Flexible graphite polar plate dipping and cleaning closed-loop water circulation system and use method thereof

Abstract

The invention belongs to the technical field of industrial cleaning and resource circulation, particularly relates to a flexible graphite polar plate dipping cleaning closed-loop water circulation system and a use method thereof, and particularly aims at cleaning wastewater containing a surfactant (OP-10). Zero emission of the cleaning agent and water (the recovery rate of OP-10 is larger than or equal to 90%, the water circulation rate is larger than or equal to 98%, and the generation amount of hazardous waste is reduced by 100%) and efficient removal of resin, graphite powder and an initiator (the removal rate of the resin / graphite powder is larger than or equal to 99%, and the degradation rate of the initiator is larger than or equal to 99.9%) are achieved, so that closed-loop recycling of ultrapure water and an active agent is achieved, it is ensured that the cleaning effect each time is consistent with that of the first time, the usage amount of OP-10 is saved every year, the cost is reduced by 80%, and the production cost is reduced. And the water consumption is reduced by 90%.

Description

Technical Field

[0001] This invention belongs to the field of industrial cleaning and resource recycling technology, specifically relating to a closed-loop water circulation system for immersion cleaning of flexible graphite plates and its usage method. Background Technology

[0002] In the manufacturing of flexible graphite plates for proton exchange membrane fuel cells, the cleaning process after resin impregnation is crucial to the product's conductivity and airtightness. Currently, the industry commonly uses ultrapure water containing surfactant OP-10 for multi-stage rinsing, but this process has the following serious drawbacks: I. Imbalance between resource consumption and efficiency Significant waste of ultrapure water occurs because of the "water quality degradation and recycling" model (the secondary rinsing tank is used as the primary tank), ultrapure water is discharged after only 3-5 batches of rinsing. The annual consumption per production line is enormous. Furthermore, the conductivity of the discharged water remains <0.1 μS / cm, allowing it to be directly reused in the electronics industry, resulting in a misallocation of high-end resources.

[0003] OP-10 has low utilization: the surfactant is deactivated after combining with the resin / graphite powder, resulting in low actual effective utilization and requiring frequent replenishment. Simultaneously, contaminant accumulation leads to a sharp decline in cleaning efficiency. As the number of cleaning cycles increases, contaminants continuously accumulate in the cleaning water, causing a gradual decrease in cleaning efficiency and making it difficult to guarantee consistent product cleaning quality.

[0004] II. Significant Environmental Compliance Risks The cleaning wastewater contains high concentrations of pollutants: Resin fragments: COD > 5,000 mg / L (10 times the limit of national standard GB 8978-1996); Graphite powder: caused SS > 2,000 mg / L (13 times the standard); OP-10 degradation products: release endocrine disruptors such as nonylphenol (NP), which have low removal rates with conventional biochemical treatment; A single production line can discharge a huge amount of such high-risk wastewater and sludge annually, facing stringent environmental penalties and pressure to upgrade its technology.

[0005] III. Limitations of Existing Technological Improvements None of the optimization solutions attempted by the industry have fundamentally solved the problem: Physically enhanced type: For example, the patent application with publication number CN114927702A uses mechanical swing to enhance rinsing. Although it reduces the amount of OP-10 used, it aggravates resin breakage and increases the burden on subsequent filters. Chemical alternatives: The patent application with publication number CN115627200A uses perfluorinated solvents, which can achieve efficient separation, but contains persistent PFOA contaminants (banned globally in 2024) and leads to an increase in the scratch rate of graphite plates. Wastewater treatment type: Due to the adhesion of resin emulsion to the membrane surface, the flux attenuation rate of membrane separation technology increases, and the operating cost soars.

[0006] Existing technologies have not broken through the linear model of "one-way resource consumption - end-of-pipe pollution treatment". There is an urgent need to develop a closed-loop resource recycling system that can achieve efficient reuse of ultrapure water, OP-10 regeneration cycle and targeted separation of pollutants while ensuring cleaning quality, so as to fundamentally solve the bottleneck of green manufacturing of flexible graphite plates. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this application provides a closed-loop water circulation system for immersion cleaning of flexible graphite plates and its usage method. Through multi-stage separation and dynamic control technology, it achieves zero discharge of cleaning agents and water, as well as efficient removal of resin, graphite powder, and initiators, thereby realizing the closed-loop recycling of ultrapure water and surfactants and ensuring that the cleaning effect is consistent with the initial cleaning.

[0008] The specific technical solution of the present invention is as follows: This invention provides a closed-loop water circulation system for immersion cleaning of flexible graphite plates, comprising: Cleaning unit: includes a cleaning tank containing an aqueous solution of surfactant, and a basket for loading graphite plates; Multi-stage treatment unit: From upstream to downstream, there are solid-liquid separation device, membrane filtration device, adsorption device and oxidative degradation device, which are used to remove solid particles, dissolved organic matter and initiator from the wastewater generated in the cleaning unit; Control unit: Enables the purified water after multi-stage treatment to be reused in the cleaning tank, and monitors the concentration of surfactant aqueous solution in the cleaning tank in real time and adds it dynamically to form a closed loop.

[0009] Furthermore, the solid-liquid separation device is a centrifuge; The membrane filtration device (which may use an ultrafiltration membrane or a ceramic filter membrane) has a molecular weight cutoff of 45-55 kDa, a surfactant permeability of ≥99.9%, and triggers a backwashing procedure when the outlet turbidity is >0.5 NTU.

[0010] Furthermore, the adsorption device is an activated carbon tower; The oxidation degradation device is an ultraviolet-ozone reactor. The ozone concentration in the ultraviolet-ozone reactor is 3-10 ppm, the ultraviolet wavelength is 254±5 nm, and the irradiation intensity is ≥80 mW / cm². 2 .

[0011] Furthermore, based on the linear positive correlation between the conductivity and concentration of the OP-10 aqueous solution (pH 6-7, temperature 25±2℃), the conductivity sensor monitors the conductivity of the cleaning solution in real time, and the OP-10 concentration is calculated using a preset concentration-conductivity calibration curve. Therefore, the control unit monitors the concentration of the surfactant aqueous solution through the conductivity sensor and adjusts the replenishment amount according to the linear relationship between conductivity κ and concentration C, C=0.008341κ+0.163798, where the unit of conductivity κ is μS / cm and the unit of concentration C is ‰.

[0012] This invention also provides a closed-loop water circulation method for immersion cleaning of flexible graphite electrode plates, using the aforementioned closed-loop water circulation system for cleaning, comprising the following steps: (1) Place the impregnated electrode plate in a basket, and then put it into a cleaning tank containing a surfactant aqueous solution to clean and remove surface residue, and obtain the cleaning wastewater; (2) Multi-stage treatment: The wastewater is treated sequentially by a solid-liquid separation device, a membrane filtration device, an adsorption device and an oxidation degradation device to obtain purified water for recycling; (3) Closed-loop circulation: The control unit returns the purified water to the cleaning tank and monitors the concentration of the surfactant aqueous solution, dynamically replenishing the mother liquor to the target concentration to achieve closed-loop circulation.

[0013] Preferably, in step (1), the surfactant is alkylphenol polyoxyethylene ether with an initial concentration of 0.38%-0.42% and a supplementary mother liquor concentration of 8%-12%.

[0014] As a preferred embodiment, in step (2), the processing time of the solid-liquid separation device is ≤45 minutes; The membrane filtration device operates at a pressure of 0.2-0.4 MPa and has a flux of 40-60 L / (m²). 2 •h); The adsorption device is an activated carbon tower, the hollow tower of which has a flow rate of 1.5-2.5 m / h and a contact time of 15-25 minutes. After treatment in the oxidative degradation device for 8-12 minutes, the residual amount of initiator after oxidative degradation is <0.5μg / L.

[0015] The beneficial effects of this invention are: This invention achieves zero discharge of cleaning agents and water (OP-10 recovery rate ≥90%, water circulation rate ≥98%, hazardous waste generation reduced by 100%) and efficient removal of resin, graphite powder, and initiator (resin / graphite powder removal rate ≥99%, initiator degradation rate ≥99.9%) through multi-stage separation and dynamic control technology. This enables closed-loop recycling of ultrapure water and surfactants, ensuring that the cleaning effect is consistent with the initial cleaning, saving 80% of OP-10 usage and reducing water consumption by 90% annually. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the closed-loop water circulation system for immersion cleaning of flexible graphite electrode plates according to the present invention, where the arrows indicate the flow direction.

[0017] The diagram shows the following labels: 101-washing tank, 102-suspended basket, 201-solid-liquid separation device, 202-membrane filtration device, 203-adsorption device, 204-oxidative degradation device, and 205-control unit. Detailed Implementation

[0018] Example 1 Depend on Figure 1 As shown, this invention provides a closed-loop water circulation system for impregnating and cleaning flexible graphite electrode plates, comprising: a cleaning unit including a cleaning tank 101 containing an aqueous solution of surfactant, and a basket 102 for loading graphite electrode plates; wherein, the cleaning tank 101 can be made of 316L stainless steel, and the surfactant in the aqueous solution can be alkylphenol polyoxyethylene ether (OP-10) with a concentration of 0.38%-0.42%; the basket 102 can be made of stainless steel frame, used to load the resin-impregnated graphite electrode plates, which enter and exit the cleaning tank by a robotic arm or overhead crane, which is existing technology and easy to implement, and is not shown in the schematic diagram; The closed-loop water circulation system also includes multi-stage treatment units: from upstream to downstream, there are a solid-liquid separation device 201, a membrane filtration device 202, an adsorption device 203, and an oxidation degradation device 204. The solid-liquid separation device 201 can be a centrifuge; in this embodiment, a horizontal screw centrifuge (3000 rpm) is selected, capable of separating resin / graphite powder with a particle size >50 μm. The membrane filtration device 202 in this embodiment is an ultrafiltration membrane module, specifically a polyethersulfone hollow fiber membrane (molecular weight cutoff 45-55 kDa), capable of removing particles from 0.1-50 μm, with a surfactant permeability ≥99.9%, and triggering a backwash procedure when the outlet turbidity >0.5 NTU. The adsorption device 203 uses an activated carbon tower filled with coconut shell activated carbon (specific surface area 1200 m²). 2 / g), adsorbent soluble resin monomers; and oxidative degradation device 204 selects to use an ultraviolet-ozone reactor: 254±5 nm ultraviolet lamp (irradiance ≥80 mW / cm2 Combined with ozone (concentration of 3-10 ppm), it degrades azo initiators; The closed-loop water circulation system of the present invention also includes a control unit 205: integrating a conductivity sensor, a turbidity meter and a PLC controller, regulating the concentration of OP-10 and linking it with the equipment, so that the purified water after the multi-stage treatment unit is reused in the cleaning tank 101, and the concentration of surfactant aqueous solution in the cleaning tank 101 is monitored in real time and dynamically replenished to form a closed-loop circulation.

[0019] This invention also provides a closed-loop water circulation method for immersion cleaning of flexible graphite electrode plates, using the aforementioned closed-loop water circulation system for cleaning, comprising the following steps: (1) Basket cleaning: The dipped plates are placed in the basket 102, and then placed in the cleaning tank 101 containing a surfactant aqueous solution and agitated for 10-20 minutes to remove surface residue. After the cleaning is completed, the basket 102 is removed and the cleaning tank 101 contains the wastewater after cleaning. (2) Multi-stage treatment: The wastewater is treated sequentially by a solid-liquid separation device, a membrane filtration device, an adsorption device and an oxidation degradation device to obtain purified water for recycling; Specifically: (2.1) Solid-liquid separation Wastewater is pumped into solid-liquid separation device 201 to separate large particulate impurities (sludge discharge cycle 30 min / time). The supernatant is filtered by membrane filtration device 202 at an operating pressure of 0.2-0.4 MPa and a flux of 40-60 L / (m³). 2 •h); (2.2) Removal of dissolved organic matter and initiator The permeate from the membrane filtration device enters the adsorption unit 203, with an empty tower flow rate of 1.5-2.5 m / h and a contact time of 15-25 minutes. The effluent from the adsorption device 203 enters the oxidation degradation device 204, where it stays for 10 minutes. After oxidation degradation, purified water is obtained, and the residual amount of initiator in the purified water is <0.5 μg / L. (3) Closed-loop circulation: The control unit 205 returns the purified water to the cleaning tank 101 and monitors the concentration of the surfactant aqueous solution, dynamically replenishing the mother liquor to the target concentration to achieve closed-loop circulation.

[0020] The method for determining the concentration of surfactant aqueous solution in control unit 205, taking OP-10 as an example: Detection principle: Based on the linear positive correlation between the conductivity and concentration of OP-10 aqueous solution (pH 6-7, temperature 25±2℃). The conductivity sensor in the control unit 205 monitors the conductivity of the cleaning fluid in real time and converts the OP-10 concentration using a preset concentration-conductivity calibration curve (Table 1).

[0021] Table 1 Calibration curve data

[0022] illustrate: Curve fitting formula: C = 0.008341κ + 0.163798 (κ is conductivity, C is concentration, R² = 0.999). Control logic: When the conductivity is <420 μS / cm (corresponding to OP-10 <0.38%), trigger the addition of 10% mother liquor to the target value (450±10 μS / cm).

[0023] Auxiliary indicators: Turbidity monitoring: When the turbidity at the ultrafiltration outlet is >0.5 NTU, it indicates that the activated carbon adsorption is saturated or the membrane is fouled, and backwashing or replacement is required. UV absorbance: Absorbance at 254 nm wavelength > 0.05 indicates initiator residue, prolonging UV-ozone residence time.

[0024] Example 2 1. Exploration of experimental conditions: Cleaning tank solution: 0.4% OP-10 ultrapure aqueous solution (initial conductivity: 25 μS / cm); Simulated pollution sources: Residues on the surface of the electrode plate after resin impregnation (resin fragments, graphite powder, azo initiators); Single-cycle water treatment capacity: 1 m³ 3 ; Testing standard: Standard Methods for Water Quality Analysis (GB / T 5750-2023); Table 2. Water Sample Test Data (Single Cycle)

[0025] Note: Data are the mean ± standard deviation of 5 parallel experiments; The concentration of OP-10 is dynamically controlled using a conductivity-concentration calibration curve. The degradation rate of the initiator was verified by HPLC-MS (detection limit 0.1 μg / L).

[0026] Table 3. Stability test of OP-10 concentration control (mean of 5 cycles)

[0027] Conclusion: The error of controlling OP-10 concentration by conductivity method is ≤ ±0.005%, which meets the process requirements (0.4 ± 0.02%).

[0028] 2. Equipment Configuration The equipment configuration is shown in Table 4.

[0029] Table 4

[0030] 3. Closed-loop operation procedure (single batch) Step 1: Initial water filling Inject 9 m into the cleaning tank 3 Ultrapure water, with the addition of 36 kg of OP-10 (to prepare a 4‰ solution), has an initial conductivity of 450 μS / cm.

[0031] Step 2: Plate cleaning A basket loaded with 360 electrode plates undergoes a 15-minute agitation and cleaning process, generating 9 cubic meters of wastewater containing contaminants. 3 (COD 5200 mg / L, SS 1850 mg / L).

[0032] Step 3: Wastewater Treatment Table 5

[0033] Step 4: Reuse and Replenishment Purified water is returned to the cleaning tank, and the conductivity value is 430 μS / cm (corresponding to OP-10 concentration of 3.85‰). The PLC automatically adds 90 L of 10% OP-10 mother liquor, restoring the concentration to 4±0.01‰.

[0034] 4. Technical performance data (after 5 consecutive batches of operation) Table 6

[0035] Note: The data for residual electrode material is the mean ± standard deviation of 5 parallel experiments; The method for detecting residual electrode material refers to standard GB / T 33920-2017 "Test Methods for Flexible Graphite Plates"; in conclusion: Water circulation rate ≥ 97.8% (cumulative fresh water consumption only 0.2 m³) 3 (5 batches) OP-10 recovery rate ≥95% (cumulative replenishment amount <15% of the initial dosage); The plate cleaning quality is stable (residual amount ≤0.1 mg / cm³). 2 ).

[0036] The total water treatment time in the cleaning tank is 3.75 hours, which is less than the working time of the preceding impregnation tank, thus meeting the process cycle time of the impregnation line.

[0037] Economic benefit analysis (annual operation of a single tank): Saving ultrapure water: Traditional process consumes 3240 m³ of water per year. 3 (9 m) 3 (Daily × 360 days), the closed-loop system consumes only 14.4 m³ of fresh water annually. 3 (Water replenishment rate 0.4%) → 99.6% savings; Savings on OP-10: Traditional process consumes 12.96 tons of OP-10 per year (36 kg / day × 360 days), while closed-circuit system consumes 2.59 tons per year (90% recovery rate) → saving 80%.

Claims

1. A closed-loop water circulation system for immersion cleaning of flexible graphite electrode plates, characterized in that, include: Cleaning unit: includes a cleaning tank containing an aqueous solution of surfactant, and a basket for loading graphite plates; Multi-stage treatment unit: From upstream to downstream, there are solid-liquid separation device, membrane filtration device, adsorption device and oxidative degradation device, which are used to remove solid particles, dissolved organic matter and initiator from the wastewater generated in the cleaning unit; Control unit: Enables the purified water after multi-stage treatment to be reused in the cleaning tank, and monitors the concentration of surfactant aqueous solution in the cleaning tank in real time and adds it dynamically to form a closed loop.

2. The closed-loop water circulation system for immersion cleaning of flexible graphite electrode plates according to claim 1, characterized in that, The solid-liquid separation device is a centrifuge; The membrane filtration device has a molecular weight cutoff of 45-55 kDa, a surfactant permeability of ≥99.9%, and triggers a backwashing procedure when the outlet turbidity is >0.5 NTU.

3. The closed-loop water circulation system for immersion cleaning of flexible graphite electrode plates according to claim 1, characterized in that, The adsorption device is an activated carbon tower; The oxidation degradation device is an ultraviolet-ozone reactor.

4. The closed-loop water circulation system for immersion cleaning of flexible graphite electrode plates according to claim 1, characterized in that, The ozone concentration in the ultraviolet-ozone reactor is 3-10 ppm, the ultraviolet wavelength is 254±5 nm, and the irradiation intensity is ≥80 mW / cm². 2 .

5. The closed-loop water circulation system for immersion cleaning of flexible graphite electrode plates according to claim 1, characterized in that, The control unit monitors the concentration of the surfactant aqueous solution through a conductivity sensor and adjusts the replenishment amount according to the linear relationship between conductivity κ and concentration C, C=0.008341κ+0.163798, where the unit of conductivity κ is μS / cm and the unit of concentration C is ‰.

6. A closed-loop water circulation method for immersion cleaning of flexible graphite electrode plates, characterized in that, Cleaning using the flexible graphite electrode plate immersion cleaning closed-loop water circulation system according to any one of claims 1-5 includes the following steps: (1) Place the impregnated electrode plate in a basket, and then put it into a cleaning tank containing a surfactant aqueous solution to clean and remove surface residue, and obtain the cleaning wastewater; (2) Multi-stage treatment: The wastewater is treated sequentially by a solid-liquid separation device, a membrane filtration device, an adsorption device and an oxidation degradation device to obtain purified water for recycling; (3) Closed-loop circulation: The control unit returns the purified water to the cleaning tank and monitors the concentration of the surfactant aqueous solution, dynamically replenishing the mother liquor to the target concentration to achieve closed-loop circulation.

7. The closed-loop water circulation method for impregnating and cleaning flexible graphite electrode plates according to claim 6, characterized in that, In step (1), the surfactant is alkylphenol polyoxyethylene ether, with an initial concentration of 0.38%-0.42% and a supplementary mother liquor concentration of 8%-12%.

8. The closed-loop water circulation method for impregnating and cleaning flexible graphite electrode plates according to claim 6, characterized in that, In step (2), the processing time of the solid-liquid separation device is ≤45 minutes; The membrane filtration device operates at a pressure of 0.2-0.4 MPa and has a flux of 40-60 L / (m²). 2 •h); The adsorption device is an activated carbon tower, the hollow tower of which has a flow rate of 1.5-2.5 m / h and a contact time of 15-25 minutes. After treatment in the oxidative degradation device for 8-12 minutes, the residual amount of initiator after oxidative degradation is <0.5 μg / L.

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