System and method for online capacity recovery of iron-chromium flow battery

Abstract

The invention discloses an on-line capacity recovery system and method for an iron-chromium flow battery, and belongs to the technical field of flow batteries, the system comprises an energy storage main system, a rebalance system and an ion recovery system which are communicated in sequence, the energy storage main system comprises a positive electrode electrolyte and a negative electrode electrolyte, the rebalance system comprises a rebalance electrolyte, and the ion recovery system comprises an ion recovery system. The rebalance electrolyte comprises a reducing gas and is used for reducing unbalanced Fe < 3 + > in the positive electrode electrolyte in the energy storage main system, and the ion recovery system comprises a reducing gas and is used for recovering unbalanced ion valence in the rebalance electrolyte. The system and the method adopted by the invention are simple to operate and low in cost, the unbalanced rebalance electrolyte is reduced by a chemical method through the reducing gas in the ion recovery system, so that the rebalance electrolyte can maintain a certain valence ion equilibrium concentration, the positive electrode electrolyte in the energy storage system can recover the capacity online, the capacity recovery time is shortened, and the energy storage efficiency is improved. The use performance of the battery is ensured.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flow battery, and particularly relates to a system and method for on-line capacity recovery of iron-chromium flow battery. BACKGROUND

[0002] The flow battery is a new type of large-scale electrochemical energy storage device, which can store electrical energy in electrolyte solution during charging and release stored energy as electrical energy during discharging. The iron-chromium flow battery is a commonly used redox flow battery at present, which has the advantages of large energy storage scale, high safety, long cycle life, environmental friendliness and the like, and is considered to be the most promising flow battery energy storage technology. In the charging and discharging process of the iron-chromium flow battery, the positive electrode is the oxidation and reduction process of iron ions at 2 / 3 valence, and the negative electrode is the oxidation and reduction process of chromium ions at 2 / 3 valence, but the standard potential of the negative electrode reaction of the iron-chromium flow battery is relatively low, which is -0.41V. This leads to the following problems: hydrogen gas is generated at the negative electrode during charging and under the condition of large overpotential, and since hydrogen evolution is an irreversible reaction, the trivalent iron in the positive electrode cannot be completely reduced to divalent iron during discharging, thereby causing the aggregation of trivalent iron ions in the positive electrode to fail to participate in discharging. In the long-term operation process of the battery, the chargeable divalent iron ions in the positive electrode electrolyte gradually decrease, causing the phenomenon of electrolyte capacity attenuation.

[0003] The existing capacity recovery technology for the iron-chromium flow battery is to match a main system with a rebalancing system. The rebalancing system uses electrolysis to reduce the reducing agent to provide electrons and hydrogen ions for the main system to reduce the trivalent iron ions in the positive electrode electrolyte of the main system to divalent iron ions, so as to restore the state of the electrolyte. The commonly used rebalancing technology at present mainly includes hydrochloric acid and hydrogen electrolysis rebalancing methods, but these methods have the following problems: 1. The battery stack of the rebalancing system is directly used for electrolytic reduction of the positive electrode electrolyte. In actual use, the reducing agent of the rebalancing system will cause a valence imbalance phenomenon during electrolytic reduction, which weakens the recovery effect of the rebalancing system on the ferrous amount, thereby reducing the capacity recovery efficiency of the flow battery; 2. The rebalancing system directly using reducing gas has a high requirement for the purity and system pressure of the gas, and there are many operation difficulties in actual project application; 3. The electrochemical process requires a higher purity than the chemical reaction, and the electrolysis process of the electrolyte such as hydrochloric acid has a high requirement for voltage, and the electrolysis of hydrochloric acid has a side reaction of chlorine gas evolution, which challenges the safety of the system.

[0004] Therefore, in order to solve the above problems, it is necessary for the application to provide a system and method for on-line capacity recovery of iron-chromium flow battery. SUMMARY

[0005] In order to solve the above problems, the application provides a system and method for online capacity recovery of iron-chromium flow battery, which can effectively isolate the reducing agent and its reduction byproducts from the main system, avoid the influence of trace residual byproducts on the charging and discharging process, efficiently recover the battery capacity online, prolong the service life of the battery and ensure the use performance of the battery.

[0006] In order to achieve the above purpose, the application provides a system for online capacity recovery of iron-chromium flow battery, which comprises an energy storage main system, a rebalancing system and an ion recovery system connected in sequence, the energy storage main system contains positive electrolyte and negative electrolyte, the rebalancing system contains rebalancing electrolyte, which is used for rebalancing the Fe 3+ Reduction, the ion recovery system contains reducing gas, which is used for recovering the ion valence state imbalance in the rebalancing electrolyte.

[0007] Further, the energy storage main system comprises a positive electrolyte storage tank, a negative electrolyte storage tank, a positive pump, a negative pump and an energy storage main system battery stack; the positive pump and the negative pump are respectively used for conveying the positive electrolyte in the positive electrolyte storage tank and the negative electrolyte in the negative electrolyte storage tank to the positive electrode and the negative electrode of the energy storage main system battery stack for electrochemical reaction.

[0008] Further, the rebalancing system comprises a positive electrolyte storage tank, a rebalancing system positive electrode storage tank, a rebalancing system positive electrode pump, a rebalancing system negative electrode pump and a rebalancing system battery stack, the positive electrolyte storage tank is used as the negative electrode storage tank of the rebalancing system, and the rebalancing system positive electrode storage tank contains the rebalancing electrolyte; the rebalancing system positive electrode pump and the rebalancing system negative electrode pump are respectively used for conveying the rebalancing electrolyte in the rebalancing system positive electrode storage tank and the positive electrolyte in the positive electrolyte storage tank to the positive electrode and the negative electrode of the rebalancing system battery stack for electrochemical reaction.

[0009] Further, the ion recovery system comprises a bubble column and a filter, the inlet of the bubble column is connected with the outlet of the rebalancing system positive electrode storage tank through a pipeline, and the outlet of the bubble column is connected with the inlet of the filter through a pipeline; the bottom of the rebalancing system positive electrode storage tank is provided with a recovery inlet, the outlet of the filter is connected with the recovery inlet of the rebalancing system positive electrode storage tank through a pipeline, and the lower part of the bubble column is provided with a gas distributor, which is used for introducing reducing gas into the bubble column.

[0010] Further, the ion recovery system comprises at least two bubble columns, and a liquid conveying pump is arranged between adjacent bubble columns, which is used for conveying the rebalancing electrolyte in the previous bubble column to the inlet of the next bubble column for valence state recovery again.

[0011] Further, the top end of the filter is provided with an inert gas inlet and a reducing gas outlet, the inert gas inlet is used to introduce inert gas to purge the reducing gas in the filter, so as to replace the reducing gas in the liquid, and the reducing gas outlet is used to return the replaced reducing gas to the bubble column.

[0012] Further, the pressure in the rebalancing system positive electrode tank and the positive electrode electrolyte tank is 0.1-0.5 MPa, and the temperature is 25-55 DEG C.

[0013] In another aspect of the application, a method for online capacity recovery of an iron-chromium flow battery is provided, which comprises the following steps: when the battery capacity of the iron-chromium flow battery is monitored to be obviously attenuated, a rebalancing system of the iron-chromium flow battery is started to perform a charging process, and the rebalancing electrolyte in the rebalancing system and the unbalanced positive electrode electrolyte in the energy storage main system are subjected to electrochemical reaction, so that Fe 3+ in the positive electrode electrolyte is reduced to Fe 2+ ;

[0014] When the unbalanced ion valence state of the rebalancing electrolyte in the rebalancing system accumulates to a preset value, the unbalanced rebalancing electrolyte is transported to an ion recovery system, and the reducing gas in the ion recovery system is subjected to chemical reaction with the unbalanced rebalancing electrolyte, so that the unbalanced ion valence state in the unbalanced rebalancing electrolyte is recovered, and the recovered rebalancing electrolyte is transported to the rebalancing system for the next rebalancing process.

[0015] Further, the rebalancing electrolyte is selected from one of ferrous salt, ferrous sulfate, ferrous chloride, potassium ferrocyanide or ferrous carbonate.

[0016] Further, the reducing gas is selected from one or more of hydrogen sulfide, carbon monoxide, hydrogen or methane.

[0017] Further, the flow rate of the reducing gas is 100-200 L / min.

[0018] Further, in the ion recovery system, the flow rate of the unbalanced rebalancing electrolyte is 30-50 L / min.

[0019] Further, in the rebalancing system, the flow rate of the positive electrode electrolyte and the rebalancing electrolyte is 30-50 L / min.

[0020] Further, the charging process of the rebalancing system adopts constant current charging, and the current density is 40-100 mA / cm 2 .

[0021] Compared with the prior art, the system and method adopted by the present application have the following beneficial effects: the system and method adopted by the present application are simple in operation and low in cost, the unbalanced rebalancing electrolyte is reduced by the reducing gas in the ion recovery system in a chemical method, the rebalancing electrolyte can maintain a certain ion balance concentration, the positive electrolyte in the energy storage system can be recovered in capacity on line, and the capacity recovery time is shortened; in addition, the unbalanced rebalancing electrolyte is reduced by the reducing gas, the gas reducing agent product can be easily removed, the ion recovery system can effectively isolate the reducing agent and its reduction product from the energy storage main system, the positive electrolyte concentration has small interference, the influence of the trace residue of the by-product on the charging and discharging process is avoided, the safety is high, and the use performance of the battery is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A structure schematic diagram of an on-line capacity recovery system of an iron-chromium flow battery in an embodiment of the present application is shown;

[0023] Figure 2 A structure schematic diagram of an ion recovery system in an embodiment of the present application is shown;

[0024] In the above drawings, the following reference signs are included: 10, energy storage main system, 11, positive electrolyte storage tank, 12, negative electrolyte storage tank, 13, positive electrode pump, 14, negative electrode pump, 15, energy storage main system battery stack, 20, rebalancing system, 21, rebalancing system positive electrode storage tank, 22, rebalancing system positive electrode pump, 23, rebalancing system negative electrode pump, 24, rebalancing system battery stack, 30, ion recovery system, 31, first-stage bubble column, 32, second-stage bubble column, 33, filter, 311, first gas distributor, 312, first distribution partition, 313, first heating / heat preservation sleeve, 314, first pressure control valve, 321, second gas distributor, 322, second distribution partition, 323, second heating / heat preservation sleeve, 324, second pressure control valve, 325, first conveying pump, 331, second conveying pump, 332, filter membrane, 333, check valve. DETAILED DESCRIPTION

[0025] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. In addition, for the numerical range in the present application, it should be understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Each smaller range between any stated value or intermediate value in the range and any other stated value or intermediate value in the range is also included in the present application. The upper limit and the lower limit of these smaller ranges can be independently included or excluded from the range. The present application will be described in detail below with reference to the embodiments.

[0026] To solve the above problems, one aspect of the present application provides a system for online capacity recovery of iron-chromium flow battery, comprising a main energy storage system, a rebalancing system and an ion recovery system connected in sequence, the main energy storage system contains positive electrolyte and negative electrolyte, the rebalancing system contains rebalancing electrolyte, which is used to transfer the deactivated ions in the main energy storage system to the rebalancing system, and the rebalancing electrolyte is used to recover the ion valence state of the rebalancing system. 3+ The ion recovery system contains reducing gas, which is used to recover the ion valence state of the rebalancing system.

[0027] The system for online capacity recovery of iron-chromium flow battery of the present application comprises a main energy storage system, a rebalancing system and an ion recovery system. The deactivated ions in the main energy storage system are converted and enriched by the rebalancing system, the unbalanced ion valence state is transferred to the rebalancing system, the volume of electrolyte that needs to be recovered is reduced, the ion valence state of the rebalancing electrolyte in the rebalancing system is adjusted by charging, and the unbalanced ion valence state in the rebalancing system is recovered by the reducing gas in the ion recovery system for the next rebalancing operation.

[0028] In a specific embodiment of the present application, the main energy storage system comprises a positive electrolyte storage tank, a negative electrolyte storage tank, a positive pump, a negative pump and a main energy storage system battery stack; the positive pump and the negative pump are respectively used to transport the positive electrolyte in the positive electrolyte storage tank and the negative electrolyte in the negative electrolyte storage tank to the positive electrode and the negative electrode of the main energy storage system battery stack for electrochemical reaction.

[0029] In a specific embodiment of the present application, the rebalancing system comprises a positive electrolyte storage tank, a rebalancing system positive electrode storage tank, a rebalancing system positive electrode pump, a rebalancing system negative electrode pump and a rebalancing system battery stack, the positive electrolyte storage tank is used as the negative electrode storage tank of the rebalancing system, and the rebalancing electrolyte is contained in the rebalancing system positive electrode storage tank; the rebalancing system positive electrode pump and the rebalancing system negative electrode pump are respectively used to transport the rebalancing electrolyte in the rebalancing system positive electrode storage tank and the positive electrolyte in the positive electrolyte storage tank to the positive electrode and the negative electrode of the rebalancing system battery stack for electrochemical reaction.

[0030] In a specific embodiment of the present application, the ion recovery system comprises a bubble column and a filter, the inlet of the bubble column is connected to the outlet of the rebalancing system positive electrode storage tank through a pipeline, and the outlet of the bubble column is connected to the inlet of the filter through a pipeline; the bottom of the rebalancing system positive electrode storage tank is provided with a recovery inlet, the outlet of the filter is connected to the recovery inlet of the rebalancing system positive electrode storage tank through a pipeline, and the lower part of the bubble column is provided with a gas distributor, which is used to introduce reducing gas into the interior of the bubble column.

[0031] The bubbling tower of the present invention is used to allow the rebalanced electrolyte with valence imbalance to come into contact with reducing gas to undergo a chemical reaction. By setting a filter, the present invention can filter out the byproducts generated by the chemical reaction of reducing gas, so that the rebalanced electrolyte after valence recovery is free of impurities and has little interference with the electrolyte. The electrolyte is then returned to the rebalance system for recycling through the recovery inlet of the positive electrode storage tank of the rebalance system, thereby reducing system costs.

[0032] In a specific embodiment of the present invention, the ion recovery system includes at least two bubble columns, and a pump is provided between adjacent bubble columns to transport the rebalancing electrolyte inside the previous bubble column to the inlet of the next bubble column for valence state recovery again.

[0033] In the primary bubbling tower, the rebalancing electrolyte is in excess, which can fully absorb reducing gases and reduce the content of waste gas. When the rebalancing electrolyte enters the secondary or multi-stage bubbling tower, the concentration of imbalanced ions is significantly reduced. Thus, in the secondary or multi-stage bubbling tower, the reducing gas is in excess, and the excess reducing gas can fully reduce the remaining imbalanced ions. This invention uses multi-stage bubbling towers to promote the reaction, resulting in a deeper reduction of the rebalancing electrolyte, reducing the residue of toxic gases in the exhaust gas, and achieving better capacity recovery of the positive electrode electrolyte.

[0034] In a specific embodiment of the present invention, the top of the filter is provided with an inert gas inlet and a reducing gas outlet. The inert gas inlet is used to purge the reducing gas in the filter with inert gas to displace the reducing gas in the liquid. The reducing gas outlet is used to return the displaced reducing gas to the bubble column. Furthermore, the reducing gas outlet of the filter is connected to a gas distributor via a pipeline, and a check valve is provided on the pipeline.

[0035] The filter of the present invention has an inert gas inlet and a reducing gas outlet. The use of inert gas can not only promote the filtration of the rebalancing electrolyte, but also disperse the residual reducing gas in the electrolyte, so as to avoid interfering with the use of the rebalancing electrolyte. Furthermore, the trace amount of reducing gas in the residual gas can be introduced into the gas distributor through the reducing gas outlet and re-enter the bubble column, and absorbed by the rebalancing electrolyte to achieve tail gas treatment and rebalancing electrolyte reduction.

[0036] In a specific embodiment of the invention, the bubble column is externally equipped with a heating / insulation jacket, and a pressure control valve is installed at the top. The heating / insulation jacket is used to heat and / or insulate the bubble column, so that the rebalancing electrolyte reacts chemically with the reducing gas at a suitable temperature; the pressure control valve is used to regulate the gas pressure and the discharge or inflow of waste gas or reducing gas. Furthermore, a filter membrane is installed inside the filter to filter impurities (e.g., solid sulfur) from the rebalancing liquid.

[0037] In a specific embodiment of the present invention, the pressure in the positive electrode storage tank and the positive electrode electrolyte storage tank of the rebalancing system is 0.1–0.5 MPa, and the temperature is 25°C–55°C. The present invention incorporates an ion recovery system in the online capacity recovery system of the iron-chromium redox flow battery. By chemically reducing the rebalancing electrolyte using reducing gases contained in the ion recovery system, the pressure required by the rebalancing system of the present invention is lower than that required by existing rebalancing systems that use electrochemical methods to reduce the rebalancing electrolyte, resulting in simpler operation and higher safety.

[0038] Another aspect of the present invention provides a method for online capacity recovery of an iron-chromium redox flow battery, comprising the following steps: when a significant capacity decay of the iron-chromium redox flow battery is detected, a rebalancing system for the iron-chromium redox flow battery is initiated for a charging process, wherein the rebalancing electrolyte in the rebalancing system undergoes an electrochemical reaction with the unbalanced positive electrode electrolyte in the main energy storage system, thereby removing Fe from the positive electrode electrolyte. 3+ Reduced to Fe 2+ ;

[0039] When the unbalanced ion valence states of the rebalancing electrolyte in the rebalancing system accumulate to a preset value, the unbalanced rebalancing electrolyte is transported to the ion recovery system. The reducing gas in the ion recovery system reacts chemically with the unbalanced rebalancing electrolyte to restore the unbalanced ion valence states in the unbalanced rebalancing electrolyte. The restored rebalancing electrolyte is then transported back to the rebalancing system for the next rebalancing process.

[0040] In specific embodiments of the present invention, the rebalancing electrolyte includes, but is not limited to, ferrous sulfate, ferrous chloride, potassium ferrocyanide, ferrous carbonate, or vanadium oxysulfate. Other types of electrolytes in the art can also be selected for the rebalancing electrolyte, enabling the rebalancing of Fe in the positive electrode electrolyte to achieve… 3+ Simply restore it.

[0041] In specific embodiments of the present invention, the reducing gas includes, but is not limited to, one or more of hydrogen sulfide, carbon monoxide, hydrogen, or methane.

[0042] For example, the rebalancing electrolyte of the present invention is selected from ferrous chloride, and the reducing gas is selected from hydrogen sulfide. The online capacity recovery process of its iron-chromium redox flow battery is as follows: In the rebalancing system, Fe in ferrous chloride... 2+ Fe in the positive electrode electrolyte 3+ An electrochemical reaction occurs, and the electrolyte is charged with a constant current, removing Fe from the positive electrode electrolyte. 3 + Reduced to Fe 2+ Rebalancing Fe in the electrolyte 2+ Oxidized to Fe 3 +In the ion recovery system, hydrogen sulfide gas removes Fe from the rebalancing liquid. 3+ Reduced to Fe 2+ H is generated at the same time + Its chemical reaction formula is 2Fe 3+ +H₂S=2Fe 2+ +2H + +S↓.

[0043] The rebalancing electrolyte in the positive electrode storage tank of the rebalancing system is sent to the ion recovery system, and hydrogen sulfide gas is introduced. At room temperature, the Fe in the rebalancing electrolyte can be rapidly reduced. 3+ H is generated at the same time + The generated H + The amount and H caused by hydrogen evolution during charging and discharging + The amount of loss is consistent. Therefore, using hydrogen sulfide can effectively remove Fe. 3+ It can reduce free acid in the electrolyte of the main energy storage system to its original concentration, effectively replenishing the H+ lost through hydrogen evolution. + This ensures the service life and charge / discharge efficiency of the electrolyte. Hydrogen sulfide acts as a reducing agent to generate solid elemental sulfur, which can be efficiently removed through filtration. No new impurities are introduced during the entire capacity recovery process, and the electrochemical process of rebalancing will not affect the main system. This process can completely restore all components in the electrolyte to their original concentrations.

[0044] For example, the rebalancing electrolyte of the present invention is selected from ferrous chloride, and the reducing gas is selected from carbon monoxide. The online capacity recovery process of its iron-chromium redox flow battery is as follows: In the rebalancing system, Fe in ferrous chloride... 2+ Fe in the positive electrode electrolyte 3+ An electrochemical reaction occurs, and the electrolyte is charged with a constant current, removing Fe from the positive electrode electrolyte. 3 + Reduced to Fe 2+ Rebalancing Fe in the electrolyte 2+ Oxidized to Fe 3+ In the ion recovery system, carbon monoxide gas depletes the Fe in the reequilibrium liquid. 3+ Reduced to Fe 2+ H is generated at the same time + Its chemical reaction formula is 2Fe 3+ +CO + H₂O = CO₂↑ + 2Fe 2+ +2H + .

[0045] The rebalancing electrolyte in the positive electrode storage tank of the rebalancing system is sent to the ion recovery system, and carbon monoxide gas is introduced. At a preset temperature, the Fe in the rebalancing electrolyte can be rapidly reduced. 3+ H is generated at the same time + The generated H +The amount and H caused by hydrogen evolution during charging and discharging + The amount of loss is consistent. Therefore, using carbon monoxide gas can effectively remove Fe. 3+ It can reduce free acid in the electrolyte of the main energy storage system to its original concentration, effectively replenishing the H+ lost through hydrogen evolution. + This ensures the service life and charge / discharge efficiency of the electrolyte. CO is used as a reducing agent to generate CO2, which is emitted through the tail gas. No new impurities are introduced during the entire capacity recovery process, and the electrochemical process of rebalancing will not affect the main system or cause the loss of active substances in the original rebalancing electrolyte. It can completely restore all the components in the electrolyte of the main system to their original concentrations. The ion recovery system consumes some water and requires a certain reaction temperature. Water can be directly added during the cooling of the rebalancing electrolyte and circulation through the bubble column, and the solution can be mixed evenly. There is no operational difficulty and no side reactions occur.

[0046] Exemplarily, the rebalancing electrolyte of the present invention is selected from vanadium oxysulfate, and the reducing gas is selected from hydrogen sulfide. The online capacity recovery process of its iron-chromium flow battery is as follows: In the rebalancing system, VO in vanadium oxysulfate... 2+ Fe in the positive electrode electrolyte 3+ An electrochemical reaction occurs, and the electrolyte is charged with a constant current, removing Fe from the positive electrode electrolyte. 3+ Reduced to Fe 2+ Rebalancing VO in the electrolyte 2+ Oxidized to VO2 + In the ion recovery system, hydrogen sulfide gas removes VO2 from the rebalanced electrolyte. + Restore to VO 2+ Its chemical reaction formula is: 2VO2 + +H2S+2H + =2VO 2+ +2H₂O + S↓. The rebalancing electrolyte in the positive electrode tank of the rebalancing system is sent to the ion recovery system, and hydrogen sulfide gas is introduced. At a preset temperature, VO₂ in the rebalancing electrolyte can be rapidly reduced. + H2S acts as a reducing agent to generate solid elemental sulfur, which can be efficiently removed by filtration. No new impurities are introduced during the entire capacity recovery process, but some hydrogen ions are consumed. The hydrogen ions in the system can be replenished by introducing a mixture of hydrogen sulfide and hydrogen chloride gas.

[0047] For example, the rebalancing electrolyte of the present invention is selected from vanadium oxysulfate, and the reducing gas is selected from carbon monoxide. The online capacity recovery process of its iron-chromium redox flow battery is as follows: In the rebalancing system, VO in vanadium oxysulfate... 2+ Fe in the positive electrode electrolyte 3+ An electrochemical reaction occurs, and the electrolyte is charged with a constant current, removing Fe from the positive electrode electrolyte. 3+ Reduced to Fe 2+Rebalancing VO in the electrolyte 2+ Oxidized to VO2 + In the ion recovery system, carbon monoxide gas will rebalance the VO2 in the electrolyte. + Restore to VO 2+ Its chemical reaction formula is: 2VO2 + +CO+2H + =CO2↑+2VO 2+ +H₂O. The rebalancing electrolyte in the positive electrode tank of the rebalancing system is sent to the ion recovery system, and hydrogen sulfide gas is introduced. At room temperature, the VO₂ in the rebalancing electrolyte can be rapidly reduced. + No new impurities are introduced during the entire capacity recovery process, but some hydrogen ions are consumed. The hydrogen ions in the system can be replenished by introducing a mixture of carbon monoxide and hydrogen chloride gas.

[0048] To further improve the capacity recovery effect of the iron-chromium redox flow battery, in some preferred embodiments of the present invention, the flow rate of the reducing gas is 100-200 L / min, for example, including but not limited to 100 L / min, 110 L / min, 120 L / min, 140 L / min, 150 L / min, 160 L / min, 170 L / min, 180 L / min, 190 L / min, and 200 L / min. In the ion recovery system, the flow rate of the imbalanced rebalancing electrolyte is 30-50 L / min, for example, including but not limited to 30 L / min, 35 L / min, 40 L / min, 45 L / min, and 50 L / min. In the rebalancing system, the flow rates of the positive electrode electrolyte and the rebalancing electrolyte are 30-50 L / min, for example, including but not limited to 30 L / min, 35 L / min, 40 L / min, 45 L / min, and 50 L / min. The rebalancing system employs constant current charging during the charging process, with a current density of 40–100 mA / cm². 2 For example, it can include, but is not limited to, 40mA / cm 2 50mA / cm 2 60mA / cm 2 70mA / cm 2 80mA / cm 2 90mA / cm 2 100mA / cm 2 .

[0049] The present application will be further described in detail below with reference to the embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0050] Example 1

[0051] An online capacity recovery system for iron-chromium redox flow batteries, such as Figure 1 and Figure 2 As shown, it includes a main energy storage system 10, a rebalancing system 20, and an ion recovery system 30 that are connected in sequence.

[0052] The main energy storage system 10 includes a positive electrolyte storage tank 11, a negative electrolyte storage tank 12, a positive pump 13, a negative pump 14, and a main energy storage system battery stack 15. The positive pump 13 and the negative pump 14 are used to transport the positive electrolyte in the positive electrolyte storage tank 11 and the negative electrolyte in the negative electrolyte storage tank 12 to the positive and negative electrodes of the main energy storage system battery stack 15 for electrochemical reaction, respectively.

[0053] The rebalancing system 20 includes a positive electrolyte storage tank 11, a rebalancing system positive electrode storage tank 21, a rebalancing system positive electrode pump 22, a rebalancing system negative electrode pump 23, and a rebalancing system battery stack 24. The positive electrolyte storage tank 11 serves as the negative electrode storage tank of the rebalancing system 20, and the rebalancing system positive electrode storage tank 21 contains rebalancing electrolyte. The rebalancing system positive electrode pump 22 and the rebalancing system negative electrode pump 23 are used to transport the rebalancing electrolyte in the rebalancing system positive electrode storage tank 21 and the positive electrolyte in the positive electrode storage tank 11 to the positive and negative electrodes of the rebalancing system battery stack 24, respectively, for electrochemical reactions.

[0054] The ion recovery system 30 includes two bubble columns, namely a primary bubble column 31 and a secondary bubble column 32, and a filter 33. The primary bubble column 31 has an inlet at the bottom, an outlet at the top and bottom, a first gas distributor 311 at the bottom, a first distribution baffle 312 inside, a first heating / insulation jacket 313 outside, and a first pressure control valve 314 at the top.

[0055] The secondary bubble column 32 has a liquid inlet at the bottom and liquid outlets at the top and bottom. A second gas distributor 321 is installed at the bottom, a second distribution baffle 322 is installed inside, a second heating / insulation jacket 323 is installed outside, and a second pressure control valve 324 is installed at the top. The liquid outlet of the primary bubble column 31 and the liquid inlet of the secondary bubble column 32 are connected by a pipeline, and a first delivery pump 325 is installed on the pipeline.

[0056] The top of the filter 33 is provided with an inert gas inlet, a reducing gas outlet, and a liquid inlet, and the bottom is provided with a liquid outlet. The liquid outlet of the filter 33 is connected to the liquid outlet of the secondary bubble column 32 through a pipeline. A second transfer pump 331 is provided on the pipeline. The filter 33 is provided with a filter membrane 332 inside. The reducing gas outlet of the filter 33 is connected to the gas distributor 311 of the primary bubble column 31 through a pipeline. A check valve 333 is provided on the pipeline.

[0057] The system's working process is as follows: During normal use, the positive electrolyte in the positive electrolyte storage tank 11 and the negative electrolyte in the negative electrolyte storage tank 12 undergo multiple cycles of charging and discharging. During discharge, the stored energy is converted into electrical energy and released; during charging, the electrical energy is stored in the electrolyte solution. The specific reaction formula is: During charging: Fe 2+ -e - →Fe 3+ Cr 3+ +e - →Cr 2+ During discharge: Fe 3+ +e - →Fe 2+ Cr 2+ -e - →Cr 3+ ;

[0058] When a significant decrease in battery capacity is detected, the rebalancing system 20 is activated. The imbalanced positive electrolyte in the positive electrolyte storage tank 11 is transported to the negative electrode of the rebalancing system battery stack 24 via the negative electrode pump 23. Meanwhile, the rebalanced electrolyte in the positive electrode storage tank 21 is transported to the positive electrode of the rebalancing system battery stack 24 via the positive electrode pump 22, initiating a constant current charging process. This process aims to remove Fe from the positive electrolyte through the rebalancing electrolyte. 3+ Reduced to Fe 2+ This allows for the online restoration of battery capacity.

[0059] When the imbalanced ion valence state of the rebalancing electrolyte accumulates to a preset value, the imbalanced rebalancing electrolyte in the positive electrode storage tank 21 of the rebalancing system first enters the primary bubble column 31 and then is introduced into the secondary bubble column 32 by the first transfer pump 325. Reducing gas is introduced into the secondary bubble column 32 through the second gas distributor 321. After the reaction is complete, the reducing gas is introduced into the primary bubble column 31 through the second pressure control valve 324 into the first gas distributor 311 to fully react with the electrolyte, restoring the valence state of the rebalancing electrolyte. The electrolyte is fed into the filter 33 via the second delivery pump 331. At the same time, inert gas is introduced into the inert gas inlet of the filter 33 to purge the reducing gas in the liquid and displace the reducing gas in the rebalanced electrolyte. The displaced gas is then fed back into the primary bubble column 31 through the pipeline between the reducing gas outlet and the gas distributor 311 to reduce the remaining rebalanced electrolyte again and absorb the reducing gas again. Finally, the remaining gas is discharged by the first control valve 314 and treated as exhaust gas.

[0060] Example 2

[0061] A method for online capacity recovery of an iron-chromium redox flow battery, using the system operation of Example 1: After multiple charge-discharge cycles, the Fe in the positive electrode electrolyte of the main energy storage system...2+ The molar concentration is 1.0 M, Fe 3+ At a molar concentration of 0.2 M, the rebalancing system is initiated for a constant current charging process (current density of 40 mA / cm²). 2 The rebalancing system uses ferrous chloride solution, with a rebalancing electrolyte flow rate of 30 L / min and a positive electrode electrolyte flow rate of 30 L / min. The rebalancing electrolyte and the Fe in the main energy storage system... 2+ An electrochemical reaction occurs, removing Fe from the positive electrode electrolyte. 3+ Reduced to Fe 2+ When the valence state of the rebalancing electrolyte in the rebalancing system is completely unbalanced, the rebalancing system transfers the unbalanced electrolyte to the ion recovery system for reduction with a reducing gas (hydrogen sulfide is selected as the reducing gas, with a flow rate of 100 L / min, and the flow rate of the unbalanced electrolyte is 30 L / min). This restores the unbalanced ion valence state in the electrolyte, and the chemical reaction is 2Fe2+ + Fe ... 3+ +H₂S=2Fe 2+ +2H + +S↓; The restored rebalanced electrolyte is then transported back to the rebalance system for the next rebalance process.

[0062] In this online capacity recovery system for an iron-chromium redox flow battery, the operating volume of the positive electrode electrolyte is 300 cubic meters, and the operating volume of the rebalancing electrolyte is 20 cubic meters. Through the above-described online capacity recovery process in this embodiment, 580 kWh of electricity was recovered, 400 kg of reducing gas was consumed, and the gas cost was 40,000 yuan. During the capacity recovery process, the Fe in each system... 2+ and Fe 3+ The ion concentrations are shown in Table 1.

[0063] Table 1

[0064]

[0065] Example 3

[0066] A method for online capacity recovery of an iron-chromium redox flow battery, using the system operation of Example 1: After multiple charge-discharge cycles, the Fe in the positive electrode electrolyte of the main energy storage system... 2+ The molar concentration is 1.0 M, Fe 3+ At a molar concentration of 0.2 M, the rebalancing system is initiated for a constant current charging process (current density of 100 mA / cm²). 2 The rebalancing system uses ferrous chloride solution, with a rebalancing electrolyte flow rate of 50 L / min and a positive electrode electrolyte flow rate of 50 L / min. The rebalancing electrolyte and the Fe in the main energy storage system... 2+ An electrochemical reaction occurs, removing Fe from the positive electrode electrolyte. 3+ Reduced to Fe2+ When the valence states of the rebalancing system are completely out of balance, the rebalancing system transfers the out-of-balance electrolyte to the ion recovery system for reduction with a reducing gas (hydrogen sulfide is selected as the reducing gas, with a flow rate of 200 L / min, and the flow rate of the out-of-balance electrolyte is 50 L / min). This restores the out-of-balance ion valence states in the electrolyte, and the chemical reaction is 2Fe2+ + Fe ... 3+ +H₂S=2Fe 2+ +2H + +S↓; The restored rebalanced electrolyte is then transported back to the rebalance system for the next rebalance process.

[0067] In the online capacity recovery process of this iron-chromium redox flow battery, the operating volume of the positive electrode electrolyte was 300 cubic meters, and the operating volume of the rebalancing electrolyte was 40 cubic meters. Through the above-described online capacity recovery process in this embodiment, 1160 kWh of electricity was recovered, 800 kg of gas was consumed, and the gas cost was 80,000 yuan. During the capacity recovery process, Fe in each system... 2+ and Fe 3+ The ion concentrations are shown in Table 2.

[0068] Table 2

[0069]

[0070] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. The present invention can also be implemented in other specific ways or forms without departing from its spirit or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of the present invention should be defined by the appended claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A system for online capacity recovery of an iron-chromium flow battery, characterized in that, The energy storage system comprises a main energy storage system, a rebalancing system and an ion recovery system connected in sequence, the main energy storage system comprises a positive electrolyte and a negative electrolyte, the rebalancing system comprises a rebalancing electrolyte, and the ion recovery system comprises a reducing gas. 3+ The rebalancing electrolyte is used for recovering the unbalanced ion valence in the rebalancing electrolyte, and the reducing gas is used for recovering the unbalanced ion valence in the rebalancing electrolyte. 2.The system for online capacity recovery of iron-chromium flow battery according to claim 1, wherein, the main energy storage system comprises a positive electrolyte storage tank, a negative electrolyte storage tank, a positive electrolyte pump, a negative electrolyte pump and a main energy storage system battery stack; the positive electrolyte pump and the negative electrolyte pump are respectively used to transport the positive electrolyte in the positive electrolyte storage tank and the negative electrolyte in the negative electrolyte storage tank to the positive electrode and the negative electrode of the main energy storage system battery stack for electrochemical reaction. 3.The system for online capacity recovery of iron-chromium flow battery according to claim 2, wherein, the rebalancing system comprises a positive electrolyte storage tank, a rebalancing system positive electrolyte storage tank, a rebalancing system positive electrolyte pump, a rebalancing system negative electrolyte pump and a rebalancing system battery stack, the positive electrolyte storage tank serving as a negative electrolyte storage tank of the rebalancing system, and the rebalancing system positive electrolyte storage tank containing the rebalancing electrolyte; the rebalancing system positive electrolyte pump and the rebalancing system negative electrolyte pump are respectively used to transport the rebalancing electrolyte in the rebalancing system positive electrolyte storage tank and the positive electrolyte in the positive electrolyte storage tank to the positive electrode and the negative electrode of the rebalancing system battery stack for electrochemical reaction. 4.The system for online capacity recovery of iron-chromium flow battery according to claim 1, wherein, the ion recovery system comprises a bubble column and a filter, the bubble column is connected to the rebalancing system positive electrolyte storage tank through a pipeline at an inlet, and the bubble column is connected to the filter through a pipeline at an outlet; the rebalancing system positive electrolyte storage tank is provided with a recovery inlet at the bottom, the filter is connected to the rebalancing system positive electrolyte storage tank through a pipeline at an outlet, and the bubble column is provided with a gas distributor at the lower part, which is used to introduce reducing gas into the bubble column. 5.The system for online capacity recovery of iron-chromium flow battery according to claim 4, wherein, the ion recovery system comprises at least two bubble columns, and a liquid pump is arranged between adjacent bubble columns to transport the rebalancing electrolyte in the previous bubble column to the inlet of the next bubble column for redox recovery again.

6. The system for online capacity recovery of iron-chromium flow battery according to claim 4 or 5, characterized in that, the filter is provided with an inert gas inlet and a reducing gas outlet at the top, the inert gas inlet is used to introduce inert gas to purge the reducing gas in the filter to replace the reducing gas in the liquid, and the reducing gas outlet is used to introduce the replaced reducing gas back into the bubble column. 7.The system for online capacity recovery of iron-chromium flow battery according to claim 3, wherein, the pressure in the rebalancing system positive electrolyte storage tank and the positive electrolyte storage tank is 0.1-0.5Mpa, and the temperature is 25-55℃.

8. A method for on-line capacity recovery of an iron-chromium flow battery using a system for on-line capacity recovery of an iron-chromium flow battery according to any one of claims 1 to 7, characterized in that comprising the following steps: When the battery capacity of the iron-chromium flow battery is monitored to be significantly attenuated, a rebalancing system of the iron-chromium flow battery is started to perform a charging process, and an electrochemical reaction occurs between the rebalancing electrolyte in the rebalancing system and the unbalanced positive electrolyte in the energy storage main system, so that Fe 3+ in the positive electrolyte is reduced to Fe 2+ ; When the imbalance ion valence of the rebalancing electrolyte in the rebalancing system accumulates to a preset value, the imbalance rebalancing electrolyte is transported to an ion recovery system, and a reducing gas in the ion recovery system chemically reacts with the imbalance rebalancing electrolyte to recover the imbalance ion valence in the imbalance rebalancing electrolyte, and the recovered rebalancing electrolyte is transported to the rebalancing system for the next rebalancing process. 9.The method of claim 8, wherein the rebalancing electrolyte is selected from one of ferrous sulfate, ferrous chloride, potassium ferrocyanide, ferrous carbonate, and vanadyl sulfate. 10.The method of claim 8, wherein the reducing gas is selected from one or more of hydrogen sulfide, carbon monoxide, hydrogen, and methane. 11.The method of claim 8, wherein the flow rate of the reducing gas is 100-200 L / min. 12.The method of claim 8, wherein the flow rate of the imbalance rebalancing electrolyte in the ion recovery system is 30-50 L / min. 13.The method of claim 8, wherein the flow rate of the positive electrolyte and the rebalancing electrolyte in the rebalancing system is 30-50 L / min. ​ ​ ​ ​ ​ 14. The method for online capacity recovery of iron-chromium flow battery according to claim 8, the charging process of the rebalancing system adopts constant current charging, the density of the current is 40-100 mA / cm 2 .

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