Cathode gas supply system and carbon recycle system

Abstract

To provide a cathode gas supply system that can reduce the concentration of carbon dioxide gas contained in a cathode gas produced by electrolysis.SOLUTION: A cathode gas supply system comprises: a carbon dioxide electrolytic apparatus that electrolyzes a carbon dioxide gas and discharges a cathode gas containing a carbon monoxide gas and the carbon dioxide gas; and a downstream side carbon dioxide recovery apparatus that recovers the carbon dioxide gas contained in the cathode gas and supplies the cathode gas to a processing unit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a cathode gas supply system and a carbon recycling system. [Background technology]

[0002] In recent years, carbon dioxide capture, utilization and storage (CCUS) technology has become known as an effective technology for dealing with the global warming issue, which has become a global concern. CCUS technology is a technology that captures and utilizes or stores carbon dioxide gas (CO2) contained in exhaust gases, etc.

[0003] One of the technologies that utilizes the recovered carbon dioxide gas is a carbon dioxide electrolysis device that electrolyzes carbon dioxide gas into carbon monoxide gas (CO). The carbon monoxide gas generated by electrolysis is discharged from the carbon dioxide electrolysis device as cathode gas. The discharged cathode gas is supplied to a downstream processing device. By reacting the carbon monoxide gas with hydrogen gas, etc. in the processing device, it is possible to produce synthetic fuels whose main component is hydrocarbons, or to produce chemical products.

[0004] The cathode gas of the carbon dioxide electrolysis device contains carbon monoxide gas and hydrogen gas as main components. The gas components of the cathode gas can be adjusted by adjusting the concentrations of the gas components in the gas supplied to the carbon dioxide electrolysis device or by changing the electrolysis conditions. Therefore, a cathode gas according to the gas components required by the above-mentioned treatment device is supplied to the treatment device.

[0005] However, the cathode gas of the carbon dioxide electrolysis device may contain unreacted carbon dioxide gas. Depending on the type of treatment device, the presence of carbon dioxide gas in the cathode gas may reduce the treatment efficiency. In some cases, it may be difficult to perform the desired treatment.

[0006] Furthermore, in order to adjust the gas components of the cathode gas or to maintain the performance of the carbon dioxide electrolysis device, the concentration of carbon dioxide gas contained in the gas supplied to the carbon dioxide electrolysis device may be increased. In this case, the concentration of carbon dioxide gas contained in the cathode gas also increases, which may reduce the processing efficiency of the processing device. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2020-189817 A Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the embodiments is to provide a cathode gas supply system and a carbon recycling system that can reduce the concentration of carbon dioxide gas contained in the cathode gas generated by electrolysis. [Means for solving the problem]

[0009] The cathode gas supply system according to the embodiment is a system for supplying a cathode gas containing carbon monoxide gas obtained by electrolyzing carbon dioxide gas to a processing device. The cathode gas supply system includes a carbon dioxide electrolysis device that electrolyzes carbon dioxide gas and discharges a cathode gas containing carbon monoxide gas and carbon dioxide gas, and a downstream carbon dioxide recovery device that recovers the carbon dioxide gas contained in the cathode gas and supplies the cathode gas to the processing device.

[0010] A carbon recycling system according to the embodiment includes the above-mentioned cathode gas supply system, and a treatment device that treats carbon monoxide gas contained in the cathode gas supplied from the cathode gas supply system. Effect of the Invention

[0011] According to the embodiment, it is possible to reduce the concentration of carbon dioxide gas contained in the cathode gas generated by electrolysis. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an overall configuration of a carbon recycling system equipped with a cathode gas supply system according to an embodiment. [Diagram 2] FIG. 2 is a diagram showing the carbon dioxide capture device shown in FIG. [Diagram 3] FIG. 3 is a schematic cross-sectional view showing an electrolytic cell of the carbon dioxide electrolysis device shown in FIG. [Figure 4] FIG. 4 is a diagram showing a modification of the carbon dioxide capture device shown in FIG. [Diagram 5] FIG. 5 is a diagram showing another modified example of the carbon dioxide capture device shown in FIG. [Figure 6] FIG. 6 is a diagram showing a modification of the cathode gas supply system shown in FIG. [Figure 7] FIG. 7 is a diagram showing another modified example of the cathode gas supply system shown in FIG. [Figure 8] FIG. 8 is a diagram showing another modified example of the cathode gas supply system shown in FIG. [Figure 9] FIG. 9 is a diagram showing another modified example of the cathode gas supply system shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The cathode gas supply system and the carbon recycling system according to the present embodiment will be described with reference to FIGS.

[0014] First, a carbon recycling system 1 according to the present embodiment will be described. As shown in Fig. 1, the carbon recycling system 1 may include a gas emission source 2, a cathode gas supply system 10, an FT synthesis device 3, and a combustion device 4.

[0015] The gas emission source 2 may be an apparatus or a plant that generates and emits carbon dioxide gas. The gas emission source 2 emits exhaust gas G1 containing carbon dioxide gas. Examples of the gas emission source 2 include a thermal power plant, a steel plant, and a waste incineration plant.

[0016] The cathode gas supply system 10 electrolyzes carbon dioxide gas contained in the exhaust gas G1 discharged from the gas emission source 2, and supplies cathode gas G5 (described later) containing carbon monoxide gas obtained by electrolysis to the FT synthesis device 3. The exhaust gas G1 is supplied to the cathode gas supply system 10 from the gas emission source 2 through a first exhaust gas line L1. The cathode gas supply system 10 according to this embodiment is configured to similarly electrolyze the exhaust gas G3 supplied from the combustion device 4 described later through a second exhaust gas line L3. The cathode gas supply system 10 will be described in detail later.

[0017] The FT synthesis device 3 is a device that processes carbon monoxide gas contained in the cathode gas G5 (described later) supplied from the cathode gas supply system 10. The FT synthesis device 3 is an example of a processing device, and may, for example, generate synthetic fuel from carbon monoxide gas. The FT synthesis device 3 may perform a catalytic reduction reaction of carbon monoxide gas. The FT synthesis device 3 is supplied with cathode gas G5 from the cathode gas supply system 10.

[0018] For example, the FT synthesis apparatus 3 may be an apparatus that generates a synthetic fuel mainly composed of a hydrocarbon, using carbon monoxide gas contained in the cathode gas G5. The FT synthesis apparatus 3 may use the Fischer-Tropsch method (FT synthesis). In this case, a liquid fuel such as aviation fuel (SAF) may be synthesized by reducing carbon monoxide gas and hydrogen gas under high temperature and high pressure in the presence of a catalyst. The hydrogen gas may be supplied from a hydrogen gas supply facility (not shown). Instead of aviation fuel, fuel such as LPG, naphtha, or diesel may be synthesized. This synthetic fuel may be used in automobiles or ships.

[0019] The FT synthesis unit 3 discharges the produced synthetic fuel and also discharges tail gas G2 containing a hydrocarbon gas. The tail gas G2 may contain methane gas as a hydrocarbon gas. The tail gas G2 may further contain carbon dioxide gas, carbon monoxide gas, and hydrogen gas. The tail gas G2 is supplied to the combustion unit 4 through a tail gas line L2. The tail gas G2 may also be referred to as off-gas.

[0020] The treatment device is not limited to the FT synthesis device 3, and may be any device that can treat the carbon monoxide gas contained in the cathode gas G5.

[0021] The combustion device 4 is a device that generates carbon dioxide gas from an anode gas G6 (described later) discharged from a carbon dioxide electrolysis device 30 described later and the above-mentioned tail gas G2 discharged from the FT synthesis device 3. The combustion device 4 is an example of a carbon dioxide generation device, and may generate carbon dioxide gas by combusting the anode gas G6 and the tail gas G2, for example. More specifically, methane gas contained in the tail gas G2 is burned as fuel, and carbon dioxide gas is generated from the methane gas as shown in the following formula (1). CH4 + 2O2 → CO2 + 2H2O (1)

[0022] The carbon dioxide gas generated in the combustion device 4 is supplied to a carbon dioxide electrolysis device 30, which will be described later. The carbon dioxide gas may be captured by an upstream carbon dioxide capture device 20, which will be described later, and supplied from the upstream carbon dioxide capture device 20 to the carbon dioxide electrolysis device 30.

[0023] More specifically, the combustion device 4 discharges exhaust gas G3 containing the generated carbon dioxide gas. The exhaust gas G3 is supplied to the cathode gas supply system 10 through a second exhaust gas line L3. The second exhaust gas line L3 may be joined to the above-mentioned first exhaust gas line L1.

[0024] The carbon dioxide gas generator is not limited to the combustion device 4, and may be any device capable of generating carbon dioxide gas from a hydrocarbon gas such as methane gas contained in the tail gas G2. For example, the carbon dioxide gas generator may be a reformer capable of generating carbon dioxide gas from a hydrocarbon gas. The reformer may generate carbon dioxide gas by a steam reforming reaction. Alternatively, the carbon recycle system 1 according to this embodiment may not be equipped with a carbon dioxide gas generator.

[0025] Next, a cathode gas supply system 10 according to the present embodiment will be described. As shown in Fig. 1, the cathode gas supply system 10 includes an upstream carbon dioxide capture device 20, a carbon dioxide electrolysis device 30, and a downstream carbon dioxide capture device 40.

[0026] The upstream carbon dioxide capture device 20 is a device that captures carbon dioxide gas from exhaust gas G1 and exhaust gas G3 containing carbon dioxide gas. The captured carbon dioxide gas is supplied to the carbon dioxide electrolysis device 30. In the following description, the upstream carbon dioxide capture device 20 will be simply referred to as the upstream capture device 20. The upstream capture device 20 is disposed upstream of the carbon dioxide electrolysis device 30. The upstream capture device 20 is supplied with exhaust gas G1 from the gas emission source 2 through a first exhaust gas line L1. The upstream capture device 20 is supplied with exhaust gas G3 from the combustion device 4 through a second exhaust gas line L3.

[0027] As shown in FIG. 2, the upstream recovery device 20 may include an upstream absorption tower 21, a regenerator 22, and a heat exchanger .

[0028] The upstream absorption tower 21 absorbs the carbon dioxide gas contained in the flue gas G1 and the flue gas G3 in an absorbing liquid such as an amine solution. The absorbing liquid absorbs the carbon dioxide gas by gas-liquid contact with the flue gas G1 and the flue gas G3. The absorbing liquid that has absorbed the carbon dioxide gas becomes a rich liquid A1 and is supplied to the heat exchanger 23 through a first rich liquid line L21. In the heat exchanger 23, the rich liquid A1 exchanges heat with a lean liquid A2 described later, and is supplied to the regeneration tower 22 through a second rich liquid line L22. In the upstream absorption tower 21, the flue gas G1 and the flue gas G3 after contact with the lean liquid A2 may be discharged from the upstream absorption tower 21.

[0029] The regenerator 22 releases carbon dioxide gas from the rich solution A1 that has absorbed carbon dioxide gas in the upstream absorption tower 21. The rich solution A1 supplied to the regenerator 22 is heated using water vapor to release carbon dioxide gas. A supply gas G4 containing the carbon dioxide gas released in the regenerator 22 is discharged from the regenerator 22 and supplied to the carbon dioxide electrolysis device 30 through a supply gas line L4. The supply gas G4 also contains water vapor. A discharge line L5 that discharges the supply gas G4 to a storage facility 5 (see FIG. 9) described later or the like branches off from the supply gas line L4.

[0030] In the regeneration tower 22, the absorbing liquid that has released carbon dioxide gas is regenerated to become lean liquid A2. The lean liquid A2 is supplied to the heat exchanger 23 through the first lean liquid line L23. In the heat exchanger 23, it exchanges heat with the rich liquid A1 described above, and is supplied to the upstream absorption tower 21 through the second lean liquid line L24. A cooler (not shown) is provided in the second lean liquid line L24, and the lean liquid A2 is cooled by the cooler. The lean liquid A2 supplied to the upstream absorption tower 21 absorbs carbon dioxide gas again.

[0031] In this manner, the absorbing liquid circulates between the upstream absorption tower 21 and the regenerator 22 while repeatedly absorbing and releasing carbon dioxide gas, and the carbon dioxide gas contained in the flue gas G1 and the flue gas G3 is recovered.

[0032] As shown in Fig. 1, the carbon dioxide electrolysis device 30 is a device that electrolyzes carbon dioxide gas contained in a supply gas G4 and discharges a cathode gas G5 containing carbon monoxide gas. The cathode gas G5 also contains unreacted carbon dioxide gas. In the following description, the carbon dioxide electrolysis device 30 will be simply referred to as the electrolysis device 30. The electrolysis device 30 according to this embodiment is supplied with a supply gas G4 from the upstream recovery device 20 described above.

[0033] The electrolysis device 30 may be configured to react carbon dioxide gas directly, making it unnecessary to dissolve the carbon dioxide gas in an aqueous solution. An example of the electrolysis device 30 will now be described in more detail.

[0034] As shown in Fig. 3, the electrolysis device 30 includes an electrolysis cell 31, a cathode separator 32, and an anode separator 33. The cathode separator 32 includes a flow path 32a for a supply gas G4 containing carbon dioxide gas, and the anode separator 33 includes a flow path 33a for an electrolytic solution. The electrolysis device 30 has a stack structure in which a plurality of electrolysis cells 31, cathode separators 32, and anode separators 33 are stacked. The electrolysis cell 31 includes a cathode electrode 34 including a gas diffusion layer 34a and a catalyst layer 34b, a solid polymer membrane 35, and an anode electrode 36.

[0035] The above-mentioned supply gas line L4 is connected to the flow path 32a of the cathode separator 32, and carbon dioxide gas is supplied to the cathode electrode 34. An electrolytic solution is supplied to the anode electrode 36. The electrolytic solution is not particularly limited, but may be, for example,

[0036] When a current is applied between the cathode electrode 34 and the anode electrode 36, a reduction reaction of carbon dioxide gas occurs at the cathode electrode 34, as shown in the following formula (2). 2CO2+H2O+2e - → CO+2OH - (2)

[0037] At the anode electrode 36, an oxidation reaction of hydroxide ions occurs as shown in the following formula (3), producing oxygen gas and water. 2OH - → 1 / 2O2+H2O+2e - (3)

[0038] In the cathode electrode 34, a three-phase interface where carbon dioxide gas (gas), water (liquid), and catalyst (solid) gather in a good balance may be formed in the catalyst layer 34b in order to directly react the carbon dioxide gas contained in the supply gas G4. However, if this balance is lost, the amount of hydrogen gas produced, which is a side reaction, may increase as shown in the following formula (4). For example, if the amount of carbon dioxide gas supplied to the catalyst layer 34b of the cathode electrode 34 decreases, the amount of hydrogen gas produced at the cathode electrode 34 may increase. If the amount of hydrogen gas produced increases, the efficiency of converting carbon dioxide gas to carbon monoxide gas may decrease. 2H2O+2e - → H2+2OH - (4)

[0039] The electrolysis device 30 discharges a cathode gas G5 containing carbon monoxide gas and hydrogen gas from the cathode electrode 34. The cathode gas G5 also contains unreacted carbon dioxide gas. A first cathode line L6 is connected to the flow path 32a of the cathode separator 32, and the cathode gas G5 is supplied to the downstream carbon dioxide capture device 40 through the first cathode line L6.

[0040] The electrolysis device 30 discharges an anode gas G6 containing unreacted carbon dioxide gas and oxygen gas from the anode electrode 36. An anode line L8 is connected to the flow path 33a of the anode separator 33, and the anode gas G6 is supplied to the combustion device 4 through the anode line L8. The anode line L8 may merge with the tail gas line L2 described above. Alternatively, the tail gas line L2 may merge with the anode line L8.

[0041] The downstream carbon dioxide capture device 40 captures carbon dioxide gas contained in the cathode gas G5 discharged from the electrolysis device 30, and supplies the cathode gas G5 to the above-mentioned FT synthesis device 3. In the following, the downstream carbon dioxide capture device 40 will be simply referred to as the downstream capture device 40. The downstream capture device 40 is disposed downstream of the electrolysis device 30.

[0042] 2, the downstream recovery device 40 is supplied with the cathode gas G5 discharged from the electrolysis device 30 through the above-mentioned first cathode line L6. The downstream recovery device 40 may include a downstream absorption tower 41.

[0043] The downstream absorption tower 41 absorbs the carbon dioxide gas contained in the cathode gas G5 discharged from the electrolysis device 30 in the absorbing liquid. The absorbing liquid absorbs the carbon dioxide gas by gas-liquid contact with the cathode gas G5. The absorbing liquid that has absorbed the carbon dioxide gas becomes the rich liquid A1. The rich liquid A1 that has absorbed the carbon dioxide gas in the downstream absorption tower 41 may be supplied to the regeneration tower 22 of the upstream recovery device 20. In the downstream absorption tower 41, the cathode gas G5 after contacting with the lean liquid A2 is discharged from the downstream absorption tower 41 and supplied to the FT synthesis device 3. In this way, the downstream absorption tower 41 is configured to recover carbon dioxide gas from the cathode gas G5.

[0044] More specifically, the rich liquid A1 discharged from the downstream absorption tower 41 may be supplied to the heat exchanger 23 of the upstream recovery device 20 through the third rich liquid line L41. For example, the third rich liquid line L41 may merge with the first rich liquid line L21 of the upstream recovery device 20. In this case, the rich liquid A1 discharged from the upstream absorption tower 21 and the rich liquid A1 discharged from the downstream absorption tower 41 may be mixed and supplied to the heat exchanger 23.

[0045] The lean liquid A2 supplied to the downstream absorption tower 41 may be supplied from the second lean liquid line L24 of the upstream recovery device 20. More specifically, a third lean liquid line L42 may branch off from the second lean liquid line L24, and the third lean liquid line L42 may be connected to the downstream absorption tower 41. In this case, a part of the lean liquid A2 discharged from the heat exchanger 23 is supplied to the downstream absorption tower 41. A cooler for cooling the lean liquid A2 may be provided in the third lean liquid line L42, or may be provided in the second lean liquid line L24 between the branch point P1 of the heat exchanger 23 and the third lean liquid line L42.

[0046] In this way, a part of the absorption liquid circulates between the downstream absorption tower 41 and the regeneration tower 22 while repeatedly absorbing and releasing carbon dioxide gas, and the carbon dioxide gas contained in the cathode gas G5 is recovered. The recovered carbon dioxide gas is supplied to the FT synthesis device 3 from the downstream recovery device 40 through the second cathode line L7.

[0047] The downstream recovery device 40 according to this embodiment is configured to recover carbon dioxide gas from the cathode gas G5 by using the regenerator 22 and the heat exchanger 23 of the upstream recovery device 20. The downstream recovery device 40 is partially integrated with the upstream recovery device 20.

[0048] Next, a method for recycling carbon using the carbon recycling system 1 including the cathode gas supply system 10 according to this embodiment having the above-described configuration will be described.

[0049] As shown in Fig. 1 and Fig. 2, the flue gas G1 discharged from the gas emission source 2 is supplied to the upstream absorption tower 21 of the upstream recovery device 20 through the first flue gas line L1. In addition, the flue gas G3 discharged from the combustion device 4 is also supplied to the upstream absorption tower 21. In the upstream absorption tower 21, the lean liquid A2 absorbs carbon dioxide gas contained in the flue gas G1 and the flue gas G3, and becomes a rich liquid A1, which is supplied to the regeneration tower 22. In the regeneration tower 22, the carbon dioxide gas is released from the rich liquid A1 and discharged from the regeneration tower 22 as a supply gas G4.

[0050] The supply gas G4 discharged from the regenerator 22 passes through a supply gas line L4 and is supplied to the cathode electrode 34 (see FIG. 3) of the electrolysis device 30. The anode electrode 36 is supplied with an electrolytic solution.

[0051] In the electrolysis device 30, a current is applied between the cathode electrode 34 and the anode electrode 36, and carbon dioxide gas is electrolyzed. As shown in the above formula (2), carbon dioxide gas is reduced at the cathode electrode 34 to generate carbon monoxide gas. The generated carbon monoxide gas is discharged from the cathode electrode 34 as cathode gas G5 together with hydrogen gas and unreacted carbon dioxide gas. As shown in the above formula (3), hydroxide ions are oxidized at the anode electrode 36 to generate oxygen gas. The generated oxygen gas is discharged from the anode electrode 36 together with unreacted carbon dioxide gas as anode gas G6.

[0052] The cathode gas G5 discharged from the electrolysis device 30 is supplied to the downstream absorption tower 41 of the downstream recovery device 40 through the first cathode line L6. In the downstream absorption tower 41, the lean liquid A2 absorbs the carbon dioxide gas contained in the cathode gas G5, becomes the rich liquid A1, and is supplied to the regeneration tower 22 of the upstream absorption tower 21. The cathode gas G5 that has come into contact with the lean liquid A2 in the downstream absorption tower 41 is discharged. The concentration of carbon dioxide gas contained in the discharged cathode gas G5 decreases.

[0053] The cathode gas G5 discharged from the downstream recovery device 40 is supplied to the FT synthesis device 3 through the second cathode line L7. In the FT synthesis device 3, as shown in the above formula (1), a catalytic reduction reaction of carbon monoxide gas contained in the cathode gas G5 is carried out under high temperature and high pressure to generate a synthetic fuel mainly composed of hydrocarbons. As described above, since the concentration of carbon dioxide gas contained in the cathode gas G5 is reduced, the production efficiency of the synthetic fuel can be improved. The generated synthetic fuel is discharged from the FT synthesis device 3. In this way, carbon can be recycled. Apart from the synthetic fuel, tail gas G2 containing methane gas is discharged from the FT synthesis device 3.

[0054] The tail gas G2 discharged from the FT synthesis apparatus 3 is supplied to the combustion apparatus 4 through the tail gas line L2. The above-mentioned anode gas G6 discharged from the electrolysis apparatus 30 is supplied to the combustion apparatus 4 through the anode line L8. In the combustion apparatus 4, methane gas contained in the tail gas G2 is combusted as fuel. As a result, carbon dioxide gas is generated from the methane gas, and exhaust gas G3 with an increased concentration of carbon dioxide gas is generated. The generated exhaust gas G3 is discharged from the combustion apparatus 4.

[0055] The exhaust gas G3 discharged from the combustion device 4 is supplied to the upstream recovery device 20 through a second exhaust gas line L3.

[0056] In this way, carbon can be recycled while being effectively utilized.

[0057] Thus, according to this embodiment, the carbon dioxide gas contained in the cathode gas G5 discharged from the electrolysis device 30 is recovered in the downstream recovery device 40. The cathode gas G5 discharged from the downstream recovery device 40 is supplied to the FT synthesis device 3. This makes it possible to lower the concentration of carbon dioxide gas contained in the cathode gas G5 generated by electrolysis and supplied to the FT synthesis device 3. In this case, it is possible to prevent a decrease in the efficiency of synthetic fuel generation in the FT synthesis device 3.

[0058] Further, according to this embodiment, as described above, the concentration of carbon dioxide gas contained in the cathode gas G5 can be reduced. In this case, the concentration of carbon dioxide gas supplied to the electrolysis device 30 can be increased. That is, the concentration of carbon dioxide gas contained in the supply gas G4 supplied to the electrolysis device 30 may be increased in order to adjust the components of the cathode gas G5 or to maintain the performance of the electrolysis device 30. In this case, the concentration of carbon dioxide gas contained in the cathode gas G5 discharged from the electrolysis device 30 may also be increased. However, according to this embodiment, the carbon dioxide gas can be recovered from the cathode gas G5 by the downstream recovery device 40. As a result, even if the concentration of carbon dioxide gas contained in the supply gas G4 is increased, the concentration of carbon dioxide gas supplied to the FT synthesis device 3 can be reduced. Therefore, the concentration of carbon dioxide gas in the cathode gas G5 supplied to the FT synthesis device 3 can be reduced while maintaining the performance of the electrolysis device 30.

[0059] Furthermore, according to this embodiment, the supply gas G4 supplied to the electrolysis device 30 is a gas containing carbon dioxide gas recovered from the exhaust gas G1 and the exhaust gas G3 in the upstream recovery device 20. This makes it possible to increase the concentration of carbon dioxide gas contained in the supply gas G4. This makes it possible to increase the amount of carbon monoxide gas produced in the electrolysis device 30. In this case, it is also possible to reduce the generation of hydroxide ions that are likely to be produced by the water electrolysis reaction when the carbon dioxide gas concentration is low at the cathode electrode 34.

[0060] According to this embodiment, the downstream recovery device 40 includes a downstream absorption tower 41 that absorbs the carbon dioxide gas contained in the cathode gas G5 into the lean liquid A2, and the rich liquid A1 that has absorbed the carbon dioxide gas is supplied to the regenerator 22 of the upstream recovery device 20. This allows the downstream recovery device 40 and the upstream recovery device 20 to share the regenerator 22. This improves the installation space efficiency of the device. Also, the energy for heating the rich liquid A1 in the regenerator 22 can be effectively used.

[0061] Furthermore, according to this embodiment, carbon dioxide gas is generated from the anode gas G6 discharged from the electrolysis device 30 and the tail gas G2 discharged from the FT synthesis device 3, and the exhaust gas G3 containing the generated carbon dioxide gas is supplied to the upstream recovery device 20. This makes it possible to effectively utilize the carbon contained in the tail gas G2.

[0062] (First Modification) In the above-described embodiment, an example has been described in which the upstream recovery device 20 recovers carbon dioxide gas from the exhaust gas G1 and exhaust gas G3 containing carbon dioxide gas and supplies the recovered carbon dioxide gas to the electrolysis device 30. However, the embodiment is not limited to this. The electrolysis device 30 may be supplied with carbon dioxide gas in any manner. For example, if the concentration of carbon dioxide gas contained in the exhaust gas discharged from the gas emission source 2 is high, the exhaust gas may be supplied to the electrolysis device 30 without passing through the upstream recovery device 20. Alternatively, for example, gas containing carbon dioxide gas transported from an area distant from the carbon recycle system 1 according to the embodiment may be supplied to the electrolysis device 30. In this case, the carbon dioxide gas may be supplied to the electrolysis device 30 without passing through the upstream recovery device 20.

[0063] (Second Modification) In the present embodiment described above, an example has been described in which the third rich liquid line L41 of the downstream side recovery device 40 merges with the first rich liquid line L21 of the upstream side recovery device 20. However, the present embodiment is not limited to this.

[0064] For example, as shown in FIG. 4, the third rich liquid line L41 may be merged with the second lean liquid line L24 of the upstream recovery device 20. In this case, the rich liquid A1 discharged from the downstream absorption tower 41 can be supplied to the upstream absorption tower 21. The third rich liquid line L41 may be merged with the second lean liquid line L24 downstream of the branch point P1 of the third lean liquid line L42 of the second lean liquid line L24. When the concentration of carbon dioxide gas contained in the cathode gas G5 supplied to the downstream absorption tower 41 is low, the carbon dioxide concentration of the rich liquid A1 discharged from the downstream absorption tower 41 is low. In this case, the rich liquid A1 discharged from the downstream absorption tower 41 may be supplied to the upstream absorption tower 21 as the lean liquid A2. This can increase the carbon dioxide concentration of the rich liquid A1 supplied to the regeneration tower 22, thereby improving the recovery efficiency of the carbon dioxide gas.

[0065] Alternatively, as shown in Fig. 5, the third rich liquid line L41 may be joined to the second rich liquid line L22. In this case, the rich liquid A1 discharged from the downstream absorption tower 41 can be supplied to the regeneration tower 22. When the concentration of carbon dioxide gas contained in the cathode gas G5 supplied to the downstream absorption tower 41 is high, the carbon dioxide concentration of the rich liquid A1 discharged from the downstream absorption tower 41 is high. In this case, the rich liquid A1 discharged from the downstream absorption tower 41 may be supplied to the regeneration tower 22 without being supplied to the upstream absorption tower 21 or the heat exchanger 23.

[0066] Other variations may be incorporated into each of the cathode gas supply systems 10 shown in Figures 4 and 5.

[0067] (Third Modification) In the above-described embodiment, an example has been described in which the cathode gas G5 discharged from the electrolysis device 30 is supplied to the FT synthesis device 3 through the downstream recovery device 40. However, the embodiment is not limited to this. For example, as shown in FIG. 6, the cathode gas supply system 10 may further include a bypass line L9 and a bypass flow rate control valve 50.

[0068] The bypass line L9 supplies a portion of the cathode gas G5 discharged from the electrolysis device 30 to the FT synthesis device 3, bypassing the downstream recovery device 40. The bypass line L9 may branch off from the first cathode line L6 and merge with the second cathode line L7.

[0069] The bypass flow rate control valve 50 is provided in the bypass line L9. The bypass flow rate control valve 50 adjusts the flow rate of the cathode gas G5 in the bypass line L9. More specifically, the bypass flow rate control valve 50 is configured to be adjustable in opening degree, thereby adjusting the flow rate of the cathode gas G5 passing through the bypass flow rate control valve 50. When a processing device such as the FT synthesis device 3 can tolerate a certain amount of carbon dioxide gas being contained in the supplied cathode gas G5, at least a part of the cathode gas G5 may be supplied to the FT synthesis device 3 without passing through the downstream recovery device 40. In this case, the energy for recovering carbon dioxide gas from the cathode gas G5 can be reduced. The bypass flow rate control valve 50 may be controlled by a first control unit 52 described later, but may also be manually operated without being controlled by the first control unit 52.

[0070] As shown in FIG. 6, the cathode gas supply system 10 may further include a downstream carbon dioxide concentration meter 51.

[0071] The downstream carbon dioxide concentration meter 51 measures the concentration of carbon dioxide gas contained in the cathode gas G5 downstream of the junction P2 of the bypass line L9 in the second cathode line L7. In the following description, the downstream carbon dioxide concentration meter 51 will be simply referred to as the downstream concentration meter 51.

[0072] The downstream concentration meter 51 is provided on the second cathode line L7 between the junction P2 of the bypass line L9 and the FT synthesis device 3. The downstream concentration meter 51 is provided downstream of the downstream recovery device 40.

[0073] The aperture of the bypass flow rate control valve 50 described above may be adjusted based on the measured value of the carbon dioxide gas concentration measured by the downstream concentration meter 51. In this case, the concentration of carbon dioxide gas contained in the cathode gas G5 supplied to the FT synthesis apparatus 3 may be adjusted to a desired concentration. For example, as the aperture of the bypass flow rate control valve 50 is increased, the concentration of carbon dioxide gas contained in the cathode gas G5 supplied to the FT synthesis apparatus 3 can be increased. On the other hand, as the aperture of the bypass flow rate control valve 50 is decreased, the concentration of carbon dioxide gas contained in the cathode gas G5 supplied to the FT synthesis apparatus 3 can be decreased.

[0074] 6, the cathode gas supply system 10 may further include a first control unit 52. The first control unit 52 may be incorporated in the same control device (not shown) as the other control units, or may be incorporated in a control device different from the other control units.

[0075] The first control unit 52 may control the bypass flow rate control valve 50 based on the concentration of carbon dioxide gas measured by the downstream concentration meter 51. For example, the first control unit 52 may adjust the aperture of the bypass flow rate control valve 50 so that the concentration of carbon dioxide gas contained in the cathode gas G5 supplied to the FT synthesis apparatus 3 becomes a desired concentration. By the first control unit 52 controlling the bypass flow rate control valve 50, the aperture of the bypass flow rate control valve 50 can be appropriately and automatically adjusted.

[0076] (Fourth Modification) As shown in FIG. 6, the cathode gas supply system 10 according to this embodiment may further include an upstream carbon dioxide concentration meter 53.

[0077] The upstream carbon dioxide concentration meter 53 measures the concentration of carbon dioxide gas contained in the cathode gas G5 discharged from the electrolysis device 30. In the following description, the upstream carbon dioxide concentration meter 53 will be simply referred to as the upstream concentration meter 53.

[0078] The upstream concentration meter 53 measures the concentration of carbon dioxide gas contained in the cathode gas G5 on the first cathode line L6 upstream of the branch point P3 of the bypass line L9. The upstream concentration meter 53 is provided on the first cathode line L6 between the electrolysis device 30 and the branch point P3 of the bypass line L9. The upstream concentration meter 53 is provided upstream of the downstream recovery device 40.

[0079] The supply current for electrolysis supplied to the electrolysis device 30 may be adjusted based on the concentration of carbon dioxide gas measured by the upstream concentration meter 53. In this case, the concentration of carbon dioxide gas contained in the cathode gas G5 discharged from the electrolysis device 30 may be adjusted to a desired concentration. For example, as the supply current is increased, the reaction according to the above formula (2) can be promoted, and the concentration of carbon dioxide gas contained in the cathode gas G5 can be reduced. On the other hand, as the supply current is decreased, the reaction according to the above formula (2) can be suppressed, and the concentration of carbon dioxide gas contained in the cathode gas G5 can be increased.

[0080] 6, the cathode gas supply system 10 may further include a second control unit 54. The second control unit 54 may be incorporated in the same control device (not shown) as the other control units, or may be incorporated in a control device different from the other control units.

[0081] The second control unit 54 may control the supply current for electrolysis supplied to the electrolysis device 30, based on the concentration of carbon dioxide gas measured by the upstream concentration meter 53. For example, the second control unit 54 may adjust the supply current so that the concentration of carbon dioxide gas contained in the cathode gas G5 discharged from the electrolysis device 30 becomes a desired concentration. By the second control unit 54 controlling the supply current, the supply current can be appropriately and automatically adjusted according to the concentration of carbon dioxide gas discharged from the electrolysis device 30.

[0082] (Fifth Modification) In the above-described embodiment, the cathode gas supply system 10 may further include a cathode gas analyzer 55, and the downstream recovery device 40 may include an absorbent flow rate control valve 42, as shown in FIG.

[0083] 7, the absorbent liquid flow rate control valve 42 is provided in the third lean liquid line L42. The absorbent liquid flow rate control valve 42 adjusts the flow rate of the lean liquid A2 supplied to the downstream absorption tower 41 of the downstream recovery device 40. More specifically, the absorbent liquid flow rate control valve 42 is configured to be adjustable in opening degree, thereby adjusting the flow rate of the absorbent passing through the absorbent liquid flow rate control valve 42. The absorbent liquid flow rate control valve 42 may be controlled by a third control unit 56 described later, or may be manually operated without being controlled by the third control unit 56.

[0084] The cathode gas analyzer 55 analyzes the cathode gas G5 supplied to the downstream recovery device 40. More specifically, the cathode gas analyzer 55 measures at least one of the concentration of carbon dioxide gas contained in the cathode gas G5 and the flow rate of the cathode gas G5. The cathode gas analyzer 55 analyzes the cathode gas G5 downstream of the branch point P3 of the bypass line L9 in the first cathode line L6. The cathode gas analyzer 55 may be provided between the branch point P3 of the bypass line L9 in the first cathode line L6 and the downstream recovery device 40. Alternatively, in the case where the cathode gas supply system 10 includes a cathode gas return line L10 (see FIG. 8) described later, the cathode gas analyzer 55 may analyze the cathode gas G5 downstream of the branch point P4 of the cathode gas return line L10 in the first cathode line L6. The cathode gas analyzer 55 may be provided in the first cathode line L6 between the branch point P4 of the cathode gas return line L10 and the downstream recovery device 40.

[0085] The opening degree of the above-mentioned absorbing liquid flow rate control valve 42 may be adjusted based on the measurement result of the cathode gas analyzer 55. In this case, the flow rate of the lean liquid A2 supplied to the downstream absorption tower 41 can be effectively adjusted.

[0086] For example, when the cathode gas analyzer 55 measures the concentration of carbon dioxide gas contained in the cathode gas G5, the aperture of the absorbing liquid flow rate control valve 42 may be decreased as the concentration of carbon dioxide gas decreases. This can reduce the flow rate of the lean liquid A2 supplied to the downstream absorption tower 41, and prevent the lean liquid A2 from being excessively supplied to the downstream absorption tower 41. This can prevent the flow rate of the lean liquid A2 supplied to the upstream absorption tower 21 from decreasing, and prevent the recovery efficiency of carbon dioxide gas in the upstream absorption tower 21 from decreasing. On the other hand, the aperture of the absorbing liquid flow rate control valve 42 may be increased as the concentration of carbon dioxide gas increases. This can increase the flow rate of the lean liquid A2 supplied to the downstream absorption tower 41, and improve the recovery efficiency of carbon dioxide gas in the downstream absorption tower 41.

[0087] Alternatively, for example, when the cathode gas analyzer 55 measures the flow rate of the cathode gas G5, the aperture of the absorption liquid flow rate control valve 42 may be decreased as the flow rate of the cathode gas G5 decreases. This makes it possible to reduce the flow rate of the lean liquid A2 supplied to the downstream absorption tower 41, and to prevent a decrease in the recovery efficiency of the carbon dioxide gas in the upstream absorption tower 21. On the other hand, the aperture of the absorption liquid flow rate control valve 42 may be increased as the flow rate of the cathode gas G5 increases. This makes it possible to increase the flow rate of the lean liquid A2 supplied to the downstream absorption tower 41, and to improve the recovery efficiency of the carbon dioxide gas in the downstream absorption tower 41.

[0088] 7, the cathode gas supply system 10 may further include a third control unit 56. The third control unit 56 may be incorporated in the same control device (not shown) as the other control units, or may be incorporated in a control device different from the other control units.

[0089] The third control unit 56 may control the absorbing liquid flow rate control valve 42 based on the measurement result of the cathode gas analyzer 55. For example, the third control unit 56 may adjust the aperture of the absorbing liquid flow rate control valve 42 so that the flow rate of the lean liquid A2 supplied to the downstream absorption tower 41 corresponds to the supply amount of carbon dioxide gas to the downstream recovery device 40. By the third control unit 56 controlling the absorbing liquid flow rate control valve 42, the flow rate of the lean liquid A2 supplied to the downstream absorption tower 41 can be appropriately and automatically adjusted.

[0090] The above-described fourth modification may be incorporated into the fifth modification of the cathode gas supply system 10 shown in FIG.

[0091] (Sixth Modification) In the present embodiment described above, the cathode gas supply system 10 may further include a cathode gas return line L10 and a cathode gas flow rate regulating valve 57, as shown in FIG.

[0092] The cathode gas return line L10 supplies a part of the cathode gas G5 discharged from the electrolysis device 30 to the electrolysis device 30. The cathode gas return line L10 may branch off from the first cathode line L6 and merge with the above-mentioned supply gas line L4. The cathode gas return line L10 may branch off from a portion of the first cathode line L6 downstream of the branch point P3 of the bypass line L9. The cathode gas return line L10 may merge with the supply gas line L4 downstream of the branch point P5 (see FIG. 2) of the discharge line L5 of the supply gas line L4. By supplying the cathode gas G5 to the electrolysis device 30, the concentration of carbon dioxide gas supplied to the electrolysis device 30 can be reduced, and in this case, the precipitation of salt that is likely to occur when the concentration of carbon dioxide gas is high can be suppressed at the cathode electrode 34.

[0093] The cathode gas flow rate control valve 57 is provided in the cathode gas return line L10. The cathode gas flow rate control valve 57 adjusts the flow rate of the cathode gas G5 in the cathode gas return line L10. More specifically, the cathode gas flow rate control valve 57 is configured to be adjustable in opening degree, thereby adjusting the flow rate of the cathode gas G5 passing through the cathode gas flow rate control valve 57. The cathode gas flow rate control valve 57 may be controlled by a fourth control unit 58 described later, but may also be manually operated without being controlled by the fourth control unit 58.

[0094] 8, the cathode gas supply system 10 may further include the above-mentioned cathode gas analyzer 55. The cathode gas analyzer 55 may have the same configuration as the cathode gas analyzer 55 shown in FIG.

[0095] The cathode gas analyzer 55 analyzes the cathode gas G5 in the first cathode line L6 downstream of the branch point P4 of the cathode gas return line L10. The cathode gas analyzer 55 is provided in the first cathode line L6 between the branch point P4 of the cathode gas return line L10 and the downstream recovery device 40.

[0096] The opening degree of the cathode gas flow rate adjustment valve 57 may be adjusted based on the measurement results of the cathode gas analyzer 55. In this case, it is possible to prevent the recovery efficiency of the carbon dioxide gas in the downstream recovery device 40 from decreasing.

[0097] For example, when the cathode gas analyzer 55 measures the concentration of carbon dioxide gas contained in the cathode gas G5, the opening degree of the cathode gas flow rate control valve 57 may be increased as the concentration of carbon dioxide gas increases. This allows the flow rate of the cathode gas G5 in the cathode gas return line L10 to be increased. This prevents the amount of carbon dioxide gas supplied to the downstream absorption tower 41 from becoming excessive, and prevents the recovery efficiency of the carbon dioxide gas in the downstream recovery device 40 from decreasing. On the other hand, the opening degree of the cathode gas flow rate control valve 57 may be decreased as the concentration of carbon dioxide gas decreases. This allows the flow rate of the cathode gas G5 in the cathode gas return line L10 to be reduced. This allows the amount of carbon dioxide gas supplied to the downstream absorption tower 41 to be increased, and prevents the recovery efficiency of the carbon dioxide gas in the downstream recovery device 40 from decreasing.

[0098] Alternatively, for example, when the cathode gas analyzer 55 measures the flow rate of the cathode gas G5, the opening degree of the cathode gas flow rate adjustment valve 57 may be increased as the flow rate of the cathode gas G5 increases. This makes it possible to increase the flow rate of the cathode gas G5 in the cathode gas return line L10, and to prevent a decrease in the recovery efficiency of the carbon dioxide gas in the downstream recovery device 40. On the other hand, the opening degree of the cathode gas flow rate adjustment valve 57 may be decreased as the flow rate of the cathode gas G5 decreases. This makes it possible to reduce the flow rate of the cathode gas G5 in the cathode gas return line L10, and to prevent a decrease in the recovery efficiency of the carbon dioxide gas in the downstream recovery device 40.

[0099] 8, the cathode gas supply system 10 may further include a fourth control unit 58. The fourth control unit 58 may be incorporated in the same control device (not shown) as the other control units, or may be incorporated in a control device different from the other control units.

[0100] The fourth control unit 58 may control the cathode gas flow rate adjustment valve 57 based on the flow rate of the cathode gas G5 measured by the cathode gas analyzer 55. For example, the fourth control unit 58 may adjust the aperture of the cathode gas flow rate adjustment valve 57 so as to prevent a decrease in the recovery efficiency of the carbon dioxide gas in the downstream recovery device 40. By the fourth control unit 58 controlling the cathode gas flow rate adjustment valve 57, the aperture of the cathode gas flow rate adjustment valve 57 can be appropriately and automatically adjusted.

[0101] (Seventh Modification) As shown in FIG. 8, the cathode gas supply system 10 according to the present embodiment may further include a supply gas flow rate adjustment valve 59 and a cathode gas analyzer 60.

[0102] The supply gas flow rate regulating valve 59 is provided in the supply gas line L4. The supply gas flow rate regulating valve 59 regulates the flow rate of the supply gas G4 supplied to the electrolysis device 30.

[0103] More specifically, the supply gas flow rate control valve 59 is configured to be adjustable in opening degree, thereby controlling the flow rate of the supply gas G4 passing through the supply gas flow rate control valve 59. The supply gas flow rate control valve 59 controls the flow rate of the supply gas G4 upstream of the junction P6 of the cathode gas return line L10 in the supply gas line L4 and downstream of the branch point P5 (see FIG. 2) of the discharge line L5. The supply gas flow rate control valve 59 is provided in the supply gas line L4 between the branch point P5 of the discharge line L5 and the junction P6 of the cathode gas return line L10. The supply gas flow rate control valve 59 may be controlled by a fifth control unit 61 described later, or may be manually operated without being controlled by the fifth control unit 61.

[0104] The cathode gas analyzer 60 may be configured similarly to the cathode gas analyzer 55 shown in FIG.

[0105] The cathode gas analyzer 60 analyzes the cathode gas G5 in the first cathode line L6 upstream of the branch point P3 of the bypass line L9. The cathode gas analyzer 60 is provided in the first cathode line L6 between the electrolysis device 30 and the branch point P3 of the bypass line L9.

[0106] The opening degree of the above-mentioned supply gas flow rate adjustment valve 59 may be adjusted based on the measurement results of the cathode gas analyzer 60. In this case, the flow rate of the supply gas G4 supplied to the electrolysis device 30 can be effectively adjusted.

[0107] For example, when the cathode gas analyzer 60 measures the concentration of carbon dioxide gas contained in the cathode gas G5, the aperture of the supply gas flow rate control valve 59 may be decreased as the concentration of carbon dioxide gas increases. This can reduce the flow rate of the supply gas G4 supplied to the electrolysis device 30, and the concentration of carbon dioxide gas contained in the cathode gas G5 discharged from the electrolysis device 30 can be decreased. On the other hand, the aperture of the supply gas flow rate control valve 59 may be increased as the concentration of carbon dioxide gas decreases. This can increase the flow rate of the supply gas G4 supplied to the electrolysis device 30, and the amount of carbon monoxide gas produced in the electrolysis device 30 can be increased.

[0108] 8, the cathode gas supply system 10 may further include a fifth control unit 61. The fifth control unit 61 may be incorporated in the same control device (not shown) as the other control units, or may be incorporated in a control device different from the other control units.

[0109] The fifth control unit 61 may control the supply gas flow rate adjustment valve 59 based on the analysis result of the cathode gas analyzer 60. For example, the aperture of the supply gas flow rate adjustment valve 59 may be adjusted so as to prevent a decrease in the amount of carbon monoxide gas produced and to prevent an increase in the concentration of carbon dioxide gas contained in the cathode gas G5. By the fifth control unit 61 controlling the supply gas flow rate adjustment valve 59, the aperture of the supply gas flow rate adjustment valve 59 can be appropriately and automatically adjusted.

[0110] (Eighth Modification) In the above-described embodiment, an example in which the downstream recovery device 40 and the upstream recovery device 20 share the regenerator 22 has been described. However, the embodiment is not limited to this. For example, as shown in FIG. 9, the downstream recovery device 40 may be configured independently of the upstream recovery device 20. In this case, although not shown, the downstream recovery device 40 may independently include the above-described upstream absorption tower 21, a regenerator that releases carbon dioxide gas from the rich liquid A1 discharged from the upstream absorption tower 21, and a heat exchanger. The gas containing carbon dioxide gas discharged from the regenerator of the downstream recovery device 40 will be referred to as recovered gas G7 and described below.

[0111] As shown in FIG. 9, the cathode gas supply system 10 according to this embodiment may further include a facility line L11, a recovered gas return line L12, and a recovered gas flow rate adjustment valve 62.

[0112] The equipment line L11 supplies the recovered gas G7 containing carbon dioxide gas recovered from the cathode gas G5 in the downstream recovery device 40 to the storage equipment 5. The storage equipment 5 is equipment for storing the recovered gas G7. A gas with a higher concentration of carbon dioxide gas from the recovered gas G7 may be stored in the storage equipment 5. The storage equipment 5 may be connected to the discharge line L5 described above, and the supply gas G4 that has passed through the discharge line L5 (see FIG. 2) may be supplied. In this case, the supply gas G4 may also be stored in the storage equipment 5.

[0113] The recovered gas return line L12 branches off from the equipment line L11 and supplies the recovered gas G7 to the electrolysis device 30. The recovered gas return line L12 supplies at least a portion of the recovered gas G7 discharged from the downstream recovery device 40 to the electrolysis device 30. The recovered gas return line L12 may merge with the above-mentioned supply gas line L4. The recovered gas return line L12 may merge with the supply gas line L4 downstream of the branch point P5 (see FIG. 2) of the discharge line L5 of the supply gas line L4. By supplying the recovered gas G7 to the electrolysis device 30, the carbon dioxide concentration in the gas supplied to the electrolysis device 30 can be increased. In this case, it is possible to reduce the generation of hydroxide ions that are likely to be generated by the water electrolysis reaction when the carbon dioxide gas concentration is low at the cathode electrode 34.

[0114] The recovered gas flow rate adjustment valve 62 is provided in the recovered gas return line L12. The recovered gas flow rate adjustment valve 62 adjusts the flow rate of the recovered gas G7 in the recovered gas return line L12. More specifically, the recovered gas flow rate adjustment valve 62 is configured to be adjustable in opening degree, thereby adjusting the flow rate of the recovered gas G7 passing through the recovered gas flow rate adjustment valve 62. The recovered gas flow rate adjustment valve 62 may be controlled by a sixth control unit 64 described later, but may also be manually operated without being controlled by the sixth control unit 64.

[0115] The equipment flow meter 63 measures the flow rate of the recovered gas G7 downstream of the branch point P7 of the recovered gas return line L12 in the equipment line L11. The equipment flow meter 63 is provided between the branch point P7 of the recovered gas return line L12 in the equipment line L11 and the storage equipment 5.

[0116] The aperture of the above-mentioned recovered gas flow rate adjustment valve 62 may be adjusted based on the flow rate of the recovered gas G7 measured by the equipment flow meter 63. For example, as the flow rate of the recovered gas G7 supplied to the storage equipment 5 increases, the aperture of the recovered gas flow rate adjustment valve 62 is increased. This makes it possible to prevent the flow rate of the cathode gas G5 supplied to the storage equipment 5 from becoming excessive.

[0117] 9, the cathode gas supply system 10 may further include a sixth control unit 64. The sixth control unit 64 may be incorporated in the same control device (not shown) as the other control units, or may be incorporated in a control device different from the other control units.

[0118] The sixth control unit 64 may control the recovered gas flow rate adjustment valve 62 based on the flow rate of the recovered gas G7 measured by the equipment flow meter 63. For example, the sixth control unit 64 may adjust the aperture of the recovered gas flow rate adjustment valve 62 so that the flow rate of the recovered gas G7 supplied to the storage equipment 5 does not become excessive. By the sixth control unit 64 controlling the recovered gas flow rate adjustment valve 62, the aperture of the recovered gas flow rate adjustment valve 62 can be appropriately and automatically adjusted.

[0119] The above-mentioned third modification may be incorporated into the eighth modification of the cathode gas supply system 10 shown in FIG. 9, or the above-mentioned fourth modification may be incorporated into it.

[0120] In the eighth modified example, as described above, the downstream recovery device 40 is configured independently of the upstream recovery device 20. An example has been described in which the upstream recovery device 20 and the downstream recovery device 40 absorb the carbon dioxide gas contained in the exhaust gases G1 and G3 by a chemical absorption method using an amine solution. However, the upstream recovery device 20 and the downstream recovery device 40 may each be configured to absorb the carbon dioxide gas by any method such as another chemical absorption method including DAC, a physical absorption method, a physical adsorption method, or a carbon dioxide membrane separation method. In addition, the upstream recovery device 20 and the downstream recovery device 40 may be configured to absorb the carbon dioxide gas by different methods from each other.

[0121] According to the embodiment described above, it is possible to reduce the concentration of carbon dioxide gas contained in the cathode gas generated by electrolysis.

[0122] Although an embodiment of the present invention has been described, this embodiment is presented as an example and is not intended to limit the scope of the invention. This new embodiment can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. In addition, it is of course possible to combine these modifications in part as appropriate within the gist of the present invention. [Explanation of symbols]

[0123] 1: Carbon recycle system, 3: FT synthesis device, 4: Combustion device, 5: Storage facility, 10: Cathode gas supply system, 20: Upstream recovery device, 21: Upstream absorption tower, 22: Regeneration tower, 30: Electrolysis device, 40: Downstream recovery device, 41: Downstream absorption tower, 42: Absorbent flow control valve, 50: Bypass flow control valve, 51: Downstream concentration meter, 53: Upstream concentration meter, 55: Cathode gas analyzer, 57: Cathode gas flow control valve, 59: supply gas flow rate control valve, 62: recovered gas flow rate control valve, 63: equipment flow meter, A1: rich liquid, A2: lean liquid, L6: first cathode line, L7: second cathode line, L9: bypass line, L10: cathode gas return line, L11: equipment line, L12: recovered gas return line, G1: exhaust gas, G2: tail gas, G3: exhaust gas, G4: supply gas, G5: cathode gas, G6: anode gas, G7: recovered gas

Claims

1. A cathode gas supply system for supplying a cathode gas containing carbon monoxide gas obtained by electrolyzing carbon dioxide gas to a treatment device, comprising: a carbon dioxide electrolysis device that electrolyzes the carbon dioxide gas and discharges a cathode gas containing the carbon monoxide gas and the carbon dioxide gas; a downstream carbon dioxide recovery device that recovers the carbon dioxide gas contained in the cathode gas and supplies the cathode gas to the treatment device; A cathode gas supply system comprising:

2. The carbon dioxide electrolysis device further includes an upstream carbon dioxide recovery device that recovers the carbon dioxide gas from the exhaust gas containing the carbon dioxide gas and supplies the carbon dioxide gas to the carbon dioxide electrolysis device. The cathode gas supply system of claim 1 .

3. the upstream carbon dioxide capture unit includes an upstream absorption tower that absorbs the carbon dioxide gas contained in the exhaust gas into an absorption liquid, and a regeneration tower that releases the carbon dioxide gas from the absorption liquid that has absorbed the carbon dioxide gas in the upstream absorption tower and supplies the carbon dioxide gas to the carbon dioxide electrolysis device, the downstream carbon dioxide capture unit includes a downstream absorption tower that absorbs the carbon dioxide gas contained in the cathode gas into the absorption liquid and supplies the cathode gas to the treatment unit, The absorption liquid having absorbed the carbon dioxide gas in the downstream absorption tower is supplied to the regeneration tower of the upstream carbon dioxide capture device. The cathode gas supply system of claim 2 .

4. a bypass line that supplies a portion of the cathode gas discharged from the carbon dioxide electrolysis device to the treatment device, bypassing the downstream carbon dioxide recovery device; a bypass flow rate regulating valve that regulates a flow rate of the cathode gas in the bypass line; Further equipped with 3. The cathode gas supply system according to claim 1 or 2.

5. a second cathode line that supplies the cathode gas from the downstream carbon dioxide capture device to the treatment device, the second cathode line being joined by the bypass line; A downstream carbon dioxide concentration meter that measures a concentration of the carbon dioxide gas contained in the cathode gas downstream of a junction point of the second cathode line and the bypass line, The cathode gas supply system according to claim 4 .

6. The carbon dioxide electrolysis device further includes an upstream carbon dioxide concentration meter that measures the concentration of the carbon dioxide gas contained in the cathode gas discharged from the carbon dioxide electrolysis device.

3. The cathode gas supply system according to claim 1 or 2.

7. The downstream carbon dioxide capture unit includes an absorption liquid flow rate control valve that adjusts the flow rate of the absorption liquid supplied to the downstream absorption tower. The cathode gas supply system according to claim 3 .

8. a cathode gas analyzer that measures at least one of a concentration of the carbon dioxide gas contained in the cathode gas supplied to the downstream carbon dioxide capture device and a flow rate of the cathode gas; The cathode gas supply system of claim 7 further comprising:

9. a cathode gas return line that supplies a portion of the cathode gas discharged from the carbon dioxide electrolysis device to the carbon dioxide electrolysis device; a cathode gas flow rate regulating valve that regulates a flow rate of the cathode gas in the cathode gas return line; Further equipped with 3. The cathode gas supply system according to claim 1 or 2.

10. a first cathode line that supplies the cathode gas discharged from the carbon dioxide electrolysis device to the downstream carbon dioxide recovery device, the first cathode line being branched off from the cathode gas return line; A cathode gas analyzer that analyzes the cathode gas in the first cathode line downstream of a branch point of the cathode gas return line. The cathode gas supply system of claim 9.

11. a supply gas flow rate regulating valve for regulating a flow rate of the supply gas containing the carbon dioxide gas to be supplied to the carbon dioxide electrolysis device; The cathode gas supply system according to claim 1 or 2, further comprising:

12. a cathode gas analyzer that measures a concentration of the carbon dioxide gas contained in the cathode gas discharged from the carbon dioxide electrolysis device; The cathode gas supply system of claim 11 further comprising:

13. an equipment line that supplies a recovered gas containing the carbon dioxide gas recovered from the cathode gas in the downstream carbon dioxide recovery device to a storage facility; a recovered gas return line branching off from the equipment line and supplying the recovered gas to the carbon dioxide electrolysis device; a recovered gas flow rate regulating valve for regulating the flow rate of the recovered gas in the recovered gas return line; an equipment flow meter that measures a flow rate of the recovered gas in the equipment line downstream of a branch point of the recovered gas return line; The cathode gas supply system according to claim 1 or 2, further comprising:

14. A cathode gas supply system according to claim 1 or 2; A treatment device for treating the carbon monoxide gas contained in the cathode gas supplied from the cathode gas supply system. Carbon recycling system.

15. a carbon dioxide generator that generates the carbon dioxide gas from an anode gas containing the carbon dioxide gas and oxygen gas discharged from the carbon dioxide electrolysis device and a tail gas containing a hydrocarbon gas discharged from the treatment device, The carbon dioxide gas generated in the carbon dioxide generation device is supplied to the carbon dioxide electrolysis device. The carbon recycling system of claim 14.

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