Methane synthesis apparatus control method

Abstract

To suppress carbon deposition in a second reaction furnace.SOLUTION: A method for controlling a methane synthesizer includes a water temperature raising step of raising a water condensation temperature of a first water condenser to a carbon deposition suppressing water temperature that suppresses carbon deposition in a second reaction furnace when a reaction furnace temperature of the second reaction furnace is expected to rise or has risen, in a methane synthesizer having a first reaction furnace that causes a methane synthesis reaction using carbon dioxide and hydrogen, the first water condenser that condenses and removes water from a first reaction product produced in the first reaction furnace, the second reaction furnace that causes a methane synthesis reaction using a first water removed product obtained in the first water condenser, and a second water condenser that condenses and removes water from a second reaction product produced in the second reaction furnace.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The technology of the present disclosure relates to a method for controlling a methane synthesis apparatus to control a methane synthesis apparatus.

Background Art

[0002] Patent Document 1 describes a methane production apparatus having a first reactor and a second reactor. In this methane production apparatus, in the first reactor, a methanation reaction is caused using a raw material gas containing carbon dioxide and hydrogen supplied from a supply source. Further, in the second reactor, a methanation reaction is caused using a reaction mixed gas containing methane generated in the first reactor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an actual methane synthesis apparatus, carbon may be deposited in a downstream reactor (second reactor), and the carbon deposition may affect the methane synthesis reaction. However, a method for controlling a methane synthesis apparatus capable of suppressing carbon deposition in the second reactor has not been proposed.

[0005] In the technology of the present disclosure, in consideration of the above facts, an object is to suppress carbon deposition in the second reactor.

Means for Solving the Problems

[0006] In the first embodiment of the methane synthesis apparatus control method, the methane synthesis apparatus includes a first reactor that generates a methane synthesis reaction using carbon dioxide and hydrogen, a first water condenser that condenses and removes water from the first reaction product generated in the first reactor, a second reactor that generates a methane synthesis reaction using the first water removed product obtained in the first water condenser, and a second water condenser that condenses and removes water from the second reaction product generated in the second reactor, and the method includes a water temperature increase step in which, when an increase in the reactor temperature of the second reactor is expected or has occurred, the water condensation temperature of the first water condenser is raised to a carbon precipitation suppression water temperature that suppresses carbon precipitation in the second reactor.

[0007] The first embodiment of the methane synthesis apparatus control method applies to a methane synthesis apparatus having two reactors, a first reactor and a second reactor. Since the methane synthesis reaction is carried out in multiple stages, it is possible to increase the methane conversion rate of the second water removal product obtained in the second water condenser as needed, compared to a configuration in which the methane synthesis reaction is carried out in one stage.

[0008] Here, if the reactor temperature of the second reactor rises while the water condensation temperature remains constant, carbon may precipitate in the second reactor. However, this methane synthesis apparatus control method includes a water temperature raising step that is performed when an increase in the reactor temperature of the second reactor is anticipated or has already occurred. In the water temperature raising step, the water condensation temperature of the first water condenser is raised to a carbon precipitation suppression water temperature that suppresses carbon precipitation in the second reactor. This makes it possible to suppress carbon precipitation in the second reactor.

[0009] The second embodiment of the methane synthesis apparatus control method includes, in the first embodiment of the methane synthesis apparatus control method, a water temperature reduction step in which, after raising the water condensation temperature to the carbon precipitation suppression water temperature in the water temperature raising step, the water condensation temperature is lowered to below the carbon precipitation suppression water temperature when the reactor temperature of the second reactor decreases or stabilizes.

[0010] In the second embodiment of the methane synthesis apparatus control method, after raising the water condensation temperature to the carbon deposition suppression temperature in the water temperature raising step, if the reactor temperature of the second reactor decreases or stabilizes, the possibility of carbon deposition in the second reactor decreases. In this state, the water temperature lowering step is performed to lower the water condensation temperature of the first water condenser to below the carbon deposition suppression temperature, thereby suppressing a decrease in the methane concentration synthesized in the second reactor.

[0011] In the third embodiment of the methane synthesis apparatus control method, in the first or second embodiment of the methane synthesis apparatus control method, the carbon deposition suppression water temperature is constant over time.

[0012] In this way, by keeping the carbon deposition suppression water temperature constant over time, it becomes easier to manage and adjust the water condensation temperature in the first water condenser. [Effects of the Invention]

[0013] In this invention, it is possible to suppress carbon deposition in the second reactor. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a diagram showing the configuration of a methane synthesis apparatus according to the first embodiment. [Figure 2] Figure 2 is a block diagram showing the hardware configuration of the control device of the methane synthesis apparatus according to the first embodiment. [Figure 3] Figure 3 is a graph showing an example of the relationship between water condensation temperature and carbon deposition temperature in the methanation reactor of a methane synthesis plant. [Figure 4] Figure 4 is a flowchart showing an example of the water condensation temperature adjustment process in the methane synthesis apparatus of the first embodiment. [Figure 5] Figure 5 is a flowchart showing an example of a water condensation temperature adjustment process in a methane synthesis apparatus according to the first embodiment. [Figure 6] Figure 6 is a graph showing an example of the relationship between the outlet gas flow rate and the assumed gas pressure in a methanation reactor of a methane synthesis plant. [Figure 7]FIG. 7 is a graph showing an example of the relationship between the outlet gas flow rate in the methanation reactor of the methane synthesis apparatus and the assumed maximum temperature of the methanation reactor. [Figure 8] FIG. 8 is a graph showing an example of the relationship between the pressure in the methanation reactor of the methane synthesis apparatus and the water condensation temperature. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an example of an embodiment of the present application will be described in detail with reference to the drawings.

[0016] FIG. 1 shows a methane synthesis apparatus 12 as an example to which the methane synthesis apparatus control method of the first embodiment is applied.

[0017] The methane synthesis apparatus 12 includes a water decomposition apparatus 14 and a methanation apparatus 16. Further, the methanation apparatus 16 includes a first methanation reactor 18, a first water condenser 20, a second methanation reactor 22, and a second water condenser 24.

[0018] In the water decomposition apparatus 14, as shown in the following formula (1), water is decomposed into hydrogen and oxygen by a water decomposition reaction. H2O → H2 + (1 / 2)O2 ΔH 0 = 285.8 kJ / mol (standard state: 25°C, 1 atm) (1) This water decomposition reaction requires an energy supply of 285.8 kJ per 1 mol of water to be decomposed, and this energy is usually supplied as electrical energy. Note that a part of the supplied energy can be supplied as heat energy. In the water decomposition apparatus 14, electrical energy is supplied by the power supply device 64, and heat energy is supplied by the heating device 26, respectively. The water decomposition apparatus 14 is a device that decomposes water by electrical energy and is also an example of a water electrolysis apparatus.

[0019] The hydrogen produced in the water splitting unit 14 is sent to the first methanation reactor 18 of the methanation unit 16. The first methanation reactor 18 is an example of the first reactor of the technology of this disclosure.

[0020] The first methanation reactor 18 contains a catalyst internally, and methane and water are produced by a methane synthesis reaction as shown in the following formula (2). The methane and water produced by the first methanation reactor 18 are examples of the first reaction products related to the technology disclosed in this application. 4H2 + CO2 → CH4 + 2H2O ΔH 0 =-165kJ / mol(Standard condition: 25℃, 1atm) (2) This methane synthesis reaction is an exothermic reaction, generating 165 kJ per mole of methane produced, and a portion of the input thermal energy is released to the outside. For example, some or all of the released thermal energy may be used to act on the water splitting apparatus 14 for the water splitting reaction.

[0021] A hydrogen gas flow sensor 58A is installed in the piping that sends hydrogen from the water splitting unit 14 to the first methanation reactor 18. The hydrogen gas flow sensor 58A detects the amount of hydrogen gas being introduced into the first methanation reactor 18. The detected hydrogen gas flow rate is transmitted to the control device 38.

[0022] Furthermore, carbon dioxide is supplied to the first methanation reactor 18 from, for example, cylinders or tanks (not shown). A carbon dioxide gas flow sensor 58B is installed in the piping that supplies carbon dioxide to the first methanation reactor 18. The carbon dioxide gas flow sensor 58B detects the amount of carbon dioxide being introduced into the first methanation reactor 18. The detected hydrogen gas flow rate is transmitted to the control device 38.

[0023] The temperature of the catalyst in the first methanation reactor 18 is controlled by a temperature control device 28, such as a heat exchanger or heater and cooler. Hereafter, the temperature of the catalyst in the first methanation reactor 18 will be referred to as the "methanation temperature M1".

[0024] The first reaction product generated in the first methanation reactor 18 is sent to the first water condenser 20 through piping.

[0025] The first water condenser 20 condenses water from the first reaction product. The resulting liquid phase water may be discharged outside the first water condenser 20 or supplied to the water splitting unit 14. The first water condenser 20 is supplied with a refrigerant adjusted to a predetermined temperature from the heat source 30, providing the necessary cooling for water condensation. Hereinafter, the temperature of the refrigerant in the first water condenser 20 will be referred to as the "water condensation temperature N1".

[0026] The first reaction product, in which water has been removed in this manner, is an example of the first water-removed product according to the technology of this disclosure. The first water-removed product is sent to the second methanation reactor 22. The second methanation reactor 22 is an example of the second reactor according to the technology of this disclosure.

[0027] Furthermore, a gas pressure sensor 60 is provided in the piping connecting the first water condenser 20 and the second methanation reactor 22, on the inlet side of the first reaction product in the second methanation reactor 22. The gas pressure sensor 60 can detect the pressure of the gas supplied to the second methanation reactor 22 at the inlet of the second methanation reactor 22. The detection result is transmitted to the control device 38.

[0028] The second methanation reactor 22, like the first methanation reactor 18, contains a catalyst internally, and methane and water are produced by the methane synthesis reaction shown in formula (2). The methane and water produced by the second methanation reactor 22 are examples of the second reaction products related to the technology of this disclosure.

[0029] The methane synthesis reaction in the second methanation reactor 22 is also an exothermic reaction of 165 kJ per mole, and a portion of the input thermal energy is released to the outside. For example, some or all of the released thermal energy may be used to act on the water splitting device 14 for the water splitting reaction.

[0030] The temperature of the catalyst in the second methanation reactor 22 is controlled by a temperature control device 32, such as a heat exchanger or heater and cooler. Hereafter, the temperature of the catalyst in the second methanation reactor 22 will be referred to as the "methanation temperature M2".

[0031] Here, the first reaction product is sent to the second methanation reactor 22 as a first water-removed product, with some of the water removed, by the first water condenser 20 located between the first methanation reactor 18 and the second methanation reactor 22. Therefore, the conversion rate to methane in the second methanation reactor 22 is higher compared to a configuration in which water is not removed from the first reaction product. The methane and water produced in the second methanation reactor 22 are an example of the second reaction product according to the technology of this disclosure.

[0032] The second reaction product, including methane and water, generated in the second methanation reactor 22, is sent to the second water condenser 24 through piping. A gas flow sensor 62 is installed in this piping on the outlet side of the second reaction product in the second methanation reactor 22. The gas flow sensor 62 can detect the flow rate of the second reaction product (volume of gas flowing per unit time) at the gas outlet from the second methanation reactor 22. The flow rate data of the second reaction product detected by the gas flow sensor 62 is transmitted to the control device 38. Hereafter, the amount of gas detected by the gas flow sensor 62 will be referred to as the "outlet gas flow rate".

[0033] The second water condenser 24 condenses water from the second reaction product. The resulting liquid phase water may be discharged outside the second water condenser 24 or supplied to the water splitting unit 14. Synthetic methane, the product of the methanation unit 16, is obtained in the second water condenser 24. Similar to the first water condenser 20, the second water condenser 24 is also supplied with a refrigerant adjusted to a predetermined temperature from the heat source 34, so that the cold energy necessary for water condensation is supplied by heat exchange or the like. Hereafter, the temperature of the refrigerant in the second water condenser 24 will be referred to as the "water condensation temperature N2".

[0034] In the second water condenser 24, the second reaction product is produced as synthetic methane with the water removed. Therefore, the concentration of synthetic methane produced in the methanation device 16 is higher compared to a configuration in which water is not removed from the second reaction product.

[0035] A discharge pipe is connected to the second water condenser 24. A gas flow sensor 36 is installed on the outlet side of the discharge pipe from the second water condenser 24. The gas flow sensor 36 can detect the flow rate of the second reaction product (volume of gas flowing per unit time) at the gas outlet from the second water condenser 24.

[0036] The flow rate data of the second reaction product detected by the gas flow sensor 36 is transmitted to the control device 38.

[0037] The control device 38 controls the heating device 26, temperature control devices 28 and 32, heat sources 30 and 34, etc., based on the flow rate information of the second reaction product obtained by the gas flow sensor 62, and various other information.

[0038] Figure 2 shows the hardware configuration of the control device 38 as a block diagram.

[0039] The control device 38 includes a computer 40. The computer 40 includes a processor 42, memory 44, storage 46, input device 48, output device 50, storage medium reader 52, and communication interface 54. Each of these elements is connected to communicate with one another via a bus 56.

[0040] The storage 46 stores a water condensation temperature control program 58 for performing the water condensation temperature control process described later. The processor 42 is capable of executing various programs and controlling each element. Specifically, the processor 42 reads a program from the storage 46 and executes the program using the memory 44 as a working area. That is, the processor 42 controls each element and performs various calculations according to the program stored in the storage 46.

[0041] Memory 44 can temporarily store programs and various data as a working area.

[0042] Storage 46 includes, for example, ROM (Read Only Memory), HDD (Hard Disk Drive), and SSD (Solid State Drive), and stores various programs and data. These programs include not only application programs such as the water condensation temperature control program mentioned above, but also the operating system.

[0043] The input device 48 is a device for providing various types of input to the computer 40. The input device 48 may include operation switches and operation buttons, as well as pointing devices such as keyboards and mice used in personal computers.

[0044] The output device 50 is a device for outputting various types of information from the computer 40, and includes, for example, a display, indicator lights, and speakers. A touch panel display can also be used as the output device 50, in which case the touch panel display also functions as an input device 48.

[0045] The storage medium reader 52 is a device that reads data stored on various storage media and writes data to storage media. Examples of storage media include CD (Compact Disc)-ROM, DVD (Digital Versatile Disc)-ROM, Blu-ray disc, and USB (Universal Serial Bus) memory.

[0046] Communication I / F54 is an interface for communicating with other devices. Standards such as Ethernet (registered trademark) and FDDI (Fiber Distributed Data Interface) are used for communication.

[0047] In this embodiment, the communication I / F 54 communicates with the heating device 26, temperature control devices 28 and 32, heat sources 30 and 34, gas pressure sensor 60 and gas flow sensors 36 and 62, and power supply device 64, thereby enabling control of these devices and acquisition of various statuses. This communication may be wireless or wired.

[0048] Furthermore, storage 46 stores data on the relationship between water condensation temperature and carbon deposition temperature depending on the methanation temperature (see Figure 3).

[0049] Next, the control method for the methane synthesis apparatus in this embodiment will be described.

[0050] As described above, the methanation temperature in the first methanation reactor 18 is denoted as M1, and the methanation temperature in the second methanation reactor 22 is denoted as M2. "Methanation temperature" refers to the temperature of the catalyst in each methanation reactor. Methanation temperatures M1 and M2 may be different values. In this embodiment, both M1 and M2 are variable, and hereafter, M1 = M2. Also, hereafter, when methanation temperatures M1 and M2 are not distinguished, they may simply be referred to as "methanation temperature M".

[0051] Furthermore, let N1 be the water condensation temperature in the first water condenser 20, and N2 be the water condensation temperature in the second water condenser 24. "Water condensation temperature" refers to the temperature of the refrigerant in each water condensation device. In this embodiment, the water condensation temperature N1 is variable, and the water condensation temperature N2 is maintained at 25°C. Hereafter, the water condensation temperature N1 may simply be referred to as "water condensation temperature N".

[0052] Figure 3 shows the relationship between the water condensation temperature N1 and the carbon deposition temperature for each case where the methanation temperature M2 in the second methanation reactor 22 is 500°C, 400°C, and 300°C. In all cases where the methanation temperature M2 is 500°C, 400°C, and 300°C, the carbon deposition temperature increases as the water condensation temperature N1 increases. This carbon deposition temperature is the boundary temperature at which carbon deposition occurs in the second methanation reactor 22 in relation to the methanation temperature M2. Therefore, when the methanation temperature M2 exceeds the carbon deposition temperature, there is a high probability of carbon deposition. It can be seen that by increasing the water condensation temperature N1, the carbon deposition temperature increases, and carbon deposition can be suppressed in the second methanation reactor 22.

[0053] Generally, the carbon deposition temperature is higher when the methanation temperature M2 is higher. However, when the methanation temperature M2 is low, for example below 400°C, the reaction rate of the carbon deposition reaction slows down. In other words, the carbon deposition reaction proceeds slowly, so the possibility of carbon deposition is low. Conversely, when the methanation temperature M2 is above 400°C, for example, the reaction rate of the carbon deposition reaction is faster than when it is below 400°C, so the possibility of carbon deposition is high. Furthermore, actual carbon deposition occurs regardless of the type of catalyst in the second methanation reactor 22.

[0054] In the methane synthesis apparatus control method of this disclosure, as shown below, when the methanation temperature M2 is high, a water temperature raising step is performed to raise the water condensation temperature N1. This water temperature raising step raises the water condensation temperature N1 to a temperature that suppresses carbon deposition in the second methanation reactor 22 (carbon deposition suppression temperature).

[0055] Figures 4 and 5 show a flowchart illustrating a specific example of the water condensation temperature adjustment process in the methane synthesis apparatus control method of this disclosure. This water condensation temperature adjustment process includes a water temperature raising step. By executing the water temperature raising step, the water condensation temperature N1 is raised to suppress carbon deposition in the second methanation reactor 22.

[0056] In the specific water condensation temperature adjustment process, the control device 38 controls the temperature adjustment device 32 in step S102 to raise the temperature of the second methanation reactor 22.

[0057] In step S104, the control device 38 determines whether the methanation temperature M2 has reached the start temperature of the methanation reaction. If this determination is negative, the process returns to step S102, and the second methanation reactor 22 continues to be heated.

[0058] If the determination in step S104 is affirmed, the control device 38 determines in step S106 whether hydrogen gas and carbon dioxide gas are being supplied to the methanation device 16. If this determination is denied, the process proceeds to step S108; if affirmed, the process proceeds to step S132.

[0059] In step S108, the control device 38 estimates the assumed temperature M2' and assumed pressure P2' from the rated conditions. The rated conditions include the hydrogen flow rate and carbon dioxide flow rate introduced into the second methanation reactor 22, the water condensation temperature N1 of the first water condenser 20, and further include the estimated outlet gas flow rate discharged from the second methanation reactor 22 under these conditions. As will be described later, in estimating the outlet gas flow rate, for example, previously obtained test results or simulation results are used. Therefore, in practice, the control device 38 can estimate the outlet gas flow rate even when hydrogen gas and carbon dioxide gas are not introduced into the second methanation reactor 22. Alternatively, if the outlet gas flow rate is set in advance, the control device 38 may be configured to estimate the hydrogen flow rate, carbon dioxide flow rate, and water condensation temperature N1 of the first water condenser 20 introduced into the second methanation reactor 22 so that the outlet gas flow rate becomes this set. When estimating the assumed temperature M2' and assumed pressure P2', the methanation temperature M2 of the second methanation reactor 22 at the time of estimation is used. The assumed temperature M2' is the assumed methanation temperature of the second methanation reactor 22, representing the value of the methanation temperature M2 under these predetermined rated conditions. The assumed pressure P2' is the assumed pressure at the inlet of the second methanation reactor 22, also under these predetermined rated conditions.

[0060] Figure 6 shows an example of the relationship between the outlet gas flow rate and pressure P1, and Figure 7 shows an example of the relationship between the outlet gas flow rate and the assumed maximum temperature. In Figure 6, pressure P1 is the inlet pressure of the second methanation reactor 22, assumed from the outlet gas flow rate under the rated conditions described above. Based on the graph in Figure 6, the assumed pressure P2' can be estimated. Similarly, the assumed maximum temperature in Figure 7 is the highest methanation temperature M2, assumed from the outlet gas flow rate under the rated conditions described above. Based on the graph in Figure 7, the assumed temperature 2' of the second methanation reactor 22 can be estimated. As an example, if the outlet gas flow rate is 20 Nm³ 3If the value is / h, then from Figures 6 and 7, it can be estimated that the assumed pressure P2' = 0.2 MPa and the assumed temperature M2' = 500°C.

[0061] The relationships shown in Figures 6 and 7 are, for example, the results of tests conducted in advance using the methanation device 16. However, instead of such test results, the results may be those calculated by simulation.

[0062] Next, the control device 38 determines the set water condensation temperature N1' in step S110 from the assumed pressure P2' and assumed temperature M2' obtained in step S108.

[0063] Figure 8 shows an example of the relationship between the pressure of the methanation reactor and the water condensation temperature for the cases where the methanation reactor temperature is 500°C and 300°C. This water condensation temperature is the threshold temperature at which carbon deposition can be suppressed in the methanation reactor. For example, in this embodiment, we assume that the methanation temperature of the second methanation reactor 22 is the assumed temperature M2' described above. In this case, we can find the water condensation temperature at which carbon deposition can be suppressed from Figure 8. In fact, since we estimate the assumed temperature M2' = 500°C here, we just need to look at the line for methanation temperature M2 = 500°C in the graph of Figure 8. Furthermore, since we estimate the assumed pressure P2' = 0.2 MPa, we can determine that the water condensation temperature is 86°C when the pressure of the methanation reactor is 0.2 MPa. That is, the water condensation temperature of 86°C obtained here is the threshold temperature at which carbon deposition occurs in the second methanation reactor 22 in this embodiment, and is an example of a "carbon deposition suppression water temperature".

[0064] Next, in step S112, the control device 38 raises the water condensation temperature N1 of the first water condenser 20 to 86°C, which is the set water condensation temperature N1' obtained in step S110 (water temperature rise step). The water condensation temperature N1 of the first water condenser 20 may exceed the set water condensation temperature N1', but since carbon deposition in the second methanation reactor 22 can be suppressed at the set water condensation temperature N1', it is not necessary to make the water condensation temperature N1 of the first water condenser 20 excessively high. Furthermore, once the set water condensation temperature N1', which is an example of a water temperature that suppresses carbon deposition, is set in this way, this set water condensation temperature N1' is maintained constant over time.

[0065] Furthermore, in step S114, the control device 38 resets the hydrogen gas flow rate and carbon dioxide gas flow rate to be introduced into the methanation device 16 and actually introduces them into the methanation device 16. As described above, when the water condensation temperature N1 of the first water condenser 20 is set to the set water condensation temperature N1' = 86°C, the outlet gas flow rate of the methane synthesis device 12 can be newly calculated based on this value. Therefore, the hydrogen gas flow rate and carbon dioxide gas flow rate are reset based on equation (2) so that this outlet gas flow rate is achieved. The volume ratio of hydrogen gas and carbon dioxide gas to be introduced is hydrogen:carbon dioxide = 4:1.

[0066] This allows the methanation device 16 to be operated at predetermined hydrogen gas flow rates and carbon dioxide gas flow rates determined by the set water condensation temperature N1', while suppressing carbon deposition in the second methanation reactor 22.

[0067] Then, in step S116, the control device 38 determines whether the methanation temperature M2 of the second methanation reactor 22 is at the rated temperature. The rated temperature at this stage is a different value from the assumed temperature M2' obtained in step S108. For example, in step S106 the assumed temperature M2' = 500°C, but in step S116 the rated temperature may be 400°C or lower. When the methanation temperature M2 is at the rated temperature, this is an example of a case where the methanation temperature M2 has decreased. In addition to cases where the methanation temperature M2 has decreased in this way, the determination in step S116 also includes cases where the methanation temperature M2 is stable within a certain temperature range.

[0068] Thus, lowering the methanation temperature M2 of the second methanation reactor 22 lowers the carbon deposition initiation temperature. However, a lower methanation temperature M2 slows down the carbon deposition reaction (the reaction proceeds more slowly), thus reducing the likelihood of carbon deposition. In other words, it is possible to suppress carbon deposition while maintaining the rated temperature M2 of the second methanation reactor 22.

[0069] If the judgment in step S116 is rejected, the control device 38 controls the temperature control device 32 in step S118 to adjust the methanation temperature M2 to the rated temperature.

[0070] If the judgment in step S116 is affirmed, the control device 38 controls the heat source 30 in step S120 to lower the water condensation temperature N1 to the rated temperature (water temperature reduction step). In this case, the water condensation temperature N1 is a temperature below the carbon precipitation suppression water temperature, for example, 25°C. Even if the water condensation temperature N1 is lowered in this way, carbon precipitation can be suppressed under conditions where the methanation temperature M2 of the second methanation reactor 22 is low (for example, the rated temperature of 400°C as described above).

[0071] The above describes the process executed when the judgment in step S106 is denied. Conversely, if the judgment in step S106 is affirmed, the process proceeds to step S132 shown in Figure 5.

[0072] In step S132, the control device 38 determines whether or not there is a fluctuation in the flow rates of hydrogen gas and carbon dioxide gas introduced into the methanation device 16. For example, this determination can be made by using the time changes in the hydrogen gas flow rates and carbon dioxide gas flow rates transmitted from the hydrogen gas flow rate sensor 58A and the carbon dioxide gas flow rate sensor 58B. Alternatively, if it is a time fluctuation in the hydrogen gas flow rate, the control device 38 can receive the monitor signal from the water splitting device 14 and detect it from the change in the monitor signal. Similarly, if it is a time change in the carbon dioxide gas flow rate, the control device 38 can receive the monitor signal from the pressure sensor in the carbon dioxide gas storage device and detect it from the change in the monitor signal.

[0073] Furthermore, in the determination in step S132, the flow rate fluctuations of hydrogen gas or carbon dioxide gas introduced into the methanation device 16 may be estimated by means other than those described above. For example, if there are time fluctuations in the electricity supplied to the water splitting device 14, the amount of hydrogen gas produced in the water splitting device 14 will fluctuate. In particular, in a configuration in which the water splitting device 14 is operated by electricity from a renewable energy power generation system, the time fluctuations of the electricity supplied to the water splitting device 14 may be known depending on the magnitude of the electricity demand. In this case, the flow rate fluctuations of hydrogen gas introduced into the methanation device 16 can be estimated from the fluctuations in the electricity supplied to the water splitting device 14. Alternatively, for example, the flow rate changes of hydrogen gas and carbon dioxide gas introduced into the methanation device 16 may be estimated in the state before or during the change from various input signals to the water splitting device 14 and the methanation device 16.

[0074] If the judgment in step S132 is denied, that is, if there is no change in the flow rates of hydrogen gas and carbon dioxide gas introduced into the methanation device 16, the process proceeds to step S134.

[0075] In step S134, the control device 38 determines whether the methanation temperature M2 of the second methanation reactor 22 is at the rated temperature. If this determination is affirmative, the process returns to step S104 (see Figure 4). If this determination is negative, the control device 38 controls the temperature control device 32 in step S136 to adjust the methanation temperature M2 to the rated temperature. Then, the process returns to step S134.

[0076] If the judgment in step S132 is affirmed, the control device 38 estimates the assumed pressure P2' and assumed temperature M2' in step S138 from the fluctuations in the hydrogen gas flow rate, the carbon dioxide gas flow rate, and the outlet flow rate introduced into the methanation device 16.

[0077] Subsequently, the control device 38 proceeds to step S110 (see Figure 4). That is, the control device 38 determines an appropriate set water condensation temperature N1' in step S110 from the assumed pressure P2' and assumed temperature M2' obtained in step S138. By setting the water condensation temperature N1 of the first water condenser 20 to this set water condensation temperature N1', it is possible to operate the methane synthesis apparatus 12 while suppressing carbon deposition in the second methanation reactor 22.

[0078] As explained above, in the methane synthesis apparatus control method according to the technology of this disclosure, when the methanation temperature M2 in the second methanation reactor 22 rises, the water condensation temperature N1 of the first water condenser 20 is raised. Specifically, the water condensation temperature N1 is the set water condensation temperature N1' in the second methanation reactor 22, which is the temperature at which carbon precipitation is suppressed. Therefore, the methane synthesis apparatus 12 can be operated in the second methanation reactor 22 while suppressing carbon precipitation.

[0079] Furthermore, in the above embodiment, after raising the water condensation temperature N1 to the set water condensation temperature N1', a water temperature reduction process is performed once the methanation temperature M2 of the second methanation reactor 22 has stabilized. In the water temperature reduction process, the temperature is lowered to below the set water condensation temperature N1'. Therefore, the decrease in the concentration of synthesized methane produced in the second methanation reactor 22, that is, the decrease in the concentration of methane that can be synthesized in the methane synthesizer 12, can be suppressed.

[0080] In particular, in the above embodiment, when the water temperature reduction process is performed, the methanation temperature M2 of the second methanation reactor 22 is reduced to a temperature at which carbon precipitation is unlikely (400°C in the above example). Therefore, even when the water condensation temperature N1 is reduced by the water temperature reduction process, carbon precipitation can be suppressed in the second methanation reactor 22.

[0081] The set water condensation temperature N1' does not need to be constant, but in the above embodiment, it is kept constant over time. This makes it easier to set and manage the set water condensation temperature N1'. [Explanation of Symbols]

[0082] 12. Methane synthesis plant 14 Water splitting equipment 16. Methanation device 18. First methanation reactor 20. First water condenser 22 Second methanation reactor 24 Second water condenser 26 Heating device 28 Temperature adjustment device 30 Heat source 32 Temperature adjustment device 34 Heat source 36 Gas flow sensor 38 Control device 64 Power supply

Claims

1. The first reactor uses carbon dioxide and hydrogen to produce a methane synthesis reaction, A first water condenser that condenses and removes water from the first reaction product generated in the first reactor, A second reactor for generating a methane synthesis reaction using the first water-removed product obtained in the first water condenser, A second water condenser for condensing and removing water from the second reaction product generated in the second reactor, For a methane synthesis apparatus having the following features: A methane synthesis apparatus control method comprising a water temperature rise step, which, when an increase in the reactor temperature of the second reactor is anticipated or has increased, raises the water condensation temperature of the first water condenser to a carbon precipitation suppression water temperature that suppresses carbon precipitation in the second reactor.

2. A method for controlling a methane synthesis apparatus according to claim 1, further comprising a water temperature lowering step, in which, after raising the water condensation temperature to the carbon deposition suppression water temperature in the water temperature raising step, the water temperature is lowered to below the carbon deposition suppression water temperature when the reactor temperature of the second reactor decreases or stabilizes.

3. The methane synthesis apparatus control method according to claim 1 or claim 2, wherein the carbon deposition suppression water temperature is constant over time.

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