JP2018001110A - Processing method of brine, processing method of desalinating salt water, processing system of brine, and processing method of desalinating salt water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing method of brine capable of reducing a processing cost by reducing energy necessary for processing brine in a brine concentration method.SOLUTION: The processing method of brine produced by concentrating salt water accompanying processing of desalinating salt water using at least any of a reverse osmotic method and an evaporation method includes: a concentration step of concentrating a part of the brine to obtain concentrated brine and of diluting the other part of the brine to obtain diluted brine; and a salt content-recovering step of recovering a salt content contained in the concentrated brine obtained by the concentration step as a crystalized salt using an evaporation method, where the concentration step includes a membrane separation step of transferring water contained in the brine in a first chamber to the brine in a second chamber through a semi-permeable membrane by flowing a part of the brine to the first chamber of a semipermeable module provided with a semipermeable membrane, and with the first chamber and a second chamber separated by the semipermeable membrane, and flowing the other part of brine to the second chamber to pressurizing the first chamber.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a brine treatment method, a saltwater desalination treatment method, a brine treatment system, and a saltwater desalination treatment system.

  Main technologies for desalination treatment of seawater and the like include membrane separation methods (mainly reverse osmosis (RO) method) and evaporation methods. In both methods, fresh water is obtained while concentrated brine called brine is discharged.

  Until now, brine has been mainly released into the ocean. However, in recent years, there has been concern about the impact on the ecosystem due to an increase in the salt concentration of seawater, and it has been considered to establish a regulation that prevents the brine from being discharged as it is.

  Therefore, a method for treating brine generated by desalination treatment such as seawater so as not to discharge high-concentration salt water has begun to be studied. As a typical method, a method called a brine concentration method is known.

  In the brine concentration method, the brine generated by the desalination treatment is further concentrated by evaporation, and finally the salt contained in the brine is recovered as a crystallized salt (solid), so that the brine with a reduced salt concentration is obtained. And fresh water are discharged (see, for example, Patent Document 1 (US Patent No. 9085471)). This method is also called “Zero Liquid Discharge (ZLD)”. By recovering crystallized salt (solid salt) from brine, high-concentration brine is not discharged and valuable salt can be produced. There are also advantages.

US Patent No. 9085471

  However, since the evaporation method used in the brine concentration method consumes a large amount of energy, there is a problem that the energy required for the brine processing increases and the processing cost increases.

  An object of this invention is to provide the processing method of a brine which can reduce the energy required for the processing of the brine in a brine concentration method, and can reduce processing cost in view of said subject.

[1]
A method for treating brine produced by concentrating the salt water along with the desalination treatment of the salt water using at least one of a reverse osmosis method and an evaporation method,
Concentrating a portion of the brine to obtain a concentrated brine and diluting another portion of the brine to obtain a diluted brine; and
A salinity recovery step of recovering a salt content contained in the concentrated brine obtained by the concentration step as a crystallized salt using an evaporation method,
The concentration step includes
A portion of the brine is allowed to flow into the first chamber of the semipermeable membrane module having a semipermeable membrane and a first chamber and a second chamber partitioned by the semipermeable membrane, and the brine is introduced into the second chamber. Membrane separation in which water contained in the brine in the first chamber is transferred to the brine in the second chamber through the semipermeable membrane by flowing the other part and pressurizing the first chamber A method for treating brine, comprising a step.

[2]
A saltwater desalination method using the brine treatment method according to [1] above.

[3]
A system for treating brine produced by concentrating the brine in a desalination treatment of the brine using at least one of a reverse osmosis method and an evaporation method,
Concentrating a portion of the brine to obtain a concentrated brine and diluting another portion of the brine to obtain a diluted brine; and
A salinity recovery device for recovering a salt content contained in the concentrated brine obtained by the concentration device as a crystallized salt using an evaporation method,
The concentrator is
A semipermeable membrane module having a semipermeable membrane, and a first chamber and a second chamber partitioned by the semipermeable membrane, wherein a portion of the brine is allowed to flow in the first chamber, and the second chamber is By flowing another part of the brine and pressurizing the first chamber, water contained in the brine in the first chamber is transferred to the brine in the second chamber through the semipermeable membrane, A brine treatment system including a membrane separator.

[4]
A saltwater desalination system comprising the brine processing system according to [3] above.

  ADVANTAGE OF THE INVENTION According to this invention, the energy required for the process of the brine in a brine concentration method can be reduced, and the process method of a brine which can reduce a process cost can be provided.

It is a schematic diagram which shows one Embodiment of the brine processing method and salt water desalination processing method of this invention.

<Brine treatment method, desalination treatment method>
The brine treatment method of the present embodiment is a treatment method for brine (concentrated salt water) generated by concentrating salt water in association with desalination treatment of salt water using at least one of a reverse osmosis method and an evaporation method. .

  According to the brine processing method of this embodiment, at least a part of the salt content in the brine is finally removed (recovered) by the brine concentration method, and the salt content of the brine discharged to the ocean or the like is reduced. It will be.

  The brine processing method of the present embodiment mainly includes a concentration step and a salt content recovery step. The brine processing method of this embodiment is characterized in that the concentration step includes a membrane separation step.

  The desalination treatment method of this embodiment is a method for obtaining fresh water from salt water. The desalination treatment method of this embodiment includes a desalination treatment step. In this desalination treatment step, brine (concentrated salt water) generated with the production of fresh water is treated using the brine treatment method of this embodiment.

  Hereinafter, the brine processing method and the desalination processing method of this embodiment will be described in detail with reference to FIG.

  As shown in FIG. 1, first, fresh water is obtained from salt water by the desalination treatment step 3. In this specification, salt water is a liquid containing at least salt and water, such as sea water and brine. The evaporation residue concentration (TDS) of the salt water is not particularly limited, but is preferably about 3 to 10% by mass.

  In addition, you may perform the pre-processing for removing the microparticles | fine-particles, microorganisms, etc. which are contained in salt water with respect to salt water. As the pretreatment, various known pretreatments used in seawater desalination technology can be carried out, and examples thereof include filtration using an NF membrane and the like, addition of sodium hypochlorite, and addition of a flocculant. Such pretreatment is preferably performed before the fresh water treatment step.

  The desalination treatment step 3 is performed using at least one of a reverse osmosis (RO) method and an evaporation method. In the desalination process 3, fresh water is produced from salt water and brine (concentrated salt water) is produced.

  The RO method is a method in which salt water pressurized by a high-pressure pump is supplied to a reverse osmosis (RO) membrane module to produce fresh water that has passed through the RO membrane by pressure. In the RO method, as fresh water is produced, concentrated salt water (brine) is generated due to the transfer of moisture through the RO membrane.

  The evaporation method is a method of obtaining fresh water by heating salt water to vaporize (evaporate) water in the salt water and cooling the vaporized water. Also in the evaporation method, concentrated brine (brine) is generated by evaporation of moisture.

  In addition, the salt content rate of the brine produced by the desalination process using RO method (RO membrane module) is usually below a saturated concentration. This is because the salt content (crystallized salt) precipitates when the salt content of the brine exceeds the saturation concentration, and the RO membrane module cannot be used continuously due to clogging of the semipermeable membrane (RO membrane). .

  Moreover, even when implementing a fresh water treatment process using an evaporation method, it is preferable that the salt content rate of the brine produced by a desalination treatment process is below a saturation concentration. When the salt content of the brine exceeds the saturation concentration, the crystallized salt is precipitated, so that it is necessary to remove or recover the crystallized salt. If such crystallized salt is removed or recovered in the fresh water treatment process, it will lead to a decrease in recovery efficiency and complexity of the equipment, and the recovery rate of valuable salts in the subsequent salt recovery process will decrease. is there.

[Concentration process]
In the concentration step 4, a part of the brine is concentrated to obtain a concentrated brine, and the other part of the brine is diluted to obtain a diluted brine. The concentration step 4 includes a membrane separation step 41.

  Here, the salt concentration of the concentrated brine finally obtained by the concentration step is preferably equal to or lower than the saturated concentration. When the salt content of the concentrated brine exceeds the saturation concentration, the crystallized salt is precipitated, so that it is necessary to remove or recover the crystallized salt. If such crystallized salt is removed or recovered in the concentration step, the recovery efficiency is lowered and the equipment is complicated, and the recovery rate of valuable salt in the subsequent salt content recovery step is reduced.

  However, it is easier to recover the crystallized salt by evaporation from a high-concentration brine that is as close as possible to the saturated concentration than to recover the crystallized salt from a low-concentration brine by evaporation. Since the amount of water is small, less energy is required to recover the crystallized salt (salt recovery step). For this reason, in the concentration step before the salinity recovery step, it is desirable to concentrate the brine to a high concentration as close to the saturation concentration as possible by a low energy processing method (membrane separation step).

(Membrane separation process)
In the membrane separation step 41, a part of the brine is caused to flow in the first chamber of the semipermeable membrane module having the semipermeable membrane and the first chamber and the second chamber partitioned by the semipermeable membrane, and the brine is supplied to the second chamber. By flowing the other part and pressurizing the first chamber, the water contained in the brine in the first chamber is transferred to the brine in the second chamber through the semipermeable membrane.

  In the present embodiment, as shown in FIG. 1, the membrane separation process is a multistage process. That is, concentration by means of membrane separation of brine is performed step by step using a plurality of semipermeable membrane modules.

  The membrane separation step may be a one-step process using one semipermeable membrane module. However, since there is a limit to the concentration rate of brine in the single-stage process, the salt concentration of the brine may not be sufficiently increased in the single-stage process. For this reason, it is preferable that a membrane separation process is a process of two steps or more.

  Referring to FIG. 1, first, the brine generated by the desalination treatment step 3 includes a semipermeable membrane 10, and a first chamber 11 and a second chamber 12 partitioned by the semipermeable membrane 10. Part of the semipermeable membrane module 1 flows into the first chamber 11 and the other part flows into the second chamber 12. Then, by pressurizing the first chamber 11, the water contained in the brine in the first chamber 11 is transferred to the brine in the second chamber 12 through the semipermeable membrane 10. As a result, concentrated brine having a higher concentration than the original brine is discharged from the first chamber 11, and diluted brine having a lower concentration than the original brine is discharged from the second chamber 12.

  In FIG. 1, the diluted brine discharged from the first semipermeable membrane module 1 is returned to the desalination process, but the diluted brine is close to the concentration of seawater or the like in the salinity concentration. For example, it may be discharged into the ocean.

  Next, the concentrated brine obtained by the first semipermeable membrane module 1 is provided with a second semi-permeable membrane 20 and a first chamber 21 and a second chamber 22 partitioned by the semipermeable membrane 20. A part thereof flows into the first chamber 21 of the permeable membrane module 2 and another part flows into the second chamber. Then, by pressurizing the first chamber 21, the water contained in the concentrated brine in the first chamber 21 is transferred to the brine in the second chamber 22 through the semipermeable membrane 20. Thereby, the concentrated brine concentrated to a higher concentration than the original concentrated brine is discharged from the first chamber 21, and the diluted brine having a lower concentration than the original concentrated brine is discharged from the second chamber 22.

  In FIG. 1, the diluted brine discharged from the second semipermeable membrane module 2 is returned to the desalination treatment step. For example, the diluted brine discharged from the first semipermeable membrane module 1 and If the salt concentration is close to seawater by mixing, etc., it may be discharged to the ocean.

  Here, at the inlet of the semipermeable membrane modules (the first semipermeable membrane module 1 and the second semipermeable membrane module 2), the brine flowing into one side and the other side of the semipermeable membrane is desalinated in seawater. The osmotic pressure is basically the same because of the brine produced by the treatment. However, in the case where the salt concentration of seawater or the like of the raw material is different between the brine flowing on one side of the semipermeable membrane and the brine flowing on the other side, penetration of the brine flowing on one side and the other side of the semipermeable membrane Pressure may be different. Even in such a case, if the osmotic pressure difference (absolute value) is about 10% or less of the pressure for pressurizing the first chamber, the membrane separation step can be performed. Therefore, the difference between the osmotic pressure of the brine flowing into one side (pressure side) of the semipermeable membrane and the osmotic pressure of the brine flowing into the other side of the semipermeable membrane is 10% or less of the pressure for pressurizing the first chamber It is preferable that

  In the desalination process using the RO method, the osmotic pressure difference on both sides of the RO membrane increases from the salt water inlet to the outlet in the RO membrane module, and the osmotic pressure difference becomes equal to the pressure of pressurization to the salt water. No more reverse osmosis. For this reason, in the RO method, there is an upper limit in the concentration rate of salt water depending on the pressure upper limit of pressurization to the salt water determined by the pressure resistance of the RO membrane module and the performance of the pump.

  The brine generated by the desalination process using the RO method is often concentrated to the upper limit of the concentration rate in the RO method in order to increase the recovery efficiency of fresh water. In addition, brine generated by a desalination treatment process using an evaporation method is often concentrated to a concentration higher than the upper limit of the concentration rate in the RO method in order to increase the recovery efficiency of fresh water. For this reason, further concentrated brine and fresh water cannot be obtained from the brine generated by the desalination treatment using the RO method.

  On the other hand, in the membrane separation process of this embodiment, the osmotic pressure of the brine flowing into one side and the other side of the semipermeable membrane is basically equal at the inlet of the semipermeable membrane module. For this reason, unlike the RO method, there is no need for high pressure to cause reverse osmosis against high osmotic pressure difference between salt water or brine and fresh water. Concentration and some other dilution can be performed. Therefore, according to the membrane separation step, it is possible to further concentrate the brine concentrated to the limit by the RO method with a low energy treatment.

  However, even in the membrane separation step, the osmotic pressure difference between the concentrated brine and the diluted brine on both sides of the semipermeable membrane cannot be higher than the pressure applied to the first chamber of the semipermeable membrane module. There is a limit to the concentration rate of brine by one step (one semipermeable membrane module). For this reason, for example, in order to concentrate the brine until the salinity concentration reaches the saturation concentration, the membrane separation step is preferably a two-step or more step.

  In the membrane separation step, normally, the salt content of concentrated brine cannot be made higher than the saturated concentration. This is because the salt content (crystallized salt) is precipitated when the salt content of the brine is equal to or higher than the saturated concentration, and the semipermeable membrane module cannot be continuously used due to clogging of the semipermeable membrane.

  In FIG. 1, the concentration step 4 includes a step of concentrating brine by the evaporation method in addition to the membrane separation step 41. However, since the evaporation method consumes a large amount of energy, it is evaporated in this concentration step in terms of energy efficiency. It is desirable not to use the law. However, according to the evaporation method, fresh water can be obtained directly in the concentration step, which is advantageous in terms of increasing the recovery rate of fresh water.

[Salt recovery process]
In the salt recovery step 5, the salt contained in the concentrated brine obtained by the concentration step is recovered as a crystallized salt using an evaporation method.

  In the salt recovery step 5, the crystallized salt can be recovered by evaporating the water from the concentrated brine, further concentrating the concentrated brine, and finally evaporating all the water. At this time, if the evaporated water is cooled, fresh water can be recovered.

<Brine processing system>
The brine treatment system of this embodiment is a brine treatment system produced by concentrating salt water in a desalination treatment of salt water using at least one of a reverse osmosis (RO) method and an evaporation method. The brine processing system of this embodiment is suitably used in the above-described brine processing method.

  The brine processing system of this embodiment is a concentration device obtained by concentrating a part of the brine to obtain a concentrated brine and diluting another part of the brine to obtain a diluted brine, and the concentration obtained by the concentration step. A salinity recovery device that recovers a salt content contained in the brine as a crystallized salt using an evaporation method.

  The concentrator includes at least a membrane separator. The membrane separation apparatus includes a semipermeable membrane module having a semipermeable membrane and a first chamber and a second chamber partitioned by the semipermeable membrane. Then, the membrane separation device flows a part of the brine into the first chamber of the semipermeable membrane module, flows the other part of the brine into the second chamber, and pressurizes the first chamber, thereby This is a device for transferring water contained in the brine to the brine in the second chamber through the semipermeable membrane.

  As the semipermeable membrane, for example, a reverse osmosis membrane (RO membrane: Reverse Osmosis membrane), a forward osmosis membrane (FO membrane: forward osmosis membrane), a nanofiltration membrane (NF membrane: nanofiltration membrane), and an ultrafiltration membrane (UF membrane). : A semipermeable membrane called Ultrafiltration Membrane). The semipermeable membrane is preferably a reverse osmosis membrane, a forward osmosis membrane or a nanofiltration membrane. In addition, when using a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane as a semipermeable membrane, the pressure of pressurization in the first chamber is preferably 0.5 to 6.5 MPa.

  Usually, the pore size of the RO membrane and the FO membrane is about 2 nm or less, and the pore size of the UF membrane is about 2 to 100 nm. The NF membrane has a relatively low rejection rate of ions and salts among the RO membrane, and the pore size of the NF membrane is usually about 1 to 2 nm. When an RO membrane, FO membrane, or NF membrane is used as the semipermeable membrane, the salt removal rate of the RO membrane, FO membrane, or NF membrane is preferably 90% or more.

  Although it does not specifically limit as a material which comprises a semipermeable membrane, For example, a cellulose resin, a polysulfone resin, a polyamide resin etc. are mentioned. The semipermeable membrane is preferably composed of a material containing at least one of a cellulose resin and a polysulfone resin.

  The cellulose resin is preferably a cellulose acetate resin. Cellulose acetate resin is resistant to chlorine, which is a bactericidal agent, and has a feature that it can suppress the growth of microorganisms. The cellulose acetate resin is preferably cellulose acetate, and more preferably cellulose triacetate from the viewpoint of durability.

  The polysulfone resin is preferably a polyethersulfone resin. The polyethersulfone resin is preferably a sulfonated polyethersulfone.

  Although it does not specifically limit as a shape of a semipermeable membrane, For example, a flat membrane, a spiral membrane, or a hollow fiber membrane is mentioned. In FIG. 1, a flat membrane is illustrated as a semipermeable membrane in a simplified manner, but is not particularly limited to such a shape. The hollow fiber membrane (hollow fiber type semipermeable membrane) is advantageous in that the membrane area per module can be increased and the permeation efficiency can be increased as compared with a spiral type semipermeable membrane.

  As an example of a specific hollow fiber type semipermeable membrane, a membrane having a single layer structure, which is entirely composed of a cellulosic resin, can be mentioned. However, the single-layer structure here does not need to be a uniform film as a whole, for example, as disclosed in Patent Document 1, a dense layer is provided in the vicinity of the outer peripheral surface, and this dense layer is substantially In particular, it is preferably a separation active layer that defines the pore diameter of the hollow fiber type semipermeable membrane.

  As another example of a specific hollow fiber type semipermeable membrane, 2 having a dense layer made of a polyphenylene resin (for example, sulfonated polyethersulfone) on the outer peripheral surface of a support layer (for example, a layer made of polyphenylene oxide) A film having a layer structure may be mentioned. Another example includes a two-layered film having a dense layer made of a polyamide resin on the outer peripheral surface of a support layer (for example, a layer made of polysulfone or polyethersulfone).

  Normally, the brine that flows to the dense layer side of the hollow fiber type semipermeable membrane is pressurized. This is because pressurizing the fluid flowing on the dense layer side, that is, the outside of the hollow fiber type semipermeable membrane, is less susceptible to pressure loss. Further, sharper fractionation can be obtained by pressurizing the dense layer side.

<Desalination system>
The desalination treatment system of this embodiment is a system for obtaining fresh water from salt water. The desalination processing system of this embodiment is provided with the apparatus for implementing said desalination processing process, and said brine processing system.

  Examples of the apparatus for carrying out the desalination treatment step include an apparatus for carrying out the RO method including the RO membrane module and the like, an apparatus for carrying out the evaporation method including the heating device and the cooling device, and the like. Various known devices can be used.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 1st semipermeable membrane module, 10 Semipermeable membrane, 11 1st chamber, 12 2nd chamber, 2 2nd semipermeable membrane module, 20 Semipermeable membrane, 21 1st chamber, 22 2nd chamber, 3 Fresh water Treatment process, 4 concentration process, 41 membrane separation process, 5 salt content recovery process.

Claims (4)

A method for treating brine produced by concentrating the salt water along with the desalination treatment of the salt water using at least one of a reverse osmosis method and an evaporation method,
Concentrating a portion of the brine to obtain a concentrated brine and diluting another portion of the brine to obtain a diluted brine; and
A salinity recovery step of recovering a salt content contained in the concentrated brine obtained by the concentration step as a crystallized salt using an evaporation method,
The concentration step includes
A portion of the brine is allowed to flow into the first chamber of the semipermeable membrane module having a semipermeable membrane and a first chamber and a second chamber partitioned by the semipermeable membrane, and the brine is introduced into the second chamber. Membrane separation in which water contained in the brine in the first chamber is transferred to the brine in the second chamber through the semipermeable membrane by flowing the other part and pressurizing the first chamber A method for treating brine, comprising a step.   A saltwater desalination method using the brine treatment method according to claim 1. A system for treating brine produced by concentrating the salt water along with desalination of salt water using at least one of reverse osmosis and evaporation,
Concentrating a portion of the brine to obtain a concentrated brine and diluting another portion of the brine to obtain a diluted brine; and
A salinity recovery device for recovering a salt content contained in the concentrated brine obtained by the concentration device as a crystallized salt using an evaporation method,
The concentrator is
A semipermeable membrane module having a semipermeable membrane, and a first chamber and a second chamber partitioned by the semipermeable membrane, wherein a portion of the brine is allowed to flow in the first chamber, and the second chamber is By flowing another part of the brine and pressurizing the first chamber, water contained in the brine in the first chamber is transferred to the brine in the second chamber through the semipermeable membrane, A brine treatment system including a membrane separator.   A saltwater desalination system comprising the brine treatment system according to claim 3.

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