Synthetic fuel production system

Abstract

This increases the temperature of the synthetic fuel production device while simultaneously reducing greenhouse gas emissions. [Solution] The synthetic fuel production system comprises a synthetic fuel production device that reacts hydrogen with carbon dioxide to produce a synthetic compound and water, a combustion unit to which the generated gas produced by the synthetic fuel production device is supplied and which burns the generated gas, and a heat supply unit that supplies the heat of combustion in the combustion unit to the synthetic fuel production device.

Description

Technical Field

[0001] The present disclosure relates to a synthetic fuel generation system.

Background Art

[0002] In recent years, a methane synthesis apparatus has been developed that includes a water electrolysis unit and a Sabatier reaction unit for synthesizing methane by reacting hydrogen with carbon dioxide. In this methane synthesis apparatus, the hydrogen gas generated in the water electrolysis unit is supplied to the Sabatier reaction unit, and methane gas as a synthetic fuel is synthesized from this hydrogen gas and a carbon dioxide-containing gas separately supplied to the Sabatier reaction unit (see Patent Document 1). Further, Patent Document 2 discloses a technique of burning the gas obtained by methanation in a combustor and supplying heat to a water electrolysis apparatus.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The methane synthesis apparatus has a problem that the startup time of the entire system becomes long because it takes time for the temperature of auxiliary equipment such as the Sabatier reactor and the heat medium oil system to rise during startup. Further, particularly during startup, there is a problem that the greenhouse gas emission amount during startup increases due to the atmospheric dispersion of off-spec gas containing greenhouse gases such as methane.

[0005] In consideration of the above facts, an object of the present disclosure is to raise the temperature of a synthetic fuel generation apparatus and reduce the greenhouse gas emission amount.

Means for Solving the Problems

[0006] The first embodiment of the synthetic fuel production system comprises a synthetic fuel production device that reacts hydrogen with carbon dioxide to produce a synthetic compound and water; a combustion unit to which the product gas produced by the synthetic fuel production device is supplied and the product gas is burned; and a heat supply unit to which the heat of combustion in the combustion unit is supplied to the synthetic fuel production device.

[0007] In the first embodiment of the synthetic fuel production system, the generated gas produced by the synthetic fuel production device is burned in the combustion section, and the resulting heat of combustion is supplied to the synthetic fuel production device by the heat supply section. Therefore, in particular, the synthetic fuel production device can be heated up when it is started up, thereby shortening the start-up time. Furthermore, compared to the case where the generated gas produced by the synthetic fuel production device is released into the atmosphere for reasons such as the concentration of the synthetic compound not reaching a predetermined specified value (off-spec), greenhouse gas emissions can be reduced.

[0008] A synthetic fuel production system according to a second embodiment includes a production gas delivery path from which the production gas is delivered from the synthetic fuel production device, a combustion supply path branched from the production gas delivery path and supplying the production gas to the combustion section, and a switching control unit that switches between a combustion mode in which the production gas is delivered to the combustion supply path and a non-combustion mode in which the production gas is not delivered to the combustion supply path.

[0009] According to the second embodiment of the synthetic fuel production system, the presence or absence of combustion of the generated gas in the combustion section can be controlled by switching between a combustion mode and a non-combustion mode in the switching control unit.

[0010] In the third embodiment of the synthetic fuel production system, the switching control unit switches to the combustion mode when the concentration of the synthetic compound in the produced gas delivered to the produced gas delivery passage is less than a predetermined specified concentration.

[0011] According to the synthetic fuel production system of the third embodiment, by burning the synthetic compound in the produced gas when its concentration is below a predetermined specified concentration, greenhouse gas emissions can be reduced compared to when the gas is released into the atmosphere without combustion.

[0012] Furthermore, especially during startup of the synthetic fuel generation device, since the concentration of synthetic compounds in the generated gas is below a predetermined specified concentration, this off-spec generated gas can be effectively utilized to raise the temperature of the synthetic fuel generation device, thereby shortening the startup time.

[0013] In the fourth embodiment of the synthetic fuel production system, the switching control unit switches to the combustion mode when the temperature of the synthetic fuel production device is below a predetermined specified temperature.

[0014] According to the synthetic fuel production system of the fourth embodiment, the synthetic fuel production device can be heated up using the heat of combustion obtained in the combustion section by burning the synthetic fuel production device when its temperature is below a predetermined specified temperature.

[0015] A synthetic fuel production system according to a fifth embodiment includes a water electrolysis device that produces hydrogen and oxygen by water electrolysis and supplies hydrogen to the synthetic fuel production device, and a sub-heat supply unit that supplies combustion heat from the combustion unit to the water electrolysis device.

[0016] According to the fifth embodiment of the synthetic fuel production system, the heat of combustion obtained in the combustion section can be used to raise the temperature of the water electrolysis device.

[0017] A synthetic fuel production system according to a sixth embodiment includes a water electrolysis temperature detection unit for detecting the temperature of the water electrolysis device, wherein the switching control unit switches to an electrolysis device heating mode in which combustion heat in the combustion unit is supplied from the sub-heat supply unit to the water electrolysis device when the temperature detected by the water electrolysis temperature detection unit is below a predetermined optimal water electrolysis temperature, and switches to an electrolysis device non-heating mode in which combustion heat in the combustion unit is not supplied to the water electrolysis device when the temperature detected by the water electrolysis temperature detection unit is above a predetermined optimal water electrolysis temperature.

[0018] According to the synthetic fuel generation system of the sixth aspect, when the temperature of the water electrolysis device is lower than the appropriate temperature for water electrolysis, the water electrolysis device can be effectively heated up.

Advantages of the Invention

[0019] According to the present disclosure, the synthetic fuel generation device can be heated up and the amount of greenhouse gas emissions can be reduced.

Brief Description of the Drawings

[0020] [Figure 1] It is a configuration diagram showing the synthetic fuel generation system of the present embodiment. [Figure 2] It is a block diagram showing the configuration of the control system of the synthetic fuel generation system of the present embodiment. [[ID=2A]] [Figure 3] It is a flowchart showing an example of the product gas combustion process of the present embodiment. [Figure 4] It is a flowchart showing an example of the product gas combustion process of a modification of the present embodiment. [Figure 5] It is a configuration diagram showing the synthetic fuel generation system of another modification of the present embodiment. [Figure 6] It is a block diagram showing the configuration of the control system of the synthetic fuel generation system of another modification of the present embodiment. [Figure 7] It is a flowchart showing an example of the product gas combustion process of another modification of the present embodiment.

Modes for Carrying Out the Invention

[0021] Hereinafter, an example of an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0022] As shown in FIG. 1, the synthetic fuel generation system 10 of the present embodiment includes a water electrolysis device 12, a synthetic fuel generation device 14, a combustor 16, a flow meter 19, and a control device 40.

[0023] The water electrolysis device 12 is connected to a water supply source 20 and a power supply source (not shown). Using the supplied electrical energy, the water electrolysis device 12 decomposes water into hydrogen and oxygen through the water electrolysis reaction shown in the following equation (1).

[0024] H2O → H2 + (1 / 2)O2(1)

[0025] The water electrolysis device 12 is connected to a hydrogen outlet 21 for discharging the generated hydrogen and an oxygen outlet 22 for discharging the generated oxygen. The hydrogen outlet 21 merges with the carbon dioxide supply source 30 and is connected to a confluence channel 23. In the confluence channel 23, carbon dioxide from the carbon dioxide supply source 30 and hydrogen from the water electrolysis device 12 are mixed. The downstream end of the confluence channel 23 is connected to a synthetic fuel generator 14, and the mixed gas of carbon dioxide and hydrogen is supplied to the synthetic fuel generator 14. Oxygen and water are discharged from the oxygen outlet 22.

[0026] The synthetic fuel production device 14 has a reactor (not shown), and inside the reactor, as an example, methane and water are produced by a methane synthesis reaction as shown in the following equation (2).

[0027] 4H2 + CO2 → CH4 + 2H2O (2)

[0028] The synthetic fuel generator 14 is equipped with a temperature sensor 18 for detecting the temperature inside the synthetic fuel generator 14. The temperature sensor 18 may detect the temperature of the reactor inside the synthetic fuel generator 14, or it may detect the temperature of other auxiliary equipment. The temperature sensor 18 is connected to the control device 40 and outputs the detected temperature T to the control device 40.

[0029] A generated gas delivery channel 24 is connected to the synthetic fuel generation device 14, and the generated gas produced in the synthetic fuel generation device 14, for example, methane and water, is sent to the generated gas delivery channel 24.

[0030] The generated gas delivery passage 24 branches off from the combustion supply passage 25 at branching section D1. A valve V1 is provided at branching section D1. A combustor 16 is connected to the downstream end of the combustion supply passage 25. A flow meter 19 is provided upstream of branching section D1 in the generated gas delivery passage 24. The flow meter measures the flow rate of the gas delivered from the synthetic fuel generation device 14 to the generated gas delivery passage 24. The flow meter 19 is connected to a control device 40 and outputs the measured flow rate data to the control device 40.

[0031] The combustor 16 burns the generated gas supplied from the combustion supply passage 25. The combustor 16 is connected to the combustion exhaust gas passage 27, and the combustion exhaust gas generated by combustion is sent to the combustion exhaust gas passage 27. The combustion exhaust gas passage 27 branches off to the combustion exhaust gas release passage 26 at branching section D2. A valve V2 is provided at branching section D2. The combustion exhaust gas passage 27 is released to the atmosphere through the discharge passage 29 after passing through the synthetic fuel generator 14 and the water electrolyzer 12. The combustion exhaust gas sent into the combustion exhaust gas passage 27 undergoes heat exchange with the synthetic fuel generator 14 and is sent to the sub-combustion exhaust gas passage 28, where it undergoes heat exchange with the water electrolyzer 12 and is released to the atmosphere through the discharge passage 29. The combustion exhaust gas functions as a heat transfer medium to heat the synthetic fuel generator 14 and the water electrolyzer 12.

[0032] Valves V1 and V2 are three-way valves and are connected to the control device 40. Valves V1 and V2 are three-way valves and their outlet switching is controlled. When valve V1 is open on the combustion supply passage 25 side and closed on the downstream side of the generated gas delivery passage 24, it is combustion mode A1 in which generated gas is supplied to the combustor 16. When valve V1 is closed on the combustion supply passage 25 side and open on the downstream side of the generated gas delivery passage 24, it is non-combustion mode A2 in which generated gas is not supplied to the combustor 16.

[0033] Switching between combustion mode A1 and non-combustion mode A2 is performed by controlling the opening and closing of the flow path of valve V1 so that when the concentration of the synthetic compound (methane, for example) in the product gas produced by the synthetic fuel generator 14 is equal to or greater than a predetermined specified concentration (hereinafter referred to as "specified concentration value C1"), it switches to non-combustion mode A2, and when it is less than the specified concentration value C1, it switches to combustion mode A1.

[0034] Here, we will explain the specified concentration value C1 and the specified concentration flow rate value C1. The specified concentration value C1 is the value required for normal operation in the synthetic fuel production system 10 and can be set as appropriate by the user. The conversion rate of the reaction in the synthetic fuel production device 14 corresponds to the concentration of the synthetic compound in the produced gas and the ratio of the flow rate of the gas sent out from the synthetic fuel production device 14 to the flow rate of the gas supplied to the synthetic fuel production device 14 (produced gas flow rate / raw material gas flow rate). If the conversion rate of the reaction is high, the concentration of the synthetic compound in the produced gas will be high, and the ratio of the flow rate of the gas sent out from the synthetic fuel production device 14 to the flow rate of the gas supplied to the synthetic fuel production device 14 (produced gas flow rate / raw material gas flow rate) will be low. The specified concentration flow rate value C1 is defined as the flow rate value C measured by the flow meter 19 when the concentration of the synthetic compound in the produced gas is the specified concentration value C1. Therefore, if the flow rate value C is greater than the specified concentration flow rate value C1, the produced gas is less than the specified concentration value C1, and if the flow rate value C is less than or equal to the specified concentration flow rate value C1, the produced gas is greater than or equal to the specified concentration value C1.

[0035] In valve V2, when the combustion exhaust gas passage 27 is open and the combustion exhaust gas discharge passage 26 is closed, the combustion exhaust gas is supplied to the synthetic fuel generator 14 and the water electrolysis device 12, resulting in heating mode B1. In valve V2, when the combustion exhaust gas passage 27 is closed and the combustion exhaust gas discharge passage 26 is open, the combustion exhaust gas is not supplied to the synthetic fuel generator 14, resulting in non-heating mode B2.

[0036] Switching between heating mode B1 and non-heating mode B2 is performed by controlling the opening and closing of the flow path of valve V2 so that if the temperature T detected by the temperature sensor 18 is equal to or greater than the optimal operating value T1 for the synthetic fuel generator 14, it switches to non-heating mode B2, and if it is less than the optimal operating value T1, it switches to heating mode B1. The optimal operating value T1 is the value required for an appropriate reaction during normal operation of the synthetic fuel generator 14, and can be set as appropriate by the user.

[0037] As shown in Figure 2, the control device 40 includes a CPU (Central Processing Unit) 42, a ROM (Read Only Memory) 43, a RAM (Random Access Memory) 44, an input / output interface (I / O) 46, and a storage unit 45.

[0038] The CPU 42, ROM 43, RAM 44, and I / O 46 are connected to each other via the bus 47. Each functional unit, including the memory unit 45, is connected to the I / O 46. These functional units are able to communicate with the CPU 42 via the I / O 46.

[0039] For the storage unit 45, for example, an HDD (Hard Disk Drive), SSD (Solid State Drive), or flash memory may be used. The storage unit 45 stores control programs for controlling the water electrolysis device 12 and the synthetic fuel production device 14, as well as various data (such as specified concentration flow rate value C1 and optimal temperature value T1). These control programs and various data may also be stored in the ROM 43.

[0040] The temperature sensor 18, flow meter 19, valve V1, and valve V2 are connected to the control device 40 via I / O 46.

[0041] Next, the operation of the synthetic fuel production system 10 will be described.

[0042] At startup, when a start command is input to the synthetic fuel production system 10, water is supplied from the water supply source 20 to the water electrolyzer 12, and power is supplied from the power supply source. In the water electrolyzer 12, the supplied water is decomposed into hydrogen and oxygen, the hydrogen is sent to the hydrogen outlet 21, and the oxygen and water are sent to the oxygen outlet 22. Carbon dioxide is sent from the carbon dioxide supply source 30, and in the confluence channel 23, the carbon dioxide from the carbon dioxide supply source 30 and the hydrogen from the water electrolyzer 12 are mixed and supplied to the synthetic fuel production device 14.

[0043] In the reactor of the synthetic fuel production device 14, a synthetic compound and water, for example methane and water, are produced and sent to the product gas delivery passage 24.

[0044] In the control device 40, upon input of a start command, the flow rate concentration determination switching process shown in Figure 3 is executed.

[0045] In step S10, the flow rate value C is obtained, and in step S12, it is determined whether the flow rate value C is greater than the specified concentration flow rate value C1 (the flow rate value corresponding to the specified concentration value C1 of the generated gas). If the determination is affirmative, the concentration of the synthesized compound in the generated gas has not reached the specified concentration, so in step S14, the system switches to combustion mode. Specifically, with respect to valve V1, the combustion supply passage 25 side is open and the downstream side of the generated gas delivery passage 24 is closed, and the generated gas is supplied to the combustor 16. The generated gas supplied to the combustor 16 is burned in the combustor 16.

[0046] If the judgment in step S12 is rejected, the system switches to non-combustion mode in step S16. Specifically, with respect to valve V1, the combustion supply passage 25 side is closed, and the downstream side of the generated gas delivery passage 24 is opened to deliver the product gas, so no generated gas is supplied to the combustor 16. After step S16, the system proceeds to step S26.

[0047] Following step S14, step S18 is used to obtain the temperature T, and step S20 is used to determine whether the temperature T is lower than the operating value T1. If the determination is positive, step S22 is used to switch to heating mode. Specifically, valve V2 is set so that the combustion exhaust gas passage 27 side is open and the combustion exhaust gas discharge passage 26 side is closed, and combustion exhaust gas is supplied as a heat transfer medium to the synthetic fuel generator 14 and the water electrolyzer 12. As a result, the synthetic fuel generator 14 and the water electrolyzer 12 are heated. After step S22, the process proceeds to step S26.

[0048] If the judgment in step S20 is rejected, the system switches to non-combustion mode in step S24. Specifically, with respect to valve V2, the combustion exhaust gas passage 27 side is closed and the combustion exhaust gas release passage 26 side is opened, and the combustion exhaust gas is released into the atmosphere. After step S24, the system proceeds to step S26.

[0049] In step S26, it is determined whether or not the operation of the synthetic fuel production system 10 has been instructed to be terminated. If the determination is affirmative, this process is terminated. If the determination is negative, the process returns to step S10 and the above process is repeated.

[0050] In the synthetic fuel production system 10 of this embodiment, it is determined whether the concentration of the synthetic compound in the produced gas has reached a predetermined value based on the flow rate value C of the produced gas sent from the synthetic fuel production device 14. If the determination is negative, the produced gas produced in the synthetic fuel production device 14 is burned in the combustor 16, and the resulting heat of combustion is supplied to the synthetic fuel production device 14. Therefore, in particular, the synthetic fuel production device 14 can be heated up when it is started up, and the start-up time can be shortened.

[0051] Furthermore, compared to the case where the generated gas produced by the synthetic fuel generation device 14 is released into the atmosphere because the concentration of the synthetic compound does not reach a predetermined value, greenhouse gas emissions can be reduced.

[0052] In this embodiment, the combustion mode A1 and non-combustion mode A2 were switched based on the flow rate value C obtained by the flow meter 19, but the combustion mode A1 and non-combustion mode A2 may also be switched based on the temperature T obtained by the temperature sensor 18.

[0053] In this case, as shown in Figure 4, the temperature T is obtained in step S30, and it is determined in step S32 whether the temperature T is lower than the operating optimal value T1. If the determination is positive, the system switches to combustion mode in step S14. As a result, the synthetic fuel generator 14 and the water electrolyzer 12 are heated.

[0054] If the judgment in step S32 is rejected, the system switches to non-combustion mode in step S16. After steps S14 and S16, the system proceeds to step S26.

[0055] When the generated gas is burned in the combustor 16, the temperature of the synthetic fuel generator 14 is always below T, so the valve V2 should be set to constant heating mode.

[0056] In step S26, it is determined whether or not the operation of the synthetic fuel production system 10 has been instructed to be terminated. If the determination is affirmative, this process is terminated. If the determination is negative, the process returns to step S30 and the above process is repeated.

[0057] In this embodiment, the concentration of the synthesized compound in the generated gas was determined from the flow rate of the generated gas using a flow meter. However, a concentration meter may be used instead of a flow meter to determine the concentration of the synthesized compound in the generated gas. In particular, using a flow meter as in this embodiment can reduce costs compared to using a concentration meter.

[0058] In addition to the configuration of this embodiment, the supply of combustion exhaust gas to the water electrolyzer 12 may be controlled based on the temperature of the water electrolyzer 12. In this case, as shown in Figure 5, a temperature detection unit 12A is provided to detect the temperature TE of the water electrolyzer 12. A branch section D3 and a three-way valve V3 are provided in the combustion exhaust gas discharge path 26, and a branch section D4 and a three-way valve V4 are provided between the synthetic fuel generator 14 and the water electrolyzer 12 in the sub-combustion exhaust gas path 28. The three-way valve V3 is connected to a bypass circuit 27A that branches off from the combustion exhaust gas discharge path 26 and merges with the sub-combustion exhaust gas path 28 at the merging section C without passing through the synthetic fuel generator 14. The three-way valve V4 is provided upstream of the merging section C, and branches one end to the water electrolyzer 12 side (sub-combustion exhaust gas path 28) and the other end to the atmospheric discharge path 28A. As shown in Figure 6, the temperature detection unit 12A, three-way valves V3 and V4 are connected to the control device 40. If the temperature TE detected by the temperature detection unit 12A is below the optimal operating temperature for the water electrolysis device 12 (optimal water electrolysis temperature TE less than 0), the control device 40 controls either the bypass 27A side of the three-way valve V3 or the water electrolysis device 12 side of the three-way valve V4 to open. If the temperature TE detected by the temperature detection unit 12A is above the optimal operating temperature for the water electrolysis device 12 (optimal water electrolysis temperature TE 0 or above), the control device 40 controls either the combustion exhaust gas discharge passage 26 side of the three-way valve V3 or the atmospheric discharge side of the three-way valve V4 to open. The optimal water electrolysis temperature TE is the lower limit of the temperature suitable for the operation of the water electrolysis device 12.

[0059] In this case, the flow rate concentration determination switching process proceeds as shown in Figure 7. If the process proceeds to step S22, in step S40 the temperature TE of the water electrolysis device 12 is obtained from the temperature sensor 12A, and in step S42 it is determined whether the temperature TE of the water electrolysis device 12 is less than the optimal water electrolysis temperature TE0. If the determination is affirmative, in step S44 the water electrolysis device 12 side of the three-way valve V4 is opened, and if the determination is negative, in step S45 the atmospheric discharge 28A side of the three-way valve V4 is opened.

[0060] If the process proceeds to step S24, in step S46 the temperature TE of the water electrolyzer 12 is obtained from the temperature sensor 12A, and in step S47 it is determined whether the temperature TE of the water electrolyzer 12 is less than the optimal water electrolysis temperature TE0. If the determination is affirmative, in step S48 the bypass circuit 27A side of the three-way valve V3 is opened, and if the determination is negative, in step S49 the combustion gas discharge passage 26 side of the three-way valve V3 is opened. After steps S44, S45, S48, and S49, the process proceeds to step S26.

[0061] Furthermore, the synthesis reaction in the synthetic fuel production apparatus 14 of this embodiment is not limited to the synthesis of methane using hydrogen and carbon dioxide as raw materials, but may also be a reaction that produces other synthetic fuels using hydrogen and carbon dioxide as raw materials. For example, a reverse shift reaction that produces carbon monoxide and water, a reaction that produces ethylene and water, a reaction that produces methanol and water, and even (CH2) n This can be described as a reaction that produces e-fuel and water, represented by [formula].

[0062] Furthermore, in this embodiment, hydrogen was supplied to the synthetic fuel generation device 14 from the water electrolysis device 12, but hydrogen may also be supplied from other means, such as other devices like a steam reforming device, or from a hydrogen tank. [Explanation of Symbols]

[0063] 10 Synthetic fuel production system 12 Water electrolysis equipment 14 Synthetic fuel generation device 16. Combustor (combustion section) 27 Combustion exhaust gas passage (heat supply section) 28. Sub-combustion exhaust gas passage (sub-heat supply section) 40 Control device (switching control unit) A1 Combustion Mode A2 Non-combustion mode B1 Heating Mode B2 Non-heating mode V1 Valve (Switching Control Unit)

Claims

1. A synthetic fuel production device that reacts hydrogen and carbon dioxide to produce synthetic compounds and water, The generated gas produced by the aforementioned synthetic fuel production device is supplied to a combustion section that burns the generated gas, A heat supply unit that supplies the combustion heat from the combustion section to the synthetic fuel production device, A synthetic fuel production system equipped with [the necessary components].

2. A generated gas delivery path from which the generated gas is delivered from the synthetic fuel generating apparatus, A combustion supply passage is branched from the generated gas delivery passage and supplies the generated gas to the combustion section, A switching control unit that switches between a combustion mode in which the generated gas is sent to the combustion supply path and a non-combustion mode in which the generated gas is not sent to the combustion supply path, A synthetic fuel production system according to claim 1, comprising:

3. The switching control unit switches to the combustion mode when the concentration of the synthetic compound in the generated gas sent to the generated gas discharge path is below a predetermined specified concentration. The synthetic fuel production system according to claim 2.

4. The switching control unit switches to the combustion mode when the temperature of the synthetic fuel generator is below a predetermined specified temperature. The synthetic fuel production system according to claim 2.

5. A water electrolysis apparatus that generates hydrogen and oxygen by water electrolysis and supplies hydrogen to the synthetic fuel generation apparatus, A sub-heat supply unit that supplies combustion heat from the combustion unit to the water electrolysis device, A synthetic fuel production system according to any one of claims 1 to 4, comprising:

6. The water electrolysis device includes a water electrolysis temperature detection unit for detecting the temperature of the water electrolysis device, The switching control unit switches to an electrolytic device heating mode in which combustion heat from the combustion unit is supplied to the water electrolytic device from the sub-heat supply unit when the temperature detected by the water electrolysis temperature detection unit is below a predetermined optimal water electrolysis temperature, and switches to an electrolytic device non-heating mode in which combustion heat from the combustion unit is not supplied to the water electrolytic device when the temperature detected by the water electrolysis temperature detection unit is above a predetermined optimal water electrolysis temperature. A synthetic fuel production system according to claim 5, relating to claim 4.

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