JP2018001111A - Processing method of desalinating salt water and processing system of desalinating salt water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing method of desalinating salt water capable of reducing a pressure necessary for desalination processing using a reverse osmosis method, and a processing system of desalinating salt water.SOLUTION: The processing method of desalinating salt water for obtaining fresh water from salt water includes: a membrane separation step of transferring water contained in the salt water in a first chamber to the salt water in a second chamber through a semipermeable membrane to discharge a dilute salt water obtained from the second chamber by dilution by flowing a part of the salt water to the first chamber of a semipermeable module provided with the semipermeable membrane, and with the first chamber and the second chamber separated by the semipermeable membrane, and flowing the other part of the salt water to the second chamber to pressurize the first chamber; and a desalination step of obtaining fresh water from the diluted salt water using a reverse osmotic method.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a desalination treatment method for salt water and a desalination treatment system for salt water.

  As a technique for desalinating salt water such as seawater, a reverse osmosis (RO) method is known. In the RO method, salt water that has been boosted to a predetermined pressure higher than the osmotic pressure by a high-pressure pump is supplied to the reverse osmosis (RO) membrane module and passed through the RO membrane, thereby removing salt and the like from seawater. It is a method of taking out.

  The RO method has been studied in recent years because it consumes less energy than the conventionally known evaporation method.

  In the treatment of associated water for recovering oil from petroleum-containing formations, in order to adjust the salinity concentration of the associated water, salt water is flowed on both sides of the reverse osmosis membrane, and the flow rate and pressure on both sides are adjusted to reverse A technique is known in which water in one salt water is transferred to the other salt water through an osmosis membrane.

US Patent Application Publication No. 2015/0260028

  In the desalination treatment by the RO method, a high-pressure pump and a treatment facility with high pressure resistance are necessary, and the pressure load on the reverse osmosis membrane is large, and thus there is a problem that the life of the reverse osmosis membrane is shortened.

  In view of the above problems, the present invention provides a salt water desalination method and a salt water desalination system that can reduce the pressure required for desalination using a reverse osmosis method. Objective.

[1]
A desalination treatment method for obtaining fresh water from salt water,
A portion of the salt water is caused to flow in the first chamber of a semipermeable membrane module including a semipermeable membrane, and a first chamber and a second chamber partitioned by the semipermeable membrane, and the salt water is supplied to the second chamber. By flowing the other part and pressurizing the first chamber, water contained in the salt water in the first chamber is transferred to the salt water in the second chamber through the semipermeable membrane, A membrane separation step of discharging diluted brine which is the brine diluted from two chambers;
A desalination treatment step of obtaining the fresh water from the diluted salt water using a reverse osmosis method.

[2]
A desalination treatment system for obtaining fresh water from salt water,
A semipermeable membrane module having a semipermeable membrane, and a first chamber and a second chamber partitioned by the semipermeable membrane, a portion of the salt water is allowed to flow in the first chamber, and the second chamber is Flowing the other part of the salt water to pressurize the first chamber, thereby transferring water contained in the salt water in the first chamber to the salt water in the second chamber through the semipermeable membrane, A membrane separation device for discharging diluted brine which is the brine diluted from the second chamber;
A desalination treatment system comprising: a reverse osmosis membrane module; and a desalination treatment device that obtains the fresh water from the diluted salt water using the reverse osmosis membrane module.

  ADVANTAGE OF THE INVENTION According to this invention, the desalination process method of salt water and the desalination system of salt water which can reduce the pressure required for the desalination process using a reverse osmosis method can be provided.

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

<Desalination treatment method>
The desalination treatment method of the present embodiment is a desalination treatment method for obtaining fresh water from salt water using a reverse osmosis (RO) method.

  The saltwater desalination method of the present embodiment is characterized by including a membrane separation step for obtaining diluted saltwater from saltwater and a desalination treatment step for obtaining the freshwater from the diluted saltwater using a reverse osmosis method. Hereinafter, the detail of the desalination processing method of this embodiment is demonstrated with reference to FIG.

(Membrane separation process)
As shown in FIG. 1, first, diluted salt water is obtained from salt water by a membrane separation step.

  In this specification, salt water is a liquid containing at least salt and water, such as sea water and brine. Although the evaporation residue density | concentration (TDS) of salt water is not specifically limited, Preferably it is about 3-13 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 implemented. For example, filtration using NF membrane, UF membrane, MF membrane, addition of sodium hypochlorite, flocculant Addition etc. are mentioned. Such pretreatment is preferably performed before the membrane separation step.

  The membrane separation step is performed using the semipermeable membrane module 1. The semipermeable membrane module 1 includes a semipermeable membrane 10 and a first chamber 11 and a second chamber 12 partitioned by the semipermeable membrane 10.

  In the membrane separation step, a part of the salt water is caused to flow in the first chamber 11 of the semipermeable membrane module 1 and the other part of the salt water is caused to flow in the second chamber 12 to pressurize the first chamber 11. Thereby, the water contained in the salt water in the first chamber 11 is transferred to the salt water in the second chamber 12 through the semipermeable membrane 10, and the diluted salt water that is diluted salt water is discharged from the second chamber 12. .

  Accordingly, the salt water in the first chamber 11 is concentrated, and the first brine that is the concentrated salt water is discharged from the first chamber 11.

  Here, at the inflow port of the semipermeable membrane module 1, since the brine flowing into one side and the other side of the semipermeable membrane is salt water such as seawater, the osmotic pressure is basically equal. For this reason, unlike the RO method, high pressure for causing reverse osmosis against the high osmotic pressure difference between salt water and fresh water is not necessary, and diluted salt water can be obtained by relatively low pressure. (Some brines can be diluted and some other brines can be concentrated).

  However, the osmotic pressure of salt water flowing on one side and the other side of the semipermeable membrane, such as when the salt water flowing on one side of the semipermeable membrane and the salt water flowing on the other side have different salinity concentrations in the stock solution such as seawater 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. For this reason, the difference between the osmotic pressure of salt water flowing into one side (pressure side) of the semipermeable membrane and the osmotic pressure of salt water 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

  The membrane separation step may be a one-step process using one semipermeable membrane module as shown in FIG. 1, but is a multi-step step using a plurality of semipermeable membrane modules 1. Also good. In the membrane separation step, the difference in osmotic pressure between the diluted brine on both sides of the semipermeable membrane and the first brine cannot be higher than the pressure applied to the first chamber of the semipermeable membrane module. There is a limit to the dilution rate of salt water by one semipermeable membrane module). For this reason, the membrane separation process may be a two or more-stage process for the purpose of further reducing the pressure required for the desalination treatment process by lowering the concentration of the diluted brine used in the desalination treatment process. .

(Desalination process)
Next, a desalination treatment step for obtaining fresh water from the diluted salt water is performed. The desalination process is performed using a reverse osmosis (RO) method. In the desalination treatment step 3, fresh water is produced from the diluted salt water, and second brine (a liquid in which the diluted salt water is concentrated) is generated.

  Specifically, diluted salt water pressurized by a high pressure pump (not shown) is supplied to the first chamber 21 of the reverse osmosis (RO) membrane module 2. Thereby, the water contained in the diluted salt water in the first chamber 21 is transferred to the second chamber 22 through the RO membrane 20 by the pressure, and fresh water is discharged from the second chamber 22.

  Accordingly, the diluted salt water in the first chamber 21 is concentrated, and salt water (second brine) having a higher concentration than the diluted salt water is discharged from the first chamber 11.

  In such a desalination process, the osmotic pressure difference between diluted salt water (salt water diluted by the membrane separation process) and fresh water is smaller than the osmotic pressure difference between the original salt water (such as seawater) and fresh water. For this reason, in this embodiment, compared with the case where the same amount of fresh water is obtained from salt water only by the RO method, fresh water can be obtained by pressurization at a lower pressure.

  Accordingly, a normal (medium pressure to low pressure) pump can be used without requiring a high pressure pump. Further, it is not necessary to increase the pressure resistance of the processing equipment, and the cost of equipment investment can be reduced. Further, the same recovery rate can be realized without using a high-pressure pump, and the power consumption can be reduced.

  In the desalination process using the RO method, the osmotic pressure difference on both sides of the RO membrane increases from the inlet to the outlet of the salt water in the RO membrane module, and the osmotic pressure difference is equal to the pressure applied to the salt water. Once equal, reverse osmosis will not proceed any further. 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 pressurizing pressure in the RO method is, for example, about 1 to 6 MPa.

  However, from the viewpoint of increasing the production efficiency of fresh water per salt water, it is desirable that the second brine is concentrated as high as possible. Although the salt concentration of a 2nd brine is not specifically limited, For example, it is about 3-10 mass%.

  Moreover, the 1st brine discharged | emitted from the semipermeable membrane module 1 and the 2nd brine discharged | emitted from the RO membrane module 2 are all the brines produced when producing the same amount of fresh water from salt water only by RO method ( Concentrated salt water).

  The salt content of the first brine produced by the membrane separation process using the semipermeable membrane module 1 and the salt content of the second brine produced by the desalination treatment process using the RO method (RO membrane module 2) are usually The saturation concentration is below. When the salt content of brine exceeds the saturation concentration, salt (crystallized salt) precipitates, so the semipermeable membrane module 1, RO membrane module 2, etc. are continuously used due to clogging of the semipermeable membrane (RO membrane). It is because it becomes impossible to do.

<Desalination system>
The desalination treatment system of this embodiment is a system for obtaining fresh water from salt water. The desalination treatment system of the present embodiment includes a membrane separation device for performing the membrane separation step and a desalination treatment device for performing the desalination treatment step.

  The membrane separation device includes a semipermeable membrane module 1. The semipermeable membrane module 1 includes a semipermeable membrane 10 and a first chamber 11 and a second chamber 12 partitioned by the semipermeable membrane 10.

  Then, the membrane separator flows a part of the salt water into the first chamber 11 of the semipermeable membrane module 1 and flows the other part of the salt water into the second chamber 12, thereby pressurizing the first chamber 11, This is a device for transferring the water contained in the salt water in the first chamber 11 to the salt water in the second chamber 12 through the semipermeable membrane 10 and discharging the diluted salt water that is diluted salt water from the second chamber 12.

  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. When a reverse osmosis membrane, a forward osmosis membrane, or a nanofiltration membrane is used as the semipermeable membrane, the pressure of 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, salt water that flows to the dense layer side of the hollow fiber type semipermeable membrane is pressurized. This is because even if the fluid flowing on the dense layer side, that is, the inner side (hollow part) of the hollow fiber type semipermeable membrane is pressurized, the pressure loss increases and the pressure does not work sufficiently.

(Desalination equipment)
The desalination apparatus includes a reverse osmosis (RO) membrane module 2. The desalination apparatus is not particularly limited as long as it is an apparatus that can obtain fresh water from the diluted salt water using the RO membrane module 2 (by the RO method). 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 Semipermeable membrane module, 10 Semipermeable membrane, 11 1st chamber, 12 2nd chamber, 2 Reverse osmosis membrane module, 20 Reverse osmosis membrane, 21 1st chamber, 22 2nd chamber.

Claims (2)

A desalination treatment method for obtaining fresh water from salt water,
A portion of the salt water is caused to flow in the first chamber of a semipermeable membrane module including a semipermeable membrane, and a first chamber and a second chamber partitioned by the semipermeable membrane, and the salt water is supplied to the second chamber. By flowing the other part and pressurizing the first chamber, water contained in the salt water in the first chamber is transferred to the salt water in the second chamber through the semipermeable membrane, A membrane separation step of discharging diluted brine which is the brine diluted from two chambers;
A desalination treatment step of obtaining the fresh water from the diluted salt water using a reverse osmosis method. A desalination treatment system for obtaining fresh water from salt water,
A semipermeable membrane module having a semipermeable membrane, and a first chamber and a second chamber partitioned by the semipermeable membrane, a portion of the salt water is allowed to flow in the first chamber, and the second chamber is Flowing the other part of the salt water to pressurize the first chamber, thereby transferring water contained in the salt water in the first chamber to the salt water in the second chamber through the semipermeable membrane, A membrane separation device for discharging diluted brine which is the brine diluted from the second chamber;
A desalination treatment system comprising: a reverse osmosis membrane module; and a desalination treatment device that obtains the fresh water from the diluted salt water using the reverse osmosis membrane module.

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