Water electrolysis system and water electrolysis system control device

Abstract

Provided is a water electrolysis system that alters power consumption by sensing a system frequency to rapidly change power consumption, wherein a suitable adjustment margin that can be accommodated instantaneously by an electrolytic cell is calculated so as to suppress deterioration or failure of the electrolytic cell. This water electrolysis system is configured by including: a rectifier that converts alternating-current power of a power system to direct-current power; an electrolysis tank that performs water electrolysis using the direct-current power from the rectifier; a gas–liquid separator that performs gas–liquid separation of oxygen and hydrogen from a fluid that is a mixture of oxygen and water from the electrolytic cell; and a cooling system that supplies water to the electrolytic cell. The water electrolysis system is characterized in that: the rectifier is controlled so as to adjust power consumption in accordance with the frequency of the power system; the power consumption is adjusted so that the power consumption in the electrolytic cell is within a limited range for power consumption; and the limited range for power consumption is determined on the basis of the temperature and deterioration rate of the electrolytic cell, the pressure of water at an exit of the electrolytic cell, and the flow rate of the supplied water.

Description

Water electrolysis system and water electrolysis system control device

[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.

[0002] Unlike fossil fuels, hydrogen is a clean energy source that does not emit carbon dioxide when burned. For this reason, it has attracted attention as a clean energy source to combat global warming, and technological development is underway regarding the production, transportation, and use of hydrogen. One method of hydrogen production is known as the water electrolysis system.

[0003] To produce clean hydrogen, renewable energy is required 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 power generation expands, a balancing function will be needed to adjust the balance between supply and demand. Therefore, it has been proposed to adjust the power consumption of water electrolysis systems to provide this balancing function.

[0004] Patent Document 1 describes an output control device that controls the output of an electrolyzer within a 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 that adjusts the amount of power consumed by an electrolysis device based on a command for adjusting the supply and demand of electricity in a commercial power grid, and determines the amount of adjustment based on factors such as the adjustment margin calculated from the difference between the maximum and minimum rated power of the electrolysis device and the current operating output, the remaining amount of hydrogen, and the future supply and demand balance.

[0006] JP 2011-50138 A JP 2021-134863 A

[0007] In the hydrogen supply systems described in Patent Documents 1 and 2, when a relatively long-cycle adjustment capability is provided that adjusts power consumption after receiving a power command, it is possible to adjust the water flow rate to the electrolytic cell to keep up with changes in power consumption. On the other hand, in short-cycle adjustment, it is difficult to keep up with rapid changes in power consumption by controlling the water flow rate and temperature. Therefore, if the power consumption is changed based on an adjustment margin calculated from the difference between the maximum and minimum ratings of the electrolytic cell and the current operating output, abnormal temperature and current distributions may occur within the electrolysis stack, resulting in deterioration or failure. Furthermore, the mixed fluid of gas and water coming out of the electrolytic cell may deviate from the appropriate gas-liquid ratio, preventing sufficient separation in the gas-liquid separator.

[0008] Therefore, an object of the present invention is to prevent deterioration and breakdown of an electrolytic cell by calculating an appropriate adjustment margin that allows the electrolytic cell to instantaneously 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.

[0010] In light of the above, the present invention provides "a water electrolysis system comprising: a rectifier that converts AC power from an electric 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 fluid mixture 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 electric power system, the adjustment is made to keep the power consumption within a power consumption limit range of 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 also 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, and adjusts the power consumption to be within a power consumption limit range of the electrolytic cell, and determines the power consumption limit range 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."

[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 abnormal temperature and current distributions do not occur, and deterioration and breakdown of the electrolytic cell can be suppressed.

[0013] 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 of the electrolytic cells 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, problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

[0015] 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. FIG. 1 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. 2 is a diagram showing an example of a command to set power consumption according to AC frequency. FIG. 3 is a diagram showing an example of a command to set power consumption according to AC frequency. FIG. 3 is a schematic diagram showing an example of the configuration of a power control command unit 21 according to the second embodiment of the present invention. FIG. 4 is a diagram showing the current-voltage characteristics of an electrolytic cell calculated based on the rate of change of internal resistance. FIG. 5 is a diagram showing the relationship between power consumption, current density, heat generation, and cell voltage. FIG. 6 is a diagram showing the relationship between power consumption, current density, heat generation, and cell voltage. FIG. 7 is a diagram showing the electrical connection circuit of an electrolytic cell 3a and the electrolytic cell number. FIG. 8 is a diagram showing the relationship between current density and average cell voltage for each of 12 sets of electrolytic cells. FIG. 9 is a diagram showing the relationship between system current density and cell voltage of each electrolytic cell 3a. FIG. 10 is a diagram showing the relationship between system current density and current of each electrolytic cell 3a. FIG. 11 is a diagram showing the relationship between system current density and heat generation of each electrolytic cell 3a. FIG. 12 is a diagram showing an example of an upper heat generation limit, an upper current density limit, and upper and lower limits of system power consumption. 1 is a diagram showing an example of upper and lower limits of current density as an electrolytic cell and system power consumption. 2 is a diagram showing an example of an upper limit of heat generation, an upper limit of current density, and system power consumption.

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

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

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

[0019] In a typical electrolyzer, the energy conversion efficiency from electricity to hydrogen is around 70 to 90%, and the remainder is converted into heat, which heats the components of the electrolyzer and the water flowing inside. As a result, the temperature increases from upstream to downstream of the water flow path, creating a temperature distribution within the electrolyzer.

[0020] Furthermore, when the flow rate of water in the electrolytic cell varies, the temperature becomes higher in the lower flow rate region, resulting in a temperature distribution. The higher the temperature of the electrolytic cell in the electrolytic cell, the lower the resistance. However, 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, causing an increase in resistance, or the electrolyte membrane that separates hydrogen and oxygen thins, increasing the amount of hydrogen and oxygen that permeates, or causing holes in the electrolyte membrane or an electrical short circuit.

[0021] Furthermore, when the temperature difference within the electrolytic cell becomes large, the difference in resistance within the electrolytic cell also becomes large, causing current to concentrate in the high temperature portion.

[0022] Furthermore, when the volume ratio of the generated gas to the water, which is the reaction raw material, is high in the flow path of the electrolytic cell, the resistance increases due to an insufficient water supply to the electrodes, and current concentrates in regions with a low gas volume ratio. Such current concentration leads to localized temperature increases, which can cause deterioration or failure. Therefore, it is important to suppress temperature differences and the occurrence of regions with a high gas volume ratio within the electrolytic cell.

[0023] Most of the heat generated in the electrolytic cell is carried out by the supplied water, and the temperature difference generated along the water flow path 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 path outlet.

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

[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 is composed of a main system and a control system that controls the main system.

[0026] Of these, the main system can be said to be composed of an isolation transformer 1 that adjusts the voltage from 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 inlet of the electrolytic cell, an electrolytic cell thermometer 15 that detects the electrolytic cell temperature, a water outlet thermometer 16 that detects the water temperature at the outlet of the electrolytic cell, a water outlet pressure meter 17 that detects the pressure on the water outlet side of the electrolytic cell 3, a hydrogen pressure meter 18 that detects the hydrogen pressure, a water flow rate 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 inlet of the electrolytic cell, and a power control command unit 21 that determines the power consumption of 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 and tank, a pressure control valve, a hydrogen dryer, and a booster may also 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 electrolysis of the water occurs using 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 feed water for the electrolytic cell 3. The amount of water consumed in the series of processes (make-up water) is supplied from the 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 instantaneously 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. Expressed simply, the calculation method of the power consumption command in Fig. 2 involves controlling the rectifier to adjust power consumption in accordance with the frequency of the power grid for a water electrolysis system including a rectifier that converts AC power from the power grid to 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 adjustment also involves adjusting the power consumption so that it falls within a power consumption limit range for 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 an upper current limit calculated from the feed water flow rate, an upper heat generation limit calculated from the feed water flow rate, or a 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, electrolytic cell representative temperature, 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. Here, the database of initial electrolysis characteristics refers to a database that stores ideal (initial) electrolysis characteristics of the electrolytic cell used in the water electrolysis system at the design stage or when the electrolytic cell is installed and starts operation, and this database also 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. Furthermore, the rate of change in internal resistance does not need to be instantaneous data, and may be calculated using data from an operating state in which the most recent rate of change in internal resistance is easy to diagnose. Specifically, data from values ​​where the rates of change in current, voltage, and temperature are small, or transient data from instantaneous output fluctuations, etc.

[0034] The calculated internal resistance change rate, the current electrolytic cell representative temperature, and the water outlet water pressure are input to an electrolysis characteristic calculation unit 102, which then compares the calculated rate with a database of initial electrolysis characteristics to calculate the relationship between power consumption and voltage, current, and heat generation amount. The relationship between voltage, current, and heat generation amount can be calculated, for example, using equation (1). [Equation 1] [Heat generation amount (W)] = ([Voltage (V)] - 1.48 V × [Number of electrolytic cell cells]) × [Current (A)] (1) The water flow rate is also input to an upper current limit calculation unit 104, which calculates the upper current limit for that water flow rate. The equation for the relationship between water flow rate and upper current 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 materials, and is therefore calculated based on a database constructed through advance testing of the electrolytic cell.

[0035] For example, as mentioned above, the volume ratio of oxygen increases downstream of the water flow path, increasing resistance, causing current to concentrate upstream of the water flow path and accelerating deterioration. The current of the electrolytic cell and the oxygen generation rate are proportional to each other, and the following relational expression (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 is preferably 80% or less. [Equation 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 calorific value upper limit calculation unit 105, which calculates the upper limit of the calorific value at that water flow rate. The relational expression between the water flow rate and the upper limit of the calorific value 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, and therefore is calculated based on a database constructed through advance testing of the electrolytic cell.

[0037] For example, as mentioned above, a temperature rise downstream of the water flow path reduces resistance, causing current concentration and aging. Assuming that the heat generated in the electrolytic cell is absorbed by the sensible heat of the water, the following relational expression (3) holds, and 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. [Equation 3] W = ΔT × FR Ｈ２Ｏ / 60 x C Ｈ２Ｏ ×ρ Ｈ２Ｏ ... (3) In equation (3), W is the heat generation amount (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] The hydrogen pressure is also 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 due to 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 through advance 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 and lower 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 of the water electrolysis system, as well as the upper and lower current limits and 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, the current AC frequency, and the AC power are input to the power consumption command calculation unit 107, which calculates a power consumption command and outputs it to the rectifier 2. The current AC power may be substituted with a power consumption command value or a planned value.

[0041] 3 and 4 show examples of power consumption setting commands (vertical axis) corresponding to AC frequency (horizontal axis). As shown in Fig. 3, power consumption may be changed linearly in response to the deviation of the frequency from the reference frequency, or as shown in Fig. 4, a section in which power consumption is not changed may be provided before and after the reference frequency. Furthermore, when the frequency deviation is large, it is preferable not to change power consumption beyond the upper or lower limit.

[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 abnormal temperature distribution and current distribution do not occur, and deterioration and breakdown of the electrolytic cell can be suppressed.

[0043] An example of a water electrolysis system according to Example 2 of the present invention is shown in Figure 5. In the example shown in Figure 1, the electrolytic cell 3 is a single electrolytic cell 3, 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. Furthermore, 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] Furthermore, in accordance with this change in the main circuit configuration, the control system has also been changed. Specifically, for example, a DC power detector 12a that detects the current and voltage of each electrolytic cell 3a, a flow meter 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 current, DC voltage, water flow rate, and electrolytic cell representative temperature of all electrolytic cells 3a are input to the power control command unit 21a.

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

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

[0050] The voltage, current, and heat generation amount of each electrolytic cell 3 a relative to the system power consumption calculated by the electrolysis characteristic calculation unit 102 a, and the upper and lower current limits and upper and lower heat generation limits of each electrolytic cell 3 a in the current state of the water electrolysis system calculated by the current upper limit calculation unit 104 a, heat generation upper limit calculation unit 105 a, and current lower limit calculation unit 106 a for each electrolytic cell 3 a are input to the power consumption upper and lower limit calculation unit 103 a to calculate the upper and lower power consumption limits. The power consumption upper and lower limits are set so as to satisfy the current upper and lower current limits and upper and lower heat generation limits of each electrolytic cell 3 a in addition to the upper and lower limits of voltage, current, heat generation, and power consumption as the water electrolysis system. The power consumption upper and lower limits calculated by the power consumption upper and lower limit calculation unit 103 a 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 AC frequency and adjusting power consumption within a few seconds, power consumption can also be adjusted within a few minutes to a few tens of minutes upon receiving a command from a grid manager. When adjusting power consumption within 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 current or heat generation based on the current water flow rate. Therefore, the upper and lower limits of power consumption are different from when adjusting power consumption by detecting AC frequency. In other words, power consumption can be adjusted according to the frequency of the power grid, and can also be adjusted upon receiving a command to adjust power consumption from a grid manager, and the adjustment range of power consumption can be wider when adjusting power consumption upon command than when adjusting power consumption according to the frequency of the power grid.

[0052] Furthermore, although the control in Example 2 is intended to change the control immediately based on the judgment result from the current input, this control can also be performed predictively. For example, in a water electrolysis system in which electrolytic cells are electrically connected in series and parallel, the current and voltage in each electrolytic cell after adjustment of the system power consumption may be predicted from the cell temperature, deterioration rate, and pressure of each electrolytic cell, the upper and lower limit ranges of power consumption for each electrolytic cell are calculated from the predicted current, voltage, and flow rate of water supplied to each electrolytic cell, and the power consumption may be adjusted so as to satisfy the upper and lower limit ranges of power consumption for 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. Therefore, it is desirable to set an upper limit on power consumption, taking into account the cost of shortening its 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 varies 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 operating conditions of the electrolytic cell and the rate of deterioration through preliminary testing.

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

[0055] The current-voltage characteristics of the electrolytic cell calculated based on the rate of change in internal resistance 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 The vertical axis shows the average cell voltage (V), and 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 example, the lower limit current density of the system is 0.4 A / cm ２ , upper limit current density 2.25A / cm ２ , upper limit heat output 1.25 W / 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] FIG. 8 shows the relationship between power consumption on the horizontal axis and current density, heat generation amount, and cell voltage on the vertical axis. ３ With pure water supplied at a flow rate of 3000 A (1.5 A / 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 1000 kJ / s.

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

[0059] FIG. 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 1000 kJ / s.

[0060] According to this, the current upper limit is 2616 A (1.31 A / cm) from the pure water flow rate. ２ ), the upper limit of the calorific value is 0.188 MW (0.42 W / 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 / cm) 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 administrator is set at 1.94 MW (4.33 W / cm) due to the upper limit of the system current density. ２ ) was set.

[0061] According to the verification in Example 3, when adjusting power consumption within a few seconds, which is difficult to follow 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 was suppressed.

[0062] In Example 4, specific settings and operation examples will also be described. In this example, the water electrolysis system has the configuration shown in Figure 5. The electrolytic cell 3a has an electrode surface area of ​​700 cm ２ The electrolytic cell was equipped with 320 electrolytic cells, and 12 electrolytic cells 3a were electrically connected in series and parallel.

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

[0064] In this example, the water temperature control unit 20 was set so that the pure water temperature at the inlet of the electrolytic cell 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 change in internal resistance calculated by the deterioration state calculation unit 101a are shown in Figure 11. The horizontal axis of Figure 11 represents current density, and the vertical axis represents 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) shows that the current IC of electrolytic cell number 6 and the current IE of electrolytic cells numbers 9 and 10 are smaller than those of the other electrolytic cells.

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

[0070] In this example, the lower limit current density of the electrolytic cell 3a is 0.4 A / cm ２ , upper limit current density 2.25A / cm ２ , upper limit heat output 1.25 W / 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] In Example 4, 6.72 m ３ With pure water supplied at a flow rate of 3150 A (1.5 A / cm ２ ), 2300V (1.80V / cell), 7.24MW (2.70W / cm２ 15 shows the water flow rates in each electrolytic cell, the upper heat generation amount limits and current density limits of electrolytic cell 3a calculated by upper current limit calculation unit 104a and upper heat generation amount limit calculation unit 105a, and the corresponding upper and lower limits of system power consumption.

[0072] As shown in Figure 15, pure water was supplied evenly to each electrolytic cell, and no significant differences were observed in the upper limits of heat generation and current density among the electrolytic cells. 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 tends to consume a lot of power, being the lowest. From this result, the upper limit of power consumption for power consumption adjustment according to AC frequency was determined to be 10.1 MW (3.77 W / cm ２ ) was set.

[0073] Figure 16 shows the upper and lower limits of 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 2100 A (1.0 A / cm ２ ), 2182V (1.70V / cell), 7.24MW (1.70W / cm ２ ) and drove.

[0075] The water flow rates in each electrolytic cell, the upper heat value limit and current density limit of electrolytic cell 3a calculated by upper current limit calculation unit 104a and upper heat value 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 was 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, the power consumption adjustment range was set in accordance with the water flow rate and current distribution, so that extreme current concentration was not caused and deterioration could be suppressed.

[0077] 1: Isolation transformer 2: Rectifier 3: Electrolyzer 4: Oxygen-side gas-liquid separator 5: Hydrogen-side gas-liquid separator 6: Pure water production system 7: Pump 8: Heat exchanger 9: Cooler 10: Cooling water adjustment 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 rate controller 20: Water temperature controller 21: Power control command unit 22: System power 23: Water 24: Oxygen 25: Hydrogen

Claims

1. A water electrolysis system comprising: 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 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 rectifier is controlled to adjust power consumption in accordance with the frequency of the power grid, the adjustment adjusts power consumption so that it is within a power consumption limit range for 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.

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

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

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

5. A water electrolysis system according to claim 1, characterized in that the upper and lower limits of power consumption are calculated so that the 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, wherein the electrolytic cell uses a solid polymer electrolytic cell.

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

8. A water electrolysis system as claimed in claim 7, characterized in that the current and voltage in each electrolytic cell after adjustment of system power consumption is predicted from the temperature, deterioration rate and pressure of each of the multiple electrolytic cells, 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 is adjusted so as to satisfy the upper and lower limit ranges of power consumption in all electrolytic cells.

9. A water electrolysis system as claimed in claim 1, characterized in that the power consumption is adjusted in accordance with the frequency of the power grid, and is capable of adjusting the power consumption in response to a command from a grid manager to adjust the power consumption, and the range of power consumption adjustment is wider when the power consumption is adjusted in response to a command than when the power consumption is adjusted in accordance with the frequency of the power grid.

10. A water electrolysis system controller 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 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 water electrolysis system controller controls the rectifier to adjust power consumption in accordance with the frequency of the power system, adjusting the power consumption so that it is within a power consumption limit range in the electrolytic cell, and determining the power consumption limit range 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.

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