CN107265742A - A kind of embrane method bitter softening method based on magnetization preconditioning technique - Google Patents

Abstract

The invention discloses a membrane-based brackish water softening method based on magnetization pretreatment technology, wherein the brackish water enters an ultrasonic cleaning device through a feed pump, and a magnetic field system is arranged in the ultrasonic cleaning device, and the ultrasonic cleaning device is turned on at regular intervals to Impurities on the pipe wall and the surface of the magnetic treatment unit are regularly removed. After magnetization pretreatment and ultrasonic separation, the product water enters the self-cleaning filter through the booster pump for filtration, and the self-cleaning filter product water enters the nanofiltration membrane module through the high-pressure pump for further filtration. Filtration and separation, run to the set time or until the flux of nanofiltration membrane product water drops to the set value, reuse part of the nanofiltration product water to the nanofiltration membrane module for physical washing to remove loose pollution on the surface of the nanofiltration membrane things. The invention adopts ultrasonic-magnetization pretreatment and nanofiltration membrane hybrid coupling technology to realize high-efficiency softening of brackish water, shorten system shutdown time caused by membrane cleaning by 30%, and reduce operating costs.

Description

A Membrane Method for Softening Brackish Water Based on Magnetization Pretreatment Technology

technical field

The invention belongs to the technical field of water treatment, and in particular relates to a method for softening brackish water by membrane method based on magnetization pretreatment technology.

Background technique

In my country, brackish water is widely distributed. According to incomplete statistics, about 38 million people in my country drink brackish water. The excessive salts and impurities in it are very harmful to human body and seriously affect the quality of life and health. In addition, brackish water is also very harmful to industrial and agricultural production, affecting soil air permeability and water retention. Membrane technology is introduced into the desalination of brackish water, which can remove harmful substances to the greatest extent. However, the problem of membrane fouling seriously affects the separation effect of this technology, which limits the further development and application of membrane separation technology. Membrane fouling is due to the suspended matter or soluble matter in the filter material liquid being intercepted during the separation process and stagnant or deposited on the surface of the membrane and the inner wall of the pores, resulting in a decrease in the water production flux of the membrane and a smaller pore size, and finally makes the membrane Retention performance produces an irreversible decline. According to literature, membrane pollution is mainly divided into three categories: inorganic pollution, organic pollution and microbial pollution. The present invention is aimed at slowing down or eliminating inorganic pollution of nanofiltration membranes in the softening process of brackish water.

Inorganic pollution mainly refers to the precipitation of divalent cations such as Ca ²⁺ and Mg ²⁺ and divalent anions such as CO ₃ ²⁻ , SO ₄ ²⁻ on the nanofiltration membrane elements due to concentration polarization and high recovery rate. Pollution caused by salt scale such as CaCO ₃ and CaSO ₄ is the most common. Inorganic pollution usually results in fouling of the membrane surface, decreased permeate flux, and poor water quality. In order to slow down or avoid the fouling phenomenon on the NF membrane surface, many researchers add flocculants, coagulants, scale inhibitors and other chemicals to the feed in the pretreatment stage, by diluting the concentration of scaling ions in the feed, Ultimately reduce the concentration polarization and scaling pollution of the NF membrane surface. However, such methods not only need to add additional operation steps in the NF membrane separation system, but also eventually lead to the addition of new pollutants in the effluent. Using physical methods such as the simplest hydraulic flushing, the removal rate of membrane fouling is very low and the membrane flux recovery is very small, and the membrane will be re-fouled soon. However, when the strong acid cleaning method is used to remove alkaline inorganic scaling on the NF membrane surface, the membrane pore structure is destroyed and the operating life of the membrane is reduced. Magnetization pretreatment can effectively slow down the membrane fouling rate, prolong the cleaning cycle of the membrane, effectively improve the separation performance of the membrane, and increase economic benefits. In the field of membrane fouling mitigation for brackish water softening, there are few related patents based on magnetization pretreatment. The patent with the publication number CN102806017A discloses a magnetic separator and a method for controlling inorganic pollution of high-pressure membranes. The article mentions the membrane pretreatment method of magnetic separation technology. The disadvantage of this technology is that the feed water after magnetization pretreatment Loose scale is formed, which will be deposited on the tube wall or magnet, and new large particles may be generated in the product water, which will aggravate membrane surface pollution and increase the risk of subsequent membrane process operation.

Contents of the invention

The technical problem to be solved by the present invention is to provide a membrane-based brackish water softening method based on magnetization pretreatment technology. Ultrasonic-magnetization pretreatment and nanofiltration membrane hybrid coupling technology realize the efficient softening of brackish water, shorten the system downtime caused by membrane cleaning by 30%, thereby reducing operating costs. The main body and supporting equipment of the present invention are compact in structure and functional Complete, easy to operate and maintain.

In order to solve the above technical problems, the present invention adopts the following technical scheme, a membrane-based brackish water softening method based on magnetization pretreatment technology, which is characterized in that the specific steps are:

(1) Suction of brackish water into the stainless steel feed box;

(2) The brackish water enters the ultrasonic cleaning device through the feed pump, and a magnetic field system is installed in the ultrasonic cleaning device. The magnetic field system is composed of a plurality of magnetic processing units arranged oppositely along the axis. The circulating flow in the unit prolongs the fouling induction period and hinders or delays the formation of inorganic pollutants;

(3) Turn on the ultrasonic cleaning device regularly to remove impurities on the pipe wall and the surface of the magnetic processing unit, and the impurities are collected into the impurity storage container through the three-way valve;

(4) After magnetization pretreatment and ultrasonic separation, the product water enters the self-cleaning filter through the booster pump for filtration, and the fine substances after multi-media filtration are filtered out to ensure the water quality filtration accuracy and protect the nanofiltration membrane module from large damage to particulate matter;

(5) The water produced by the self-cleaning filter enters the nanofiltration membrane module through the high-pressure pump for filtration and separation, and the nanofiltration produced water enters the produced water storage tank;

(6) When running to the set time or running until the flux of nanofiltration membrane product water drops to the set value, reuse part of the nanofiltration product water to the nanofiltration membrane module for physical washing to remove loose pollution on the surface of the nanofiltration membrane things.

Further preferably, the brackish water is the brackish water at the junction of the North China piedmont alluvial plain and the central alluvial plain, belongs to the bicarbonate-sulfate type, and has a total solid salt content of 500-4000 mg·L ⁻¹ , The pH value of the brackish water is 6.80-9.50, and the mass concentrations of Ca ²⁺ , Mg ²⁺ , SO ₄ ²⁻ and HCO ₃ ⁻ are 10-150mg·L ⁻¹ , 20-500mg·L ⁻¹ , 30 -1000mg·L ⁻¹ and 5-350mg·L ⁻¹ .

Further preferably, the magnetic material in the magnetic treatment unit is selected from permanent magnetic material, soft magnetic material or functional magnetic material according to the different water quality and convenience of treatment, and the magnetic yoke adopts soft iron, A3 steel and soft magnetic alloy with higher magnetic permeability Or ferrite material, the gap is filled with stainless steel wool or magnetic gathering medium according to different concentrations of water inflow, the steel wool diameter is 30-50μm, the filling rate is 10%, the average magnetic field strength of the entire magnetic field system is 0.34-4.86T, The soft magnetic material used in the magnetic gathering medium is mesh or filamentary, and the filling rate is 2%-15%. The strength and potential are significantly reduced, and the dense pollution layer before magnetization forms loose pollution after magnetization.

Further preferably, the ultrasonic cleaning device is turned on after 15-24 hours of magnetization pretreatment by the magnetic field system to remove impurities on the tube wall and the surface of the magnetic processing unit, and the frequency of the ultrasonic wave in the ultrasonic cleaning device is ≧50 Hz.

Further preferably, the water loss of the self-cleaning filter is 0.08%-0.62% of the filtered water, the backwashing flow rate is 0.5-9m ³ ·h ⁻¹ , and the backwashing time is 7-45s.

Further preferably, the nanofiltration membrane module adopts one-stage or multi-stage operation, and multiple pressure vessels are connected in parallel according to the water production scale, and 2-6 nanofiltration membrane elements are connected in series in each pressure vessel, and the nanofiltration membrane adopts Roll or hollow fiber composite membrane, the nanofiltration membrane can effectively soften brackish water, and the rejection rates for Ca ²⁺ , Mg ²⁺ , CO ₃ ²⁻ and SO ₄ ²⁻ are ≧40%, ≧45 %, ≧50% and ≧80%.

Further preferably, the operating period of the nanofiltration membrane module is 6-48h, the low-pressure physical flushing time is 5-20min, the operating pressure during flushing is 0-0.20MPa, and the tangential flow velocity on the membrane surface is 0.35-0.76m·s ^{− 1.} Since the pollutants formed after magnetization are soft and loose, they can be removed with concentrated water during the physical flushing process. After flushing, the membrane flux recovery rate can reach more than 85%, effectively removing inorganic pollution.

Further preferably, after 200-1200 hours of operation of the permeated water after magnetization pretreatment and ultrasonic separation, the flux of membrane permeate water decreases by nearly 10%, while permeate water without magnetization pretreatment and ultrasonic separation passes through 100 hours. After -500h of operation, the flux of membrane produced water decreased by nearly 10%, so magnetization pretreatment and ultrasonic separation can effectively reduce inorganic pollution.

Compared with the prior art, the present invention has the following beneficial effects: for the pretreatment process of nanofiltration membrane brackish water softening, the magnetization technology is used to effectively magnetize the influent water body, thereby reducing its own surface tension and reducing the formation of inorganic substances. The microscopic process of nucleation and crystallization is easy to form a loose pollution layer, and the inorganic pollution can be effectively removed by low-pressure physical washing. Using ultrasonic hybrid coupling technology, the impurities deposited on the magnetic field are regularly removed from the magnetic field, and the impurities are collected into the impurity storage container through the three-way valve. The equipment of the present invention has simple structure, high recovery rate of produced water, small footprint, obvious removal effect on inorganic pollutants, no secondary pollution, good effluent quality, safety and reliability, and can effectively prolong nanofiltration membrane cleaning cycle and Reduce the cost of softened water, reduce the number of chemical cleaning and damage to nanofiltration membrane elements, this technology has considerable economic and environmental benefits.

Description of drawings

Fig. 1 is a process flow diagram of the present invention.

In the figure: 1. Stainless steel feeding box, 2. Agitator, 3. Feed water pump, 4. Water inlet valve, 5. Magnetic field system, 6. Ultrasonic cleaning device, 7. Three-way valve, 8. Impurity storage container, 9 . Flow meter, 10. Booster pump, 11. Self-cleaning filter, 12. High pressure pump, 13. Bypass valve, 14. Pressure gauge, 15. Nanofiltration membrane module, 16. Produced water storage tank.

detailed description

The above-mentioned contents of the present invention are described in further detail below through the embodiments, but this should not be interpreted as the scope of the above-mentioned themes of the present invention being limited to the following embodiments, and all technologies realized based on the above-mentioned contents of the present invention all belong to the scope of the present invention.

With reference to accompanying drawing 1, the brackish water softening device that the magnetic field pretreatment of the present invention slows down nanofiltration membrane fouling comprises stainless steel feeding box 1, agitator 2, water supply pump 3, water inlet valve 4, magnetic field system 5, ultrasonic cleaning device 6. Three-way valve 7, impurity storage container 8, flow meter 9, booster pump 10, self-cleaning filter device 11, high-pressure pump 12, bypass valve 13, pressure gauge 14, nanofiltration membrane module 15 and water production and liquid storage Box 16 and agitator 2 are built in stainless steel feeding box 1, the outlet of stainless steel feeding box 1 is connected to the inlet of feed water pump 3, the outlet of feed water pump 3 is connected to the inlet of water inlet valve 4, and the outlet of water inlet valve 4 It is connected to the inlet of the ultrasonic cleaning device 6, the magnetic field system 5 is built in the ultrasonic cleaning device 6, the outlet of the ultrasonic cleaning device 6 is connected to the inlet of the three-way valve 7, and the outlet of the three-way valve 7 is respectively connected to the impurity storage container 8 and the flow meter 9, the outlet of the flow meter 9 is connected to the inlet of the booster pump 10, the outlet of the booster pump 10 is connected to the inlet of the self-cleaning filter 11, the outlet of the self-cleaning filter 11 is connected to the inlet of the high-pressure pump 12, The outlet of the high-pressure pump 12 is connected to the inlet of the bypass valve 13, the outlet of the bypass valve 13 is connected to the inlet of the nanofiltration membrane module 15 after passing through the pressure gauge 14, and the outlet of the nanofiltration membrane module 15 is connected to the outlet of the produced water storage tank 16. import connection.

Example 1

The bicarbonate-sulphate type brackish water sample at the junction of the North China piedmont alluvial plain and the central alluvial plain was drawn into the stainless steel inlet tank, and the TDS and pH values of the brackish water were 1000 mg·L ^{− 1} and 6.80, the concentrations of Ca ²⁺ , Mg ²⁺ , SO ₄ ²⁻ , and HCO ₃ ⁻ were 70mg·L ⁻¹ , 40mg·L ⁻¹ , 106mg·L ⁻¹ and 112mg·L ⁻¹ , respectively. The 5 groups of magnetic processing units corresponding to the upper and lower sides are arranged correspondingly along the axis. The magnetic material of the magnetic processing unit is permanent magnet material. The yoke is made of soft iron, A3 steel or soft magnetic alloy with relatively high magnetic permeability, and the gap is filled with stainless steel. The diameter of wool and steel wool is 30 μm, the filling rate is 2%, the average magnetic field strength of the entire magnetic field area is 0.86T, so that the incoming water circulates in the upper and lower magnetic processing units, and the ultrasonic cleaning device (frequency 80Hz) starts to work after 15 hours of operation , to remove part of the loose floc deposited on the pipe wall and the magnetic treatment unit. The produced water after magnetization pretreatment and ultrasonic separation enters the self ^- cleaning filter through the booster pump, and the water loss accounts for only ^0.08 % of the filtered water. The flushing water volume is 20L. Then the water inlet nanofiltration membrane module adopts multiple pressure vessels in parallel according to the water production scale, and each pressure vessel adopts two nanofiltration membranes in series, and the nanofiltration membrane adopts a roll-type composite membrane of anti-pollution material with excellent performance. By comparing the LSI index before and after the concentrated water magnetization pretreatment to predict the fouling trend of CaCO ₃ in the concentrated aqueous solution of the membrane to judge the effect of magnetization, it was found that the LSI value in the concentrated aqueous solution of the membrane after the magnetization pretreatment decreased significantly and was less than zero, indicating that CaCO ₃ Scaling phenomenon has been reduced. The nanofiltration membrane can effectively soften brackish water, and the rejection rates of Ca ²⁺ , Mg ²⁺ , CO ₃ ²⁻ and SO ₄ ²⁻ ions are 52%, 78%, 80% and 98%, respectively. The operating period of the nanofiltration membrane module is 6h, the pressure is adjusted to 0.15-0.60MPa, the tangential flow velocity on the membrane surface is 0.60m·s ⁻¹ , and the low-pressure backwashing time is 20min. Since the pollutants formed after magnetization pretreatment are soft and loose, they can be removed with the concentrated water during the physical flushing process, and the membrane flux recovery rate after flushing can reach 96%, effectively removing inorganic pollution. Without magnetization pretreatment and ultrasonic separation, the membrane flux decreased by nearly 10% after 287 hours of operation, but it dropped to 90% after 624 hours of operation with magnetization pretreatment and ultrasonic separation.

Example 2

The bicarbonate-sulphate type brackish water sample at the junction of the North China piedmont alluvial plain and the central alluvial plain was drawn into the stainless steel water inlet tank, and the TDS and pH values of the brackish water were 4000mg·L ^{− 1} and 9.50, the concentrations of Ca ²⁺ , Mg ²⁺ , SO ₄ ²⁻ , and HCO ₃ ⁻ were 150mg·L ⁻¹ , 80mg·L ⁻¹ , 300mg·L ⁻¹ and 350mg·L ⁻¹ , respectively. The 10 groups of magnetic processing units corresponding to the upper and lower sides are arranged correspondingly along the axis. The magnetic processing unit can be made of soft magnetic materials. This type of magnetic material has high magnetic permeability and magnetic induction intensity. The loss should be small. The yoke can be made of an alloy with a relatively high magnetic permeability, and the gap is filled with filamentous or mesh-like magnetic gathering material or steel wool with a diameter of 10 μm, the filling rate is 10%, and the average magnetic field strength of the entire magnetic field area is 0.34T , so that the incoming water circulates in the upper and lower magnetic treatment units. After 24 hours of operation, the ultrasonic cleaning device (frequency 80Hz) starts to work to remove part of the loose flocs deposited on the pipe wall and the magnetic treatment unit. The produced water after magnetization pretreatment and ultrasonic separation enters the self ^- cleaning filter through the booster pump, and the water loss accounts for only ^0.65 % of the filtered water. The flushing water volume is 40L. Then the water inlet nanofiltration membrane module adopts multiple pressure vessels in parallel according to the water production scale, and each pressure vessel adopts 6 nanofiltration membranes in series, and the nanofiltration membrane adopts hollow fiber composite membrane with excellent performance and anti-pollution material. By comparing the LSI index before and after magnetization of the concentrated water to predict the scaling trend of CaCO ₃ in the concentrated aqueous solution of the membrane to judge the effect of magnetization, it was found that the LSI value in the concentrated aqueous solution of the membrane after magnetization pretreatment was significantly reduced, indicating that the scaling phenomenon of CaCO ₃ was reduced. lighten. The nanofiltration membrane can effectively remove softened brackish water, and the rejection rates of Ca ²⁺ , Mg ²⁺ , CO ₃ ²⁻ and SO ₄ ²⁻ ions are 48%, 72%, 81% and 96%, respectively. The operating period of the nanofiltration membrane element is 48h, the pressure is adjusted between 0.20-0.80MPa, the tangential flow velocity on the membrane surface is 0.44m·s ⁻¹ and the low-pressure backwashing time is 15min. Since the pollutants formed after magnetization are soft and loose, they can be removed with concentrated water during the physical flushing process, and the membrane flux recovery rate after flushing is as high as 92%, effectively removing inorganic pollution. Before magnetization pretreatment and ultrasonic separation, the membrane flux decreased by nearly 10% after 100 hours of operation, but after magnetization pretreatment and ultrasonic separation, the membrane flux decreased to 90% after 256 hours of operation.

The above embodiments have described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What are described in the above embodiments and description are only to illustrate the principles of the present invention. Without departing from the scope of the principle of the present invention, there will be various changes and improvements in the present invention, and these changes and improvements all fall within the protection scope of the present invention.

Claims (8)

1. A membrane process brackish water softening method based on magnetization pretreatment technology, characterized in that the specific steps are: (1) Suction of brackish water into the stainless steel feed box; (2) The brackish water enters the ultrasonic cleaning device through the feed pump, and a magnetic field system is installed in the ultrasonic cleaning device. The magnetic field system is composed of a plurality of magnetic processing units arranged oppositely along the axis. The circulating flow in the unit prolongs the fouling induction period and hinders or delays the formation of inorganic pollutants; (3) Turn on the ultrasonic cleaning device regularly to remove impurities on the pipe wall and the surface of the magnetic processing unit, and the impurities are collected into the impurity storage container through the three-way valve; (4) After magnetization pretreatment and ultrasonic separation, the product water enters the self-cleaning filter through the booster pump for filtration, and the fine substances after multi-media filtration are filtered out to ensure the water quality filtration accuracy and protect the nanofiltration membrane module from large damage to particulate matter; (5) The water produced by the self-cleaning filter enters the nanofiltration membrane module through the high-pressure pump for filtration and separation, and the nanofiltration produced water enters the produced water storage tank; (6) When running to the set time or running until the flux of nanofiltration membrane product water drops to the set value, reuse part of the nanofiltration product water to the nanofiltration membrane module for physical washing to remove loose pollution on the surface of the nanofiltration membrane things. 2. The membrane-based brackish water softening method based on magnetization pretreatment technology according to claim 1, characterized in that: the brackish water is the brackish water at the junction of the North China Piedmont alluvial plain and the central alluvial plain, Belonging to bicarbonate-sulfate type, the total solid salt content is 500-4000mg·L ⁻¹ , the pH value of the brackish water is 6.80-9.50, Ca ²⁺ , Mg ²⁺ , SO ₄ ²⁻ and HCO The mass concentrations of ₃ ⁻ are 10-150mg·L ⁻¹ , 20-500mg·L ⁻¹ , 30-1000mg·L ⁻¹ and 5-350mg·L ⁻¹ , respectively. 3. The membrane method for softening brackish water based on magnetization pretreatment technology according to claim 1, characterized in that: in the magnetic treatment unit, the magnetic material is selected from permanent magnetic material, soft water according to the different water quality and convenience of treatment. Magnetic material or functional magnetic material. The yoke is made of soft iron, A3 steel, soft magnetic alloy or ferrite material with high magnetic permeability. The gap is filled with stainless steel wool or magnetic gathering medium according to different concentrations of water inflow. The diameter of steel wool 30-50μm, the filling rate is 10%, the average magnetic field strength of the whole magnetic field system is 0.34-4.86T, the soft magnetic material used in the magnetic gathering medium is mesh or filament, the filling rate is 2%-15%, after magnetization The surface tension, viscosity and electrical conductivity of the produced water all decreased, and the scaling strength and potential of inorganic pollution in the influent components decreased significantly. The dense pollution layer before magnetization formed loose pollution after magnetization. 4. The brackish water softening method based on the membrane method of magnetization pretreatment technology according to claim 1, characterized in that: the ultrasonic cleaning device is turned on after 15-24 hours of magnetization pretreatment of the magnetic field system to remove the pipe wall and magnetic treatment For impurities on the surface of the unit, the frequency of the ultrasonic wave in the ultrasonic cleaning device is ≧50Hz. 5. The membrane-based brackish water softening method based on magnetization pretreatment technology according to claim 1, characterized in that: the water loss of the self-cleaning filter is 0.08%-0.62% of the filtered water, and the backwash flow rate is 0.5-9m ³ ·h ⁻¹ , backwashing time is 7-45s. 6. The membrane-based brackish water softening method based on magnetization pretreatment technology according to claim 1, characterized in that: the nanofiltration membrane module adopts one-stage or multi-stage operation, and adopts multiple pressures according to the water production scale The vessels are connected in parallel, and 2-6 nanofiltration membrane elements are used in series in each pressure vessel. The nanofiltration membrane adopts a roll-type or hollow fiber composite membrane. The nanofiltration membrane can effectively soften brackish water and treat Ca ²⁺ , The rejection rates of Mg ²⁺ , CO ₃ ²⁻ and SO ₄ ²⁻ are ≧40%, ≧45%, ≧50% and ≧80%, respectively. 7. The membrane-based brackish water softening method based on magnetization pretreatment technology according to claim 1, characterized in that: the operating cycle of the nanofiltration membrane module is 6-48h, and the low-pressure physical flushing time is 5-20min , the operating pressure during flushing is 0-0.20MPa, and the tangential flow velocity on the membrane surface is 0.35-0.76m·s ⁻¹ . Since the pollutants formed after magnetization are soft and loose, they can be discharged with the concentrated water during the physical flushing process. After flushing The membrane flux recovery rate can reach more than 85%, effectively removing inorganic pollution. 8. The membrane-based brackish water softening method based on magnetization pretreatment technology according to claim 1, characterized in that: after 200-1200 hours of operation of the magnetization pretreatment and ultrasonic separation, the membrane produces The decrease of water flux is close to 10%, but after 100-500 hours of operation of the permeated water without magnetization pretreatment and ultrasonic separation, the decrease of membrane permeated water flux is close to 10%, so magnetization pretreatment and ultrasonic separation can effectively Reduce inorganic pollution.