Electrolysis system

Abstract

To control a composition of gas generated by electrolytic reaction.SOLUTION: An electrolysis system comprises: a supply unit for generating a first mixed gas containing a water vapor, a carbon dioxide gas, and a hydrogen gas; an electrolytic unit for generating a second mixed gas containing a hydrogen gas and a carbon monoxide gas by electrolytic reaction using the first mixed gas; a detection unit for detecting a proportion of at least one gas included in the second mixed gas; and a control unit for calculating a ratio of the hydrogen gas to the carbon monoxide gas in the second mixed gas based on the detected proportion, and for controlling the supply unit so as to adjust a ratio of the water vapor to the carbon dioxide gas in the first mixed gas depending on the calculated ratio.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE An embodiment of the present invention relates to an electrolysis system. [Background technology]

[0002] Hydrogen is one of the new energy sources. One application of hydrogen is fuel cells, which convert chemical energy into electrical energy by electrochemically reacting hydrogen with oxygen. Fuel cells have a high energy utilization efficiency, and are being developed as large-scale distributed power sources, domestic power sources, and mobile power sources.

[0003] Fuel cells are classified into solid polymer type, phosphoric acid type, molten carbonate type, solid oxide type, etc. according to the temperature range and the type of material and fuel used, but from the viewpoint of efficiency, solid oxide fuel cells (SOFCs) that obtain electrical energy through electrochemical reactions using an electrolyte made of solid oxide are attracting attention. In addition, hydrogen production involves the electrolysis of water, but research is being conducted on high-temperature steam electrolysis (SOEC), which electrolyzes water in a steam state at high temperatures. The operating principle of SOEC is the reverse reaction of SOFC, and similarly uses an electrolyte made of solid oxide.

[0004] In recent years, co-electrolysis using SOEC to simultaneously electrolyze carbon dioxide (CO2) in addition to water vapor has attracted attention because of its potential for reducing carbon dioxide emissions and generating fuel. In co-electrolysis using SOEC, carbon dioxide and water vapor are simultaneously electrolyzed, making it possible to generate a mixed gas (syngas) of carbon monoxide (CO) and hydrogen (H2) with high efficiency. Syngas is a useful gas that can be used as a raw material for various fuels, including methane.

[0005] One of the challenges in syngas generation by co-electrolysis is to arbitrarily control the composition of the mixed gas to an optimal ratio of carbon monoxide and hydrogen, which differs depending on the application. In general, the ratio of carbon monoxide to hydrogen in the generated gas (CO / H2) can be changed by the ratio of carbon dioxide to water vapor (CO2 / H2O) in the mixed gas supplied to the electrolysis section and operating conditions such as the electrolysis temperature. However, the ratio (CO / H2) in the generated gas is affected by various factors such as the deterioration of the cell stack and the device configuration, so the desired ratio (CO / H2) cannot be obtained by simply setting certain operating conditions. Furthermore, even if the desired composition is obtained initially, it may fluctuate over the course of operating time. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6037385 [Patent Document 2] JP 2019-192394 A [Patent Document 3] JP 2019-44238 A [Patent Document 4] Patent Publication No. 2021-17469 Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to control the composition of the gas produced by the electrolytic reaction. [Means for solving the problem]

[0008] An electrolysis system according to an embodiment includes a supply unit that generates a first mixed gas containing water vapor, carbon dioxide gas, and hydrogen gas; an electrolysis unit that generates a second mixed gas containing hydrogen gas and carbon monoxide gas by performing an electrolysis reaction using the first mixed gas; a detection unit that detects a ratio of at least one gas contained in the second mixed gas; and a control unit that calculates a ratio of hydrogen gas to carbon monoxide gas in the second mixed gas based on the detected ratio and controls the supply unit to adjust the ratio of water vapor to carbon dioxide gas in the first mixed gas in accordance with the calculated ratio. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram showing a configuration example of an electrolysis system. [Diagram 2] 4 is a block diagram showing a configuration example of a supply unit; FIG. [Diagram 3] FIG. 13 is a block diagram showing another example of the configuration of the supply unit. [Figure 4] FIG. 2 is a diagram showing a configuration example of an electrolysis unit. [Diagram 5] FIG. 4 is a graph showing the relationship between the ratio of hydrogen gas and the ratio of carbon monoxide gas in the product mixed gas. [Figure 6] FIG. 1 is a block diagram showing a first modified example of an electrolysis system. [Figure 7] FIG. 13 is a block diagram showing a second modified example of the electrolysis system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described with reference to the drawings. In each embodiment shown below, substantially the same components are denoted by the same reference numerals, and some of the descriptions thereof may be 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.

[0011] In this specification, unless otherwise specified, "connect" may include not only a direct connection but also an indirect connection.

[0012] (Example of electrolysis system configuration) Fig. 1 is a block diagram showing an example of the configuration of an electrolysis system according to an embodiment. The electrolysis system shown in Fig. 1 includes a supply unit 1, an electrolysis unit 2, a collection unit 3, a detection unit 4, and a control unit 5.

[0013] [Supply section 1] The supply unit 1 can supply a supply mixed gas. The supply mixed gas is a mixed gas supplied from the supply unit 1. The supply mixed gas contains, for example, water vapor (H2O), carbon dioxide gas (CO2), and hydrogen gas (H2). The supply unit 1 is connected to a pipe P1.

[0014] The supply mixed gas contains, for example, A% water vapor, B% carbon dioxide gas, and C% hydrogen gas. A, B, and C are numbers that represent the ratios (volume ratios) of water vapor, carbon dioxide gas, and hydrogen gas, respectively, when the entire supply mixed gas is taken as 100%. That is, the composition of the supply mixed gas is represented by water vapor:carbon dioxide gas:hydrogen gas=A%:B%:C%. A, B, and C are each any number equal to or greater than 0. A% is, for example, 10% or more and 80% or less. B% is, for example, 10% or more and 80% or less. C% is, for example, 5% or more and 20% or less. The sum of A%, B%, and C% is 100%. The values ​​of A, B, and C can be appropriately adjusted, for example, by changing the mixing ratio of water vapor, carbon dioxide gas, and hydrogen gas by the supply unit 1.

[0015] 2 is a block diagram showing an example of the configuration of the supply unit 1. The supply unit 1 has, for example, a water vapor supply source 101, a carbon dioxide gas supply source 102, and a hydrogen gas supply source 103.

[0016] The water vapor supply source 101 can supply water vapor. The water vapor supply source 101 has, for example, a tank that stores water (liquid), a mass flow controller that adjusts the flow rate of water supplied from the tank, and a heater that generates water vapor by heating water having a controlled flow rate. The water vapor generated by the heater flows through a pipe PA. The mass flow controller can be controlled by a control unit 5.

[0017] The carbon dioxide gas supply source 102 can supply carbon dioxide gas. The carbon dioxide gas supply source 102 has, for example, a cylinder cabinet that stores carbon dioxide gas, and a mass flow controller that adjusts the flow rate of the carbon dioxide gas that flows through a pipe PB connected to the cylinder cabinet. The mass flow controller can be controlled by the control unit 5.

[0018] The hydrogen gas supply source 103 can supply hydrogen gas. The hydrogen gas supply source 103 includes, for example, a cylinder cabinet that supplies hydrogen gas, and a mass flow controller that adjusts the flow rate of the hydrogen gas that flows through a pipe PC connected to the cylinder cabinet. The mass flow controller can be controlled by the control unit 5.

[0019] The pipes PA, PB, and PC are connected to each other at a connection point NA, and are connected to a pipe P1. The supply unit 1 mixes water vapor from the pipe PA, carbon dioxide gas from the pipe PB, and hydrogen gas from the pipe PC at the connection point NA to generate a supply mixed gas, and supplies the supply mixed gas to the electrolysis unit 2 via the pipe P1.

[0020] The configuration example of the supply unit 1 is not limited to the configuration example shown in Fig. 2. Fig. 3 is a block diagram showing another configuration example of the supply unit 1. The configuration example of the supply unit 1 shown in Fig. 3 differs from the configuration example of the supply unit 1 shown in Fig. 2 in that the carbon dioxide gas supply source 102 and the hydrogen gas supply source 103 are connected in front of the water vapor supply source 101, and the water vapor supply source 101 is connected to a connection point NB between the pipe PB and the pipe PC. Below, configurations different from the configuration example of the supply unit 1 shown in Fig. 2 will be described.

[0021] The supply unit 1 shown in FIG. 3 can mix carbon dioxide gas flowing from a carbon dioxide gas supply source 102 through a pipe PB and hydrogen gas flowing from a hydrogen gas supply source 103 through a pipe PC at a connection point NB. In addition, the supply unit 1 can generate a supply mixed gas by heating water in a tank in a water vapor supply source 101 with a heater and passing a mixed gas of carbon dioxide gas and hydrogen gas through the generated water vapor to humidify the mixed gas. The degree of humidification can be controlled by the temperature of the water. The supply mixed gas is supplied to the electrolysis unit 2 through a pipe P1 connected to a pipe PA. The other explanations of the supply unit 1 can be appropriately cited from the explanation of the supply unit 1 shown in FIG. 2.

[0022] [Electrolytic section 2] The electrolysis unit 2 can perform an electrolysis reaction using a mixed gas containing, for example, water vapor, carbon dioxide gas, and hydrogen gas, and generate a product mixed gas containing carbon monoxide gas and hydrogen gas. The product mixed gas is a mixed gas generated by the electrolysis unit 2. The electrolysis unit 2 is connected to a pipe P1 shown in FIG. 1. The pipe P1 can connect the supply unit 1 and the electrolysis unit 2. The pipe P1 functions as a flow path through which the supply mixed gas flows.

[0023] The electrolysis unit 2 preferably has, for example, a solid oxide electrochemical cell. The solid oxide electrochemical cell can be operated at high temperatures, and the electrolysis reaction in the electrolysis unit 2 is carried out at a temperature of, for example, 500° C. or higher and 1000° C. or lower. The electrolysis unit 2 may have a heater for heating the solid oxide electrochemical cell. The solid oxide electrochemical cell may be provided in an electric furnace capable of controlling the temperature of the electrolysis unit 2. The solid oxide electrochemical cell has, for example, a catalyst for promoting the electrolysis reaction.

[0024] FIG. 4 is a diagram showing a configuration example of the electrolysis unit 2. The electrolysis unit 2 has a solid oxide electrochemical stack having a solid oxide electrochemical cell 15. Although FIG. 4 shows a flat-plate stack, the stack is not limited to a flat-plate stack, and may be, for example, a cylindrical stack. The solid oxide electrochemical cell 15 is a flat-plate electrochemical cell and an anode-supported cell. The solid oxide electrochemical stack is connected to, for example, a power source capable of supplying a voltage or current for carrying out an electrolysis reaction.

[0025] The electrolysis unit 2 includes, for example, a plurality of solid oxide electrochemical cells 15. The solid oxide electrochemical cells 15 are stacked in order. The solid oxide electrochemical cells 15 include an oxygen electrode 11, an electrolyte 12, a hydrogen electrode 13, and a support 14. The solid oxide electrochemical stack is disposed, for example, between a support 26 and a support 27.

[0026] The electrolytic reaction in the electrolysis unit 2 is carried out, for example, as follows. Gases such as carbon dioxide gas, water vapor, and hydrogen gas are supplied to the hydrogen electrode 13 side. By the electrolytic reaction at the hydrogen electrode 13, for example, hydrogen gas can be produced from water vapor, and carbon monoxide gas can be produced from carbon dioxide gas. Gases such as carbon dioxide gas, water vapor, hydrogen gas, and carbon monoxide gas are discharged from the hydrogen electrode 13 side.

[0027] A gas such as air is supplied to the oxygen electrode 11 side. The air is supplied, for example, to purge oxygen generated during electrolysis. Oxygen can be generated by an electrolytic reaction at the oxygen electrode 11. Air having an oxygen concentration higher than that in the atmosphere is discharged from the oxygen electrode 11 side.

[0028] The oxygen electrode 11 includes, for example, a porous electrical conductor. Examples of the porous electrical conductor include perovskite-type oxides.

[0029] The oxygen electrode 11 further includes, for example, a catalyst that promotes an electrolytic reaction contained in the produced mixed gas. The catalyst includes, for example, at least one element of platinum (Pt), ruthenium (Ru), cerium (Ce), lanthanum (La), cobalt (Co), nickel (Ni), aluminum (Al), and copper (Cu). The catalyst is supported, for example, on the surface of an electric conductor. The catalyst may form a catalyst layer provided on the surface of the electric conductor.

[0030] The electrolyte 12 includes, for example, an ion conductor that does not conduct electricity. Examples of the ion conductor include solid oxides such as stabilized zirconia, perovskite-type oxides, and ceria-based solid solution molded bodies.

[0031] The hydrogen electrode 13 has, for example, a porous electric conductor. Examples of the porous electric conductor include a mixed sintered body (cermet) of a metal and a solid oxide. Examples of the mixed sintered body include yttria-stabilized zirconia and scandia-stabilized zirconia.

[0032] In the solid oxide electrochemical stack, the atmospheres of the adjacent solid oxide electrochemical cells 15 can be isolated from each other by, for example, a separator 21. In addition, the atmospheres of the hydrogen electrode 13 and the oxygen electrode 11 of the same solid oxide electrochemical cell 15 can be isolated from each other by providing a partition plate 22 on the dense electrolyte 12 of the solid oxide electrochemical cell 15. The solid oxide electrochemical stack may further include a sealant 24 between the partition plate 22 and the separator 21. The solid oxide electrochemical stack may further include a gas flow passage 23 and a gas flow passage 25 that penetrate the outer periphery of the solid oxide electrochemical cell 15 along the stacking direction of the solid oxide electrochemical cell 15. The gas flow passage 23 and the gas flow passage 25 constitute flow passages for the raw material gas supplied to the hydrogen electrode 13 and the oxygen electrode 11, respectively, and the reaction product gas generated by the hydrogen electrode 13 and the oxygen electrode 11. The gas flow passage 23 and the gas flow passage 25 are connected to, for example, a pipe P1 or a pipe P2.

[0033] The solid oxide electrochemical stack can, for example, produce a product gas mixture containing carbon monoxide gas and hydrogen gas by electrolytically reacting water vapor and carbon dioxide gas using the hydrogen electrode 13 .

[0034] [Collection Section 3] The collecting unit 3 can collect, for example, the produced mixed gas contained in the fluid discharged from the electrolysis unit 2. The collecting unit 3 is connected to a pipe P2 shown in Fig. 1. The pipe P2 can connect the electrolysis unit 2 and the collecting unit 3. The pipe P2 functions as a flow path through which the produced mixed gas flows.

[0035] The collection unit 3 may generate a purified mixed gas by removing water vapor and carbon dioxide gas by purifying the produced mixed gas. The collection unit 3 has, for example, a tank capable of storing a fluid containing the produced mixed gas, and a gas-liquid separator capable of separating the produced mixed gas and water contained in the fluid from the electrolysis unit 2. The collection unit 3 may have a gas separation membrane capable of separating at least one of water vapor and carbon dioxide gas contained in the produced mixed gas.

[0036] [Detection unit 4] The detection unit 4 is connected to a pipe P3 which is connected to a pipe P2 as shown in FIG. 1, for example. The electrolysis system of the embodiment may further include a valve V1 in the pipe P3. Examples of the valve V1 include a solenoid valve. The valve V1 can be opened and closed in response to a control signal from the control unit 5, for example. Opening and closing the valve V1 can control the connection and disconnection between the electrolysis unit 2 and the detection unit 4 via the pipe P3.

[0037] The detection unit 4 can directly or indirectly detect, for example, the ratio (volume ratio) of at least one gas contained in the produced mixed gas. The detection unit 4 can generate and output a detection signal by converting data indicating the measured ratio into an electrical signal. The dashed-dotted arrow in FIG. 1 indicates the detection signal.

[0038] The detection unit 4 has, for example, a gas chromatograph. The gas chromatograph can measure, for example, the ratio of at least one of hydrogen gas and carbon monoxide gas in the produced mixed gas by separating and quantifying each component gas contained in the produced mixed gas. Even if the water vapor contained in the produced mixed gas condenses and turns into water, the ratio of water vapor can be indirectly detected by measuring the ratio of other gases contained in the produced mixed gas by the gas chromatograph. The detection unit 4 is not limited to a gas chromatograph, and may have another detector capable of detecting the ratio of at least one component contained in the fluid discharged from the electrolysis unit 2.

[0039] [Control unit 5] The control unit 5 can receive a detection signal from the detection unit 4. The control unit 5 can calculate the composition of the produced mixed gas (ratio of each gas) using data such as ratios included in the detection signal, and can thereby calculate, for example, the ratio (CO / H2) of carbon monoxide gas to hydrogen gas in the produced mixed gas. Furthermore, the control unit 5 can control the supply unit 1 to adjust the ratio (H2O / CO2) of water vapor to carbon dioxide gas in the supply mixed gas according to the calculated ratio (CO / H2). The control unit 5 may further control the supply unit 1 to adjust the ratio of hydrogen gas in the supply mixed gas according to the calculated ratio (CO / H2). The control unit 5 can, for example, generate and output control signals for controlling the states of the supply unit 1 and the valve V1 according to the calculated parameters. The dotted arrows in FIG. 1 each indicate a control signal. The control unit 5 is connected to, for example, the supply unit 1, the detection unit 4, and the valve V1 by wired or wireless connection. The control unit 5 may be connected to at least one of the electrolysis unit 2 and the collection unit 3 via a wired or wireless connection, and may control the operation of at least one of the electrolysis unit 2 and the collection unit 3.

[0040] The control unit 5 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.

[0041] (Method of operating electrolysis system) Next, an example of an electrolysis system according to an embodiment will be described. An example of a method for driving the electrolysis system includes supplying a supply mixed gas containing water vapor, carbon dioxide gas, and hydrogen gas at any flow rate and ratio from the supply unit 1. The supply mixed gas can be supplied from the supply unit 1 to the electrolysis unit 2 at any flow rate and ratio by, for example, driving the supply unit 1 based on a control signal from the control unit 5.

[0042] When the supply mixed gas is supplied to the electrolysis unit 2, the electrolysis unit 2 generates a product mixed gas by electrolysis reaction (co-electrolysis). The product mixed gas contains AX% water vapor, BY% carbon dioxide gas, C+X% hydrogen gas, and Y% carbon monoxide gas. That is, the composition of the product mixed gas is represented by water vapor:carbon dioxide gas:hydrogen gas:carbon monoxide gas=A+X%:BY%:C+X%:Y%. X and Y each represent an unknown number. X% is, for example, 90% or less of A. Y% is, for example, 90% or less of B.

[0043] The electrolysis system is driven by setting the operating conditions of the electrolysis system according to the type of substance (target product) to be generated by the electrolysis unit 2. The operating conditions according to the target product vary, for example, depending on the material, structure, and configuration of the solid oxide electrochemical stack, and further vary depending on the degree of deterioration of the electrolysis unit 2 due to continuous operation. In contrast, it is required to set the operating conditions of the electrolysis system so as to continuously obtain a desired ratio (CO / H2) in the generated mixed gas, even if the material, structure, configuration, and degree of deterioration of the solid oxide electrochemical stack vary.

[0044] Therefore, the electrolysis system of the embodiment detects parameters such as the ratio of at least one gas contained in the produced mixed gas, calculates the composition of the produced mixed gas (ratio of each gas) based on the detected parameters, and adjusts the composition of the supplied mixed gas (ratio of each gas) according to the calculated composition. This operation is also called a feedback operation. Here, as an example, a case will be described in which the target value (reference value) of the ratio of carbon monoxide gas to hydrogen gas in the produced mixed gas (CO(Y%) / H2(C+X%)) is CO(30%) / H2(50%).

[0045] The ratio (H2O(A%) / CO2(B%)) in the supply mixed gas can be set, for example, by adjusting the flow rate of water vapor from the water vapor supply source 101, the flow rate of carbon dioxide gas from the carbon dioxide gas supply source 102, and the flow rate of hydrogen gas from the hydrogen gas supply source 103. The total flow rate of water vapor and carbon dioxide gas can be determined, for example, by calculating from the total ratio of hydrogen gas and carbon monoxide gas to be generated by the electrolysis reaction in the product mixed gas and the fuel utilization rate required for the electrolysis reaction (the proportion of the flow rate of water vapor+the flow rate of carbon dioxide gas that is electrolyzed). The ratio (H2O(A%) / CO2(B%) in the supply mixed gas needs to be adjusted according to the desired ratio (CO / H2) (reference value) of the product mixed gas to be generated by the electrolysis reaction, but the value to which it needs to be set varies depending on various conditions, such as the constituent material and structure of the electrolysis unit 2, the configuration and temperature of the electrolysis system, etc. Therefore, when setting the ratio (H2O / CO2) in the supply mixed gas at the beginning of operation of the electrolysis system, the ratio (H2O / CO2) can be set, for example, by referring to the actual value for the electrochemical stack to be used or the literature value for an electrochemical stack similar to the electrochemical stack to be used.

[0046] In the electrolysis system of the embodiment, a reaction (CO2+H2←→CO+H2O: reverse shift reaction) may occur in which hydrogen gas and carbon dioxide gas contained in the supply mixed gas react chemically to generate water vapor and carbon monoxide gas. The reverse shift reaction is likely to occur, for example, in the pipe P1 or the electrolysis unit 2. If the reverse shift reaction occurs more than expected and the ratio of hydrogen gas in the supply mixed gas becomes too low, the catalyst in the electrolysis unit 2 may be oxidized and deteriorated. For example, in the electrolysis unit 2, nickel, which is a general catalyst, is oxidized to form nickel oxide when the hydrogen concentration is too low. Therefore, it is preferable that the ratio of hydrogen gas in the supply generated gas is always at a certain concentration or higher, for example, 10% or higher.

[0047] As described above, the feed mixed gas having a composition of, for example, water vapor: 45% (A = 45), carbon dioxide gas: 45% (B = 45), and hydrogen gas: 10% (C = 10) is supplied from the feed unit 1 to the electrolysis unit 2 to carry out an electrolysis reaction. Then, water vapor is electrolyzed to generate hydrogen, and carbon dioxide gas is electrolyzed to generate carbon monoxide. At this time, the ratio of each gas in the generated Kong gas is unknown: water vapor: 45-X%, carbon dioxide gas: 45-Y%, hydrogen gas: 10+X%, and carbon monoxide gas: Y%.

[0048] A portion of the fluid from the electrolysis unit 2 is sent to the detection unit 4 via a pipe P3, and the remainder is sent to the collection unit 3. A portion of the fluid can be supplied to the detection unit 4 via a pipe P3 branched off from the pipe P2, for example, by temporarily opening a valve V1 using the control unit 5.

[0049] The collection unit 3 removes water vapor and carbon dioxide gas from the fluid discharged from the electrolysis unit 2 to generate a purified mixed gas containing hydrogen gas and carbon monoxide gas. The purified mixed gas is stored in a container such as a tank, or is supplied to a plant that uses the purified mixed gas. The water vapor and carbon dioxide gas removed by the collection unit 3 may be sent to, for example, a water vapor supply source 101 and a carbon dioxide gas supply source 102, respectively, and used to generate a supply mixed gas.

[0050] The purified mixed gas contains 10% to 90% (volume ratio) of hydrogen gas and 10% to 90% (volume ratio) of carbon monoxide gas. The total ratio of hydrogen gas and carbon monoxide gas in the purified mixed gas is 90% to 100%. The purified mixed gas does not need to contain water vapor or carbon dioxide gas.

[0051] The detection unit 4 detects the ratio of at least one of, for example, water vapor, carbon dioxide gas, and hydrogen gas to generate a detection signal. The detection signal of the detection unit 4 is sent to the control unit 5. The control unit 5 calculates the ratio of each gas in the resulting mixed gas based on data such as ratios included in the detection signal, and can obtain a result that the resulting mixed gas is represented by a composition represented by, for example, water vapor: 8% (45-37%), carbon dioxide gas: 12% (45-33%), hydrogen gas: 47% (10+37%), and carbon monoxide gas: 33%. From this value, it can be seen that the ratio of hydrogen gas is low and the ratio of carbon monoxide gas is high compared to the target values ​​(reference values) of hydrogen gas: 50% and carbon monoxide gas: 30% in the resulting mixed gas. In this way, when the calculated ratios of each gas or the ratio (CO / H2) are lower than the first reference value, the supply unit 1 is controlled based on this calculation result, and the supply unit 1 is driven based on a control signal from the control unit 5 to, for example, increase the ratio of water vapor in the supplied mixed gas and decrease the ratio of carbon dioxide gas. Furthermore, when the calculated ratio of each gas or the ratio (CO / H2) is higher than the second reference value, the supply unit 1 is controlled based on this calculation result, for example, by driving the supply unit 1 based on a control signal from the control unit 5 so as to reduce the ratio of water vapor in the supply mixed gas and increase the ratio of carbon dioxide gas. At this time, it is preferable that the increase / decrease amount of the water vapor ratio and the decrease / increase amount of the carbon dioxide gas ratio are the same value so that the total flow rate does not change. The extent to which each ratio should be changed can be determined by referring to, for example, actual values ​​for the electrochemical stack used or literature values ​​for electrochemical stacks similar to the electrochemical stack used. The sample of the generated mixed gas used for measurement by the detection unit 4 is small, so it may be discarded after measurement.

[0052] For example, FIG. 5 is a diagram showing the relationship between the ratio (H2O / CO2) in the supply mixed gas and the ratio of hydrogen gas and carbon monoxide gas in the generated mixed gas when the temperature of the electrolysis unit 2 is 700°C. Data showing such a relationship may be stored in advance in a recording medium of the control unit. From FIG. 5, it can be seen that the larger the ratio (H2O / CO2), the lower the ratio of hydrogen gas and the higher the ratio of carbon monoxide gas. Based on such a relationship, when the calculated ratio of each gas or the ratio (CO / H2) is lower than a first reference value, the control unit 5 controls the supply unit 1 to increase the ratio of water vapor by several percent and decrease the ratio of carbon dioxide gas by several percent in the supply generated gas. Also, when the calculated ratio of each gas or the ratio (CO / H2) is higher than a second reference value, the control unit 5 controls the supply unit 1 to decrease the ratio of water vapor by several percent and increase the ratio of carbon dioxide gas by several percent in the supply generated gas. Under these conditions, the ratio of at least one gas in the product mixed gas discharged from the electrolysis unit 2 is detected again by the detection unit 4, and if there is a deviation from the target value, a feedback operation to the supply unit 1 is performed again. The above operation is repeated until the deviation from the target value falls within an allowable range. The allowable range of deviation is preferably, for example, the target value ±2%. That is, the first reference value may be not less than the target value -2% and not more than the target value, and the second reference value may be not less than the target value and not more than the target value +2%.

[0053] Even if the composition of the supply mixed gas is adjusted once so that the target ratio (H2 / CO) is obtained in the product mixed gas, the composition may deviate due to deterioration of the electrolysis unit 2 caused by continuous operation. For this reason, the product mixed gas is monitored by performing a detection operation by the detection unit 4 periodically, for example, once a week, and if there is a deviation from the target value, the ratio of each gas in the supply mixed gas is controlled by the above-mentioned feedback operation to match the target ratio (H2 / CO). The relationship between the conditions of the supply mixed gas composition, flow rate, electrolysis current, temperature, etc., and the result of the ratio (H2 / CO) detected by the detection unit 4 is accumulated, and the control unit 5 may estimate, for example, an optimal value of the ratio (H2 / CO) based on the multiple accumulated data, and the supply unit 1 may be controlled based on the estimated optimal value to optimize the subsequent feedback operation.

[0054] Furthermore, the ratio of hydrogen gas in the produced mixed gas may be detected by the detection unit 4, and the ratio of hydrogen gas in the supply mixed gas may be calculated based on the ratio of hydrogen gas detected by the control unit 5. If the calculated ratio of hydrogen gas is less than a reference value, for example, lower than 5%, a feedback operation may be performed by controlling the supply unit 1 to increase the ratio of hydrogen gas. In general, when hydrogen is generated by co-electrolysis, the hydrogen concentration is unlikely to be less than 5%. However, in a state where the supply of current to the electrolysis unit 2 is stopped and the supply mixed gas flows through the electrolysis unit 2 (hot standby state), hydrogen is consumed in the reverse shift reaction and the ratio of hydrogen gas may become low, so it is preferable to increase the ratio of hydrogen gas in the supply mixed gas by a feedback operation. Such adjustment of the ratio of hydrogen gas is not limited to the hot standby state, and may be performed during normal operation of the electrolysis system.

[0055] (First variant of electrolysis system) Fig. 6 is a block diagram showing a first modified example of the electrolysis system shown in Fig. 1. The electrolysis system shown in Fig. 6 differs from the electrolysis system shown in Fig. 1 in that it includes a detection unit 4a as the detection unit 4 and does not have a valve V1 and a pipe P3. Components different from the electrolysis system shown in Fig. 1 will be described below, and the description of the electrolysis system shown in Fig. 1 can be used as appropriate for descriptions of the other components.

[0056] The detector 4a can indirectly detect, for example, the ratio of at least one gas in the produced mixed gas. The detector 4a can generate and output a detection signal (detection gas data signal) by converting data indicating the measured ratio into an electrical signal. The dashed arrow in FIG. 6 indicates the detection signal.

[0057] The detection unit 4a is provided in the middle of the pipe P2. The detection unit 4a can measure the ratio of water vapor contained in the produced mixed gas. The detection unit 4a has, for example, a dew point meter that can measure the concentration of water vapor flowing through the pipe P2. By using the dew point meter, the ratio of water vapor contained in the produced mixed gas can be measured, and the ratio of at least one of hydrogen gas and carbon monoxide gas in the produced mixed gas can be indirectly detected. By providing the dew point meter in the middle of the pipe P2, condensation of water vapor can be suppressed, so that the ratio of water vapor can be measured with high accuracy. The detection unit 4a is not limited to the dew point meter, and may have another detector capable of detecting the concentration of water vapor. The description of the detection unit 4 can be appropriately cited for other descriptions of the detection unit 4a.

[0058] The control unit 5 can receive a detection signal from the detection unit 4a. The control unit 5 can calculate the composition of the generated mixed gas (ratio of each gas) using data such as the ratio of water vapor contained in the detection signal, and can thereby calculate, for example, the ratio (CO / H2) of carbon monoxide gas to hydrogen gas in the generated mixed gas. Furthermore, the control unit 5 can control the supply unit 1 to adjust the ratio (H2O / CO2) of water vapor to carbon dioxide gas in the supply mixed gas according to the calculated ratio (CO / H2). The control unit 5 may further control the supply unit 1 to adjust the ratio of hydrogen gas in the supply mixed gas according to the calculated ratio (CO / H2). The control unit 5 can generate and output, for example, a control signal for controlling the state of the supply unit 1 according to the calculated parameters. The dotted arrows shown in FIG. 6 each indicate a control signal. The control unit 5 is connected, for example, to the supply unit 1 and the detection unit 4b by wired or wireless connection. The other explanations of the control unit 5 can be appropriately cited from the explanation of the control unit 5 shown in FIG. 1.

[0059] In the driving method of the electrolysis system shown in FIG. 6, the ratio of water vapor in the produced mixed gas is detected by the detection unit 4a to generate a detection signal, the control unit 5 calculates the composition of the produced mixed gas based on data such as the ratio included in the detection signal sent from the detection unit 4a to the control unit 5, and the supply unit 1 is controlled based on the calculation result, thereby performing a feedback operation. Since the total value (X+Y) of the amount of water vapor reduction (X) and the amount of carbon dioxide gas reduction (Y) in the produced mixed gas can be calculated from the current value supplied to the electrochemical cell stack, if the value of X is known, the value of Y can be calculated by the control unit 5. The feedback operation may be repeated, for example, until the deviation from the target value of the ratio (H2 / CO) is within ±2%. This allows the composition of the produced mixed gas to be controlled. By using a dew point meter, the device configuration can be simplified compared to when a gas chromatograph is used, and therefore the manufacturing cost of the electrolysis system can be reduced.

[0060] (Second variant of electrolysis system) Fig. 7 is a block diagram showing a second modified example of the electrolysis system shown in Fig. 1. The electrolysis system shown in Fig. 7 differs from the electrolysis system shown in Fig. 1 in that it includes a detection unit 4b as the detection unit 4, and has a valve V2 and a pipe P4 instead of the valve V1 and the pipe P3. Components different from the electrolysis system shown in Fig. 1 will be described below, and the description of the electrolysis system shown in Fig. 1 can be used as appropriate for descriptions of the other components.

[0061] The detector 4b can indirectly detect, for example, the ratio of at least one gas in the produced mixed gas. The detector 4b can generate and output a detection signal (detection gas data signal) by converting data indicating the measured ratio into an electrical signal. The dashed arrow in FIG. 6 indicates the detection signal.

[0062] The detection unit 4b is connected to a pipe P4. The pipe P4 is connected to the collection unit 3. The valve V2 is provided in the middle of the pipe P4. Examples of the valve V2 include a solenoid valve and the like. The valve V2 is opened and closed in response to a control signal from the control unit 5, for example. Opening and closing the valve V2 can control the connection and disconnection between the collection unit 3 and the detection unit 4 via the pipe P4.

[0063] The detection unit 4b can measure the weight of water separated from the fluid containing the produced mixed gas in the collection unit 3. The detection unit 4b has, for example, a weighing scale that can measure the weight of water supplied from the collection unit 3 through the pipe P4 by opening the valve V2. By using the weighing scale, for example, the weight of water contained in the fluid containing the produced mixed gas per unit time can be measured, and the ratio of at least one gas in the produced mixed gas can be indirectly detected. Without being limited to a weighing scale, the detection unit 4b may have another detector capable of detecting the concentration of water vapor. For other explanations of the detection unit 4b, the explanations of the detection unit 4 can be appropriately cited.

[0064] The control unit 5 can receive a detection signal from the detection unit 4b. The control unit 5 can calculate the composition of the produced mixed gas (ratio of each gas) using data such as the weight of water included in the detection signal, and can thereby calculate, for example, the ratio (CO / H2) of carbon monoxide gas to hydrogen gas in the produced mixed gas. Furthermore, the control unit 5 can control the supply unit 1 to adjust the ratio (H2O / CO2) of water vapor to carbon dioxide gas in the supply mixed gas according to the calculated ratio (CO / H2). The control unit 5 may further control the supply unit 1 to adjust the ratio of hydrogen gas in the supply mixed gas according to the calculated ratio (CO / H2). The control unit 5 can generate and output, for example, control signals for controlling the states of the supply unit 1 and the valve V2 according to the calculated parameters. The dotted arrows shown in FIG. 7 each indicate a control signal. The control unit 5 is connected, for example, to the supply unit 1, the detection unit 4b, and the valve V2 by wired or wireless connection. The rest of the description of the control unit 5 can be appropriately referred to the description of the control unit 5 shown in FIG. 1.

[0065] In the driving method of the electrolysis system shown in FIG. 7, the valve V2 is opened in response to a control signal from the control unit 5 to send water separated from the produced mixed gas from the collection unit 3 to the detection unit 4b. Furthermore, the weight of the water separated by the detection unit 4b per unit time is measured, the control unit 5 calculates the composition of the produced mixed gas in response to the measured weight, and the supply unit 1 is controlled based on the calculation result, thereby performing a feedback operation. Since the total value (X+Y) of the amount of water vapor reduction (X) and the amount of carbon dioxide gas reduction (Y) in the produced mixed gas can be calculated from the current value supplied to the electrochemical stack, if the value of X is known, the value of Y can be calculated by the control unit 5. The feedback operation may be repeated, for example, until the deviation from the target value is within ±2%. This allows the composition of the produced mixed gas to be controlled. By using a weight scale, the device configuration can be simplified compared to the case of using a gas chromatograph, and the manufacturing cost of the electrolysis system can be reduced.

[0066] The second modified example of the electrolysis system can be appropriately combined with the first modified example of the electrolysis system.

[0067] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0068] 1...supply section, 2...electrolysis section, 3...collection section, 4...detection section, 4a...detection section, 4b...detection section, 5...control section, 11...oxygen electrode, 12...electrolyte, 13...hydrogen electrode, 14...support, 15...solid oxide electrochemical cell, 21...separator, 22...partition plate, 23...gas flow path, 24...sealing material, 25...gas flow path, 26...support, 27...support, 101...water vapor supply source, 102...carbon dioxide gas supply source, 103...hydrogen gas supply source, NA...connection point, NB...connection point, P1...piping, P2...piping, P3...piping, P4...piping, PA...piping, PB...piping, PC...piping, V1...valve, V2...valve.

Claims

1. A supply unit that generates a first mixed gas containing water vapor, carbon dioxide gas, and hydrogen gas; an electrolysis unit that generates a second mixed gas containing hydrogen gas and carbon monoxide gas by performing an electrolysis reaction using the first mixed gas; a detection unit that detects a ratio of at least one gas contained in the second mixed gas; a control unit that calculates a ratio of the hydrogen gas to the carbon monoxide gas in the second mixed gas based on the detected ratio, and controls the supply unit to adjust the ratio of the water vapor to the carbon dioxide gas in the first mixed gas in accordance with the calculated ratio; An electrolysis system comprising:

2. 2. The electrolysis system according to claim 1, wherein the detection unit comprises a gas chromatograph that measures a ratio of at least one gas selected from the group consisting of the hydrogen gas and the carbon monoxide gas contained in the second mixed gas.

3. The detection unit has a dew point meter that measures the ratio of water vapor contained in the second mixed gas.

2. The electrolysis system of claim 1.

4. A supply unit that generates a first mixed gas containing water vapor, carbon dioxide gas, and hydrogen gas; an electrolysis unit that generates a second mixed gas containing hydrogen gas and carbon monoxide gas by performing an electrolysis reaction using the first mixed gas; a collection section having a gas-liquid separator that separates water from a fluid discharged from the electrolysis section and that includes the second mixed gas; a detection unit having a weight sensor for measuring a weight of the separated water per unit time; a control unit that calculates a ratio of the hydrogen gas to the carbon monoxide gas in the second mixed gas based on the measured weight, and controls the supply unit to adjust the ratio of the water vapor to the carbon dioxide gas in the first mixed gas in accordance with the calculated ratio; An electrolysis system comprising:

5. the control unit controls the supply unit to increase the ratio of the carbon dioxide gas in the first mixed gas when the calculated ratio is lower than a first reference value, and to decrease the ratio of the carbon dioxide gas in the first mixed gas when the calculated ratio is higher than a second reference value.

5. The electrolysis system according to claim 1.

6. The detection unit periodically detects the ratio of the at least one gas, the control unit accumulates a plurality of data indicating a ratio of the at least one gas detected periodically, estimates an optimum value of the ratio of the water vapor to the carbon dioxide gas in the first mixed gas based on the plurality of data, and controls the supply unit based on the estimated optimum value.

2. The electrolysis system of claim 1.

7. the control unit calculates a ratio of the hydrogen gas in the first mixed gas based on the detected ratio, and controls the supply unit to increase the ratio of the hydrogen gas in the first mixed gas when the calculated ratio is less than a reference value.

2. The electrolysis system of claim 1.

8. The electrolysis unit has a solid oxide electrochemical cell.

5. The electrolysis system according to claim 1.

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