Water electrolysis system

Abstract

To provide a water electrolysis system that can accurately acquire hydrogen concentration in a gas exhausted from an oxygen electrode using a hot-wire semiconductor type concentration measurement unit.SOLUTION: A water electrolysis system comprises: a water electrolysis unit that includes an oxygen electrode for generating oxygen by water electrolysis; a mixture unit that can mix an exhaust gas exhausted from the oxygen electrode and a dilution gas; a hot-wire semiconductor type concentration measurement unit that measures hydrogen concentration in a target gas sent from the mixture unit; a concentration correction unit in which corrected hydrogen concentration is acquired by correcting the measured hydrogen concentration, which is hydrogen concentration measured by the concentration measurement unit, based on oxygen concentration in the target gas; and a concentration calculation unit that calculates hydrogen concentration in the exhaust gas using the corrected hydrogen concentration. The concentration correction unit includes: increasing and correcting the measured hydrogen concentration to acquire the corrected hydrogen concentration when the oxygen concentration in the target gas is set concentration or more; and decreasing and correcting the measured hydrogen concentration to acquire the corrected hydrogen concentration when the oxygen concentration in the target gas is less than the set concentration.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a water electrolysis system. [Background technology]

[0002] Conventionally, water electrolysis systems are known that include an oxygen electrode that generates oxygen by the electrolysis (electrolysis) of water and a hydrogen electrode that generates hydrogen. In a water electrolysis system, a small amount of the hydrogen generated may permeate through the electrolyte membrane to the oxygen electrode. The hydrogen contained in the exhaust gas discharged from the oxygen electrode after permeation is usually hardly detectable, or if detected, at a very low concentration. However, the hydrogen concentration should be obtained with high accuracy as an indicator in case of an abnormality in the water electrolysis system. The gas generation system disclosed in Patent Document 1 is a water electrolysis system equipped with a catalytic combustion type gas sensor that detects the hydrogen concentration in the exhaust gas discharged from the oxygen electrode. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-9023 [Overview of the project] [Problems that the invention aims to solve]

[0004] Catalytic combustion gas sensors are prone to degradation due to sintering and other factors because the target gas being measured and the catalyst promoting that combustion are repeatedly heated. Furthermore, catalytic combustion gas sensors tend to have poor resolution at low concentrations. Therefore, they were unsuitable for detecting trace amounts of hydrogen in exhaust gas emitted from an oxygen electrode. On the other hand, while hot-wire semiconductor sensors offer high durability and resolution at low concentrations, their measurements are affected by the oxygen content in the exhaust gas. Consequently, even with hot-wire semiconductor sensors, accurately obtaining the hydrogen concentration in exhaust gas emitted from an oxygen electrode presented a challenge.

[0005] The present invention has been made to solve at least some of the above-mentioned problems, and aims to provide a water electrolysis system that can accurately obtain the hydrogen concentration in exhaust gas discharged from an oxygen electrode using a hot-wire semiconductor type concentration measuring unit. [Means for solving the problem]

[0006] The present invention has been made to solve at least some of the above-mentioned problems and can be realized in the following forms.

[0007] (1) According to one embodiment of the present invention, a water electrolysis system is provided. This water electrolysis system includes a water electrolysis unit including an oxygen electrode that generates oxygen by electrolysis of water, a mixing unit capable of mixing exhaust gas discharged from the oxygen electrode with a diluent gas, a hot-wire semiconductor type concentration measuring unit that measures the hydrogen concentration in a target gas sent from the mixing unit, a concentration correction unit that corrects the measured hydrogen concentration, which is the hydrogen concentration measured by the concentration measuring unit, with the oxygen concentration in the target gas as the reference to obtain a corrected hydrogen concentration, and a concentration calculation unit that calculates the hydrogen concentration in the exhaust gas using the corrected hydrogen concentration, wherein the concentration correction unit increases the measured hydrogen concentration to obtain the corrected hydrogen concentration when the oxygen concentration in the target gas is equal to or greater than a set concentration, and decreases the measured hydrogen concentration to obtain the corrected hydrogen concentration when the oxygen concentration in the target gas is lower than the set concentration.

[0008] The hot-wire semiconductor concentration measuring unit is suitable for measuring hydrogen concentrations in target gases where hydrogen is barely detectable or detected at very low concentrations, due to its high resolution at low concentrations. Furthermore, since measurements using the hot-wire semiconductor concentration measuring unit utilize gas adsorption to the surface of the unit, degradation due to sintering caused by heating does not occur. On the other hand, the measured hydrogen concentration, which is the hydrogen concentration measured by the concentration measuring unit, is affected by the oxygen contained in the target gas. Specifically, when measuring a target gas with an oxygen concentration higher than that of the atmosphere, the measured hydrogen concentration tends to be lower compared to when measuring a target gas with an oxygen concentration the same as that of the atmosphere. Conversely, when measuring a target gas with an oxygen concentration lower than that of the atmosphere, the measured hydrogen concentration tends to be higher compared to when measuring a target gas with an oxygen concentration the same as that of the atmosphere. Taking these tendencies into consideration, this configuration corrects the measured hydrogen concentration based on the oxygen concentration in the target gas, thereby making the measured hydrogen concentration value for any target gas with an oxygen concentration the same as that of the atmosphere. Furthermore, when the target gas is a mixture of exhaust gas and diluent gas emitted from the oxygen electrode, the hydrogen concentration in the exhaust gas emitted from the oxygen electrode is calculated using a corrected hydrogen concentration that reduces the influence of such oxygen. Therefore, the hydrogen concentration in the exhaust gas emitted from the oxygen electrode can be accurately obtained using a hot-wire semiconductor concentration measuring unit.

[0009] (2) In the water electrolysis system of the above form, the target gas may be a mixed gas of the exhaust gas and the dilution gas. Water contained in exhaust gas may hinder gas adsorption on the surface of the concentration measuring unit. However, with this configuration, since the target gas measured by the concentration measuring unit is a mixture of exhaust gas and diluent gas, the concentration measuring unit measures the target gas, which has lower humidity than the exhaust gas, thus reducing the likelihood of water hindering gas adsorption. Furthermore, if the exhaust gas contains hydrogen, the target gas is generated by diluting the exhaust gas with the diluent gas. Since the concentration measuring unit, which has high resolution at low concentrations, measures the target gas, which has a lower hydrogen concentration compared to the exhaust gas before dilution, the measured hydrogen concentration can be detected with high accuracy. Then, by calculating the hydrogen concentration in the exhaust gas using the corrected hydrogen concentration, which corrects for the accuracy of the measured hydrogen, the hydrogen concentration in the exhaust gas can be obtained with even greater accuracy using a hot-wire semiconductor type concentration measuring unit.

[0010] (3) In the water electrolysis system of the above form, the system may further include a determination unit for determining whether or not there is an abnormality in the water electrolysis system, and the determination unit may output a statement indicating that there is an abnormality in the water electrolysis system if the hydrogen concentration in the exhaust gas calculated by the concentration calculation unit is equal to or greater than a threshold concentration. With this configuration, if the hydrogen concentration in the exhaust gas calculated by the concentration calculation unit is above a threshold concentration, an output indicating a malfunction in the water electrolysis system is issued, allowing for countermeasures against the malfunction in the water electrolysis system.

[0011] (4) In the water electrolysis system of the above form, the system further includes a supply switching unit that can switch between supplying the exhaust gas to the mixing unit and stopping the supply, wherein the dilution gas is the air in the room where the water electrolysis system is installed, and when the supply of the exhaust gas to the mixing unit is being performed, the target gas is a mixture of the exhaust gas and the dilution gas, and when the supply of the exhaust gas to the mixing unit is stopped, the target gas may be the air. With this configuration, when exhaust gas is supplied to the mixing unit, the mixed gas of exhaust gas and diluent gas can be used as the target gas and measured by the concentration measuring unit. In this case, the hydrogen concentration in the exhaust gas can be calculated from the hydrogen concentration measured by the concentration measuring unit. On the other hand, when the supply of exhaust gas to the mixing unit is stopped, the air in the room where the water electrolysis system is installed can be used as the target gas and measured by the concentration measuring unit. Therefore, the hydrogen concentration in the air in the room where the water electrolysis system is installed can be measured without having to install a separate device for measuring the hydrogen concentration in the air in the room where the water electrolysis system is installed, separate from the water electrolysis system itself.

[0012] (5) In the water electrolysis system of the above form, the system further includes a determination unit for determining whether or not there is an abnormality in the water electrolysis system, and when the exhaust gas is being supplied to the mixing unit, the determination unit may output a statement indicating that there is an abnormality in the water electrolysis system if the hydrogen concentration in the exhaust gas calculated by the concentration calculation unit is equal to or greater than a first threshold concentration, and when the supply of the exhaust gas to the mixing unit is stopped, the determination unit may output a statement indicating that there is an abnormality in the water electrolysis system if the corrected hydrogen concentration is equal to or greater than a second threshold concentration. With this configuration, if the hydrogen concentration in the exhaust gas calculated by the concentration calculation unit is equal to or greater than the first threshold concentration, or if the corrected hydrogen concentration is equal to or greater than the second threshold concentration, an output indicating an abnormality in the water electrolysis system will be issued, thus enabling a response to abnormalities in the water electrolysis system.

[0013] Furthermore, the present invention can be realized in various forms, for example, as a control method for a water electrolysis system, a computer program for controlling the electrolysis of water in a water electrolysis system, a server device for distributing the computer program, a non-temporary storage medium storing the computer program, and so on. [Brief explanation of the drawing]

[0014] [Figure 1]This is an explanatory diagram showing the configuration of the water electrolysis system according to the first embodiment. [Figure 2] This is an explanatory diagram showing the detailed configuration of the water electrolysis cell that makes up the water electrolysis unit. [Figure 3] This is an explanatory diagram illustrating the measurement trends of a hot-wire semiconductor type concentration measuring unit. [Figure 4] This is an explanatory diagram of a graph converted to a logarithmic scale. [Figure 5] This is an explanatory diagram showing each of the standardized measured hydrogen concentrations. [Figure 6] This is an explanatory diagram showing the configuration of the water electrolysis system according to the fourth embodiment. [Modes for carrying out the invention]

[0015] <First Embodiment> Figure 1 is an explanatory diagram showing the configuration of a water electrolysis system 1 according to the first embodiment of the present invention. The water electrolysis system 1 is a system that generates oxygen and hydrogen by the electrolysis of water. The water electrolysis system 1 comprises a tank 5, an oxygen vapor-liquid separation unit 10, a water electrolysis unit 20, a DC power supply 25, a hydrogen vapor-liquid separation unit 30, a control unit 40, a dehumidification unit 50, an air supply pump 60, an air supply pump 70, a mixing unit 80, and a concentration measuring unit 90.

[0016] Tank 5 is a water storage tank. Flow path F1 is a flow path connecting Tank 5 and the oxygen-liquid separation unit 10. Water is supplied to the oxygen-liquid separation unit 10 from Tank 5. The oxygen-liquid separation unit 10 receives a mixed gas of oxygen and water generated in the water electrolysis unit 20 via flow path F4, and then separates at least some of the water from this mixed gas. Flow path F4 is a flow path for supplying the mixed gas of oxygen and water generated in the water electrolysis unit 20 to the oxygen-liquid separation unit 10. The gaseous portion of the mixed gas is sent to the dehumidification unit 50 via flow path F2, which connects the upper part of the oxygen-liquid separation unit 10 in the direction of gravity to the dehumidification unit 50. The water separated from the mixed gas and the water supplied from Tank 5 are supplied to the water electrolysis unit 20 via flow path F3.

[0017] Flow path F3 is a flow path for supplying water from the oxygen vapor-liquid separation unit 10 to the water electrolysis unit 20. A circulation pump P is provided in the piping (not shown) that forms flow path F3. The circulation pump P circulates water between the oxygen vapor-liquid separation unit 10, flow path F3, water electrolysis unit 20, and flow path F4 by sending water from the oxygen vapor-liquid separation unit 10 to the water electrolysis unit 20.

[0018] The water electrolysis unit 20 generates oxygen and hydrogen by electrolysis of water. The mixed gas of oxygen and water generated in the water electrolysis unit 20 is sent to the oxygen gas-liquid separation unit 10 via the flow path F4. The mixed gas of hydrogen and water generated in the water electrolysis unit 20 is sent to the hydrogen gas-liquid separation unit 30 via the flow path F5. Flow path F5 is a flow path for supplying the mixed gas of hydrogen and water generated in the water electrolysis unit 20 to the hydrogen gas-liquid separation unit 30. Control valves may be provided in the piping (not shown) forming flow paths F4 and F5. Multiple cell voltage sensors 21V measure the voltage of each water electrolysis cell 21 (explained in Figure 2) that constitutes the water electrolysis unit 20.

[0019] The hydrogen gas-liquid separation unit 30 separates at least some of the water from the mixed gas of hydrogen and water generated in the water electrolysis unit 20. The gaseous portion of the mixed gas is sent to the outside of the water electrolysis system 1 via a flow path (not shown) connected to the upper part of the hydrogen gas-liquid separation unit 30 in the direction of gravity. The water separated from the mixed gas is supplied to the water electrolysis unit 20 via a flow path (not shown) connected to the lower part of the hydrogen gas-liquid separation unit 30 in the direction of gravity. The water separated from the mixed gas may also be supplied to the oxygen gas-liquid separation unit 10 via the same flow path.

[0020] The control unit 40 controls the operation of the entire water electrolysis system 1 based on information obtained from various sensors provided by the water electrolysis system 1. Examples of control by the control unit 40 include controlling the amount of water delivered by the circulation pump P and controlling the power supply from the DC power supply 25 to the water electrolysis unit 20.

[0021] Figure 2 is an explanatory diagram showing the detailed configuration of the water electrolysis cell 21 that constitutes the water electrolysis unit 20. The water electrolysis unit 20 is composed of multiple water electrolysis cells 21 stacked on top of each other. The water electrolysis cell 21 is a PEM (Polymer Electrolyte Membrane: solid polymer electrolyte membrane) type water electrolysis cell. The water electrolysis cell 21 has a membrane electrode assembly (hereinafter referred to as "MEA") 22. The MEA 22 is a proton (H + An electrolyte membrane 24 that can pass water is joined to both sides of an oxygen electrode 26 that decomposes water to generate oxygen, hydrogen ions, and electrons, and a hydrogen electrode 28 that generates hydrogen from hydrogen ions and electrons. On the surface of the oxygen electrode 26 opposite to the electrolyte membrane 24, a power supply body 26f made of a metal mesh or the like is provided. A gasket 26g is provided around the oxygen electrode 26 and the power supply body 26f. On the other hand, on the surface of the hydrogen electrode 28 opposite to the electrolyte membrane 24, a power supply body 28f is similarly provided, and a gasket 28g is provided around the hydrogen electrode 28 and the power supply body 28f.

[0022] The assembled structure of gasket 26g, power supply unit 26f, MEA 22, gasket 28g, and power supply unit 28f is sandwiched between separator 26s provided on the oxygen electrode 26 side and separator 28s provided on the hydrogen electrode 28 side. In this sandwiched state, separator 26s forms a channel Fc through which water supplied to the water electrolysis unit 20 and a mixed gas of oxygen and water generated in the water electrolysis unit 20 flow. Separator 28s forms a channel Fa through which a mixed gas of hydrogen and water generated in the water electrolysis unit 20 flows. Separators 26s and 28s are so-called bielectrode plates.

[0023] As described above, the water electrolysis cell 21, as explained using Figure 2, is stacked to form the water electrolysis unit 20 (see Figure 1). That is, the water electrolysis unit 20 includes multiple oxygen electrodes 26 that generate oxygen by the electrolysis of water. The mixed gas of oxygen and water generated at each of the oxygen electrodes 26 can also be called the exhaust gas discharged from each of the oxygen electrodes 26. Hereafter, "exhaust gas" refers to the gas discharged from each of the oxygen electrodes 26. This exhaust gas is received by the oxygen gas-liquid separation unit 10 via the flow path F4.

[0024] As described above, the exhaust gas, after at least some of the water has been separated in the oxygen-liquid separation unit 10, is sent to the dehumidification unit 50 via the flow path F2. The dehumidification unit 50 dehumidifies the exhaust gas sent via the flow path F2.

[0025] The exhaust gas dehumidified in the dehumidification unit 50 is sent to the outside of the water electrolysis system 1 via the flow path F6. The flow path F7, which branches off from the flow path F6, is a flow path for supplying the exhaust gas dehumidified in the dehumidification unit 50 to the air supply pump 60. The air supply pump 60 is a pump capable of adjusting the flow rate of the exhaust gas supplied to the mixing unit 80 via the flow path F8. The adjustment of the flow rate of the exhaust gas by the air supply pump 60 is controlled by the control unit 40. The flow path F8 is a flow path connecting the air supply pump 60 and the mixing unit 80.

[0026] The air supply pump 70 is a pump that can adjust the flow rate of air that takes in air from the room where the water electrolysis system 1 is installed and supplies it to the mixing unit 80 via the flow path F9. The adjustment of the air flow rate by the air supply pump 70 is also controlled by the control unit 40. The flow path F9 is a flow path that connects the air supply pump 70 and the mixing unit 80.

[0027] The mixing section 80 is a part where exhaust gas and diluent gas can be mixed. Here, the diluent gas is air supplied from the air supply pump 70. In other words, the mixing section 80 is a part where exhaust gas supplied from the air supply pump 60 via the flow path F8 and air supplied from the air supply pump 70 via the flow path F9 can be mixed. In this embodiment, the mixing section 80 is a cylindrical container with a relatively large diameter. Flow paths F8, F9 and flow path F10 (described later) are connected to such a container from different directions in order to promote the mixing of exhaust gas and air.

[0028] The flow path F10 is a flow path for sending the gas mixed in the mixing unit 80 to the outside of the water electrolysis system 1. The concentration measuring unit 90 is a hot-wire semiconductor type hydrogen concentration sensor installed in the piping (not shown) that forms the flow path F10, and measures the hydrogen concentration in the target gas sent from the mixing unit 80. The target gas here refers to the gas that the concentration measuring unit 90 measures, and is the gas flowing through the flow path F10. In this embodiment, the target gas is a mixed gas of exhaust gas and dilution gas. The signal indicating the hydrogen concentration in the target gas measured by the concentration measuring unit 90 is output to the control unit 40. Note that when the concentration measuring unit 90 measures a target gas whose oxygen concentration is the same as that of the atmosphere, the hydrogen concentration value is assumed to be calibrated based on the hydrogen concentration value obtained when the same target gas is measured by gas chromatography.

[0029] Figure 3 is an explanatory diagram illustrating the measurement trend by the hot-wire semiconductor concentration measuring unit 90. The vertical axis of the graph in Figure 3 represents the measured hydrogen concentration (ppm), which is the hydrogen concentration measured by the concentration measuring unit 90. The horizontal axis of the graph in Figure 3 represents the oxygen concentration (%) in the target gas used for measurement by the concentration measuring unit 90. This target gas is produced by keeping the electrolysis conditions in the water electrolysis unit 20 (current, temperature, flow rate per unit time supplied to the oxygen electrode, etc.) constant to keep the composition of the exhaust gas (the amount of oxygen making up the majority of the exhaust gas and the amount of trace amounts of hydrogen) constant, and then mixing this exhaust gas with a diluent gas (a gas obtained by mixing nitrogen and air in an arbitrary ratio) in a constant proportion. By adjusting the amount of nitrogen and air in the diluent gas contained in each target gas used for measurement (the mixing ratio of nitrogen and air), the oxygen concentration in the target gas is adjusted, while the proportion of exhaust gas in the total target gas remains constant. Therefore, the hydrogen concentration in the target gas remains constant regardless of the mixing ratio in the diluent gas.

[0030] In Figure 3, rectangles S1 to S3 show the results of measuring the oxygen concentration of each target gas at a flow rate of 26 L / min using the concentration measuring unit 90. Each rectangle shows the results of measuring the oxygen concentration of each target gas at a flow rate of 26 L / min using the concentration measuring unit 90. Here, since the hydrogen concentration in each target gas used to obtain the results of rectangles S1 to S3 is constant, the measured hydrogen concentrations shown in rectangles S1 to S3 should ideally be the same value. However, the measured hydrogen concentrations shown in rectangles S1 to S3 were different values.

[0031] In Figure 3, triangles T1 to T5 show the results of measuring the oxygen concentration of each target gas using the concentration measuring unit 90 under a flow rate of 32.5 L / min. Circles C1 to C3 in Figure 3 show the results of measuring the oxygen concentration of each target gas using the concentration measuring unit 90 under a flow rate of 52 L / min. Here again, even though the hydrogen concentration in each target gas used to obtain the results of triangles T1 to T5 and circles C1 to C3 was constant, the measured hydrogen concentrations shown by triangles T1 to T5 and circles C1 to C3 were different values. Note that in Figure 3, square S1, triangle T2, and circle C2 represent the results of measuring the oxygen concentration of a target gas with an oxygen concentration of approximately 20% (the same composition as the Earth's atmosphere) using the concentration measuring unit 90.

[0032] Figure 4 shows the graph obtained by converting the vertical and horizontal axes of the graph shown in Figure 3 to logarithmic scales. In Figure 4 and Figure 5, which will be explained next, the signs of the squares S1-S3, triangles T1-T5, and circles C1-C3 are omitted for illustrative purposes, but each square, triangle, and circle corresponds to squares S1-S3, triangles T1-T5, and circles C1-C3, respectively. As shown in Figure 4, it was confirmed that the slopes of the respective regression lines drawn based on the results shown by each of the squares, triangles, and circles are almost the same.

[0033] Figure 5 shows the results when the measured hydrogen concentrations indicated by the squares, triangles, and circles in Figure 3 are normalized by dividing them by their respective reference measured hydrogen concentrations. Here, the reference is the measured hydrogen concentration indicated by square S1 for each square, the measured hydrogen concentration indicated by triangle T2 for each triangle, and the measured hydrogen concentration indicated by circle C2 for each circle. As shown in Figure 5, it was confirmed that the curvature of the regression curves drawn based on the normalized squares, triangles, and circles is approximately the same.

[0034] The results shown for the squares, triangles, and circles represent results under different flow rate conditions. Therefore, the results shown in Figures 4 and 5 confirm that the influence of differences in flow rate conditions on measurements by the hot-wire semiconductor concentration measuring unit 90 is not significant. Furthermore, the results shown in Figures 3 to 5 confirm that the influence of oxygen concentration in the target gas should be considered when measuring with the hot-wire semiconductor concentration measuring unit 90. Specifically, it was confirmed that when the concentration measuring unit 90 measures a target gas with an oxygen concentration higher than that of the atmospheric composition, the measured hydrogen concentration tends to be lower compared to when the concentration measuring unit 90 measures a target gas with an oxygen concentration the same as that of the atmospheric composition (see squares S2 and S3 for square S1, triangles T3 to T5 for triangle T2, and circle C3 for circle C2 in Figure 3). On the other hand, when the concentration measuring unit 90 measured a target gas with an oxygen concentration lower than that of the atmospheric composition, it was confirmed that the measured hydrogen concentration tended to be higher compared to when the concentration measuring unit 90 measured a target gas with an oxygen concentration the same as that of the atmospheric composition (see triangle T1 for triangle T2 and circle C1 for circle C2 in Figure 3).

[0035] Taking into account the trends confirmed in Figures 3 to 5, the control unit 40, as a concentration correction unit, corrects the measured hydrogen concentration, which is the hydrogen concentration measured by the concentration measuring unit 90, based on the oxygen concentration in the target gas to correct the hydrogen concentration C C H2 In other words, if the oxygen concentration in the target gas is above the set concentration, the control unit 40 increases the measured hydrogen concentration to correct the hydrogen concentration C. C H2 Furthermore, if the oxygen concentration in the target gas is lower than the set concentration, the control unit 40 reduces the measured hydrogen concentration to correct the hydrogen concentration C. C H2Let it be so. Here, the grasping of the oxygen concentration in the target gas will be described later. The set concentration is set to the same oxygen concentration as the atmospheric composition. Also, the degree of increase correction and decrease correction is such that, among various target gases with the same hydrogen concentration but different oxygen concentrations, the measured hydrogen concentration obtained by previously measuring them with the concentration measurement unit 90 under the same flow rate conditions is based on the difference between the measured hydrogen concentration of the target gas with the same oxygen concentration as the atmospheric composition and the measured hydrogen concentration of other target gases. Each group of target gases with the same hydrogen concentration is prepared for each of various concentrations, and each group is to be measured by the concentration measurement unit 90 under various flow rate conditions. Also, prior to this measurement, it is assumed that the measured hydrogen concentration of the target gas with the same oxygen concentration as the atmospheric composition has been calibrated based on the hydrogen concentration measured by gas chromatography of the same target gas. For the calibration of this measured hydrogen concentration, in addition to the hydrogen concentration measured by gas chromatography of the same target gas, the oxygen concentration and nitrogen concentration measured simultaneously with that hydrogen concentration may be referred to.

[0036] In this embodiment, the corrected hydrogen concentration C C H2 is represented by the following formula (1).

Equation

[0037] This section explains how to determine the oxygen concentration in the target gas, which serves as a reference when correcting the measured hydrogen concentration. In this embodiment, the control unit 40 can determine the oxygen concentration in the target gas based on the assumption that the diluent gas in the target gas is air, which has a self-evident oxygen concentration, that the exhaust gas in the target gas is considered to be almost entirely oxygen (see the explanation of Equation 3 below for details), and that the control unit 40 can acquire the values ​​of V0 and V1. Specifically, the control unit 40 can determine the oxygen concentration in the target gas using the right-hand side of Equation 2, which will be explained in the second embodiment.

[0038] Furthermore, the control unit 40, acting as a determination unit, determines whether or not there is an abnormality in the water electrolysis system 1. Specifically, the control unit 40 determines the hydrogen concentration C in the exhaust gas calculated by the concentration calculation unit. O H2 If the concentration exceeds a threshold, the water electrolysis system 1 outputs a message indicating a malfunction. The threshold concentration is set to, for example, 0.4%, based on the lower explosive limit concentration of hydrogen, which is 4%. The message indicating a malfunction in the water electrolysis system 1 may be a notification to the administrator of the water electrolysis system 1, or it may be a control to stop the power supply from the DC power supply 25 to the water electrolysis unit 20 or a control to stop the water supply to the water electrolysis unit 20 in order to stop electrolysis by the water electrolysis unit 20. The control to stop the water supply is performed by stopping the water being sent out by the circulation pump P.

[0039] As explained above, the water electrolysis system 1 of the first embodiment is suitable for measuring the hydrogen concentration in a target gas where hydrogen is hardly detectable or, if detected, is at a very low concentration, because the concentration measuring unit 90 is a hot-wire semiconductor type and therefore has high resolution at low concentrations. Furthermore, when measuring with the hot-wire semiconductor type concentration measuring unit 90, the measurement is performed by utilizing gas adsorption to the surface of the concentration measuring unit 90, so deterioration due to sintering caused by heating does not occur. On the other hand, the measured hydrogen concentration, which is the hydrogen concentration measured by the concentration measuring unit 90, is affected by the oxygen contained in the target gas, as explained in Figures 3 to 5. Specifically, when the concentration measuring unit 90 measures a target gas in which the oxygen concentration is higher than that of the atmospheric composition, the measured hydrogen concentration tends to be lower compared to when the concentration measuring unit 90 measures a target gas in which the oxygen concentration is the same as that of the atmospheric composition. Conversely, when the concentration measuring unit 90 measures a target gas in which the oxygen concentration is lower than that of the atmospheric composition, the measured hydrogen concentration tends to be higher compared to when the concentration measuring unit 90 measures a target gas in which the oxygen concentration is the same as that of the atmospheric composition. Taking this trend into consideration, according to the water electrolysis system 1 of the first embodiment, the measured hydrogen concentration is corrected to a corrected hydrogen concentration C based on the oxygen concentration in the target gas. C H2 Therefore, regardless of the oxygen concentration of the target gas, the measured hydrogen concentration value obtained with that target gas can be brought closer to the value that would be measured if the oxygen concentration were the same as that of the atmosphere. Furthermore, in the water electrolysis system 1 of the first embodiment, the corrected hydrogen concentration C reduces the influence of oxygen. C H2 Using this method, the hydrogen concentration C in the exhaust gas discharged from the oxygen electrode 26 is measured. O H2 To calculate the hydrogen concentration C in the exhaust gas emitted from the oxygen electrode 26, the hot-wire semiconductor type concentration measuring unit 90 is used. O H2 It can be obtained with high accuracy.

[0040] Water contained in the exhaust gas may inhibit gas adsorption on the surface of the concentration measuring unit 90. In this respect, according to the water electrolysis system 1 of the first embodiment, since the target gas measured by the concentration measuring unit 90 is a mixture of exhaust gas and diluent gas, the concentration measuring unit 90 measures the target gas, which has a lower humidity than the exhaust gas, thus making it less likely for water to inhibit gas adsorption. Furthermore, if the exhaust gas contains hydrogen, the target gas is generated by diluting the exhaust gas with the diluent gas, so the concentration measuring unit 90, which has high resolution at low concentrations, measures the target gas, which has a lower hydrogen concentration than the exhaust gas before dilution, thus enabling accurate detection of the measured hydrogen concentration. And the corrected hydrogen concentration C corrected for such measured hydrogen accuracy C H2 Using the hydrogen concentration C in exhaust gas O H2 Since the hydrogen concentration C in the exhaust gas is calculated using a hot-wire semiconductor type concentration measuring unit 90, O H2 This allows for more accurate acquisition.

[0041] Furthermore, in the water electrolysis system 1 of the first embodiment, the hydrogen concentration C in the exhaust gas is calculated by the concentration calculation unit. O H2 If the concentration exceeds the threshold, an output indicating a malfunction in the water electrolysis system 1 will be generated, allowing for action to be taken against the malfunction in the water electrolysis system 1.

[0042] <Second Embodiment> The water electrolysis system of the second embodiment (not shown) is the same as the water electrolysis system of the first embodiment, except that the concentration measuring unit 90 is different and the control unit 40, which functions as a concentration calculation unit, uses a different formula than formula 1. Therefore, the apparent configuration is the same as that of Figure 1.

[0043] In the water electrolysis system of the second embodiment, the concentration measuring unit 90 includes a galvanic cell type oxygen concentration sensor in addition to a hot-wire semiconductor type hydrogen concentration sensor. The galvanic cell type oxygen concentration sensor has high resolution at high concentrations. That is, in the water electrolysis system of the second embodiment, it is possible to measure not only the hydrogen concentration in the target gas but also the oxygen concentration in the target gas.

[0044] In this embodiment, the measured oxygen concentration C is the oxygen concentration measured by the concentration measuring unit 90. O2 This is expressed by the following equation 2.

number

number

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number

[0045] <Third Embodiment> The water electrolysis system of the third embodiment (not shown) is the same as the water electrolysis system of the first embodiment, except that the concentration measuring unit 90 is different and the target gas measured by the concentration measuring unit 90 is switched. Therefore, the apparent configuration is the same as in Figure 1.

[0046] In the third embodiment of the water electrolysis system, similar to the second embodiment, the concentration measuring unit 90 includes a galvanic cell type oxygen concentration sensor in addition to a hot-wire semiconductor type hydrogen concentration sensor. That is, in the third embodiment of the water electrolysis system, it is possible to measure not only the hydrogen concentration in the target gas but also the oxygen concentration in the target gas.

[0047] In the first embodiment, the target gas was always a mixture of exhaust gas and diluent gas, but in the third embodiment, the target gas is either a mixture of exhaust gas and diluent gas, or the air in the room where the water electrolysis system is installed. More specifically, in the third embodiment, the air supply pump 60 acts as a supply switching unit that can switch between supplying exhaust gas to the mixing unit 80 and stopping it, and this switching is controlled by the control unit 40. That is, when exhaust gas is being supplied to the mixing unit 80, the target gas is a mixture of exhaust gas and diluent gas. When exhaust gas is being supplied to the mixing unit 80, the control unit 40 acts as a determination unit to determine whether or not there is an abnormality in the water electrolysis system, and the hydrogen concentration C in the exhaust gas O H2 If the hydrogen concentration C is above the first threshold concentration, an output indicating a malfunction in the water electrolysis system will be displayed. O H2 This is the hydrogen concentration C calculated when the control unit 40 functions as a concentration calculation unit. O H2 The first threshold concentration is set to, for example, 0.4%, using 4% as a guideline, which is the lower explosive limit concentration of hydrogen, as in the first embodiment.

[0048] On the other hand, when the supply of exhaust gas to the mixing unit 80 is stopped, only dilution gas from the air supply pump 70 (air from the room where the water electrolysis system is installed) is sent to the mixing unit 80, so the target gas is that air. In this case, the concentration measuring unit 90 measures the hydrogen concentration in that air as the hydrogen concentration in the target gas. Furthermore, the control unit 40, acting as a concentration correction unit, corrects the measured hydrogen concentration, which is the hydrogen concentration in the air measured by the concentration measuring unit 90, based on the oxygen concentration in that air to obtain a corrected hydrogen concentration C C H2 In this case, the oxygen concentration in the air is likely to be the same as the oxygen concentration in the atmospheric composition (i.e., the set concentration), and in such cases, no increase or decrease correction is performed. However, even for measured hydrogen concentrations where no increase or decrease correction was performed, the corrected hydrogen concentration C C H2 This shall be considered. When the supply of exhaust gas to the mixing unit 80 is stopped, the control unit 40 acts as a determination unit to determine whether or not there is an abnormality in the water electrolysis system, and the corrected hydrogen concentration C C H2 If the concentration is above the second threshold concentration, an output indicating an abnormality in the water electrolysis system is issued. The second threshold concentration may be set in the same way as the first threshold concentration, or it may be set using a different standard than the first threshold concentration. Immediately after the exhaust gas supply to the mixing unit 80 switches from active to stopped, exhaust gas remains in the gas flowing through the flow path F10. Since the exhaust gas consists mostly of oxygen with a small amount of hydrogen, it is possible to confirm that the gas flowing through the flow path F10 no longer contains exhaust gas by monitoring the oxygen concentration in the gas flowing through the flow path F10. Therefore, the concentration measurement unit 90 performs the measurement after a period of time has elapsed from the time the exhaust gas supply to the mixing unit 80 switches from active to stopped until the gas flowing through the flow path F10 no longer contains exhaust gas, and the corrected hydrogen concentration C is determined based on the measurement result. C H2 It is preferable that this be compared to the second threshold concentration.

[0049] According to the water electrolysis system of the third embodiment described above, when the supply of the exhaust gas to the mixing unit 80 is being executed, the mixed gas of the exhaust gas and the dilution gas can be used as the target gas and measured by the concentration measurement unit 90. In this case, from the hydrogen concentration measured by the concentration measurement unit 90, the hydrogen concentration C in the exhaust gas can be calculated as described in the first embodiment. O H2 can be calculated. On the other hand, when the supply of the exhaust gas to the mixing unit 80 is stopped, since the air in the room where the water electrolysis system is installed can be used as the target gas and measured by the concentration measurement unit 90, the hydrogen concentration in the air in the room where the water electrolysis system is installed can be measured without separately installing a device for measuring the hydrogen concentration in the air in the same room from the water electrolysis system. Also, compared with the case where the air in the room where the water electrolysis system is installed is the target gas, when the mixed gas of the exhaust gas and the dilution gas is the target gas, since the oxygen concentration in the target gas is high, the burden on the measurement by the concentration measurement unit 90 is large. Therefore, by appropriately switching the target gas, the life of the concentration measurement unit 90 can be extended.

[0050] Also, in the water electrolysis system of the third embodiment, when the hydrogen concentration C in the exhaust gas O H2 is equal to or higher than the first threshold concentration, or when the corrected hydrogen concentration C C H2 is equal to or higher than the second threshold concentration, an output indicating that there is an abnormality in the water electrolysis system is performed in either case, so that the abnormality of the water electrolysis system can be dealt with.

[0051] <Fourth Embodiment> FIG. 6 is an explanatory diagram showing the configuration of the water electrolysis system 1a of the fourth embodiment of the present invention.The water electrolysis system 1a of the fourth embodiment is the same as the water electrolysis system 1 of the first embodiment, except that the concentration measurement unit 90 is different, the blower 45 is provided, and a different mathematical formula from Formula 1 is used when the control unit 40 functions as the concentration calculation unit.

[0052] In the fourth embodiment of the water electrolysis system 1a, similar to the second and third embodiments, the concentration measuring unit 90 includes a galvanic cell type oxygen concentration sensor in addition to a hot-wire semiconductor type hydrogen concentration sensor. That is, in the fourth embodiment of the water electrolysis system 1a, it is possible to measure not only the hydrogen concentration in the target gas but also the oxygen concentration in the target gas. In this embodiment, the target gas is always a mixed gas of exhaust gas and dilution gas (air in the room where the water electrolysis system 1a is installed).

[0053] The blower 45 is a device that can adjust the flow rate of air taken in from the room where the water electrolysis system 1a is installed and supplied to the flow path F2 via the flow path F11. The adjustment of the air flow rate by the blower 45 is also controlled by the control unit 40. The flow path F11 is a flow path that branches off from the flow path F2 and connects to the blower 45. In the water electrolysis system 1a, when the power supplied from the DC power supply 25 to the water electrolysis unit 20 is relatively low, the hydrogen concentration in the exhaust gas tends to increase. Relatively low power supply conditions include situations where the power decreases when the power is varied and supplied to the water electrolysis unit 20, or immediately after starting or just before stopping the water electrolysis system 1a. In such cases, the exhaust gas is diluted by supplying air from the blower 45 to the flow path F2.

[0054] In this embodiment, when electrolysis is being performed by the water electrolysis unit 20 and air is being supplied from the blower 45 to the flow path F2 (hereinafter referred to as exhaust gas dilution), the measured oxygen concentration C is the oxygen concentration measured by the concentration measuring unit 90. O2 This is expressed by the following formula 6.

number

[0055] The right side of Equation 6 is derived using the following Equations 7 to 9.

Number

Number

Number

[0056] Returning to the explanation of Equation 6. Since the control unit 40 adjusts the flow rates of the air supply pump 70 and the blower 45, the values of V1 and V3 can be obtained. Also, since the control unit 40 controls the power supply from the DC power supply 25 to the water electrolysis unit 20, the value of V2 can be estimated by referring to this power. Therefore, the control unit 40 can calculate the flow rate V0 by substituting the measured oxygen concentration C O2 , the oxygen concentration C in the exhaust gas O O2 (known from Equation 3), the oxygen concentration C in the air 1 O2 , the flow rates V1, V2, and V3 into Equation 6.

[0057] Furthermore, in this embodiment, the corrected hydrogen concentration C C H2 This is expressed by the following formula 10.

number

[0058] <Modified form of this embodiment> The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit, for example, the following modifications are also possible.

[0059] In the embodiment described above, the water electrolysis unit 20 was constructed by stacking a plurality of water electrolysis cells 21, but it is not limited to this. The water electrolysis unit 20 may be composed of a single water electrolysis cell 21.

[0060] In the embodiment described above, the mixing section 80 was a cylindrical container, but it is not limited to this. For example, the mixing section 80 can be any shape as long as it is a part that can efficiently mix the exhaust gas sent from the air pump 60 via the flow path F8 and the dilution gas sent from the air pump 70 via the flow path F9. Also, in the embodiment described above, it was assumed that the flow paths F8, F9 and F10 are connected from different directions to promote mixing of the exhaust gas and air, but it is not limited to this. Instead of connecting the flow paths F8, F9 and F10 from different directions, a static mixer may be provided inside at least one of the flow paths F8, F9 and F10. Of course, a static mixer may be provided inside at least one of the flow paths F8, F9 and F10 that are connected from different directions.

[0061] In the embodiment described above, the set concentration, which is the criterion for increasing or decreasing the measured hydrogen concentration, was set to the same oxygen concentration as the atmospheric composition, but it is not limited to this. For example, the set concentration may be set to any oxygen concentration different from the atmospheric composition. In this case, the degree of increase and decrease correction is determined according to the difference between the measured hydrogen concentration of a target gas whose oxygen concentration is the same as the set concentration and the measured hydrogen concentration of other target gases, based on the measured hydrogen concentrations of various target gases with the same hydrogen concentration but different oxygen concentrations measured in the concentration measuring unit 90 under the same flow rate conditions. Furthermore, prior to this measurement, the measured hydrogen concentration of a target gas whose oxygen concentration is the same as the set concentration is assumed to have been calibrated based on the hydrogen concentration of the same target gas measured by gas chromatography.

[0062] In the fourth embodiment described above, the control unit 40 calculated the value of the flow rate V0 using formula 6, but it is not limited to this. The control unit 40 adjusts the flow rate of the air supply pump 60 and may acquire the value of V0 if it is possible to acquire the value of V0.

[0063] In the third embodiment described above, the target gas was switched to either a mixed gas of exhaust gas and dilution gas, or the air in the room where the water electrolysis system is installed, by switching between supplying exhaust gas to the mixing unit 80 and stopping the supply. In the fourth embodiment, the target gas may be switched in a similar manner. Of course, even in this case, the presence or absence of an abnormality in the water electrolysis system 1a may be determined using a first threshold concentration or a second threshold concentration, depending on the target gas measured by the concentration measuring unit 90.

[0064] The embodiments of this specification have been described above based on the embodiments and modifications described above. The embodiments described above are for the purpose of facilitating understanding of this specification and do not limit it. This specification may be modified and improved without departing from its spirit and the scope of the claims, and equivalents thereof are included in this specification. Furthermore, any technical features that are not described as essential in this specification may be deleted as appropriate.

[0065] The present invention can also be realized in the following forms. [Application Example 1] A water electrolysis system, A water electrolysis unit containing an oxygen electrode that generates oxygen by electrolysis of water, A mixing unit capable of mixing exhaust gas discharged from the oxygen electrode with a diluent gas, A hot-wire semiconductor type concentration measuring unit for measuring the hydrogen concentration in the target gas sent from the mixing unit, A concentration correction unit corrects the measured hydrogen concentration, which is the hydrogen concentration measured by the concentration measuring unit, based on the oxygen concentration in the target gas to obtain a corrected hydrogen concentration. The system includes a concentration calculation unit that calculates the hydrogen concentration in the exhaust gas using the corrected hydrogen concentration, The aforementioned concentration correction unit, If the oxygen concentration in the target gas is equal to or greater than the set concentration, the measured hydrogen concentration is increased to obtain the corrected hydrogen concentration. A water electrolysis system that, when the oxygen concentration in the target gas is lower than the set concentration, reduces the measured hydrogen concentration to obtain the corrected hydrogen concentration. [Application Example 2] The water electrolysis system described in Application Example 1, The target gas is a mixed gas of the exhaust gas and the diluent gas in a water electrolysis system. [Application Example 3] A water electrolysis system as described in Application Example 1 or Application Example 2, further comprising: The system includes a determination unit that determines whether or not there is an abnormality in the water electrolysis system, The determination unit outputs a message indicating that there is an abnormality in the water electrolysis system if the hydrogen concentration in the exhaust gas calculated by the concentration calculation unit is equal to or greater than a threshold concentration. [Application Example 4] A water electrolysis system described in any of Application Examples 1 to 3, further comprising: The system includes a supply switching unit that can switch between supplying the exhaust gas to the mixing unit and stopping the supply, The dilution gas is the air in the room where the water electrolysis system is installed. When the exhaust gas is being supplied to the mixing unit, the target gas is a mixed gas of the exhaust gas and the dilution gas. A water electrolysis system in which, when the supply of the exhaust gas to the mixing section is stopped, the target gas is air. [Application Example 5] A water electrolysis system described in any of Application Examples 1 to 4, further comprising: The system includes a determination unit that determines whether or not there is an abnormality in the water electrolysis system, When the exhaust gas is being supplied to the mixing unit, the determination unit outputs a message indicating that there is an abnormality in the water electrolysis system if the hydrogen concentration in the exhaust gas calculated by the concentration calculation unit is equal to or greater than the first threshold concentration. A water electrolysis system in which, when the supply of exhaust gas to the mixing unit is stopped, the determination unit outputs a message indicating that there is an abnormality in the water electrolysis system if the corrected hydrogen concentration is equal to or greater than the second threshold concentration. [Explanation of Symbols]

[0066] 1,1a...Water electrolysis system 5... Tank 10…Oxygen-liquid separation unit 20...Water electrolysis section 21...Water electrolysis cell 21V...Cell voltage sensor 24...Electrolyte membrane 25…DC power supply 26…Oxygen electrode 26f,28f…Power supply 26g, 28g... gasket 26s, 28s... Separator 28…Hydrogen electrode 30…Hydrogen gas-liquid separation section 40... Control Unit 45... Blower 50...Dehumidification section 60, 70… Air supply pumps 80…Mixing section 90...Concentration measuring section F1~F11...flow channels Fa, Fc…flow channels P...Circulation pump

Claims

1. A water electrolysis system, A water electrolysis unit containing an oxygen electrode that generates oxygen by electrolysis of water, A mixing unit capable of mixing exhaust gas discharged from the oxygen electrode with a diluent gas, A hot-wire semiconductor type concentration measuring unit for measuring the hydrogen concentration in the target gas sent from the mixing unit, A concentration correction unit corrects the measured hydrogen concentration, which is the hydrogen concentration measured by the concentration measuring unit, based on the oxygen concentration in the target gas to obtain a corrected hydrogen concentration. The system includes a concentration calculation unit that calculates the hydrogen concentration in the exhaust gas using the corrected hydrogen concentration, The aforementioned concentration correction unit, If the oxygen concentration in the target gas is equal to or greater than the set concentration, the measured hydrogen concentration is increased to obtain the corrected hydrogen concentration. A water electrolysis system that, when the oxygen concentration in the target gas is lower than the set concentration, reduces the measured hydrogen concentration to obtain the corrected hydrogen concentration.

2. A water electrolysis system according to claim 1, The target gas is a mixed gas of the exhaust gas and the diluent gas in a water electrolysis system.

3. The water electrolysis system according to claim 2, further, The system includes a determination unit that determines whether or not there is an abnormality in the water electrolysis system, The determination unit outputs a message indicating that there is an abnormality in the water electrolysis system if the hydrogen concentration in the exhaust gas calculated by the concentration calculation unit is equal to or greater than a threshold concentration.

4. A water electrolysis system according to claim 1, further, The system includes a supply switching unit that can switch between supplying the exhaust gas to the mixing unit and stopping the supply, The dilution gas is the air in the room where the water electrolysis system is installed. When the exhaust gas is being supplied to the mixing unit, the target gas is a mixed gas of the exhaust gas and the dilution gas. A water electrolysis system in which, when the supply of the exhaust gas to the mixing section is stopped, the target gas is air.

5. The water electrolysis system according to claim 4, further, The system includes a determination unit that determines whether or not there is an abnormality in the water electrolysis system, When the exhaust gas is being supplied to the mixing unit, the determination unit outputs a message indicating that there is an abnormality in the water electrolysis system if the hydrogen concentration in the exhaust gas calculated by the concentration calculation unit is equal to or greater than the first threshold concentration. A water electrolysis system in which, when the supply of exhaust gas to the mixing unit is stopped, the determination unit outputs a message indicating that there is an abnormality in the water electrolysis system if the corrected hydrogen concentration is equal to or greater than the second threshold concentration.

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