Synthetic fuel generation system

Abstract

This synthetic fuel generation system comprises: a synthetic fuel generation device that reacts hydrogen and carbon dioxide to generate a synthetic compound and water; a product gas delivery path through which a product gas is delivered from the synthetic fuel generation device; a flowmeter that is provided in the product gas delivery path and measures the flow rate of the product gas; a resupply path that is branched off from the product gas delivery path and returns the product gas to the synthetic fuel generation device; and a switching unit that, when the ratio between the flow rate measured by the flowmeter and the flow rate of the raw material gas supplied to the synthetic fuel generation device exceeds a prescribed ratio, performs switching such that the entire amount of the product gas is delivered to the resupply path when the synthetic fuel generation device is running and such that the amount of the product gas exceeding the flow rate corresponding to the prescribed ratio is delivered to the resupply path when the synthetic fuel generation device is not running.

Description

Synthetic fuel production system

[0001] This disclosure relates to a synthetic fuel production system.

[0002] In recent years, methane synthesis apparatuses have been developed that include a water electrolysis unit and a Sabatier reaction unit that synthesizes methane by reacting hydrogen and carbon dioxide. In this methane synthesis apparatus, hydrogen gas produced in the water electrolysis unit is supplied to the Sabatier reaction unit, and methane gas as a synthetic fuel is synthesized using this hydrogen gas and a carbon dioxide-containing gas separately supplied to the Sabatier reaction unit (see Japanese Patent Publication No. 2019-89713).

[0003] Furthermore, Japanese Patent Publication No. 2019-156761 discloses a technique in which, if the methane concentration of the product gas obtained by methanation is below a predetermined concentration, the gas is sent to an off-gas line and subjected to the reaction again in the reactor.

[0004] As described in Japanese Patent Publication No. 2019-156761, if the methane concentration in the generated gas does not reach a predetermined concentration, the decrease in the concentration of the product gas can be suppressed by recovering it separately as a non-product gas. However, since Japanese Patent Publication No. 2019-156761 uses a methane concentration meter, the cost is high.

[0005] This disclosure takes the above facts into consideration and aims to reduce costs and suppress the decrease in product concentration of the generated gas in the synthetic fuel production device.

[0006] A synthetic fuel production system according to the first embodiment includes: a synthetic fuel production device that reacts hydrogen with carbon dioxide to produce a synthetic compound and water; a product gas delivery path from which the product gas is delivered from the synthetic fuel production device; a flow meter provided in the product gas delivery path for measuring the flow rate of the product gas; a resupply path branched from the product gas delivery path for returning the product gas to the synthetic fuel production device; and a switching unit that switches to sending at least a portion of the product gas to the resupply path if the ratio of the flow rate measured by the flow meter to the flow rate of the raw material gas supplied to the synthetic fuel production device exceeds a specified ratio.

[0007] In the first embodiment of the synthetic fuel production system, if the ratio of the flow rate measured by the flow meter to the flow rate of the raw material gas supplied to the synthetic fuel production device exceeds a specified ratio, the switching unit switches so that at least a portion of the produced gas is sent to the resupply path.

[0008] There is a correlation between the conversion rate in a synthetic fuel generator, the concentration of synthetic fuel in the generated gas, and the flow rate ratio of the generated gas to the raw material gas. When the conversion rate is low, the concentration of synthetic fuel also decreases, and the flow rate ratio of the generated gas to the raw material gas increases. Therefore, if the ratio of the flow rate measured by the flow meter to the flow rate of the raw material gas supplied to the synthetic fuel generator exceeds a specified ratio, the concentration of synthetic fuel in the generated gas is considered to be below the specified concentration, and the generated gas is supplied to the resupply line. This allows the flow rate in the generated gas to be measured using a flow meter, and the decrease in the product concentration of the generated gas in the synthetic fuel generator can be suppressed.

[0009] Furthermore, since no concentration sensor is used, costs can be reduced.

[0010] In the second embodiment of the synthetic fuel production system, the switching unit switches the entire amount of the produced gas to be sent to the resupply path when the synthetic fuel production device is started.

[0011] According to the second embodiment of the synthetic fuel production system, off-spec gas can be effectively utilized by returning all of the off-spec gas at startup to the synthetic fuel production device.

[0012] In the third embodiment of the synthetic fuel production system, the switching unit switches the generated gas in excess of the flow rate corresponding to the specified ratio to the resupply path when the synthetic fuel production device is not running.

[0013] According to the third embodiment of the synthetic fuel production system, the supply of product gas can be continued even when the system is not running.

[0014] A synthetic fuel production system according to a fourth embodiment has a raw material supply channel that combines hydrogen and carbon dioxide and supplies them to the synthetic fuel production device, wherein the raw material supply channel has a reuse supply channel equipped with a fluid drive source and a direct supply channel without the fluid drive source formed in parallel, and the reuse supply channel is connected to the upstream side of the fluid drive source in the reuse supply channel.

[0015] According to the synthetic fuel production system of the fourth embodiment, when there is a return of product gas from the resupply channel, a driving force for gas supply is required, so raw material gas is supplied to the synthetic fuel production device from a reuse supply channel equipped with a fluid drive source. On the other hand, when there is no return of product gas from the resupply channel, hydrogen output can be used as the driving force for gas supply, so the driving energy of the fluid drive source can be saved by using a direct supply channel that does not have a fluid drive source.

[0016] The fifth embodiment of the synthetic fuel production system includes a water electrolysis device that produces hydrogen and oxygen by water electrolysis and supplies hydrogen to the synthetic fuel production device.

[0017] According to the synthetic fuel production system of the fifth embodiment, synthetic fuel can be produced using hydrogen produced by a water electrolysis device.

[0018] According to this disclosure, it is possible to reduce costs and suppress the decrease in the product concentration of the generated gas in the synthetic fuel production device.

[0019] This is a diagram showing the configuration of the synthetic fuel production system of this embodiment. This is a block diagram showing the configuration of the control system of the synthetic fuel production system of this embodiment. This is a flowchart showing an example of the production gas return process of this embodiment.

[0020] Hereinafter, an example of an embodiment of this disclosure will be described in detail with reference to the drawings.

[0021] As shown in Figure 1, the synthetic fuel production system 10 of this embodiment includes a water electrolyzer 12, a synthetic fuel production device 14, and a control device 40.

[0022] The water electrolysis device 12 is connected to a water supply source 20 and a power supply source (not shown). In the water electrolysis device 12, water is decomposed into hydrogen and oxygen by the water electrolysis reaction shown in the following equation (1) using the supplied electrical energy.

[0023] H ２ O→H ２ + (1 / 2) O ２ (1)

[0024] 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.

[0025] The combined channel 23 branches into a reused supply channel 23A and a direct supply channel 23B, with an ejector 16 provided in the reused supply channel 23A. The downstream end of the resupply channel 25, which will be described later, is connected to the ejector 16. Downstream of the ejector 16, the reused supply channel 23A and the direct supply channel 23B merge. The downstream end of the rejoined combined channel 23 is connected to a synthetic fuel generator 14, and a mixture of carbon dioxide and hydrogen gas is supplied to the synthetic fuel generator 14 via valve V1. Oxygen and water are discharged from the oxygen discharge channel 22.

[0026] Valve V1 is capable of adjusting the flow rate of gas sent downstream and is connected to the confluence channel 23, the reuse supply channel 23A, and the direct supply channel 23B. Valve V1 is connected to the control device 40, which switches the flow of gas from the confluence channel 23 to either the reuse supply channel 23A or the direct supply channel 23B, and controls the outflow rate by adjusting the opening degree.

[0027] 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).

[0028] 4H ２ +CO ２ →CH ４+2H ２ O (2)

[0029] The synthetic fuel generator 14 is equipped with a temperature sensor 17 for detecting the temperature inside the synthetic fuel generator 14. The temperature sensor 17 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 17 is connected to the control device 40 and outputs the detected temperature T to the control device 40.

[0030] A generated gas outlet 24 is connected to the synthetic fuel generator 14, and the generated gas produced in the synthetic fuel generator 14, for example, methane and water, is sent to the generated gas outlet 24. The generated gas outlet 24 is equipped with a flow meter 18 for measuring the flow rate of the generated gas. The flow meter 18 is connected to a control device 40 and outputs the measured flow rate value C to the control device 40. The flow meter 18 measures the volumetric flow rate value of the generated gas flowing per unit time.

[0031] The generated gas delivery channel 24 branches into a resupply channel 25 and a product channel 26 at a branching point D1 downstream of the flow meter 18. A valve V2 is provided in the resupply channel 25. The downstream end of the resupply channel 25 merges with the upstream side of the ejector 16 of the reuse supply channel 23A. The valve V2 is flow-adjustable and is connected to the control device 40. The valve V2 adjusts its opening degree in response to a signal from the control device 40 to adjust the flow rate of the generated gas branching to the resupply channel 25. A valve V3 is provided in the product channel 26. The valve V3 is an on / off valve and is connected to the control device 40. The opening and closing of the valve V3 is controlled by a signal from the control device 40.

[0032] Next, the control of valves V1, V2, and V3 will be described. In this embodiment, they are controlled in a pattern consisting of a startup mode M1, a flow rate adjustment mode M2, and a specified concentration mode M3.

[0033] In startup mode M1, the mode is used from immediately after the startup of the synthetic fuel generation system 10 until the concentration of the synthetic compound (methane, for example) in the generated gas reaches a predetermined specified concentration (hereinafter referred to as "generated gas specified concentration value C1"). In this mode, valve V1 is open on the reuse supply path 23A side, closed on the direct supply path 23B side, valve V2 is open (fully open), and valve V3 is closed. At this time, since the concentration of the synthetic compound in the generated gas is lower than the generated gas specified concentration value C1, the entire amount of generated gas is sent to the resupply path 25.

[0034] In flow rate adjustment mode M2, the synthetic fuel generation system 10 is inactive, and the concentration of the synthetic compound in the generated gas is lower than the specified concentration value C1 of the generated gas. In this embodiment, inactive means the normal operation period after transitioning from startup to normal operation mode. Valve V1 is open on the reuse supply path 23A side, closed on the direct supply path 23B side, valve V2 is open, and valve V3 is open. The amount of generated gas exceeding the specified concentration flow rate value C1 corresponding to the specified concentration value C1 of the generated gas is sent to the resupply path 25 by valve V2, and the remaining generated gas (flow rate equivalent to the specified concentration flow rate value C1) is sent to the product flow path 26. In inactive mode, if the load on the water electrolyzer 12 and the synthetic fuel generation device 14 fluctuates due to changes in the required flow rate of the product gas, the concentration of the synthetic compound may fall below the specified concentration value C1 of the generated gas. In flow rate adjustment mode M2, product gas with a concentration of synthetic compounds lower than the specified concentration value C1 of the produced gas is sent to the product flow path 26, but product gas with a certain concentration of synthetic compounds is supplied to the synthetic fuel generator 14. Therefore, compared to the case where raw material gas without synthetic compounds is supplied to the synthetic fuel generator 14, the concentration of synthetic compounds in the gas sent to the product flow path 26 can be increased.

[0035] In the specified concentration mode M3, the concentration of the synthesized compound in the generated gas is equal to or greater than the specified concentration value C1 of the generated gas. Valve V1 is closed on the reuse supply path 23A side and open on the direct supply path 23B side, valve V2 is closed and valve V3 is open, and all of the generated gas is sent to the product flow path 26.

[0036] Here, we will explain the specified concentration value C1 and the specified concentration flow rate value C1.

[0037] 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 volumetric flow rate of the gas discharged from the synthetic fuel production device 14 to the volumetric flow rate of the gas supplied to the synthetic fuel production device 14 (produced gas volumetric flow rate / raw material gas volumetric 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 volumetric flow rate of the gas discharged from the synthetic fuel production device 14 to the volumetric flow rate of the gas supplied to the synthetic fuel production device 14 (produced gas volumetric flow rate / raw material gas volumetric 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 18 when the concentration of the synthetic compound in the produced gas is the specified concentration value C1. The flow rate value C measured by the flow meter 18 when the specified concentration value C1 is is changed by the raw material gas flow rate, but the raw material gas flow rate can be determined according to the amount of hydrogen produced required by the water electrolysis device 12. Therefore, if the flow rate value C is greater than the specified concentration flow rate value C1, the generated gas will be 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 generated gas will be equal to or greater than the specified concentration value C1.

[0038] 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.

[0039] 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 storage 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.

[0040] As the storage unit 45, for example, an HDD (Hard Disk Drive), an SSD (Solid State Drive), a flash memory, etc. are used. In the storage unit 45, a control program for controlling the water electrolysis device 12, the synthetic fuel generation device 14, etc. and various data (such as the specified concentration flow value C1, etc.) are stored. Note that this control program and various data may be stored in the ROM 45.

[0041] The temperature sensor 17, the flow meter 18, the valves V1, V2, and V3 are connected to the control device 40 via the I / O 46.

[0042] Next, the operation of the synthetic fuel generation system 10 will be described.

[0043] At startup, the valves V1, V2, and V3 are closed, and the startup mode flag is set to on.

[0044] When a startup instruction is input to the synthetic fuel generation system 10, water is supplied from the water supply source 20 to the water electrolysis device 12, and power is supplied from the power supply source. In the water electrolysis device 12, the supplied water is decomposed into hydrogen and oxygen, the hydrogen is sent to the hydrogen delivery path 21, and the oxygen and water are sent to the oxygen delivery path 22. Carbon dioxide is sent from the carbon dioxide supply source 30, and in the confluence path 23, the carbon dioxide from the carbon dioxide supply source 30 and the hydrogen from the water electrolysis device 12 are mixed and supplied to the synthetic fuel generation device 14.

[0045] [[ID=;15]] In the reactor of the synthetic fuel generation device 14, synthetic fuel and water, for example, methane and water are generated and sent to the generated gas delivery path 24.

[0046] In the control device 40, when a startup instruction is input, the flow rate concentration determination switching process shown in FIG. 3 is executed.

[0047] 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. If the determination is affirmative, the concentration of the synthesized compound in the generated gas has not reached the specified concentration, so the process proceeds to step S14 to determine whether the start mode is ON. If the start mode is ON, it is determined that the synthetic fuel generation system 10 is in an activated state, and the process proceeds to step S16. In step S16, the start mode M1 process is executed. Specifically, valve V1 is opened on the reuse supply path 23A side and closed on the direct supply path 23B side, valve V2 is opened (fully open), and valve V3 is closed. As a result, the entire amount of generated gas is sent to the resupply path 25.

[0048] If the judgment in step S14 is denied, that is, if the start mode is not ON, it is determined that the synthetic fuel generation system 10 is not in an activated state, and the process proceeds to step S18. In step S18, the flow rate adjustment mode M2 ​​process is executed. Specifically, valve V1 is set to open on the reuse supply path 23A side and closed on the direct supply path 23B side, valve V2 is opened, and valve V3 is opened. The amount of generated gas exceeding the specified concentration flow rate value C1 corresponding to the specified concentration value C1 of the generated gas is sent to the resupply path 25 by valve V2, and the remaining generated gas is sent to the product flow path 26.

[0049] If the judgment in step S12 is rejected, that is, if the flow rate value C is less than or equal to the specified concentration flow rate value C1, the concentration of the synthesized compound in the generated gas has reached the specified concentration, so the process proceeds to step S20 and the specified concentration mode M3 processing is executed. Specifically, valve V1 is closed on the reuse supply path 23A side and opened on the direct supply path 23B side, valve V2 is closed and valve V3 is opened, and all the generated gas is sent to the product flow path 26.

[0050] After step S20, in step S22, it is determined whether the startup mode is ON. If the determination is negative, in step S24, the startup mode flag is turned OFF. As a result, if the generated gas reaches the specified concentration C1 even once, it is determined that the system has transitioned from startup to steady state.

[0051] If the process in steps S16, S18, and S24 is completed, or if the judgment in step S22 is rejected, proceed to step S26.

[0052] 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.

[0053] In the synthetic fuel production system 10 of this embodiment, the system determines 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. Since a concentration sensor is not used, costs can be reduced.

[0054] Furthermore, at startup, if the concentration of the synthesized compound in the generated gas has not reached a predetermined value, the entire amount of generated gas is sent to the resupply path 25 and subjected to the reaction again. This allows for the effective utilization of off-spec gas and suppresses a decrease in the concentration of the product gas.

[0055] Furthermore, in this embodiment, when the system is not running, any generated gas exceeding the specified concentration flow rate value C1 is sent to the resupply path, and the generated gas up to the specified concentration flow rate value C1 is sent to the product flow path 26. Therefore, the supply of product gas can be continued even when the system is not running.

[0056] Furthermore, in this embodiment, when there is return product gas from the resupply path 25, the ejector 16 of the reuse supply path 23A can be used to deliver the raw material gas to the synthetic fuel generator 14. On the other hand, when there is no return product gas from the resupply path 25, the hydrogen output from the water electrolyzer 12 can be used as the driving force for gas supply, so by using the direct supply path 23B which does not have an ejector 16, driving energy can be saved.

[0057] In this embodiment, the raw material gas was supplied to the synthetic fuel production device 14 using the ejector 16, but a pump may be used instead of the ejector 16.

[0058] In addition, in the present embodiment, when the generated gas once reaches the specified concentration C1, it is determined that the transition from the startup state to the steady state has occurred. However, based on the temperature T detected by the temperature sensor 17, when the steady-state temperature T1 is reached, it may be determined that the transition to the steady state has occurred.

[0059] In addition, the synthesis reaction in the synthetic fuel generation device 14 of the present embodiment is not limited to the case of synthesizing methane using hydrogen and carbon dioxide as raw materials, and may also be a reaction for generating other synthetic fuels using hydrogen and carbon dioxide as raw materials. For example, the reverse shift reaction for generating carbon monoxide and water, the reaction for generating ethylene and water, the reaction for generating methanol and water, and further, the reaction for generating e-fuel represented by (CH ２ ) ｎ and water can be used.

[0060] Also, in the present embodiment, hydrogen is supplied to the synthetic fuel generation device 14 from the water electrolysis device 12. However, other hydrogen supply means, for example, hydrogen supply from other devices such as a steam reforming device or hydrogen supply from a hydrogen tank may also be used.

[0061] The disclosure of Japanese Application No. 2025-011545 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference.

Claims

1. A synthetic fuel generation system comprising: a synthetic fuel generation device that reacts hydrogen and carbon dioxide to produce a synthetic compound and water; a generated gas delivery path from which the generated gas is delivered from the synthetic fuel generation device; a flow meter provided in the generated gas delivery path for measuring the flow rate of the generated gas; a resupply path branched from the generated gas delivery path for returning the generated gas to the synthetic fuel generation device; and a switching unit that, when the ratio of the flow rate measured by the flow meter to the flow rate of the raw material gas supplied to the synthetic fuel generation device exceeds a specified ratio, switches to deliver the entire amount of the generated gas to the resupply path when the synthetic fuel generation device is started, and when the synthetic fuel generation device is not started, switches to deliver the amount of the generated gas exceeding the flow rate corresponding to the specified ratio to the resupply path.

2. A synthetic fuel production system according to claim 1, comprising a raw material supply passage for combining hydrogen and carbon dioxide and supplying them to the synthetic fuel production device, wherein the raw material supply passage comprises a reuse supply passage equipped with a fluid drive source and a direct supply passage without a fluid drive source, formed in parallel, and the reuse supply passage is connected to the upstream side of the fluid drive source in the reuse supply passage.

3. A synthetic fuel production system according to claim 1 or claim 2, comprising a water electrolysis device that generates hydrogen and oxygen by water electrolysis and supplies hydrogen to the synthetic fuel production device.

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