Gas circulation system of flow battery

Abstract

The utility model belongs to the technical field of flow batteries, and particularly relates to a gas circulation system of a flow battery. The flow battery gas circulation system comprises a positive electrode liquid storage tank, a negative electrode liquid storage tank, a gas inlet pipeline, a gas exhaust pipeline, a gas pressure balance pipeline and a gas transfer device, the upstream end of the air inlet pipeline is positioned above the liquid level of the positive electrode liquid storage tank; the downstream end of the gas inlet pipeline is communicated with the inlet of the gas transfer device; the outlet of the gas transfer device is communicated with the upstream end of the exhaust pipeline; the downstream end of the exhaust pipeline is located below the liquid level of the negative electrode liquid storage tank. And two ends of the air pressure balance pipeline are respectively communicated to positions above the liquid levels of the positive electrode liquid storage tank and the negative electrode liquid storage tank. The gas transfer and reactive gas absorption process is realized, volatile gas and toxic waste gas can be quickly and effectively absorbed, the pressure balance of the positive and negative electrode liquid storage tanks is maintained, the change of active components of the electrolyte during operation is avoided, and the safety and high efficiency of long-time operation of the flow battery are maintained.

Description

Technical Field

[0001] This utility model belongs to the field of flow battery technology, specifically relating to a flow battery gas circulation system. Background Technology

[0002] Currently, the electrolytes in flow batteries are mainly divided into three major systems: sulfuric acid-based solutions, hydrochloric acid-based solutions, and mixed solutions of sulfuric acid and hydrochloric acid. The latter two types of hydrochloric acid-containing electrolytes, if a localized overcharge occurs within the battery stack during operation, will produce chlorine gas in the positive electrode electrolyte. Chlorine gas is toxic, and if released directly into the atmosphere without any treatment, it will harm human health and the environment.

[0003] The existing technology for treating chlorine gas is as follows:

[0004] Some patents (CN201810973123.1 and CN202410609201.5) utilize venturi tubes to mix and absorb the oxidizing waste gas (chlorine) generated by overcharging the positive electrode electrolyte with the negative electrode electrolyte to alleviate long-term capacity decay. However, the reaction sites of chlorine and the negative electrode electrolyte include pipelines and internal flow paths of the battery stack. Chlorine that fails to react in time can oxidize and corrode materials such as pipelines, electrodes, membranes, and bipolar plates, indirectly affecting the negative electrode reaction conversion process. It can even cause internal short circuits during long-term operation, resulting in loss of material function, reduced battery performance and efficiency, and consequently increasing the replacement frequency and cost of the battery stack and pipelines. If chlorine is not effectively separated before entering the negative electrode electrolyte, it can enter the negative electrode electrolyte indiscriminately along with gases above the positive electrode storage tank (such as air, nitrogen, inert gases, etc.), forming bubbles in the negative electrode electrolyte flow path and creating reaction dead zones, especially inside porous electrodes and in the flow field region. This inhibits the uniform distribution of the electrolyte and reduces electrolyte efficiency. The increased contact area between the electrodes and the battery increases the internal resistance of the stack and reduces reaction efficiency. It also creates voltage differences within the electrodes, triggering new side reactions (such as hydrogen evolution), reducing battery capacity, energy, and electrolyte utilization. According to the principle of Venturi tube operation, the gas absorption process can only occur when the stack pumping device is running. Specifically, if the battery system is left to stand after being fully charged, the positive electrode electrolyte contains a large amount of pentavalent vanadium ions, which slowly oxidize chloride ions to chlorine gas. At this time, the stack pumping device cannot effectively remove the generated chlorine gas. To further remove chlorine gas, a high-power pumping device needs to be activated, which not only increases the electrical cost of the pumping device but also reduces the energy efficiency of the vanadium redox flow battery system. In addition, some gases (such as nitrogen and inert gases) do not react with the negative electrode electrolyte and enter the upper area of ​​the negative electrode storage tank with the negative electrode electrolyte. Without a pressure balancing device, this causes increased internal pressure, posing a certain safety hazard.

[0005] Other patents (such as CN202411438680.5 and CN202410609201.5) utilize catalytic reaction devices or alkaline absorption devices to absorb oxidizing gases such as chlorine. Although this eliminates the need to add a restoring agent to the positive electrode solution to maintain the valence balance of the positive and negative electrode solutions, thus avoiding electrolyte contamination, it has certain drawbacks. The process is cumbersome; introducing catalysts and alkaline solutions alters the active components of the electrolyte, requiring the addition of chloride ion solutions (such as hydrochloric acid) to adjust the concentration of active species. This significantly increases the cost of chlorine treatment. Furthermore, some devices require high-temperature operation, which is detrimental to battery system integration design and safety management. In the process of developing this application, the inventors discovered the following shortcomings of the prior art:

[0006] 1. Using external reagents such as alkali solutions and catalysts to absorb the released chlorine gas results in a complex device design, high equipment requirements, and the need for timely replacement of the absorbent, increasing equipment installation and post-processing costs. Furthermore, the need to replenish chloride ion solutions (such as hydrochloric acid) to maintain the effective use of the electrolyte significantly increases electrolyte costs.

[0007] 2. Although a non-active transfer device (such as a venturi tube) indiscriminately transfers the gas above the positive electrode reservoir to the negative electrode inlet and outlet pipes, once the pumping device stops operating, there is no liquid flow in the inlet and outlet pipes, and the device will cease operation. Oxidizing gases such as chlorine above the reservoir will not be actively transferred or absorbed. Other non-reactive gases (such as nitrogen and inert gases) present in the gas transferred by the non-active transfer device will not chemically react with the negative electrode electrolyte. Therefore, localized bubbles will be generated in the flow path inside the stack, inhibiting the uniform distribution of the electrolyte, reducing the contact area between the electrolyte and the electrodes, causing a decrease in stack mass transfer efficiency and an increase in internal resistance. This affects battery performance and electrolyte utilization, and may even lead to other serious consequences. The redox reaction between chlorine and the negative electrode electrolyte is an exothermic reaction. Excessive local electrolyte temperature can lead to other side reactions or the volatilization of hydrogen chloride gas. At the same time, chlorine can oxidize and corrode the negative electrode pipeline and internal materials of the battery stack, which greatly affects the performance and durability of the materials, is not conducive to the efficient and long-term operation of the battery, and also increases the cost of material replacement.

[0008] 3. The detection system detects the released chlorine gas, which only triggers an alarm and cuts off the power supply to stop the fuel cell stack, but it does not explain how to effectively post-treat the chlorine gas.

[0009] This application is submitted in order to address the above issues. Utility Model Content

[0010] This application uses a gas transfer device to intermittently or continuously transfer the gas above the positive or negative electrode storage tank to below the liquid surface of the negative or positive electrode storage tank, realizing the gas transfer and reactive gas absorption process. This helps to quickly and effectively absorb volatile gases and toxic waste gases, maintain the pressure balance of the positive and negative electrode storage tanks, avoid changes in the active components of the electrolyte during operation, and maintain the safety and efficiency of the flow battery during long-term operation.

[0011] The specific proposal of this application is as follows:

[0012] The first aspect of this application provides a flow battery gas circulation system, which includes: a positive electrode storage tank 1, a negative electrode storage tank 3, an inlet pipe 8, an exhaust pipe 9, a pressure balance pipe 10, and a gas transfer device 7.

[0013] The upstream end of the air inlet pipe 8 is located above the liquid surface of the positive electrode storage tank 1, and is used to transport the gas above the liquid surface of the positive electrode storage tank 1; the downstream end of the air inlet pipe 8 is connected to the inlet of the gas transfer device 7, and the outlet of the gas transfer device 7 is connected to the upstream end of the exhaust pipe 9; the downstream end of the exhaust pipe 9 is located below the liquid surface of the negative electrode storage tank 3, and is used to transport the gas inside it to the area below the liquid surface of the negative electrode storage tank 3.

[0014] The two ends of the pressure balancing pipeline 10 are respectively connected to the positions above the liquid surface of the positive electrode storage tank 1 and the negative electrode storage tank 3, in order to achieve pressure balance between the positive electrode storage tank 1 and the negative electrode storage tank 3.

[0015] Preferably, the flow battery gas circulation system further includes an ion balance pipeline 11; the two ends of the ion balance pipeline 11 are respectively connected to the positions below the liquid surface of the positive electrode storage tank 1 and the negative electrode storage tank 3, for realizing the ion balance between the positive electrode storage tank 1 and the negative electrode storage tank 3.

[0016] Preferably, the ion balance pipeline 11 is equipped with a switch valve 5.

[0017] Preferably, the flow battery gas circulation system can be used in a flow battery system. The flow battery system includes: a positive electrode storage tank 1, a positive electrode circulation pump 2, a negative electrode storage tank 3, a negative electrode circulation pump 4, a fuel cell stack 6, positive and negative electrode inlet and outlet pipelines, and a power control system not shown.

[0018] Specifically: the liquid outlet of the positive electrode storage tank 1 is connected to the positive electrode electrolyte inlet of the fuel cell stack 6 through a positive electrode inlet pipe, and the positive electrode electrolyte outlet of the fuel cell stack 6 is connected to the liquid inlet of the positive electrode storage tank 1 through a positive electrode outlet pipe;

[0019] The liquid outlet of the negative electrode storage tank 3 is connected to the negative electrode electrolyte inlet of the fuel cell stack 6 through a negative electrode inlet pipe, and the negative electrode electrolyte outlet of the fuel cell stack 6 is connected to the liquid inlet of the negative electrode storage tank 3 through a negative electrode outlet pipe.

[0020] Preferably, a positive electrode circulation pump 2 and a positive electrode inlet valve are provided on the positive electrode inlet pipe, and a negative electrode circulation pump 4 and a negative electrode inlet valve are provided on the negative electrode inlet pipe.

[0021] Preferably, the gas transfer device 7 is a fan or an air circulation pump.

[0022] Preferably, the gas transfer device 7 is a small axial flow fan or air circulation pump. The internal material of the axial flow fan or air circulation pump is a corrosion-resistant material, including but not limited to PVC, PVDF, PP, PTFE, etc., and its rated power is lower than that of the positive electrode circulation pump 2 and the negative electrode circulation pump 4.

[0023] A second aspect of this application provides a gas circulation method for a flow battery, wherein the gas circulation method uses the flow battery gas circulation system described in any one of the first aspects, and the gas circulation method includes the following steps:

[0024] When gas is generated in the positive electrolyte in the positive electrode storage tank 1, the gas transfer device 7 is turned on, so that the gas above the liquid surface of the positive electrode storage tank 1 is transported to the liquid surface below the liquid surface of the negative electrode storage tank 3, and reacts with the electrolyte in the negative electrode storage tank 3.

[0025] The unreacted excess gas in the negative electrode storage tank 3 returns to the liquid surface of the positive electrode storage tank 1 along the pressure balance pipeline 10.

[0026] Preferably, when the gas circulation method is used in the flow battery gas circulation system described above, the gas circulation method further includes the following step: the electrolytes in the positive electrode storage tank 1 and the negative electrode storage tank 3 are mixed through the ion balance pipeline 11 to achieve ion balance between the positive electrode storage tank 1 and the negative electrode storage tank 3.

[0027] Preferably, the gas circulation method can be used whether the fuel cell stack or fuel cell stack pumping device is running or stationary.

[0028] Preferably, the gas is a side reaction gas generated by the electrolyte in the positive electrode storage tank 1 when the battery is overcharged, the state of charge (SOC) is too high, or the temperature is too high.

[0029] The unreacted excess gas in the negative electrode storage tank 3 can return to the liquid surface of the positive electrode storage tank 1 via the pressure balance pipeline 10 through spontaneous or non-spontaneous movement. Spontaneous movement is preferred, meaning that a gas transfer device is not required on the pressure balance pipeline 10.

[0030] The side reaction gases include, but are not limited to, chlorine, hydrogen chloride, and oxygen.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. Chlorine-containing electrolytes generate harmful and strongly oxidizing gases such as chlorine and volatile gases such as hydrogen chloride during the operation of the positive electrode battery. Using the device of this application, gases can be quickly pumped or pneumatically introduced into the negative electrode electrolyte, increasing the contact area between the gas and the electrolyte, which helps the gas to react fully with a large amount of negative electrode electrolyte and improves the reaction rate. Furthermore, this application also includes a pressure balancing pipeline between the positive and negative electrode storage tanks. Gases that do not participate in the reaction can return to the positive electrode storage tank through the pressure balancing pipeline, maintaining pressure balance above the positive and negative electrode storage tanks.

[0033] 2. This application allows for gas circulation during operation or quiescent of the fuel cell stack or fuel cell stack pumping device, thereby changing the reaction site of the gas, inhibiting harmful gases from entering the fuel cell stack, pipelines and other materials to carry out oxidation-reduction reactions, reducing their excessive accumulation and residence time inside the fuel cell stack, and also avoiding the generation of gas cavitation inside the fuel cell stack, which would reduce the flow rate and thus affect the mass transfer process and efficient operation of the fuel cell stack.

[0034] 3. This application does not utilize external reagents such as alkaline solutions or catalysts to absorb the precipitated chlorine and other side reaction gases. The device design is simple and efficient, and the equipment is easy to install, greatly reducing the cost of complex equipment installation and post-processing. At the same time, it avoids the change in the active components of the electrolyte caused by the reduction of chloride ion content, as well as the cost of additional electrolyte replenishment.

[0035] 4. This application includes an ion balance pipeline 11 between the positive and negative electrode storage tanks. The electrolytes in the positive electrode storage tank 1 and the negative electrode storage tank 3 can be mixed through the ion balance pipeline 11 to achieve ion balance between them. In particular, when byproduct reaction gases such as chlorine continuously enter the negative electrode storage tank 3, the prolonged absorption and reaction process can lead to chloride ion imbalance between the positive electrode storage tank 1 and the negative electrode storage tank 3. The ion balance pipeline 11 can reduce the chloride ion concentration difference between the positive electrode storage tank 1 and the negative electrode storage tank 3, maintaining chloride ion balance between them. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a flow battery gas circulation system according to the first embodiment of this application.

[0037] Figure 2 This is a schematic diagram of a flow battery gas circulation system according to the first embodiment of this application.

[0038] List of reference numerals in the attached diagram:

[0039] 1. Positive electrode storage tank; 2. Positive electrode circulation pump; 3. Negative electrode storage tank; 4. Negative electrode circulation pump; 5. Switch valve; 6. Fuel cell stack; 7. Gas transfer device; 8. Inlet pipe; 9. Exhaust pipe; 10. Pressure balance pipe; 11. Ion balance pipe. Detailed Implementation

[0040] The present application will now be described in further detail with reference to the embodiments.

[0041] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the field or according to the product manual. Materials or equipment whose manufacturers are not specified are all conventional products that can be obtained by purchase.

[0042] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. In the description of this application, unless otherwise stated, “a plurality” means two or more. It should be further understood that the term “comprising” as used in the specification of this application means the presence of the stated feature, integer, step, operation, element, and / or component, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is “connected” to another element, it can be directly connected to the other element, or there may be an intermediate element. Furthermore, the term “connected” as used herein can include wireless connections.

[0043] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0045] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0046] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0047] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0048] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0049] This application discloses a gas circulation system for a flow battery. The gas circulation system includes a negative electrode storage tank, a positive electrode storage tank, a gas transfer device, and a gas connecting pipe. The gas transfer device intermittently or continuously transfers gas from above the positive or negative electrode storage tank to below the liquid surface in the negative or positive electrode storage tank, realizing gas transfer and reactive gas absorption processes. This helps to quickly and effectively absorb volatile gases and toxic waste gases, maintain the pressure balance between the positive and negative electrode storage tanks, avoid changes in the active components of the electrolyte during operation, and maintain the safety and high efficiency of the flow battery during long-term operation.

[0050] Figure 1 This is a schematic diagram of a flow battery gas circulation system according to the first embodiment of this application.

[0051] The flow battery gas circulation system includes: positive electrode storage tank 1, negative electrode storage tank 3, air inlet pipe 8, air outlet pipe 9, gas pressure balance pipe 10, and gas transfer device 7.

[0052] The upstream end of the air inlet pipe 8 is located above the liquid surface of the positive electrode storage tank 1, and is used to transport the gas above the liquid surface of the positive electrode storage tank 1; the downstream end of the air inlet pipe 8 is connected to the inlet of the gas transfer device 7, and the outlet of the gas transfer device 7 is connected to the upstream end of the exhaust pipe 9; the downstream end of the exhaust pipe 9 is located below the liquid surface of the negative electrode storage tank 3, and is used to transport the gas inside it to the area below the liquid surface of the negative electrode storage tank 3.

[0053] The two ends of the pressure balancing pipeline 10 are respectively connected to the positions above the liquid surface of the positive electrode storage tank 1 and the negative electrode storage tank 3, in order to achieve pressure balance between the positive electrode storage tank 1 and the negative electrode storage tank 3.

[0054] The flow battery gas circulation system further includes an ion balance pipeline 11; the two ends of the ion balance pipeline 11 are respectively connected to the position below the liquid surface of the positive electrode storage tank 1 and the negative electrode storage tank 3, so as to achieve ion balance between the positive electrode storage tank 1 and the negative electrode storage tank 3.

[0055] The ion balance pipeline 11 is equipped with a switch valve 5.

[0056] The flow battery gas circulation system is used in a flow battery. The flow battery also includes: a fuel cell stack 6;

[0057] The liquid outlet of the positive electrode storage tank 1 is connected to the positive electrode electrolyte inlet of the fuel cell stack 6 through a positive electrode inlet pipe, and the positive electrode electrolyte outlet of the fuel cell stack 6 is connected to the liquid inlet of the positive electrode storage tank 1 through a positive electrode outlet pipe.

[0058] The liquid outlet of the negative electrode storage tank 3 is connected to the negative electrode electrolyte inlet of the fuel cell stack 6 through a negative electrode inlet pipe, and the negative electrode electrolyte outlet of the fuel cell stack 6 is connected to the liquid inlet of the negative electrode storage tank 3 through a negative electrode outlet pipe.

[0059] The positive electrode inlet pipe is equipped with a positive electrode circulation pump 2 and a positive electrode inlet valve, and the negative electrode inlet pipe is equipped with a negative electrode circulation pump 4 and a negative electrode inlet valve.

[0060] In this embodiment, the gas transfer device 7 is an electrically controlled star-shaped axial flow fan.

[0061] The gas recirculation method for flow batteries is as follows:

[0062] An external power source controls the axial flow fan to start, sequentially guiding the gas above the positive electrode storage tank 1 through the inlet pipe 8, the small axial flow fan, and the exhaust pipe 9, ultimately entering the negative electrode storage tank below the liquid level 3 for complete reaction. Gas that does not participate in the reaction returns to the positive electrode storage tank through the pressure balance pipe 10 to maintain pressure balance above both tanks. The switch valve 5 can be opened in real-time or intermittently to maintain the balance of active species at the positive and negative electrodes. This active species is a complex formed by chloride and vanadium ions.

[0063] The second embodiment of this application is as follows: Figure 2 As shown. The difference from the first embodiment is that the gas transfer device 7 is an air circulation pump.

[0064] The gas recirculation method for flow batteries is as follows:

[0065] An external power source controls the start of the air circulation pump 7, which pumps the gas above the positive electrode storage tank 1 sequentially through the inlet pipe 8, the air circulation pump, and the exhaust pipe 9, ultimately entering the negative electrode storage tank 3 below the liquid surface for complete reaction. Gases not participating in the reaction return to the positive electrode storage tank 1 through the pressure balance pipe 10 to maintain pressure balance above the positive and negative electrode storage tanks. The switch valve 5 can be opened in real-time or intermittently to maintain the balance of active species at the positive and negative electrodes.

[0066] The following uses this application Figure 1 The flow battery gas circulation system was specifically tested.

[0067] Example 1

[0068] A mixed acid electrolyte containing chloride ions was added to the positive and negative electrode storage tanks. To effectively test for the generation of harmful gases, the upper limit of SOC was set to 92%–96%. Charge-discharge cycles were performed for 50, 100, 150, and 200 times. During the cycle operation, the axial flow fan and ion balance tube 11 were turned on. At the beginning and at the end of each charge-discharge cycle, a small amount of electrolyte from the positive electrode storage tank 1 was taken, and the chloride ion concentration was tested using a chloride ion titrator. The initial and final chloride ion concentrations were 5.635, 5.633, 5.631, 5.632, and 5.634 mol / L, respectively. The data shows that the chloride ion concentration changed within 0.1% during the cycle operation, and the axial flow fan and ion balance tube effectively maintained the chloride ion concentration in the electrolyte.

[0069] Example 2

[0070] A mixed acid electrolyte containing chloride ions was added to the positive and negative electrode storage tanks. To effectively test for the generation of harmful gases, the upper limit of SOC was set to 92%–96%. Charge-discharge cycles were performed for 50, 100, 150, and 200 cycles. During the cycle, the axial flow fan and ion balance tube were turned off. However, during the time interval between the end of the previous cycle and the start of the next cycle, the axial flow fan and ion balance tube were turned on, with the time interval set to 30 minutes to 1 hour, to allow for sufficient reaction with the negative electrode electrolyte. A small amount of electrolyte from the positive electrode storage tank was then taken, and the chloride ion concentration was tested using a chloride ion titrator. The initial and final chloride ion concentrations were 5.635, 5.631, 5.633, 5.630, and 5.631 mol / L, respectively. The data showed that the chloride ion concentration did not change significantly during the cycle, remaining within 0.1%.

[0071] Comparative Example 1

[0072] A mixed acid electrolyte containing chloride ions was added to the positive and negative electrode storage tanks. To effectively detect the generation of harmful gases, the upper limit of the SOC range was set to 92%–96%. Charge-discharge cycles were performed for 50, 100, 150, and 200 times, with the axial flow fan and ion balance tube turned off during the cycles. At the beginning and at the end of each charge-discharge cycle, a small amount of electrolyte from the positive electrode storage tank was taken, and the chloride ion concentration was measured using a chloride ion titrator. The initial and final chloride ion concentrations were 5.635, 5.427, 5.179, 5.008, and 4.885 mol / L, respectively. The data shows that the chloride ion concentration gradually decreased during the cycle (maximum 13.3%), and continued to decrease with increasing cycle count.

[0073] In addition, after each charge-discharge cycle, the composition of the gas at the outlet of the one-way valve of the positive electrode storage tank was measured using a chlorine gas detector. During each test, the chlorine detector alarmed, indicating that the chlorine content exceeded the standard (>20 ppm). This indicates that chloride ions in the electrolyte of the positive electrode storage tank were oxidized into chlorine gas, and a portion of this gas was discharged through the one-way valve outlet of the positive electrode storage tank, causing air pollution (Note: For the safety of personnel and the experimental environment, a tail gas absorption device was added to this experiment). Of course, some chlorine gas will inevitably enter the fuel cell stack and pipelines along with the electrolyte, causing damage.

[0074] Comparative Example 2

[0075] A mixed acid electrolyte containing chloride ions was added to the positive and negative electrode storage tanks. To effectively detect the generation of harmful gases, the upper limit of the SOC range was set to 92%–96%. Charge-discharge cycles were performed for 50, 100, 150, and 200 cycles. During the cycle operation, the axial flow fan was turned on, but the ion balance tube was turned off. At the beginning and at the end of each charge-discharge cycle, a small amount of electrolyte from the positive electrode storage tank was taken, and the chloride ion concentration was measured using a chloride ion titrator. The initial and final chloride ion concentrations were 5.635, 5.607, 5.583, 5.574, and 5.566 mol / L, respectively. The data shows that the chloride ion concentration decreased slowly during the cycle operation (maximum 1.2%).

[0076] In addition, after each charge-discharge cycle, the composition of the gas at the outlet of the one-way valve of the positive electrode reservoir was measured using a chlorine gas detector. The average readings of the chlorine gas detector were 0 ppm, 7 ppm, 12 ppm, 14 ppm, and 16 ppm from the initial value. This indicates that chloride ions in the electrolyte of the positive electrode reservoir were oxidized into chlorine gas, and a portion of it was discharged through the one-way valve outlet of the positive electrode reservoir, causing air pollution (Note: For the safety of the experimenters and the experimental environment, a tail gas absorption device was added to this experiment).

[0077] Based on the above embodiments and comparative examples, it is evident that the axial flow fan and ion balance tube can effectively maintain the chloride ion concentration in the electrolyte whether the electrolyte pumping device is running or stationary, thus helping to maintain the long-term stability of active species in the electrolyte. This device is simple and efficient in design, significantly reducing the installation, maintenance, and post-treatment costs of waste gas treatment equipment.

Claims

1. A gas circulation system for a flow battery, characterized in that, The flow battery gas circulation system includes: a positive electrode storage tank (1), a negative electrode storage tank (3), an inlet pipe (8), an exhaust pipe (9), a pressure balance pipe (10), and a gas transfer device (7). The upstream end of the air inlet pipe (8) is located above the liquid surface of the positive electrode storage tank (1) and is used to transport the gas above the liquid surface of the positive electrode storage tank (1); the downstream end of the air inlet pipe (8) is connected to the inlet of the gas transfer device (7) and the outlet of the gas transfer device (7) is connected to the upstream end of the exhaust pipe (9); the downstream end of the exhaust pipe (9) is located below the liquid surface of the negative electrode storage tank (3) and is used to transport the gas inside it to the liquid surface below the liquid surface of the negative electrode storage tank (3). The two ends of the pressure balancing pipeline (10) are respectively connected to the positions above the liquid surface of the positive electrode storage tank (1) and the negative electrode storage tank (3) to achieve pressure balancing between the positive electrode storage tank (1) and the negative electrode storage tank (3).

2. The liquid flow battery gas circulation system of claim 1, wherein, The flow battery gas circulation system further includes an ion balance pipeline (11), the two ends of which are connected to the positions below the liquid surface of the positive electrode storage tank (1) and the negative electrode storage tank (3), respectively, to achieve ion balance between the positive electrode storage tank (1) and the negative electrode storage tank (3).

3. The liquid flow battery gas circulation system of claim 2, wherein, The ion balance pipeline (11) is equipped with a switch valve (5).

4. The liquid flow battery gas circulation system of claim 1, wherein, The electrolyte in the positive electrode storage tank (1) and the negative electrode storage tank (3) is a chlorine-containing electrolyte.

5. The flow battery gas circulation system according to claim 1, characterized in that, The gas transfer device (7) is an axial flow fan or an air circulation pump.

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