JP7427890B2 - Concentration system - Google Patents

Description

The present invention relates to a concentration system.

For example, in order to reduce the energy required for desalination treatment using reverse osmosis (RO), a high-pressure target liquid is flowed into the first chamber of a semipermeable membrane module, and a low-pressure target liquid 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 through the semipermeable membrane, the concentrated target liquid is discharged from the first chamber and transferred to the second chamber. A membrane separation method (brine concentration) in which a diluted target liquid is discharged is being considered (for example, see Patent Document 1: Japanese Patent Application Laid-Open No. 2018-1110).

In addition, the concentrated liquid discharged from the RO module is allowed to flow into the first chamber of the semipermeable membrane module, which can be operated at a higher pressure, and the concentrated liquid is further processed by the brine concentration (BC) described above under ultra-high pressure conditions than in the RO method. Concentration systems are also being considered.

Unexamined Japanese Patent Publication No. 2018-1110

In semipermeable membrane modules used for brine concentration, impurities such as turbidity (e.g., fine particles, microorganisms, scale components) adhere to the surface of the semipermeable membrane over time depending on the amount of membrane separation of the target liquid. , separation performance (filtration efficiency) decreases. Therefore, it is desirable that the semipermeable membrane of the semipermeable membrane module be cleaned at regular intervals depending on the degree of adhesion of impurities.

However, in actual plants, the availability rate is important, so cleaning frequency is reduced to avoid a drop in availability, and as a result, semipermeable membranes are cleaned at appropriate timings depending on the degree of adhesion of impurities. There is a concern that it will become difficult to implement. If the timing of cleaning is delayed, the state of the semipermeable membrane may not be sufficiently restored, and as a result, the separation performance of the semipermeable membrane module may deteriorate or its life may be shortened. On the other hand, if the cleaning frequency becomes higher than necessary, there is a concern that the processing efficiency will decrease.

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

(1) A reverse osmosis module that separates and recovers water from a stock solution pressurized to a predetermined pressure via a reverse osmosis membrane and discharges a concentrated stock solution that is the concentrated stock solution;
It has a semipermeable membrane, and a first chamber and a second chamber partitioned by the semipermeable membrane, and the concentrated stock solution is flowed into the first chamber at a predetermined pressure as a first target liquid, and the second target liquid is flowed into the first chamber at a predetermined pressure. by flowing into the second chamber at a pressure lower than the predetermined pressure, water contained in the first target liquid in the first chamber is transferred to the second target liquid in the second chamber through the semipermeable membrane. a semipermeable membrane module that discharges the concentrated liquid from the first chamber and the diluted liquid from the second chamber, the concentration system comprising:
The concentration system includes a plurality of the semipermeable membrane modules,
For at least one of the semipermeable membrane modules 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 The concentrating system further comprises a control mechanism for controlling the washing of the liquid.

(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 storing a cleaning liquid for cleaning the semipermeable membrane.

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

It is a schematic diagram showing a concentration system of an embodiment.

Embodiments of the present invention will be described below with reference to the drawings. In addition, in the drawings, the same reference numerals represent the same or corresponding parts. Further, dimensional relationships such as length, width, thickness, depth, etc. have been appropriately changed for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

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

In the reverse osmosis module 2, water is separated and recovered from the stock solution pressurized to a predetermined pressure via the reverse osmosis membrane 20, and a concentrated stock solution that is a concentrated stock solution is discharged.
The semipermeable membrane modules 1a, 1b, and 1c each have a semipermeable membrane 10 and a first chamber 11 and a second chamber 12 partitioned by the semipermeable membrane, and have a predetermined concentrated stock solution as a first target solution. By 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 The contained water is transferred to the second target liquid in the second chamber 12 through the semipermeable membrane, the concentrated liquid is discharged from the first chamber 11, and the diluted liquid is discharged from the second chamber 12.
For at least one semipermeable membrane module selected from the plurality of semipermeable membrane modules, the control mechanism 3 stops the supply of the first target liquid to some of the semipermeable membrane modules at a predetermined timing, and control to perform cleaning.

[Reverse osmosis module]
The concentration system of this embodiment includes a high-pressure pump 2 a upstream of the reverse osmosis (RO) module 2 . The high-pressure pump 2a increases the pressure of 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 (permeate water) from the stock solution that has been pressurized to a predetermined pressure through a reverse osmosis (RO) membrane 20 to the second chamber 22 side, thereby converting the concentrated stock solution into a concentrated stock solution. The first chamber 21 is drained, and the water is drained from the second chamber 22.

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

Note that a pretreatment device (not shown) may be provided upstream of the high-pressure pump 2a in order to remove suspended matter (fine particles, microorganisms, scale components, etc.) contained in the stock solution. Examples of pretreatment equipment include sand filtration equipment, filtration equipment using UF (Ultrafiltration) membranes, MF (Microfiltration) membranes, etc., chlorine, sodium hypochlorite, flocculants, and scale. Examples include devices for adding inhibitors and the like, devices for adjusting pH, and the like. Note that the scale inhibitor is an additive that has the effect of preventing or suppressing the precipitation of scale components in the liquid as scale. Examples of scale inhibitors include polyphosphoric acid-based, phosphonic acid-based, phosphinic acid-based, and polycarboxylic acid-based compounds.

In this embodiment, semipermeable membrane modules 1a, 1b, and 1c are connected downstream 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, and 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, the concentrated stock solution is sent to the semipermeable membrane module side by the pressure.

[Semi-permeable membrane module]
Each of the plurality of semipermeable membrane modules 1a, 1b, and 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 (the 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 flows into the second chamber 11 at a pressure lower than the predetermined pressure. into chamber 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 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. The first target liquid) is discharged, and the diluted liquid (the diluted second target liquid) is discharged from the second chamber 12.

Note that 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 caused to flow into the second chamber at a pressure lower than the predetermined pressure by passing through the pressure reducing device 4. Good too.

The pressure reduction device 4 may be, for example, a flow divider valve or a pressure reducer that can separate the 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 may be used. Here, the pressure reducing device 4 (divider 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. Note that the use of such a pressure reduction device has the advantage that, for example, only one flow path for the target liquid is required upstream of the semipermeable membrane module.

In the case of FIG. 1, 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, and 1c) are the same liquid, so they are basically equal. Has osmotic pressure. For this reason, unlike the RO method, there is no need for high pressure to cause reverse osmosis against the high osmotic pressure difference between the target liquid (high osmotic pressure liquid) and fresh water, and by applying relatively low pressure, Membrane separation of target liquids can be performed (some target liquids can be diluted and other target liquids can be concentrated).

However, in this 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.

Even if the first target liquid flowing into the first chamber 11 and the second target liquid flowing into the second chamber 12 are different liquids and have different concentrations, the osmotic pressure difference (absolute value) is the same as the first target liquid. As long as the pressure is lower than the pressure of the first target liquid supplied to the chamber 11, membrane separation using BC is theoretically possible. 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 pressure is preferably 30% or less of the predetermined pressure of the first target liquid supplied to the first target liquid.

Note that each of the semipermeable membrane modules 1a, 1b, and 1c may be one semipermeable membrane module as shown in FIG. Preferably, it is a group (train) of permeable membrane modules. Control by the control mechanism described later is performed, for example, for each group of semipermeable membrane modules.

Furthermore, the BC process in each of the semipermeable membrane modules 1a, 1b, and 1c may be a one-stage process using one semipermeable membrane module as shown in FIG. It may also be a multi-stage process using multiple semipermeable membrane modules (connected).

In brine concentration (BC), which is a membrane separation process in a 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, The pressure of the first target liquid supplied to the first chamber 11 needs to be greater 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 stage process (one semipermeable membrane module), it is necessary to supply it at a correspondingly high pressure, and the energy cost for operating the pump increases. There are disadvantages such as an increase in For this reason, BC may be carried out in a multistage process using a plurality of semipermeable membrane modules in order to perform the concentration step in stages and reduce the pressure required for BC. BC using such a multi-stage process is disclosed in, for example, Japanese Patent Application Publication No. 2018-069198.

Examples of the semipermeable membrane include semipermeable membranes called reverse osmosis (RO) membranes, forward osmosis (FO) membranes, and nanofiltration (NF) membranes. Note that 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.

Typically, RO and FO membranes have pore sizes of about 2 nm or less, and UF membranes have pore sizes of about 2-100 nm. NF membranes are RO membranes that have a relatively low rejection rate for ions and salts, and typically have a pore diameter of 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.

The material constituting the semipermeable membrane is not particularly limited, and examples thereof include cellulose resins, polysulfone resins, polyamide resins, and the like. Preferably, the semipermeable membrane is made 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 disinfectant, and has the characteristic of suppressing the growth of microorganisms. The cellulose acetate resin is preferably cellulose acetate, more preferably cellulose triacetate in terms of durability.

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

The shape of the semipermeable membrane 10 (and the above-mentioned reverse osmosis membrane 20) is not particularly limited, and examples thereof include a flat membrane and a hollow fiber membrane. Although FIG. 1 shows a simplified flat membrane as the semipermeable membrane 10, the shape is not limited to this. Note that hollow fiber membranes (hollow fiber semipermeable membranes) are advantageous over spiral semipermeable membranes and the like in that the membrane area per module can be increased and the permeation efficiency can be increased.

The form of the semipermeable membrane module (and the above-mentioned reverse osmosis module 2) is not particularly limited, but when using hollow fiber membranes, there may be a module in which the hollow fiber membranes are arranged straight, or a module in which the hollow fiber membranes are arranged in a core tube. Examples include cross-wound modules. When flat membranes are used, examples include a stacked module in which flat membranes are stacked, a spiral module in which flat membranes are wrapped around a core tube in an envelope shape, and the like.

A specific example of a hollow fiber membrane is a single-layer membrane entirely composed of cellulose resin. However, the single layer structure here does not necessarily mean that the entire layer is a uniform film; for example, as disclosed in Japanese Patent Application Laid-Open No. 2012-115835, it has a dense layer near the outer peripheral surface. It is preferable that the dense layer serves as a separation active layer that substantially defines the pore size of the hollow fiber membrane.

Another example of a specific hollow fiber membrane is a two-layer structure having a dense layer made of a polyphenylene resin (e.g., sulfonated polyether sulfone) on the outer peripheral surface of a support layer (e.g., a layer made of polyphenylene oxide). Examples include membranes. Another example is a two-layer membrane 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 addition, in a semipermeable membrane module using a hollow fiber membrane, the first chamber is usually located outside the hollow fiber membrane. This is because even if the fluid flowing inside the hollow fiber membrane (hollow portion) is pressurized, the pressure loss becomes large and it is difficult to apply sufficient pressure.

[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, and 1c. and control the concentration system to perform cleaning of the semipermeable membrane.

Cleaning is performed with at least some semipermeable membrane modules (semipermeable membrane module group) discontinued, but other semipermeable membrane modules (semipermeable membrane module group) continue to be used, Preferably, the entire concentration system continues to operate. Thereby, a decrease in processing efficiency of the concentration system can be suppressed. Further, the processing of the concentration system can be carried out continuously, and complicated work such as initial adjustment when temporarily stopping the operation of the entire system and restarting the operation can be omitted.

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

The order and timing of cleaning, the cleaning time and degree of cleaning for each semipermeable membrane module are determined by various well-known simulations, etc. based on indicators that indicate the degree of contamination of the semipermeable membrane (degree of adhesion of scale, etc.). can do.

As indicators 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, the pressure difference in the semipermeable membrane module, Examples include the amount of permeated water (difference in flow rate between the inlet and outlet sides).

Methods for cleaning the semipermeable membrane (semipermeable membrane module) include, but are not particularly limited to, cleaning with a cleaning liquid, backwashing (back pressure cleaning), flushing, and the like.

(Cleaning with cleaning liquid)
For cleaning with a cleaning liquid, for example, one of the three-way valves 31, 32, and 33 is turned off to stop supplying the first target liquid to the semipermeable membrane module, and the cleaning liquid stored in the cleaning liquid tank 5 is applied to the semipermeable membrane. Drive the pump 5a in a switched state so that the supply 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, and 1c). It can be implemented by doing this.

The cleaning liquid used for chemical cleaning is not particularly limited as long as it can clean stains on the semipermeable membrane. Examples of the cleaning liquid include water and chemical solutions. Examples of the cleaning liquid include permeated water discharged from the second chamber 22 of the RO module 2, diluted liquid obtained by BC (diluted second target liquid discharged from the second chamber of the semipermeable membrane module), etc. May be used.

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

Note that, for example, both cleaning with water and cleaning with a chemical solution may be performed. 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 refers to moving the water passing through the semipermeable membrane 10 in the opposite direction to the direction in which the concentration system is operating, so that the water physically adheres to the semipermeable membrane 10. This is a cleaning method that removes dirt.

Note that such backwashing is carried out by providing the necessary flow paths, three-way valves, pumps, etc. in the concentration system, and controlling switching of the flow paths by the three-way valves, driving of the pumps, etc. by the control mechanism 3. 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 cleaning liquid at low pressure and high flow rate. As the cleaning liquid, the same water, chemical liquid, etc. as mentioned above can be used. Flushing is an effective method for removing relatively lightly attached dirt. Therefore, for example, by periodically performing flushing before the semipermeable membrane becomes contaminated, it is possible to obtain the effect of preventing membrane contamination.

In order to perform the cleaning as described above, the concentration system preferably further includes a flow path switching device for switching the flow path connected to the semipermeable membrane module. Moreover, it is preferable that the concentration system further includes a cleaning liquid tank storing a cleaning liquid for cleaning the semipermeable membrane.

The embodiments disclosed this time should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and it is intended that all changes within the meaning and range equivalent to the claims are included.

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 Second chamber, 3 Control mechanism, 31, 32, 33 Three-way valve, 4 Pressure reducing device, 5 Cleaning liquid tank, 5a Pump.

Claims (2)

A reverse osmosis module that separates and recovers water from a stock solution pressurized to a predetermined pressure via a reverse osmosis membrane and discharges a concentrated stock solution that is the concentrated stock solution;
It has a semipermeable membrane, and a first chamber and a second chamber partitioned by the semipermeable membrane, and the concentrated stock solution is flowed into the first chamber at a predetermined pressure as a first target liquid, and the second target liquid is flowed into the first chamber at a predetermined pressure. by flowing into the second chamber at a pressure lower than the predetermined pressure, water contained in the first target liquid in the first chamber is transferred to the second target liquid in the second chamber through the semipermeable membrane. a semipermeable membrane module that discharges the concentrated liquid from the first chamber and the diluted liquid from the second chamber, the concentration system comprising:
The concentration system includes a plurality of semipermeable membrane modules connected in parallel to each other ,
a cleaning liquid tank storing a cleaning liquid for cleaning the semipermeable membrane;
For switching between a flow path for supplying the first target liquid to the first chamber of the semipermeable membrane module and a flow path for supplying the cleaning liquid to the first chamber of the semipermeable membrane module. a flow path switching device;
At least one of the semipermeable membrane modules selected from the plurality of semipermeable membrane modules is supplied with the first target liquid to some of the semipermeable membrane modules by the flow path switching device at a predetermined timing. A concentrating system further comprising: a control mechanism configured to stop and perform cleaning of the semipermeable membrane. The concentration system according to claim 1, wherein the semipermeable membrane module is a semipermeable membrane module group consisting of a plurality of semipermeable membrane modules connected in parallel to each other .

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