Nanofiltration membrane flushing method and device

Abstract

The invention discloses a nanofiltration membrane flushing method and device, and relates to the technical field of membrane pollution treatment. The nanofiltration membrane flushing method is used for flushing a nanofiltration membrane group, and the nanofiltration membrane group has intermediate produced water; the nanofiltration membrane flushing method comprises the following steps: performing forward flushing on a nanofiltration membrane group by taking intermediate produced water as flushing water; wherein the temperature of the washing water is 25-45 DEG C, and the washing time is 3-15 minutes; ultrasonic-assisted cleaning is started in the washing process, the ultrasonic frequency is 20-60 kHz, and the duration time is 3-15 min. The nanofiltration intermediate produced water is used as a closed flushing water source, so that lithium ion dilution loss caused by introduction of an external agent or an external water source is avoided, secondary pollution caused by osmotic pressure mutation is effectively inhibited by utilizing the ion concentration compatibility of the nanofiltration intermediate produced water and an original brine system, chemical agent dependence is reduced from the source, and the quality of the brine system is improved. The recovery efficiency and the operation stability of the system are obviously improved; and meanwhile, the non-stop operation of the nanofiltration membrane group can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane fouling treatment, and particularly to a nanofiltration membrane flushing method and device. Background Art

[0002] As an important carrier of liquid lithium resources, the efficient development of salt lake brine is of strategic significance for the development of the new energy industry. At present, the nanofiltration membrane separation process in the salt lake lithium extraction technology has become the core means for the efficient extraction of lithium resources, but its large-scale application is still restricted by the problem of the decline in operating efficiency caused by membrane fouling. In the salt lake brine system, high-concentration divalent ions (such as Mg 2 + , Ca 2+ , SO 4 2- ) are prone to complexation, crystallization or adsorption with the membrane surface during the membrane separation process, forming a dense pollutant layer, resulting in a decrease in membrane flux and an increase in the system operating pressure. To maintain production capacity, the existing technology generally adopts a pollution control strategy that combines chemical cleaning and physical flushing: the former dissolves pollutants by adding acidic / alkaline agents or scale inhibitors, but frequent chemical intervention is likely to cause irreversible damage such as membrane material swelling and pore structure distortion, and at the same time generates wastewater containing agents, increasing the environmental protection treatment burden and introducing external ions; the latter relies on external water sources for periodic reverse flushing. Although it avoids the risk of chemical pollution, it causes the mixing of the flushing concentrated water and the main process flow, resulting in the dilution loss of lithium ions, a decrease in the system recovery rate, and the low stripping efficiency of the conventional water washing for the dense scaling layer on the membrane surface, making it difficult to achieve long-term stable operation.

[0003] Furthermore, although chemical cleaning can quickly restore the membrane flux, it sacrifices the membrane life and environmental friendliness; although physical flushing avoids agent pollution, its open flushing mode causes water resource waste and lithium resource loss. More seriously, the traditional flushing process lacks targeted regulation of the pollutant binding mechanism - low-temperature flushing is difficult to weaken the binding energy between pollutants and the membrane surface, and single hydraulic scouring cannot effectively destroy the microscopic structure of the crystalline scale layer, resulting in frequent cleaning and severely restricting the continuous operation ability of the device. Therefore, developing a membrane cleaning method with zero agent addition, internal water circulation, and the ability to synergistically weaken the pollutant binding strength has become the key technical requirement for breaking through the energy efficiency bottleneck of the salt lake lithium extraction nanofiltration system. Summary of the Invention

[0004] The technical problem to be solved by the present invention is the deficiencies or defects mentioned in the background art, and to develop a membrane cleaning method with zero agent addition, internal water circulation, and the ability to synergistically weaken the pollutant binding strength.

[0005] To solve the above problems, the present invention proposes the following technical solutions:

[0006] In a first aspect, the present invention provides a method for flushing a nanofiltration membrane, which is used to flush a nanofiltration membrane module, and the nanofiltration membrane module has intermediate product water; the method for flushing the nanofiltration membrane includes:

[0007] Using the intermediate product water as the flushing water to perform forward flushing on the nanofiltration membrane module; wherein, the temperature of the flushing water is 25 - 45 °C, and the flushing time is 3 - 15 min; during the flushing process, ultrasonic-assisted cleaning is started, the ultrasonic frequency is 20 - 60 kHz, and the duration is 3 - 15 min.

[0008] A further technical solution thereof is that the ultrasonic power density is 2 - 5 W / cm 2 .

[0009] A further technical solution thereof is that the method for flushing the nanofiltration membrane further includes that when it is detected that the operating pressure of the nanofiltration membrane module exceeds 1.9 MPa or the product water flow rate is lower than 1.3 m 3 / h, the forward flushing is performed.

[0010] A further technical solution thereof is that the method for flushing the nanofiltration membrane further includes:

[0011] Obtaining the pollution degree of the nanofiltration membrane module;

[0012] Based on the pollution degree, determining the parameters for performing forward flushing on the nanofiltration membrane module.

[0013] A further technical solution thereof is that the pollution degree includes mild pollution, moderate pollution, and severe pollution. Determining the parameters for performing forward flushing on the nanofiltration membrane module based on the pollution degree includes:

[0014] If the pollution degree of the nanofiltration membrane module is mild pollution, the parameters for performing forward flushing on the nanofiltration membrane module are: the temperature of the flushing water is 25 - 30 °C, the flushing time is 3 - 5 min, the ultrasonic frequency during the flushing process is 20 - 30 kHz, and the duration is 3 - 5 min;

[0015] If the pollution degree of the nanofiltration membrane module is moderate pollution, the parameters for performing forward flushing on the nanofiltration membrane module are: the temperature of the flushing water is 30 - 35 °C, the flushing time is 5 - 10 min, the ultrasonic frequency during the flushing process is 30 - 45 kHz, and the duration is 5 - 8 min;

[0016] If the pollution degree of the nanofiltration membrane module is severe pollution, the parameters for performing forward flushing on the nanofiltration membrane module are: the temperature of the flushing water is 35 - 45 °C, the flushing time is 10 - 15 min, the ultrasonic frequency during the flushing process is 45 - 60 kHz, and the duration is 8 - 15 min.

[0017] A further technical solution thereof is that obtaining the pollution degree of the nanofiltration membrane module includes:

[0018] Collecting the transmembrane pressure difference rising rate of the nanofiltration membrane module;

[0019] If the transmembrane pressure difference rising rate k satisfies 0.02 MPa / h ≤ k < 0.05 MPa / h, it is determined that the pollution degree of the nanofiltration membrane module is mild pollution;

[0020] If the transmembrane pressure difference rising rate k satisfies 0.05 MPa / h ≤ k < 0.15 MPa / h, it is determined that the pollution degree of the nanofiltration membrane module is moderate pollution;

[0021] If the transmembrane pressure difference rising rate k satisfies k ≥ 0.15 MPa / h, it is determined that the pollution degree of the nanofiltration membrane module is severe pollution.

[0022] A further technical solution thereof is that collecting the transmembrane pressure difference rising rate of the nanofiltration membrane module includes:

[0023] Collecting the transmembrane pressure difference rising difference of the nanofiltration membrane module at a preset time interval;

[0024] Determining the transmembrane pressure difference rising rate based on the transmembrane pressure difference rising difference and the time interval.

[0025] In a second aspect, an embodiment of the present invention further provides a nanofiltration membrane flushing device, which includes a unit for executing the above method.

[0026] In a third aspect, an embodiment of the present invention further provides a computer device, which includes a memory and a processor, and a computer program is stored on the memory, and when the processor executes the computer program, the above method is implemented.

[0027] In a fourth aspect, an embodiment of the present invention further provides a computer-readable storage medium, and the storage medium stores a computer program, and when the computer program is executed by a processor, the above method can be implemented.

[0028] Compared with the prior art, the technical effects that the present invention can achieve include:

[0029] The nanofiltration membrane flushing method provided by the present invention is used to flush a nanofiltration membrane module, and the nanofiltration membrane module has intermediate product water; the nanofiltration membrane flushing method includes: using the intermediate product water as flushing water to perform forward flushing on the nanofiltration membrane module; wherein, the temperature of the flushing water is 25-45 °C, and the flushing time is 3-15 min; during the flushing process, ultrasonic-assisted cleaning is started, the ultrasonic frequency is 20-60 kHz, and the duration is 3-15 min. By using the intermediate product water of nanofiltration as a closed flushing water source, the present invention not only avoids the dilution loss of lithium ions caused by the introduction of external agents or external water sources, but also utilizes its ion concentration compatibility with the original brine system to effectively inhibit the secondary pollution caused by sudden changes in osmotic pressure, reduces the dependence on chemical agents from the source, and significantly improves the system recovery efficiency and operation stability. At the same time, combining the cavitation synergistic effect of warm water flushing at 25-45 °C and ultrasonic waves at 20-60 kHz forms a physical strengthening path for pollutant stripping: moderate heating weakens the binding strength between crystalline pollutants such as CaSO 4 and Mg(OH) 2 and the membrane surface, and the cavitation effect of high-frequency ultrasonic waves can directionally impact the dense scaling layer, realizing efficient recovery of membrane flux on the premise of avoiding damage to the membrane material.

[0030] The nanofiltration membrane flushing method provided by the present invention constructs a precise matching mechanism between the pollution degree and the cleaning intensity through the dynamic adaptation of the flushing time and ultrasonic parameters. Compared with the traditional flushing mode with a fixed cycle, the present invention can flexibly adjust the cleaning strategy according to the real-time pollution state, while ensuring the full stripping of pollutants, significantly shortening the ineffective cleaning time, reducing the system shutdown frequency and energy consumption level. It resolves the contradictions such as the attenuation of membrane life caused by chemical cleaning, the waste of resources in physical flushing, and the mismatch between the cleaning cycle and pollution dynamics, providing green and sustainable technical support for the long-term operation of nanofiltration membranes in high-salt complex systems. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is a schematic structural diagram of the nanofiltration membrane flushing system provided by the embodiment of the present invention.

[0033] Figure 2 It is a schematic diagram of the installation angle of the ultrasonic transducer in the nanofiltration membrane element provided by the embodiment of the present invention.

[0034] Reference Signs

[0035] 1 Concentrated water tank, 2 Liquid level sensor, 3 Feed water pump, 4 Second valve, 5 Heating device, 6 High-pressure pump, 7 Ultrasonic transducer, 8 Nanofiltration membrane module, 9 Storage tank, 10 Product water tank, 11 Controller, 12 Operation terminal, 13 First valve. Detailed implementation manner

[0036] The following will clearly and completely describe the technical solutions in the embodiments with reference to the accompanying drawings in the embodiments of the present invention. Similar component numbers in the drawings represent similar components. Obviously, the embodiments described below are only some of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0037] It should be understood that when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0038] It should also be understood that the terms used in the specification of the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present invention. As used in the specification of the embodiments of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an", and "the" are intended to include the plural forms.

[0039] See Figure 1 , which is a schematic structural diagram of a nanofiltration membrane system. As can be seen from the figure, the nanofiltration membrane system includes a raw water tank, a heating device 5, a nanofiltration membrane module 8, and a storage tank 9, which are specifically introduced below:

[0040] The raw water tank stores raw water, which is raw material lye and is the raw material for extracting lithium from salt lakes.

[0041] The nanofiltration membrane module 8 is provided with an intermediate water outlet chamber, the intermediate water outlet chamber is communicated with the storage tank 9, the storage tank 9 and the nanofiltration membrane module 8 are communicated through a first pipeline and the on-off of the first pipeline is controlled by a first valve 13, and the heating device 5 is arranged on the first pipeline; the raw water tank and the nanofiltration membrane module 8 are communicated through a second pipeline and the on-off of the second pipeline is controlled by a second valve 4; the operation of the nanofiltration membrane flushing system is controlled by controlling the on-off of the first valve 13 and the second valve 4; the nanofiltration membrane module 8 includes at least one series-connected and / or parallel-connected nanofiltration membrane element, and 3 ultrasonic transducers 7 are arranged in the water inlet pipe of the nanofiltration membrane element.

[0042] See Figure 2, in this embodiment, three ultrasonic transducers 7 are arranged along the water inlet pipe of the nanofiltration membrane element. Among them, the angle transformation range of the first ultrasonic transducer 7 is (40°, 50°), the angle transformation range of the second ultrasonic transducer 7 is (40°, 140°), and the third ultrasonic transducer 7 is installed symmetrically with the first ultrasonic transducer 7 in a mirror image.

[0043] The nanofiltration membrane module 8 has a first water outlet and a second water outlet; the first water outlet is connected to the product water tank 10 through a third pipeline, and the second water outlet is connected to the concentrated water tank 1 through a fourth pipeline. The first water outlet (product water) and the second water outlet (concentrated water) are respectively connected to the product water tank 10 and the concentrated water tank 1 through independent pipelines, realizing the directional diversion of product water and concentrated water.

[0044] When the second valve 4 is closed and the first valve 13 is opened, it is the flushing mode. The flushing water is provided by the water storage tank to flush the nanofiltration membrane module 8 in the forward direction. In the flushing mode, the obtained concentrated water is transported to the concentrated water tank 1, the final product water is transported to the product water tank 10, and the intermediate product water is transported to the water storage tank 9; when the second valve 4 is opened and the first valve 13 is closed, it is the filtration mode. The raw water is provided by the raw water tank and filtered through the nanofiltration membrane module 8. In the filtration mode, the obtained concentrated water is transported to the concentrated water tank 1, the final product water is transported to the product water tank 10, and the intermediate product water is transported to the water storage tank 9.

[0045] The described nanofiltration membrane system further includes a high-pressure pump 6 and a controller 11; the first pipeline and the second pipeline are connected to the nanofiltration membrane module 8 through the high-pressure pump 6; the first pipeline and the second pipeline are both provided with a feed water pump 3. The raw water tank, the water storage tank 9, the product water tank 10, and the concentrated water tank 1 are all provided with liquid level sensors 2; the controller 11 is electrically connected to the first valve 13, the second valve 4, the heating device 5, the liquid level sensor 2, the high-pressure pump 6, the feed water pump 3 and other execution units respectively.

[0046] In specific implementation, the controller 11 is a PLC (Programmable Logic Controller) controller.

[0047] In specific implementation, the controller 11 is connected to the operation terminal 12 to realize human-machine interaction.

[0048] It can be understood that the controller 11 integrates the control logics of valves, heating devices 5 and other execution units, and dynamically adjusts the flushing cycle, water temperature and ultrasonic intensity by receiving sensor signals such as liquid level and temperature.

[0049] Based on the above nanofiltration membrane system, an embodiment of the present invention provides a nanofiltration membrane flushing method for flushing the nanofiltration membrane module in the above nanofiltration membrane system.

[0050] Understandably, the core structure of a traditional nanofiltration membrane module usually includes a fresh water chamber (water production side) and a concentrated water chamber (concentration side), and ion sieving is achieved through the selective separation of the nanofiltration membrane. In the nanofiltration membrane module in the embodiments of the present invention, by optimizing the flow channel distribution, part of the permeate forms an independent collection path between the membrane layers, that is, an intermediate water outlet chamber, so as to obtain intermediate water production.

[0051] The method for flushing a nanofiltration membrane according to an embodiment of the present invention includes:

[0052] Using the intermediate water production as flushing water to perform forward flushing on the nanofiltration membrane module; wherein, the temperature of the flushing water is 25 - 45 °C, and the flushing time is 3 - 15 min; during the flushing process, ultrasonic assisted cleaning is started, the ultrasonic frequency is 20 - 60 kHz, and the duration is 3 - 15 min.

[0053] In this embodiment, the intermediate water production is used as flushing water to perform forward flushing on the nanofiltration membrane module, and the concentrated nanofiltration water after flushing is transported back to the concentrated water tank for reuse. It not only does not cause pollution to the environment, but also can be reused secondarily, without introducing additional chemical agents or external water sources, achieving the purpose of energy conservation and environmental protection. Further, through the switching of valve pipelines, the switching between the cleaning and filtration modes can be realized under the normal operation of the nanofiltration membrane module.

[0054] Within a certain temperature range, increasing the temperature of the flushing water helps to accelerate the diffusion movement of ions and speed up the cleaning process; at the same time, with the assistance of ultrasonic cleaning, the cleaning efficiency of the nanofiltration membrane is improved. The specific introduction is as follows:

[0055] Ultrasonic cleaning achieves efficient cleaning based on multiple physical mechanisms such as cavitation effect, depolymerization, and enhanced diffusion. When the short-wave mechanical energy generated by the ultrasonic generator is transmitted to the flushing water, an alternating sound pressure field of density and sparsity is formed in the liquid, inducing the generation of a large number of micron-sized bubbles. These bubbles experience rapid expansion and violent collapse under the action of the sound pressure, and the shock wave instantaneously released can generate a local high pressure of thousands of atmospheres, directly stripping the pollutant particles attached to the membrane surface and achieving physical fragmentation and dispersion of the deposits on the membrane surface. This cavitation process not only targets macroscopic pollutants, but also can break the stable hydration structure formed by ions and water molecules in the aqueous solution through high-frequency vibration, promoting the dissociation of large molecular clusters into smaller molecular units that are more easily migratory and weakening the adsorption strength of pollutants on the membrane surface.

[0056] In addition, the periodic mechanical disturbance of ultrasonic waves can change the microscopic mass transfer environment on the membrane surface. The microfluidic impact generated by the cavitation effect can temporarily expand the mass transfer path in the membrane pores, enhancing the diffusion rate of ions and molecules; while the vortex turbulence formed by the acoustic streaming further strengthens the reverse migration of pollutants from the membrane surface to the bulk solution. This dynamic regulation of membrane permeability not only avoids the risk of membrane structure damage caused by chemical cleaning but also significantly improves the desorption efficiency of pollutants during the flushing process, forming a synergistic mechanism of physical cleaning and mass transfer enhancement.

[0057] In a specific embodiment, the ultrasonic power density is 2 - 5 W / cm 2 . Within this power density range, it can ensure the effective stripping of pollutants by the cavitation effect while avoiding membrane structure damage caused by excessive power, achieving a balance between the cleaning intensity and the tolerance of the membrane material.

[0058] In some embodiments, the nanofiltration membrane flushing method further includes performing the forward flushing when it is detected that the operating pressure of the nanofiltration membrane module exceeds 1.9 MPa or the water production flow rate is lower than 1.3 m 3 / h. This embodiment triggers the cleaning program based on the real-time thresholds of the operating pressure (>1.9 MPa) or the water production flow rate (<1.3 m 3 / h), which can promptly respond to the membrane fouling state, prevent the accumulation of pollutants from entering the irreversible stage, and thus maintain the stability of the system operating pressure and water production flow rate.

[0059] In some embodiments, the nanofiltration membrane flushing method further includes:

[0060] Obtaining the fouling degree of the nanofiltration membrane module;

[0061] Determining the parameters for forward flushing the nanofiltration membrane module based on the fouling degree. Through a multi-level parameter regulation and dynamic monitoring mechanism, the nanofiltration membrane cleaning process is systematically optimized.

[0062] In a specific embodiment, the fouling degree includes mild fouling, moderate fouling, and severe fouling. Determining the parameters for forward flushing the nanofiltration membrane module based on the fouling degree includes:

[0063] If the fouling degree of the nanofiltration membrane module is mild fouling, the parameters for forward flushing the nanofiltration membrane module are: the temperature of the flushing water is 25 - 30 °C, the flushing time is 3 - 5 min, the ultrasonic frequency during the flushing process is 20 - 30 kHz, and the duration is 3 - 5 min. For mild fouling, an energy-saving mode with low temperature (25 - 30 °C), short time (3 - 5 min), and low-frequency ultrasonic waves (20 - 30 kHz) is adopted to reduce energy consumption and membrane mechanical loss.

[0064] If the pollution degree of the nanofiltration membrane module is medium pollution, the parameters for forward flushing the nanofiltration membrane module are as follows: the temperature of the flushing water is 30 - 35 °C, the flushing time is 5 - 10 min, the ultrasonic frequency during the flushing process is 30 - 45 kHz, and the duration is 5 - 8 min. For medium pollution, a mode of medium temperature (30 - 35 °C), medium frequency ultrasonic wave (30 - 45 kHz), and extended cleaning time (5 - 10 min) is adopted to balance the cleaning efficiency and resource consumption.

[0065] If the pollution degree of the nanofiltration membrane module is severe pollution, the parameters for forward flushing the nanofiltration membrane module are as follows: the temperature of the flushing water is 35 - 45 °C, the flushing time is 10 - 15 min, the ultrasonic frequency during the flushing process is 45 - 60 kHz, and the duration is 8 - 15 min. For severe pollution, high temperature (35 - 45 °C), high frequency ultrasonic wave (45 - 60 kHz), and the maximum cleaning duration (10 - 15 min) are adopted to completely remove the dense fouling layer.

[0066] The above - mentioned grading mechanism can ensure the precise matching of cleaning parameters and pollution dynamics, and avoid the attenuation of membrane performance caused by over - cleaning or insufficient cleaning.

[0067] The pollution degree of the nanofiltration membrane module can be quantitatively evaluated by monitoring indicators such as the rising rate of transmembrane pressure difference, the attenuation slope of water production flow rate, and the cumulative gradient of ion concentration.

[0068] For example, deploy a multi - parameter sensor array (Ca 2+ , Mg 2+ ion - selective sensors, conductivity sensors, etc.) at the inlet and concentrated water outlet of the nanofiltration membrane module to obtain key water quality indicators in real - time. Through the correlation analysis of conductivity and ion concentration data, identify the types of pollutants (such as calcium sulfate scaling, magnesium hydroxide colloid deposition). Common types of pollution include: lithium ions are monovalent ions and can usually pass freely through the nanofiltration membrane, with a low pollution risk; however, they may form a thin - layer pollution at high concentrations or when co - deposited with other ions. Chloride ions have strong penetrability, but at high concentrations, they may form salts (such as NaCl) with sodium, potassium, etc., resulting in slight scaling on the membrane surface. Magnesium ions are easy to combine with carbonate ions and hydroxide ions to form insoluble precipitates (such as MgCO 3 , Mg(OH) 2 ), resulting in hard scaling on the membrane surface. Sulfate ions are easy to form sulfate precipitates (such as CaSO 4 , MgSO 4 ) with calcium and magnesium ions, clogging the membrane pores.

[0069] In this embodiment, the pollution degree is quantitatively measured by dynamically monitoring the rising rate of transmembrane pressure difference, and a grading cleaning strategy is constructed. Obtaining the pollution degree of the nanofiltration membrane module includes:

[0070] Collect the transmembrane pressure difference rising rate of the nanofiltration membrane module;

[0071] If the transmembrane pressure difference rising rate k of the nanofiltration membrane module satisfies 0.02 MPa / h ≤ k < 0.05 MPa / h, it is determined that the pollution degree of the nanofiltration membrane module is mild pollution;

[0072] If the transmembrane pressure difference rising rate k of the nanofiltration membrane module satisfies 0.05 MPa / h ≤ k < 0.15 MPa / h, it is determined that the pollution degree of the nanofiltration membrane module is moderate pollution;

[0073] If the transmembrane pressure difference rising rate k of the nanofiltration membrane module satisfies k ≥ 0.15 MPa / h, it is determined that the pollution degree of the nanofiltration membrane module is severe pollution.

[0074] In this embodiment, collecting the transmembrane pressure difference rising rate of the nanofiltration membrane module includes:

[0075] Collect the transmembrane pressure difference rising difference of the nanofiltration membrane module at a preset time interval;

[0076] Determine the transmembrane pressure difference rising rate based on the transmembrane pressure difference rising difference and the time interval.

[0077] Based on Figure 1 For the nanofiltration membrane system shown, when operating in the raw water filtration mode, sample and record the SO 4 2- concentration, the operating pressure of the nanofiltration membrane module, and the water production flow rate at the inlet of the nanofiltration membrane module within 1 h. In the initial stage (about 0 - 40 min), the SO 4 2- concentration shows a rapid increase. After 40 min, the SO 4 2- concentration changes very little, reaches the peak value (about 3700+ ppm) and remains basically constant; from 10 - 25 min, the system operating pressure rapidly rises from 1.6 MPa to 1.89 MPa, and after 25 min, it slowly rises to the highest 1.96 MPa and remains basically stable. The water production flow rate rapidly drops from 1.92 m 3 / h to 0.77 m 3 / h within 10 - 30 min, and then slowly decreases to 0.67 m 3 / h with time after 30 min and remains basically stable. It shows that pollutants (such as sulfates) rapidly accumulate on the membrane surface, resulting in an increase in hydraulic resistance and a decrease in flux. After 40 min, the deposition of pollutants reaches a dynamic equilibrium, but at this time the system is already in an inefficient operating state.

[0078] Now, the following cleaning methods are respectively adopted to compare the cleaning effects of different methods:

[0079] (1) Based on Figure 1The shown nanofiltration membrane system is switched to the operation cleaning mode (without heating and ultrasonic), the flushing water temperature is 20 °C, and the system operation pressure and water production flow rate are respectively recorded at the operation times of 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, and 10 min. The results show that as the flushing time increases, the initial filtration pressure slowly decreases from 1.96 MPa to about 1.66 MPa, and basically remains unchanged after 8 min; the initial water production flow rate slowly increases from 0.67 m 3 / h to about 1.93 m 3 / h, and basically remains unchanged after 9 min. In this cleaning mode, the flushing time of 9 min has the best effect.

[0080] (2) Based on Figure 1 the shown nanofiltration membrane system, it is switched to the operation cleaning mode (heating is turned on, without ultrasonic), and the system operation pressure and water production flow rate are recorded at the flushing water temperatures of 15 °C, 20 °C, 25 °C, 30 °C, 40 °C, and 45 °C with the operation time of 9 min. The results show that as the flushing water temperature increases, the system operation pressure can be more quickly reduced to about 1.71 MPa, and the water production flow rate increases to 1.39 m 3 / h, that is, the increase in water temperature helps to shorten the flushing time.

[0081] (3) Based on Figure 1 the shown nanofiltration membrane system, it is switched to the operation cleaning mode (ultrasonic is turned on, without heating), and the system operation pressure and water production flow rate are recorded at the flushing water temperature of 20 °C with the operation time of 9 min and the ultrasonic frequencies of 20 KHZ, 25 KHZ, 30 KHZ, 40 KHZ, 45 KHZ, 50 KHZ, 55 KHZ, 60 KHZ, and 65 KHZ. The results show that when the ultrasonic frequency is between 20 and 40 KHz, the water production flow rate rapidly rises from 1.24 m 3 / h to 1.38 m 3 / h, and the operation pressure slowly drops from 1.83 MPa to 1.72 MPa; the operation pressure and water production flow rate at 40 - 60 KHz for 9 min are both maintained at about 1.72 MPa and 1.38 m 3 / h; after 60 KHz, the operation pressure rises and the water production flow rate drops, which may have the risk of damaging the membrane. When the frequency is controlled within 40 - 60 KHZ, increasing the ultrasonic frequency can improve the flushing efficiency and shorten the flushing time.

[0082] (4) Based on Figure 1The shown nanofiltration membrane system is switched to the operation cleaning mode (heating is turned on, without ultrasonic), the flushing water temperature is 35°C, and the system operation pressure and water production flow rate at the operation times of 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, and 10 min are respectively recorded. The results show that at 35°C, with the increase of the flushing time, the initial filtration pressure slowly decreases from 1.89 MPa to about 1.66 MPa, and basically remains unchanged after 8 min; the initial water production flow rate slowly increases from 0.76 m 3 / h to about 1.93 m 3 / h, and basically remains unchanged after 8 min. Therefore, when the water temperature is 35°C, the best flushing time is 8 min.

[0083] (5) Based on Figure 1 the shown nanofiltration membrane system, it is switched to the operation cleaning mode (ultrasonic is turned on, without heating), the ultrasonic frequency is 50 KHZ, and the flushing water temperature is 20°C. The system operation pressure and water production flow rate at the operation times of 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, and 10 min are respectively recorded. The results show that at the ultrasonic frequency of 50 KHz, with the increase of the flushing time, the initial filtration pressure slowly decreases from 1.88 MPa to about 1.57 MPa, and basically remains unchanged after 8 min; the initial water production flow rate slowly increases from 0.77 m 3 / h to about 1.90 m 3 / h, and basically remains unchanged after 8 min. Therefore, when the water temperature is 20°C, the ultrasonic frequency is 50 KHZ, and the best flushing time is 8 min.

[0084] (6) Based on Figure 1 the shown nanofiltration membrane system, it is switched to the operation cleaning mode (ultrasonic and heating are turned on), the ultrasonic frequency is 50 KHZ, and the flushing water temperature is 35°C. The system operation pressure and water production flow rate at the operation times of 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, and 10 min are respectively recorded. The results show that with the increase of the flushing time, the initial filtration pressure slowly decreases from 1.85 MPa to about 1.63 MPa, and basically remains unchanged after 5 min; the initial water production flow rate slowly increases from 0.91 m 3 / h to about 1.91 m 3 / h, and basically remains unchanged after 5 min. Starting the heating device and the ultrasonic generator simultaneously has the effect of improving the flushing efficiency and shortening the flushing time, and the best effect can be achieved after flushing for about 5 min.

[0085] As can be seen from the above results, the present invention adopts a physical flushing mode. The improvement in the effect of using only hot flushing water or ultrasonic-assisted flushing is not obvious compared with that of normal-temperature flushing. By combining heating (35°C) and ultrasonic waves (50 kHz), the optimal flushing time is shortened to 5 minutes, and the efficiency is increased by 60% compared with the single method. Under the synergistic mode, the initial water production flow rate recovery rate > 95%, the pressure fluctuation range is compressed to ±0.1 MPa, the system operates stably, the intermediate water production reuse rate is 100%, and there is no external water source consumption; it avoids the swelling of membrane pores caused by chemical cleaning, and it is expected that the service life of the nanofiltration membrane will be extended by more than 30%.

[0086] The embodiment of the present invention also provides a nanofiltration membrane flushing device, which includes a unit for performing the nanofiltration membrane flushing method of the above embodiment.

[0087] The embodiment of the present invention also provides a computer device, which includes a memory and a processor. A computer program is stored on the memory, and when the processor executes the computer program, the nanofiltration membrane flushing method of the above embodiment is implemented.

[0088] The embodiment of the present invention also provides a computer-readable storage medium, and the storage medium stores a computer program. When the computer program is executed by a processor, the nanofiltration membrane flushing method of the above embodiment can be implemented.

[0089] It should be noted that those skilled in the art can clearly understand the specific implementation processes of the above nanofiltration membrane flushing device and each unit. They can refer to the corresponding descriptions in the foregoing method embodiments. For the convenience and conciseness of description, they will not be repeated here.

[0090] In several embodiments provided by the present invention, it should be understood that the disclosed device and method can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of each unit is only a logical function division, and there can be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed.

[0091] The steps in the method embodiments of the present invention can be adjusted, combined, and deleted according to actual needs. The units in the device embodiments of the present invention can be combined, divided, and deleted according to actual needs. In addition, in each embodiment of the present invention, each functional unit can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit.

[0092] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a terminal, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention.

[0093] In the above embodiments, the descriptions of the various embodiments have their own emphases. For the parts not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0094] The above is the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for flushing a nanofiltration membrane, characterized in that: Used for flushing a nanofiltration membrane group, the nanofiltration membrane group has intermediate water production; the nanofiltration membrane flushing method comprises: The intermediate produced water is used as flushing water to forward flush the nanofiltration membrane group; wherein the temperature of the flushing water is 25-45°C, and the flushing time is 3-15min; ultrasonic assisted cleaning is started during the flushing process, the ultrasonic frequency is 20-60kHz, and the duration is 3-15min.

2. The nanofiltration membrane flushing method according to claim 1, characterized in that: The ultrasonic power density is 2-5W / cm 2 .

3. The nanofiltration membrane flushing method according to claim 1, characterized in that: The nanofiltration membrane flushing method further comprises: detecting that the operating pressure of the nanofiltration membrane group exceeds 1.9 MPa or the produced water flow rate is lower than 1.3 m 3 / h, perform the forward flushing.

4. The nanofiltration membrane flushing method according to claim 1, characterized in that: The nanofiltration membrane flushing method also includes: Obtaining the contamination degree of the nanofiltration membrane group; Parameters for forward flushing the nanofiltration membrane group are determined based on the degree of contamination.

5. The nanofiltration membrane flushing method according to claim 4, characterized in that: The pollution degree includes light pollution, moderate pollution and heavy pollution. The parameters for forward flushing the nanofiltration membrane group are determined based on the pollution degree, including: If the pollution degree of the nanofiltration membrane group is light pollution, the parameters for forward flushing the nanofiltration membrane group are: the temperature of the flushing water is 25-30°C, the flushing time is 3-5 minutes, the ultrasonic frequency during the flushing process is 20-30kHz, and the duration is 3-5 minutes; If the pollution degree of the nanofiltration membrane group is moderate pollution, the parameters for forward flushing the nanofiltration membrane group are: the temperature of the flushing water is 30-35°C, the flushing time is 5-10 minutes, the ultrasonic frequency during the flushing process is 30-45kHz, and the duration is 5-8 minutes; If the pollution degree of the nanofiltration membrane group is severe pollution, the parameters for forward flushing of the nanofiltration membrane group are: the temperature of the flushing water is 35-45°C, the flushing time is 10-15 minutes, the ultrasonic frequency during the flushing process is 45-60kHz, and the duration is 8-15 minutes.

6. The nanofiltration membrane flushing method according to claim 4, characterized in that: The obtaining of the contamination degree of the nanofiltration membrane group comprises: Collecting the transmembrane pressure difference rising rate of the nanofiltration membrane group; If the transmembrane pressure difference rising rate k satisfies 0.02MPa / h≤k<0.05MPa / h, the contamination degree of the nanofiltration membrane group is determined to be light contamination; If the transmembrane pressure difference rising rate k satisfies 0.05MPa / h≤k<0.15MPa / h, the contamination degree of the nanofiltration membrane group is determined to be moderate contamination; If the transmembrane pressure difference rising rate k satisfies k≥0.15 MPa / h, the pollution degree of the nanofiltration membrane group is determined to be severe pollution.

7. The nanofiltration membrane flushing method according to claim 1, characterized in that: The collecting the transmembrane pressure difference rising rate of the nanofiltration membrane group comprises: Collecting the transmembrane pressure difference rise difference of the nanofiltration membrane group at preset time intervals; The transmembrane pressure difference rising rate is determined based on the transmembrane pressure difference rising difference and the time interval.

8. A nanofiltration membrane flushing device, characterized in that: The method comprises a unit for executing the method according to any one of claims 1 to 7.

9. A computer device, characterized in that: The computer device includes a memory and a processor, the memory stores a computer program, and the processor implements the method according to any one of claims 1 to 7 when executing the computer program.

10. A computer-readable storage medium, characterized in that: The storage medium stores a computer program, and when the computer program is executed by a processor, the method according to any one of claims 1 to 7 can be implemented.

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