Alkali liquor secondary separation circulating system of alkaline electrolytic bath and working method of alkali liquor secondary separation circulating system

Abstract

The invention relates to the technical field of alkaline hydrogen production, and discloses an alkaline liquor secondary separation circulating system of an alkaline electrolytic bath and a working method of the alkaline liquor secondary separation circulating system. The system comprises an alkaline electrolytic bath, an anode side gas-liquid separation tank, a cathode side gas-liquid separation tank, an anode side secondary gas-liquid separation tank, a cathode side secondary gas-liquid separation tank, an alkali liquor circulating pump and a valve group. Through selective opening and closing of the valve group, the system can be switched between a conventional mixed circulation mode and a secondary separation mixed circulation mode, so that secondary gas-liquid separation of circulating alkali liquor on the anode side and the cathode side is realized; and according to the change of the hydrogen content in the oxygen in the anode side gas, the alkali liquor circulation flow is adjusted in a secondary separation mixed circulation mode. Through switching of the gas-liquid separation modes and cooperative adjustment of the alkali liquor circulation flow, the content of dissolved gas in the alkali liquor under different operation conditions is reduced, the operation safety and stability of the alkaline electrolytic bath are improved, and the adaptability of an electrolytic hydrogen production system to renewable energy sources is improved.

Description

Technical Field

[0001] This disclosure relates to a gas-liquid separation system for hydrogen production via alkaline water electrolysis, and more particularly to an alkaline liquid secondary separation and circulation system for an alkaline electrolyzer and its operating method. Background Technology

[0002] Currently, alkaline electrolysis hydrogen production technology is a scalable, economical, and flexible hydrogen production technology suitable for renewable energy power generation scenarios. However, because alkaline electrolysis hydrogen production technology uses an alkaline solution mixing and circulation method, the electrolytes on the anode and cathode sides are completely mixed during operation. When the renewable energy output is low, the electrolyzer will operate in a low-load range, and the gas production at the anode and cathode will be significantly reduced. However, since the cross-flow of gas brought in by the alkaline solution mixing circulation and membrane permeation is not significant, this leads to severe gas mixing on the anode and cathode sides. When the gas mixture enters the explosive zone, it can easily cause serious accidents, which is the fundamental reason for the narrow operating range of alkaline water electrolysis hydrogen production systems. There are several ways to solve this problem. One approach is to develop a diaphragm with better gas barrier properties to reduce the amount of gas cross-linking caused by diaphragm permeation. However, this leads to a significant increase in cost, and the reduction in diaphragm gas permeation is often accompanied by an increase in resistance, thus affecting the energy efficiency of the electrolyzer. Another approach is to develop an alkaline electrolysis hydrogen production system with independent alkali circulation. However, when the electrolyzer operates under varying loads, the gas production on the cathode and anode sides fluctuates greatly, posing a significant challenge to the liquid level control of the electrolyzer hydrogen production system. A third approach is to reduce the alkali circulation rate at low loads. However, reducing the alkali circulation rate causes gas to accumulate on the electrode surface, leading to an increase in activation overpotential, which in turn increases the energy consumption of the electrolyzer and accelerates the wear and tear of the electrode materials. Summary of the Invention

[0003] The purpose of this disclosure is to propose a secondary separation and circulation system for alkaline solutions in an alkaline electrolyzer and its operating method, which solves the problem of severe gas mixing on the anode and cathode sides of the alkaline electrolyzer under low-cost and easy-to-operate conditions.

[0004] This disclosure is achieved through the following technical solution: An alkaline solution circulation system coupled with secondary separation includes: an alkaline electrolyzer, an anode-side gas-liquid separator, a cathode-side gas-liquid separator, an anode-side secondary gas-liquid separator, a cathode-side secondary gas-liquid separator, a filter, an alkaline solution circulation pump, a heat exchanger, a valve group, and connecting pipes. The alkaline solution circulation system has a conventional mixing circulation mode and a secondary separation mixing circulation mode. In the conventional mixing circulation mode, the alkaline solution undergoes mixing and circulation after passing through the anode-side and cathode-side gas-liquid separators. In the secondary separation mixing circulation mode, after passing through the anode-side and cathode-side gas-liquid separators, the alkaline solution enters the anode-side and cathode-side secondary gas-liquid separators respectively for secondary gas-liquid separation before mixing and circulation. A monitoring device for monitoring the hydrogen content in oxygen is provided on the anode side of the alkaline electrolyzer. When the hydrogen content in the oxygen gas on the anode side exceeds a preset threshold, the alkaline solution circulation system switches from the conventional mixing circulation mode to the secondary separation mixing circulation mode. The alkaline solution circulation pump is a variable frequency pump.

[0005] Furthermore, the valve group includes a first valve, a second valve, a third valve, a fourth valve, a fifth valve, a sixth valve, a seventh valve, and an eighth valve.

[0006] Furthermore, the anode electrolyte outlet of the alkaline electrolyzer is connected to the inlet of the anode-side gas-liquid separator. The alkaline outlet of the anode-side gas-liquid separator is connected to a first valve and a second valve via connecting pipes. The first valve is connected to the outlet pipes of the filter and the third valve via connecting pipes. The second valve is connected to the inlet of the anode-side secondary gas-liquid separator via connecting pipes. The outlet of the anode-side secondary gas-liquid separator is connected to the outlet pipe of the cathode-side secondary gas-liquid separator and the filter via pipes. The filter outlet is connected to the alkaline circulation pump via pipes.

[0007] Furthermore, the cathode electrolyte outlet of the alkaline electrolytic cell is connected to the inlet of the cathode-side gas-liquid separator, the alkaline outlet of the cathode-side gas-liquid separator is connected to the third valve and the fourth valve through a connecting pipe, the third valve is connected to the outlet pipe of the first valve (9) through a connecting pipe, the fourth valve is connected to the inlet of the cathode-side secondary gas-liquid separator through a connecting pipe, and the alkaline outlet of the cathode-side secondary gas-liquid separator is connected to the alkaline outlet pipe of the anode-side secondary gas-liquid separator through a pipe.

[0008] Furthermore, in the conventional mixed circulation mode, the first and third valves are open, and the second, fourth, fifth, sixth, seventh, and eighth valves are closed, with the anode-side secondary gas-liquid separator and the cathode-side secondary gas-liquid separator in an idle state; in the secondary separation mixed circulation mode, the second, fourth, fifth, sixth, seventh, and eighth valves are open, and the first and third valves are closed, with the anode-side secondary gas-liquid separator and the cathode-side secondary gas-liquid separator entering the working state.

[0009] Furthermore, the second and fourth valves are preferably pressure reducing valves, and the sixth and eighth valves are preferably pressure control valves or check valves.

[0010] Furthermore, the valve group is connected to a host computer, which is used to control the opening and closing of each valve in the valve group.

[0011] Furthermore, the host computer is also connected to the alkali circulation pump; when the external power input changes, the host computer is used to change the flow rate of the alkali circulation pump.

[0012] Furthermore, the host computer is used to change the flow rate of the alkali circulation pump, specifically as follows: When the alkali circulation mode is the conventional mixed circulation mode, the flow rate of the alkali circulation pump is maintained at the set flow rate value corresponding to the rated current; When the alkali circulation mode is a secondary separation and mixing circulation mode, and the hydrogen content of oxygen in the anode side gas is continuously rising and exceeds a preset time threshold, the host computer controls the opening and closing status of the valves in the valve group related to the flow rate regulation of the alkali circulation pump to reduce the circulation flow rate of the alkali circulation pump.

[0013] Furthermore, the alkaline solution secondary separation and circulation system switches the alkaline solution circulation mode through the valve group according to the power load status of the alkaline electrolyzer, specifically as follows: When the alkaline electrolyzer is operating under rated power load, the alkaline solution circulation system operates in conventional mixed circulation mode; When the alkaline electrolyzer is operating under low power load and the hydrogen content of oxygen in the anode gas is higher than a preset threshold, the host computer controls the valve opening and closing status of the valve group related to the secondary separation mixing circulation mode, so that the alkaline solution circulation system switches to the secondary separation mixing circulation mode.

[0014] Compared with the prior art, the beneficial effects of this disclosure are: This disclosure provides a secondary separation and circulation system for alkaline solutions in an alkaline electrolyzer. By adding a secondary gas-liquid separator and valve assembly, the opening and closing of the valve assembly can be adjusted as needed to achieve secondary separation of the circulating alkaline solutions on the cathode and anode sides. This significantly reduces the dissolved oxygen and hydrogen content in the alkaline solutions under different operating conditions. When the electrolyzer is running at its rated load, a conventional mixed circulation mode for the alkaline solutions can be adopted. When the electrolyzer is running at a low load, the mixed circulation mode with secondary separation of the alkaline solutions can significantly reduce the dissolved gases in the alkaline solutions on both the anode and cathode sides, thereby improving operational safety.

[0015] Furthermore, the alkali circulation pump adopts a variable frequency pump, which can be combined with the host computer to realize active adjustment of the alkali flow rate, further reducing the content of gas impurities brought in by diaphragm permeation on the cathode and anode sides when the electrolyzer is operating at low load, and expanding the load operating range of the electrolyzer; when the alkali circulation mode is the conventional mixed circulation mode, the flow rate of the alkali circulation pump is maintained at the set flow rate value at the rated current; when the alkali circulation mode is the secondary separation and mixing circulation mode, it is determined whether the hydrogen content in the oxygen in the gas on the anode side continues to rise for more than a preset time. If the determination result is yes, the flow rate of the alkali circulation pump is reduced; if the determination result is no, the flow rate of the alkali circulation pump is maintained at the set value.

[0016] This disclosure also discloses the working method of the alkaline solution secondary separation and circulation system. By switching the gas-liquid separation mode and autonomously adjusting the alkaline solution circulation flow rate, the alkaline electrolyzer can achieve safe, stable and efficient operation under different loads and during variable load processes. At the same time, it expands the load operating range of the electrolyzer and improves the renewable energy absorption rate of the electrolysis hydrogen production system. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an electrolytic hydrogen production system with coupled alkaline solution secondary separation disclosed herein.

[0018] Among them, 1 is an alkaline electrolytic cell, 2 is an anode-side gas-liquid separator, 3 is a cathode-side gas-liquid separator, 4 is an anode-side secondary gas-liquid separator, 5 is a cathode-side secondary gas-liquid separator, 6 is a filter, 7 is an alkaline solution circulation pump, 8 is a heat exchanger, 9 is the first valve, 10 is the second valve, 11 is the third valve, 12 is the fourth valve, 13 is the fifth valve, 14 is the sixth valve, 15 is the seventh valve, and 16 is the eighth valve.

[0019] Figure 2 This is a flowchart of valve opening and closing and alkali pump flow control according to an exemplary embodiment of the present disclosure. Detailed Implementation

[0020] Specific embodiments of this disclosure are provided below. Those skilled in the art should understand that the embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention as defined by the claims in any way.

[0021] Figure 1 This is a schematic diagram illustrating the structure of an exemplary embodiment of this disclosure. Figure 1 As shown, the anode electrolyte outlet of the alkaline electrolytic cell 1 is connected to the inlet of the anode-side gas-liquid separator 2. The alkaline outlet of the anode-side gas-liquid separator 2 is connected to the first valve 9 and the second valve 10 via connecting pipes. The first valve 9 is connected to the inlet of the filter 6 and the outlet pipe of the third valve 11 via connecting pipes. The second valve 10 is connected to the inlet of the anode-side secondary gas-liquid separator 4 via connecting pipes. The alkaline outlet of the anode-side secondary gas-liquid separator 4 is connected to the alkaline outlet pipe of the cathode-side secondary gas-liquid separator 5 and the inlet of the filter 6 via pipes. The outlet of the filter 6 is connected to the alkaline circulation pump 7 via pipes.

[0022] The cathode electrolyte outlet of the alkaline electrolytic cell 1 is connected to the inlet of the cathode-side gas-liquid separator 3. The alkaline outlet of the cathode-side gas-liquid separator 3 is connected to the third valve 11 and the fourth valve 12 via connecting pipes. The third valve 11 is connected to the outlet pipe of the first valve 9 via connecting pipes. The fourth valve 12 is connected to the inlet of the cathode-side secondary gas-liquid separator 5 via connecting pipes. The alkaline outlet of the cathode-side secondary gas-liquid separator 5 is connected to the outlet pipe of the anode-side secondary gas-liquid separator 4 via a pipe.

[0023] The outlet pipe of the anode-side secondary gas-liquid separator is equipped with a fifth valve 13 and a seventh valve 15, and the outlet pipe of the cathode-side secondary gas-liquid separator is equipped with a sixth valve 14 and an eighth valve 16.

[0024] Two different alkaline solution separation and circulation modes are achieved by controlling the opening and closing of the valve group: the conventional mixed circulation mode via the gas-liquid separator and the secondary separation mixed circulation mode via the gas-liquid separator-secondary gas-liquid separator.

[0025] In the conventional mixing and circulation mode via the gas-liquid separator, valves 9 and 11 are open, while valves 10, 12, 13, 14, 15, and 16 are closed. In the secondary separation and mixing circulation mode via the gas-liquid separator-secondary gas-liquid separator, the second valve 10, the fourth valve 12, the fifth valve 13, the sixth valve 14, the seventh valve 15 and the eighth valve 16 are open, and the first valve 9 and the third valve 11 are closed. Even better, the opening and closing of valves and the flow rate of the alkali circulation pump within the system can be controlled in real time via a host computer. The operating mode of the alkali separation and circulation system can be controlled via the host computer according to changes in the electrolyzer's power load.

[0026] Figure 2 A flowchart illustrating valve opening and closing and alkali circulation pump flow control according to an exemplary embodiment of the present disclosure is shown.

[0027] like Figure 2 As shown, in step 201, the hydrogen content of oxygen in the anode side gas of electrolytic cell 1 is detected and determined to be higher than a preset threshold.

[0028] If the judgment result of step 201 is negative, proceed to step 202, control the valve group to make the system work in the normal alkali separation circulation mode, specifically: open the first valve 9 and the third valve 11, and close the second valve 10, the fourth valve 12, the fifth valve 13, the sixth valve 14, the seventh valve 15 and the eighth valve 16; at the same time, the circulation flow rate of the alkali circulation pump 7 is maintained at the set value.

[0029] When the judgment result of step 201 is yes, proceed to step 203 and control the valve group to switch to the alkaline solution secondary separation mixing circulation mode, specifically: open the second valve 10, the fourth valve 12, the fifth valve 13, the sixth valve 14, the seventh valve 15 and the eighth valve 16, and close the first valve 9 and the third valve 11.

[0030] After switching to the alkaline solution secondary separation and mixing cycle mode, the process proceeds to step 204, where it is determined whether the hydrogen content of oxygen in the anode side gas continues to rise within a preset time.

[0031] When the judgment result of step 204 is yes, proceed to step 205. While maintaining the secondary separation and mixing circulation mode of alkali solution, the host computer controls the opening and closing state of the valve group to reduce the circulation flow of the alkali solution circulation loop.

[0032] If the judgment result of step 204 is negative, proceed to step 206, maintain the current alkali circulation mode, and keep the circulation flow rate of alkali circulation pump 7 at the set value.

Claims

1. An alkaline solution circulation system coupled with secondary alkaline solution separation, characterized in that, include: An alkaline electrolytic cell (1), an anode-side gas-liquid separator (2), a cathode-side gas-liquid separator (3), an anode-side secondary gas-liquid separator (4), a cathode-side secondary gas-liquid separator (5), a filter (6), an alkaline solution circulation pump (7), a heat exchanger (8), a valve group, and connecting pipes; the alkaline solution circulation system is equipped with a conventional mixing circulation mode and a secondary separation mixing circulation mode, wherein: in the conventional mixing circulation mode, the alkaline solution is mixed and circulated after passing through the anode-side gas-liquid separator (2) and the cathode-side gas-liquid separator (3); in the secondary separation ... After passing through the anode-side gas-liquid separator (2) and the cathode-side gas-liquid separator (3), the liquid enters the anode-side secondary gas-liquid separator (4) and the cathode-side secondary gas-liquid separator (5) for secondary gas-liquid separation, and then undergoes mixing and circulation. A monitoring device for monitoring the hydrogen content in oxygen is provided on the anode side of the alkaline electrolytic cell (1). When the hydrogen content in the oxygen in the anode-side gas exceeds a preset threshold, the alkaline liquid circulation system switches from the conventional mixing circulation mode to the secondary separation mixing circulation mode. The alkaline liquid circulation pump (7) is a variable frequency pump.

2. The alkaline solution secondary separation and circulation system for an alkaline hydrogen production electrolyzer according to claim 1, characterized in that, The valve group includes a first valve (9), a second valve (10), a third valve (11), a fourth valve (12), a fifth valve (13), a sixth valve (14), a seventh valve (15), and an eighth valve (16).

3. The alkaline solution secondary separation and circulation system for an alkaline hydrogen production electrolyzer according to claim 2, characterized in that, The anode electrolyte outlet of the alkaline electrolytic cell (1) is connected to the inlet of the anode-side gas-liquid separator (2). The alkaline outlet of the anode-side gas-liquid separator (2) is connected to the first valve (9) and the second valve (10) via a connecting pipe. The first valve (9) is connected to the outlet pipe of the filter (6) and the third valve (11) via a connecting pipe. The second valve (10) is connected to the inlet of the anode-side secondary gas-liquid separator (4) via a connecting pipe. The outlet of the anode-side secondary gas-liquid separator (4) is connected to the outlet pipe of the cathode-side secondary gas-liquid separator (5) and the filter (6) via a pipe. The filter outlet is connected to the alkaline circulating pump (7) via a pipe.

4. The alkaline solution secondary separation and circulation system of an alkaline hydrogen production electrolyzer according to claim 2, characterized in that, The cathode electrolyte outlet of the alkaline electrolytic cell (1) is connected to the inlet of the cathode-side gas-liquid separator (3). The alkaline outlet of the cathode-side gas-liquid separator (3) is connected to the third valve (11) and the fourth valve (12) through a connecting pipe. The third valve (11) is connected to the outlet pipe of the first valve (9) through a connecting pipe. The fourth valve (12) is connected to the inlet of the cathode-side secondary gas-liquid separator (5) through a connecting pipe. The alkaline outlet of the cathode-side secondary gas-liquid separator (5) is connected to the alkaline outlet pipe of the anode-side secondary gas-liquid separator (4) through a pipe.

5. The alkaline solution secondary separation and circulation system for an alkaline hydrogen production electrolyzer according to claim 2, characterized in that, In the conventional mixed circulation mode, the first valve (9) and the third valve (11) are open, and the second valve (10), the fourth valve (12), the fifth valve (13), the sixth valve (14), the seventh valve (15), and the eighth valve (16) are closed. The anode-side secondary gas-liquid separator (4) and the cathode-side secondary gas-liquid separator (5) are idle. In the secondary separation mixed circulation mode, the second valve (10), the fourth valve (12), the fifth valve (13), the sixth valve (14), the seventh valve (15), and the eighth valve (16) are open, and the first valve (9) and the third valve (11) are closed. The anode-side secondary gas-liquid separator (4) and the cathode-side secondary gas-liquid separator (5) enter the working state.

6. The alkaline solution secondary separation and circulation system for an alkaline hydrogen production electrolyzer according to claim 2, characterized in that, The second and fourth valves are preferably pressure reducing valves, and the sixth and eighth valves are preferably pressure control valves or check valves.

7. The alkaline solution secondary separation and circulation system for an alkaline hydrogen production electrolyzer according to claim 2, characterized in that, The valve group is connected to a host computer, which is used to control the opening and closing of each valve in the valve group.

8. The alkaline solution secondary separation and circulation system of an alkaline hydrogen production electrolyzer according to claim 2, characterized in that, The host computer is also connected to the alkali circulation pump (7); when the external power input power changes, the host computer is used to change the flow rate of the alkali circulation pump.

9. The alkaline solution secondary separation and circulation system for an alkaline hydrogen production electrolyzer according to claim 7, characterized in that, The host computer is used to change the flow rate of the alkali circulation pump, specifically: When the alkali circulation mode is the conventional mixed circulation mode, the flow rate of the alkali circulation pump is maintained at the set flow rate value corresponding to the rated current; When the alkali circulation mode is a secondary separation and mixing circulation mode, and the hydrogen content of oxygen in the anode side gas is continuously rising and exceeds the preset time threshold, the host computer controls the opening and closing status of the valves in the valve group related to the flow regulation of the alkali circulation pump (7) to reduce the circulation flow of the alkali circulation pump (7).

10. The alkaline solution secondary separation and circulation system of an alkaline hydrogen production electrolyzer according to claim 9, characterized in that, The alkaline solution secondary separation and circulation system switches the alkaline solution circulation mode through the valve group according to the power load status of the alkaline electrolyzer (1), specifically as follows: When the alkaline electrolytic cell (1) is running under rated power load, the alkaline solution circulation system operates in conventional mixed circulation mode; When the alkaline electrolytic cell (1) is operating under low power load and the hydrogen content of oxygen in the anode gas is higher than the preset threshold, the host computer controls the valve opening and closing status of the valve group related to the secondary separation mixing cycle mode, so that the alkaline solution circulation system switches to the secondary separation mixing cycle mode.

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