KR20170089230A - Desalination method of sea water using hybrid process of nanofiltration and draw solution assisted reverse osmosis - Google Patents

Abstract

The present invention relates to a seawater desalination method using a nanofiltration method and a reverse osmosis method using an induction solution. According to the present invention, the seawater desalination method lowers maximum pressure required for the same compared to existing reverse osmosis methods, by using the nanofiltration method and the reverse osmosis method using the induction solution, while reducing fouling and consuming low energy. In addition, through reduction in costs for membrane replacement and installation of devices, it is possible to produce high quality and cost-effective fresh water.

Description

Technical Field The present invention relates to a desalination method using a reverse osmosis method and an nano filtration method using an induction solution,

The present invention relates to a method for desalination of seawater, and more particularly, to a method of desalination using seawater desalination and nano filtration using an induction solution, ≪ / RTI >

There is still a greater need for societal, agricultural and industrial water, but there are still many places in the world where water is not available. Seawater is not available because it contains saline, but existing desalination methods are slow, difficult, costly, and require a lot of energy. Seawater desalination technology is a technology that produces fresh water that can be used as drinking water and domestic water from seawater, which accounts for more than 97% of the world's water. The importance of this technology has been emphasized as the population is increasing rapidly around the world and the problem of water shortage is becoming a big issue. In order to produce freshwater from such seawater, it is necessary to separate water from many solutes dissolved in seawater. In general, it is necessary to use a thermal process using heat and a membrane process using a semi-permeable membrane Can be divided. The evaporation method includes multi-staged flash, multi effect distillation, and the membrane separation method includes reverse osmosis and forward osmosis. The most efficient and widely used method is the reverse osmosis method.

Reverse osmosis means that the solute is not easily permeable, but the solvent is a method of moving only the water molecules in seawater to the product water by applying a pressure greater than the osmotic pressure that is present through the semi-permeable membrane which can be easily permeated. The concentration of seawater is generally known to be 3.5% and requires a high pressure of approximately 60-70 bar to produce water from these seawater. Therefore, a high-pressure pump is required to apply a high pressure and a large energy is required to drive the high-pressure pump. In addition, membrane contamination due to high pressure and the increase in membrane replacement cost are also problematic.

Nanofiltration has been widely used as a technique for converting cyanide into solid or removing organic solutes. The membrane pore used in nanofiltration is larger than the membranes used for reverse osmosis but is smaller than ultrafiltration, so the energy required for separation is very low compared to reverse osmosis. These nanofiltration methods have excellent separation ability for ions having a valence of 2 or more, but have a very low resolution for monovalent ions. Therefore, it is not appropriate as a method for separating water from seawater where most solute is salt.

Therefore, a new seawater desalination method is needed to overcome the disadvantages of the conventional arts in order that the energy demand is lower than that of the conventional reverse osmosis method and at the same time, the separation performance against the salt does not appear as in the nano filtration method.

KR 10-2006-0133299

The inventors of the present invention found that the desalination method using the induction solution and the desalination method using the nanofiltration method have a lower maximum required pressure than the conventional reverse osmosis method, And further, the membrane replacement cost and the installation cost of the apparatus are reduced, thereby producing economical and excellent quality fresh water. Thus, the present invention has been completed.

Accordingly, the present invention provides a reverse osmosis method using an induction solution and a desalination method using a nano filtration method.

Accordingly, the present invention provides a desalination system using an induction solution and a desalination system using a nano-filtration method.

The present invention also provides a seawater desalination apparatus using the seawater desalination system.

In order to achieve the above object,

The present invention

(1) introducing seawater into a reverse osmosis device containing an inductive solution having a concentration lower than that of seawater in a direction opposite to the osmotic membrane;

(2) transferring the water of the seawater into the induction solution by applying pressure to the introduced seawater; And

(3) recovering the fresh water by nano-filtration of the induction solution in which the water has been transferred.

In addition,

(1) a seawater inlet for introducing seawater in a direction opposite the osmotic membrane to a reverse osmosis device comprising an inductive solution having a lower concentration than seawater;

(2) a reverse osmosis part for applying pressure to the introduced seawater to move the water of the seawater to the guiding solution; And

(3) a nano-filtration unit for nano-filtration of the induction solution in which the water is moved to recover fresh water.

The present invention also provides a seawater desalination apparatus using the seawater desalination system.

The seawater desalination method according to the present invention uses a reverse osmosis method and a nano filtration method using an induction solution, thereby lowering the maximum required pressure, reducing membrane contamination, and requiring low energy compared with the conventional reverse osmosis method.

In addition, the membrane replacement cost and the installation cost of the apparatus are reduced, thereby producing economical and excellent quality fresh water.

FIG. 1 is a flow chart sequentially showing a method of desalinating sea water according to the present invention.
2 is a diagram illustrating an exemplary process of a seawater desalination method and system of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the following embodiments are provided only for the purpose of easier understanding of the present invention, and the contents of the present invention are not limited by the embodiments.

(1) introducing seawater in a reverse osmotic membrane direction to a reverse osmosis device comprising an inductive solution having a lower concentration than seawater; (2) transferring the water of the seawater into the induction solution by applying pressure to the introduced seawater; And (3) recovering the fresh water by nano-filtration of the induction solution into which the water has been transferred. The present invention also provides a reverse osmosis-based seawater desalination method.

More specifically, the present invention relates to a reverse osmosis method based seawater desalination method, wherein the concentration of the inducing solution is set to be lower than sea water to reduce the osmotic pressure difference in the reverse osmosis module to lower the required pressure, To produce final fresh water and also to recover pressure energy from the resulting broth. A seawater desalination system including a seawater desalination unit, a reverse osmosis unit, and a nano-filtration unit and including an energy recovery unit for recovering pressure energy from concentrated brine, a booster pump unit for supplementing pressure loss, .

The step (1) is a step of introducing seawater into the reverse osmosis device including the induction solution having a concentration lower than that of the seawater in a direction opposite to the osmosis membrane.

Usually, natural sea water contains impurities, floats, or foreign matter. In order to produce freshwater from the desalination process, it is necessary to remove impurities in the seawater first. At this time, a membrane or the like may be used, and natural sea water may be filtered through a membrane having an average pore size of 0.05 to 5.0 μm to remove impurities in the seawater. As the type of the film, a microfilter, an ultrafilter, or the like can be used. The micro filter preferably has a pore size of 0.2 m or less. If the pore size exceeds 0.2 탆, large suspended solids present in the seawater may fall, but it may be difficult to remove suspended solids or microorganisms of small size. The ultrafilter preferably has a pore size of 0.1 mu m or less. If the pore size exceeds 0.1 탆, it may be difficult to remove microorganisms having a small size in water.

The concentration means the salt concentration.

The inductive solution used in the reverse osmosis module is generally different from the inductive solution used in the positive osmosis module. In the forward osmosis module, the concentration of the inducing solution is higher than that of the seawater to allow the water to move spontaneously from seawater to the inducing solution through the osmosis phenomenon. However, in the reverse osmosis module of the present invention, the concentration of the inducing solution is set to be lower than that of sea water, thereby reducing the osmotic pressure difference in the reverse osmosis module. That is, the induction solution of the present invention is characterized by having a concentration lower than that of sea water, particularly a salt concentration lower than that of sea water.

The derivatizing solution may comprise a derivatized solute of cation, anion or salt. The conditions of the induction solute required in the induction solution are not harmful to the human body and must be soluble enough to be used as an inducing solution and should be low in price for cost effectiveness of the process. Further, a material containing a divalent ion is preferable because it must be separable through nanofiltration. Specifically, the guide solute is a divalent be a salt ion, For _{example, Na 2 CO 3, K 2} CO 3, MgCO 3, CaCO 3, Na 2 SO 4, K 2 SO 4, MgSO 4, CaSO 4, MgCl ₂ , CaCl ₂ , C ₆ H ₁₂ O ₆ , and the like.

In the step (2), the water in the seawater is moved to the induction solution by applying pressure to the seawater.

The inflowing seawater is pressurized by a high pressure pump in a reverse osmosis device, and the pressure difference is larger than the osmotic pressure between the seawater and the induction solution, so that the water in the seawater flows through the semi-permeable membrane to the induction solution.

The pressure applied to the seawater may be less than 60 bar, preferably 10 to 50 bar, applied to seawater in a conventional reverse osmosis unit. If the pressure is less than 10 bar, the movement of water is not properly performed. If the pressure is more than 50 bar, severe film contamination, an increase in installation cost, and an increase in energy cost may occur. More preferably, the pressure applied to the seawater may be 40 to 50 bar.

The driving temperature in the reverse osmosis process and the nano filtration process may be 20 to 40 ° C. If the temperature is lower than 20 ° C, the movement of water is not smoothly performed and more energy is required. If the temperature is higher than 40 ° C, excessive water migration may lead to deterioration of water quality and loss of inducing solution. Preferably, the driving temperature may be 25 to 35 占 폚.

In the seawater desalination process, a large amount of concentrated brine is produced in an amount equal to that of the desalted water produced. The concentrated brine can be obtained by passing through a reverse osmosis membrane for seawater. The reverse osmosis membrane for seawater has a removal efficiency of at least 99% at a salt rejection rate of at least 99%. As the module type, a spiral wound type membrane having a high degree of integration of a membrane area can be used. The concentrated brine may comprise a salt concentration of 1 to 50 wt.%, And preferably a salt concentration of 6 wt.%. The concentrated brine is discharged out of the process after the pressure energy is recovered through the energy recovery device. In this case, due to the efficiency of the energy recovery device, the pressure loss in the reverse osmosis module, and the pressure loss in the pipeline, the flow of the seawater inlet through the energy recovery device becomes lower than the inlet flow of the seawater through the existing high- This loss is compensated by the booster pump.

In the step (3), the induction solution in which the water is moved is subjected to nanofiltration to recover the fresh water.

Through the reverse osmosis process, the induction solution into which the water is introduced is subjected to the nanofiltration process, thereby separating the induction solution and producing final fresh water. After recovering the fresh water, the concentrated inductive solution can be reintroduced into step (1) and recycled to the reverse osmosis process (step (4)). Therefore, the amount of water to be separated in the nanofiltration process for recycling should be equal to the amount of water introduced from the seawater in the reverse osmosis process. In order to perform the nanofiltration process, a nanofiltration membrane may be used, and the nanofiltration membrane should have a smaller permeation molecular weight than that of the induction solute. In addition, the pressure applied to the nanofiltration process may be 20 to 30 bar, and when the pressure is less than 20 bar, the water is not properly moved. When the pressure exceeds 30 bar, severe membrane contamination, And the like.

(1) a seawater inflow section for introducing seawater in a direction opposite to the osmotic membrane to a reverse osmosis device including an induction solution having a concentration lower than that of seawater; (2) a reverse osmosis part for applying pressure to the introduced seawater to move the water of the seawater to the guiding solution; And (3) a nano-filtration unit for nano-filtration of the induction solution in which the water is moved to recover fresh water.

The seawater desalination system may further include an energy recovery unit for recovering pressure energy from the concentrated brine generated in the step (2).

The seawater desalination system may further include a high-pressure pump unit for pressurizing seawater and a booster pump unit for supplementing pressure loss.

The present invention also provides a seawater desalination apparatus using the seawater desalination system.

1 and 2 illustrate a flow chart and an exemplary process of the seawater desalination method according to the present invention. The seawater desalination apparatus according to the present invention comprises: A reverse osmosis process is performed in which water in the seawater is moved to an induction solution. The concentrated brine is discharged from the process after the pressure energy is recovered through the energy recovery device. In addition, the induction solution in which the water is transferred produces fresh water by performing a nanofiltration process, and the separated induction solution is introduced into the reverse osmosis process and recycled.

Claims (13)

(1) introducing seawater into a reverse osmosis device containing an inductive solution having a concentration lower than that of seawater in a direction opposite to the osmotic membrane;
(2) transferring the water of the seawater into the induction solution by applying pressure to the introduced seawater; And
(3) recovering the fresh water by nano-filtration of the induction solution in which the water has been transferred. The method according to claim 1,
Wherein the seawater is pretreated by filtering the impurities in the step (1). The method according to claim 1,
Wherein the inducing solution in step (1) comprises an induced solute of a cation, anion or salt. The method of claim 3,
Wherein the derivatized solute is a substance containing divalent ions. The method of claim 3,
Wherein said derivatized solute is selected from the group consisting of Na ₂ CO ₃ , K ₂ CO ₃ , MgCO ₃ , CaCO ₃ , Na ₂ SO ₄ , K ₂ SO ₄ , MgSO ₄ , CaSO ₄ , MgCl ₂ , CaCl ₂ , and C ₆ H ₁₂ O ₆ Wherein the one or more seawater desalination units are selected from the group consisting of: The method according to claim 1,
Wherein the pressure in step (2) is 10 to 50 bar. The method according to claim 1,
Wherein the temperature in the step (2) or (3) is 20 to 40 ° C. The method according to claim 1,
Further comprising the step of recovering pressure energy from the concentrated brine produced in step (2). The method according to claim 1,
Wherein the nanofiltration is carried out using a nanofiltration membrane having a smaller permeation molecular weight than the molecular weight of the induction solute in the step (3). The method according to claim 1,
(4) re-introducing the inductive solution from which the fresh water has been recovered into the reverse osmosis unit of step (1). (1) a seawater inlet for introducing seawater in a direction opposite the osmotic membrane to a reverse osmosis device comprising an inductive solution having a lower concentration than seawater;
(2) a reverse osmosis part for applying pressure to the introduced seawater to move the water of the seawater to the guiding solution; And
(3) a nanofiltration unit for nanofiltering the induction solution in which the water is transferred to recover fresh water. 12. The method of claim 11,
Further comprising an energy recovery unit for generating concentrated brine in the step (2), and recovering pressure energy therefrom. A seawater desalination apparatus using the seawater desalination system of claim 11.

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