approximately 100°C in the figure, if the first reactor 30 is pressurized, the boiling point exceeds 100°C. For example, if the internal pressure of the first reactor 30 is 0.2 MPaG, the boiling point of water is approximately 120°C. Therefore, the temperature threshold used for determination only needs to be set corresponding to the boiling point corresponding to the internal pressure.

[0066] On the other hand, if the lower part of the catalyst 50 is not wetted, the heat of the refrigerant will not be used as heat of vaporization. Therefore, the temperature measured by the first temperature sensor 35 will not stagnate near the boiling point, but will rise at a predetermined rate, as shown by the dashed line Wn. Therefore, if the temperature of such catalyst 50 and its rate of rise exceed a preset threshold, it can be determined that it is not wetted (time t1) or that the wetted state has been eliminated (time t2).

[0067] The methane production apparatus 10 of the third embodiment described above, in addition to performing the same functions as the first embodiment, also has the effect of accurately determining whether the catalyst 50 is in a wet state. Since it is possible to accurately detect when the catalyst 50 is no longer wet, it is possible to suppress the temperature rise of the catalyst 50 and the like caused by co-current flow, and to sufficiently suppress the impact on the durability of the container of the first reactor 30 or the lifespan of the catalyst 50.

[0068] In the above embodiments, the flow direction of the refrigerant in the second reactor 60 is set to be constant, but it can also be switched from countercurrent flow opposite to the flow direction of the raw material gas to parallel flow in the same direction as the first reactor 30, depending on the wettability of the catalyst 70.

[0069] In the above embodiments, a portion of the hardware-implemented structure can be replaced with software. At least a portion of the software-implemented structure can also be implemented using discrete circuit structures. Furthermore, when part or all of the functionality of the present invention is implemented in software, the software (computer program) can be provided in the form of a computer-readable recording medium. "Computer-readable recording medium" is not limited to portable recording media such as floppy disks or CD-ROMs, but also includes internal storage devices within a computer such as various RAMs or ROMs, or external storage devices fixed to the computer such as hard disks. That is, "computer-readable recording medium" has a broad meaning, including any recording medium capable of permanently rather than temporarily storing data packets.

[0070] This invention is not limited to the embodiments described above, and can be implemented in various structures without departing from its spirit. For example, to address some or all of the above-described problems, or to achieve some or all of the above-described effects, technical features in embodiments corresponding to the technical features in the various methods described in the summary section of the invention can be appropriately replaced or combined. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately omitted.

[0071] Symbol Explanation

[0072] 10-Methane production unit; 20-Feed gas supply unit; 25-Feed gas flow path; 30-First reactor; 31-Inlet; 32-Upper inlet; 33-Refrigerant flow path; 34-Outlet; 35-First temperature sensor; 36-Lower inlet; 37-Upper outlet; 38-Lower outlet; 40-Pump; 41-First switching valve; 42-Refrigerant storage tank; 43-Upper supply path; 44-First supply path; 45-First condenser; 46-First storage tank; 47-First water level gauge; 50-Catalyst; 51-Second switching valve. 52-Lower exhaust path, 53-Upper exhaust path, 55-Second temperature sensor, 56-Mixed gas supply path, 60-Second reactor, 61-Inlet, 63-Refrigerant flow path, 64-Outlet, 66-Lower inlet, 67-Upper outlet, 70-Catalyst, 73-Upper exhaust path, 74-Second supply path, 75-Second condenser, 76-Second storage tank, 77-Second water level gauge, 79-Gas exhaust path, 80-Storage tank, 82-Circulation path, 85-Throttle valve, 90-Control unit, 91-CPU, 92-Memory.

Claims

1. A methane manufacturing apparatus, characterized in that, The methane manufacturing apparatus includes a reactor that uses carbon dioxide and hydrogen as feedstock gases to produce methane, and the methane manufacturing apparatus includes: A feed gas flow path that allows the feed gas to flow between the first and second regions of the reactor; A catalyst is contained in the first and second regions of the reactor in a manner that allows it to contact the flowing feed gas and to generate methane from the feed gas; A refrigerant flow path that allows refrigerant to flow between the first and second regions within the reactor; and The control unit, while allowing the raw material gas and the refrigerant to circulate in the first and second regions within the reactor, after a predetermined period of methane production, raises the temperature on the side of the first and second regions that was at a low temperature during the predetermined period by changing the flow direction of the raw material gas and the refrigerant.

2. The methane manufacturing apparatus according to claim 1, characterized in that, The feed gas flow path allows the feed gas to flow from the first region of the reactor toward the second region. The control unit performs the following controls: The specified period is defined as the period during which the amount of water accumulated in the reactor is less than a preset accumulation threshold, during which the refrigerant flows from the second region of the reactor toward the first region. and After the specified period, the refrigerant is allowed to flow from the first region of the reactor toward the second region.

3. The methane manufacturing apparatus according to claim 1, characterized in that, During the specified period, the flow directions of the raw material gas and the refrigerant are set to opposite directions. After the specified period, the flow direction of the raw material gas and the refrigerant is set to the same direction.

4. The methane manufacturing apparatus according to any one of claims 1 to 3, characterized in that, The raw material gas flow path and the refrigerant flow path are respectively arranged to extend from the upper part to the lower part of the reactor along the direction of gravity. The first region is located in the upper part, and the second region is located in the lower part.

5. The methane manufacturing apparatus according to claim 4, characterized in that, have: A cooler for cooling the methane produced in the reactor; and The tank recovers the effluent discharged from the reactor via the cooler. If the amount of generated water estimated based on the amount of methane produced is more than a predetermined amount than the amount of discharged water recovered into the tank, the control unit causes the refrigerant in the refrigerant flow path to flow from the top to the bottom of the reactor.

6. The methane manufacturing apparatus according to claim 4, characterized in that, Equipped with a temperature sensor, which detects the temperature inside the reactor. When the detected temperature is above 100°C and the rate of temperature rise is less than a preset speed threshold, the control unit causes the refrigerant in the refrigerant flow path to flow from the upper part to the lower part of the reactor.

7. A method for producing methane, characterized in that, Methane is produced using a reactor that generates methane from carbon dioxide and hydrogen as feedstock gases. The methane production method includes the following steps: The feed gas is allowed to flow in a feed gas flow path spanning the first and second regions of the reactor; The catalyst for generating methane from the feed gas is contained in the first and second regions of the reactor in a manner that allows it to contact the flowing feed gas. The refrigerant is allowed to flow in a refrigerant path spanning the first and second regions within the reactor; and With the raw material gas and the refrigerant flowing through the first and second regions within the reactor, after a specified period of methane production, the temperature on the side of the first and second regions that was at a low temperature during the specified period is raised by changing the flow direction of the raw material gas and the refrigerant.

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