JP7580911B2 - Concentration System - Google Patents

Description

The present invention relates to a concentration system.

For example, in order to reduce the energy required for desalination using reverse osmosis (RO), a membrane separation method (brine concentration) has been studied in which a high-pressure target liquid is passed through a first chamber of a semipermeable membrane module, a low-pressure target liquid is passed through a second chamber, and water contained in the target liquid in the first chamber is transferred to the target liquid in the second chamber via the semipermeable membrane, thereby discharging a concentrated target liquid from the first chamber and a diluted target liquid from the second chamber (see, for example, Patent Document 1: JP 2018-1110 A).

A concentration system is also being considered in which the concentrated liquid discharged from the RO module is passed through the first chamber of a semipermeable membrane module that can be operated at even higher pressures, and the concentrated liquid is further concentrated under ultra-high pressure conditions using the above-mentioned brine concentration (BC).

JP 2018-1110 A

If the raw solution, such as seawater, supplied to the RO module contains scale components (hard components such as bicarbonate), when it is concentrated in the RO module, the scale components are concentrated and precipitate as scale (carbonate, etc.) on the surface of the semipermeable membrane, causing problems such as clogging of the semipermeable membrane. For this reason, when the raw solution contains scale components, a treatment is applied to the raw solution to suppress or reduce the precipitation of scale components, such as by adding a scale inhibitor, to the extent that scale does not precipitate in the RO module.

Here, the level of inhibition or reduction of scale component precipitation (such as the amount of scale inhibitor added) needs to be at a level where scale does not precipitate due to concentration in the RO module, and there is no need to completely remove scale components from the raw solution. For this reason, the concentrated solution discharged from the RO module may have a solution composition at a level where scaling would easily occur if the concentration was increased any further.

For this reason, in a concentration system that combines a brine concentration (BC) module after the RO module to further concentrate the solution, there is a risk of scale forming in the semipermeable membrane module used in the BC when the concentrated solution discharged from the RO module is further concentrated by the BC. In addition, if the water temperature or pH of the solution fluctuates during the BC, there is a risk of scale (hard components) precipitating.

If scale precipitates in the semipermeable membrane modules used in BC, problems such as membrane blockage (clogging) may occur.

In addition, the raw liquid such as seawater supplied to the RO module may contain turbid components (organic matter, microorganisms, etc.). For these turbid components, the raw liquid is usually subjected to a process to reduce the turbid components to the extent that they do not cause membrane blockage in the RO module. However, when the concentrated liquid discharged from the RO module is further concentrated by the BC, the turbid components may become highly concentrated in the semipermeable membrane module used in the BC, which may cause problems similar to those caused by scale components.

Therefore, the present invention aims to suppress membrane blockage and other problems in the semipermeable membrane module used in brine concentration (BC) in a concentration system in which the concentrated liquid discharged from a reverse osmosis (RO) module is further concentrated by brine concentration (BC).

(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;
A purification device that removes at least one of hard components and turbid components from the concentrated raw liquid and discharges the resultant as a first target liquid;
a semipermeable membrane module having a semipermeable membrane and a first chamber and a second chamber separated by the semipermeable membrane, wherein the first target liquid is caused to flow into the first chamber at a predetermined pressure and the second target liquid is caused to flow into the second chamber at a pressure lower than the predetermined pressure, thereby transferring water contained in the first target liquid in the first chamber through the semipermeable membrane to the second target liquid in the second chamber, discharging a concentrated liquid from the first chamber, and discharging a diluted liquid from the second chamber;
A concentrating system comprising:

(2) The concentration system described in (1), in which the purification device removes turbid components and hard components from the concentrated stock solution in that order and discharges the resultant as a first target liquid.

(3) The concentration system according to (1) or (2), in which a flow path connecting the reverse osmosis module and the purification device has a branch flow path for supplying a portion of the concentrated raw liquid to the first chamber of the semipermeable membrane module without passing through the purification device.

(4) A concentration system according to any one of (1) to (3), comprising an energy recovery device that recovers the energy of the concentrated raw liquid.

According to the present invention, in a concentration system in which the concentrated liquid discharged from a reverse osmosis (RO) module is further concentrated by a brine concentration (BC), it is possible to suppress membrane blockage and the like in the semipermeable membrane module used in the BC.

FIG. 1 is a schematic diagram showing a concentration system according to a first embodiment. FIG. 1 is a schematic diagram showing an example of a concentration system according to a first embodiment. FIG. 2 is a schematic diagram showing another example of the concentration system of the first embodiment. FIG. 2 is a schematic diagram showing another example of the concentration system of the first embodiment. FIG. 2 is a schematic diagram showing a modified example of the concentration system of the first embodiment. FIG. 4 is a schematic diagram showing a concentration system of a second embodiment.

Embodiments of the present invention will be described below with reference to the drawings. Note that in the drawings, the same reference symbols represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been changed as appropriate to clarify and simplify the drawings, and do not represent actual dimensional relationships.

<Embodiment 1>
Referring to FIG. 1 , the concentration system of this embodiment includes a reverse osmosis module 2 , a purification device 3 , and a semipermeable membrane module 1 .

In the reverse osmosis module 2, water is separated and recovered from the raw liquid pressurized to a predetermined pressure via the reverse osmosis membrane 20, and the concentrated raw liquid, which is the concentrated raw liquid, is discharged.
In the purification device 3, at least one of hard components and turbid components is removed from the concentrated stock liquid, and the resulting liquid is discharged as a first target liquid.
The semipermeable membrane module 1 has a semipermeable membrane 10 and a first chamber 11 and a second chamber 12 separated by the semipermeable membrane. By flowing a first target liquid into the first chamber 11 at a predetermined pressure and flowing a second target liquid into the second chamber 12 at a pressure lower than a predetermined pressure (the pressure of the first target liquid), 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, and the concentrated liquid is discharged from the first chamber 11 and the diluted liquid is discharged from the second chamber 12.

In addition, in the purification device 3, "removing" at least one of the hard components and the turbid components does not necessarily mean completely removing at least one of the hard components and the turbid components, but rather it is sufficient to remove at least a portion of at least one of the hard components and the turbid components. In other words, it is sufficient to be able to reduce the amount of at least one of the hard components and the turbid components.

The details of the concentration system of this embodiment are described below.

[Reverse Osmosis Module]
The concentration system of this embodiment includes a high-pressure pump 2a upstream of a reverse osmosis (RO) module 2. The high-pressure pump 2a pressurizes the stock solution to a predetermined pressure and supplies it to a first chamber 21 of the RO module 2. The RO module 2 separates water (permeate) from the stock solution pressurized to the predetermined pressure via a reverse osmosis (RO) membrane 20 and sends it to a second chamber 22, thereby discharging the concentrated stock solution, which is the concentrated stock solution, from the first chamber 21 and discharging water from the second chamber 22.

In this specification, the "raw liquid" 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 raw liquid include seawater, river water, brackish water, and wastewater. Examples of wastewater include industrial wastewater, domestic wastewater, and wastewater from oil or gas fields.

A pretreatment device (not shown) may be provided upstream of the high-pressure pump 2a to remove turbid matter (particulates, microorganisms, scale components, etc.) contained in the raw liquid. Examples of pretreatment devices include a sand filter, a filtration device using a UF (Ultrafiltration) membrane, an MF (Microfiltration) membrane, etc., an addition device for chlorine, sodium hypochlorite, a coagulant, a scale inhibitor, etc., and a pH adjustment device. A scale inhibitor is an additive that prevents or inhibits the precipitation of scale components in the liquid as scale. Examples of scale inhibitors include polyphosphate-based, phosphonic acid-based, phosphinic acid-based, polycarboxylic acid-based compounds, etc.

In this embodiment, the purification device 3 and the semipermeable membrane module 1 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 1 is a liquid from which at least one of the hard components and turbid components has been removed from at least a portion of the concentrated stock liquid.

The concentrated stock solution discharged from the RO module 2 has a high pressure, and is sent to the semipermeable membrane module 1 side by that pressure. However, since the purification device 3 often does not have a high pressure resistance, the concentrated stock solution is usually supplied to the purification device 3 with its pressure reduced by the pressure reduction device 3a. For this reason, a boost pump 1a for sending the first target liquid to the semipermeable membrane module 1 is usually provided in the flow path between the purification device 3 and the semipermeable membrane module 1. Examples of the pressure reduction device 3a include a diverter valve, a pressure reducer, and an energy recovery device.

[Purification device]
In the purification device 3, at least one of hard components and turbid components is removed from the concentrated raw liquid discharged from the RO module 2, and the resulting liquid is discharged as a first target liquid.

The removal of hard components from the concentrated raw liquid is carried out, for example, by a water softening device 31 (see FIG. 2) which will be described later.
The removal of turbidity components from the concentrated stock solution is carried out, for example, by a turbidity removal device 32 (see FIG. 3) described below.

In the purification device 3, either the hard components or the turbid components may be removed from the concentrated stock solution, or both the hard components and the turbid components may be removed.
That is, the purification device 3 may, for example, include only a water softening device 31 as shown in FIG. 2, may include only a turbidity removal device 32 as shown in FIG. 3, or may include both a water softening device 31 and a turbidity removal device 32 as shown in FIG. 4.

When both the hard components and the turbid components are removed from the concentrated stock solution in the purifier 3, it is preferable that the turbid components and the hard components are removed from the concentrated stock solution in this order and discharged as the first target liquid. That is, when the purifier 3 includes both the water softener 31 and the turbidity remover 32, it is preferable that the turbidity remover 32 and the water softener 31 are provided in this order from the upstream side of the flow of the concentrated stock solution (see FIG. 4).
When removing hard components, membranes with finer pores, such as nanofiltration membranes, are used, which are prone to membrane clogging. Therefore, removing the turbid components first is less likely to cause problems such as membrane clogging when removing the hard components.

In this embodiment, a branch flow path 6 may be provided in the flow path connecting the reverse osmosis module 2 and the purification device 3 to supply a portion of the concentrated stock solution to the first chamber 11 of the semipermeable membrane module 1 without passing through the purification device 3 (see Figures 1 to 4). The degree of purification (softening or turbidity removal) required can be calculated based on conditions such as the concentration of BC in the subsequent process, the components contained in the concentrated stock solution, and the pH of the concentrated stock solution. Therefore, it is possible to adjust the amount of concentrated stock solution to be subjected to purification by the branch flow path 6, thereby reducing the amount of purification.

When the branch flow path 6 is provided, it is preferable to provide a pressure reducing valve 6a, for example, as shown in Figures 1 to 4. This reduces the pressure on the outlet side of the purification device 3, and the purified liquid (first target liquid) is smoothly discharged from the purification device 3. In this case, it is preferable to provide a boost pump 1a in the flow path downstream of the branch flow path 6 and upstream of the semipermeable membrane module 1 in order to supply the first target liquid in a pressurized state to the first chamber 11 of the semipermeable membrane module 1.

Also, for example, as shown in FIG. 5, boost pump 1b may be provided downstream of purification device 3 and upstream of the flow path downstream of branch flow path 6. In this case, it is possible to smoothly discharge purified liquid (first target liquid) from purification device 3 even without pressure reducing valve 6a provided in branch flow path 6 and boost pump 1a provided downstream of branch flow path 6 as shown in FIGS. 1 to 4.

It is possible to carry out a purification process (removal of at least one of the hard components and turbid components) on the raw liquid supplied to the RO module 2 to a higher degree than before (to an extent that does not cause membrane blockage during the downstream BC process), but performing a purification process on the concentrated raw liquid discharged from the RO module 2 requires less processing volume in the purification device 3, so less space is required for the equipment and initial investment costs are lower.

(Water softener)
The water softener 31 is a device that removes hard components (multivalent ions such as calcium ions and magnesium ions) from the concentrated raw liquid discharged from the RO module 1, thereby obtaining liquid with a reduced amount of hard components.

Examples of water softening devices include filtration devices using NF (Nanofiltration) membranes and treatment devices using ion exchange resins. Such water softening devices are disclosed, for example, in Sato Nagahisa et al., "Water softening using modified RO membranes," Membrane, 38(6), 304-309, 2013.

It is preferable to carry out maintenance of the water softening device 31 during periods when the concentration system is not in operation. Examples of maintenance include chemical cleaning in the case of a filtration device using an NF membrane, and regeneration of the ion exchange resin in the case of a treatment device using ion exchange resin.

(Turbidity removal device)
The turbidity removal device 32 is a device that removes turbidity components (insoluble matter such as organic matter and microorganisms) from the concentrated raw liquid discharged from the RO module 1, thereby obtaining a liquid with a reduced amount of turbidity components.

Examples of turbidity removal devices include filtration devices that use UF (Ultrafiltration) membranes.

It is preferable to carry out maintenance of the turbidity removal device during periods when the concentration system is out of operation. For example, in the case of a filtration device using a UF membrane, maintenance may include back pressure cleaning and chemical cleaning.

[Semipermeable membrane module]
The semipermeable membrane module 1 has a semipermeable membrane 10 and a first chamber 11 and a second chamber 12 separated by the semipermeable membrane 10 .

The first target liquid (concentrated undiluted liquid from which at least one of the hard components and turbid components has been removed) flows into the first chamber 11 at a predetermined pressure, and the second target liquid flows into the second chamber 12 at a pressure lower than the predetermined pressure. As a result, the water contained in the first target liquid in the first chamber 11 transfers through the semipermeable membrane 10 to the second target liquid in the second chamber 12, and the concentrated liquid (concentrated first target liquid) is discharged from the first chamber 11, 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 portion of the first target liquid having a predetermined pressure may be passed through a pressure reducing device 4 and flow into the second chamber at a pressure lower than the predetermined pressure.

The pressure reduction device 4 may be, for example, a shunt valve, a pressure reducer, or an energy recovery device that can divide the first target liquid having a predetermined pressure into a flow path to the second chamber 12 of the semipermeable membrane module 1 and another flow path. Here, the pressure reduction device 4 (shunt valve) has the function of reducing the pressure of the target liquid flowing into the second chamber 12 to a pressure lower than a predetermined pressure. The use of such a pressure reduction device has the advantage that, for example, only one flow path for the target liquid upstream of the semipermeable membrane module is required.

In the case of FIG. 1, the target liquid flowing into the first chamber 11 and the second chamber 12 of the semipermeable membrane module 1 is the same liquid, and therefore has essentially the same osmotic pressure. Therefore, unlike the RO method, high pressure is not required to cause reverse osmosis against the high osmotic pressure difference between the target liquid (high osmotic pressure liquid) and fresh water, and membrane separation of the target liquid can be performed by applying a relatively low pressure (a portion of the target liquid can be diluted and another portion of the target liquid can be concentrated).

However, in this embodiment, the second target liquid supplied to the second chamber 12 of the semipermeable membrane module 1 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, membrane separation by BC is theoretically possible as long as the osmotic pressure difference (absolute value) is smaller than the pressure of the first target liquid supplied to the first chamber 11. In this case, it is preferable that 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 30% or less of the predetermined pressure of the first target liquid supplied to the first chamber 11.

The BC process may be a single-stage process using one semipermeable membrane module 1 as shown in FIG. 1, but it may also be a multi-stage process using multiple semipermeable membrane modules.

In the brine concentration (BC) which is a membrane separation process in the semipermeable membrane module 1, in order to transfer water from the first chamber 11 to the second chamber 12 through the semipermeable membrane 10 of the semipermeable membrane module 1, the pressure of the first target liquid supplied to the first chamber 11 must 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 a single step (one semipermeable membrane module), it is necessary to supply it at a correspondingly high pressure, which has disadvantages such as increased energy costs for operating the pump. For this reason, BC may be carried out by a multi-step process using multiple semipermeable membrane modules in order to perform the concentration process in stages and reduce the pressure required for BC. Such BC by a multi-step process is disclosed, for example, in JP 2018-069198 A.

Examples of semipermeable membranes include those called reverse osmosis (RO) membranes, forward osmosis (FO) membranes, and nanofiltration (NF) membranes. When a reverse osmosis membrane, forward osmosis membrane, or 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, the pore size of RO and FO membranes is approximately 2 nm or less, and the pore size of UF membranes is approximately 2 to 100 nm. Among RO membranes, NF membranes have a relatively low rejection rate for ions and salts, and typically the pore size of NF membranes is approximately 1 to 2 nm. When an RO membrane, FO membrane, or NF membrane is used as the semipermeable membrane, the salt rejection 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, but examples include cellulose-based resin, polysulfone-based resin, polyamide-based resin, etc. It is preferable that the semipermeable membrane is composed of a material containing at least one of cellulose-based resin and polysulfone-based resin.

The cellulose-based resin is preferably a cellulose acetate-based resin. Cellulose acetate-based resins are resistant to chlorine, a disinfectant, and have the characteristic of being able to inhibit the growth of microorganisms. The cellulose acetate-based resin is preferably cellulose acetate, and from the viewpoint of durability, is more preferably cellulose triacetate.

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

The shape of the semipermeable membrane 10 (and the reverse osmosis membrane 20 described above) is not particularly limited, but examples include a flat membrane and a hollow fiber membrane. Note that in FIG. 1, the semipermeable membrane 10 is depicted as a simplified flat membrane, but is not particularly limited to this shape. Note that hollow fiber membranes (hollow fiber type semipermeable membranes) are advantageous in that they can increase the membrane area per module compared to spiral type semipermeable membranes and the like, thereby increasing the permeation efficiency.

The form of the semipermeable membrane module 1 (and the above-mentioned reverse osmosis module 2) is not particularly limited, but when hollow fiber membranes are used, examples include a module in which the hollow fiber membranes are arranged in a straight line, and a cross-wound type module in which the hollow fiber membranes are wound around a core tube. When flat membranes are used, examples include a stacked type module in which flat membranes are stacked, and a spiral type module in which flat membranes are wrapped around a core tube in an envelope shape.

A specific example of a hollow fiber membrane is a membrane with a single layer structure that is entirely made of a cellulose-based resin. However, the single layer structure mentioned here does not necessarily mean that the entire layer is a uniform membrane, and it is preferable that the membrane has a dense layer near the outer peripheral surface, as disclosed in JP 2012-115835 A, for example, and that this dense layer is essentially the separation active layer that determines the pore size of the hollow fiber membrane.

Another specific example of a hollow fiber membrane is a two-layer membrane having a dense layer of polyphenylene resin (e.g., sulfonated polyethersulfone) on the outer surface of a support layer (e.g., a layer made of polyphenylene oxide). Another example is a two-layer membrane having a dense layer of polyamide resin on the outer surface of a support layer (e.g., a layer made of polysulfone or polyethersulfone).

In a semipermeable membrane module using hollow fiber membranes, 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 portion) is pressurized, the pressure loss becomes large and it becomes difficult to apply pressure sufficiently.

<Embodiment 2>
6, the concentration system of the present embodiment includes an energy recovery device 5 that recovers the energy of the concentrated raw liquid. Since the other points are the same as those in the first embodiment, the overlapping description will be omitted.

(Energy recovery device)
The concentrated stock solution discharged from the first chamber 21 of the RO module 2 is at high pressure and has high pressure energy. The pressure energy of the concentrated stock solution is recovered by various energy recovery devices 5 and the recovered energy is used to pressurize the first target liquid discharged from the purification device 3, thereby making it possible to reduce the energy consumption of the boost pump 1a and the like, or to omit the boost pump 1a, for example. In addition, by providing the energy recovery device 5 at the position shown in FIG. 6, it is also possible to omit the pressure reduction device 3a.

Examples of energy recovery devices include electric energy recovery devices that use turbines or the like to recover energy in the form of electricity, and mechanical energy recovery devices that mechanically recover energy from concentrated liquid. Mechanical energy recovery devices, which have smaller energy conversion losses than electric energy recovery devices, usually have a greater effect on reducing power consumption.

A known mechanical energy recovery device is a power transmission type energy recovery device that uses a turbocharger or a water wheel connected coaxially to the drive shaft of a high-pressure pump to recover the pressure energy of the concentrated liquid as power. Another example of a mechanical energy recovery device is a pressure transmission type energy recovery device that directly recovers the pressure of the concentrated liquid, such as a pressure exchanger (PX).

Such energy recovery devices are disclosed, for example, in JP 2004-81913 A and JP 1-123605 A.

In the concentration system shown in FIG. 6, if the energy recovery device 5 is a pressure transmission type energy recovery device, it is usually necessary to provide a booster pump in the flow path through which the purified concentrated raw liquid (first target liquid) (from which at least one of hard components and turbid components has been removed) flows from the purification device 3 to the energy recovery device 5. If the energy recovery device 5 is a power transmission type energy recovery device, a booster pump is usually not required.

In this embodiment, if a branch flow path 6 is provided as in embodiment 1, the branch flow path 6 may be provided either upstream or downstream of the energy recovery device 5.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

1 Semipermeable membrane module, 1a, 1b Booster pump, 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 Purification device, 3a Pressure reduction device, 31 Water softening device, 32 Turbidity removal device, 4 Pressure reduction device, 5 Energy recovery device, 6 Branch flow path, 6a Pressure reducing valve.

Claims (3)

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;
A purification device that removes turbid components and hard components from the concentrated raw liquid in this order and discharges the resultant as a first target liquid;
a semipermeable membrane module having a semipermeable membrane and a first chamber and a second chamber separated by the semipermeable membrane, wherein the first target liquid is caused to flow into the first chamber at a predetermined pressure and the second target liquid is caused to flow into the second chamber at a pressure lower than the predetermined pressure, thereby transferring water contained in the first target liquid in the first chamber through the semipermeable membrane to the second target liquid in the second chamber, discharging a concentrated liquid from the first chamber, and discharging a diluted liquid from the second chamber;
Equipped with
The raw solution has turbid components and hard components removed to such an extent that membrane clogging and scale precipitation due to turbid components do not occur due to concentration in the reverse osmosis module,
In the purification device, the turbid components and hard components are removed to an extent that membrane clogging and scale deposition due to the turbid components do not occur due to concentration in the semipermeable membrane module . The concentration system according to claim 1, wherein the flow path connecting the reverse osmosis module and the purification device has a branch flow path for supplying a portion of the concentrated raw liquid to the first chamber of the semipermeable membrane module without passing through the purification device. The concentration system according to claim 1 or 2, further comprising an energy recovery device that recovers the energy of the concentrated raw liquid.

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