JP7808011B2 - water electrolysis equipment - Google Patents

Description

The present invention relates to a water electrolysis device that electrolyzes water to generate hydrogen and oxygen.

Water electrolysis systems that use natural energy to produce hydrogen have been developed. As disclosed in Patent Document 1, this type of water electrolysis system is equipped with a circulation pump that circulates water by supplying it from an oxygen gas-liquid separator to an electrolytic cell.

Japanese Patent Application Laid-Open No. 2002-173788

When using unstable natural energy sources with large power fluctuations, the electrolytic current in the electrolytic cell changes, so it is desirable to change the circulating water flow rate in accordance with changes in the electrolytic current. However, in the past, the rotation speed of the circulating pump was controlled to a constant value, which could result in excessive circulating water flow rate during low-load operation, reducing overall energy efficiency.

One aspect of the present invention was made in consideration of the above-mentioned conventional problems, and aims to reduce the power consumption of a water electrolysis device by adjusting the rotation speed of the circulation pump to change the flow rate of circulating water.

In order to solve the above problems, one aspect of the present invention provides a water electrolysis device that includes an electrolytic cell that electrolyzes water, a gas-liquid separator that separates water from gas generated in the electrolytic cell, a circulation pump installed in a water circulation line that circulates water by supplying water from the gas-liquid separator to the electrolytic cell, an inverter connected to the circulation pump and supplying power to the circulation pump, and a control unit that controls the inverter to change the flow rate of circulating water in the water circulation line.

According to one aspect of the present invention, the power consumption of the water electrolysis device can be reduced by adjusting the rotation speed of the circulation pump to change the flow rate of the circulating water.

1 is a diagram showing a schematic configuration of a water electrolysis device according to an embodiment of the present invention. 4 is a flowchart illustrating an example of circulating water flow rate change control executed by the water electrolysis apparatus. 3 is a graph showing an example of total power consumption calculated in step S5 shown in FIG. 2 . 3 is a graph showing an example of control in step S9 shown in FIG. 2 . 3 is a graph showing an example of control in step S10 shown in FIG. 2 . 3 is a graph showing an example of control in step S12 shown in FIG. 2 . 3 is a graph showing an example of control in step S13 shown in FIG. 2 .

[Configuration of water electrolysis device 100]
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the following description is an example of a water electrolysis device according to the present invention, and the technical scope of the present invention is not limited to the illustrated example.

(Configuration of water electrolysis device)
First, a configuration example of a water electrolysis apparatus 100 according to one embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a configuration diagram showing a schematic configuration of the water electrolysis apparatus 100 according to this embodiment. The water electrolysis apparatus 100 according to this embodiment electrolyzes pure water in an electrolytic cell 20 to generate hydrogen ( _H2 ) and oxygen ( _O2 ).

As shown in FIG. 1 , the water electrolysis system 100 includes an electrolytic cell 20, a hydrogen gas-liquid separator 21, an oxygen gas-liquid separator (gas-liquid separator) 22, a water circulation line 23, a first ion exchanger 24, a pure water tank 25, a branch line 41, and a second ion exchanger 43. The water electrolysis system 100 also includes a circulation pump 27 installed in the water circulation line 23, an inverter 50 connected to the circulation pump 27, and a control unit 60 that controls the operation of the entire water electrolysis system 100, including the inverter 50. The control unit 60 controls the inverter 50 to adjust the rotation speed of the circulation pump 27, thereby changing the flow rate of circulating water circulating through the water circulation line 23. In this way, the control unit 60 optimizes the circulating water flow rate and reduces the power consumption of the water electrolysis system 100.

The water circulation line 23 circulates water from the hydrogen gas-liquid separator 21 and the oxygen gas-liquid separator 22 to the electrolytic cell 20. The water circulation line 23 is equipped with a circulation pump 27 for circulating the water and a circulation water cooler (heat exchanger) 28 for cooling the circulating water before supplying it to the electrolytic cell 20. The illustrated example shows a configuration in which the circulating water cooler 28 is installed downstream of the circulation pump 27, i.e., between the electrolytic cell 20 and the circulation pump 27. Installing the circulating water cooler 28 downstream of the circulation pump 27 facilitates the circulating water passing through the circulating water cooler 28 by utilizing the discharge pressure of the circulation pump 27. Furthermore, if the circulating water cooler 28 were installed upstream of the circulation pump 27, the pressure upstream of the circulation pump 27 would be low, potentially causing cavitation. To suppress this cavitation, it is preferable to install the circulating water cooler 28 downstream of the circulation pump 27. However, it is also possible to install the circulating water cooler 28 upstream of the circulation pump 27.

The branch line 41 is a line that extracts and treats a portion of the circulating water from the water circulation line 23 and sends the treated water to the pure water tank 25. The branch line 41 is equipped with a blow water cooler 42 that cools the circulating water extracted from the water circulation line 23 and a second ion exchanger 43 that performs ion exchange on the cooled water. A blow water thermometer TT3 that detects the temperature of the blow water flowing through the branch line 41 is installed between the blow water cooler 42 and the second ion exchanger 43. The downstream end of the branch line 41 is connected to the pure water tank 25. The upstream end of the branch line 41 is connected to the water circulation line 23 between the electrolytic cell 20 and the circulating water cooler 28. A blow valve 29 is installed upstream of the branch line 41. The opening and closing of the blow valve 29 is automatically controlled by the electrical conductivity of the circulating water obtained from an electrical conductivity controller 30 installed between the electrolytic cell 20 and the circulating water cooler 28 on the water circulation line 23.

The electrolytic cell 20 electrolyzes water to generate oxygen (O ₂ ) at the anode and hydrogen (H ₂ ) at the cathode. The electrolytic cell 20 is supplied with the power required for water electrolysis. The power supplied to the electrolytic cell 20 can be power from a commercial power source, or renewable energy such as solar power generation or wind power generation, or surplus power thereof. The oxygen generated at the anode of the electrolytic cell 20 is sent to an oxygen gas-liquid separator 22. The hydrogen generated at the cathode of the electrolytic cell 20 is sent to a hydrogen gas-liquid separator 21.

An inlet thermometer TT1 is installed on the circulating water inlet side of the electrolytic cell 20 to detect the temperature of the circulating water supplied to the electrolytic cell 20. An outlet thermometer TT2 is installed on the circulating water outlet side of the electrolytic cell 20 to detect the temperature of the circulating water discharged from the electrolytic cell 20. Furthermore, a circulating water flow meter FT is installed upstream of the inlet thermometer TT1 to detect the flow rate of the circulating water circulating through the water circulation line 23.

The water electrolysis device 100 may be, for example, a solid polymer water electrolysis device that electrolyzes pure water by applying a voltage to a solid polymer electrolyte membrane to pass a current, thereby generating hydrogen and oxygen. However, the water electrolysis device 100 is not limited to a solid polymer water electrolysis device, and may also be, for example, an alkaline water electrolysis device, an anion exchange membrane water electrolysis device, or the like.

Oxygen generated at the anode of the electrolytic cell 20 is sent to the oxygen-liquid separator 22. Hydrogen generated at the cathode of the electrolytic cell 20 is sent to the hydrogen-liquid separator 21. The hydrogen-liquid separator 21 separates the hydrogen generated at the cathode of the electrolytic cell 20 from the water. The oxygen-liquid separator 22 separates the oxygen generated at the anode of the electrolytic cell 20 from the water. Most of the water discharged from the electrolytic cell 20 is sent to the oxygen-liquid separator 22.

The liquid levels of the hydrogen gas-liquid separator 21 and the oxygen gas-liquid separator 22 are controlled independently. A hydrogen cooler 31 is installed in the hydrogen outlet path of the hydrogen gas-liquid separator 21, and an oxygen cooler 32 is installed in the oxygen outlet path of the oxygen gas-liquid separator 22. The water discharged from the oxygen gas-liquid separator 22 is resupplied to the electrolytic cell 20 via the water circulation line 23, and a portion of it is sent to the pure water tank 25 via the branch line 41. The hydrogen gas-liquid separator 21 and the pure water tank 25 may be connected by piping, and the water discharged from the hydrogen gas-liquid separator 21 may be sent to the pure water tank 25 via this piping.

The pure water tank 25 stores water to be electrolyzed in the electrolytic cell 20. The pure water tank 25 stores water obtained by treating new supply water (such as city water) supplied to the electrolytic cell 20 using the first ion exchanger 24. The pure water tank 25 also stores water obtained by treating circulating water extracted from the water circulation line 23 via branch line 41 using the second ion exchanger 43. A supply pump 26 is installed in the piping connecting the pure water tank 25 and the oxygen-gas-liquid separator 22 to send water from the pure water tank 25 to the oxygen-gas-liquid separator 22. Water temporarily stored in the pure water tank 25 is sent to the oxygen-gas-liquid separator 22 by the supply pump 26 according to the preset level setting for the oxygen-gas-liquid separator 22.

The circulating water flowing through the water circulation line 23 is adjusted to a predetermined temperature (e.g., 65°C to 70°C) by the circulating water cooler 28 and sent to the electrolytic cell 20 by the circulation pump 27. The set temperature of the circulating water for flowing through the branch line 41 is, for example, 1 μS/cm or less; if the temperature is higher, the blowdown valve 29 opens, and if the temperature is lower, the blowdown valve 29 closes. The circulating water extracted to the branch line 41 is cooled to room temperature by the blowdown water cooler 42 and supplied to the second ion exchanger 43, where it is treated to have an electrical conductivity of, for example, 0.5 μS/cm or less, and then supplied to the pure water tank 25. In this way, by extracting a portion of the circulating water from the water circulation line 23 to the branch line 41 and treating it, the impurity content in the circulating water can be reduced.

The circulation pump 27 circulates water by supplying circulating water from the water circulation line 23 to the electrolytic cell 20, and cools the electrolytic cell 20 by supplying circulating water cooled by the circulating water cooler 28 to the electrolytic cell 20. In the water electrolysis system 100, an inverter 50 is connected to the circulation pump 27. The inverter 50 supplies frequency-converted power to the circulation pump 27, making it possible to adjust the rotation speed of the circulation pump 27. The circulation pump 27 is driven at a rotation speed that corresponds to the frequency of the power supplied from the inverter 50, and the flow rate of circulating water in the water circulation line 23 increases or decreases depending on this rotation speed.

The inverter 50 is an electrical circuit that supplies frequency-converted power to the circulation pump 27. A control signal is input to the inverter 50 from the control unit 60. The inverter 50 outputs power to the circulation pump 27 at a frequency corresponding to the frequency specification signal (current value signal or voltage value signal) input by the control unit 60, and adjusts the rotation speed of the circulation pump 27.

The control unit 60 comprehensively controls the operation of the water electrolysis device 100. The control unit 60 is composed of, for example, a processor such as a CPU (Central Processing Unit), a logic circuit formed in an integrated circuit (IC chip), etc.

The control unit 60 controls the operation of the electrolytic cell 20, for example, by controlling the power supply to the electrolytic cell 20. The control unit 60 also changes the circulating water flow rate in the water circulation line 23, for example, by controlling the inverter 50 to adjust the rotation speed of the circulation pump 27. During electrolysis operation of the electrolytic cell 20, the control unit 60 also stores various values, such as the circulating water flow rate, the temperature of the electrolytic cell 20, and the power consumption of the circulation pump 27, in a memory (not shown) as past history information.

Note that Figure 1 shows an example configuration in which an oxygen gas-liquid separator 22 is installed in the water circulation line 23 as the gas-liquid separator. However, a hydrogen gas-liquid separator 21 may be installed in the water circulation line 23 instead of the oxygen gas-liquid separator 22, or both the hydrogen gas-liquid separator 21 and the oxygen gas-liquid separator 22 may be installed in the water circulation line 23.

(Control of water electrolysis device 100)
Next, control of the water electrolysis system 100 will be described with reference to Figures 2 to 7. Hereinafter, circulating water flow rate change control for changing the circulating water flow rate in the water circulation line 23 will be described as an example of a control method for the water electrolysis system 100.

Figure 2 is a flowchart showing an example of circulating water flow rate change control executed by the water electrolysis system 100. After the electrolysis operation of the electrolytic cell 20 begins, the control unit 60 repeatedly executes the control flow shown in Figure 2 at intervals of, for example, a few tenths of a second to a few seconds. The following description uses as an example the circulating water flow rate change control executed the kth time (k is a natural number equal to or greater than 2) since the electrolysis operation of the electrolytic cell 20 begins.

In the circulating water flow rate change control, the control unit 60 calculates the calorific value P _E (k) of the electrolytic cell 20 (step S1). For example, the control unit 60 may calculate the calorific value P E (k) of the electrolytic cell 20 based on the values of the current and voltage of the electrolytic cell 20 (power consumption of the electrolytic cell 20) and the amount of _hydrogen generated at the cathode of the electrolytic cell 20 (generated energy).

Next, the control unit 60 determines whether the outlet temperature of the circulating water from the electrolytic bath 20 is higher than a threshold temperature T _m (e.g., 80°C) (step S2). Generally, an upper limit is set for the temperature of the electrolytic bath 20, and the outlet temperature of the circulating water from the electrolytic bath 20 is adjusted to be lower than the threshold temperature T _m . The control unit 60 determines whether the outlet temperature from the electrolytic bath 20 is higher than the threshold temperature T _m , and changes the circulating water flow rate based on the determination result. This makes it possible to perform optimal circulating water flow rate control according to the outlet temperature.

If the outlet temperature of electrolytic bath 20 is equal to or lower than threshold temperature _Tm (No in step S2), control unit 60 calculates (step S3) the circulating water flow rate based on the specific heat of water and the heat generation amount of electrolytic bath 20. Given the specific heat of water C _H2O , the heat generation amount of electrolytic bath 20 P _E , the upper limit of the temperature difference between the inlet and outlet temperatures of the circulating water in electrolytic bath 20 (set value of the inlet/outlet temperature difference) ΔT _m , and the set value of the circulating water flow rate N _{S ,} control unit 60 may calculate the set value of the circulating water flow rate N _S using the following formula:
The upper limit temperature difference ΔT _m of the electrolytic cell 20 is a set value for the inlet/outlet temperature difference, which is the outlet temperature of the electrolytic cell 20 minus the inlet temperature, and is set, for example, in the range of 10°C to 15°C, depending on the design specifications and operating conditions of the electrolytic cell 20. The control unit 60 calculates a set value N _S at which the circulating water flow rate will be reduced to the set upper limit temperature difference ΔT _m . This reduces the rotation speed of the circulating pump 27, thereby reducing power consumption. Specifically, the control unit 60 controls the inverter 50 to adjust the rotation speed of the circulating pump 27 so that the circulating water flow rate becomes the calculated set value N _S. In this way, the control unit 60 controls the inverter 50 to change the circulating water flow rate to the set value N _S , and ends the circulating water flow rate change control.

On the other hand, if the outlet temperature of the electrolytic cell 20 is higher than the threshold temperature _Tm (Yes in step S2), the control unit 60 measures the power consumption P _P (k) of the circulation pump 27 (step S4). The control unit 60 may measure the power consumption P _P (k) of the circulation pump 27, for example, using a power meter (not shown) connected to the circulation pump 27. The control unit 60 may also calculate the power consumption of the circulation pump 27 based on the output current and output voltage of the inverter 50 connected to the circulation pump 27, for example.

Next, the control unit 60 calculates the total power consumption P _SUM (k) based on the power consumption P _P (k) of the circulation pump 27 calculated in step S4 and the heat generation amount P _E (k) of the electrolytic cell 20 calculated in step S1 (step S5).

FIG. 3 is a graph showing an example of the total power consumption P _SUM (k) calculated in step S5. As shown in FIG. 3 , as the power consumption P _P (k) of the circulation pump 27 increases, the rotational speed increases, and the circulating water flow rate increases accordingly. Typically, the power consumption of the circulation pump 27 is proportional to the cube of the circulating water flow rate (rotational speed). Furthermore, as the circulating water flow rate increases, the increase in the outlet temperature of the electrolytic cell 20 is suppressed, and the temperature difference between the inlet and outlet of the electrolytic cell 20 decreases. The temperature of the electrolytic cell 20 during electrolysis operation has an upper limit (upper limit of the electrolytic cell temperature). Taking this upper limit into account, the smaller the inlet and outlet temperature difference, the higher the inlet temperature can be, thereby reducing the power consumption of the electrolytic cell 20 (i.e., improving the conversion efficiency). Therefore, as the circulating water flow rate increases, the heat generation amount P _E (k) of the electrolytic cell 20 decreases.

The control unit 60 calculates the total power consumption PSUM(k) by adding the power consumption P _P (k) of the circulation pump 27 and the heat generation amount P _E (k) of the electrolytic cell 20. _{The total power consumption PSUM (} k) forms a curve that is convex downward, and the apex of the curve is the minimum power consumption P that indicates the minimum value of the total power consumption _PSUM (k). The control unit 60 records the calculated total power consumption _PSUM (k) in memory.

Next, the control unit 60 reads from memory the total power consumption P _SUM (k-1) calculated in the previous (past) (k-1) circulating water flow rate change control, and determines whether the total power consumption P _SUM (k) calculated in step S5 and the previous total power consumption P _SUM (k-1) are the same value (step S6). Note that if the operating cycle of the circulating water flow rate change control is relatively short (for example, if the operating cycle is 0.5 seconds), it _{is also possible to use the previous previous total power consumption P SUM (} k-2) or the like as the value of the past total power consumption P _SUM instead of the previous total power consumption P SUM (k-1).

There may be a slight time lag between when control unit 60 controls inverter 50 to adjust the rotation speed of circulation pump 27 and when a change in the circulating water flow rate is actually confirmed. For this reason, if total power consumption P _SUM (k) and the previous total power consumption P _SUM (k-1) are the same value (Yes in step S6), that is, if total power consumption P _SUM has not changed since the previous circulating water flow rate change control, control unit 60 may take the time lag, etc. into consideration, and terminate the circulating water flow rate change control without changing the circulating water flow rate, and change the circulating water flow rate in the next or subsequent circulating water flow rate change control.

On the other hand, if the total power consumption P _SUM (k) and the previous (past) total power consumption P _SUM (k-1) are not the same value (No in step S6), the control unit 60 determines whether the total power consumption P _SUM (k) has increased from the previous total power consumption P _SUM (k-1) (step S7).

In step S7, if the total power consumption P _SUM (k) is less than or equal to the previous total power consumption P _SUM (k-1) (No in step S7), the control unit 60 reads from memory the circulating water flow rate N(k-1) at the time of the previous (k-1) circulating water flow rate change control, and determines whether the circulating water flow rate N(k) has increased from the previous circulating water flow rate N(k-1) (step S8).

If the circulating water flow rate N(k) is higher than the previous circulating water flow rate N(k-1) (Yes in step S8), the control unit 60 controls the inverter 50 to increase the circulating water flow rate N(k) (step S9).

FIG. 4 is a graph showing an example of the control in step S9. As shown in FIG. 4, if the total power consumption P _SUM (k) is lower than the previous total power consumption P _SUM (k-1) (arrow A in the figure) and the circulating water flow rate is increasing (arrow B in the figure), it is estimated that further increasing the circulating water flow rate N(k) (arrow C in the figure) will result in a further decrease in the total power consumption P _SUM (k) (arrow D in the figure). Therefore, in step S9, the control unit 60 controls the inverter 50 to increase the circulating water flow rate N(k). In the example shown, the control unit 60 controls the inverter 50 to increase the circulating water flow rate N(k) so that it approaches 380 [L/min], which is the circulating water flow rate for the minimum power consumption P. This allows the total power consumption P _SUM (k) to approach the minimum power consumption P, thereby reducing the power consumption of the water electrolysis device 100.

On the other hand, if the circulating water flow rate N(k) is less than or equal to the previous circulating water flow rate N(k-1) (No in step S8), the control unit 60 controls the inverter 50 to reduce the circulating water flow rate N(k) (step S10).

5 is a graph showing an example of the control in step S10. As shown in FIG. 5, if the total power consumption P _SUM (k) is lower than the previous total power consumption P _SUM (k-1) (arrow A in the figure) and the circulating water flow rate is lower (arrow B in the figure), it is estimated that further reducing the circulating water flow rate (arrow C in the figure) will result in a further reduction in the total power consumption P _SUM (k) (arrow D in the figure). Therefore, in step S10, the control unit 60 controls the inverter 50 to reduce the circulating water flow rate N(k). This allows the total power consumption P _SUM (k) to approach the minimum power consumption P, thereby reducing the power consumption of the water electrolysis device 100.

Furthermore, in step S7, if the total power consumption P _SUM (k) has increased from the previous total power consumption P _SUM (k-1) (Yes in step S7), the control unit 60 reads from memory the circulating water flow rate N(k-1) at the time of the previous (k-1) circulating water flow rate change control, and determines whether the circulating water flow rate N(k) has increased from the previous circulating water flow rate N(k-1) (step S11).

If the circulating water flow rate N(k) is higher than the previous circulating water flow rate N(k-1) (Yes in step S11), the control unit 60 controls the inverter 50 to decrease the circulating water flow rate N(k) (step S12).

6 is a graph showing an example of the control in step S12. As shown in FIG. 6, if the total power consumption P _SUM (k) has increased (arrow A in the figure) compared to the previous total power consumption P _SUM (k-1) and the circulating water flow rate has increased (arrow B in the figure), it is estimated that decreasing the circulating water flow rate (arrow C in the figure) will result in a decrease (arrow D in the figure) in the total power consumption P _SUM (k). Therefore, in step S12, the control unit 60 controls the inverter 50 to decrease the circulating water flow rate N(k). This allows the total power consumption P _SUM (k) to approach the minimum power consumption P, thereby reducing the power consumption of the water electrolysis device 100.

On the other hand, if the circulating water flow rate N(k) is equal to or less than the previous circulating water flow rate N(k-1) (No in step S11), the control unit 60 controls the inverter 50 to increase the circulating water flow rate N(k) (step S13).

7 is a graph showing an example of the control in step S13. As shown in FIG. 7, if the total power consumption P _SUM (k) has increased (arrow A in the figure) compared to the previous total power consumption P _SUM (k-1) and the circulating water flow rate has decreased (arrow B in the figure), it is estimated that increasing the circulating water flow rate (arrow C in the figure) will result in a decrease (arrow D in the figure) in the total power consumption P _SUM (k). Therefore, in step S13, the control unit 60 controls the inverter 50 to increase the circulating water flow rate N(k). This allows the total power consumption P _SUM (k) to approach the minimum power consumption P, thereby reducing the power consumption of the water electrolysis device 100.

Effects of the water electrolysis device 100
As described above, the water electrolysis apparatus 100 according to the present embodiment comprises the electrolytic cell 20 that electrolyzes water, the oxygen-gas-liquid separator 22 that separates water from oxygen generated in the electrolytic cell 20, the circulation pump 27 installed in the water circulation line 23 that circulates water by supplying water from the oxygen-gas-liquid separator 22 to the electrolytic cell 20, the inverter 50 connected to the circulation pump 27 and supplying power to the circulation pump 27, and the control unit 60 that controls the inverter 50 to change the flow rate of circulating water in the water circulation line 23.

According to this embodiment, the power consumption of the water electrolysis system 100 can be reduced by optimizing the circulating water flow rate by adjusting the rotation speed of the circulation pump 27. Furthermore, because this embodiment can reduce the power consumption of the water electrolysis system 100, it also contributes to achieving, for example, Goal 7 of the Sustainable Development Goals (SDGs) advocated by the United Nations, "Ensure access to affordable, reliable, sustainable and modern energy for all (renewable energy, etc.)."

[Modification]
In the above description, an example of control has been described in which the control unit 60 changes the circulating water flow rate in the processing from step S5 onwards so that the total power consumption P _SUM (k) approaches the minimum power consumption P. Instead of this control, the control unit 60 can also change the circulating water flow rate by the following control.

(Variation 1)
The control unit 60 may change the circulating water flow rate based on past history information. For example, the control unit 60 may change the circulating water flow rate based on history information such as the past circulating water flow rate, the past heat generation amount of the electrolytic cell 20, and the past power consumption of the circulating pump 27. Table 1 shows an example of history information stored in the memory.
As shown in Table 1, the historical information includes the past power consumption of the circulating pump 27, the past heat generation amount of the electrolytic bath 20, the past total power consumption, and the past circulating water flow rate. When changing the circulating water flow rate, the control unit 60 may extract from the historical information a combination of the power consumption of the circulating pump 27 and the heat generation amount of the electrolytic bath 20 that minimizes the total power consumption (No. 1 in the table), and change the circulating water flow rate to approach the circulating water flow rate for the extracted combination. In this way, by optimizing the circulating water flow rate based on the past historical information, the processing load of the control unit 60 in circulating water flow rate change control can be reduced.

(Variation 2)
The control unit 60 may also change the circulating water flow rate based on the derivative of a function that represents the calculated total power consumption in terms of the circulating water flow rate. When the total power consumption is expressed as a function P=F(N) of the circulating water flow rate, the derivative P'=f'(N) at N represents the slope of the curve of the total power consumption P _SUM (k) shown in FIG. 3 . Therefore, when the derivative P' is positive (+), increasing the circulating water flow rate increases the total power consumption. Therefore, when the derivative P' is positive, the control unit 60 controls the inverter 50 to decrease the circulating water flow rate. On the other hand, when the derivative P' is negative (-), increasing the circulating water flow rate decreases the total power consumption. Therefore, when the derivative P' is negative, the control unit 60 controls the inverter 50 to increase the circulating water flow rate. When the absolute value of this derivative P' is large, the slope of the curve becomes steeper. This increases the amount of change in the circulating water flow rate, allowing the total power consumption to quickly approach the minimum power consumption P.

For example, if C is a negative constant and the current circulating water flow rate is N(k), the circulating water flow rate N(k+1) that minimizes the total power consumption can be determined using the following equation.
In this way, the control unit 60 may calculate the circulating water flow rate by performing a calculation using the differential value of a function that expresses the total power consumption in terms of the circulating water flow rate, and thereby optimize the circulating water flow rate.

〔summary〕
A water electrolysis apparatus according to a first aspect of the present invention includes an electrolytic cell that electrolyzes water, a gas-liquid separator that separates water from gas generated in the electrolytic cell, a circulation pump installed in a water circulation line that circulates water by supplying water from the gas-liquid separator to the electrolytic cell, an inverter connected to the circulation pump and supplying power to the circulation pump, and a controller that controls the inverter to change the flow rate of circulating water in the water circulation line.

Furthermore, in the water electrolysis apparatus according to aspect 2 of the present invention, in accordance with aspect 1, the control unit may change the circulating water flow rate based on the power consumption of the circulating pump and the heat generation amount of the electrolytic cell.

Furthermore, in the water electrolysis apparatus according to aspect 3 of the present invention, in accordance with aspect 1, the control unit may change the flow rate of the circulating water based on the amount of heat generated by the electrolytic cell and a set value for the temperature difference between the inlet and outlet of the circulating water in the electrolytic cell.

Furthermore, in the water electrolysis apparatus according to Aspect 4 of the present invention, in Aspect 2, the control unit may calculate the total power consumption of the circulation pump and the electrolytic cell, and change the circulating water flow rate so as to reduce the total power consumption.

Furthermore, in the water electrolysis apparatus according to aspect 5 of the present invention, in accordance with aspect 4, the control unit may compare the calculated total power consumption with the past total power consumption, and if the calculated total power consumption differs from the past total power consumption, change the circulating water flow rate.

Furthermore, in the water electrolysis apparatus according to aspect 6 of the present invention, in any one of aspects 1 to 5, the control unit may determine whether the outlet temperature of the circulating water in the electrolytic cell is higher than a threshold temperature, and change the flow rate of the circulating water based on the determination result.

Furthermore, in the water electrolysis apparatus according to Aspect 7 of the present invention, in Aspect 4, the control unit may change the circulating water flow rate based on historical information regarding the past circulating water flow rate, the past heat generation amount of the electrolytic cell, and the past power consumption of the circulating pump.

Furthermore, in the water electrolysis apparatus according to Aspect 8 of the present invention, in Aspect 4, the control unit may change the circulating water flow rate based on the derivative of a function that expresses the calculated total power consumption in terms of the circulating water flow rate.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the embodiments are also included in the technical scope of the present invention.

20: Electrolytic cell 22: Oxygen gas-liquid separator (gas-liquid separator)
23: Water circulation line 27: Circulation pump 50: Inverter 60: Control unit 100: Water electrolysis device

Claims (7)

an electrolytic cell for electrolyzing water;
a gas-liquid separator that separates the gas and water generated in the electrolytic cell;
a circulation pump installed in a water circulation line that circulates water by supplying water from the gas-liquid separator to the electrolytic cell;
an inverter connected to the circulation pump and supplying power to the circulation pump;
a control unit that controls the inverter to change the flow rate of circulating water in the water circulation line;
Equipped with
The control unit changes the flow rate of the circulating water based on the power consumption of the circulating pump and the heat generation amount of the electrolytic cell. an electrolytic cell for electrolyzing water;
a gas-liquid separator that separates the gas and water generated in the electrolytic cell;
a circulation pump installed in a water circulation line that circulates water by supplying water from the gas-liquid separator to the electrolytic cell;
an inverter connected to the circulation pump and supplying power to the circulation pump;
a control unit that controls the inverter to change the flow rate of circulating water in the water circulation line;
Equipped with
The control unit changes the flow rate of the circulating water based on a heat generation amount of the electrolytic cell and a set value of a temperature difference between an inlet and an outlet of the circulating water in the electrolytic cell. an electrolytic cell for electrolyzing water;
a gas-liquid separator that separates the gas and water generated in the electrolytic cell;
a circulation pump installed in a water circulation line that circulates water by supplying water from the gas-liquid separator to the electrolytic cell;
an inverter connected to the circulation pump and supplying power to the circulation pump;
a control unit that controls the inverter to change the flow rate of circulating water in the water circulation line;
Equipped with
The control unit determines whether an outlet temperature of the circulating water in the electrolytic cell is higher than a threshold temperature, and changes the flow rate of the circulating water based on a result of the determination. The water electrolysis apparatus according to claim 1 , wherein the control unit calculates a total power consumption of the circulation pump and the electrolytic cell, and changes the flow rate of the circulating water so as to reduce the total power consumption. The water electrolysis device described in claim 4, wherein the control unit compares the calculated total power consumption with the past total power consumption, and if the calculated total power consumption differs from the past total power consumption, changes the circulating water flow rate. The water electrolysis device described in claim 4, wherein the control unit changes the circulating water flow rate based on historical information regarding the past circulating water flow rate, the past heat generation amount of the electrolytic cell, and the past power consumption of the circulating pump. The water electrolysis device described in claim 4, wherein the control unit changes the circulating water flow rate based on the differential value of a function that expresses the calculated total power consumption in terms of the circulating water flow rate.