Carbon dioxide conversion device and carbon dioxide conversion method

Abstract

To improve efficiency in utilizing carbon dioxide.SOLUTION: A carbon dioxide conversion device includes: a carbon dioxide supply unit for supplying a supply gas including a carbon dioxide gas; a flow rate adjustment unit including a plurality of flow rate adjustment valves for distributing the supply gas supplied from the carbon dioxide supply unit; an electrolysis unit including a plurality of electrolysis cell stacks receiving / supplying the supply gas distributed via the plurality of flow rate adjustment valves; a voltage measurement unit including a plurality of voltmeters for measuring a voltage of each of the plurality of electrolysis cell stacks; and a control unit for receiving a voltage signal from each of the plurality of voltmeters to adjust an opening degree of each of the plurality of flow rate adjustment valves.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE Embodiments of the present invention relate to a carbon dioxide conversion apparatus and method. [Background technology]

[0002] With the progress of global warming, there is a demand for a reduction in the use of natural gas, coal, and oil, which generate carbon dioxide (CO2). In addition, the development of chemical synthesis using carbon dioxide as a raw material is being promoted. As a part of this, there is a carbon dioxide conversion device that electrolyzes carbon dioxide to generate a gas containing carbon monoxide (CO). The carbon dioxide conversion device has a plurality of electrolytic cell stacks, and each electrolytic cell stack is formed by stacking a plurality of electrolytic cells. In an electrolytic cell stack in which the amount of carbon dioxide supplied is insufficient relative to the load current, the amount of hydrogen generated increases, and the power load increases due to the increase in voltage. On the other hand, in an electrolytic cell stack in which the amount of carbon dioxide supplied is excessive relative to the load current, the amount of unreacted carbon dioxide increases, and the carbon monoxide transfer rate decreases. To solve these problems, a carbon dioxide conversion device and a carbon dioxide conversion method that equalize the amount of carbon dioxide supplied to each electrolytic cell stack are required.

[0003] However, in the carbon dioxide conversion apparatuses that have been considered so far, the supplied carbon dioxide is distributed to each electrolytic cell stack from a distribution pipe installed upstream of each electrolytic cell stack, and the distribution ratio is determined on an ongoing basis. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-137607 A Summary of the Invention [Problem to be solved by the invention]

[0005] The problem to be solved by the present invention is to improve the efficiency of carbon dioxide utilization. [Means for solving the problem]

[0006] The carbon dioxide conversion device of the embodiment includes a carbon dioxide supply unit that supplies a supply gas containing carbon dioxide gas, a flow control unit including a plurality of flow control valves that distribute the supply gas supplied from the carbon dioxide supply unit, an electrolysis unit that includes a plurality of electrolytic cell stacks that receive the supply gas distributed via the plurality of flow control valves, a voltage measurement unit that includes a plurality of voltmeters that measure the voltages of the plurality of electrolytic cell stacks, and a control unit that adjusts the opening degrees of the plurality of flow control valves in response to voltage signals from the plurality of voltmeters. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing a configuration example of a carbon dioxide conversion apparatus according to an embodiment. [Diagram 2] 2 is a diagram for further illustrating an example of the configuration of some of the components shown in FIG. 1. FIG. [Diagram 3] FIG. 2 is a schematic cross-sectional view showing an example of the structure of an electrolysis cell laminate CS. [Figure 4] 10 is a flowchart for explaining an example of a method for adjusting the opening degree of each flow rate regulating valve FC in an example of a carbon dioxide conversion method. [Diagram 5] FIG. 13 is a diagram showing the relationship between the increase rate of the flow rate of the supply gas and the voltage Vi. [Figure 6] FIG. 4 is a graph showing the relationship between the rate of increase in the flow rate of the supply gas and the amount of carbon monoxide produced. [Figure 7] 13 is a flowchart for explaining another example of a method for adjusting the opening degree of each flow rate regulating valve FC in the example of the carbon dioxide conversion method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the carbon dioxide conversion device of the embodiment will be described with reference to the drawings. In each embodiment shown below, the substantially same components are given the same reference numerals, and the description thereof may be partially omitted. The drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each part, etc. may differ from the actual ones.

[0009] In this specification, "connect" includes not only direct connection but also indirect connection unless otherwise specified. Furthermore, in this specification, "connect" includes not only physical connection but also electrical connection unless otherwise specified.

[0010] A configuration example of a carbon dioxide conversion apparatus according to an embodiment will be described below. Fig. 1 is a schematic diagram showing a configuration example of a carbon dioxide conversion apparatus according to an embodiment. Fig. 1 shows a carbon dioxide conversion apparatus 100.

[0011] The carbon dioxide conversion device 100 includes a carbon dioxide supply unit (CO2 supply unit) 1, a flow rate adjustment unit 2, an electrolysis unit 3, a voltage measurement unit 4, a control unit 5, a power source 6, a cooler 7, a gas-liquid separator 8, a purification unit 9, a gas-liquid separator 10, a cooler 11, a gas-liquid separator 12, a water removal unit (H2O removal unit) 13, a carbon dioxide capture unit (CO2 capture unit) 14, a cooler 15, a tank 16, and a pump 17.

[0012] Fig. 2 is a diagram for further explaining an example of the configuration of some of the components shown in Fig. 1. Fig. 2 shows a carbon dioxide supply unit 1, a flow rate adjustment unit 2, an electrolysis unit 3, a voltage measurement unit 4, and a control unit 5.

[0013] The carbon dioxide supply unit 1 includes, for example, a carbon dioxide supply source SS. The carbon dioxide supply source SS can supply, for example, a supply gas containing carbon dioxide gas to the electrolysis unit 3. The carbon dioxide supply unit 1 is connected to the electrolysis unit 3 via, for example, a flow rate adjustment unit 2. The carbon dioxide conversion device may have a humidifier that humidifies the carbon dioxide gas from the carbon dioxide supply source SS, and supply the gas humidified by the humidifier to the electrolysis unit 3.

[0014] The carbon dioxide supply source SS can separate and recover carbon dioxide gas from exhaust gas (CO2-containing gas) containing carbon dioxide gas discharged from facilities such as thermal power plants, waste incineration plants, and steelworks, and supply the separated supply gas containing carbon dioxide gas to the electrolysis unit 3. The carbon dioxide supply unit 1 can use methods such as a chemical absorption method using a chemical absorption liquid such as an amine aqueous solution, a physical absorption method using a physical absorption liquid such as methanol or a polyethylene glycol solution, a solid absorption method using a solid absorbent such as an amine compound, a membrane separation method using a carbon dioxide separation membrane, a physical adsorption method using an inorganic material such as zeolite as an adsorbent, a pressure swing adsorption (PSA) method, and a thermal swing adsorption (TSA) method. For example, a chemical absorption method and device using an amine aqueous solution can supply exhaust gas to an absorption tower where an amine aqueous solution is sprayed, and the amine aqueous solution that has absorbed carbon dioxide can be heated in a regeneration tower to recover carbon dioxide released from the amine aqueous solution. The carbon dioxide supply source SS can apply various methods and devices that can recover carbon dioxide from exhaust gas (CO2-containing gas).

[0015] The flow rate adjustment unit 2 includes, for example, a flow rate adjustment valve FC. The flow rate adjustment valve FC can adjust the flow rate of the supply gas from the carbon dioxide supply source SS. The flow rate adjustment unit 2 includes a plurality of flow rate adjustment valves FC. The plurality of flow rate adjustment valves FC are provided, for example, in the middle of a plurality of pipes that branch off midway from the carbon dioxide supply unit 1 to the electrolysis unit 3, and can distribute the supply gas from the carbon dioxide supply unit 1. FIG. 2 shows flow rate adjustment valves FC1, FC2, FC3, FC4, and FC5 as the plurality of flow rate adjustment valves FC, but the number of the plurality of flow rate adjustment valves FC may be n-1 (n is a natural number of 2 or more) and is not limited to the number shown in FIG. 2.

[0016] The electrolysis unit 3 includes, for example, an electrolysis cell stack CS. The electrolysis cell stack CS can receive, for example, a supply gas distributed from the flow rate control unit 2 and a supply liquid supplied from the tank 16 via a pump 17. The electrolysis cell stack CS can perform, for example, an electrolysis reaction using a supply gas and a supply liquid. The electrolysis unit 3 includes a plurality of electrolysis cell stacks CS. FIG. 2 shows electrolysis cell stacks CS1, CS2, CS3, CS4, CS5, and CS6 as the plurality of electrolysis cell stacks CS, but the number of the plurality of electrolysis cell stacks CS may be n (n is a natural number of 2 or more) and is not limited to the number shown in FIG. 2. For example, the carbon dioxide conversion device may not have a flow rate control valve FC corresponding to the n-th electrolysis cell stack CS. The n-th electrolysis cell stack CS may not be connected to any flow rate control valve FC. The electrolysis cell stack CS1 is connected to a flow rate control valve FC1. The electrolysis cell stack CS2 is connected to a flow rate control valve FC2. The electrolysis cell stack CS3 is connected to a flow rate control valve FC3. The electrolytic cell stack CS4 is connected to a flow control valve FC4. The electrolytic cell stack CS5 is connected to a flow control valve FC5. The electrolytic cell stack CS6 is connected to a pipe from the carbon dioxide supply unit 1 to the electrolysis unit 3, and is not connected to any of the flow control valves FC.

[0017] Fig. 3 is a cross-sectional schematic diagram showing a structural example of an electrolysis cell laminate CS. The electrolysis cell laminate CS shown in Fig. 3 has a cathode 21, an anode 22, a diaphragm 23, and a flow path plate 24. Fig. 3 shows an X-axis, a Y-axis, and a Z-axis. The X-axis, the Y-axis, and the Z-axis perpendicularly intersect with each other. The Z-axis is along the thickness direction of the carbon dioxide electrolysis cell 20. Fig. 3 shows a part of an XZ cross section including the X-axis and the Z-axis. Fig. 3 shows a plurality of cathodes 21, a plurality of anodes 22, a plurality of diaphragms 23, and a plurality of flow path plates 24.

[0018] The cathode 21, the anode 22, and the diaphragm 23 are stacked in the Z-axis direction, for example, to form the carbon dioxide electrolysis cell 20.

[0019] Examples of the electrolysis cell stack CS include a carbon dioxide electrolysis cell stack. The electrolysis cell stack CS has, for example, a plurality of carbon dioxide electrolysis cells 20. The plurality of carbon dioxide electrolysis cells 20 are stacked with a flow path plate 24 sandwiched therebetween. The plurality of carbon dioxide electrolysis cells 20 may be disposed, for example, between a plurality of supports (not shown). The number of stacked carbon dioxide electrolysis cells 20 is not particularly limited, but is, for example, eight or more.

[0020] The cathode 21 is connected to the power source 6, for example, via a cathode current collector provided at an end of the electrolysis cell stack CS. The cathode 21 can, for example, reduce carbon dioxide to produce carbon compounds such as carbon monoxide. The cathode 21 further includes, for example, a catalyst that promotes the electrolysis reaction. The catalyst is supported on the surface of a conductive substrate such as a metal. The catalyst may form a catalyst layer provided on the surface of the conductive substrate.

[0021] The anode 22 is connected to the power source 6, for example, via an anode current collector provided at an end of the electrolysis cell stack CS. The anode 22 can, for example, oxidize water to generate oxygen gas. The anode 22 further includes, for example, a catalyst that promotes the electrolysis reaction. The catalyst is supported on the surface of a conductive substrate such as a metal. The catalyst may form a catalyst layer provided on the surface of the conductive substrate.

[0022] The diaphragm 23 is disposed, for example, between the cathode 21 and the anode 22. The diaphragm 23 may be provided in contact with each of the cathode 21 and the anode 22. The diaphragm 23 is, for example, a hydrogen ion (H + ), hydroxide ion (OH - ), carbonate ion (CO3 2- ), hydrogen carbonate ion (HCO3 - The diaphragm 23 includes, for example, at least an ion exchange membrane or a porous membrane.

[0023] The flow path plate 24 is provided to separate the two carbon dioxide electrolysis cells 20. The flow path plate 24, for example, can isolate the atmospheres of the adjacent carbon dioxide electrolysis cells 20. The flow path plate 24 can be formed using a material such as a metal, a carbon material, or a conductive ceramic.

[0024] The flow path plate 24 has a flow path 24a and a flow path 24b. The shapes of the flow paths 24a and 24b are not limited to the shapes shown in Fig. 3. The shapes of the flow paths 24a and 24b may be serpentine or rectangular on the surfaces of the flow path plate 24 facing the cathode 21 and the anode 22, respectively.

[0025] The flow path 24a is provided on the surface of the flow path plate 24 on the cathode 21 side, and faces the cathode 21. The flow path 24a can pass, for example, a supply gas or a fluid containing reduction products such as carbon compounds. The flow path 24a can form, for example, a cathode chamber. The flow path 24a has, for example, an inlet connected to the flow rate control valve FC, and an outlet from which a fluid (cathode fluid) containing carbon compounds such as carbon monoxide is discharged.

[0026] The flow path 24b is provided on the surface of the flow path plate 24 on the anode 22 side (opposite to the flow path 24a) and faces the anode 22. The flow path 24b can pass, for example, a supply liquid or a fluid containing an oxidation product such as water, oxygen gas, or carbon dioxide gas. The flow path 24b can form, for example, an anode chamber. The flow path 24b has, for example, an inlet connected to the pump 17 and an outlet from which a fluid containing oxygen (anode fluid) is discharged.

[0027] The supply liquid includes, for example, an electrolyte. An example of the electrolyte is a solution using water (H2O), for example, an aqueous solution containing any electrolyte. An example of the aqueous solution containing an electrolyte is a solution containing phosphate ions (PO4 2- ), borate ion (BO3 3- ), sodium ion (Na + ), potassium ion (K + ), calcium ion (Ca 2+ ), lithium ion (Li +), Cesium ion (Cs + ), magnesium ion (Mg 2+ ), chloride ion (Cl - ), hydrogen carbonate ion (HCO3 - ), carbonate ion (CO3 2- ), hydroxide ion (OH - ) and the like. Examples of the electrolyte include an alkaline aqueous solution in which KOH, KHCO3, K2CO3, and the like are dissolved.

[0028] The voltage measurement unit 4 includes, for example, a voltmeter VM. The voltmeter VM can measure, for example, the voltage applied to the electrolytic cell stack CS during electrolysis operation. The voltage measurement unit 4 can transmit the voltage measured by the voltmeter VM as a data signal to the control unit 5. The voltage measurement unit 4 includes multiple voltmeters VM. FIG. 2 shows voltmeters VM1, VM2, VM3, VM4, VM5, and VM6 as the multiple voltmeters VM, but the number of multiple voltmeters VM may be n (n is a natural number equal to or greater than 2) and is not limited to the number shown in FIG. 2. The voltmeter VM may be provided, for example, for each electrolytic cell stack CS.

[0029] The control unit 5 includes, for example, a control device CT. The control device CT can receive a data signal (voltage signal) indicating the measured voltage from the multiple voltmeters VM. The control device CT can control the opening of the multiple flow rate control valves FC using the measured voltage data included in the voltage signal. The control device CT can generate and output a control signal for controlling the opening of the flow rate control valve FC according to the measured voltage, for example. The dotted arrows shown in FIG. 2 indicate control signals. The control device CT can generate, for example, multiple control signals. Each control signal can control the opening of the flow rate control valve FC corresponding to the voltage measured by each voltmeter VM. The control device CT is connected, for example, to each of the multiple flow rate control valves FC by wired or wireless connection. The control device CT may be connected, for example, to at least one of the carbon dioxide supply source SS and the electrolysis cell stack CS by wired or wireless connection, and control the operation of at least one of the carbon dioxide supply source SS and the electrolysis cell stack CS.

[0030] The control device CT has hardware having an arithmetic unit such as a processor, etc. Each operation may be stored as an operation program in a computer-readable recording medium such as a memory, and each operation may be executed by appropriately reading the operation program stored in the recording medium by the hardware.

[0031] The remaining components of the carbon dioxide conversion system 100 will now be further described with reference to FIG.

[0032] The power source 6 can, for example, supply a load current to each electrolysis cell stack CS. The power source 6 can, for example, be electrically connected to each of the cathodes 21 and anodes 22 of the electrolysis cell stack CS and supply a current to the electrolysis cell stack CS via the cathode current collector and the anode current collector.

[0033] The cooler 7 can cool the cathode fluid discharged from the flow path 24a to a predetermined temperature, for example. The cooler 7 may be connected to each flow path 24a, or may be connected to a connection point of the multiple flow paths 24a when the multiple flow paths 24a are connected to each other to form one cathode discharge flow path.

[0034] The gas-liquid separator 8 can, for example, treat the cathode fluid to separate water from the cathode fluid. The gas-liquid separator 8 is connected, for example, to the rear stage of the cooler 7.

[0035] The purification unit 9 can separate carbon compounds such as carbon monoxide from the cathode fluid, for example, by purifying the cathode fluid treated by the gas-liquid separator 8. The purification unit 9 is connected to the rear stage of the gas-liquid separator 8, for example.

[0036] The purification unit 9 can generate the cathode fluid by using, for example, a pressure swing adsorption (CO-PSA) method using a copper ion-zeolite adsorbent, a copper ion-activated carbon adsorbent, a copper chloride-aluminum-crosslinked polystyrene solid adsorbent, a copper chloride-aluminum-activated carbon adsorbent, or the like, a cuprammonium washing method, a copper chloride-aluminum complex solution absorption method, a copper chloride-aluminum-polystyrene polymer complex solution absorption method, a cryogenic method, or the like. The purified cathode fluid is stored in a storage container such as a tank (not shown), or is sent to an organic synthesis reactor such as a methane synthesis reactor, an alcohol synthesis reactor, or a Fischer-Tropsch reactor, which reacts carbon monoxide with hydrogen. These organic synthesis reactors may be used instead of the purification unit 9 to which the CO-PSA or the like is applied. The purified residual gas after purifying the cathode fluid is discharged from the purification unit 9. The purified residual gas may contain remaining gases such as carbon monoxide, hydrogen, and carbon dioxide.

[0037] The gas-liquid separator 10 can process the anode fluid discharged from the flow path 24b and separate gases such as oxygen and carbon dioxide from the anode fluid. The gas-liquid separator 10 may be connected to each flow path 24b, for example, or may be connected to a connection point of the multiple flow paths 24b when the multiple flow paths 24b are connected to each other to form one anode discharge flow path.

[0038] The cooler 11 can cool, for example, a fluid containing gases such as oxygen and carbon dioxide separated from the anode fluid by the gas-liquid separator 10 to a predetermined temperature. The cooler 11 is connected, for example, to a stage subsequent to the gas-liquid separator 10.

[0039] The gas-liquid separator 12 can, for example, process the fluid cooled by the cooler 11 to separate oxygen gas from the cooled fluid. The fluid processed by the gas-liquid separator 12 may be supplied to a tank 16.

[0040] The water removal unit 13 can, for example, treat a fluid containing oxygen gas and carbon dioxide separated by the gas-liquid separator 12 to remove water remaining in the fluid. The water removal unit 13 is, for example, connected to the rear stage of the gas-liquid separator 12. The water removal unit 13 has, for example, a water vapor removal polymer membrane or a water vapor adsorbent such as zeolite, silica gel, mesoporous silica, or activated carbon.

[0041] The carbon dioxide capture unit 14 can, for example, treat the fluid treated by the water removal unit 13 to remove the carbon dioxide contained in the fluid. This makes it possible to capture carbon dioxide. The fluid treated by the carbon dioxide capture unit 14 may contain oxygen. The carbon dioxide capture unit 14 is connected, for example, to the rear stage of the water removal unit 13. The carbon dioxide capture unit 14 has, for example, a carbon dioxide adsorbent. Examples of the carbon dioxide adsorbent include primary or secondary amine supports, FAU type zeolites, GIS type zeolites, Co-MOFs (Metal Organic Frameworks) obtained by using 1,4-benzenedicarbohydroxamic acid as an organic ligand and isonicotinic acid as an auxiliary ligand and reacting them with cobalt nitrate, ZIF-69 (CAS No. 1018477-10-5, chemical formula: C 10 Carbon dioxide can be separated and captured using adsorbents such as H6N5O2ClZn, Cubic[Zn4O(piperazine dicarbamate)3], etc., using the Pressure Swing Adsorption (PSA) method or the Temperature Swing Adsorption (TSA) method, depending on the adsorbent.

[0042] The carbon dioxide capture unit 14 may use an organic semiconductor such as a porous material of tetracyanoquinodimethane (CAS No. 1518-16-7, chemical formula: (NC)2CC6H4C(CN)2) as an oxygen adsorbent, separate and capture oxygen by pressure swing adsorption (PSA) or temperature swing adsorption (TSA), and capture carbon dioxide as a result. The carbon dioxide capture unit 14 may use a Faradaic electro-swing reactive adsorption method in which poly-1,4-anthraquinone is used as a carbon dioxide adsorption electrode and polyvinylferrocene is used as a counter electrode.

[0043] The cooler 15 can, for example, cool the anode fluid treated by the gas-liquid separator 10 to a predetermined temperature. The cooler 15 is connected to the rear stage of the gas-liquid separator 10, for example.

[0044] The tank 16 can accommodate, for example, an anode fluid cooled by the cooler 15. The anode fluid cooled by the cooler 15 includes, for example, water and an electrolyte. The tank 16 is connected, for example, to a stage subsequent to the cooler 15. The tank 16 may be connected to a make-up water tank. The anode fluid accommodated in the tank may be replenished with water by receiving water from the make-up water tank.

[0045] The pump 17 can supply, for example, an anode fluid contained in the tank 16 as a supply liquid to each flow path 24b of the electrolysis unit 3. The pump 17 is provided, for example, midway through a circulation flow path that connects the tank 16 and the inlets of each flow path 24b.

[0046] The carbon dioxide conversion apparatus shown in FIG. 1 may appropriately include devices such as a blower, a pump, a compressor, etc., and these devices may control the flow of fluids such as gases and liquids.

[0047] Next, a description will be given of an example of a carbon dioxide conversion method using a carbon dioxide conversion apparatus having the configuration shown in Figure 1 and Figure 2. Here, an example of producing carbon monoxide as a carbon compound will be described.

[0048] In the example of the carbon dioxide conversion method, in each electrolytic cell stack CS, a supply gas containing carbon dioxide gas distributed from the carbon dioxide supply unit 1 by the flow rate adjustment unit 2 is supplied to each flow path 24a via the inlet of each flow path 24a, a supply liquid containing an electrolyte is supplied from the tank 16 using the pump 17 to each flow path 24b via the inlet of each flow path 24b, and a current is supplied from the power source 6. This allows an electrolytic reaction to occur in each of the cathode 21 and the anode 22.

[0049] Carbon dioxide supplied to each flow path 24a is converted into carbon monoxide and hydroxide ions by an electrolytic reaction at the cathode 21. This reaction is represented by the following formula (1). CO2+2H2O+2e - → CO+2OH - (1)

[0050] Water in the electrolyte is converted into hydrogen and hydroxide ions by an electrolytic reaction at the cathode 21. This reaction is represented by the following formula (2). 2H2O+2e - →H2+2OH - (2)

[0051] The hydroxide ions produced by the electrolytic reaction represented by formula (2) react with carbon dioxide to produce carbonate ions and water. This reaction is represented by the following formula (3). CO2+2OH - →CO3 2- +H2O···(3)

[0052] The produced carbonate ions are converted into carbon dioxide and oxygen by an electrolytic reaction at the anode 22. This reaction is represented by the following formula (4). CO3 2- →CO2+0.5O2+2e - (4)

[0053] Unreacted hydroxide ions that are not used in the reaction to produce carbonate ions represented by formula (3) are converted to water and oxygen by an electrolytic reaction at the anode 22. This reaction is represented by the following formula (5). 2OH - →H2O+0.5O2+2e - (5)

[0054] The carbon monoxide and hydrogen produced in the cathode 21 are discharged as cathode fluid from each flow channel 24a together with unreacted carbon dioxide via the outlet of each flow channel 24a.

[0055] Carbon dioxide, oxygen, and water produced at the anode 22 are discharged as an anode fluid together with the electrolyte from each flow channel 24a via the outlet of each flow channel 24b.

[0056] If an equal load current flows through the multiple electrolytic cell stacks CS, the flow rate FR of the supply gas containing carbon dioxide gas supplied from the carbon dioxide supply unit 1 is CO2 (mol / s) and the load current I (A) of the electrolytic cell stack CS are controlled to satisfy the relationship expressed by the following equation (6). FR CO2 = mnIU CO2 / F···(6)

[0057] In formula (6), m represents the number of stacked carbon dioxide electrolysis cells 20 in the electrolysis cell stack CS, n represents the number of electrolysis cell stacks CS, U CO2 represents the theoretical flow rate ratio of the supply gas containing carbon dioxide gas, and F represents the Faraday constant (96485 C / mol). Note that the flow rate FR of the supply gas to one electrolytic cell stack CS is CO2 Depending on / n, the opening degree of the corresponding flow rate regulating valve FC is set to the set initial value. CO2、Alternatively, a load current I having a theoretical current value according to the flow rate of the supply gas is given as a set value. For example, a supply gas having a flow rate according to the sum of the load currents of the multiple electrolytic cell stacks CS is distributed and supplied to the multiple electrolytic cell stacks CS, or a uniform load current having a theoretical current value according to the flow rate of the supply gas supplied from the carbon dioxide supply unit 1 is supplied to the multiple electrolytic cell stacks CS. The carbon dioxide supply unit 1 supplies a flow rate FR CO2 The power supply 6 has a function of maintaining a set value of the load current I. When the set value is changed, the change is made at a preset time interval, and the opening degree of each flow rate regulating valve FC is changed in accordance with the new set value.

[0058] FIG. 4 is a flow chart for explaining an example of a method for adjusting the opening degree of each flow control valve FC in an example of a carbon dioxide conversion method. As shown in FIG. 4, the voltage Vi of each electrolytic cell stack CS is measured by a corresponding voltmeter VM to generate a voltage signal (data signal), and an average voltage (average stack voltage) Vmean of the voltages Vi applied to the multiple electrolytic cell stacks CS is calculated from data indicating the measured voltage Vi contained in the generated voltage signal (step S1). For example, the voltage Vi of the electrolytic cell stack CS1 is measured by a voltmeter V1, the voltage Vi of the electrolytic cell stack CS2 is measured by a voltmeter V2, and the voltages Vi of the electrolytic cell stacks CS3, CS4, and CS5 are measured by voltmeters V3, V4, and V5, respectively. The voltage measurement unit 4 may measure the voltage Vi of at least one electrolytic cell stack CS in sequence, or may simultaneously measure the voltages Vi of multiple electrolytic cell stacks CS. The average voltage Vmean may be calculated, for example, by receiving a voltage signal from the control unit 5, or may be calculated by a calculation device such as a personal computer connected to the control unit 5. The average voltage Vmean is obtained by dividing the sum of the voltages Vi by the number of electrolytic cell stacks CS, and is expressed, for example, by the following equation (7). Vmean = ΣVi / n (7)

[0059] Next, in the control unit 5, a value of 1 is input to the numerical value i representing the target electrolytic cell stack CS (i = 1) (step S2). This indicates that the target electrolytic cell stack CS is the first-stage electrolytic cell stack CS1.

[0060] Next, the voltage Vi of the target electrolytic cell stack CS and the average voltage Vmean are compared (step S3). When i = 1, the voltage Vi of the electrolytic cell stack CS1 and the average voltage Vmean are compared. The above comparison is performed, for example, by calculating the difference (Vi - Vmean) between the voltage Vi and the average voltage Vmean. The above calculation may be performed, for example, by the control unit 5, or may be performed by an arithmetic device such as a personal computer connected to the control unit 5.

[0061] When the value of the voltage Vi is greater (higher) than the value of the average voltage Vmean (S3: Vi > Vmean), the opening degree of the flow rate adjustment valve FC corresponding to the target electrolytic cell stack CS is increased (step S4-1). Thereby, the flow rate of the supply gas supplied to the target electrolytic cell stack CS can be increased. For example, when the voltage Vi of the electrolytic cell stack CS1 is greater than the average voltage Vmean, the opening degree of the flow rate adjustment valve FC1 can be increased to increase the flow rate of the supply gas supplied to the electrolytic cell stack CS1. The increased amount of the supply gas is appropriately set, for example, so that the supply gas supplied to the target electrolytic cell stack CS is used without excess or deficiency.

[0062] When the value of the voltage Vi is smaller (lower) than the value of the average voltage Vmean (S3: Vi < Vmean), the opening degree of the flow rate adjustment valve FC corresponding to the target electrolytic cell stack CS is decreased (step S4-2). Thereby, the flow rate of the supply gas supplied to the target electrolytic cell stack CS can be decreased. For example, when the voltage Vi of the electrolytic cell stack CS1 is smaller than the average voltage Vmean, the opening degree of the flow rate adjustment valve FC1 can be decreased to decrease the flow rate of the supply gas supplied to the electrolytic cell stack CS1. The decreased amount of the supply gas is appropriately set, for example, so that the supply gas supplied to the target electrolytic cell stack CS is used without excess or deficiency.

[0063] If the value of the voltage Vi is equal to the average voltage Vmean (S3: Vi=Vmean), the aperture of the flow control valve FC corresponding to the target electrolytic cell stack CS is not changed (step S4-3). For example, if the voltage Vi of the electrolytic cell stack CS1 is equal to the average voltage Vmean, the aperture of the flow control valve FC1 is maintained unchanged.

[0064] FIG. 5 is a diagram showing the relationship between the rate of increase in the flow rate of the supply gas and the voltage Vi. A and another electrolytic cell stack CS B 4 shows the relationship between the rate of increase in the flow rate of each of the supply gases and the voltage Vi. The voltage Vi is a normalized value, and the value of the voltage Vi based on the specifications of the electrolytic cell stack CS is set to 1.000.

[0065] As shown in FIG. 5, the voltage Vi of the electrolysis cell stack CS increases with an increase in the flow rate of the supply gas. A In the case of the electrolysis cell stack CS, it is preferable to reduce the opening of the corresponding flow control valve FC to reduce the flow rate of the supply gas until the voltage Vi value becomes equal to the reference value. The reference value is, for example, 1.000. As shown in FIG. 5, the electrolysis cell stack CS has a voltage Vi that decreases with an increase in the flow rate of the supply gas. B It is preferable to decrease the opening of the corresponding flow rate regulating valve FC to decrease the flow rate of the supply gas until the value of the voltage Vi reaches the reference value.

[0066] Fig. 6 is a graph showing the relationship between the rate of increase in the flow rate of the supply gas and the amount of carbon monoxide produced. A and another electrolytic cell stack CS B The relationship between the increase rate of the flow rate of each supply gas and the amount of carbon monoxide generated is shown in FIG. The amount of carbon monoxide generated is a normalized value, and the value of the amount of carbon monoxide generated based on the specifications of the electrolysis cell stack CS is set to 1.000.

[0067] As shown in Figure 6, the amount of carbon monoxide produced increases with increasing supply gas flow rate. AIn the case of the electrolysis cell stack CS, it is preferable to reduce the opening of the corresponding flow control valve FC so that the flow rate of the supply gas is reduced until the amount of carbon monoxide generated reaches a reference value. The reference value is, for example, 1.000. As shown in FIG. 6, the amount of carbon monoxide generated decreases with an increase in the flow rate of the supply gas. B It is preferable to reduce the opening of the corresponding flow rate regulating valve FC to reduce the flow rate of the supply gas until the amount of carbon monoxide produced reaches the reference value.

[0068] Next, the control unit 5 adds 1 to the numerical value i (i=i+1) (step S5). This indicates that the target electrolysis cell stack CS transitions to the next electrolysis cell stack CS.

[0069] Next, it is determined whether i=n, ​​i.e., whether the subject electrolysis cell stack CS is the n-th electrolysis cell stack CS (step S6). This determination may be performed, for example, by the control unit 5 or by a calculation device such as a personal computer connected to the control unit 5.

[0070] If i=n is not satisfied (S6: NO), the process returns to step S3, and the same steps as for the electrolytic cell stack CS1 are performed on the next target electrolytic cell stack CS. For example, after steps S1 to S3 are performed on the electrolytic cell stack CS1, steps S1 to S3 are performed on the next electrolytic cell stack CS2. This process is repeated up to the (n-1)th electrolytic cell stack CSn-1.

[0071] If i=n (S6: YES), the adjustment is completed, and the process ends. The above is an explanation of the carbon dioxide conversion method. The opening degree of each flow rate control valve FC shown in FIG. 4 may be adjusted periodically at predetermined time intervals.

[0072] In the carbon dioxide conversion device of the embodiment, the flow rate of the supply gas supplied to the electrolytic cell stacks CS can be adjusted by adjusting the aperture of the corresponding flow control valve FC in accordance with the voltage of the electrolytic cell stack CS. This allows the electrolytic cell stacks CS to be supplied with just the right amount of carbon dioxide gas, thereby improving the efficiency of carbon dioxide use in the electrolytic cell stacks CS.

[0073] The method of adjusting the aperture of the flow control valve FC is not limited to the method represented by the flowchart shown in Fig. 4. Fig. 7 is a flowchart for explaining another example of the method of adjusting the aperture of each flow control valve FC in the carbon dioxide conversion method example. The flowchart shown in Fig. 7 differs from the flowchart shown in Fig. 4 in that it has step S7 instead of step S3 and step S4 (S4-1, S4-2, S4-3). Below, the parts of the other example of the method of adjusting the aperture of each flow control valve FC that differ from the flowchart shown in Fig. 4 will be explained, and the explanation of the flowchart shown in Fig. 4 can be used as appropriate for the other parts.

[0074] In step S7, if the flow control valve FC has a linear characteristic (characteristic in which the CV value is proportional to the valve opening), the opening of the flow control valve FC is adjusted in each electrolytic cell stack CS so that it is proportional to the ratio Vi / Vmean of the voltage Vi to the average voltage Vmean (opening * Vi / Vmean). This operation is repeated up to the n-1th electrolytic cell stack CSn-1. This allows the flow rate of the supply gas supplied to the multiple electrolytic cell stacks CS to be adjusted. The flow rate of the supply gas supplied to the electrolytic cell stack CSn can be indirectly adjusted by adjusting the opening of the flow control valve FC corresponding to all other electrolytic cell stacks CS. Therefore, carbon dioxide gas can be supplied to the multiple electrolytic cell stacks CS without excess or deficiency, thereby improving the utilization efficiency of carbon dioxide in the multiple electrolytic cell stacks CS.

[0075] The information indicating the relationship between the load current I in each flow rate regulating valve FC and the opening degree of the flow rate regulating valve FC may be updated. The update may be performed, for example, periodically or after the flow rate has stabilized, or when the difference with the information stored in the control unit 5 becomes equal to or greater than a set value.

[0076] The carbon dioxide conversion apparatus may further include an alarm. The alarm may generate an alarm if the difference between the voltage Vi of the target electrolytic cell stack CS and the average voltage Vmean is outside an acceptable range after the voltage comparison (step S3) and before adjusting the aperture of the flow control valve FC. The operation of the target electrolytic cell stack CS may be stopped in response to the alarm. The operation of the electrolytic cell stack CS may be stopped, for example, by stopping the supply of the supply gas and the supply liquid and the supply of the electric current. The alarm may be connected to the control unit 5 and controlled by the control unit 5, for example.

[0077] In the embodiment, an example has been described in which the number of flow control valves FC is n-1 (n is a natural number of 2 or more) and the number of electrolytic cell stacks CS is n, but the numbers of flow control valves FC and electrolytic cell stacks CS provided in the carbon dioxide conversion apparatus are not limited to this. For example, the carbon dioxide conversion apparatus may be provided with any number of flow control valves FC and any number of electrolytic cell stacks CS, such as n or more flow control valves FC and n+1 or more electrolytic cell stacks CS.

[0078] The configurations of the above-mentioned embodiments can be applied in combination with each other, and some of them can be replaced. Here, several embodiments of the present invention have been described, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0079] 1...carbon dioxide supply section, 2...flow rate adjustment section, 3...electrolysis section, 4...voltage measurement section, 5...control section, 6...power supply, 7...cooler, 8...gas-liquid separator, 9...purification section, 10...gas-liquid separator, 11...cooler, 12...gas-liquid separator, 13...water removal section, 14...carbon dioxide recovery section, 15...cooler, 16...tank, 17...pump, 20...carbon dioxide electrolysis cell, 21...cathode, 22...anode, 23...diaphragm, 24...flow path plate, 24a...flow path, 24a...anode 22 side (flow path, 24b...flow path, 100...carbon dioxide conversion device, SS...carbon dioxide supply source, CT...control device, CS...electrolysis cell stack, FC...flow rate adjustment valve, VM...voltmeter.

Claims

1. a carbon dioxide supply unit for supplying a supply gas containing carbon dioxide gas; A flow rate adjusting unit including a plurality of flow rate adjusting valves that distribute the supply gas supplied from the carbon dioxide supply unit; an electrolysis unit including a plurality of electrolysis cell stacks that receive the supply gas distributed through the plurality of flow rate control valves; a voltage measurement unit including a plurality of voltmeters for measuring the voltages of the plurality of electrolysis cell stacks; a control unit that receives voltage signals from the plurality of voltmeters and adjusts the opening degrees of the plurality of flow rate regulating valves; A carbon dioxide conversion apparatus comprising:

2. supplying a uniform load current having a theoretical current value corresponding to a flow rate of the supply gas supplied from the carbon dioxide supply unit to the plurality of electrolysis cell stacks; 2. The carbon dioxide conversion apparatus of claim 1.

3. supplying the supply gas from the carbon dioxide supply unit at a flow rate corresponding to a sum of load currents of the plurality of electrolysis cell stacks; 2. The carbon dioxide conversion apparatus of claim 1.

4. The control unit calculates an average voltage of the voltages, When one of the voltages is lower than the average voltage, reducing an opening degree of one of the plurality of flow rate control valves corresponding to one of the voltages; When one of the voltages is higher than the average voltage, increasing an opening degree of one of the plurality of flow rate control valves corresponding to one of the voltages.

2. The carbon dioxide conversion apparatus of claim 1.

5. The control unit calculates an average voltage of the voltages, and adjusts an opening degree of one of the corresponding flow rate adjustment valves so as to be proportional to a ratio of one of the voltages to the average voltage.

2. The carbon dioxide conversion apparatus of claim 1.

6. Distributing a supply gas including carbon dioxide gas through a plurality of flow control valves to supply the supply gas to the plurality of electrolysis cell stacks, and supplying a load current to the plurality of electrolysis cell stacks; measuring a voltage of the plurality of electrolysis cell stacks, and adjusting the opening degree of the plurality of flow rate control valves in response to the voltage; Carbon dioxide conversion methods.

7. supplying a uniform load current having a theoretical current value corresponding to a flow rate of the supply gas to the plurality of electrolytic cell stacks; 7. The carbon dioxide conversion process according to claim 6.

8. distributing the supply gas having a flow rate corresponding to the sum of the load currents of the plurality of electrolytic cell stacks and supplying the gas to the plurality of electrolytic cell stacks; 7. The carbon dioxide conversion process according to claim 6.

9. Calculating an average voltage of the voltages; When one of the voltages is lower than the average voltage, reducing an opening degree of one of the plurality of flow rate control valves corresponding to one of the voltages; When one of the voltages is higher than the average voltage, increasing an opening degree of one of the plurality of flow rate control valves corresponding to one of the voltages.

7. The carbon dioxide conversion process according to claim 6.

10. Calculating an average voltage of the voltages; adjusting an opening degree of one of the plurality of flow rate control valves corresponding to the one of the voltages in proportion to a ratio of the one of the voltages to the average voltage; 7. The carbon dioxide conversion process according to claim 6.

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