JP2021041359A - Concentration system - Google Patents

Abstract

To provide a system for cleaning a semi-permeable membrane module used for BC while maintaining a high operation rate in a concentration system which further concentrates a concentrated solution of a reverse osmosis module by brine concentration (BC).SOLUTION: A concentration system includes: a reverse osmosis module 2 which separates water from an original liquid increased in pressure to a predetermined pressure through a reverse osmosis membrane 20 and discharges the concentrated original liquid; a plurality of semi-permeable membrane modules 1a to 1c which have a first chamber 11 and a second chamber 12 separated by a semi-permeable membrane 10, transfer water contained in a first target liquid to a second target liquid through the semi-permeable membrane by flowing the concentrated original liquid into a first chamber at a predetermined pressure as the first target liquid and flowing the second target liquid into a second chamber at a pressure lower than the predetermined pressure, and discharge the concentrated liquid from the first chamber and discharge a diluted liquid from the second chamber; and a control mechanism which stops the supply of the first target liquid at a predetermined timing for at least one module selected from the semi-permeable membrane modules, and carries out cleaning of the semi-permeable membrane.SELECTED DRAWING: Figure 1

Description

The present invention relates to a concentration system.

For example, for the purpose of reducing the energy required for desalination using the reverse osmosis (RO) method, a high-pressure target liquid is flowed through the first chamber of the semipermeable membrane module, and a low-pressure target is flowed into the second chamber. By flowing the liquid and transferring the water contained in the target liquid in the first chamber to the target liquid in the second chamber via the semipermeable membrane, the concentrated target liquid is discharged from the first chamber and the second chamber is discharged. A membrane separation method (brine concentration) for discharging the target liquid diluted from the above has been studied (see, for example, Patent Document 1: Japanese Patent Application Laid-Open No. 2018-1110).

In addition, the concentrated liquid discharged from the RO module is flowed into the first chamber of the semipermeable membrane module that can be operated at a higher pressure, and the concentrated liquid is further subjected to ultra-high pressure conditions compared to the RO method by the above-mentioned brine concentration (BC). Concentration systems for concentrating are also being considered.

Japanese Unexamined Patent Publication No. 2018-1110

In the semipermeable membrane module used for brine concentration, impurities such as turbid substances (for example, fine particles, microorganisms, scale components) adhere to the surface of the semipermeable membrane over time according to the amount of the membrane separation process of the target liquid. , Separation performance (filtration efficiency) decreases. Therefore, it is desirable that the semipermeable membrane of the semipermeable membrane module be washed at regular intervals according to the degree of adhesion of impurities.

However, in an actual plant, since the operating rate is important, the frequency of cleaning is reduced in order to avoid a decrease in the operating rate, and as a result, the semipermeable membrane is cleaned at an appropriate timing according to the degree of adhesion of impurities. Is concerned that it will be difficult to execute. If the cleaning timing is delayed, the state of the semipermeable membrane cannot be sufficiently restored, and as a result, the separation performance of the semipermeable membrane module may be deteriorated or the life of the semipermeable membrane module may be shortened. On the contrary, if the cleaning frequency becomes higher than necessary, there is a concern that the processing efficiency will decrease.

Therefore, the present invention is a semipermeable membrane module used for BC while increasing the operating rate as much as possible in a concentration system in which the concentrate discharged from the reverse osmosis (RO) module is further concentrated by brine concentration (BC). The purpose is to clean the module at an appropriate time.

(1) A reverse osmosis module that separates and recovers water from a stock solution that has been pressurized to a predetermined pressure via a reverse osmosis membrane, and discharges the concentrated stock solution that is the concentrated stock solution.
It has a semipermeable membrane and first and second chambers partitioned by the semipermeable membrane, and the concentrated stock solution is used as the first target solution and flowed into the first chamber at a predetermined pressure to form a second target solution. By flowing the water into the second chamber at a pressure lower than the predetermined pressure, the water contained in the first target liquid in the first chamber is passed through the semipermeable membrane to the second target in the second chamber. A concentrating system including a semipermeable membrane module that transfers to a liquid, discharges the concentrated liquid from the first chamber, and discharges the diluted liquid from the second chamber.
The concentration system comprises a plurality of the semipermeable membrane modules.
For at least one semipermeable membrane module selected from the plurality of semipermeable membrane modules, the supply of the first target liquid to some of the semipermeable membrane modules is stopped at a predetermined timing, and the semipermeable membrane is stopped. Concentration system with additional control mechanism that controls to perform cleaning of.

(2) The concentration system according to (1), further comprising a flow path switching device for switching the flow path connected to the semipermeable membrane module.

(3) The concentration system according to (1) or (2), further comprising a cleaning liquid tank in which a cleaning liquid for cleaning the semipermeable membrane is stored.

According to the present invention, in a concentration system in which the concentrate discharged from the reverse osmosis (RO) module is further concentrated by brine concentration (BC), the concentrate discharged from the reverse osmosis (RO) module is subjected to brine concentration ( In a concentration system that further concentrates with BC), the semipermeable membrane module used for BC can be washed at an appropriate timing while keeping the operating rate as high as possible.

It is a schematic diagram which shows the enrichment system of an embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals represent the same parts or equivalent parts. Further, the dimensional relationships such as length, width, thickness, and depth are appropriately changed for the purpose of clarifying and simplifying the drawings, and do not represent the actual dimensional relationships.

<Concentration system>
With reference to FIG. 1, the concentration system of the present embodiment includes a reverse osmosis module 2, a plurality of semipermeable membrane modules 1a, 1b, 1c, and a control mechanism 3.

In the reverse osmosis module 2, water is separated and recovered from the undiluted solution pressurized to a predetermined pressure via the reverse osmosis membrane 20, and the concentrated undiluted solution, which is the concentrated undiluted solution, is discharged.
The semipermeable membrane modules 1a, 1b, and 1c each have a semipermeable membrane 10 and chambers 11 and 2 12 partitioned by the semipermeable membrane, and a concentrated stock solution is designated as the first target solution. By flowing the second target liquid into the first chamber 11 at the pressure of the above and flowing the second target liquid into the second chamber 12 at a pressure lower than a predetermined pressure (pressure of the first liquid), the first target liquid in the first chamber 11 is formed. The contained water is transferred to the second target liquid in the second chamber 12 via the semipermeable membrane, the concentrated liquid is discharged from the first chamber 11, and the diluted liquid is discharged from the second chamber 12.
The control mechanism 3 stops the supply of the first target liquid to some of the semipermeable membrane modules at a predetermined timing for at least one semipermeable membrane module selected from the plurality of semipermeable membrane modules, and the semipermeable membrane Control to perform cleaning.

[Reverse osmosis module]
The concentration system of this embodiment includes a high pressure pump 2a on the upstream side of the reverse osmosis (RO) module 2. The high-pressure pump 2a boosts the stock solution to a predetermined pressure and supplies it to the first chamber 21 of the RO module 2. The RO module 2 separates water (permeated water) from the undiluted solution pressurized to a predetermined pressure to the second chamber 22 side via the reverse osmosis (RO) membrane 20, thereby producing a concentrated undiluted solution which is a concentrated undiluted solution. The water is discharged from the first chamber 21 and the water is discharged from the second chamber 22.

In the present specification, the "stock solution" is not particularly limited as long as it is a liquid containing water supplied to the RO module 2, and may be either a solution or a suspension. Examples of the undiluted solution include seawater, river water, brackish water, wastewater and the like. Examples of wastewater include industrial wastewater, domestic wastewater, oil field or gas field wastewater, and the like.

A pretreatment device (not shown) may be provided on the upstream side of the high-pressure pump 2a in order to remove turbid substances (fine particles, microorganisms, scale components, etc.) contained in the undiluted solution. Examples of the pretreatment device include a sand filtration device, a filtration device using a UF (Ultrafiltration) membrane, an MF (Microfiltration) membrane, etc., chlorine, sodium hypochlorite, a flocculant, and scale. Examples include an addition device such as an inhibitor and a pH adjustment device. The scale inhibitor is an additive having an action of preventing or suppressing the precipitation of scale components in the liquid as scale. Examples of the anti-scale agent include compounds such as polyphosphoric acid-based, phosphonic acid-based, phosphinic acid-based, and polycarboxylic acid-based compounds.

In the present embodiment, the semipermeable membrane modules 1a, 1b, and 1c are connected to the downstream side of the RO module 2 (first chamber 21). The first target liquid supplied to the first chamber 11 of the semipermeable membrane module (each of the semipermeable membrane modules 1a, 1b, 1c) is a concentrated stock solution discharged from the first chamber 21 of the RO module 2. Since the concentrated stock solution discharged from the RO module 2 has a high pressure, it is sent to the semipermeable membrane module side by the pressure.

[Semipermeable membrane module]
Each of the plurality of semipermeable membrane modules 1a, 1b, 1c has a semipermeable membrane 10 and a first chamber 11 and a second chamber 12 partitioned by the semipermeable membrane 10.

The first target liquid (concentrated stock solution discharged from the first chamber 21 of the RO module 2) flows into the first chamber 11 at a predetermined pressure, and the second target liquid is a second at a pressure lower than the predetermined pressure. It flows into the room 12. As a result, the water contained in the first target liquid in the first chamber 11 is transferred to the second target liquid in the second chamber 12 via the semipermeable membrane 10, and is concentrated (concentrated) from the first chamber 11. The first target liquid) is discharged, and the diluted liquid (diluted second target liquid) is discharged from the second chamber 12.

The first target liquid and the second target liquid may be the same liquid. For example, as shown in FIG. 1, a part of the first target liquid having a predetermined pressure is flowed into the second chamber at a pressure lower than the predetermined pressure by passing through the pressure lowering device 4. May be good.

The pressure lowering device 4 includes, for example, a flow dividing valve and a decompressor that can separately flow a first target liquid having a predetermined pressure into a flow path to the second chamber 12 of the semipermeable membrane module and another flow path. Alternatively, an energy recovery device or the like can be mentioned. Here, the pressure lowering device 4 (flow dividing valve) has a function of reducing the pressure of the target liquid flowing into the second chamber 12 to a pressure lower than a predetermined pressure. By using such a pressure reducing device, for example, there is an advantage that only one flow path of the target liquid on the upstream side of the semipermeable membrane module is required.

In the case of FIG. 1, since the target liquids flowing into the first chamber 11 and the second chamber 12 of the semipermeable membrane module (each of the semipermeable membrane modules 1a, 1b, 1c) are the same liquid, they are basically the same. Has osmotic pressure. Therefore, unlike the RO method, a high pressure for causing reverse osmosis against the high osmotic pressure difference between the target liquid (high osmotic liquid) and fresh water is not required, and pressure is applied at a relatively low pressure. Membrane separation of the target solution can be performed (some target solutions can be diluted and some other target solutions can be concentrated).

However, in the present embodiment, the second target liquid supplied to the second chamber 12 of the semipermeable membrane module may be a liquid independent of the first target liquid supplied to the first chamber 11.

The first target liquid flowing through the first chamber 11 and the second target liquid flowing through the second chamber 12 are different liquids, and even if the concentrations are different between the two, the osmotic pressure difference (absolute value) is the first. Theoretically, membrane separation by BC is feasible if the pressure is lower than the pressure of the first target liquid supplied to the chamber 11. In this case, the difference between the osmotic pressure of the first target liquid flowing into the first chamber 11 (high pressure side) and the osmotic pressure of the second target liquid supplied to the second chamber 12 (low pressure side) is the first chamber 11 It is preferably 30% or less of the predetermined pressure of the first target liquid supplied to the water.

Each of the semipermeable membrane modules 1a, 1b, and 1c may be one semipermeable membrane module as shown in FIG. 1, but is a semipermeable membrane module composed of a plurality of semipermeable membrane modules connected in parallel. It is preferably a permeable membrane module group (train). The control by the control mechanism described later is carried out for each such semipermeable membrane module group, for example.

Further, the BC step in each of the semipermeable membrane modules 1a, 1b, and 1c may be a one-step step using one semipermeable membrane module as shown in FIG. 1, but (in series). It may be a multi-stage process using a plurality of semipermeable membrane modules (connected).

In the brine concentration (BC), which is a membrane separation process in the semipermeable membrane module, in order to transfer water from the first chamber 11 to the second chamber 12 via the semipermeable membrane 10 of the semipermeable membrane module, a first It is necessary to make the pressure of the first target liquid supplied to the chamber 11 larger than the osmotic pressure difference between the first target liquid and the second target liquid flowing on both sides of the semipermeable membrane 10. Therefore, in order to highly concentrate the first target liquid in one step (one semipermeable membrane module), it is necessary to supply at a correspondingly high pressure, and the energy cost for operating the pump is high. There are disadvantages such as an increase in. Therefore, BC may be carried out by a multi-step process using a plurality of semipermeable membrane modules for the purpose of stepwise concentration step and reducing the pressure required for BC. BC by such a multi-step process is disclosed in, for example, Japanese Patent Application Laid-Open No. 2018-069198.

Examples of the semipermeable membrane include a semipermeable membrane called a reverse osmosis (RO) membrane, a forward osmosis (FO) membrane, and a nanofiltration (NF) 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 target liquid supplied to the first chamber 11 is preferably 6 to 10 MPa.

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

The material constituting the semipermeable membrane is not particularly limited, and examples thereof include a cellulosic resin, a polysulfone resin, and a polyamide resin. The semipermeable membrane is preferably composed of a material containing at least one of a cellulosic resin and a polysulfone resin.

The cellulosic resin is preferably a cellulosic acetate resin. Cellulose acetate-based resins are resistant to chlorine, which is a bactericidal agent, and have the characteristic of being able to suppress the growth of microorganisms. The cellulose acetate-based resin is preferably cellulose acetate, and more preferably tricellulose triacetate from the viewpoint of durability.

The polysulfone-based resin is preferably a polyether sulfone-based resin. The polyether sulfone-based resin is preferably a sulfonated polyether sulfone.

The shape of the semipermeable membrane 10 (and the reverse osmosis membrane 20 described above) is not particularly limited, and examples thereof include a flat membrane and a hollow fiber membrane. In FIG. 1, the semipermeable membrane 10 is a simplified drawing of the flat membrane, but the shape 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 improved as compared with a spiral type semipermeable membrane or the like.

The form of the semipermeable membrane module (and the reverse osmosis module 2 described above) is not particularly limited, but when a hollow fiber membrane is used, a module in which the hollow fiber membrane is arranged straight or a hollow fiber membrane is used as a core tube. Examples include a wrapped cross-wind module. When a flat film is used, examples thereof include a laminated module in which flat films are stacked, and a spiral module in which the flat film is wound around a core tube in an envelope shape.

As an example of a specific hollow fiber membrane, there is a single-layer structure membrane which is entirely composed of a cellulosic resin. However, the monolayer structure referred to here does not have to be a uniform film as a whole, and has, for example, a dense layer in the vicinity of the outer peripheral surface as disclosed in Japanese Patent Application Laid-Open No. 2012-115835. It is preferable that the dense layer is a separation active layer that substantially defines the pore size of the hollow fiber membrane.

As another specific example of the hollow fiber membrane, a two-layer structure having a dense layer made of a polyphenylene resin (for example, sulfonated polyether sulfone) on the outer peripheral surface of a support layer (for example, a layer made of polyphenylene oxide). Membrane is mentioned. Another example is 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).

In a semipermeable membrane module using a hollow fiber membrane, the outside of the hollow fiber membrane is usually the first chamber. This is because even if the fluid flowing inside the hollow fiber membrane (hollow fiber portion) is pressurized, the pressure loss becomes large and it is difficult for the pressurization to work sufficiently.

[Control mechanism]
The control mechanism 3 stops the supply of the first target liquid to some of the semipermeable membrane modules at a predetermined timing for at least one semipermeable membrane module selected from the plurality of semipermeable membrane modules 1a, 1b, 1c. And control the concentration system to perform a cleaning of the semipermeable membrane.

Cleaning is performed with at least some of the semipermeable membrane modules (semipermeable membrane module group) discontinued, but the other semipermeable membrane modules (semipermeable membrane module group) continue to be used. The operation of the enrichment system as a whole is preferably continued. As a result, it is possible to suppress a decrease in the processing efficiency of the concentration system. Further, the processing of the concentration system can be continuously carried out, and complicated work such as initial adjustment when the operation of the entire system is temporarily stopped and the operation is disclosed again can be omitted.

The cleaning may be performed one by one in a predetermined order and timing for, for example, a plurality of semipermeable membrane modules (semipermeable membrane module group) 1a, 1b, 1c.

The order and timing of cleaning, the cleaning time of each semipermeable membrane module, and the degree of cleaning are determined by various known simulations, etc., based on an index indicating the degree of contamination of the semipermeable membrane (degree of adhesion of scales, etc.). can do.

As an index of the degree of contamination of the semipermeable membrane for each semipermeable membrane module (semipermeable membrane module group), for example, the pressure difference between the inflow side and the discharge side of the semipermeable membrane module, and the semipermeable membrane module. Examples include the amount of permeated water (difference in flow rate between the inflow side and the discharge side).

The method for cleaning the semipermeable membrane (semipermeable membrane module) is not particularly limited, and examples thereof include cleaning with a cleaning liquid, backwashing (back pressure cleaning), and flushing.

(Cleaning with cleaning liquid)
In cleaning with a cleaning liquid, for example, one of the three-way valves 31, 32, and 33 is stopped from being supplied with the first target liquid to the semipermeable membrane module, and the cleaning liquid stored in the cleaning liquid tank 5 is a semipermeable membrane. Drive the pump 5a in a switched state so that it is supplied to the first chamber 11 (or both the first chamber 11 and the second chamber 12) of the module (each of the semipermeable membrane modules 1a, 1b, 1c). By doing so, it can be carried out.

The cleaning solution used for cleaning the chemical solution is not particularly limited as long as it can clean the stains on the semipermeable membrane. Examples of the cleaning liquid include water and chemicals. Examples of the cleaning liquid include permeated water discharged from the second chamber 22 of the RO module 2, a diluted liquid obtained by BC (diluted second target liquid discharged from the second chamber of the semipermeable membrane module), and the like. You may use it.

Drugs used in chemical solutions include, for example, removal of scales (calcium sulfate, magnesium sulfate, calcium carbonate, silicate, etc.) adhering to the semipermeable membrane, and removal of organic substances produced by organisms that cause biofouling. Drugs that can be used. Examples of such agents include surfactants, acid agents (inorganic acids such as hydrochloric acid, organic acids such as carboxylic acids, etc.), alkaline agents and the like. As a specific drug, for example, citric acid, sodium hypochlorite and the like are preferably used. Citric acid is preferably used for stains caused by inorganic substances. Sodium hypochlorite is suitably used for stains caused by organic substances.

In addition, for example, both cleaning with water and cleaning with a chemical solution may be carried out. For example, after cleaning with water, cleaning with a chemical solution may be performed, and then cleaning with water may be performed.

(Backwash)
In the semipermeable membrane module used for BC, backwashing means physically adhering to the semipermeable membrane 10 by making the direction of movement of water passing through the semipermeable membrane 10 opposite to that during operation of the concentration system. This is a cleaning method that removes dirt.

It should be noted that such backwashing is carried out by providing a flow path, a three-way valve, a pump, etc. necessary for the concentration system, and controlling the flow path switching by the three-way valve, the drive of the pump, etc. by the control mechanism 3. It is possible.

(Flushing)
Flushing is a cleaning method in which dirt adhering to the surface of the semipermeable membrane 10 is washed away with a low-pressure, high-flow rate cleaning liquid. As the cleaning liquid, the same water, chemical solution, etc. as described above can be used. Flushing is an effective method for removing relatively lightly adhered stains. Therefore, for example, by regularly performing flushing before the semipermeable membrane contamination progresses, the effect of preventing the membrane contamination can be obtained.

In order to carry out the cleaning as described above, it is preferable that the concentration system further includes a flow path switching device for switching the flow path connected to the semipermeable membrane module. Further, the concentration system preferably further includes a cleaning liquid tank in which a cleaning liquid for cleaning the semipermeable membrane is stored.

The embodiments disclosed this time should be considered to be exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and it is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1a, 1b, 1c semipermeable membrane module, 10 semipermeable membrane, 11 first chamber, 12 second chamber, 2 reverse osmosis (RO) module, 2a high pressure pump, 20 reverse osmosis (RO) membrane, 21 first chamber, 22 2nd chamber, 3 control mechanism, 31, 32, 33 three-way valve, 4 pressure drop device, 5 cleaning liquid tank, 5a pump.

Claims (3)

A reverse osmosis module that separates and recovers water from a stock solution that has been pressurized to a predetermined pressure via a reverse osmosis membrane, and discharges the concentrated stock solution that is the concentrated stock solution.
It has a semipermeable membrane and first and second chambers partitioned by the semipermeable membrane, and the concentrated stock solution is used as the first target solution and flowed into the first chamber at a predetermined pressure to form a second target solution. By flowing the water into the second chamber at a pressure lower than the predetermined pressure, the water contained in the first target liquid in the first chamber is passed through the semipermeable membrane to the second target in the second chamber. A concentrating system including a semipermeable membrane module that transfers to a liquid, discharges the concentrated liquid from the first chamber, and discharges the diluted liquid from the second chamber.
The concentration system comprises a plurality of the semipermeable membrane modules.
For at least one semipermeable membrane module selected from the plurality of semipermeable membrane modules, the supply of the first target liquid to some of the semipermeable membrane modules is stopped at a predetermined timing, and the semipermeable membrane is stopped. Concentration system with additional control mechanism that controls to perform cleaning of. The concentration system according to claim 1, further comprising a flow path switching device for switching the flow path connected to the semipermeable membrane module. The concentration system according to claim 1 or 2, further comprising a cleaning liquid tank in which a cleaning liquid for cleaning the semipermeable membrane is stored.

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