Gas electrolysis system and control method for a gas electrolysis system

Abstract

This method allows the electrochemical reaction to continue while suppressing damage to the electrochemical cell. [Solution] The gas electrolysis system according to this embodiment comprises an electrolysis stack composed of multiple electrochemical cells stacked on top of each other, a voltmeter for measuring the cell voltage of the electrochemical cells, a flow controller capable of adjusting the flow rate of the supply gas supplied to the electrolysis stack, and a control unit for controlling the flow controller. The control unit controls the flow controller to increase the flow rate of the supply gas based on the cell voltage.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a gas electrolysis system and a method for controlling a gas electrolysis system. [Background technology]

[0002] An electrochemical cell generates an electrochemical reaction by supplying a fluid consisting of a liquid, gas, or a mixture of liquid and gas (hereinafter referred to as anode fluid, cathode fluid, etc.) to at least one of the anode and cathode electrodes, which are separated by a diaphragm such as an electrolyte membrane, and then applying an external potential difference between the anode and cathode electrodes to pass an electric current, causing ionized substances to pass through the diaphragm. Electrochemical cells are used, for example, in water electrolysis, where water (H2O) is supplied to the anode and hydrogen (H2) is extracted from the cathode outlet, or in carbon dioxide electrolysis, where water (H2O) is supplied to the anode and carbon dioxide (CO2) is supplied to the cathode and carbon monoxide (CO) is extracted from the cathode outlet. In addition, an electrolyte solution containing a small amount of ionic substance dissolved in the liquid necessary for the reaction may be used as the anode fluid or cathode fluid to promote the electrochemical reaction.

[0003] Electrolytic stacks are constructed by stacking multiple electrochemical cells to increase the rate of chemical reaction. Therefore, variations in the distribution of supplied gas to each electrochemical cell can occur. These distribution variations can lead to insufficient gas supply to some electrochemical cells. As a result, short circuits can occur within the electrode plates, potentially causing overheating of components due to the short-circuit current, melting of the diaphragm, and even cross-leakage. In particular, in carbon dioxide electrolysis, the mixing of carbon monoxide (CO) on the cathode side and oxygen (O2) on the anode side can generate significant heat through a chemical reaction. This heat can affect adjacent electrochemical cells, potentially damaging all electrochemical cells in the electrolytic stack. In conventional electrolytic stacks, the cell voltage of each electrochemical cell was measured using a voltmeter, and if variations in cell voltage were detected, it was assumed that distribution variations were occurring, leading to the shutdown of the electrolytic stack and the cessation of the electrochemical reaction. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-43734 [Patent Document 2] Japanese Patent Publication No. 2022-143968 [Patent Document 3] Japanese Patent Publication No. 2022-143980 [Overview of the project] [Problems that the invention aims to solve]

[0005] In view of the above, this embodiment aims to provide a gas electrolysis system and a control method for the gas electrolysis system that can suppress damage to the electrochemical cell while continuing the electrochemical reaction. [Means for solving the problem]

[0006] The gas electrolysis system according to this embodiment comprises an electrolysis stack composed of multiple electrochemical cells stacked on top of each other, a voltmeter for measuring the cell voltage of the electrochemical cells, a flow controller capable of adjusting the flow rate of the supply gas supplied to the electrolysis stack, and a control unit for controlling the flow controller. The control unit controls the flow controller to increase the flow rate of the supply gas based on the cell voltage.

[0007] Furthermore, the control method for the gas electrolysis system according to the embodiment comprises an electrolysis stack composed of multiple electrochemical cells stacked on top of each other, a voltmeter for measuring the cell voltage of the electrochemical cells, and a flow controller capable of adjusting the flow rate of the supply gas supplied to the electrolysis stack. The control method for the gas electrolysis system controls the flow controller to increase the flow rate of the supply gas based on the cell voltage. [Effects of the Invention]

[0008] According to this embodiment, it is possible to suppress damage to the electrochemical cell while continuing electrolysis.

Brief Description of Drawings

[0009] [Figure 1] FIG. 1 is a configuration diagram of a gas electrolysis system according to an embodiment. [Figure 2] FIG. 2 is an image diagram of cell voltage monitoring by the control unit. [Figure 3] FIG. 3 is a diagram for explaining the flow rate increase mode. [Figure 4] FIG. 4 is a diagram for explaining the cancellation of the flow rate increase mode.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, a gas electrolysis system and a control method for the gas electrolysis system according to an embodiment of the present invention will be described with reference to the drawings.

[0011] FIG. 1 is a configuration diagram of a gas electrolysis system 1 according to an embodiment. As shown in FIG. 1, the gas electrolysis system 1 may include an electrolysis stack 10, a voltmeter 20, a flow rate controller 30, a humidifier 40, a dew point meter 50, a DC power supply 60, and a control unit 70.

[0012] The electrolysis stack 10 is configured by stacking a plurality of electrochemical cells 12. That is, the electrolysis stack 10 includes a plurality of electrochemical cells 12 stacked on each other. The electrochemical cell 12 is also referred to as an electrolytic cell. The electrochemical cell 12 includes a diaphragm, an anode electrode, and a cathode electrode. The diaphragm may be an ion filtration membrane such as a solid polymer membrane (ion exchange membrane) or a solid electrolyte membrane (electrolyte membrane). The anode electrode and the cathode electrode are arranged with the diaphragm interposed therebetween. The anode electrode and the cathode electrode may be configured by attaching a catalyst containing a metal such as nickel, iridium, gold, silver, platinum, or a metal oxide such as nickel oxide, iridium dioxide, cobalt oxide to a gas-permeable base material made of carbon or metal.

[0013] The electrochemical cell 12 is configured to generate an electrochemical reaction (electrolysis reaction) using a gas (supply gas). More specifically, the electrochemical cell 12 applies a potential difference between the anode electrode and the cathode electrode and allows a current to flow while supplying a gas to at least one of the anode electrode and the cathode electrode, so that the ionized substance passes through the diaphragm and an electrochemical reaction occurs. For example, by supplying water (H2O) to the anode electrode and carbon dioxide (CO2) to the cathode electrode, a reaction of carbon dioxide electrolysis in which a mixed gas containing carbon monoxide (CO) is taken out from the cathode electrode side may be obtained.

[0014] The voltmeter 20 is configured to measure the cell voltage of the electrochemical cell 12. The cell voltage means the voltage generated in the electrochemical cell 12 during the electrochemical reaction. The voltmeter 20 may measure the cell voltages of all the electrochemical cells 12 included in the electrolysis stack 10 respectively. The voltmeter 20 may measure the cell voltages of some of the electrochemical cells 12 included in the electrolysis stack 10 respectively. The voltmeter 20 may measure the cell voltage of one electrochemical cell 12 included in the electrolysis stack 10. The voltmeter 20 may measure the cell voltage of the electrochemical cell 12 by being connected to the electrode terminal of the electrochemical cell 12.

[0015] The flow rate controller 30 is configured to be able to adjust the flow rate of the supply gas supplied to the electrolysis stack 10. For example, in the case of carbon dioxide electrolysis, the supply gas is carbon dioxide (CO2). The flow rate controller 30 may be a mass flow controller that measures the mass flow rate of the gas and controls the flow rate using PID control. The flow rate controller 30 is arranged upstream of the electrolysis stack 10.

[0016] The humidifier 40 is configured to humidify the supply gas. The humidifier 40 is positioned between the flow controller 30 and the electrolytic stack 10. That is, the humidifier 40 is positioned downstream of the flow controller 30 and upstream of the electrolytic stack 10. The supply gas supplied from the flow controller 30 is humidified in the humidifier 40 and supplied to the electrolytic stack 10. A heater 42 may also be provided inside the humidifier 40. The heater 42 is configured to heat the supply gas inside the humidifier 40. The heater 42 heats the supply gas supplied from the flow controller 30 and supplied to the electrolytic stack 10.

[0017] The dew point meter 50 is configured to measure the dew point of the supply gas. The dew point meter 50 measures the dew point temperature at which water vapor in the supply gas begins to condense. The dew point meter 50 may also measure the temperature and humidity of the supply gas and calculate the dew point temperature from that data. The dew point meter 50 may be placed between the humidifier 40 and the electrolytic stack 10. That is, the dew point meter 50 may be placed downstream of the humidifier 40 and upstream of the electrolytic stack 10. The dew point meter 50 may be installed in the piping connecting the humidifier 40 and the electrolytic stack 10. The dew point meter 50 may measure the dew point of the supply gas flowing through this piping.

[0018] The DC power supply 60 is configured to supply a DC current to the electrolytic stack 10. By supplying a DC current to the electrolytic stack 10 while the supply gas is supplied, the DC power supply 60 causes an electrochemical reaction to occur in each electrochemical cell 12 contained in the electrolytic stack 10. The current at this time is also called the electrolytic current.

[0019] The control unit 70 is configured to control the DC power supply 60. The control unit 70 sends a signal to the DC power supply 60 to command a current value, and the DC power supply 60 receives the signal and supplies the current of that value to the electrolytic stack 10. The electrolytic current increases or decreases according to the amount of product gas produced by the electrochemical reaction. For example, in the case of carbon dioxide electrolysis, the product gas is carbon monoxide (CO). To increase the amount of product gas produced, the electrolytic current is increased. To decrease the amount of product gas produced, the electrolytic current is decreased.

[0020] Furthermore, the control unit 70 is configured to control the flow controller 30. The control unit 70 transmits a signal to the flow controller 30 to command the flow rate, and the flow controller 30 receives the signal and adjusts the flow rate of the supply gas to supply the specified flow rate of supply gas to the electrolytic stack 10. During the electrochemical reaction, the flow rate of the supply gas is increased or decreased in accordance with the electrolytic current. The flow rate of the supply gas is changed so that it has a one-to-one correspondence with the electrolytic current. Normally, when increasing the electrolytic current to increase the amount of product gas produced, the flow rate of the supply gas is increased before increasing the electrolytic current. Also, when decreasing the electrolytic current to decrease the amount of product gas produced, the flow rate of the supply gas is decreased after decreasing the electrolytic current.

[0021] Furthermore, the control unit 70 monitors the cell voltage measured by the voltmeter 20. The voltmeter 20 transmits the measured cell voltage value to the control unit 70, and the control unit 70 acquires the cell voltage value measured by the voltmeter 20. Then, based on the cell voltage measured by the voltmeter 20, the control unit 70 controls the flow rate controller 30 to increase the flow rate of the supply gas supplied to the electrolytic stack 10.

[0022] The control unit 70 may control the flow controller 30 to increase the flow rate of the supply gas when the cell voltage exceeds a specified value. In particular, during static operation, the control unit 70 may control the flow controller 30 to gradually increase the flow rate of the supply gas when the cell voltage deviates from a predetermined range. Static operation means operating the electrolytic stack 10 under a constant electrolytic current.

[0023] Furthermore, the control unit 70 may control the flow rate controller 30 such that, when the cell voltage falls within a predetermined range as a result of increasing the flow rate of the supplied gas, it stops increasing the flow rate of the supplied gas to maintain the flow rate of the supplied gas, and then decreases the flow rate of the supplied gas after a predetermined time has elapsed.

[0024] Furthermore, the control unit 70 may be configured to control the heater 42 inside the humidifier 40. The control unit 70 may also monitor the dew point of the gas measured by the dew point meter 50. That is, the dew point meter 50 may transmit the measured dew point of the gas to the control unit 70, and the control unit 70 may acquire the dew point of the gas measured by the dew point meter 50. When increasing the flow rate of the supply gas, the control unit 70 may control the heater 42 to heat the supply gas to maintain the dew point of the supply gas.

[0025] Next, the control by the control unit 70, that is, the control method of the gas electrolysis system 1, will be explained in more detail.

[0026] Figure 2 is an illustrative diagram of the cell voltage monitoring by the control unit 70. Figure 2 shows a graph illustrating the relationship between the electrolytic current I and the cell voltage V. In Figure 2, the horizontal axis represents the electrolytic current I, and the vertical axis represents the cell voltage V.

[0027] As shown in Figure 2, as the electrolytic current I increases, the cell voltage V also increases. During static operation, the control unit 70 sets the cell voltage V within an allowable voltage range V corresponding to the electrolytic current I. R It monitors whether the cell voltage V is within a predetermined range. That is, it monitors whether the cell voltage V is within the lower limit of the allowable voltage V corresponding to the electrolytic current I. L The above is true, and the allowable voltage upper limit V is corresponding to the electrolytic current I. U It is monitored to see if the value is below (a specified value).

[0028] The control unit 70 determines that during static operation, the cell voltage V is within the allowable voltage range V. R If it deviates from the limit, the flow rate increase mode is executed. For example, if the cell voltage V is above the allowable voltage limit V U If it exceeds a certain value, the flow rate increase mode is executed. Also, for example, if the cell voltage V is below the allowable lower voltage limit V L If the value falls below a certain level, the flow rate increase mode is activated.

[0029] In the flow rate increase mode, the control unit 70 transmits a signal instructing the flow rate controller 30 to increase the flow rate. The flow rate controller 30 receives the signal and increases the flow rate of the supply gas. In particular, in the flow rate increase mode, the flow rate controller 30 may increase the flow rate of the supply gas step by step.

[0030] When the cell voltage V deviates from the allowable voltage range V R it is presumed that there is an electrochemical cell 12 with insufficient supply gas due to uneven distribution of the supply gas to each electrochemical cell 12 in the electrolytic stack 10. Therefore, by increasing the flow rate of the supply gas in the flow rate increase mode, the insufficient supply of the supply gas to the electrochemical cell 12 can be eliminated, and the cell voltage V can be brought within the allowable voltage range V R

[0031] FIG. 3 is a diagram for explaining the flow rate increase mode. FIG. 3 shows a graph of time series data of the cell voltage V and the flow rate Q of the supply gas. In FIG. 3, the horizontal axis represents time T, and the vertical axis represents the cell voltage V and the flow rate Q of the supply gas. FIG. 3 shows an example when the flow rate increase mode is executed with the cell voltage V exceeding the allowable voltage upper limit value V U

[0032] In the example shown in FIG. 3, in the initial section A, the cell voltage V exceeds the allowable voltage upper limit value V U . Therefore, in the next section B, the flow rate Q of the supply gas is increased. As a result, in section B, the cell voltage V decreases. Here, also in section B, the cell voltage V exceeds the allowable voltage upper limit value V U . Therefore, in the next section C, the flow rate Q of the supply gas is further increased. As a result, in section C, the cell voltage V decreases. As a result, in section C, the cell voltage V falls within the allowable voltage range V R . That is, the cell voltage V is equal to or higher than the allowable voltage lower limit value V L and equal to or lower than the allowable voltage upper limit value V U .

[0033] ​​In this flow rate increase mode, the cell voltage V is within the allowable voltage range V R The supply gas flow rate Q is gradually increased until it stays within the acceptable range. Even when the supply gas flow rate Q is increased, the cell voltage V remains within the allowable voltage range V. R If it does not fit inside, the control unit 70 may stop the operation of the electrolytic stack 10.

[0034] In this flow rate increase mode, if the flow rate of the supplied gas is increased, the heater 42 in the humidifier 40 may not be able to raise the temperature of the supplied gas in time, which may cause the dew point of the supplied gas to drop. For this reason, when the flow rate of the supplied gas is increased, the control unit 70 sends a signal to the heater 42 to instruct it to increase the temperature, and the heater 42 receives the signal and heats the supplied gas to maintain the dew point of the supplied gas.

[0035] In the flow rate increase mode, as a result of increasing the flow rate of the supplied gas, the cell voltage V is within the allowable voltage range V R If the flow rate is contained within the specified range, the increase in the supply gas flow rate is stopped, and the increased supply gas flow rate is maintained. Then, after a predetermined period of time has elapsed, the flow rate increase mode is deactivated. Here, the predetermined period may be a few minutes, for example, between 1 minute and 10 minutes.

[0036] In order to deactivate the flow rate increase mode, the control unit 70 sends a signal to the flow rate controller 30 instructing it to reduce the flow rate, and the flow rate controller 30 receives the signal and reduces the flow rate of gas supplied to the electrolytic stack 10. In particular, the flow rate controller 30 may reduce the flow rate of gas supplied to the electrolytic stack 10 in stages.

[0037] One possible cause of insufficient supply of gas to the electrochemical cell 12 is that precipitates from the electrolyte solution block the gas flow path. In this case, increasing the flow rate of the supply gas can push out the precipitates, preventing future supply shortages. Therefore, the flow rate of the supply gas can be reduced after the supply shortage has been resolved.

[0038] Figure 4 is a diagram illustrating the deactivation of the flow rate increase mode. Figure 4 shows a graph of time-series data for the supply gas flow rate Q and cell voltage V. In Figure 4, the horizontal axis represents time T, and the vertical axis represents the supply gas flow rate Q and cell voltage V. Figure 4 shows an example where the flow rate increase mode is deactivated after the flow rate increase mode shown in Figure 3.

[0039] In the example shown in Figure 4, in section C, the cell voltage V is within the allowable voltage range V R It is contained within. Therefore, in the next section D, the flow rate Q of the supply gas is reduced. Here, even in section D, the cell voltage V is within the allowable voltage range V R It is contained within. Therefore, in the next section E, the flow rate Q of the supply gas is further reduced. Here, even in section E, the cell voltage V is within the allowable voltage range V R It is contained within.

[0040] In this manner, when deactivating the flow rate increase mode, the flow rate Q of the supply gas, which was increased by the flow rate increase mode, is gradually reduced until it reaches a flow rate corresponding to the electrolysis current. Then, the operation of the electrolysis stack 10 is returned to normal static constant operation. As a result of reducing the supply gas flow rate Q, the cell voltage V returns to the allowable voltage range V. R If the operation deviates from the specified range, the control unit 70 may stop the operation of the electrolytic stack 10.

[0041] Next, the effects and advantages of this embodiment will be described.

[0042] As described above, the electrolytic stack 10 is composed of multiple electrochemical cells 12 stacked on top of each other. Therefore, variations may occur in the distribution of the supplied gas to each electrochemical cell 12. Due to these distribution variations, some electrochemical cells may experience insufficient supply of gas. As a result, a short circuit may occur within the electrode plate, potentially leading to overheating of components due to the short-circuit current, melting of the diaphragm, and even cross-leakage. In particular, in the case of carbon dioxide electrolysis, the carbon monoxide (CO) on the cathode side and oxygen (O2) on the anode side mix, and it is conceivable that a chemical reaction will generate a large amount of heat. This heat can affect adjacent electrochemical cells 12, and there is a risk that all electrochemical cells 12 contained in the electrolytic stack 10 may be damaged. In conventional electrolytic stacks, the cell voltage of each electrochemical cell was measured using a voltmeter, and if variations in cell voltage were detected, it was assumed that distribution variations were occurring, and the operation of the electrolytic stack was stopped and the electrochemical reaction was halted.

[0043] In contrast, according to this embodiment, the control unit 70 controls the flow rate controller 30 to increase the flow rate of the supply gas supplied to the electrolytic stack 10 based on the cell voltage measured by the voltmeter 20. As a result, when it is estimated by monitoring the cell voltage that there is a shortage of supply gas to the electrochemical cell 12, sufficient supply gas can be supplied to the undersupplied electrochemical cell 12, thereby resolving the shortage of supply gas to the electrochemical cell 12. Therefore, damage to the electrochemical cell 12 can be suppressed while continuing the electrochemical reaction.

[0044] Furthermore, according to this embodiment, the control unit 70 controls the flow rate controller 30 to increase the flow rate of the supplied gas when the cell voltage exceeds a specified value. If a supply shortage of supplied gas occurs in the electrochemical cell 12 due to flow distribution variations, the cell voltage of that electrochemical cell 12 is expected to increase. Therefore, by increasing the flow rate of the supplied gas when the cell voltage exceeds a specified value, the supply shortage of supplied gas to the electrochemical cell 12 can be resolved. As a result, damage to the electrochemical cell 12 can be effectively prevented.

[0045] In particular, according to this embodiment, the control unit 70 controls the flow rate controller 30 to gradually increase the flow rate of the supply gas when the cell voltage deviates from a predetermined range during static operation. Generally, when there is a shortage of supply gas to an electrochemical cell 12, the cell voltage of that electrochemical cell 12 increases. However, if there is some damage to the electrochemical cell 12, for example, causing a minor short circuit, the cell voltage may decrease. Therefore, by gradually increasing the flow rate of the supply gas when the cell voltage deviates from a predetermined range, the shortage of supply gas to the electrochemical cell 12 can be resolved more reliably. As a result, damage to the electrochemical cell 12 can be prevented more effectively.

[0046] Furthermore, according to this embodiment, when the flow rate of the supply gas is increased, the control unit 70 controls the heater 42 to heat the supply gas in order to maintain its dew point. When the flow rate of the supply gas is increased, the heater 42 may not be able to heat the supply gas fast enough, which could cause the dew point of the supply gas to drop. This could cause the water vapor contained in the supply gas to condense and condensation to occur. In contrast, according to this embodiment, by heating the supply gas with the heater 42 in order to maintain its dew point, the occurrence of condensation in the supply gas can be suppressed.

[0047] Furthermore, according to this embodiment, when the cell voltage falls within a predetermined range as a result of increasing the supply gas flow rate, the control unit 70 stops increasing the supply gas flow rate to maintain the supply gas flow rate, and after a predetermined time has elapsed, controls the flow rate controller 30 to decrease the supply gas flow rate. One possible cause of supply gas flow variations and supply shortages is that precipitates of materials contained in the electrolyte solution block the gas flow path. In this case, increasing the supply gas flow rate can push out the precipitates with the supply gas, and thereafter supply gas flow variations and supply shortages may not occur. Therefore, by decreasing the supply gas flow rate after the supply gas shortage has been resolved, the amount of supply gas consumed can be suppressed.

[0048] According to the embodiments described above, it is possible to suppress damage to the electrochemical cell while continuing the electrochemical reaction.

[0049] 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 variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0050] 1: Gas electrolysis system, 10: Electrolytic stack, 12: Electrochemical cell, 20: Voltmeter, 30: Flow controller, 40: Humidifier, 42: Heater, 50: Dew point meter, 70: Control unit

Claims

1. A gas electrolysis system, An electrolytic stack composed of multiple electrochemical cells stacked on top of each other, A voltmeter for measuring the cell voltage of the electrochemical cell, A flow controller capable of adjusting the flow rate of the supply gas supplied to the electrolytic stack, The system comprises a control unit for controlling the flow rate controller, A gas electrolysis system in which the control unit controls the flow controller to increase the flow rate of the supply gas based on the cell voltage.

2. The gas electrolysis system according to claim 1, wherein the control unit controls the flow rate controller to increase the flow rate of the supplied gas when the cell voltage exceeds a specified value.

3. The gas electrolysis system according to claim 1, wherein the control unit controls the flow rate controller to gradually increase the flow rate of the supply gas when the cell voltage deviates from a predetermined range during static operation.

4. A humidifier for humidifying the supply gas, The system further comprises a dew point meter for measuring the dew point of the supply gas, A heater is provided inside the humidifier. The gas electrolysis system according to claim 1, wherein the control unit controls the heater to heat the supply gas to maintain the dew point when increasing the flow rate of the supply gas.

5. The gas electrolysis system according to claim 3, wherein the control unit controls the flow rate controller such that, when the cell voltage falls within the predetermined range as a result of increasing the flow rate of the supply gas, it stops increasing the flow rate of the supply gas to maintain the flow rate of the supply gas, and after a predetermined time has elapsed, it reduces the flow rate of the supply gas.

6. A control method for a gas electrolysis system comprising an electrolytic stack formed by stacking multiple electrochemical cells, a voltmeter for measuring the cell voltage of the electrochemical cells, and a flow controller capable of adjusting the flow rate of the supply gas supplied to the electrolytic stack, A control method for a gas electrolysis system, comprising controlling the flow controller to increase the flow rate of the supply gas based on the cell voltage.

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