Water electrolysis system, and water electrolysis system controlling device

Abstract

To prevent deterioration and failure of an electrolysis tank by calculating a suitable adjustment reserve capacity that is instantaneously adaptable, in a water electrolysis system changing the power consumption by detecting the system frequency to rapidly change the power consumption.SOLUTION: The water electrolysis system is configured to include a rectifier changing an AC power of the electric power system to a DC power, an electrolysis tank electrolyzing water using the DC power from the rectifier, a gas-liquid separator separating oxygen and hydrogen from a mixed fluid of oxygen and hydrogen flowing from the electrolysis tank, and a cooling system supplying the electrolytic tank with water. The water electrolysis system controls the rectifier to adjust the power consumption according to the frequency of the electric power system to adjust the power consumption within the restricted range of the power consumption in the electrolysis tank, and determines the restricted range of the power consumption according to the temperature of the electrolysis tank, the deterioration rate, the water pressure at the outlet of the electrolysis tank, and the flow rate of the water being supplied.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a water electrolysis system and a water electrolysis system control device that detects a grid frequency and changes power consumption. [Background technology]

[0002] Hydrogen is a clean energy source that does not emit carbon dioxide when burned, unlike fossil fuels. For this reason, it has been drawing attention as one of the clean energy sources for global warming countermeasures, and technological development is being promoted for the production, transportation, and use of hydrogen. One method of hydrogen production is the water electrolysis system.

[0003] To produce clean hydrogen, renewable energy is necessary as an energy source. Renewable energy sources such as solar and wind power have large fluctuations in the amount of power generated over time, and as the amount of power generated increases, an adjustment capability is required to adjust the balance between power supply and demand. Therefore, it has been proposed to use the adjustment capability by adjusting the power consumption of water electrolysis systems.

[0004] Patent Document 1 describes an output control device that controls the output of an electrolyzer within the range of rated output or maximum output based on a command for adjusting power demand over a time period of about 2-3 minutes to several hours, or based on a change in system frequency for adjusting power demand over a time period of about several seconds to several tens of seconds.

[0005] Patent Document 2 describes a hydrogen supply system, a hydrogen station, and a hydrogen supply and demand management method in which the amount of power consumption of an electrolysis device is adjusted based on a command for adjusting the power supply and demand of a commercial power grid, and the amount of adjustment is determined based on an adjustment margin calculated from the difference between the maximum and minimum rated values ​​of the electrolysis device and the current operating output, the remaining amount of hydrogen, the future supply and demand balance, etc. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2011-50138 A [Patent Document 2] JP 2021-134863 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the hydrogen supply system described in Patent Document 1 and Patent Document 2, when a relatively long-period adjustment capability is provided to adjust the power consumption after receiving a power command, it is possible to change the flow rate of water to the electrolytic cell to follow the change in power consumption. On the other hand, in the case of short-period adjustment, it is difficult to make the water flow rate change and temperature control follow the rapid change in power consumption. Therefore, if the power consumption is changed by calculating the adjustment margin from the difference between the maximum and minimum ratings of the electrolytic cell and the current operating output, an abnormal temperature distribution or current distribution may occur inside the electrolysis stack, causing deterioration or failure. In addition, the mixed fluid of gas and water coming out of the electrolytic cell may deviate from the appropriate gas-liquid ratio and may not be sufficiently separated by the gas-liquid separator.

[0008] Therefore, an object of the present invention is to prevent deterioration or failure of an electrolytic cell by calculating an appropriate adjustment margin that allows the electrolytic cell to instantly respond in a water electrolysis system in which power consumption is changed by detecting a grid frequency in order to rapidly change power consumption.

[0009] Furthermore, the present invention aims to suppress deterioration and failure of the electrolytic device due to rapid changes in power consumption, even in a system in which multiple electrolytic cells are electrically connected in series and parallel and the power consumption of each electrolytic cell cannot be controlled individually. [Means for solving the problem]

[0010] In view of the above, the present invention provides "a water electrolysis system comprising a rectifier that converts AC power from a power system into DC power, an electrolytic cell that performs water electrolysis using the DC power from the rectifier, a gas-liquid separator that separates oxygen and hydrogen into gas-liquid from a mixed fluid of oxygen and water from the electrolytic cell, and a cooling system that supplies water to the electrolytic cell, wherein the rectifier is controlled to adjust power consumption in accordance with the frequency of the power system, the adjustment is made to adjust the power consumption so that it falls within a power consumption limit range in the electrolytic cell, and the power consumption limit range is determined from the temperature of the electrolytic cell, the deterioration rate, the pressure of water at the outlet of the electrolytic cell, and the flow rate of supplied water."

[0011] The present invention provides "a control device for a water electrolysis system including a rectifier that converts AC power from a power system into DC power, an electrolytic cell that performs water electrolysis using the DC power from the rectifier, a gas-liquid separator that separates oxygen and hydrogen into gas and liquid from a mixed fluid of oxygen and water from the electrolytic cell, and a cooling system that supplies water to the electrolytic cell, wherein the control device controls the rectifier to adjust power consumption in accordance with the frequency of the power system, adjusts the power consumption so that it is within a limited range of power consumption in the electrolytic cell, and determines the limited range of power consumption from the temperature of the electrolytic cell, the deterioration rate, the pressure of water at the outlet of the electrolytic cell, and the flow rate of supplied water." Effect of the Invention

[0012] According to the present invention, the power consumption adjustment margin is determined taking into account the flow rate of water to the electrolytic cell, so that abnormal temperature distributions and current distributions do not occur, and deterioration and breakdowns of the electrolytic cell can be suppressed.

[0013] In addition, in a water electrolysis system according to another embodiment, the regulating capacity of the system is determined so as to be within the range of the regulating capacity of each electrolytic cell electrically connected in series and parallel. This prevents abnormal temperature distribution or current distribution from occurring in any of the electrolytic cells, making it possible to suppress deterioration or failure of the electrolytic cells.

[0014] Further features related to the present invention will become apparent from the description of the present specification and the accompanying drawings. Furthermore, the objects, configurations and effects other than those described above will become apparent from the following description of the embodiments. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing an example of the overall configuration of a water electrolysis system according to a first embodiment of the present invention. [Diagram 2] 2 is a schematic diagram showing an example of the configuration of a power control command unit 21 according to the first embodiment of the present invention. FIG. [Diagram 3] FIG. 11 is a diagram showing an example of a setting command for power consumption according to an AC frequency. [Figure 4] FIG. 11 is a diagram showing an example of a setting command for power consumption according to an AC frequency. [Diagram 5] FIG. 1 is a schematic diagram showing an example of the overall configuration of a water electrolysis system according to a second embodiment of the present invention. [Figure 6] FIG. 11 is a schematic diagram showing an example of the configuration of a power control command unit 21 according to a second embodiment of the present invention. [Figure 7] FIG. 13 is a graph showing the current-voltage characteristics of an electrolytic cell calculated based on the rate of change in internal resistance. [Figure 8] A diagram showing the relationship between power consumption, current density, heat generation, and cell voltage. [Figure 9] A diagram showing the relationship between power consumption, current density, heat generation, and cell voltage. [Figure 10] A diagram showing the electrical connection circuit and electrolytic cell number of electrolytic cell 3a. [Figure 11] A graph showing the relationship between current density and average cell voltage for each of the 12 electrolytic cells. [Figure 12] FIG. 4 is a diagram showing the relationship between the system current density and the cell voltage of each electrolytic cell 3a. [Figure 13] FIG. 4 is a diagram showing the relationship between the system current density and the current of each electrolytic cell 3a. [Figure 14] FIG. 4 is a diagram showing the relationship between the system current density and the amount of heat generated in each electrolytic cell 3a. [Figure 15] 4 is a diagram showing an example of an upper limit of heat generation, an upper limit of current density, and an upper and lower limit of system power consumption. [Figure 16]FIG. 1 is a diagram showing an example of upper and lower limits of current density as an electrolytic cell and system power consumption. [Figure 17] 5A and 5B are diagrams showing an example of an upper limit of heat generation, an upper limit of current density, and system power consumption. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. The same components are denoted by the same reference numerals, and the description of the same components may be omitted if they are repeated. The present invention is not limited to the following embodiments and examples.

[0017] Before describing the embodiments of the present invention, prerequisites for a water electrolysis system will be summarized below.

[0018] First, electrolytic cells used in water electrolysis systems include alkaline type, solid polymer type, anion exchange membrane type, etc. The present invention is applicable to any type of electrolytic cell, but a solid polymer type, which has excellent output responsiveness, will be shown as an example.

[0019] In a typical electrolytic cell, the efficiency of energy conversion from electricity to hydrogen is about 70-90%, and the remainder becomes heat, which heats the components of the electrolytic cell and the water flowing inside. For this reason, the temperature increases from the upstream to the downstream of the water flow path, creating a temperature distribution inside the electrolytic cell.

[0020] In addition, when the flow rate of water in the electrolytic cell varies, the temperature is higher in the low flow rate area, and a temperature distribution occurs. The higher the temperature of the electrolytic cell of the electrolytic cell, the lower the resistance becomes, but when the temperature exceeds the heat resistance temperature of 60 to 100°C, the electrolyte membrane and electrode catalyst that make up the electrolytic cell deteriorate and the resistance increases, the electrolyte membrane that separates hydrogen and oxygen is thinned and the amount of hydrogen and oxygen that permeates increases, holes are formed in the electrolyte membrane, and an electrical short circuit occurs.

[0021] Furthermore, when the temperature difference in the electrolytic cell becomes large, the resistance difference in the electrolytic cell also becomes large, and current is concentrated in the high temperature portion.

[0022] In addition, when the volume ratio of the generated gas to the water, which is the raw material for the reaction, is high in the flow path of the electrolytic cell, the resistance increases due to insufficient water supply to the electrodes, and the current concentrates in the area where the volume ratio of the gas is low. Such current concentration leads to a localized temperature rise, which may cause deterioration or failure. Therefore, it is important to suppress the occurrence of temperature differences and high gas volume ratio areas in the electrolytic cell.

[0023] Most of the heat generated in the electrolytic cell is carried out by the supplied water to the outside of the cell, and the temperature difference generated in the water flow direction inside the electrolytic cell is proportional to the amount of heat generated in the electrolytic cell and inversely proportional to the water flow rate. In addition, the amount of gas generated is proportional to the current, and the higher the current value, the higher the gas volume ratio at the flow outlet.

[0024] For this reason, in order to suppress the occurrence of temperature differences and high gas volume ratio regions within the electrolytic cell, it is important to supply a sufficient amount of water in accordance with the current and output of the electrolytic cell. EXAMPLES

[0025] 1 shows an example of the configuration of a water electrolysis system according to a first embodiment of the present invention. The water electrolysis system includes a main system and a control system for controlling the main system.

[0026] Of these, the main system can be said to be composed of an insulating transformer 1 that adjusts the voltage from the system power 22 and insulates the water electrolysis system side from the system side, a rectifier 2 that converts AC power to DC power, an electrolytic cell 3 that performs water electrolysis using the DC power from the rectifier 2, an oxygen-side gas-liquid separator 4 that separates oxygen 24 into gas and liquid from a mixed fluid of oxygen and water from the electrolytic cell 3, a hydrogen-side gas-liquid separator 5 that separates hydrogen 25 into gas and liquid from a mixed fluid of hydrogen and water from the electrolytic cell 3, a pure water production device 6 that purifies water 23, a pump 7 that supplies pure water to the electrolytic cell 3, a heat exchanger 8 that cools the pure water, a cooler 9 that supplies cooling water to the heat exchanger 8, and a cooling water regulating valve 10 that adjusts the flow rate of cooling water to the heat exchanger 8.

[0027] In contrast, the control system that controls the main system can be said to be configured to include an AC power detection unit 11 that detects AC voltage, current, and frequency, a DC power detection unit 12 that detects DC current and voltage to the electrolytic cell, a flow meter 13 that detects the water flow rate to the electrolytic cell 3, a water inlet thermometer 14 that detects the water temperature at the electrolytic cell inlet, an electrolytic cell thermometer 15 that detects the electrolytic cell temperature, a water outlet thermometer 16 that detects the water temperature at the electrolytic cell outlet, a water outlet pressure gauge 17 that detects the pressure on the water outlet side of the electrolytic cell 3, a hydrogen pressure gauge 18 that detects the hydrogen pressure, a water flow control unit 19 that controls the water flow rate to the electrolytic cell 3, a water temperature control unit 20 that controls the water temperature at the electrolytic cell inlet, and a power control command unit 21 that determines the power consumption in the water electrolysis system.

[0028] The electrolytic cell thermometer 15 and the water outlet thermometer 16 may be omitted, and the temperature may be estimated from the water inlet thermometer 14 and the DC current and voltage detected by the DC power detector 12. The heat exchanger 8 may be disposed in a different position, or may be added. Other devices such as a pure water purifier or tank, a pressure control valve, a hydrogen dryer, and a booster may be added.

[0029] According to the main system configuration of the water electrolysis system in Figure 1, water is supplied to the electrolytic cell 3 with its flow rate and temperature controlled by the pump 7 and heat exchanger 8, and the water is electrolyzed by a direct current supplied from the rectifier 2, producing hydrogen and oxygen. The produced hydrogen and oxygen are each discharged from the electrolytic cell 3 together with the water. The oxygen is separated in the oxygen-side gas-liquid separator 4 and discharged from the system. The hydrogen is separated in the hydrogen-side gas-liquid separator 5 and discharged from the system. The water separated in the gas-liquid separators 4 and 5 is reused as supply water for the electrolytic cell 3. The amount of water consumed in this series of processes (make-up water) is supplied from a pure water production system 6.

[0030] The power control command unit 21, which is used to appropriately control the entire main system, receives as input the AC frequency and AC power from the AC power detection unit 11, the DC current and DC voltage from the DC power detection unit 12, the water flow rate from the flowmeter 13, the electrolytic cell representative temperature from the water inlet thermometer 14, the electrolytic cell thermometer 15 and the water outlet thermometer 16, the water outlet pressure from the water outlet pressure gauge 17, and the hydrogen pressure from the hydrogen pressure gauge 18. In response to this, the power control command unit 21 calculates the range of power consumption that the electrolytic cell can instantly change based on the input information, and if it detects a frequency deviation, it issues a command to the rectifier 2 to change the power consumption within the upper and lower limits so as to cancel out the deviation.

[0031] Fig. 2 shows a method for calculating a power consumption command in the power control command unit 21. In a very simple way, the method for calculating a power consumption command in Fig. 2 is a method for controlling the rectifier to adjust the power consumption in a water electrolysis system including a rectifier that converts AC power from a power grid into DC power, an electrolytic cell that performs water electrolysis using the DC power from the rectifier, a gas-liquid separator that separates oxygen and hydrogen from a mixed fluid of oxygen and water from the electrolytic cell, and a cooling system that supplies water to the electrolytic cell, and the rectifier is controlled to adjust the power consumption according to the frequency of the power grid, and the adjustment is performed so that the power consumption is within the power consumption limit range of the electrolytic cell. The power consumption limit range is determined from the temperature, deterioration rate, and water pressure at the outlet of the electrolytic cell, or from the upper current limit calculated from the supply water flow rate, the upper heat generation limit calculated from the supply water flow rate, or the lower current limit calculated from the hydrogen pressure.

[0032] The method for determining the limit range of power consumption for each factor is described below. First, the DC current, DC voltage, representative temperature of the electrolytic cell, and water outlet pressure are input to the degradation state calculation unit 101, and the rate of change in internal resistance is calculated from a database of initial electrolysis characteristics. The database of initial electrolysis characteristics here refers to a database that holds ideal (initial state) electrolysis characteristics at the design stage of the electrolytic cell used in the water electrolysis system, or at the state when the electrolytic cell is installed and starts operation, and includes the value of the internal resistance of the electrolytic cell in the initial state. The degradation state calculation unit 101 estimates the current internal resistance value from the input, and calculates and outputs the rate of change from the internal resistance value in the initial state (internal resistance change rate) as an index indicating the degradation state of the electrolytic cell.

[0033] This internal resistance may be expressed as an equivalent circuit consisting of not only one resistance component, but also multiple resistance components. Also, the internal resistance change rate does not need to use instantaneous data, and may be calculated using data from an operating state in which the most recent internal resistance change rate is easy to diagnose. Specifically, data for values ​​where the rate of change of current, voltage, and temperature is small, or transient data when the output fluctuates instantaneously, etc.

[0034] The calculated internal resistance change rate, the current representative temperature of the electrolytic cell, and the water outlet water pressure are input to the electrolysis characteristic calculation unit 102, and the relationship between the power consumption and the voltage, current, and heat generation is calculated by comparing with a database of initial electrolysis characteristics. The relationship between the voltage, current, and heat generation can be calculated, for example, by equation (1). [Number 1] [Heat generation (W)] = ([Voltage (V)] - 1.48 V × [Number of electrolytic cell]) × [Current (A)] (1) The water flow rate is input to the current upper limit calculation unit 104, and the current upper limit at that water flow rate is calculated. Since the relational expression between the water flow rate and the current upper limit varies depending on the detailed configuration of the electrolytic cell, such as the water flow path structure of the electrolytic cell and the heat resistance and resistivity of the electrolytic cell material, the calculation is based on a database constructed by prior testing of the electrolytic cell.

[0035] For example, as mentioned above, the oxygen volume ratio increases downstream of the water flow path, increasing resistance, causing current concentration upstream of the water flow path and accelerating deterioration. The electrolytic cell current and oxygen generation rate are proportional to each other, and the following relational equation (2) holds, so the current value at the upper limit of the oxygen volume ratio can be calculated. The oxygen volume ratio at the outlet should be 80% or less. [Number 2] I = α / (1-α) × FR H2O / N×F / 15 / Vm(T,P) (2) In equation (2), I is the current (A), α is the oxygen volume ratio, FR H2O is the water flow rate (ml / min), N is the number of cells in the electrolytic cell, F is the Faraday constant (C / mol), and Vm(T,P) is the molar volume of oxygen (ml / mol) at temperature T and pressure P.

[0036] The water flow rate is input to the heat generation amount upper limit calculation unit 105, and the upper limit of the heat generation amount at that water flow rate is calculated. Since the relational expression between the water flow rate and the upper limit of the heat generation amount varies depending on the detailed configuration of the electrolytic cell, such as the water flow path structure of the electrolytic cell and the heat resistance and resistivity of the electrolytic cell material, the calculation is based on a database constructed by prior testing of the electrolytic cell.

[0037] For example, as mentioned above, a rise in temperature downstream of the water flow path reduces resistance, causing current concentration and aging. If we assume that the heat generated in the electrolytic cell is absorbed by the sensible heat of the water, the following relational expression (3) holds, so the amount of heat generated at the upper limit of the inlet / outlet temperature difference can be calculated. The inlet / outlet temperature difference is preferably 10°C or less, and more preferably 5°C or less. [Number 3] W=ΔT×FR H2O / 60×C H2O ×ρ H2O (3) In equation (3), W is the amount of heat generated (W), ΔT is the temperature difference between the inlet and outlet (K), and FR H2O is the water flow rate (ml / min), C H2O is the specific heat of water (J / g / K), ρ H2O is the specific gravity of water (g / ml).

[0038] In addition, the hydrogen pressure is input to a current lower limit calculation unit 106 to calculate a lower limit current. When the current falls below the lower limit, the ratio of the rate at which hydrogen permeates the electrolytic cell and diffuses to the anode side to the rate at which hydrogen is generated at the cathode of the electrolytic cell by electrolysis increases, resulting in a decrease in electrolysis efficiency and degradation due to reduction of the anode catalyst. The relationship between the hydrogen pressure and the lower limit current varies depending on the detailed configuration of the electrolytic cell, such as the membrane thickness and material of the electrolytic cell, and is therefore calculated based on a database constructed by prior testing of the electrolytic cell. It is preferable that the electrolytic cell be a solid polymer electrolytic cell.

[0039] The voltage, current, and heat generation amount relative to power consumption calculated by the electrolysis characteristic calculation unit 102, and the upper and lower current limits and upper heat generation amount limits in the current state of the water electrolysis system calculated by the current upper limit calculation unit 104, the heat generation amount upper limit calculation unit 105, and the current lower limit calculation unit 106 are input to the power consumption upper and lower limit calculation unit 103 to calculate the upper and lower power consumption limits. In this way, the upper and lower power consumption limits are set so as to satisfy the upper and lower limits of voltage, current, heat generation amount, and power consumption as the water electrolysis system, as well as the upper and lower current limits and the upper and lower heat generation amount limits in the current state of the water electrolysis system.

[0040] The upper and lower power consumption limits calculated by the power consumption upper and lower limit calculation unit 103 and the current AC frequency and AC power are input to a power consumption command calculation unit 107, which calculates a power consumption command and issues it to the rectifier 2. The current AC power may be substituted with a power consumption command value or a planned value.

[0041] Figures 3 and 4 show examples of power consumption setting commands (vertical axis) according to AC frequency (horizontal axis). As shown in Figure 3, power consumption may be changed linearly with respect to the deviation of the frequency from the reference frequency, or as shown in Figure 4, a section in which power consumption is not changed may be provided before and after the reference frequency. Also, when the frequency deviation is large, it is advisable not to change power consumption beyond the upper or lower limits.

[0042] According to the first embodiment of the present invention, the power consumption adjustment margin is determined taking into account the flow rate of water to the electrolytic cell, so that abnormal temperature distribution and current distribution do not occur, and deterioration and breakdown of the electrolytic cell can be suppressed. EXAMPLES

[0043] An example of a water electrolysis system according to Example 2 of the present invention is shown in Fig. 5. In the example shown in Fig. 1, an example in which there is one electrolytic cell 3 has been described, but in Example 2, the electrolytic cell 3 is made up of a plurality of electrolytic cells 3a.

[0044] For this reason, the power supply system and water supply system for the electrolytic cells are configured to be connected in series and parallel. For example, the power supply system has power supply lines for the multiple electrolytic cells 3a electrically connected in series and parallel, and then connected to the rectifier 2. In addition, the water supply system has pipes for supplying pure water to the multiple electrolytic cells 3a, discharging oxygen and water, and discharging hydrogen and water, which are connected in parallel to each electrolytic cell 3a.

[0045] In addition, the control system has also been changed in accordance with this change in the main circuit configuration. Specifically, for example, a DC power detector 12a that detects the current and voltage of each electrolytic cell 3a, a flowmeter 13a that detects the water flow rate to each electrolytic cell 3a, an electrolytic cell thermometer 15a that detects the temperature of each electrolytic cell 3a, and a water outlet thermometer 16a that detects the outlet water temperature of each electrolytic cell 3a are provided for each individual electrolytic cell. Note that FIG. 5 shows only one electrolytic cell. The DC currents, DC voltages, water flow rates, and electrolytic cell representative temperatures of all electrolytic cells 3a are input to the power control command unit 21a.

[0046] Fig. 6 shows a method for calculating a power consumption command in power control command unit 21a. The processing in Fig. 6 is basically the same as that in Fig. 2, but differs in that the processing other than that in power consumption command calculation unit 107 is calculated for each individual electrolytic cell. Steps 101a-106a are executed for each individual electrolytic cell, and power consumption command calculation unit 107 calculates a power consumption command using the individually calculated upper and lower power consumption limits. For this reason, power consumption upper and lower limit calculation unit 103a sets upper and lower power consumption limits so as to satisfy the current upper and lower limits and heat generation upper limit of each electrolytic cell 3a at present, in addition to the upper and lower limits of voltage, current, heat generation, and power consumption as a water electrolysis system.

[0047] The DC current, DC voltage, electrolytic cell representative temperature and water outlet pressure of each electrolytic cell 3a are input to the deterioration state calculation unit 101a, and the rate of change in the internal resistance of each electrolytic cell 3a is calculated from a database of initial electrolysis characteristics. The rate of change in internal resistance does not need to use instantaneous data, and may be calculated using data in an operating state in which the most recent rate of change in internal resistance is easy to diagnose.

[0048] The calculated internal resistance change rate of each electrolytic cell 3a, the current electrolytic cell representative temperature of each electrolytic cell 3a, and the water outlet water pressure are input into the electrolysis characteristic calculation unit 102a, and the relationship between the system power consumption and the voltage, current, and heat generation of each electrolytic cell 3a is calculated by comparing with a database of initial electrolysis characteristics.

[0049] The water flow rate of each electrolytic cell 3a is input to upper current limit calculation unit 104a, which calculates the upper current limit of each electrolytic cell 3a at that water flow rate. The water flow rate of each electrolytic cell 3a is input to upper heat generation amount limit calculation unit 105a, which calculates the upper heat generation amount limit of each electrolytic cell 3a at that water flow rate. The hydrogen pressure is input to lower current limit calculation unit 106a, which calculates the lower current limit.

[0050] The voltage, current, and heat generation amount of each electrolytic cell 3a relative to the system power consumption calculated by the electrolysis characteristic calculation unit 102a, and the upper and lower current limits and the upper heat generation amount upper limit of each electrolytic cell 3a in the current state of the water electrolysis system calculated by the current upper limit calculation unit 104a, the heat generation amount upper limit calculation unit 105a, and the current lower limit calculation unit 106a of each electrolytic cell 3a are input to the power consumption upper and lower limit calculation unit 103a to calculate the power consumption upper and lower limits. The power consumption upper and lower limits are set so as to satisfy the current upper and lower current limits and the heat generation amount upper limit of each electrolytic cell 3a in addition to the upper and lower limits of the voltage, current, heat generation amount, and power consumption of the water electrolysis system. The power consumption upper and lower limits calculated by the power consumption upper and lower limit calculation unit 103a and the current AC frequency and AC power are input to the power consumption command calculation unit 107 to calculate a power consumption command and issue it to the rectifier 2.

[0051] In addition to detecting the AC frequency and adjusting the power consumption in about a few seconds, the power consumption may be adjusted in about a few minutes to a few tens of minutes upon receiving a command from a grid manager. When adjusting the power consumption in about a few minutes to a few tens of minutes, the water flow rate can be adjusted accordingly, so there is no need to set conditions for the current or heat generation amount according to the current water flow rate. For this reason, the upper and lower limits of power consumption are different from when adjusting the power consumption by detecting the AC frequency. In other words, it is possible to adjust the power consumption according to the frequency of the power grid, and to adjust the power consumption upon receiving a command from the grid manager to adjust the power consumption, and to make it possible to adjust the power consumption in a wider range when adjusting the power consumption upon receiving a command than when adjusting the power consumption according to the frequency of the power grid.

[0052] Furthermore, the control in the second embodiment is intended to change the control immediately based on the judgment result from the input at the current time, but this control can also be performed predictively. For example, in the case of a water electrolysis system in which electrolytic cells are electrically connected in series and parallel, the current and voltage in each electrolytic cell after the system power consumption adjustment is predicted from the temperature, deterioration rate, and pressure of each electrolytic cell, and the upper and lower limit ranges of power consumption in each electrolytic cell are calculated from the predicted current, voltage, and the flow rate of water supplied to each electrolytic cell, and the power consumption may be adjusted to satisfy the upper and lower limit ranges of power consumption in all electrolytic cells.

[0053] The higher the temperature and voltage, the faster the electrolytic cell deteriorates, shortening its lifespan and leading to increased equipment costs. For this reason, it is desirable to set an upper limit on power consumption, taking into consideration the cost of shortening the cell's lifespan due to increased power consumption and the profits from providing an adjustment amount. Even with the same power consumption, if the electrolytic cell is highly deteriorated or has high resistance at low temperatures, the voltage will be high, and deterioration will progress further. The rate of deterioration also differs depending on the configuration of the electrolytic cell. It is advisable to set an upper limit on power consumption based on a database of the relationship between the electrolytic cell's operating conditions and the rate of deterioration in advance tests. EXAMPLES

[0054] In Example 3, a specific setup and operation example will be described. In this example, the water electrolysis system has the configuration shown in FIG. 1. The electrolytic cell 3 has an electrode surface area of ​​2000 cm.2 The electrolysis cell was equipped with 224 cells. The water temperature control unit 20 was set so that the temperature of the pure water at the inlet of the electrolysis cell was 60° C., and the water outlet pressure was controlled to be 0.1 MPaG and the hydrogen pressure was controlled to be 0.9 MPaG.

[0055] The current-voltage characteristics of the electrolytic cell calculated based on the internal resistance change rate calculated by the deterioration state calculation unit 101 at this time are shown in FIG. 7. The horizontal axis of FIG. 7 represents the current density (A / cm 2 ) and the vertical axis indicates the average cell voltage (V). According to this characteristic, the voltage had a linear relationship with the current in the current density range (0.5-2.0) of the operating range.

[0056] In this embodiment, the lower limit of the current density of the system is 0.4 A / cm 2 , upper limit current density 2.25A / cm 2 , maximum heat output 1.25W / cm 2 The upper limit cell voltage was set to 1.95 V, the current upper limit calculation unit 104 set the current upper limit so that the oxygen volume ratio was 70% or less, and the heat generation amount upper limit calculation unit 105 set the heat generation amount upper limit so that the inlet / outlet temperature difference was 5°C or less.

[0057] Figure 8 shows the relationship between power consumption on the horizontal axis and current density, heat generation, and cell voltage on the vertical axis. 3 / min flow rate of pure water, 3000A (1.5A / cm 2 ), 401V (1.79V / cell), 1.20MW (2.69W / cm 2 The graph shows the relationship between power consumption, current density, heat generation, and cell voltage when the battery is operated at 100 V.

[0058] According to this, the current limit is 5450A (2.73A / cm2) based on the pure water flow rate. 2 ), the upper limit of heat output is 0.392MW (0.875W / cm 2) was calculated. As a result, the upper limit of power consumption for power consumption adjustment according to AC frequency was set at 1.78 MW (3.98 W / cm2) based on the upper limit of heat generation. Meanwhile, the upper limit of power consumption for power consumption adjustment based on instructions from the grid manager was set at 1.94 MW (4.33 W / cm2) based on the upper limit of the system current density.

[0059] Figure 9 also shows the relationship between power consumption on the horizontal axis and current density, heat generation, and cell voltage on the vertical axis. When pure water was supplied at a flow rate of 0.54 m3 / min, the current density was 2000 A (1.0 A / cm 2 ), 381V (1.70V / cell), 0.76MW (1.70W / cm 2 The graph shows the relationship between power consumption, current density, heat generation, and cell voltage when the battery is operated at 100 V.

[0060] According to this, the current limit is 2616A (1.31A / cm2) based on the pure water flow rate. 2 ), the upper limit of heat output is 0.188MW (0.42W / cm 2 As a result, the upper limit of power consumption for adjusting the power consumption according to the AC frequency was calculated to be 1.03 MW (2.30 W / cm2) from the upper limit of current. 2 On the other hand, the upper limit of power consumption for power consumption adjustments in response to instructions from the grid manager is set at 1.94 MW (4.33 W / cm) due to the system upper limit current density. 2 ) was set.

[0061] According to the verification of Example 3, when adjusting power consumption within a few seconds, when it is difficult to keep up with changes in water flow rate, the power consumption adjustment range was set to match the water flow rate, so extreme current concentration was not caused and deterioration could be suppressed. EXAMPLES

[0062] A specific example of the setup and operation will be described in Example 4. In this example, the water electrolysis system was configured as shown in FIG. 5. The electrolytic cell 3a had an electrode surface area of ​​700 cm. 2 The electrolytic cells were electrically connected in series and parallel to each other.

[0063] The electrical connection circuit and electrolytic cell numbers of the electrolytic cells 3a are shown in Fig. 10. There were 12 electrolytic cells 3a. Here, the currents flowing through the respective electrolytic cells 3a were designated IA to IF.

[0064] In this example of the above configuration, the water temperature control unit 20 was set so that the pure water temperature at the electrolytic cell inlet was 60° C., and the water outlet pressure was controlled to be 0.1 MPaG and the hydrogen pressure to be 0.9 MPaG.

[0065] The current-voltage characteristics of each electrolytic cell 3a calculated based on the rate of internal resistance change calculated by the deterioration state calculation unit 101a are shown in Figure 11. The horizontal axis of Figure 11 is the current density, and the vertical axis is the average cell voltage, and the characteristics are shown for each of the 12 sets of electrolytic cells. In this case, electrolytic cells 9, 6, and 10 had higher resistance than the other electrolytic cells.

[0066] 12, 13 and 14 are diagrams showing the relationship between the system current density (horizontal axis) calculated by the electrolysis characteristic calculation unit 102a based on the current-voltage characteristics of each electrolytic cell 3a and the cell voltage, current and heat generation amount of each electrolytic cell 3a.

[0067] In terms of the relationship between the system current density (horizontal axis) and the cell voltage (vertical axis) of each electrolytic cell 3a, as shown in FIG. 12, electrolytic cells 9, 6, and 10 did not have a higher voltage than the other electrolytic cells relative to the system current.

[0068] This is because, as shown in Figure 13, the relationship between the system current density (horizontal axis) and the current of each electrolytic cell 3a (vertical axis: electrolytic cell current density), the current IC of electrolytic cell number 6 and the current IE of electrolytic cell numbers 9 and 10 are smaller than those of the other electrolytic cells.

[0069] In addition, in terms of the relationship between the system current density (horizontal axis) and the amount of heat generated by each electrolytic cell 3a (vertical axis: amount of heat generated per cell area), as shown in Figure 14, the amounts of heat generated by electrolytic cells 9, 6, and 10 were equivalent to those of the other electrolytic cells, and electrolytic cell number 7 generated the largest amount of heat relative to the system current.

[0070] In this embodiment, the lower limit current density of the electrolytic cell 3a is 0.4 A / cm 2 , upper limit current density 2.25A / cm 2 , maximum heat output 1.25W / cm 2 The upper limit cell voltage was set to 1.95 V, the current upper limit calculation unit 104a set the current upper limit so that the oxygen volume ratio was 70% or less, and the heat generation amount upper limit calculation unit 105a set the heat generation amount upper limit so that the inlet / outlet temperature difference was 5°C or less.

[0071] 6.72 m in Example 4 3 / min flow rate of pure water, 3150A (1.5A / cm 2 ), 2300V (1.80V / cell), 7.24MW (2.70W / cm 2 15 shows the water flow rate in each electrolytic cell, the upper heat generation limit and current density limit of electrolytic cell 3a calculated by current upper limit calculation unit 104a and heat generation limit calculation unit 105a, and the corresponding upper and lower limits of system power consumption.

[0072] According to Figure 15, pure water was supplied to each electrolytic cell evenly, and no significant differences were observed in the upper limits of heat generation and current density for each electrolytic cell. However, differences were observed in the corresponding system power consumption, with the upper limit of system power consumption corresponding to the upper limit of heat generation for electrolytic cell number 7, which is prone to high power consumption, being the lowest. From this result, it was decided that the upper limit of power consumption for power consumption adjustment according to AC frequency should be 10.1 MW (3.77 W / cm2). 2 ) was set.

[0073] Figure 16 shows the upper and lower limits of the current density as an electrolytic cell and the corresponding system power consumption. From the results of Figure 16, the upper and lower limits of power consumption adjustments instructed by the system administrator are 2.1 MW (0.78 W / cm 2 )~11.0MW(4.1W / cm 2 ) was set.

[0074] In Example 4, 3.23 m 3 With pure water supplied at a flow rate of 2100A (1.0A / cm 2), 2182V (1.70V / cell), 7.24MW (1.70W / cm 2 ) was driven.

[0075] The water flow rate in each electrolytic cell, the upper heat generation limit and current density limit of electrolytic cell 3a calculated by upper current limit calculation unit 104a and upper heat generation limit calculation unit 105a, and the corresponding system power consumption are shown in Figure 17. The system power consumption corresponding to the upper current density limit of electrolytic cell number 7 is 5.76 MW (2.14 W / cm). 2 ) was the smallest value, and was set as the upper limit of power consumption for adjusting power consumption according to AC frequency.

[0076] According to the verification of Example 4, since the power consumption adjustment range was set according to the water flow rate and the current distribution, extreme current concentration was not caused and deterioration could be suppressed. [Explanation of symbols]

[0077] 1: Isolation transformer 2: Rectifier 3: Electrolytic cell 4: Oxygen side gas-liquid separator 5: Hydrogen side gas-liquid separator 6: Pure water production equipment 7: Pump 8: Heat exchanger 9:Cooler 10: Cooling water regulating valve 11: AC power detector 12: DC power detector 13:Flow meter 14: Water inlet thermometer 15: Electrolyzer thermometer 16: Water outlet thermometer 17: Water outlet pressure gauge 18: Hydrogen pressure gauge 19: Water flow control section 20: Water temperature control unit 21: Power Control Command 22: Grid power 23:Water 24: Oxygen 25: Hydrogen

Claims

1. A water electrolysis system comprising: a rectifier that converts AC power from a power system into DC power; an electrolytic cell that performs water electrolysis using the DC power from the rectifier; a gas-liquid separator that separates oxygen and hydrogen from a mixed fluid of oxygen and water from the electrolytic cell; and a cooling system that supplies water to the electrolytic cell, controlling the rectifier to adjust the power consumption in response to the frequency of the power grid, the adjustment adjusting the power consumption so that the power consumption is within a limit range of the power consumption of the electrolytic cell; a limit range for the power consumption is determined based on a temperature of the electrolytic cell, a deterioration rate, a water pressure at an outlet of the electrolytic cell, and a supply water flow rate.

2. The water electrolysis system according to claim 1, a limit range for the power consumption is determined based on an upper limit of a heat generation amount calculated from a flow rate of the supplied water.

3. The water electrolysis system according to claim 1, a limit range of the power consumption is determined based on a lower limit of current determined from a hydrogen pressure.

4. The water electrolysis system according to claim 1, a water electrolysis system, wherein upper and lower limits of power consumption are calculated so that a volume ratio of a gas phase at a water flow path outlet of the electrolytic cell is 80% or less.

5. The water electrolysis system according to claim 1, a water electrolysis system, wherein upper and lower limits of power consumption are calculated so that a temperature difference between the water inlet and outlet of the electrolytic cell is 10° C. or less.

6. The water electrolysis system according to claim 1, A water electrolysis system, characterized in that the electrolytic cell uses a solid polymer electrolytic cell.

7. The water electrolysis system according to claim 1, A water electrolysis system comprising a plurality of electrolytic cells electrically connected in series and parallel to supply power to the electrolytic cells.

8. The water electrolysis system according to claim 7, a current and voltage in each of the electrolytic cells after adjustment of system power consumption is predicted from the cell temperature, deterioration rate and pressure of each of the plurality of electrolytic cells; an upper and lower limit range of power consumption for each electrolytic cell is calculated from the predicted current, voltage and flow rate of water supplied to each electrolytic cell; and power consumption is adjusted so as to satisfy the upper and lower limit ranges of power consumption for all of the electrolytic cells.

9. The water electrolysis system according to claim 1, a water electrolysis system that adjusts power consumption in accordance with a frequency of the power grid and is capable of adjusting the power consumption in response to a command for adjusting the power consumption from a power grid manager, and that has a wider adjustment range for the power consumption when the power consumption is adjusted in response to the command than when the power consumption is adjusted in accordance with the frequency of the power grid.

10. A water electrolysis system control device comprising: a rectifier that converts AC power from a power system into DC power; an electrolytic cell that performs water electrolysis using the DC power from the rectifier; a gas-liquid separator that separates oxygen and hydrogen from a mixed fluid of oxygen and water from the electrolytic cell; and a cooling system that supplies water to the electrolytic cell, the control device controls the rectifier to adjust the power consumption in response to a frequency of a power grid, the adjustment adjusting the power consumption so that the power consumption is within a limit range of the power consumption in the electrolytic cell; a power consumption limit range determined based on a temperature of the electrolytic cell, a deterioration rate, a water pressure at an outlet of the electrolytic cell, and a supply water flow rate.

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