A treatment system for filter core pollution of a polishing system

Abstract

This invention discloses a system for treating filter clogging in a pre-filter of a fine treatment system. The system includes a pre-filter, a cleaning water tank, a cleaning water pump, an inlet pipe, and a return pipe connected in sequence. It also includes a polymer dosing device, an unstable flow channel, and several passive vortex generators. The polymer dosing device adds a non-ionic, water-soluble polymer to the cleaning fluid, transforming it into a viscoelastic fluid. The unstable flow channel is located on the inlet pipe. The cleaning water pump is driven to circulate at a Reynolds number Re < 500. The geometry of the unstable flow channel is configured such that the Weissenberg number Wi ≥ 5 for the viscoelastic fluid at this flow rate, thereby triggering elastic turbulence within the channel. The passive vortex generators are fixed to the inner wall of the housing, extending axially along the pleated filter element with their flow-facing side directly opposite the Z-shaped pleat opening. They are used to induce flow-direction vortices within the housing, maintaining elastic turbulence as the viscoelastic fluid flows over the outer surface of the filter element. This solves the problems of uneven cleaning of multiple filter elements in parallel and difficulty in cleaning deep pleats.

Description

Technical Field

[0001] This invention relates to a system for treating filter cartridge clogging in a fine treatment system, belonging to the field of filter cartridge clogging technology. Background Technology

[0002] During long-term operation, pre-filters in power plant condensate polishing systems accumulate complex contaminants on their surfaces and within their pores, including iron oxides, silicates, copper oxides, and oil. Iron oxides account for up to 28.8% of these contaminants, while silicates account for 36.6%. These contaminants do not simply adhere to the filter element surface; rather, they react with the fiber pores to form a bond, leading to increased pressure differential, shortened operating cycles, increased backwashing frequency, and poor backwashing effectiveness. Currently, the industry primarily employs chemical cleaning processes such as alkaline washing for oil removal and citric acid washing for iron removal, combined with physical methods like air wiping and hydraulic backwashing for filter element regeneration. However, relying solely on physical cleaning measures like air wiping and hydraulic backwashing is insufficient to remove all impurities.

[0003] Chinese patent CN110760389A discloses a chemical cleaning agent for filter elements in a pre-filter of a condensate polishing system and its application. It uses an alkaline cleaning agent to remove oil and an acidic stripping agent to remove iron oxides and silicates, combined with soaking and compressed air impact for filter element cleaning. However, this solution mainly relies on the dissolving effect of chemical agents and the impact disturbance of compressed air, which is insufficient for the physical stripping ability of particles deep in the folds. Moreover, the cleaning uniformity is greatly affected by the filter element structure, making it difficult to balance cleaning efficiency and filter element protection. Summary of the Invention

[0004] In order to solve the above-mentioned problems in the existing technology, the present invention provides a treatment system for the clogging of the pre-filter cartridge of the fine treatment system, which solves the problems of uneven cleaning of multiple filter cartridges in parallel and difficulty in cleaning deep folds.

[0005] The technical solution of the present invention is as follows: A system for treating filter clogging in a pre-filter of a fine treatment system includes a pre-filter, a cleaning water tank, an inlet pipe, and a return pipe. The pre-filter contains several pleated filter elements. The cleaning water tank stores cleaning solution. A central tube is located at the center of each pleated filter element, and a central tube control valve is located at the outlet of the central tube. During cleaning, the central tube control valve closes, sequentially connecting the cleaning water tank, inlet pipe, pre-filter, and return pipe to form a cleaning solution circulation loop. The system also includes a polymer dosing device, an unstable flow channel, and several passive vortex generators. The polymer dosing device is used for… The cleaning fluid is transformed into a viscoelastic fluid. A cleaning water pump is installed at the outlet of the cleaning water tank. The cleaning water pump is configured to drive the viscoelastic fluid circulation at a volumetric flow rate of Reynolds number Re < 500. The geometry of the unstable flow channel is configured such that the Weissenberg number Wi ≥ 5 of the viscoelastic fluid at this flow rate, thereby triggering elastic turbulence in the unstable flow channel. A passive vortex generator is used to generate longitudinal vortices and local high shear zones in the housing cavity of the pre-filter, so that the viscoelastic fluid entering the housing cavity maintains an elastic turbulent state with a Weissenberg number Wi ≥ 5 when flowing through the outer surface of the pleated filter element.

[0006] The polymer dosing device includes a polymer dosing tank, a metering pump, and a mixing tank. The outlet of the polymer dosing tank is connected to the inlet of the mixing tank via the metering pump. The outlet of the mixing tank is connected in series between the outlet of the cleaning water pump and the inlet pipeline. The polymer dosing tank contains a high molecular weight polymer, which transforms the cleaning fluid into a viscoelastic fluid in the mixing tank. An unstable flow channel is located on the inlet pipeline downstream of the polymer dosing device and has a converging section, a throat, and a diverging section connected in sequence. Several passive vortex generators are fixedly installed on the inner wall of the pre-filter housing. Each passive vortex generator is an airfoil protruding from the inner wall of the housing. The airfoil extends along the axial direction of the pleated filter element, and the flow-facing side of the airfoil faces the Z-shaped pleated opening of the pleated filter element.

[0007] The polymer used is a non-ionic, water-soluble polymer, added at a concentration of 0.05% to 0.2%. The cleaning solution contains an iron ion chelating agent. A monitoring sensor is installed on the return pipeline to monitor the elastic modulus of the cleaning solution in real time. And iron ion concentration; a bypass discharge branch is provided on the return liquid line and downstream of the monitoring sensor, and a bypass discharge valve is provided on the bypass discharge branch; a clean water replacement branch is also provided on the return liquid line, and a clean water injection valve is provided on the clean water replacement branch.

[0008] The monitoring sensor, polymer dosing device, and bypass discharge valve are electrically connected to a supplementary discharge control unit; the supplementary discharge control unit performs the following operations: when the elastic modulus... When the concentration of iron ions is below the first preset threshold, the polymer dosing device is controlled to add non-ionic water-soluble polymers in batches; when the iron ion concentration is above the second preset threshold, the bypass discharge valve is opened to discharge the aging cleaning solution; after cleaning, the clean water injection valve is opened to inject clean water for replacement rinsing.

[0009] The nonionic water-soluble polymer is polyethylene oxide; the iron ion chelating agent is one or more of citric acid and citrate; the first preset threshold is the initial elastic modulus after cleaning. 30%; the second preset threshold is an iron ion concentration of 50 ppm.

[0010] The feature is that it further includes a pulsation generator and a cross-flow discharge branch. The pulsation generator is connected in series on the inlet pipe and located downstream of the unstable flow channel, so that the viscoelastic fluid entering the pre-filter housing cavity has an axial velocity component that oscillates with time; the pulsation frequency of the pulsation generator... Configured to satisfy , where λ is the relaxation time of polyethylene oxide in viscoelastic fluid; the pleats of the pleated filter element gradually contract from the outer circumference of the pleated filter element towards the center of the pleated filter element, forming a gradually narrowing flow channel; one end of the cross-flow discharge branch is connected to the pipeline between the outlet of the central pipe and the control valve of the central pipe through a tee, and the other end is connected to the return port of the cleaning water tank. A cross-flow control valve is provided on the cross-flow discharge branch.

[0011] The compressed air injection device includes a compressed air source and a compressed air injection pipe. One end of the compressed air injection pipe is connected to the compressed air source, and the other end is connected to the pipeline between the central pipe outlet and the cross-flow control valve via a tee. The compressed air injection pipe is equipped with a compressed air control valve. The supplementary discharge control unit is also configured to intermittently open the cross-flow control valve and close the compressed air control valve during the cleaning process, so that some viscoelastic fluid passes through the pleated wall of the filter element from the housing cavity into the central pipe and flows back through the cross-flow discharge branch.

[0012] The inlet pipe is connected to the outlet of the cleaning water pump at one end and to the inlet of the pre-filter at the other end; the return pipe is connected to the return port of the pre-filter at one end and to the return port of the cleaning water tank at the other end.

[0013] The present invention has the following beneficial effects: This invention uses a cleaning water pump to drive the circulation of a viscoelastic fluid with a Reynolds number Re < 500. Combined with an unstable flow channel having a converging section, a throat, and a expanding section, it triggers elastic turbulence with a Weissenberg number Wi ≥ 5. In addition, a passive vortex generator extending along the axial direction of the folded filter element on the inner wall of the housing induces flow-directing vortices. This achieves the goal of maintaining an elastic turbulent state at the fold opening at low flow rates and directing tensile stress to the depth of the folds. The purpose is to use the tensile stress of the elastic fluid to peel off iron oxide particles in the folds and reduce the energy consumption of the water pump.

[0014] This invention achieves dynamic maintenance of the elastic modulus G' and iron ion concentration in real time by setting an online monitoring sensor on the return liquid pipeline, and controls the polymer dosing device to add non-ionic water-soluble polymer in batches when the elastic modulus is below the threshold, and opens the bypass discharge valve to discharge the aging cleaning liquid when the iron ion concentration is above the threshold. This achieves the effect of delaying polymer degradation and avoiding excessive accumulation of coordination complexes that leads to deterioration of rheological properties.

[0015] This invention achieves pulsed reverse flushing and alternating air-water disturbance of particles deep in the folds and micropores of the filter element by periodically opening the flow control valve during the cleaning stage to allow the cleaning fluid to flow backward through the filter element and into the central tube for discharge. After cleaning, compressed air is injected into the central tube through the compressed air injection device to perform air-water backflushing. This achieves the effect of further loosening and removing the embedded dirt and restoring the filter element's flow rate. Attached Figure Description

[0016] Figure 1 This is a block diagram of the system.

[0017] The reference numerals in the figure are as follows: 1. Pre-filter; 2. Cleaning water tank; 3. Cleaning water pump; 4. Inlet pipe; 5. Return pipe; 6. Pleated filter element; 61. Central pipe; 7. Unstable flow channel; 8. Passive vortex generator; 10. Bypass discharge branch; 11. Clean water replacement branch; 12. Clean water injection valve; 13. Bypass discharge valve; 14. Pulsation generator; 15. Cross-flow discharge branch; 16. Compressed air source; 17. Compressed air injection pipe; 91. Polymer dosing tank; 92. Metering pump; 93. Mixing tank. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0019] Please see Figure 1 The invention provides a technical solution: A system for treating clogging of pre-filter cartridges in a fine treatment system is mainly used for online cleaning of pre-filters in condensate fine treatment systems of power plants. It can also be applied to the cleaning of precision filter cartridges in industries such as chemical, pharmaceutical, and metallurgical.

[0020] The system includes a pre-filter 1, a cleaning water tank 2, a cleaning water pump 3, an inlet pipe 4, and a return pipe 5. The pre-filter 1 is a pressure-bearing shell structure, and inside it are several parallel pleated filter elements 6. The pleated filter elements 6 are made of high molecular weight filter membranes such as polypropylene or polyethersulfone, which are folded and enclosed. The pleats extend along the filter element axis and are evenly arranged in the circumferential direction to form a so-called Z-shaped pleated structure. At the center of each pleated filter element 6, there is a perforated central tube 61. The central tube 61 is usually a porous stainless steel tube or an engineering plastic tube with radial through holes densely distributed on its wall. The main function of the central tube 61 is to support the inner side of the pleated filter element 6 to prevent the filter membrane from being crushed under pressure difference. At the same time, it serves as a collection channel for the filtered clean liquid. Under normal filtration conditions, the raw water to be treated enters the housing cavity from the liquid inlet of the pre-filter 1 and passes through the filter membrane of the filter element 6 from the outside to the inside under pressure. Impurities are trapped on the outside of the filter membrane, while the clean water passes through the membrane wall into the central tube 61 and flows out of the filter through the outlet of the central tube 61.

[0021] The cleaning water tank 2 is used to store the prepared cleaning solution. Its outlet is connected to the inlet of the cleaning water pump 3. The cleaning water pump 3 is preferably a corrosion-resistant centrifugal pump or diaphragm pump. Its outlet is connected to one end of the liquid inlet pipe 4. The other end of the liquid inlet pipe 4 is connected to the shell-side liquid inlet of the pre-filter 1. One end of the return pipe 5 is connected to the shell-side return port of the pre-filter 1, and the other end is connected to the return port of the cleaning water tank 2, thus forming a circulation loop for the cleaning solution.

[0022] It should be noted that during the cleaning process, the central tube control valve at the outlet of the central tube 61 is closed, making the central tube 61 a closed cavity. At this time, the cleaning fluid cannot be discharged through the central tube 61, but can only flow in the shell cavity of the pre-filter 1 and return to the cleaning water tank 2 through the shell-side return port. This is because the liquid is incompressible. Once the outlet of the central tube 61 is closed, the pressure on the inside and outside of the filter element 6 will quickly reach equilibrium, the driving force for penetrating the filter membrane will disappear, and the cleaning fluid will no longer forcefully penetrate the filter element 6, but will form a shell-side circulation along the shell cavity. The advantage of this circulation method is that the cleaning fluid acts entirely on the outer surface and pleat gaps of the filter element 6, avoiding the decrease in cleaning efficiency and the increase in polymer adsorption residue caused by a large amount of cleaning fluid penetrating the filter membrane.

[0023] To further improve the cleaning effect, the system also includes a polymer dosing device, an unstable flow channel 7, and several passive vortex generators 8. The polymer dosing device is used to add high molecular polymers to the cleaning fluid and transform the cleaning fluid into a viscoelastic fluid with viscoelastic properties. Specifically, the polymer dosing device includes a polymer dosing tank 91, a metering pump 92, and a mixing tank 93. The polymer dosing tank 91 is used to store the prepared concentrated polymer solution. Its outlet is connected to the inlet of the mixing tank 93 through the metering pump 92. The outlet of the mixing tank 93 is connected in series between the outlet of the cleaning water pump 3 and the liquid inlet pipe 4. During operation, the metering pump 92 injects the concentrated polymer solution into the mixing tank 93 at a set flow rate, which is fully mixed with the cleaning liquid from the cleaning water pump 3, so that the polymer concentration in the cleaning liquid reaches the target range of 0.05% to 0.2%, thereby transforming it into a viscoelastic fluid.

[0024] The cleaning pump 3 is configured to drive a viscoelastic fluid to circulate throughout the loop at a volumetric flow rate with a Reynolds number Re less than 500. The Reynolds number is a dimensionless number that characterizes the ratio of fluid inertial force to viscous force. A Re less than 500 indicates that the flow is in the laminar flow range. In this range, ordinary Newtonian fluids cannot generate turbulence, and the cleaning effect is very limited. However, due to the presence of polymer molecular chains, viscoelastic fluids can still trigger so-called elastic turbulence through elastic instability under low Reynolds number conditions.

[0025] The unstable flow channel 7 is located on the inlet pipe 4 and downstream of the polymer dosing device. It has a converging section, a throat, and a diverging section connected in sequence, and is an overall Venturi tube structure. The geometry of the unstable flow channel 7 is configured such that, under the flow conditions where Re is less than 500, the Weissenberg number Wi when the viscoelastic fluid flows through the throat is greater than or equal to 5. The Weissenberg number is a dimensionless number characterizing the ratio of elastic force to viscous force in a viscoelastic fluid. It is defined as the product of the fluid's relaxation time and characteristic shear rate. When Wi is greater than or equal to 5, the elastic force dominates the flow. The viscoelastic fluid experiences strong stretching and shearing flow in the converging section and throat of the unstable flow channel 7, and the polymer molecular chains are stretched significantly. Subsequently, the flow velocity decreases and the molecular chains relax in the diverging section. This periodic stretching and relaxation process amplifies small disturbances in the flow, thereby triggering elastic turbulence within the unstable flow channel 7.

[0026] Elastic turbulence differs from traditional Newtonian fluid turbulence. It is a disordered three-dimensional flow driven by fluid elasticity. Its core feature is that it can generate abundant microscale vortices and strong velocity pulsations even at extremely low Reynolds numbers. The size of these microscale vortices can be as small as the gaps between the pleats of the pleated filter element 6, thus enabling them to penetrate deep into the pleats to flush out the clogging. At the same time, the viscoelastic fluid generates a significant first normal stress difference in the tortuous flow. This stress difference manifests as an additional stress perpendicular to the wall surface, which can peel off the clogging particles attached to the surface of the pleated filter element 6 and embedded deep in the pleats from the wall surface. This is an advantage that ordinary laminar flow cleaning does not have.

[0027] However, after the elastic turbulence is triggered in the unstable flow channel 7, when it flows along the liquid inlet pipe 4 and enters the large volume shell cavity of the pre-filter 1, the flow cross-sectional area suddenly increases, the flow velocity drops sharply, and the shear rate decreases significantly. The elastic turbulence is at risk of decaying or even disappearing. Therefore, the system has several passive vortex generators 8 fixedly installed on the inner wall of the shell of the pre-filter 1. Each passive vortex generator 8 is an airfoil plate protruding from the inner wall of the shell towards the center of the shell. The airfoil plate extends along the axial direction of the pleated filter element 6, and the airfoil plate faces the Z-shaped pleated opening of the pleated filter element 6. The Z-shaped pleated opening referred to here is the radial gap opening formed between two adjacent pleated walls on the outer circumference of the pleated filter element 6. Since the pleated cross section is V-shaped and arranged alternately along the circumference, it presents a continuous broken line shape similar to Z when viewed from the cross section. Therefore, the gap opening on its outer circumference is called the Z-shaped pleated opening.

[0028] The passive vortex generator 8 functions by generating a pressure difference between the front and back surfaces of the airfoil when the viscoelastic fluid flows through it, thus forming longitudinal vortices and local high-shear zones. These longitudinal vortices and high-shear zones provide a continuous energy input for maintaining elastic turbulence, ensuring that the viscoelastic fluid entering the shell cavity maintains an elastic turbulence state with a Weissenberg number Wi greater than or equal to 5 when flowing through the outer surface of the pleated filter element 6. This effectively prevents the attenuation of elastic turbulence in a large space. At the same time, the longitudinal vortices generated by the airfoil can transport the highly elastic turbulent fluid in the center of the shell cavity to the surface of the pleated filter element 6 and directly introduce the micro-scale vortices of elastic turbulence into the Z-shaped pleated openings, further enhancing the cleaning effect on the dirt deep in the pleats.

[0029] In actual cleaning operations, a cleaning solution containing an iron ion chelating agent is first prepared in the cleaning water tank 2. The cleaning water pump 3 is started and the polymer dosing device is turned on, so that the viscoelastic fluid establishes circulation in the loop. After the viscoelastic fluid triggers elastic turbulence through the unstable flow channel 7, it enters the housing cavity of the pre-filter 1. Under the action of the passive vortex generator 8, the elastic turbulence state is maintained and the outer surface and pleat gaps of the pleated filter element 6 are continuously flushed. After the dirt is removed, it returns to the cleaning water tank 2 with the cleaning solution through the return pipe 5.

[0030] In the preparation of the above-mentioned viscoelastic fluid, the polymer is selected as a non-ionic water-soluble polymer, and its addition concentration in the cleaning solution is controlled between 0.05% and 0.2%. The advantage of non-ionic polymers is that their molecular chains are not charged and will not interact electrostatically with metal ions or other charged groups present in the cleaning solution, thus preventing flocculation or precipitation. Therefore, they can maintain good solubility stability and viscoelasticity in cleaning solutions containing metal cations such as iron ions. During the cleaning process, the cleaning solution will continuously dissolve the iron oxide clogging on the folded filter element 6, and the iron ion concentration will continue to increase. If ionic polymers are used, they are very likely to fail due to charge neutralization.

[0031] In specific implementation, the nonionic water-soluble polymer is preferably polyethylene oxide (PEO). PEO is a linear polymer obtained by ring-opening polymerization of ethylene oxide, and its molecular weight is usually selected between one million and eight million. PEO in this molecular weight range can impart significant viscoelasticity and tensile rheological properties to aqueous solutions at extremely low concentrations. At the same time, its aqueous solution has good temperature resistance and chemical stability, and can maintain a stable molecular structure without significant degradation under the water temperature conditions commonly found in power plant condensate polishing systems.

[0032] The concentration of polyethylene oxide is set within the range of 0.05% to 0.2% after comprehensive consideration. When the concentration is below 0.05%, the entanglement between polymer molecular chains is insufficient, the viscoelasticity of the cleaning solution is weak, and the Weissenberg number is difficult to reach the threshold required to trigger elastic turbulence, resulting in a significant decrease in cleaning effect. When the concentration is above 0.2%, the viscosity of the cleaning solution will increase significantly, which will not only increase the energy consumption and circulation resistance of the cleaning water pump 3, but also lead to a significant increase in the amount of polymer adsorbed and residual on the surface and in the micropores of the pleated filter element 6, making subsequent water replacement difficult and increasing the cost of the reagents.

[0033] To complement the physical scouring effect of the viscoelastic fluid, the cleaning solution also contains an iron ion chelating agent, which plays a dual role in this system. The first role is to remove iron oxide blockages through a combination of chemical dissolution and complexation. The blockages in the pre-filter of the power plant condensate polishing system mainly originate from iron oxides produced by the corrosion of carbon steel pipes in the water supply and condensate systems, including ferric oxide and magnetite. These iron oxides are deposited in particulate form on the surface of the pleated filter element 6 and embedded deep within the Z-shaped folds. The physical tensile stress of elastic turbulence alone is insufficient to completely remove them. The iron ion chelating agent is selected from citric acid, citrate, or formate. In an acidic cleaning solution with a pH of 3-5, the iron ion chelating agent first dissolves the iron oxides on the pleated wall surface. The resulting ferric ions then form a stable water-soluble complex with the chelating agent molecules, preventing the iron ions from redepositing or hydrolyzing to form ferric hydroxide. This allows the iron oxides to gradually loosen and detach from the pleated surface, facilitating the complete removal of them from the depths of the pleats by the chaotic tensile stress generated by elastic turbulence. The second function is to protect the elastic properties of the viscoelastic fluid. During the cleaning process, a large number of iron ions stripped from the filter element surface will interact with the polymer. Among them, ferric ions form soluble coordination complexes with non-ionic water-soluble polymers such as polyethylene oxide. When the iron ion concentration continues to accumulate, the coordination complex may change the rheological properties of the cleaning fluid. Therefore, it is necessary to control the iron ion concentration through bypass discharge. The iron ion chelating agent locks the free ferric ions in a stable complex structure, blocking the coordination and cross-linking path between the polymer molecular chain and the iron ions. This ensures that the viscoelastic fluid maintains an elastic turbulent state with a Weissenberg number Wi≥5 throughout the entire cleaning cycle, avoiding cleaning failure due to the deterioration of rheological properties.

[0034] The preferred iron ion chelating agent is one or more of citric acid and citrate. Citric acid is a tricarboxylic acid with a strong complexing ability for iron ions. Its complexation products have good water solubility under weakly acidic to neutral conditions. At the same time, citric acid and its salts are environmentally friendly, non-toxic, and easily biodegradable, and will not cause irreversible pollution to the mixed bed resin of the subsequent fine treatment system. Citrate can be used in combination with citric acid according to the pH adjustment requirements of the cleaning solution to obtain the best chelation effect and pH buffering capacity.

[0035] To achieve closed-loop control of the cleaning process, a monitoring sensor is installed on the return line 5. This sensor is used to monitor the elastic modulus of the cleaning fluid in real time. Two key parameters are iron ion concentration and elastic modulus. Elastic modulus is the core indicator reflecting the elastic properties of viscoelastic fluids. It is directly related to the Weissenberg number and whether elastic turbulence can be maintained. During the cleaning process, the polyethylene oxide molecular chains will break and degrade to varying degrees under the strong stretching action of cyclic shearing and unstable flow channels, resulting in a decrease in molecular weight and elastic modulus. When the elastic modulus drops to a certain level, the elastic turbulence effect of viscoelastic fluid will be significantly weakened or even disappear. Therefore, real-time monitoring of elastic modulus is of great significance for judging the degree of polymer degradation and deciding whether to add polymer.

[0036] Online monitoring of elastic modulus can be achieved using vibration rheological sensors or ultrasonic rheological sensors. These sensors calculate the dynamic viscoelastic parameters by measuring the response of the cleaning fluid under vibration excitation, enabling continuous online measurement without sampling.

[0037] Monitoring the iron ion concentration is used to determine the degree of dissolution saturation of the cleaning solution for the blockage. As cleaning proceeds, iron oxides are continuously dissolved by the chelating agent, and the iron ion concentration in the cleaning solution continues to rise. When the iron ion concentration reaches a certain level, the complexing ability of the chelating agent tends to saturate, and the dissolution efficiency of the cleaning solution for iron oxides will decrease significantly. Continuing to use the cleaning solution will have limited cleaning effect. Therefore, it is necessary to monitor the iron ion concentration to determine whether the cleaning solution is aging and whether it needs to be discharged and replaced.

[0038] Online monitoring of iron ion concentration can be achieved using a colorimetric sensor or an electrochemical ion-selective electrode, which can reflect the iron ion content level in the cleaning solution in real time. The location of the monitoring sensor on the return liquid line 5 is reasonably selected. The cleaning solution in the return liquid line 5 flows out from the pre-filter housing cavity, representing the actual state of the cleaning solution after cleaning by the pleated filter element 6. Monitoring at this location can accurately reflect the elastic modulus and iron ion concentration of the cleaning solution, avoiding measurement deviations caused by uneven mixing or the absence of the pleated filter element 6 when monitoring in the cleaning water tank or inlet liquid line.

[0039] A bypass discharge branch 10 is located on the return liquid line 5 and downstream of the monitoring sensor. A bypass discharge valve 13 is installed on the bypass discharge branch 10. The function of the bypass discharge branch 10 is to discharge part of the aged cleaning liquid from the system when the cleaning liquid ages. The bypass discharge valve 13 can be a solenoid valve, pneumatic valve or electric valve, which can receive electrical signals to realize automatic opening and closing control. The outlet of the bypass discharge branch 10 can be connected to the wastewater treatment system of the power plant to centrally treat the discharged aged cleaning liquid and discharge it in compliance with standards. Alternatively, a recovery device can be set up as needed to recover the useful components in the cleaning liquid.

[0040] A clean water replacement branch 11 is also provided on the return liquid pipeline 5. A clean water injection valve 12 is provided on the clean water replacement branch 11. The water source of the clean water replacement branch 11 is preferably the demineralized water or refined water from the power plant. Its water quality should meet the inlet water requirements of the fine treatment system to avoid introducing impurities that contaminate the filter element and subsequent systems. The clean water injection valve 12 is also an automatically controllable valve. It is opened after cleaning to inject clean water into the system to replace the residual viscoelastic cleaning fluid.

[0041] The monitoring sensors, polymer dosing device, and bypass discharge valve 13 are all electrically connected to the supplementary discharge control unit. The supplementary discharge control unit is the control core of the entire cleaning system. Its hardware can be a programmable logic controller, a microcontroller, or an industrial control computer. It has a built-in data acquisition module, logic operation module, and valve drive module. It can receive real-time signals from the monitoring sensors and output control commands according to the preset control logic to drive the metering pump and valves of the polymer dosing device.

[0042] The replenishment and discharge control unit performs the following operations: when the monitoring sensor detects that the elastic modulus of the cleaning fluid is lower than the first preset threshold, it controls the polymer dosing device to replenish non-ionic water-soluble polymer in batches. The reason for replenishing in batches rather than all at once is that injecting a large amount of concentrated polymer solution at once can easily lead to excessively high local concentrations and uneven mixing, which in turn can cause sudden changes in viscosity and unstable flow in the pipeline. Replenishing in batches allows the polymer concentration in the cleaning fluid to gradually and steadily recover. After each replenishment, a certain mixing time is given, and it is decided whether to continue replenishing after the elastic modulus recovers to a reasonable range, thereby avoiding over-dosing.

[0043] When the monitoring sensor detects that the iron ion concentration is higher than the second preset threshold, the replenishment and discharge control unit opens the bypass discharge valve 13 to discharge part of the aged cleaning fluid through the bypass discharge branch 10. After the aged cleaning fluid is discharged, the liquid level in the cleaning water tank 2 will drop accordingly. At this time, an equal amount of fresh cleaning fluid or clean water can be added through the replenishment port of the cleaning water tank 2 to maintain the stability of the liquid level in the circulation loop and the balance of the total amount of cleaning fluid, so as to avoid interruption of circulation due to the cleaning water pump sucking in air because the liquid level is too low.

[0044] After cleaning, the replenishment and discharge control unit opens the clean water injection valve 12, injecting clean water into the system through the clean water replacement branch 11 for replacement rinsing. The clean water flows in the circulation loop and gradually replaces the residual viscoelastic cleaning fluid, rinsing away the residual polyethylene oxide and chelating agent in the pipelines and filters. The waste liquid generated by the replacement can be discharged through the bypass discharge branch 10 or through the system's drain outlet. In terms of specific parameter settings, the first preset threshold is 30% of the initial elastic modulus of the cleaning solution. The basis for setting this threshold is that when the elastic modulus of polyethylene oxide drops to 30% of its initial value due to mechanical degradation, its molecular weight has decreased significantly, the stretching orientation ability of the molecular chains and the elastic feedback effect are greatly weakened, the Weissenberg number is difficult to maintain above 5, and the elastic turbulence state tends to be unstable. At this time, fresh polymer must be added to restore the viscoelasticity of the cleaning fluid. If the threshold is set too high, it will lead to frequent replenishment and waste of reagents. If the threshold is set too low, it will only be added after the elastic turbulence has obviously decayed, affecting the cleaning efficiency.

[0045] The second preset threshold is an iron ion concentration of 50 ppm. This threshold is determined based on engineering practice experience and the chelating capacity of citric acid. When the iron ion concentration in the cleaning solution reaches 50 ppm, a considerable proportion of the iron ion complexing capacity of citric acid has been consumed, and the dissolution rate of iron oxides by the cleaning solution decreases significantly. At the same time, the presence of high concentrations of iron ions may also have a certain impact on the stability of polyethylene oxide. Therefore, at this concentration, discharging part of the aged cleaning solution and replenishing it with fresh solution is economical and reasonable. If the threshold is set too high, the cleaning solution will be in an inefficient dissolution state for a long time, prolonging the cleaning time. If the threshold is set too low, the discharge will be too frequent, increasing the consumption of reagents and the amount of wastewater treated. The completion of cleaning can be determined using a combination of methods. For example, when the iron ion concentration remains stable at a low level for a sustained period and no longer rises, it indicates that the iron oxide clogging on the pleated filter element 6 has been largely removed. Alternatively, when both the elastic modulus and iron ion concentration remain stable and the pressure difference between the filter element's inlet and outlet returns to normal, cleaning can be considered complete, followed by the clean water replacement phase. The endpoint of clean water replacement can be determined by monitoring the total organic carbon content or conductivity in the wastewater. When the wastewater indicators approach the background value of clean water, it indicates that residual polyethylene oxide and chelating agents have been sufficiently removed. Furthermore, the supplementary discharge control unit can interact with the power plant's distributed control system or overall plant automation system via a communication interface, enabling remote monitoring, parameter setting, and operation recording of the cleaning process, thereby improving the automation level of the entire fine treatment system.

[0046] To further enhance the maintenance effect of elastic turbulence within the pleats of the 6-folded filter element and to solve the problems of difficult cleaning of the micropores of the filter medium and the presence of polyethylene oxide residue, the system also includes a pulsation generator 14, a cross-flow discharge branch 15, and a compressed air injection device.

[0047] The pulsation generator 14 is connected in series on the inlet pipe 4 and located downstream of the unstable flow channel 7. The pulsation generator 14 can adopt a reciprocating diaphragm pulsator, a rotary valve pulsation generator, or a piezoelectric driven pulsator. Its core function is to apply periodic velocity disturbances to the viscoelastic fluid after triggering elastic turbulence through the unstable flow channel 7, so that the viscoelastic fluid entering the housing cavity of the pre-filter 1 has an axial velocity component that oscillates with time. This axial velocity oscillation will be superimposed on the steady-state circulating velocity of the viscoelastic fluid to form pulsating flow.

[0048] The reason why the pulsation generator 14 is located downstream of the unstable flow channel 7 rather than upstream is that the unstable flow channel 7 first triggers elastic turbulence under steady-state flow conditions, generating an initial disordered vortex structure. Subsequently, the pulsation generator 14 applies flow velocity oscillation to the fluid that is already in an elastic turbulent state, which is equivalent to supplementing the elastic turbulence with alternating energy, preventing it from attenuating due to a sudden drop in flow velocity after entering the large-volume shell cavity of the pre-filter 1. If the pulsation generator 14 is located upstream of the unstable flow channel 7, the steady-state pulsating flow can also trigger elastic turbulence when passing through the unstable flow channel 7, but it lacks continuous energy input after leaving the unstable flow channel 7, and will still attenuate when it reaches the shell cavity.

[0049] The pulsation frequency f of the pulsation generator 14 is configured to satisfy and The product of is greater than or equal to 0.5, where Let be the relaxation time of polyethylene oxide in a viscoelastic fluid. Relaxation time is a physical quantity characterizing the time required for the molecular chains of a viscoelastic fluid to recover from a stretched state to an equilibrium state. The physical significance of this frequency condition lies in ensuring that the pulsation period is on the same order of magnitude as the relaxation time of the polymer molecular chains. and When the product of and is greater than or equal to 0.5, the pulsation period T equals 1 divided by . Less than or equal to 2 times This means that between two pulsating peaks, the polyethylene oxide molecular chains do not have time to fully relax to an equilibrium state and remain in a partially stretched orientation state. When the next pulsating peak arrives, the molecular chains continue to be stretched from the partially stretched state, and the elastic effect can continue to accumulate without decaying. This phenomenon is called the elastic memory effect of viscoelastic fluids, which is the key physical mechanism by which pulsating flow can maintain elastic turbulence.

[0050] If the pulse rate is too low and If the product is much less than 0.5, the molecular chain has enough time to fully relax between the two pulsations, the elastic effect cannot accumulate, and the pulsation only plays a normal role in the flow velocity disturbance, which is difficult to effectively maintain elastic turbulence. If the pulsation frequency is too high, it exceeds the response capability of the polyethylene oxide molecular chain, and it also cannot effectively excite elastic instability.

[0051] The pleats of the pleated filter element 6 gradually narrow from the outer circumference towards the center, forming a converging flow channel. The geometric constraint of this converging channel results in a higher shear rate at the root of the pleats compared to the opening, facilitating the penetration of elastic turbulence into the deeper pleats. Specifically, the pleats of the pleated filter element 6 have a V-shaped or U-shaped cross-section. The gap between two adjacent pleat walls is wider at the outer circumference and gradually decreases in width as it extends towards the center. This geometric structure causes the flow cross-sectional area to gradually decrease and the flow velocity to gradually increase as the viscoelastic fluid flows from the pleat opening towards the pleat root. The shear rate also increases monotonically, and the Weissenberg number Wi equals the relaxation time. The product of the shear rate and the shear rate means that Wi is higher at the root of the fold than at the opening of the fold. This means that the elastic turbulence will not only not attenuate in the depth of the fold, but will be further enhanced by the geometric constraints of the narrowing channel, which solves the problem that conventional backwashing cannot reach the root of the fold.

[0052] The pulsating flow velocity generated by the pulsating generator 14 has a synergistic effect with the gradually narrowing channel of the pleated filter element 6. The pulsating flow generates periodic oscillating shear and stretching flow in the gradually narrowing channel. At the peak flow velocity stage, the molecular chains are strongly stretched and elastic instability is excited. At the trough flow velocity stage, due to the high shear rate in the gradually narrowing channel itself, and the fact that the molecular chains do not have time to fully relax, elastic turbulence is maintained. The two work together to maintain an elastic turbulent state with a Weissenberg number Wi greater than or equal to 5 throughout the pleat gap. The micro-scale vortex of elastic turbulence can penetrate to the root of the pleat along the pleat depth direction and thoroughly flush away the dirt deposited deep in the pleats.

[0053] One end of the through-flow discharge branch 15 is connected to the pipeline between the outlet of the central pipe 61 and the central pipe control valve via a tee, and the other end is connected to the return port of the cleaning water tank 2. The through-flow discharge branch 15 is equipped with a through-flow control valve. It should be noted that the outlet of the central pipe 61 and the return port of the pre-filter 1 are two independent interfaces. The return port of the pre-filter 1 is located on the shell wall and is connected to the return pipeline 5 for return during shell circulation. The outlet of the central pipe 61 is located at the end of the pleated filter element 6 and is connected to the central pipe 61. It is the normal outlet of the filtered cleaning liquid. During the cleaning operation, the central pipe control valve is closed, and the central pipe 61 becomes a closed cavity. The through-flow discharge branch 15 is connected in parallel to the outlet of the central pipe 61 via a tee to provide a controllable drainage channel for the central pipe 61.

[0054] The compressed air injection device includes a compressed air source 16 and a compressed air injection pipe 17. The compressed air source 16 can be the existing compressed air pipeline network of the power plant, or it can be equipped with an independent air compressor. One end of the compressed air injection pipe 17 is connected to the compressed air source 16, and the other end is connected to the pipeline between the outlet of the central pipe 61 and the cross-flow control valve through a tee. The compressed air injection pipe 17 is equipped with a compressed air control valve. Thus, the outlet of the central pipe 61 is connected to three branches through a tee connector. These branches are the central pipe control valve branch leading to the normal filtration system, the cross-flow discharge branch 15 leading to the cleaning water tank 2, and the compressed air injection pipe 17 leading to the compressed air source 16. The combination of the opening and closing of the three valves determines the connection state of the central pipe 61. The supplementary discharge control unit is also configured to intermittently open the cross-flow control valve and simultaneously close the compressed air control valve and the central pipe control valve during the cleaning process. At this time, the central pipe 61 is connected to the return port of the cleaning water tank 2 through the cross-flow discharge branch 15. The pressure on the central pipe 61 side decreases, and the pressure difference between the inside and outside of the pleated filter element 6 is re-established. Under the pressure difference, some viscoelastic fluid passes through the pleated wall of the filter element 6 from the shell cavity into the central pipe 61, and then flows back to the cleaning water tank 2 through the cross-flow discharge branch 15, forming a cross-flow pulse.

[0055] The core function of the through-flow pulse is to clean the dirt inside the micropores of the pleated filter element 6. In the shell-side circulation mode, the viscoelastic fluid mainly acts on the outer surface and pleat gaps of the pleated filter element 6. For iron oxide particles and organic pollutants embedded in the micropores of the filter membrane, it is difficult to reach them by simply relying on the outer surface rinsing. However, the through-flow pulse forces the liquid to pass through the filter membrane from the outside of the pleated filter element 6 and enter the central tube 61. When the liquid passes through the micropores of the filter membrane, due to the extremely small pore size and the even smaller effective pore size after being clogged, an extremely high instantaneous shear rate is generated, making the Weissenberg number Wi in the micropore channel reach more than 10, which is much higher than the Wi value in the shell side. Under such high Wi conditions, the viscoelastic fluid generates strong elastic turbulence and normal stress difference in the micropore channel, which can peel off the dirt particles embedded deep in the pore channel from the pore wall and carry them out with the through-flow liquid, thus achieving deep cleaning of the inside of the filter medium.

[0056] The intermittent rather than continuous flow of the cross-flow pulse is a result of comprehensive consideration. While continuous flow provides strong cleaning power, it can lead to a large amount of polyethylene oxide solution passing through the filter membrane and increasing the amount of polymer adsorbed and residual in the micropores of the filter membrane. It can also increase the energy consumption of the cleaning pump and the consumption of cleaning fluid. Intermittent flow, on the other hand, ensures that the micropores are thoroughly cleaned periodically while keeping polymer residue and operating energy consumption within a reasonable range. A typical cross-flow pulse cycle can be set to open the cross-flow control valve for 30 seconds to 2 minutes every 5 to 10 minutes. The specific parameters can be adjusted according to the degree of fouling of the pleated filter element 6 and the state of the cleaning fluid.

[0057] During the clean water replacement phase after cleaning, the replenishment and discharge control unit first opens the cross-flow control valve and closes the compressed air control valve and the central tube control valve, allowing clean water to pass through the pleated wall of the filter element 6 from the housing cavity into the central tube 61 and be discharged through the cross-flow discharge branch 15, performing forward cross-flow replacement on the pleated filter element 6. The purpose of this step is to use clean water to forcibly replace the polyethylene oxide solution remaining in the pleated gaps and micropores of the filter membrane, gradually reducing the polymer concentration from 0.05% to 0.2% during cleaning to near zero. After the forward cross-flow replacement continues for a period of time, the replenishment and discharge control unit closes the housing inlet and the cross-flow control valve, and at the same time opens the compressed air control valve. Compressed air enters the central tube 61 from the compressed air source 16 through the compressed air injection pipe 17. Since both the central tube control valve and the cross-flow control valve are closed, the compressed air can only pass through the pleated wall of the filter element 6 from the inside to the outside of the central tube 61 in the opposite direction, forming a gas-water two-phase flow with the clean water remaining in the filter membrane and pleated gaps. This two-phase air-water reverse purging method has a stronger cleaning effect than single-phase water replacement. On the one hand, the aggregation and rupture of bubbles in the micropores and pleats of the filter membrane generate strong micro-jet streams and local impacts, which can strip off the polyethylene oxide molecules adsorbed on the surface and pores of the filter membrane. On the other hand, the reverse flow direction is opposite to the forward flow direction during cleaning, which can push out particles and residual polymers embedded in the micropores during forward cleaning. At the same time, the compressibility of the gas makes the two-phase flow have a higher velocity and stronger shear in the narrow channel. After the two-phase air-water reverse purging, the residual polyethylene oxide and chelating agent in the pleated filter element 6 are completely removed, without affecting the mixed bed resin and effluent quality of the subsequent fine treatment system. During the entire cleaning and replacement process, the on / off states of the central pipe control valve, the cross-flow control valve, and the compressed air control valve are strictly interlocked. Only one valve can be open at any time to prevent cross-contamination of liquids or gases between different flow paths into the cleaning water tank 2. The replenishment and discharge control unit ensures safe and reliable operation through built-in valve interlock logic.

[0058] The embodiments described above are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A system for treating clogging of a pre-filter cartridge in a fine treatment system, characterized in that: The system includes a pre-filter (1), a cleaning water tank (2), an inlet pipe (4), and a return pipe (5). The pre-filter (1) is equipped with several pleated filter elements (6). The cleaning water tank (2) is used to store the cleaning solution. A central pipe (61) is also provided at the center of the pleated filter element (6). A central pipe control valve is provided at the outlet of the central pipe (61). During cleaning, the central pipe control valve is closed, so that the cleaning water tank (2), the inlet pipe (4), the pre-filter (1), and the return pipe (5) are connected in sequence to form a cleaning solution circulation loop. The system also includes a polymer dosing device, an unstable flow channel (7), and several passive vortex generators (8). The cleaning fluid is converted into a viscoelastic fluid. The outlet of the cleaning tank (2) is equipped with a cleaning water pump (3), which is configured to drive the viscoelastic fluid circulation at a volumetric flow rate of Reynolds number Re < 500. The geometry of the unstable flow channel (7) is configured such that the Weissenberg number Wi ≥ 5 of the viscoelastic fluid at this flow rate, thereby triggering elastic turbulence in the unstable flow channel (7). The passive vortex generator (8) is used to generate longitudinal vortices and local high shear zones in the housing cavity of the pre-filter (1), so that the viscoelastic fluid entering the housing cavity maintains an elastic turbulent state with a Weissenberg number Wi ≥ 5 when flowing through the outer surface of the pleated filter element (6).

2. The system for treating filter clogging of a pre-filter element in a fine treatment system as described in claim 1, characterized in that: The polymer dosing device includes a polymer dosing tank (91), a metering pump (92), and a mixing tank (93). The outlet of the polymer dosing tank (91) is connected to the inlet of the mixing tank (93) through the metering pump (92). The outlet of the mixing tank (93) is connected in series between the outlet of the cleaning water pump (3) and the inlet pipe (4). The polymer dosing tank (91) contains a high molecular polymer, which transforms the cleaning liquid into a viscoelastic fluid in the mixing tank (93). The unstable flow channel (7) is set on the inlet pipe (4) and located downstream of the polymer dosing device. It has a tapered section, a throat, and a diffusing section connected in sequence. Several passive vortex generators (8) are fixedly installed on the inner wall of the housing of the pre-filter (1). Each passive vortex generator (8) is an airfoil protruding from the inner wall of the housing. The airfoil extends along the axial direction of the folded filter element (6), and the flow-facing side of the airfoil faces the Z-shaped pleated opening of the folded filter element (6).

3. The system for treating filter cartridge clogging in a pre-filter of a fine treatment system as described in claim 2, characterized in that: The polymer is a non-ionic water-soluble polymer, with an addition concentration of 0.05%~0.2%. The cleaning solution contains an iron ion chelating agent. A monitoring sensor is installed on the return pipeline (5) to monitor the elastic modulus of the cleaning solution in real time. And iron ion concentration; a bypass discharge branch (10) is provided on the return liquid pipeline (5) and downstream of the monitoring sensor, and a bypass discharge valve (13) is provided on the bypass discharge branch (10); a clean water replacement branch (11) is also provided on the return liquid pipeline (5), and a clean water injection valve (12) is provided on the clean water replacement branch (11).

4. The system for treating filter cartridge clogging in a pre-filter of a fine treatment system as described in claim 3, characterized in that: The monitoring sensor, polymer dosing device, and bypass discharge valve (13) are electrically connected to a supplementary discharge control unit; the supplementary discharge control unit performs the following operations: when the elastic modulus When the concentration of iron ions is below the first preset threshold, the polymer dosing device is controlled to add non-ionic water-soluble polymers in batches; when the iron ion concentration is above the second preset threshold, the bypass discharge valve (13) is opened to discharge the aging cleaning solution; after cleaning, the clean water injection valve (12) is opened to inject clean water for replacement rinsing.

5. The system for treating filter cartridge clogging in a pre-filter of a fine treatment system as described in claim 4, characterized in that: The nonionic water-soluble polymer is polyethylene oxide; the iron ion chelating agent is one or more of citric acid and citrate; the first preset threshold is the initial elastic modulus after cleaning. 30%; the second preset threshold is an iron ion concentration of 50 ppm.

6. The system for treating filter cartridge clogging in a pre-filter of a fine treatment system as described in claim 5, characterized in that: It also includes a pulsation generator (14) and a cross-flow discharge branch (15). The pulsation generator (14) is connected in series on the inlet pipe (4) and located downstream of the unstable flow channel (7), so that the viscoelastic fluid entering the housing cavity of the pre-filter (1) has an axial velocity component that oscillates with time. The pulsation frequency of the pulsation generator (14) Configured to satisfy ,in The relaxation time of polyoxyethylene in a viscoelastic fluid; The pleats of the pleated filter element (6) gradually shrink from the outer circumference of the pleated filter element (6) towards the center of the pleated filter element (6), forming a gradually narrowing flow channel; one end of the through-flow discharge branch (15) is connected to the pipeline between the outlet of the central pipe (61) and the central pipe control valve through a tee, and the other end is connected to the return port of the cleaning water tank (2). A through-flow control valve is provided on the through-flow discharge branch (15).

7. The system for treating filter cartridge clogging in a pre-filter of a fine treatment system as described in claim 6, characterized in that: The compressed air injection device includes a compressed air source (16) and a compressed air injection pipe (17). One end of the compressed air injection pipe (17) is connected to the compressed air source (16), and the other end is connected to the pipeline between the outlet of the central pipe (61) and the flow control valve through a tee. The compressed air injection pipe (17) is equipped with a compressed air control valve. The supplementary discharge control unit is also configured to intermittently open the flow control valve and close the compressed air control valve during the cleaning process, so that some viscoelastic fluid passes through the pleated wall of the pleated filter element (6) from the housing cavity into the central pipe (61) and flows back through the flow discharge branch (15).

8. The system for treating filter cartridge clogging in a pre-filter of a fine treatment system as described in claim 1, characterized in that: One end of the inlet pipe (4) is connected to the outlet of the cleaning water pump (3), and the other end is connected to the shell-side inlet of the pre-filter (1); one end of the return pipe (5) is connected to the shell-side return port of the pre-filter (1), and the other end is connected to the return port of the cleaning water tank (2).

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