Water electrolysis hydrogen production system and control method thereof

Abstract

The invention discloses a water electrolysis hydrogen production system and a control method thereof.The water electrolysis hydrogen production system comprises an electrolytic tank, a pyrolysis tank, a buffer cooling device, a buffer heating device and an electrode changing mechanism, a cathode and an auxiliary electrode are arranged in the electrolytic tank, alkaline electrolyte is poured into the electrolytic tank, and a first movable door capable of being electrically opened is arranged at the position, above the auxiliary electrode, of the top of the electrolytic tank; a plurality of groups of auxiliary electrodes are placed in the pyrolysis tank, a second movable door capable of being electrically opened is arranged at the top of the pyrolysis tank and above the auxiliary electrodes, pyrolysis liquid is poured into the pyrolysis tank, the electrode changing mechanism comprises a plurality of groups of manipulators, and the manipulators move above the electrolytic tank, the pyrolysis tank, the buffer cooling device and the buffer heating device and grab the auxiliary electrodes for rapid replacement. The device has the advantages that oxygen evolution and hydrogen evolution can be separated spatially to improve safety, and efficient utilization of the auxiliary electrodes can be realized through the electrode changing mechanism, so that the utilization rate of the electrolytic cell device is improved, and the cost of unit hydrogen production is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrogen production by water electrolysis, and particularly relates to a hydrogen production system by water electrolysis and a control method thereof. BACKGROUND

[0002] Hydrogen, as a clean and efficient secondary energy, is a key carrier for promoting energy structure transformation and achieving the "double carbon" goal. Among various hydrogen production technologies, water electrolysis is considered as one of the most promising green hydrogen production methods due to its advantages such as easy availability of raw materials, high product purity, and zero carbon emissions.

[0003] Currently, the alkaline water electrolysis technology widely used in industry usually separates the anode chamber and the cathode chamber by a diaphragm in an electrolytic cell filled with alkaline electrolyte (such as KOH solution). Under the action of direct current, hydrogen is generated at the cathode, and oxygen is generated at the anode. However, this structure has inherent defects: first, the oxygen generated at the anode and the hydrogen generated at the cathode are only separated by a diaphragm, which has the risk of hydrogen and oxygen gas interpenetration and mixing due to diaphragm damage or sealing failure, which will cause serious safety accidents when the mixed gas concentration reaches the explosion limit. Second, in order to achieve gas separation, the diaphragm material requires high density, strength and long-term stability, which directly leads to an increase in system cost.

[0004] The step-by-step hydrogen production electrolytic cell is a safer electrolytic cell. This electrolytic cell uses a 2-step hydrogen production method, using Ni(OH)2 as an auxiliary electrode. The electrolytic cell has three electrodes or two electrodes, including a cathode, an auxiliary electrode, and an anode, and the most commonly used auxiliary electrode material is Ni(OH)2. In the first step of hydrogen evolution, hydrogen is evolved on the cathode, while no oxygen is evolved on the auxiliary electrode as the anode, and the Ni(OH)2 material on the auxiliary electrode is converted to NiOOH under the action of electricity. In the second step of oxygen evolution, the polarity of the power supply is reversed, the auxiliary electrode is connected to the negative electrode, and the electrolysis is performed in conjunction with the anode. At this time, the NiOOH on the auxiliary electrode is reduced to Ni(OH)2, and oxygen is evolved on the anode.

[0005] This 2-step hydrogen production electrolytic cell separates the evolution of hydrogen and oxygen in time, completely separating the two gas evolution processes, and avoids the contact of the two gases, thus being safer. However, since the hydrogen evolution and oxygen evolution are not synchronized in time, the utilization rate of the electrolytic cell is low. Under the same hydrogen production capacity, the cost of this electrolytic cell is more than twice that of the ordinary alkaline water electrolysis hydrogen production electrolytic cell.

[0006] Another idea is a step-by-step hydrogen production by electrolysis + pyrolysis, the principle of which is to produce hydrogen by electrolysis in the first step, and to reduce NiOOH on the auxiliary electrode to Ni(OH)2 in the second step by pyrolysis, but still using the time-asynchronous method to isolate H2 and O2 to improve safety, but this way also has the problem of low electrode utilization. SUMMARY

[0007] The purpose of the present application is to provide a water electrolysis hydrogen production system and its control method, which can separate the oxygen evolution and hydrogen evolution processes in space to improve safety, and can realize efficient utilization of auxiliary electrodes through the electrode replacement mechanism, thereby improving the utilization rate of the electrolytic cell device and reducing the cost of unit hydrogen production.

[0008] The above technical purpose of the present application is achieved by the following technical scheme: A water electrolysis hydrogen production system, characterized in that it comprises an electrolytic cell, a pyrolysis tank, a buffer cooling device, a buffer heating device and an electrode replacement mechanism, the electrolytic cell is provided with a cathode and an auxiliary electrode respectively, the cathode and the auxiliary electrode are connected with a power supply negative electrode and a power supply positive electrode respectively, the electrolytic cell is filled with an alkaline electrolyte, the top of the electrolytic cell is provided with a first movable door which can be opened electrically at the upper part of the auxiliary electrode, the buffer cooling device and the buffer heating device are both provided with an upper opening, the buffer cooling device and the buffer heating device are respectively filled with cold water and hot water, the pyrolysis tank is provided with a plurality of auxiliary electrodes, the top of the pyrolysis tank is provided with a second movable door which can be opened electrically at the upper part of the auxiliary electrode, the pyrolysis tank is filled with a pyrolysis liquid, and the electrode replacement mechanism comprises a plurality of mechanical hands which are movable above the electrolytic cell, the pyrolysis tank, the buffer cooling device and the buffer heating device and can grab the auxiliary electrode for quick replacement.

[0009] Preferably, the alkaline electrolyte is a 30wt% KOH solution or a 20wt%-25wt% NaOH solution.

[0010] Preferably, the cathode is a nickel-based material plate or a stainless steel plate covered with Raney nickel, and the auxiliary electrode is Ni(OH)2.

[0011] Preferably, the electrolytic cell is a hexahedron or a cylinder structure, and the electrolytic cell is provided with an electrolyte inlet and an electrolyte outlet on one side, the electrolyte inlet is located at the low position of the electrolytic cell, and the electrolyte outlet is located at the high position of the electrolytic cell.

[0012] Preferably, the pyrolysis tank is provided with an auxiliary heater, and the pyrolysis tank is provided with a water inlet and a water outlet on the outside, the water inlet is located at the low position of the pyrolysis tank, and the water outlet is located at the high position of the pyrolysis tank.

[0013] Preferably, a plurality of groups of the electrolytic cells are arranged in series, electrolyte inlets of the plurality of groups of the electrolytic cells are communicated through a main inlet pipe, electrolyte outlets of the plurality of groups of the electrolytic cells are communicated through a main outlet pipe, cathodes and auxiliary electrodes of the electrolytic cells at two ends are connected with a negative pole and a positive pole of a power supply respectively, and cathodes and auxiliary electrodes of adjacent electrolytic cells are connected through wires.

[0014] A control method of a hydrogen production system by electrolysis of water, comprising the following steps: The electrolytic cell is powered on, and hydrogen produced by electrolysis flows out from the electrolyte outlet, and electrolysis is stopped when the conversion upper limit of the auxiliary electrode is reached; The first movable door is opened, the auxiliary electrode in the electrolytic cell is taken out by the mechanical hand, the auxiliary electrode that has been reduced and cooled in the buffer cooling device is taken out by another mechanical hand and placed in the electrolytic cell, and the first movable door is closed to start electrolysis, and then the taken-out auxiliary electrode is moved and placed in the buffer heating device; After the buffer heating device completes the buffer heating of the auxiliary electrode, the mechanical hand takes out the auxiliary electrode for standby; After the pyrolysis tank completes the pyrolysis for oxygen production and reduction of the auxiliary electrode, the second movable door is opened, the auxiliary electrode that has been reduced in the pyrolysis tank is taken out by the mechanical hand, and then the auxiliary electrode that has completed buffer heating is placed in the pyrolysis tank by another mechanical hand for pyrolysis, and the auxiliary electrode that has completed reduction is taken out and placed in the buffer cooling device for buffer cooling; The above steps are repeated to complete the spatial isolation of the continuous hydrogen production and oxygen production processes.

[0015] Preferably, the water temperature in the buffer heating device is 70-80 DEG C.

[0016] Preferably, the working temperature of the pyrolysis liquid in the pyrolysis tank is 90-97 DEG C.

[0017] Preferably, a plurality of groups of the electrolytic cells are arranged in series, and when it is necessary to replace the auxiliary electrode by powering off the specified electrolytic cell, the two groups of wires are short-circuited by a conductive cable inside or outside the electrolytic cell.

[0018] In summary, the present application has the following beneficial effects: 1. The present application realizes near-continuous hydrogen production by quickly replacing the auxiliary electrode, separates the hydrogen production and oxygen production processes in space, and does not use a diaphragm like an ordinary alkaline electrolytic cell, thereby achieving higher safety.

[0019] 2. The present application sequentially produces hydrogen in the electrolytic cell with a plurality of auxiliary electrodes, greatly reduces the Ni(OH)2 load of a single auxiliary electrode under the premise of realizing the same hydrogen production capacity, and greatly reduces the cost of the electrolytic cell.

[0020] 3. The pyrolysis cell can simultaneously perform pyrolysis reduction operations on the auxiliary electrodes of multiple electrolytic cells, which greatly reduces the reduction cost per unit electrode of the electrolytic cell and also significantly improves the reduction efficiency of the auxiliary electrodes. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the electrolytic water hydrogen production system of the present invention; Figure 2 This is a schematic diagram of the series electrolytic cell structure of the present invention; Figure 3 This is a schematic diagram of the electrolytic cell short-circuit structure of the present invention. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. These embodiments do not constitute a limitation on the present invention.

[0023] like Figure 1 The illustrated water electrolysis hydrogen production system includes an electrolytic cell 1, a pyrolysis cell 2, a buffer cooling device 3, a buffer heating device 4, and an electrode switching mechanism 5. A cathode 6 and an auxiliary electrode 7 are respectively installed in the electrolytic cell 1. The cathode 6 and the auxiliary electrode 7 are connected to the negative terminal 8 and the positive terminal 9 of a power supply, respectively. An alkaline electrolyte 11 is injected into the electrolytic cell 1. Electrolysis occurs between the cathode 6 and the auxiliary electrode 7 through ions in the alkaline electrolyte 11. A first electrically operable movable door 12 is provided at the top of the electrolytic cell 1 above the auxiliary electrode 7. Both the buffer cooling device 3 and the buffer heating device 4 are top-opening. The setup includes a buffer cooling device 3 and a buffer heating device 4 filled with cold water and hot water, respectively. Multiple sets of auxiliary electrodes 7 are placed inside the pyrolysis tank 2. A second, electrically operable door 21 is located on the top of the pyrolysis tank 2 above the auxiliary electrodes 7. The pyrolysis tank 2 is filled with pyrolysis liquid 25. The electrode switching mechanism 5 includes multiple sets of robotic arms 51. The robotic arms 51 move above the electrolyzer 1, pyrolysis tank 2, buffer cooling device 3, and buffer heating device 4, grasping and quickly replacing the auxiliary electrodes 7. The robotic arms 51 can hold and move the auxiliary electrodes 7, improving their utilization rate and increasing hydrogen production efficiency. The robotic arms 51 can be grippers or any other automated mechanism capable of grasping, fixing, moving, and transporting electrodes.

[0024] The alkaline electrolyte 11 uses a 30wt% KOH solution or a 20-25wt% NaOH solution.

[0025] The cathode 6 is made of nickel-based material or stainless steel plate covered with Raney nickel, and the auxiliary electrode 7 is Ni(OH)2.

[0026] Electrolytic cell 1 has a hexahedral or cylindrical structure. An electrolyte inlet 13 and an electrolyte outlet 14 are provided on one side of the electrolytic cell 1. The electrolyte inlet 13 is located at the lower position of the electrolytic cell 1, and the electrolyte outlet 14 is located at the higher position of the electrolytic cell 1. The alkaline electrolyte 11 flows in from the electrolyte inlet 13 and flows out from the electrolyte outlet 14, maintaining a continuous and stable flow rate during electrolysis.

[0027] The pyrolysis tank 2 has an auxiliary heater 22 built in, and the heating power can be adjusted as needed to maintain a constant reaction temperature of the pyrolysis liquid 25 in the tank. The pyrolysis tank 2 is provided with an inlet 23 and an outlet 24 on the outside. The inlet 23 is located at the lower position of the pyrolysis tank 2, and the outlet 24 is located at the higher position of the pyrolysis tank 2.

[0028] Since the pyrolysis tank 2 is an insulated container and operates at atmospheric pressure, its manufacturing and operating costs are very low. The pyrolysis tank 2 can be manufactured on a large scale to pyrolyze the oxidized auxiliary electrodes 7 produced by multiple electrolysis tanks 1, thus reducing the pyrolysis cost of a single auxiliary electrode 7. The pyrolysis tank 2 can be pressurized to allow the operating temperature inside the tank to exceed 100°C with the movable door closed, thereby accelerating the pyrolysis rate and improving the pyrolysis temperature and efficiency.

[0029] like Figure 2 As shown, multiple electrolytic cells 1 are connected in series. The electrolyte inlets 13 of the multiple electrolytic cells 1 are connected through the main inlet pipe 15, and the electrolyte outlets 14 of the multiple electrolytic cells 1 are connected through the main outlet pipe 16. The cathodes 6 and auxiliary electrodes 7 of the two electrolytic cells 1 are connected to the negative terminal 8 and the positive terminal 9 of the power supply, respectively. The cathodes 6 and auxiliary electrodes 7 of adjacent electrolytic cells 1 are connected through wires 17.

[0030] A control method for a water electrolysis hydrogen production system includes the following steps: When the electrolytic cell 1 is energized, the hydrogen gas generated by electrolysis flows out from the electrolyte outlet 14. Electrolysis stops when the upper limit of conversion of the auxiliary electrode 7 is reached.

[0031] The working principle of hydrogen production by electrolysis is as follows: at cathode 6, a hydrogen evolution reaction occurs. Water is electrolyzed under the action of the catalyst at cathode 6, producing gaseous H2 and OH-. - ion: 4H2O+4e - —>2H2+4OH - An oxidation reaction of Ni(OH)2 occurs at the auxiliary electrode 7 (anode), where Ni(OH)2 is converted into NiOOH: 4Ni(OH)2+4OH - -4e->4NiOOH+4H2O The electrolysis reaction in electrolytic cell 1 only produces gaseous H2 and liquid water, without producing O2, thus ensuring high safety. The generated H2 flows out from electrolyte outlet 14 along with the alkaline electrolyte 11, entering the next process (gas-liquid separation and purification).

[0032] When the above reaction proceeds to a certain extent, most of the Ni(OH)2 on the auxiliary electrode 7 has been converted into NiOOH, and the rate of H2 generation also begins to decrease. At this point, electrolysis is stopped.

[0033] The first movable door 12 is opened, and the auxiliary electrode 7 in the electrolyzer 1 is taken out by the robotic arm 51. Then, the auxiliary electrode 7, which has been reduced and cooled in the buffer cooling device 3, is taken out by another robotic arm 51 and placed in the electrolyzer 1. The reduced and cooled auxiliary electrode 7 can be held near the first movable door 12 by the robotic arm 51 and wait. The first movable door 12 is closed and electrolysis is started to continue the electrolytic hydrogen production operation. Then, the taken-out auxiliary electrode 7 is moved into the buffer heating device 4. This effectively shortens the electrode switching time of the electrolyzer 1 and allows the electrolyzer 1 to be in a near-continuous electrolytic hydrogen production process. Compared with the conventional stepwise hydrogen production electrolyzer 1, it has a higher efficiency advantage.

[0034] The auxiliary electrode 7, removed from electrolytic cell 1, still carries a small amount of alkaline H2 solution remaining from the hydrogen evolution process, and its temperature is below 50°C. Therefore, for safety, to ensure temperature balance within pyrolysis cell 2, and to buffer heating the electrode rather than rapidly heating it to avoid reducing its material strength and causing it to detach, it is necessary to remove the H2 from the electrode and increase its temperature. The buffer heating device 4 is filled with flowing water at a temperature of 70°C-80°C. A robotic arm 51 places the auxiliary electrode 7 into the buffer heating device 4 for buffer heating, raising the electrode temperature to 70-80°C.

[0035] After the buffer heating device 4 completes the buffer heating of the auxiliary electrode 7, the robotic arm 51 takes out the auxiliary electrode 7 and waits for it to be ready.

[0036] After the pyrolysis oxygen production and reduction of the auxiliary electrode 7 are completed in the pyrolysis tank 2, the second movable door 21 is opened. The robotic arm 51 takes out the auxiliary electrode 7 that has been reduced in the pyrolysis tank 2. Then, another robotic arm 51 puts the auxiliary electrode 7 that has been buffered and heated into the pyrolysis tank 2 for pyrolysis. After the auxiliary electrode 7 that has been reduced is taken out, it is put into the buffer cooling device 3 for buffer cooling.

[0037] Since the auxiliary electrode 7301 is mainly made of NiOOH, it will spontaneously undergo pyrolysis in the hydrothermal solution within the pyrolysis tank 2. An oxygen evolution reaction occurs on the auxiliary electrode 7, where NiOOH and water pyrolyze to release gaseous O2 and Ni(OH)2, thus reducing the auxiliary electrode 7.

[0038] The reaction equation is as follows: NiOOH + ½H₂O → Ni(OH)₂ + ¼O₂ During operation, the movable door on pyrolysis tank 2 is closed to maintain a constant internal temperature. Since the above reaction can be completed spontaneously without the need for external heat supplementation, the main energy loss of pyrolysis tank 2 comes from the heat dissipation required to maintain the system temperature.

[0039] Repeat the above steps to achieve spatial isolation between the continuous hydrogen and oxygen production processes.

[0040] The water temperature filled in the buffer heating device 4 is 70-80℃.

[0041] The working temperature of the pyrolysis liquid 25 in the pyrolysis tank 2 is 90-97℃.

[0042] like Figure 2 and 3 As shown, multiple electrolytic cells 1 are connected in series. When the auxiliary electrode 7 of one electrolytic cell 1 is replaced after oxidation, during the short period when electrolysis in that electrolytic cell 1 stops, the solution in that electrolytic cell 1 is conductive. Therefore, the electrolytic cell 1 with the auxiliary electrode 7 removed can still conduct electrical energy to other electrolytic cells 1, allowing the electrolysis operation of the other electrolytic cells 1 to proceed normally. This ensures the continuous operation of the stacked electrolytic cells 1 of this invention. Simultaneously, to prevent the auxiliary electrode 7 and cathode 6 within the electrolytic cell 1 from forming a new conductive circuit and generating a small amount of oxygen, two methods are used for short-circuiting: short-circuiting the wires 17 of the auxiliary electrode 7 and cathode 6 within the electrolytic cell 1 using a conductive cable 18; or short-circuiting the wires 17 of the auxiliary electrode 7 and cathode 6 outside the electrolytic cell 1 using a conductive cable 18. This prevents hydrogen evolution reaction inside the wires 17 of the stopped auxiliary electrode 7 and cathode 6, while ensuring normal power supply and hydrogen evolution operation in the other electrolytic cells 1.

[0043] The electrolytic water hydrogen production system of this invention consists of an electrolyzer, a pyrolysis cell, and an electrode switching mechanism, employing a separate structure. Hydrogen is produced in the electrolyzer, and oxygen is produced in the pyrolysis cell. This device can spatially separate the oxygen evolution and hydrogen evolution processes to improve safety. Simultaneously, the electrode switching mechanism enables efficient utilization of the auxiliary electrode (Ni(OH)2 electrode), thereby improving the utilization rate of the electrolyzer and reducing the cost per unit of hydrogen production.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within the scope of its essence and protection. Such modifications or equivalent substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A water electrolysis hydrogen production system, characterized in that, The system includes an electrolytic cell, a pyrolysis cell, a buffer cooling device, a buffer heating device, and an electrode switching mechanism. The electrolytic cell contains a cathode and an auxiliary electrode, which are connected to the negative and positive terminals of a power supply, respectively. The electrolytic cell is filled with alkaline electrolyte. A first electrically operated door is located on the top of the electrolytic cell above the auxiliary electrodes. Both the buffer cooling device and the buffer heating device are top-opening and filled with cold and hot water, respectively. The pyrolysis cell contains multiple sets of auxiliary electrodes. A second electrically operated door is located on the top of the pyrolysis cell above the auxiliary electrodes. The pyrolysis cell is filled with pyrolysis electrolyte. The electrode switching mechanism includes multiple robotic arms that move above the electrolytic cell, pyrolysis cell, buffer cooling device, and buffer heating device to grasp and quickly replace auxiliary electrodes.

2. The water electrolysis hydrogen production system according to claim 1, characterized in that: The alkaline electrolyte is a 30wt% KOH solution or a 20-25wt% NaOH solution.

3. The water electrolysis hydrogen production system according to claim 1, characterized in that: The cathode is made of nickel-based material or stainless steel plate covered with Raney nickel, and the auxiliary electrode is Ni(OH)2.

4. The water electrolysis hydrogen production system according to claim 1, characterized in that: The electrolytic cell has a hexahedral or cylindrical structure. An electrolyte inlet and an electrolyte outlet are provided on one side of the electrolytic cell. The electrolyte inlet is located at the lower position of the electrolytic cell, and the electrolyte outlet is located at the higher position of the electrolytic cell.

5. The water electrolysis hydrogen production system according to claim 1, characterized in that: The pyrolysis tank has an auxiliary heater built in, and an inlet and an outlet are provided on the outside of the pyrolysis tank. The inlet is located at the lower position of the pyrolysis tank, and the outlet is located at the higher position of the pyrolysis tank.

6. The water electrolysis hydrogen production system according to claim 4, characterized in that: Multiple sets of electrolytic cells are connected in series. The electrolyte inlets of the multiple sets of electrolytic cells are connected through a main inlet pipe, and the electrolyte outlets of the multiple sets of electrolytic cells are connected through a main outlet pipe. The cathodes and auxiliary electrodes of the two end electrolytic cells are connected to the negative and positive terminals of the power supply, respectively. The cathodes and auxiliary electrodes of adjacent electrolytic cells are connected by wires.

7. A control method for a water electrolysis hydrogen production system according to any one of claims 1 to 6, characterized in that: Includes the following steps: The electrolytic cell is energized, and the hydrogen produced by electrolysis flows out from the electrolyte outlet. Electrolysis is stopped after the upper limit of conversion of the auxiliary electrode is reached. Open the first movable door, use a robotic arm to remove the auxiliary electrode from the electrolytic cell, then use another robotic arm to remove the reduced and cooled auxiliary electrode from the buffer cooling device and place it in the electrolytic cell, close the first movable door and start electrolysis, then move the removed auxiliary electrode into the buffer heating device. After the buffer heating device completes the buffer heating of the auxiliary electrode, the robotic arm removes the auxiliary electrode and puts it into standby mode. After the pyrolysis oxygen production and reduction of the auxiliary electrode are completed in the pyrolysis tank, the second movable door is opened. The robotic arm takes out the auxiliary electrode that has been reduced in the pyrolysis tank, and then another robotic arm puts the auxiliary electrode that has been buffered and heated into the pyrolysis tank for pyrolysis. After the auxiliary electrode that has been reduced is taken out, it is put into the buffer cooling device for buffer cooling. Repeat the above steps to achieve spatial isolation between the continuous hydrogen and oxygen production processes.

8. The control method for a water electrolysis hydrogen production system according to claim 7, characterized in that: The water temperature injected into the buffer heating device is 70℃-80℃.

9. The control method for a water electrolysis hydrogen production system according to claim 7, characterized in that: The working temperature of the pyrolysis liquid in the pyrolysis tank is 90-97℃.

10. The control method for a water electrolysis hydrogen production system according to claim 7, characterized in that: Multiple sets of electrolytic cells are connected in series. When it is necessary to disconnect the power of a specific electrolytic cell to replace the auxiliary electrode, the two sets of wires are short-circuited inside or outside the electrolytic cell by a conductive cable.

Images