CN116216849A - Double-film process method for sea water desalination plant - Google Patents
Double-film process method for sea water desalination plant Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 65
- 230000008569 process Effects 0.000 title claims abstract description 26
- 238000010612 desalination reaction Methods 0.000 title claims abstract description 14
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- 238000000108 ultra-filtration Methods 0.000 claims abstract description 116
- 238000004140 cleaning Methods 0.000 claims abstract description 51
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- 239000003344 environmental pollutant Substances 0.000 claims abstract description 25
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- 239000002033 PVDF binder Substances 0.000 claims abstract description 18
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- 238000002360 preparation method Methods 0.000 claims abstract description 11
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- XNWFRZJHXBZDAG-UHFFFAOYSA-N 2-METHOXYETHANOL Chemical compound COCCO XNWFRZJHXBZDAG-UHFFFAOYSA-N 0.000 claims description 6
- FXHOOIRPVKKKFG-UHFFFAOYSA-N N,N-Dimethylacetamide Chemical compound CN(C)C(C)=O FXHOOIRPVKKKFG-UHFFFAOYSA-N 0.000 claims description 6
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Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/444—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by ultrafiltration or microfiltration
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
- B01D65/02—Membrane cleaning or sterilisation ; Membrane regeneration
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
- B01D67/0011—Casting solutions therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
- B01D67/0013—Casting processes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/08—Hollow fibre membranes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/30—Polyalkenyl halides
- B01D71/32—Polyalkenyl halides containing fluorine atoms
- B01D71/34—Polyvinylidene fluoride
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
- B01D2321/02—Forward flushing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
- B01D2321/04—Backflushing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
- B01D2321/16—Use of chemical agents
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
- B01D2321/16—Use of chemical agents
- B01D2321/162—Use of acids
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
- B01D2321/16—Use of chemical agents
- B01D2321/164—Use of bases
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/08—Seawater, e.g. for desalination
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A20/00—Water conservation; Efficient water supply; Efficient water use
- Y02A20/124—Water desalination
- Y02A20/131—Reverse-osmosis
Abstract
The invention discloses a double-membrane process method for a sea water desalination plant, which comprises the steps of ultrafiltration membrane material selection, ultrafiltration membrane preparation, ultrafiltration membrane component structure, water temperature adjustment, operation pressure adjustment, ultrafiltration membrane component operation, ultrafiltration membrane component cleaning and ultrafiltration membrane component storage, wherein the ultrafiltration membrane material selection is to select polyvinylidene fluoride as a raw material, and the polyvinylidene fluoride has the characteristics of strong oxidation resistance, good chemical stability, good flexibility and strong ductility, and the polyvinylidene fluoride also has the characteristics of pollution resistance and easy cleaning; the ultrafiltration membrane preparation comprises a non-solvent induced phase separation method. The invention utilizes the double-membrane process, has small occupied area, high filtering precision, stable effluent quality, higher pollutant removal rate, strong oxidation resistance of the ultrafiltration membrane, good chemical stability, good flexibility, strong ductility, pollution resistance and easy cleaning, and can remove bacteria.
Description
Technical Field
The invention relates to the technical field of double-membrane processes, in particular to a double-membrane process method for a sea water desalination plant.
Background
The membrane is a high-efficiency filtering unit adopting a physical method, namely a thin condensed phase is arranged in one fluid phase or between two fluid phases, the fluid phase is divided into two parts which are not communicated with each other, mass transfer effect can be generated between the two parts, and the membrane is divided into micro filtration, ultrafiltration, nanofiltration and reverse osmosis membrane according to the trapped pore size.
The traditional filtering technology has large occupied area, low filtering precision, incapability of removing bacteria, unstable effluent quality and low pollutant removal rate, and the defects of the traditional technology need to be overcome.
Disclosure of Invention
The invention aims to solve the defects of the prior art, such as large occupied area, low filtering precision, incapability of removing bacteria, unstable effluent quality and low pollutant removal rate, and provides a double-membrane process method for a sea water desalination plant based on the problems.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the double-membrane process method for the sea water desalination plant comprises the steps of ultrafiltration membrane material selection, ultrafiltration membrane preparation, ultrafiltration membrane component structure, water temperature adjustment, operation pressure adjustment, ultrafiltration membrane component operation, ultrafiltration membrane component cleaning and ultrafiltration membrane component storage, wherein the ultrafiltration membrane material selection is to select polyvinylidene fluoride as a raw material, and the polyvinylidene fluoride has the characteristics of strong oxidation resistance, good chemical stability, good flexibility and strong ductility, and also has the characteristics of pollution resistance and easiness in cleaning;
the ultrafiltration membrane preparation comprises a non-solvent induced phase separation method, wherein ethylene glycol monomethyl ether is used as an additive, N-dimethylacetamide is used as a solvent, polyvinylidene fluoride and ethylene glycol monomethyl ether are added into N-dimethylacetamide, stirring and dissolving are carried out to form a homogeneous solution, water is slowly added into the homogeneous solution, the solvent is extracted to form a two-phase structure which takes polyvinylidene fluoride as a continuous phase and water as a disperse phase, and the solvent and the additive are removed to obtain a hollow fiber membrane with a certain pore structure;
the ultrafiltration membrane preparation also comprises a thermally induced phase separation method, n-butanol is used as a diluent, polyvinylidene fluoride and n-butanol are stirred and mixed and subjected to high-temperature treatment, a homogeneous phase solution is formed at high temperature, the mixture solution is prepared into hollow fibers, the solution is subjected to phase separation by cooling, water is used as a solvent for extraction and removal of n-butanol to obtain the hollow fiber membrane, the ultrafiltration membrane is obtained by adopting the thermally induced phase separation method on the basis of the non-solvent induced phase separation method, and a compact layer made of the same material is compounded on the surface of the hollow fiber membrane, so that the ultrafiltration membrane has the advantages of the two methods.
Preferably, the ultrafiltration membrane comprises a separation skin layer with a very thin and compact surface and a porous supporting layer below the separation skin layer, wherein the compact skin layer is a functional layer and has the functions of filtering and trapping pollutants.
Preferably, the ultrafiltration membrane component structure adopts an external pressure type component structure, the specific surface area of the ultrafiltration membrane is larger than that of the internal pressure membrane, the water yield is larger under the same condition, the formed component flow channel is wide and smooth, the pollution is difficult to block, the impact resistance is stronger, the pollution is attached to the outer wall of the membrane, the reverse flushing is easy to fall off, the reverse flushing is easy to discharge, the cleaning is more convenient, the gas-water double-cleaning can be adopted, the consumption of self-consumed water is reduced, and the water yield is improved.
Preferably, the water temperature adjustment comprises proper water temperature control, wherein the water temperature is one of important indexes affecting the filtration performance of the ultrafiltration membrane, the water temperature is increased, the water viscosity is reduced, the water yield is increased, and conversely, the water temperature is reduced, the water viscosity is increased, the water yield is reduced, and the flux of the ultrafiltration membrane is changed by about 2% when the water temperature is changed by 1 ℃.
Preferably, the operating pressure is adjusted to be the water inlet pressure, the concentrated water pressure and the water producing pressure of the membrane system, the maximum water inlet pressure allowed by the ultrafiltration membrane component structure is 300kPa, the concentrated water pressure and the water producing pressure are simultaneously concerned in the running process of the system, and the maximum transmembrane pressure difference (TMP) allowed by the ultrafiltration membrane is 200kPa.
Preferably, the operation of the ultrafiltration membrane component comprises a cross-flow filtration mode and a dead-end filtration mode, wherein part of the inflow water is changed into produced water through the surface of the ultrafiltration membrane in the cross-flow filtration mode, and the other part of the inflow water is discharged into concentrated water with impurities.
Preferably, the cleaning ultrafiltration membrane component comprises physical cleaning, chemical cleaning and maintenance cleaning, the physical cleaning comprises forward cleaning and backward cleaning, the forward cleaning has no filtering effect, when clear water passes through the outer side of the fiber at a certain flow rate, pollutants on the outer side of the ultrafiltration membrane can be washed out, the backward cleaning and the filtering process are reversed, the clear water is enabled to permeate from the raw water side to the raw material liquid side under a certain pressure, and the pollutants on the side of the feed liquid and the blocking matters permeated into the micropores are washed out.
Preferably, the physical cleaning further comprises soaking and air and water backwashing, the soaking comprises soaking the ultrafiltration membrane component by using clear water or liquid medicine, the soaking can loosen pollutants, soaking for a certain time is often an effective method for removing the pollutants, the air and water backwashing comprises introducing a certain amount of compressed air from a water inlet when the ultrafiltration membrane component is backwashed, and the hollow fiber membranes can swing under the action of ascending air flow to realize mutual friction collision, so that the pollutants attached to the surfaces of the hollow fiber membranes are peeled off and are discharged from a sewage outlet.
Preferably, the storage mode of the ultrafiltration membrane component after use comprises stopping the system for 1-7 days, filling 10-100 ppm NaClO solution into the ultrafiltration membrane component for 7-30 days, filling 1% NaHSO3 solution for more than 30 days, and filling 1% NaHSO3 solution, wherein periodic replacement is needed to ensure that the pH value of the internal solution is more than 3.
Compared with the prior art, the invention has the beneficial effects that:
1. the double-membrane process is utilized, the occupied area is small, the filtering precision is high, bacteria can be removed, the effluent quality is stable, and the pollutant removal rate is high;
2. the ultrafiltration membrane has the advantages of strong oxidation resistance, good chemical stability, good flexibility, strong ductility, pollution resistance and easy cleaning;
3. the ultrafiltration membrane product adopts an external pressure type component structure, has the specific surface area of the ultrafiltration membrane larger than that of the internal pressure membrane, has larger water yield under the same condition, has wide and smooth flow passage, is difficult to block, has stronger impact resistance, has dirt attached to the outer wall of the membrane, is easy to fall off after back flushing, is easy to discharge, can adopt gas-water double-washing, reduces the consumption of self-consumed water and improves the water yield.
Drawings
FIG. 1 is a block diagram of the operation mode of an ultrafiltration membrane component in a double-membrane process method of a sea water desalination plant;
fig. 2 is a schematic block diagram of an ultrafiltration membrane cleaning module in a double-membrane process method of a sea water desalination plant.
Description of the embodiments
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments.
Referring to fig. 1-2, a double-membrane process method for a sea water desalination plant comprises ultrafiltration membrane material selection, ultrafiltration membrane preparation, ultrafiltration membrane component structure adjustment, water temperature adjustment, operation pressure adjustment, ultrafiltration membrane component operation, ultrafiltration membrane component cleaning and ultrafiltration membrane component storage, wherein the ultrafiltration membrane material selection is to select polyvinylidene fluoride as a raw material, and the polyvinylidene fluoride has the characteristics of strong oxidation resistance, good chemical stability, good flexibility and strong ductility, and the polyvinylidene fluoride also has the characteristics of pollution resistance and easy cleaning.
The preparation of the ultrafiltration membrane comprises a non-solvent induced phase separation method, wherein ethylene glycol monomethyl ether is used as an additive, N-dimethylacetamide is used as a solvent, polyvinylidene fluoride and ethylene glycol monomethyl ether are added into N-dimethylacetamide, stirring and dissolving are carried out to form a homogeneous solution, water is slowly added into the homogeneous solution, the solvent is extracted, and a two-phase structure with polyvinylidene fluoride as a continuous phase and water as a disperse phase is formed, and the solvent and the additive are removed to obtain the hollow fiber membrane with a certain pore structure.
The preparation of ultrafiltration membrane also comprises a thermally induced phase separation method, n-butanol is used as a diluent, polyvinylidene fluoride and n-butanol are stirred and mixed and are subjected to high-temperature treatment, homogeneous phase solution is formed at high temperature, the mixture solution is prepared into hollow fibers, the solution is subjected to phase separation by cooling, water is used as solvent for extraction and removal of n-butanol to obtain the hollow fiber membrane, the ultrafiltration membrane is obtained by adopting the thermally induced phase separation method on the basis of the non-solvent induced phase separation method, and a compact layer made of the same material is compounded on the surface of the hollow fiber membrane, so that the ultrafiltration membrane has the advantages of the two methods.
The ultrafiltration membrane comprises a separation skin layer with a very thin and compact surface and a porous supporting layer below the separation skin layer, wherein the compact skin layer is a functional layer, has the functions of filtering and intercepting pollutants, and the factors influencing the performance of the ultrafiltration membrane mainly comprise an ultrafiltration membrane material, an ultrafiltration membrane component structure, temperature, operation pressure, water inlet turbidity and the like, the ultrafiltration membrane component structure adopts an external pressure type component structure, the specific surface area of the ultrafiltration membrane is larger than that of an internal pressure membrane, the water yield is larger under the same condition, the formed component flow channel is wide and smooth, the pollution is difficult to block, the impact resistance is stronger, the pollutants are attached to the outer wall of the membrane, the reverse flushing is easy to drop, the reverse flushing is easy to discharge, the cleaning is more convenient, the air-water double-flushing can be adopted, the consumption of the self-consumption water is reduced, and the water yield is improved.
The water temperature is controlled to be proper, the water temperature is one of important indexes affecting the filtering performance of the ultrafiltration membrane, the water temperature is increased, the water viscosity is reduced, the water yield is increased, and conversely, the water temperature is reduced, the water viscosity is increased, the water yield is reduced, and the flux of the ultrafiltration membrane is changed by about 2 percent when the water temperature is changed by 1 ℃.
The operation pressure is adjusted to be the water inlet pressure, the concentrated water pressure and the water production pressure of the ultrafiltration membrane system, the maximum water inlet pressure allowed by the ultrafiltration membrane component structure is 300kPa, the concentrated water pressure and the water production pressure are simultaneously concerned in the operation process of the system, the maximum transmembrane pressure difference (TMP) allowed by the ultrafiltration membrane is 200kPa, the water inlet quality is one of important factors influencing the operation stability of the ultrafiltration membrane system, when the water inlet quality is better, the pollution rate of the ultrafiltration membrane is lower, the cleaning period is longer, the blocking of the ultrafiltration membrane is easier to be caused when the water inlet quality is worse, and the cleaning period of the ultrafiltration membrane is more frequent.
The operation of the ultrafiltration membrane component comprises a cross-flow filtration mode and a dead-end filtration mode, in the cross-flow filtration mode, part of water is permeated through the surface of the ultrafiltration membrane to form produced water, the other part of water is carried with impurities to be discharged to form concentrated water, the dead-end filtration energy consumption is low, but the pollution speed on the surface of the ultrafiltration membrane is higher, the operation mode of dead-end filtration can be adopted when the quality of raw water is better, the energy consumption is higher because the concentrated water is required to be refluxed or discharged in the cross-flow filtration, the operation mode of cross-flow filtration can be adopted when the quality of raw water is worse and the content of suspended matters is higher, the pollution on the surface of the ultrafiltration membrane can be effectively reduced, and longer working time is maintained.
When the ultrafiltration membrane system performs filtration work, colloid, suspended matters, macromolecular organic matters and other impurities in the inlet water can be trapped on the surface of the ultrafiltration membrane, as the thickness of an impurity layer on the surface of the ultrafiltration membrane is increased along with the time, the flow passing resistance is increased, the transmembrane pressure difference is increased along with the increase, when the transmembrane pressure difference is increased to a certain degree, the ultrafiltration membrane is required to be cleaned, the excessive deposition of the pollutants on the ultrafiltration membrane is prevented, the normal water production capacity of membrane wires is maintained, and the membrane surface can be subjected to various pollution of different degrees in the material liquid filtering process, so that the ultrafiltration membrane is required to be cleaned.
The method comprises the steps of cleaning an ultrafiltration membrane component, wherein the physical cleaning comprises forward cleaning and backwashing, the forward cleaning has no filtering effect, residual materials in the component are removed by clear water, when clear water passes through the outer side of fibers at a certain flow rate, pollutants on the outer side of the ultrafiltration membrane can be washed out, at the moment, a concentrate valve is fully opened, a water producing valve is fully closed, the cleaning time is determined according to the situation, the backwashing and the filtering process are reversed, the clear water is enabled to permeate from the raw water producing side to the raw material liquid side under a certain pressure, the pollutants on the feed liquid side and the blocking matters permeated into micropores are washed out, and in the actual operation, the backwashing frequency and the backwashing strength can be determined through monitoring parameters such as transmembrane pressure difference, accumulated working time, membrane flux and the like.
The physical cleaning also comprises soaking, soaking and air and water backwashing, wherein the soaking comprises soaking the ultrafiltration membrane component by using clear water or liquid medicine, the soaking can loosen pollutants, soaking for a certain time is often an effective method for removing the pollutants, the air and water backwashing comprises introducing a certain amount of compressed air from a water inlet when the ultrafiltration membrane component is backwashed, and the hollow fiber membranes can swing under the action of ascending air flow to realize mutual friction collision, so that the pollutants attached to the surfaces of the hollow fiber membranes are peeled off and fall off, and are discharged from a sewage outlet.
In most cases, a physical cleaning method can be used to achieve a better decontamination effect on the hollow fiber membrane, if the physical cleaning is not ideal, chemical cleaning is needed, chemical cleaning is generally carried out for 30-90 days for one time, the chemical cleaning adopts common water treatment agents with excellent sterilization performance, such as sodium hypochlorite or chlorine dioxide, and the like to carry out systematic sterilization treatment, adopts sodium hypochlorite or sodium hydroxide solution to remove organic matter pollution, adopts acid or EDTA sodium salt solution to remove inorganic salt scaling and other pollution, so that the membrane flux is recovered, and the chemical cleaning comprises the following steps:
s1: alkali cleaning: circulating sodium hydroxide (pH=12) solution for 20 min at low pressure (less than 0.05 MPa) in the membrane system, soaking for 20-40 min, washing with water to neutrality, and preparing after solid alkali must be fully dissolved;
s2: sodium hypochlorite cleaning: using: cleaning for 40-60 min with 300-3000 ppm sodium hypochlorite aqueous solution, wherein the cleaning agent is suitable for microbial pollution, and the common industrial sodium hypochlorite is 10% of available chlorine;
s3: dilute acid cleaning: the cleaning agent is cleaned and soaked for 40 to 60 minutes by hydrogen chloride solution (pH=2), and the cleaning agent is applicable to inorganic pollution, such as: the high hardness water quality is generally calculated by 30% of the concentration of the hydrogen chloride product, oxalic acid (0.3%), citric acid (1% -2%), nitric acid (pH=2) and the like can be used for cleaning, and disodium salt and tetrasodium salt can be adopted as EDTA sodium salt, and the concentration is generally 0.5% -2.0%.
The basic process of maintenance cleaning is similar to chemical cleaning, but the cleaning process is shorter, and the concentration of the chemical cleaning agent is lower than that of chemical cleaning, and the maintenance cleaning is carried out once in 1-3 days.
The storage method of the ultrafiltration membrane module, which is not used, comprises the following steps: the membrane is placed in a shade place, direct sunlight is avoided, ultraviolet irradiation (the direct sunlight and the ultraviolet irradiation can cause irreparable damage to a membrane tube and a seal), the storage temperature is 5-35 ℃, and the protection liquid in the membrane assembly is strictly forbidden to be discharged.
The storage mode of the ultrafiltration membrane component after use comprises stopping the system for 1-7 days, filling 10-100 ppm NaClO solution into the ultrafiltration membrane component, filling 1% NaHSO3 solution for 7-30 days, filling 1% NaHSO3 solution for more than 30 days, and periodically replacing to ensure that the pH of the internal solution is more than 3, and after long-term stopping, the ultrafiltration membrane component is subjected to medical washing by sodium hypochlorite solution and then is filled with 1% NaHSO3 solution, wherein the pH of the ultrafiltration membrane component protective solution is between 3 and 6, and in general, naHSO3 is easily oxidized into H2SO4, the pH is reduced to a certain extent, and the protective solution is replaced again when the pH is less than 3, SO that the ultrafiltration membrane component is prevented from freezing and causing unrecoverable damage when the weather is cold.
According to the invention, a double-membrane process is utilized, the occupied area is small, the filtering precision is high, bacteria can be removed, the effluent quality is stable, the pollutant removal rate is higher, the oxidation resistance of the ultrafiltration membrane is strong, the chemical stability is good, the flexibility is good, the ductility is strong, the pollution resistance is high, the cleaning is easy, the ultrafiltration membrane product adopts an external pressure type component structure, the specific surface area of the ultrafiltration membrane is larger than that of an internal pressure membrane, the water yield is larger under the same condition, the formed component flow channel is wide and smooth, the pollution is difficult to block, the impact resistance is higher, dirt is attached to the outer wall of the membrane, the reverse flushing is easy to fall off, the discharge is easy, the gas-water double-flushing can be adopted, the consumption of water is reduced, and the water yield is improved.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.
Claims (9)
1. The double-membrane process method for the sea water desalination plant comprises the steps of ultrafiltration membrane material selection, ultrafiltration membrane preparation, ultrafiltration membrane component structure, water temperature adjustment, operation pressure adjustment, ultrafiltration membrane component operation, ultrafiltration membrane component cleaning and ultrafiltration membrane component storage, and is characterized in that polyvinylidene fluoride is selected as a raw material, has the characteristics of strong oxidation resistance, good chemical stability, good flexibility and strong ductility, and is resistant to pollution and easy to clean;
the ultrafiltration membrane preparation comprises a non-solvent induced phase separation method, wherein ethylene glycol monomethyl ether is used as an additive, N-dimethylacetamide is used as a solvent, polyvinylidene fluoride and ethylene glycol monomethyl ether are added into N-dimethylacetamide, stirring and dissolving are carried out to form a homogeneous solution, water is slowly added into the homogeneous solution, the solvent is extracted to form a two-phase structure which takes polyvinylidene fluoride as a continuous phase and water as a disperse phase, and the solvent and the additive are removed to obtain a hollow fiber membrane with a certain pore structure;
the ultrafiltration membrane preparation also comprises a thermally induced phase separation method, n-butanol is used as a diluent, polyvinylidene fluoride and n-butanol are stirred and mixed and subjected to high-temperature treatment, a homogeneous phase solution is formed at high temperature, the mixture solution is prepared into hollow fibers, the solution is subjected to phase separation by cooling, water is used as a solvent for extraction and removal of n-butanol to obtain the hollow fiber membrane, the ultrafiltration membrane is obtained by adopting the thermally induced phase separation method on the basis of the non-solvent induced phase separation method, and a compact layer made of the same material is compounded on the surface of the hollow fiber membrane, so that the ultrafiltration membrane has the advantages of the two methods.
2. The double-membrane process of a sea water desalination plant according to claim 1, wherein the ultrafiltration membrane comprises a separation skin layer with a very thin and compact surface and a porous supporting layer below the separation skin layer, and the compact skin layer is a functional layer and has the functions of filtering and trapping pollutants.
3. The double-membrane process method for the sea water desalination plant according to claim 1, wherein the ultrafiltration membrane component structure adopts an external pressure type component structure, the specific surface area of the ultrafiltration membrane is larger than that of an internal pressure membrane, the water yield is larger under the same condition, the formed component flow passage is wide and smooth, the fouling is difficult to block, the impact resistance is stronger, the fouling is adhered to the outer wall of the membrane, the reverse flushing is easy to fall off, the drainage is easy, the cleaning is more convenient, the gas-water double-cleaning can be adopted, the consumption of self-consumed water is reduced, and the water yield is improved.
4. The method according to claim 1, wherein the water temperature adjustment comprises controlling a proper water temperature, wherein the water temperature is one of important indexes affecting the filtration performance of the ultrafiltration membrane, and the water temperature is increased, the water viscosity is reduced, the water yield is increased, and conversely, the water temperature is reduced, the water viscosity is increased, the water yield is reduced, and the ultrafiltration membrane flux is changed by about 2% when the water temperature is changed by about 1 ℃.
5. The method according to claim 1, wherein the operating pressure is adjusted to be the water inlet pressure, the concentrated water pressure and the water producing pressure of the membrane system, the maximum water inlet pressure allowed by the ultrafiltration membrane component structure is 300kPa, the concentrated water pressure and the water producing pressure are simultaneously concerned during the running process of the system, and the maximum transmembrane pressure difference (TMP) allowed by the ultrafiltration membrane is 200kPa.
6. The double-membrane process method of a seawater desalination plant according to claim 1, wherein the operation of the ultrafiltration membrane assembly comprises a cross-flow filtration mode and a dead-end filtration mode, and in the cross-flow filtration mode, part of inlet water penetrates through the surface of the ultrafiltration membrane to become produced water, and the other part of inlet water is discharged to become concentrated water with impurities.
7. The method according to claim 1, wherein the washing ultrafiltration membrane component comprises physical washing, chemical washing and maintenance washing, the physical washing comprises forward washing and reverse washing, the forward washing has no filtering effect, when clear water passes through the outer side of the fiber at a certain flow rate, pollutants on the outer side of the ultrafiltration membrane can be washed out, the reverse washing and the filtering process are reversed, and under a certain pressure, the clear water is made to permeate from the raw water side to the raw material liquid side, and the pollutants on the feed liquid side and the blocking matters permeated into micropores are washed out.
8. The method for preparing the double-membrane technology of the sea water desalination plant according to claim 7, wherein the physical cleaning further comprises soaking and air and water backwashing, the soaking comprises soaking the ultrafiltration membrane component by using clear water or liquid medicine, the soaking can loosen pollutants, the soaking for a certain time is an effective method for removing the pollutants, the air and water backwashing comprises the steps of introducing a certain amount of compressed air from a water inlet while the ultrafiltration membrane component is backwashed, and the hollow fiber membranes can swing under the action of ascending air flow to realize mutual friction collision, so that the pollutants attached to the surfaces of the hollow fiber membranes are peeled off and are discharged from a sewage outlet.
9. The method according to claim 1, wherein the ultrafiltration membrane module is stored in a mode after use, wherein the ultrafiltration membrane module is stopped for 1-7 days, 10-100 ppm NaClO solution is filled into the ultrafiltration membrane module, 7-30 days, 1% NaHSO3 solution is filled, more than 30 days, 1% NaHSO3 solution is filled, and periodic replacement is required to ensure that the pH of the internal solution is more than 3.
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