Water electrolysis system

Abstract

This technology provides a way to reduce the difference in current flowing through multiple water electrolysis stacks. [Solution] The water electrolysis system comprises a power supply unit, a plurality of water electrolysis stacks connected in parallel to the power supply unit, an IV characteristic adjustment unit connected to the plurality of water electrolysis stacks, and a control device that controls the operation of the IV characteristic adjustment unit. The IV characteristic adjustment unit is configured to supply ions to the reaction water supplied to the oxygen electrode of the water electrolysis stack, or to supply CO to the hydrogen electrode of the water electrolysis stack. The control device controls the operation of the IV characteristic adjustment unit so that the difference in current flowing through each of the plurality of water electrolysis stacks is smaller than when the IV characteristic adjustment unit is not operating.

Description

Technical Field

[0001] The present specification relates to a water electrolysis system.

Background Art

[0002] Patent Document 1 discloses a water electrolysis system including a power supply unit, a plurality of parallel circuits arranged in parallel with each other with respect to the power supply unit, a plurality of water electrolysis stacks respectively disposed in the plurality of parallel circuits, and a control device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a plurality of water electrolysis stacks are connected in parallel to each other with respect to a power supply unit, the voltage of each water electrolysis stack becomes equal. The IV characteristic of each water electrolysis stack varies depending on the degree of deterioration and the like of each water electrolysis stack. For this reason, when a plurality of water electrolysis stacks are connected in parallel to each other with respect to the power supply unit, the current flowing through each water electrolysis stack differs. It is desired to reduce the difference between the currents respectively flowing through the plurality of water electrolysis stacks.

[0005] The present specification provides a technique capable of reducing the difference between the currents respectively flowing through a plurality of water electrolysis stacks.

Means for Solving the Problems

[0006] In a first aspect disclosed herein, the water electrolysis system may include a power supply unit, a plurality of water electrolysis stacks connected in parallel to the power supply unit, an IV characteristic adjustment unit connected to the plurality of water electrolysis stacks, and a control device for controlling the operation of the IV characteristic adjustment unit. The IV characteristic adjustment unit may be configured to supply ions to the reaction water supplied to the oxygen electrode of the water electrolysis stack, or to supply CO to the hydrogen electrode of the water electrolysis stack. The control device may control the operation of the IV characteristic adjustment unit such that the difference in current flowing through each of the plurality of water electrolysis stacks is smaller than when the plurality of IV characteristic adjustment units are not operating.

[0007] According to the water electrolysis system described above, the control device can make the IV characteristics of each of the multiple water electrolysis stacks match or approximate by controlling the operation of the IV characteristic adjustment unit. Therefore, the difference in current flowing through each of the multiple water electrolysis stacks can be reduced. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram shows an overview of the water electrolysis system 2. [Figure 2] This figure shows the circuit diagram of water electrolysis system 2. [Figure 3] This is a flowchart of the adjustment process performed by the control device 100. [Modes for carrying out the invention]

[0009] (First embodiment) As shown in Figure 1, the water electrolysis system 2 comprises a power supply unit 10, a rectifier 12, multiple parallel circuits 14A to 14C, multiple water electrolysis stacks 16A to 16C, multiple current sensors 18A to 18C, multiple voltage sensors 20A to 20C, and a control device 100. The water electrolysis system 2 is a system that produces hydrogen by electrolyzing reactant water.

[0010] The power supply unit 10 supplies alternating current power. For example, the power supply unit 10 is a device that converts commercial power or renewable energy into alternating current power.

[0011] One end of the rectifier 12 is connected to the power supply unit 10. The other end of the rectifier 12 is connected to multiple parallel circuits 14A to 14C. The rectifier 12 converts the AC power supplied from the power supply unit 10 into DC power. The rectifier 12 also adjusts the power supplied to the multiple parallel circuits 14A to 14C.

[0012] Multiple parallel circuits 14A to 14C are connected in parallel to each other with respect to the rectifier 12. Multiple water electrolysis stacks 16A to 16C are each located within the multiple parallel circuits 14A to 14C. As shown in Figure 2, the multiple water electrolysis stacks 16A to 16C include multiple cells C stacked in a specific direction (left-right direction in Figure 2). The multiple water electrolysis stacks 16A to 16C produce hydrogen by electrolyzing reaction water.

[0013] As shown in Figure 1, multiple current sensors 18A to 18C are arranged in multiple parallel circuits 14A to 14C, respectively. Similarly, multiple voltage sensors 20A to 20C are arranged in multiple parallel circuits 14A to 14C, respectively.

[0014] As shown in Figure 2, the water electrolysis system 2 further comprises an oxygen electrode unit 30 and a hydrogen electrode unit 80.

[0015] The oxygen electrode unit 30 comprises a tank 32, a pump 34, a heat exchanger 36, an ion exchanger 38, a first gas-liquid separator 40, valves 42A to 42C, and an ion source 44.

[0016] The oxygen electrode side unit 30 further includes a first supply pipe 50, a plurality of second supply pipes 52A to 52C, a plurality of first discharge pipes 54A to 54C, a second discharge pipe 56, a third discharge pipe 58, a fourth discharge pipe 60, and a bypass pipe 62. The upstream end of the first supply pipe 50 is connected to the tank 32. The first supply pipe 50 is provided with a pump 34, a heat exchanger 36, an ion exchanger 38, and a valve 42A in order from the upstream side.

[0017] The plurality of second supply pipes 52A to 52C are connected in parallel to each other with respect to the first supply pipe 50. The downstream ends of the plurality of second supply pipes 52A to 52C are connected to the plurality of water electrolysis stacks 16A to 16C, respectively. The ion generation source 44 is connected to the plurality of second supply pipes 52A to 52C.

[0018] The upstream ends of the plurality of first discharge pipes 54A to 54C are connected to the plurality of water electrolysis stacks 16A to 16C, respectively. The plurality of first discharge pipes 54A to 54C are connected in parallel to each other with respect to the second discharge pipe 56. The downstream end of the second discharge pipe 56 is connected to the first gas-liquid separator 40. The second discharge pipe 56 is provided with a valve 42B.

[0019] The upstream end of the third discharge pipe 58 and the upstream end of the fourth discharge pipe 60 are connected to the first gas-liquid separator 40. The downstream end of the third discharge pipe 58 is connected to the tank 32. The downstream end of the fourth discharge pipe 60 is open to the outside of the water electrolysis system 2.

[0020] The bypass pipe 62 connects the first supply pipe 50 and the second discharge pipe 56. The bypass pipe 62 is provided with a valve 42C.

[0021] The hydrogen electrode side unit 80 includes a second gas-liquid separator 82, a plurality of fifth discharge pipes 84A to 84C, a sixth discharge pipe 86, a seventh discharge pipe 88, and an eighth discharge pipe 90.

[0022] The upstream ends of the plurality of fifth discharge pipes 84A to 84C are respectively connected to the hydrogen electrode sides of the plurality of water electrolysis stacks 16A to 16C. The plurality of fifth discharge pipes 84A to 84C are connected in parallel to each other with respect to the sixth discharge pipe 86. The downstream end of the sixth discharge pipe 86 is connected to the second gas-liquid separator 82. The upstream end of the seventh discharge pipe 88 and the upstream end of the eighth discharge pipe 90 are connected to the second gas-liquid separator 82. The downstream end of the seventh discharge pipe 88 is connected to a device that stores hydrogen. The downstream end of the eighth discharge pipe 90 is open to the outside of the water electrolysis system 2.

[0023] The control device 100 in Figure 1 is a computer configured with a CPU, ROM, RAM, and the like. The control device 100 controls the operation of each component of the water electrolysis system 2.

[0024] (Adjustment processing; Figure 3) With reference to Figure 3, the adjustment processing executed by the control device 100 of the water electrolysis system 2 will be described. Note that the control device 100 determines a common target current for the plurality of water electrolysis stacks 16A to 16C before executing the hydrogen generation processing.

[0025] In S10, the control device 100 identifies the stack voltage corresponding to the target current for each of the plurality of water electrolysis stacks 16A to 16C.

[0026] In S12, the control device 100 uses the multiple stack voltages identified in S10 to identify the water electrolysis stack with the lowest performance among the multiple water electrolysis stacks 16A to 16C as the reference water electrolysis stack. The water electrolysis stack with the lowest performance is the water electrolysis stack with the highest stack voltage identified in S10 among the multiple water electrolysis stacks 16A to 16C. The water electrolysis stack with the lowest performance is also the water electrolysis stack with the lowest stack current for the same stack voltage. Hereafter, water electrolysis stacks other than the reference water electrolysis stack will be referred to as "target water electrolysis stacks". Also below, the stack voltage corresponding to the target current in the reference water electrolysis stack and the stack voltage corresponding to the target current in the target water electrolysis stack will be referred to as "reference voltage" and "target voltage", respectively.

[0027] In S14, the control device 100 calculates the target ion amount to make the voltage difference zero. The voltage difference is the difference between the target voltage and the reference voltage. The target ion amount is the amount of ions to be supplied to the target water electrolysis stack. For example, if water electrolysis stack 16A is the reference water electrolysis stack and water electrolysis stacks 16B and 16C are the target water electrolysis stacks, the control device 100 calculates the target ion amount corresponding to water electrolysis stacks 16B and 16C, respectively.

[0028] In S16, the control device 100 operates the ion generator 44 using the target ion amount calculated in S14. As a result, water with a high ionic content is supplied to the target water electrolysis stack, increasing the proton resistance at the oxygen electrode. Consequently, the target water electrolysis stack temporarily deteriorates, and its IV characteristics decrease. That is, the stack voltage relative to the stack current in the target water electrolysis stack becomes higher. Through the above process, the IV characteristics of the target water electrolysis stack match or approximate those of the reference water electrolysis stack.

[0029] In S18, the control device 100 determines whether the current difference, which is the difference between the detected values ​​detected by each current sensor 18A to 18C, is within a predetermined value. If the current difference is not within a predetermined value (NO in S20), the control device 100 proceeds to S22. On the other hand, if the current difference is within a predetermined value (YES in S20), the control device 100 proceeds to S24.

[0030] In S22, the control device 100 controls the operation of the ion generator 44 so that the current difference is within a predetermined value. Specifically, the control device 100 adjusts the amount of CO supplied to the target water electrolysis stack.

[0031] In S24, the control device 100 determines whether a predetermined time has elapsed since the execution of S10. If the control device 100 determines that the predetermined time has elapsed (YES in S24), it proceeds to S26. On the other hand, if the control device 100 determines that the predetermined time has not elapsed (NO in S24), it proceeds to S30.

[0032] In S26, the control device 100 performs a refresh process. Specifically, the control device 100 stops the ion generator 44 and supplies ultrapure water to multiple water electrolysis stacks 16A to 16C. This restores the proton resistance of the oxygen electrode of the target water electrolysis stack. In other words, the temporary degradation of the target water electrolysis stack is eliminated. When S26 is completed, the control device 100 returns to S10.

[0033] Furthermore, in S30, the control device 100 determines whether or not a termination signal has been received. If a termination signal is received (YES in S30), the control device 100 terminates the process shown in Figure 3. On the other hand, if a termination signal is not received (NO in S30), the control device 100 returns to S20.

[0034] As described above, the water electrolysis system 2 comprises a power supply unit 10, a plurality of water electrolysis stacks 16A to 16C connected in parallel to each other to the power supply unit 10, an ion generator 44 (an example of an "IV characteristic adjustment unit") connected to the plurality of water electrolysis stacks 16A to 16C, and a control device 100 that controls the operation of the ion generator 44. The ion generator 44 is configured to supply ions to the reaction water supplied to the oxygen electrodes of the water electrolysis stacks 16A to 16C. The control device 100 controls the operation of the ion generator 44 so that the difference in current flowing through each of the plurality of water electrolysis stacks 16A to 16C is smaller than when the ion generator 44 is not operating.

[0035] According to the water electrolysis system 2 described above, the control device 100 can match or approximate the IV characteristics of each of the multiple water electrolysis stacks 16A to 16C by controlling the operation of the ion source 44. Therefore, the difference in current flowing through each of the multiple water electrolysis stacks 16A to 16C can be reduced.

[0036] (Second example) Referring to Figure 2, the water electrolysis system 2 of the second embodiment will be described. Components common to both embodiments are denoted by the same reference numerals, and their descriptions are omitted.

[0037] The water electrolysis system 2 of the second embodiment differs from the water electrolysis system 2 of the first embodiment in that it has a CO generation source 244 instead of an ion generation source 44. The CO generation source 244 is connected to the hydrogen electrodes of the water electrolysis stacks 16A to 16C.

[0038] (Adjustment process; Figure 3) The control device 100 in this embodiment is also configured to perform the adjustment process shown in Figure 3. In the hydrogen generation process of this embodiment, the processing contents of S14, S16, S22, and S26 differ from the adjustment process of the first embodiment.

[0039] In S14, the control device 100 calculates the target amount of CO to make the voltage difference zero. The target amount of CO is the amount of CO to be supplied to the target water electrolysis stack.

[0040] In S16, the control device 100 operates the CO source 244 using the target amount of CO calculated in S14. As a result, CO is supplied to the target water electrolysis stack, and the CO is adsorbed onto the hydrogen electrode of the target water electrolysis stack. This reduces the catalytic performance of the hydrogen electrode. Consequently, the target water electrolysis stack temporarily deteriorates, and its IV characteristics decrease. Through the above process, the IV characteristics of the target water electrolysis stack match or approximate those of the reference water electrolysis stack.

[0041] Furthermore, in S22, the control device 100 controls the operation of the CO source 244 so that the current difference is within a predetermined value. Specifically, the control device 100 adjusts the amount of CO supplied to the target water electrolysis stack.

[0042] In the refresh process in S26, the control device 100 stops the CO source 244 and applies a voltage of approximately 0.5V to the hydrogen electrode of the target water electrolysis stack. This restores the catalytic performance of the hydrogen electrode of the target water electrolysis stack.

[0043] According to the water electrolysis system 2 described above, the control device 100 can match or approximate the IV characteristics of each of the multiple water electrolysis stacks 16A to 16C by controlling the operation of the CO generation source 244 (an example of an "IV characteristic adjustment unit"). Therefore, the difference in current flowing through each of the multiple water electrolysis stacks 16A to 16C can be reduced. [Explanation of Symbols]

[0044] 2: Water electrolysis system, 10: Power supply unit, 12: Rectifier, 14A~14C: Parallel circuit, 16A~16C: Water electrolysis stack, 18A~18C: Current sensor, 20A~20C: Voltage sensor, 30: Oxygen electrode side unit, 32: Tank, 34: Pump, 36: Heat exchanger, 38: Ion exchanger, 40: First gas-liquid separator, 42A: Valve, 42B: Valve, 42C: Valve, 44: Ion Source, 50: First supply pipe, 52A~52C: Second supply pipe, 54A~54C: First discharge pipe, 56: Second discharge pipe, 58: Third discharge pipe, 60: Fourth discharge pipe, 62: Bypass pipe, 80: Hydrogen electrode side unit, 82: Second gas-liquid separator, 84A~84C: Fifth discharge pipe, 86: Sixth discharge pipe, 88: Seventh discharge pipe, 90: Eighth discharge pipe, 100: Control device, 244: CO source

Claims

[Claim 1] A water electrolysis system, Power supply unit, A plurality of water electrolysis stacks connected in parallel to each other to the aforementioned power supply unit, An IV characteristic adjustment unit connected to the plurality of water electrolysis stacks, The system includes a control device for controlling the operation of the IV characteristic adjustment unit, The IV characteristic adjustment unit is configured to supply ions to the reaction water supplied to the oxygen electrode of the water electrolysis stack, or to supply CO to the hydrogen electrode of the water electrolysis stack. The control device controls the operation of the IV characteristic adjustment unit so that the difference in current flowing through each of the plurality of water electrolysis stacks is smaller than when the IV characteristic adjustment unit is not operating. Water electrolysis system.

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