KR101446205B1 - Seawater desalination system - Google Patents

Abstract

The present invention relates to a method and apparatus for desalination of seawater, and more particularly, to a method and apparatus for desalination of seawater by introducing a pretreatment that can prevent a scale problem in advance, And more particularly, to a method and an apparatus for desalination of seawater that improve the energy efficiency and production efficiency, which can reduce the operation cost of the system, as well as improve the lifetime of the separation membrane used in the process.

Description

Seawater Desalination System < RTI ID = 0.0 >

 The present invention relates to a desalination method for desalination of fresh water by removing salt existing in seawater, and more particularly, to a desalination method for desalination by introducing pretreatment for preventing scale induction, And more particularly, to a desalination method of seawater having an increased freshwater recovery rate.

Water and energy are important sources of human survival. According to the United Nations report, 38% of the 7.8 billion people in 2025 and 42% of the 9.4 billion people in 2050 will suffer from water shortages. In addition, the problem facing the world economy is not only the lack of water but also the lack of energy, high oil prices due to the depletion of fossil fuels, global warming due to the use of fossil raw materials, and restriction of carbon emissions. In addition to the water shortage, competition among countries is fierce in the development of technologies that can solve energy problems.

Currently, the freshwater production method uses a heat source to heat the seawater and to condense the generated steam through a pretreatment process to remove fine impurities from the seawater through an ultrafilter membrane (UF) or a microfilter membrane (MF) (Reverse Osmosis, RO), which produces fresh water by passing seawater through semi-permeable membranes using reverse osmosis by applying high pressure to seawater, and multi-stage evaporation And multi-stage utility evaporation methods suitable for medium-sized plants.

In the multi-stage evaporation method, the brine is heated by using solar heat, air is injected into the chamber, the temperature is heated to about 100 ° C or about 80 ° C, and when the seawater is boiled, water is vaporized by the steam, . At this time, the remaining concentrated salt solution can be sent to the factory to be used as salt, but most of the above methods require high temperature and energy of 60-100 ° C. In addition, the recovery rate from seawater to freshwater is 10 to 20% (20 to 35% for MED) compared to high energy costs.

The reverse osmosis method requires a relatively small amount of energy to produce a unit volume of water as compared with the evaporation method, and the system recovery rate is about 45%, which is relatively high compared to the evaporation method. In this regard, reverse osmosis is widely used and currently accounts for 50% of the seawater desalination methods. The reverse osmosis method separates the components contained in seawater or sea water into product water (or treated water) and concentrated water using a polymer membrane (reverse osmosis membrane). The product water is used as water and drinking water by diluting the component concentration. The conventional reverse osmosis membrane applied to the seawater desalination method inevitably produces a membrane contamination phenomenon called fouling and scaling while obtaining purified water from seawater and consumes a large amount of chemicals to solve the problem , And reverse water for removing pollutants. This process has been reported to account for 20% of the energy consumed in the entire water treatment process. Therefore, new water treatment technology which is environmentally friendly, low energy consumption, low cost and low energy is required, and research and development of a seawater desalination method using nano separator is being conducted.

  The Nano Filtration Membrane is characterized by permeating monovalent ions while eliminating ions with a valence of two or more. Due to these properties, there is a problem that the membrane through which all monovalent ions are permeated does not substantially reduce the salt concentration in the sea water. For example, if only calcium ions, magnesium ions and sulfate ions, which are bivalent ions, are excluded, monovalent ions such as sodium, chlorine and potassium ions permeate the membrane and are included in the production water. In other words, assuming that only multivalent ions are excluded, the salinity concentration of produced water is 86% of the salinity of supplied sea water, so there is no significant difference from the salinity concentration in seawater.

As an example of application of a nanofiber separator to a seawater desalination system, the following proposal for a nanofiber separation process using one or more conventional nanofiber membrane modules under pressurized conditions was proposed. Undesired ions are removed by using a nanofiber separation membrane in an aqueous solution of high salt concentration containing polyvalent ions such as sodium sulfate or sodium dichromate and then the treated water composed of monovalent ions such as sodium chloride or sodium chloride is separated and concentrated The process was presented. This process is useful for lowering the concentration of undesirable ions such as silica and chromic acid ions contained in chloralkalates and chlorates, but the problem of residual calcium and magnesium still needs to be improved.

As another example, it is proposed to combine and use the RO membrane and the NF membrane to produce drinking water from seawater. Seawater is pressurized to 250 ~ 350 psi to permeate more than one NF module, and the produced water is included in the seawater flowing into the RO shear through the storage tank. The NF production number and the existing inflowing seawater are mixed and flowed into one or more RO vessels, and the production number is the final production number. Concentrated water flowing through RO can be continuously operated as it passes through at least one NF module installed at the rear end. It has been proposed that about 95% of divalent ions are removed and about 50% of monovalent ions are removed from the production water produced by NF. Since Na ⁺ and Cl ^- are present in seawater at a high concentration, it has been proposed that the salt concentration of the initial production water is about 10,000 to 15,000 mg / l. In the RO of the second stage, the sodium content of the influent water is lowered, so that it can be operated at lower pressure. It is suggested that the yield of NF production is at least 40-45% of the supply sea water and that the yield of RO production under typical operating conditions is about 80-85% of the NF production. The pressure applied to the NF and RO stages is 72MPa to 2.41MPa (250psi to 350psi), respectively, and the overall recovery rate of drinking water produced from seawater is about 26-30%.

It has been proposed to produce seawater as drinking water using only nano separator. In many RO systems, one vessel is composed of 6 ~ 8 modules and one or two stages may be constructed depending on the required water quality. However, this is a high performance nano separator, and a drinking water production process has been proposed through a two stage construction. 35,000ppm by the water treatment in the primary nano-membrane NaCl 86 ~ 88% at 525psi pressure ^{_{conditions, SO 4 2- 99.7%, Ca}} 2+ 2 a 97.8% removal, and the pressure condition at 300psi the number of primary separators produced nano the primary treatment to produce potable water was removed ^{_{NaCl 95%, SO 4 2- 100}} %, Ca 2+ 95.9%. Compared with existing seawater desalination RO process, it is necessary to apply pressure of 800 psi or more. Therefore, possibility of producing enough drinking water at low pressure is suggested.

However, in the above-described seawater desalination process, 95% of the divalent ions are removed through the nanofiber separation membrane, so that divalent ions are concentrated on the surface of the nanofiber separation membrane to form insoluble salts such as CaSO ₄ , BaSO ₄ and SrSO ₄ , There is a problem. In addition, there is a problem in that the production rate produced by the reverse osmosis operation at a high pressure is about 45% of the total recovery rate of the system, and the recovery rate of the production water is as low as about 30%, which is not economical.

 SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a pretreatment method capable of preventing a scale problem occurring in a seawater desalination process, And to provide a method for desalination of seawater capable of reducing the operating cost of the system as well as improving the lifetime of the separation membrane used in the process, while increasing the freshwater recovery rate throughout the system.

 In order to solve the above-described problems,

A method for seawater desalination, comprising: (1) a pretreatment step of filtering seawater through a separation membrane which selectively removes divalent anions and divalent cations to form pretreated water; And (2) desalting the pretreated water to form a fresh water.

According to a preferred embodiment of the present invention, the pretreatment step (1) can be performed by filtering the nano separator having a divalent anion removal rate of 45% or more higher than the divalent cation removal rate when the seawater is permeated under the inlet pressure of 75 to 125 psi have.

According to another preferred embodiment of the present invention, the pretreatment step (1) comprises: when the seawater is permeated under an inlet pressure of 75 to 125 psi, the removal rate by ion is not less than 98% of the sulfate ion (SO ₄ ^2- ) The ion (Ca ²⁺ ) can be filtered with a nanoparticle membrane of 33% or less.

According to another preferred embodiment of the present invention, when the raw water of 2000 ppm MgSO ₄ , 2000 ppm NaCl is permeated at a pressure of 5.3 kgf / cm ² , the separation membrane has a MgSO ₄ removal rate of 98% or more and a NaCl removal rate of 35% Nano separator.

According to another preferred embodiment of the present invention, the pretreatment step (1) includes a first pre-treatment step of removing floating matters from seawater to form a first pretreatment water; And a second pre-treatment step of selectively removing a divalent anion and a divalent cation from the first pre-aqueous solution to form a second pre-treatment water.

According to another preferred embodiment of the present invention, (2) the step of forming fresh water comprises the steps of (1) mixing the pretreated water formed in the pretreatment step with at least one selected from the group consisting of reverse osmosis, multistage evaporation, Fresh water can be formed through the desalination process.

According to another preferred embodiment of the present invention, the seawater desalination method may have a fresh water recovery rate of 70% or more.

The present invention also provides a seawater desalination apparatus comprising: a pretreatment unit for filtering seawater through a separation membrane that selectively removes divalent anions and divalent cations to form pretreated water; And a desalination unit for desalinating the pre-treatment water introduced from the pre-treatment unit to form fresh water.

According to another preferred embodiment of the present invention, when the seawater is permeated under an inlet pressure of 75 to 125 psi, the removal rate of ions is equal to or higher than 98% of the sulfate ion (SO ₄ ^2- ) ²⁺ ) may include nanoparticles of 33% or less.

According to another preferred embodiment of the present invention, when the raw water of 2000 ppm MgSO ₄ and 2000 ppm NaCl is permeated at a pressure of 5.3 kgf / cm ² , the separation membrane has a MgSO ₄ removal rate of 98% or more and a NaCl removal rate of 35% Lt; / RTI >

According to another embodiment of the present invention, the separation membrane may be a polyamide composite nano separator comprising a polyamide layer.

According to another preferred embodiment of the present invention, the pre-processing unit includes: a module including the selective ion removing membrane; A vessel in which at least one of the modules is formed; A stage in which at least one vessel is arranged in parallel; And at least one of the stages may be installed in series.

According to another preferred embodiment of the present invention, the module including the selective ion removing membrane may be a spiral wound module.

According to another preferred embodiment of the present invention, the pretreatment unit comprises: a primary pretreatment unit for removing suspended solids from the seawater; And a secondary pretreatment unit for selectively removing divalent anions and divalent cations from the seawater introduced through the primary pretreatment unit.

 According to another preferred embodiment of the present invention, the primary pretreatment unit includes at least one selected from the group consisting of a sand filter, a disk filter, a fiber yarn filter, a MF (microfiltration membrane), and an ultrafiltration membrane (UF) Can be removed.

 The seawater desalination method of the present invention can increase the fresh water recovery rate of the entire system while allowing a process operation to be performed at a lower pressure than the conventional seawater desalination method by introducing a pretreatment that can prevent the scale problem in advance. Furthermore, it is possible to provide a seawater desalination method which improves energy efficiency and production efficiency, which not only improves the life of the separation membrane used in the process, but also reduces the operation cost of the system.

1 is a process diagram of a desalination process according to a preferred embodiment of the present invention.
2 is a schematic view of a seawater desalination apparatus according to a preferred embodiment of the present invention.
3 is a schematic diagram of a stage included in the selective ion removal pretreatment unit according to a preferred embodiment of the present invention.
4 is a schematic diagram of a selective ion removal pretreatment unit according to a preferred embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

As described above, in the conventional seawater desalination system, 95% of the divalent ions are removed through the nanofiber separation membrane, so that divalent ions are concentrated on the surface of the nanofiber separation membrane to form insoluble salts such as CaSO ₄ , BaSO ₄ and SrSO ₄ , There is a problem that can be caused. In addition, the total recovered yield of the system produced through reverse osmosis operation at high pressure is about 45%, whereas the recovery rate of produced water is only about 30% at the process using nanofiber separation membrane, which is not economical.

Accordingly, the present invention provides a seawater desalination method comprising the steps of: (1) pre-treating seawater by filtering seawater through a separation membrane that selectively removes divalent anions and divalent cations; And (2) desalinating the pretreated water to form fresh water. The present invention has been made to solve the above-mentioned problems. As a result, it is possible to prevent the scale from occurring and to operate the system at a low pressure compared with existing seawater desalination methods, to increase the fresh water recovery rate of the entire system, to improve the lifetime of the membrane used in the process, Thereby providing a seawater desalination method with enhanced energy efficiency and production efficiency.

 The seawater desalination method of the present invention may further include a first pre-treatment step (S1) for removing floating matters of seawater introduced from the sea, and the first pretreatment water from which suspended matters are removed may include a divalent anion and a divalent cation And a second pre-treatment step (S2) of filtering through a separating membrane that selectively removes water to form a second pretreated water. The second pre-treatment water that selectively removes divalent anions and divalent cations contained in seawater proceeds to a desalination step (S3) for producing final desalted water through a reverse osmosis method, a multi-stage evaporation method, or a multi-stage effect evaporation method. (See Fig. 1)

The primary pretreatment water from which suspended substances are removed is filtered through a separation membrane that selectively removes divalent anions and divalent cations, thereby forming secondary pretreatment water in which ions forming scale are selectively separated and removed.

The selective ion removal pretreatment step selectively removes ions forming a scale by removing part of monovalent ions and divalent cations while removing sulfate ions (SO ₄ ^2- ) with a high rejection rate to prevent scale generation in advance , It is possible to operate the system at a low pressure, and the recovery rate of fresh water can be increased while improving separation membrane life.

The selective ion removal pretreatment step may more preferably filtrate the nanoparticle membrane having a divalent anion removal rate of 45% or more higher than the divalent cation removal rate when the seawater is filtered at an inlet pressure of 75 to 125 psi. Most preferably the ion-specific removal rate when sikyeoteul sulfate was filtered from 75 to 125psi inlet pressure conditions the water (SO ₄ ^2-) is at least 98%, and the monovalent ions are less than 10%, a calcium ion (Ca ²⁺⁾ The above object can be achieved by including the nano-separator of 33% or less.

 The nanostructured membrane used in the selective ion removal pretreatment step is not particularly limited as long as it can selectively remove divalent anions and divalent cations as described above, but is more preferably a porous support layer; And a polyamide layer formed on one surface of the porous support layer, wherein the polyamide layer is formed by interfacial polymerization of a polyfunctional amine and a polyfunctional acid halide compound.

The porous support layer is not particularly limited as long as it can form a nanostructured membrane. However, in consideration of mechanical strength, it is preferable to use a polymer having a weight average molecular weight in the range of 65,000 to 150,000, and preferred examples thereof include polysulfone or polyethersulfone Based polymers such as polyamide-based polymers, polyimide-based polymers, polyester-based polymers, and polypropylene, polybenzimidazole polymers, polyvinylidene fluoride or polyacrylonitrile, Mixed form.

The polyamide layer formed on the porous support layer can be formed by interfacial polymerization by dipping in an aqueous solution containing a polyfunctional amine and then contacting the organic solution containing the polyfunctional acid halide compound. Specifically, the polyfunctional amine may be a polyamine having two or three amine functional groups per monomer, and may include a primary amine or a secondary amine. As the polyfunctional amine, an aromatic primary diamine may be used as the metaphenylenediamine, paraphenylenediamine, orthophenyldiamine and a substituent. As another example, aliphatic primary diamine, cyclic aliphatic diamine such as cyclohexenediamine, Cyclic aliphatic secondary amines such as piperazine, primary amines, piperazine, and aromatic secondary amines. More preferably, mephenylenediamine, which is an aromatic primary diamine among the above-mentioned polyfunctional amines, or piperazine, which is a cycloaliphatic secondary diamine, can be used.

 The polyfunctional amine aqueous solution is used in a concentration of 0.1 to 20 wt%, more preferably 0.5 to 8 wt% of a polyamine aqueous solution. The pH of the polyfunctional amine aqueous solution ranges from 7 to 13, and can be adjusted by adding 0.001 to 5% by weight of an acid or base. Examples of such acids and bases include hydroxides, carboxylates, carbonates, borates, phosphates of alkyl metals, trialkylamines, and the like. In addition, a basic acid acceptor capable of neutralizing the acid (HCl) generated during interfacial polymerization may be added to the polyfunctional amine aqueous solution, and a polar solvent, an amine salt, or a polyfunctional tertiary amine may be added as another additive have.

Upon forming the polyamide layer of the present invention, the polyfunctional amine-containing aqueous solution may be applied onto the porous support for 0.1 to 10 minutes, more preferably for 0.5 to 1 minute.

The material that reacts with the polyfunctional amine used in forming the polyamide layer of the present invention is a polyfunctional acid halide, that is, a polyfunctional acyl halide, a polyfunctional sulfonyl halide, a polyfunctional isocyanate, and the like. Preferably, it may be used alone or in a mixed form of trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, and the like. At this time, the use of the mixed form is most preferable in terms of the salt removal rate. The polyfunctional acid halide compound is generally used in an amount of 0.005 to 5% by weight (more preferably 0.01 to 0.5% by weight) in an organic solvent which is immiscible with water. Examples of the organic solvent include halogenated hydrocarbons such as Freon, hexane, cyclohexane, heptane, and alkanes having 8 to 12 carbon atoms.

The polyamide composite nano separator used in the selective ion removal pretreatment step can control sulfate ion (SO ₄ ^2- ), calcium ion (Ca ²⁺ ), and monovalent ion removal in seawater depending on the membrane characteristics. According to the pore size of the polyamide formed on the nano-separator, the 1,2-valent ions are partially removed and the anion removal rate contained in the seawater can be improved due to the electrical repulsive force due to the negative charge characteristic of the membrane surface.

The polyamide composite nano-separator used in the selective ion removal pretreatment step of the present invention enhances the removal performance of sulfate ions (SO ₄ ^2- ) when the seawater is filtered, and the divalent cationic calcium ions (Ca ^{2 +} ) Is 33% or less, it is possible to minimize the scale generation of the concentrated water through the raw water or the pretreatment process to be introduced into the reverse osmosis process or the evaporation process. Calcium sulfate (CaSO ₄₎ is a salt having a solubility depending on the temperature and the pH is liable to be significant because without being affected supersaturated solubility limit of calcium sulfate (CaSO ₄₎ as well as nano-membrane determines the maximum enrichment factor of a reverse osmosis membrane. Therefore, sulfate ion and calcium ion forming calcium sulfate (CaSO ₄ ) can be separated and removed, thereby preventing scale formation in the concentrated water through the raw water or the nanofiber separation membrane to be introduced into the desalination process, thereby increasing the recovery rate of the final production water.

As described above, in order to minimize the generation of scale by selectively separating and removing the divalent cationic Ca ²⁺ removal rate to 33% or less while securing a removal rate of sulfate ion (SO ₄ ^2- ) of 98% or more, when nano-membrane used in the selective ion removal step of preprocessing the desalination process sikyeoteul transmitted through the raw water of the nano-membrane industry-standard conditions of 2000ppm MgSO _4, 2000ppm NaCl at a pressure of 5.3kgf / cm ^2, more than 98% MgSO ₄ and removal 35 % Or less of NaCl. When the NaCl removal rate exceeds 35%, when it is applied to the high concentration of seawater filtration, the removal rate of calcium ion (Ca ²⁺ ) is higher than 45%, and the permeate flow rate is remarkably decreased due to scale formation in the concentrated water .

The selective ion removal pretreatment step may be performed according to a preferred embodiment using SRM (Sulfate Removal Nanomembrane) nanoparticles of Woongjin Chemical.

The final pretreatment water that selectively separates the ions forming scale by permeating a part of monovalent ions and divalent cations and removing sulfate ions (SO ₄ ^2- ) with a high rejection rate is then desalted through a desalination step Produce final production number.

 The desalting step may be performed by a desalting process such as a reverse osmosis method, a multi-stage evaporation method, or a multi-stage effect evaporation method.

As described above, the seawater desalination method of the present invention can prevent the scale problem that may occur in the desalination process by applying the selective ion removal pretreatment process, and can operate the system at a low pressure, .

The present invention also provides a seawater desalination apparatus for implementing the seawater desalination method described above. Specifically, in a seawater desalination apparatus, a pretreatment unit for filtering seawater through a separation membrane that selectively removes divalent anions and divalent cations to form pretreated water; And a desalination unit for desalinating the pre-treatment water introduced from the pre-treatment unit to form fresh water.

2 is a schematic diagram of a seawater desalination apparatus according to a preferred embodiment of the present invention. 2, the first pretreatment unit 100 may include a first pretreatment unit 100 for removing suspended solids from the inflowed seawater, and a second pretreatment unit 100 for removing suspended solids from the inflowed seawater, A secondary pretreatment unit 200 for selectively removing cations; And a desalination unit 300 for desalinating the pretreatment water introduced from the pretreatment unit to form fresh water.

The primary pretreatment unit 100 for removing suspended solids from the influent seawater can be a floating material from seawater by a single or mixed form of a sand filter, a disk filter, a fiber filter, a microfiltration membrane (MF), or an ultrafiltration membrane (UF) The first pre-treatment water can be generated.

The secondary pretreatment unit 200 for selectively removing ions from the seawater introduced from the primary pretreatment unit 100 includes a separation membrane for selectively removing divalent anions and divalent cations.

The separation membrane contained in the secondary pretreatment unit 200 may be a nano-separator having a divalent anion removal rate of 45% or more higher than a divalent cation removal rate when the seawater is filtered under an inlet pressure of 75 to 125 psi. Most preferably the ion-specific removal rate when sikyeoteul sulfate was filtered from 75 to 125psi inlet pressure conditions the water (SO ₄ ^2-) is at least 98%, and the monovalent ions are less than 10%, a calcium ion (Ca ²⁺⁾ The above object can be achieved by including the nano-separator of 33% or less.

 The nano separator included in the selective ion removal pretreatment unit 200 includes a porous support layer; And a polyamide layer formed on one surface of the porous support layer, wherein the polyamide layer is formed by interfacial polymerization of a polyfunctional amine and a polyfunctional acid halide compound.

The polyamide composite nano separator can control the removal of sulfate ions (SO ₄ ^2- ), calcium ions (Ca ²⁺ ), and monovalent ions in the seawater depending on the membrane characteristics. According to the pore size of the polyamide formed on the nano-separator, the 1,2-valent ions are partially removed and the anion removal rate contained in the seawater can be improved due to the electrical repulsive force due to the negative charge characteristic of the membrane surface.

As described above, in order to minimize the generation of scale by selectively separating and removing the divalent cationic Ca ²⁺ removal rate to 33% or less while securing a removal rate of sulfate ion (SO ₄ ^2- ) of 98% or more, The nano-separator included in the selective ion removal pretreatment unit 200 has an MgSO ₄ removal rate of 98% or more and a removal efficiency of 35% or more when the raw water of 2000 ppm MgSO ₄ , 2000 ppm NaCl, which is an industry standard condition of the nano separator, is permeated at a pressure of 5.3 kgf / cm ² , Or less of NaCl. When the NaCl removal rate exceeds 35%, when it is applied to the high concentration of seawater filtration, the removal rate of calcium ion (Ca ²⁺ ) is higher than 45%, and the permeate flow rate is remarkably decreased due to scale formation in the concentrated water .

The selective ion removal pretreatment unit 200 may include a SRM (sulfur removal nanomembrane) nanofiber separation membrane of Woongjin Chemical Co., Ltd. according to a preferred embodiment of the present invention.

 Furthermore, the selective ion removal pretreatment unit 200 may include a module 221 including the selective ion removal separation membrane; A vessel 222 in which at least one of the modules is formed; A stage 220 in which at least one vessel is arranged in parallel; And at least one of the stages may be installed in series. FIG. 3 is a schematic diagram of one stage 220 included in the selective ion removal pretreatment unit 200 according to an embodiment of the present invention. As shown in FIG. 3, there is a casing 222 in which at least one, more preferably three to eight, polyamide composite nano separator modules are installed, and a module 221 including the polyamide composite nano separator, At least one of the vessels 222 may be arranged in parallel to form one stage 220.

The module 221 including the selective ion removing membrane may be a spiral wound module. A spiral wound module is a compact size with a large membrane area integrated into a compact size, which can produce a large quantity of production volume relative to the size of the module and the size of the process. In the selective ion removal pretreatment of the present invention, the operating pressure of the nanofiber separation membrane module is preferably 10 kgf / cm 2 or less.

3, one or more stages according to a preferred embodiment of the present invention may be installed in series to constitute a selective ion removal pretreatment unit 200. FIG. And a selective ion removal pre-treatment unit 200 according to an embodiment of the present invention. In the preferred selective ion removal pre-treatment unit 200 of the present invention, at least one of the stages 220, 230 and 240 may be arranged in series. Stage system in which one or more stages are connected in series in order to increase the recovery rate of the seawater pretreated through the nano-separator, and the concentrated water 21 obtained in the first stage 220 is connected to the next stage 230), the recovery rate of the pretreated seawater can be recovered up to 90%, and the improvement of the permeate yield of such a pretreatment system can improve the overall recovery of the seawater desalination system.

Through the selective ion removal pretreatment unit 200, a part of monovalent ions and divalent cations are permeated, and sulfate ions (SO ₄ ^2- ) are removed at a high rejection rate, The water (50) then produces the desalted final water through the desalination unit (300).

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples should not be construed as limiting the scope of the present invention, and should be construed to facilitate understanding of the present invention.

 Ion analysis was conducted on the basis of the Korean East Sea seawater, and synthetic sea water containing the ion composition as shown in Table 1 was prepared as test water.

Ion type Concentration (ppm) Na ⁺ 10731.9 Cl ^- 19417.5 K ⁺ 393.3 Mg ²⁺ 666.4 Ca ²⁺ 986.6 SO ₄ ^2- 2701.2

≪ Example 1 >

The raw water was passed through an individual module composed of SRM (Sulfate removal nanomembrane) polyamide composite nano separator of Woongjin Chemical Co., Ltd., and the static pressure operation method set to 15% of individual recovery rate was carried out. Under the conditions of 25 ° C and pH 8, Cm < 2 >. As a result of testing the polyamide composite nano separator under the standard conditions of the nanometer membrane industry, when the raw water of 2000 ppm MgSO ₄ and 2000 ppm NaCl was permeated at 5.3 kgf / cm ² pressure, 98% MgSO ₄ and less than 35% 12000GPD, and when the membrane module was used in the raw water condition of high concentration of seawater, the concentration of 1,2-cations and the flow rate of permeated water in the treated water were observed.

≪ Comparative Example 1 &

Except that a high-flow polyamide composite nano separator (NE40) (Woongjin Chemical Co., Ltd.) was used. As a result of testing the nano-separator under the standard conditions of the nanometer membrane industry, when the raw water of 2000 ppm MgSO ₄ and 2000 ppm NaCl was permeated at 5.3 kgf / cm ² pressure, 98% MgSO ₄ and 40 ~ 70% NaCl removal performance and 12500 GPD production Flow rate.

≪ Comparative Example 2 &

Polyamide composite nano separator (Woongjin Chemical Co., Ltd., NE70) was used. As a result of testing the nano separator under the standard conditions of the nanometer membrane industry, when the raw water of 2000 ppm MgSO ₄ and 2000 ppm NaCl was permeated at a pressure of 5.3 kgf / cm ² , 98% MgSO ₄ and 70% NaCl removal performance and 7800 GPD production flow rate Respectively.

The performance of the nanofiber separator shown in Example 1 and Comparative Examples 1 and 2 was evaluated and shown in Table 2 below. Ion concentration in seawater and treated water was measured by ion chromatography (Ion Chromatography).

division flux Ion Removal Rate (%) GPD Cl ^- SO ₄ ^2- Na ⁺ K ⁺ Ca ²⁺ Mg ²⁺ Example 1 11122.7 7.16 98.30 7.82 8.63 30.94 39.40 Comparative Example 1 7635.4 11.98 98.65 4.70 6.55 55.62 74.71 Comparative Example 2 4226.9 16.68 99.3 5.53 7.78 69.93 88.47

As can be seen from the above Table 2, it can be confirmed that the production flow rate is different depending on the ion removal performance by using the high concentration synthetic sea water as the raw water. Comparative Example 2 is a sulfate ion (SO ₄ ^2-), but the removal of more than 99%, a calcium ion (Ca ²⁺⁾ is also a high possibility calcium sulfate scale in the concentrated water by removing occur about 70%. CaSO ₄ , which is one of the causes of membrane contamination when using high concentration of raw water such as seawater, does not occur only in the desalination process, but also in the concentrated water of the pretreatment process that selectively removes ions by applying a nanofiber membrane Lt; / RTI > Such membrane contamination may cause a decrease in the production flow rate in the future.

Comparative Example 1 and Example 1 showed the same level of flow rate under the standard conditions (2000 ppm MgSO ₄ , 2000 ppm NaCl, and 5.3 kgf / cm ² ), but calcium ions (Ca ²⁺ ) and divalent cations It can be seen that Comparative Example 1, in which the magnesium ion (Mg ²⁺ ) removal ratio is higher, has a remarkably low production flow rate. Example 1 having a production flow rate of 11000 GPD or more even under high concentration sea water conditions is expected to be useful for designing a desalination system for increasing the fresh water recovery rate of the present invention.

The pretreatment process using ultrafiltration membranes (UF) or microfiltration membranes (MF) to remove suspended solids shows a high recovery rate of 85 to 90%. Therefore, the selective ion removal pretreatment process using nano- It should be operated under conditions.

Table 3 below shows the concentrations of the concentrated water in the pretreatment process of 90% recovery rate according to the removal rates of the ions of Example 1 and Comparative Examples 1 and 2 in Table 2 above.

Concentration of concentrated water (mg / L) = (production water concentration X recovery rate / raw water concentration) / (recovery rate? 1)

division Selective Ion Removal Nanoparticle Pretreatment Concentration (mg / L) by ion at 90% recovery rate Cl ^- SO ₄ ^2- Na ⁺ K ⁺ Ca ²⁺ Mg ²⁺ Example 1 31932.1 26599.2 18282.4 698.9 3734.2 3029.5 Comparative Example 1 40348.8 26684.7 15267.3 625.3 5925.2 5146.9 Comparative Example 2 48567.4 26842.3 19424.7 668.9 7196.3 5972.3

Table 3 above shows concentrations of concentrated water ions when the recovery rate of the selective ion removal pretreatment system using nano-separator is 90%. From the above results, it can be seen that the concentration of calcium ions (Ca ²⁺ ) in concentrated water is about 37% to 48% lower in Example 1 than in Comparative Examples 1 and 2. This is largely eliminated by the nanoparticles, and the concentrations of calcium ions (Ca ²⁺ ) that can form salts with sulfuric acid ions (SO ₄ ^2- ), which are excessively contained in the concentrated water, ₄ ) It is possible to reduce scale problems that may occur due to salt formation.

10: Inflow water (sea water) 210: High pressure pump
21: 1 Concentration 220, 230, 240: stage
22: 1 Process 221: Module
31: Concentration in the second stage 222: Bezel
32: Two-stage process number
41: Concentration of 3 stages
42: Three-stage process number
50: Final preprocessing water

Claims (15)

In the seawater desalination method,
(1) a pretreatment step in which seawater is filtered through a nanofiber separation membrane which removes monovalent ions, divalent anions and divalent cations at different removal rates to form pretreated water; And
(2) desalting the pretreated water to form fresh water,
The pretreatment step (1) is a step in which the removal rate of ions is 98% or more of sulfate ions (SO ₄ ^2- ) and 33% or less of calcium ions (Ca ²⁺ ) when the seawater is permeated under an inlet pressure of 75 to 125 psi Wherein the filtration is carried out by a centrifugal separator. The method according to claim 1,
Wherein the pretreatment step (1) is performed by filtration with a nano-separator having a divalent anion removal rate of at least 45% higher than a divalent cation removal rate when the seawater is permeated under an inlet pressure of 75 to 125 psi. delete The method according to claim 1,
Wherein the separation membrane is a nanofiber separation membrane having a MgSO ₄ removal rate of 98% or more and a NaCl removal rate of 35% or less when raw water of 2000 ppm MgSO ₄ and 2000 ppm NaCl is permeated at a pressure of 5.3 kgf / cm ² . The method according to claim 1,
The pre-processing step (1)
A primary pretreatment step of removing the suspended matter from seawater to form primary pretreatment water; And
And a second pre-treatment step of selectively removing the divalent anion and the divalent cation from the primary pre-wash water to form a secondary pretreatment water.
The method according to claim 1,
(2) The fresh water forming step is characterized in that the pretreatment water formed in the step (1) is desalinated through at least one desalting process selected from the group consisting of reverse osmosis, multi-stage evaporation and multi-stage evaporation Seawater desalination method. The method according to claim 1,
Wherein the seawater desalination method has a fresh water recovery rate of 70% or more. In a seawater desalination apparatus,
A pretreatment unit for filtering the seawater through a nanofiber separation membrane which removes monovalent ions, divalent anions and divalent cations at different removal rates to form pretreated water;
And a desalination unit for desalinating the pretreatment water introduced from the pretreatment unit to form fresh water,
The nano-separator of the pretreatment unit is characterized in that when the seawater is permeated under an inlet pressure of 75 to 125 psi, the removal rate of ions is 98% or more of sulfate ions (SO ₄ ^2- ) and 33% or less of calcium ions (Ca ²⁺ ) A seawater desalination device. delete 9. The method of claim 8,
Wherein the separation membrane is a nanofiber separation membrane having a MgSO ₄ removal rate of 98% or more and a NaCl removal rate of 35% or less when raw water of 2000 ppm MgSO ₄ and 2000 ppm NaCl is permeated at a pressure of 5.3 kgf / cm ² . 9. The method of claim 8,
Wherein the separation membrane comprises a polyamide composite membrane. ≪ RTI ID = 0.0 > 15. < / RTI > 9. The method of claim 8,
The pre-
A module including the nano-separator;
A vessel in which at least one of the modules is formed;
A stage in which at least one vessel is arranged in parallel; And
Wherein at least one of the stages is installed in series. 13. The method of claim 12,
Wherein the module comprising the nano-separator is a spiral wound module. 9. The method of claim 8,
The pre-
A primary pretreatment unit for removing suspended solids from the influent seawater; And
And a secondary pretreatment unit for selectively removing divalent anions and divalent cations from the seawater introduced through the primary pretreatment unit. 15. The method of claim 14,
Wherein the primary pretreatment unit includes at least one selected from the group consisting of a sand filter, a disk filter, a fiber yarn filter, a microfiltration membrane (MF), and an ultrafiltration membrane (UF) to remove suspended matters.

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