Water recovery method

A water recovery method for improving water recovery efficiency may include inflowing a low concentration solution including water into an in-series flow path. The in-series flow path may include a plurality of flow paths for a low concentration solution coupled in series. The method may additionally include inflowing a high concentration solution having the same concentration into a plurality of flow paths for a high concentration solution. Each of the plurality of flow paths for the high concentration solution may be connected to each of plurality of flow paths for the low concentration solution via a respective semipermeable membrane being interposed therebetween.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2012-252182, filed in the Japanese Patent Office on Nov. 16, 2012, and Korean Patent Application No. 10-2013-0128717, filed in the Korean Intellectual Property Office on Oct. 28, 2013, the entire contents of each of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a water recovery method for beverage water or industrial water. More particularly, the present disclosure generally relates to a water recovery method for water from a natural system (for example, water obtained from a sea, river, lake, swamp, pond, and the like), wherein the water may be, for example, sea water, brackish water, river water, and the like, industrial drain water, various water drained from homes, and the like.

2. Description of the Related Art

A water recovery process (method) by an FO (forward osmosis) method is considered to lessen the energy consumption required for water recovery compared with a water recovery process by a RO (reverse osmosis) method. Accordingly, in recent times, developments on a water recovery process by an FO method have been actively made. Herein, the water recovery process by an FO method includes partitioning a low concentration solution (a solution subject to water recovery, for example sea water), and a high concentration solution having a higher osmotic pressure than the low concentration solution with a forward osmotic membrane, and inflowing water of the low concentration solution into the high concentration solution.

Specifically, in a water recovery process by an FO method, water of the low concentration solution flows into the high concentration solution using an FO membrane module. Herein, the FO membrane module includes a flow path for a low concentration solution where a low concentration solution is distributed, a flow path for a high concentration solution where a high concentration solution is distributed, and a forward osmotic membrane partitioning the flow path for a low concentration solution and the flow path for a high concentration solution. The high concentration solution may also be referred to be as a draw solution (DS). The water is recovered from the high concentration solution.

In a water recovery process by an FO method, because water moves spontaneously from a low concentration solution to a high concentration solution unlike a water recovery process by an RO method, it is not necessary to apply pressure to the low concentration solution.

Accordingly, the water recovery process by an FO method may lessen energy consumption for water recovery compared with the water recovery process by an RO method.

On the other hand, in a water recovery process by an FO method, FO membrane modules are coupled in series and thereby a large amount of low concentration solution may be treated. This process may be referred to be as a multiple water recovery process. In a conventional multiple water recovery process, a flow path for a low concentration solution and a flow path for a high concentration solution are respectively coupled in series. In addition, in the conventional multiple water recovery process, a low concentration solution is distributed in an in-series flow path for a low concentration solution including flow paths for a low concentration solution coupled in series, while high concentration solution is distributed in an in-series flow path for a high concentration solution including flow paths for a high concentration solution coupled in series.

However, in the conventional multiple water recovery process, as the number of steps from an inlet of an in-series flow path for a low concentration solution to an FO membrane module increases, an osmotic pressure difference between a low concentration solution and a high concentration solution in an FO membrane module decreases. This is because, as the number of steps from the inlet of the in-series flow path for a low concentration solution to an FO membrane module increases, the concentration of the low concentration solution in an FO membrane module becomes higher, and the concentration of the high concentration solution becomes lower. As the osmotic pressure difference between a low concentration solution and a high concentration solution decreases, an amount of water that flows from the low concentration solution to the high concentration solution decreases. Accordingly, in the conventional multiple water recovery process, water recovery efficiency decreases in an FO membrane module at a rear end, and furthermore recovery efficiency of the whole process also decreases.

A method of increasing a flow rate of a high concentration solution has been suggested to solve the above problem. However, this method requires high pump energy to distribute the massive amount of the high concentration solution. In addition, since water needs to be recovered from the massive amount of the high concentration solution, inconvenience of recovering water from the high concentration solution is increased. Thus, the method may not fundamentally solve the aforementioned problem.

SUMMARY

In a multiple water recovery method using forward osmosis, a water recovery method may include inflowing a low concentration solution including water into an in-series flow path including a plurality of first flow paths for a low concentration solution coupled in series, and inflowing a high concentration solution having the same concentration into a plurality of second flow paths for a high concentration solution, each of which being connected to each of the first flow paths for a low concentration solution via a respective semipermeable membrane being interposed therebetween.

An osmotic pressure difference in each FO membrane module (a module consisting of a flow path for a low concentration solution, a flow path for a high concentration solution, and a semipermeable membrane partitioning them), particularly an osmotic pressure difference in an FO membrane module at a rear end, may be maintained at a relatively high level. Therefore, water recovery efficiency in the FO membrane module at a rear end is remarkably improved. Furthermore, the recovery efficiency of an entire water recovery method is remarkably improved.

An outlet flow rate of the in-series flow path for the low concentration solution may be higher than the sum of the inlet flow rate of each of the plurality of second flow paths for the high concentration solution.

Because a flow rate of the high concentration solution is much less than the low concentration solution, pump energy required for supplying the high concentration solution is very low. In addition, the inconvenience to recover water from the high concentration solution may be lessened.

An inlet flow rate of the in-series flow path for the low concentration solution may be higher than the sum of the inlet flow rate of each of the plurality of second flow paths for the high concentration solution.

Because a flow rate of the high concentration solution is much less than that of the low concentration solution, the pump energy required for supplying the high concentration solution is very low. In addition, the inconvenience to recover water from the high concentration solution may be lessened.

In addition, the flow path for a high concentration solution may be narrower than the flow path for a low concentration solution by disposing a semipermeable membrane in the flow path for a high concentration solution.

Because of the narrower flow path, a flux of the high concentration solution in the flow path for a high concentration solution is improved, and furthermore, concentration polarization in the high concentration solution is decreased.

In addition, a permeability coefficient of the semipermeable membrane may be increased, as the number of steps from an inlet of an in-series flow path to the semipermeable membrane is increased.

The permeability coefficient of an FO membrane increases as the number of steps from an inlet of an in-series flow path to the semipermeable membrane increases, and thus the amount of water passing each FO membrane, that is, a load of the water, is standardized.

The low concentration solution may be sea water.

Water may be recovered from sea water with a relatively high recovery efficiency.

In a multiple water recovery method using forward osmosis, a water recovery method ma also include inflowing a low concentration solution including water into an in-series flow path including a plurality of first flow paths for a low concentration solution coupled in series, and inflowing a high concentration solution into a plurality of second flow paths for a high concentration solution, each of which being connected to each of the plurality of first flow paths for a low concentration solution via a respective semipermeable membrane being interposed therebetween, wherein the high concentration solution has higher concentration as the number of steps from an inlet of the in-series flow path to the flow path for a high concentration solution is larger.

According to the non-limiting embodiment, an osmotic pressure difference in each FO membrane module becomes more uniform.

DETAILED DESCRIPTION

Hereinafter, example embodiments are described in further detail with reference to the drawings.

In the present specification and drawings, the same reference numbers are assigned for constituent elements having substantially equivalent functions, and thus duplicated descriptions thereof are omitted. Hereinafter, a concentration (mass %) of a solute refers to mass % of a solute relative to a total mass of a solution. FO membranes (forward osmotic membranes) used in each FO membrane module in embodiments may be any membrane, for example an FO membrane, an RO membrane, an NF membrane, and the like which are available as semipermeable membranes. Herein, a semipermeable membrane is theoretically a membrane passing water molecules due to an osmotic pressure difference, but not passing all the solutes, and actually not passing almost all the solutes.

According to the embodiments, provided are multiple water recovery devices1,2, and3and a multiple water recovery process (method) using the multiple water recovery devices1,2, and3according to the following embodiments by examining a background technology, that is, water recovery technology using an FO method. Accordingly, first of all, the background technology for the following embodiments is illustrated.

(Water Recovery Device Using Single Module)

First, a structure of a water recovery device100using a single module is described referring toFIG. 4.

The water recovery device100is one using an FO method, where water from a low concentration solution of water (fresh water) is flowed into a high concentration solution. The water recovery device100includes an FO membrane module10, connecting flow paths140and141for the low concentration solution, and connecting flow paths150and151for the high concentration solution.

The FO membrane module10includes a flow path11for the low concentration solution, connectors11aand11bfor the low concentration solution, a flow path12for the high concentration solution, connectors12aand12bfor the high concentration solution, and an FO membrane13. The flow path11is for distributing the low concentration solution, and the low concentration solution is distributed in the flow path11in a parallel direction with the FO membrane13(a rightward direction ofFIG. 4). Herein, the low concentration solution is a solution including water, that is to say, an aqueous solution.

The connectors11aand11bare respectively an inlet and an outlet for the low concentration solution. In this embodiment, the connector11ais an inlet for the low concentration solution, and the connector11bis an outlet for the low concentration solution. That is, the low concentration solution flows in from the connector11ato the flow path11and is distributed in the flow path11. The low concentration solution is released from the connector11boutside the flow path11.

The flow path11is connected to the flow path12through the FO membrane13. In other words, the flow path11and the flow path12are partitioned by the FO membrane13in the FO membrane module10. The flow path12is for distributing the high concentration solution, and the high concentration solution is distributed in the same direction (in a rightward direction inFIG. 4) as the low concentration solution in the flow path12. Herein, the high concentration solution is a solution including water, that is to say, an aqueous solution. In addition, the high concentration solution includes a solute in a higher concentration than that of the low concentration solution, that is, has a higher osmotic pressure than that of the low concentration solution. The high concentration solution may also be referred to be as a draw solution (DS).

The connectors12aand12bare respectively an inlet and an outlet for the high concentration solution. In this embodiment, the connector12ais an inlet for the high concentration solution, and the connector12bis an outlet for the high concentration solution. That is, the high concentration solution flows in from the connector12ato the flow path12, and is distributed in the flow path12. The high concentration solution is released through the connector12bto be discharged outside the flow path12.

The FO membrane13partitions the flow path11for a low concentration solution and the flow path12for a high concentration solution. In addition, the high concentration solution has higher osmotic pressure than the low concentration solution, and thus water in the low concentration solution naturally flows into the high concentration solution. In other words, the water in the low concentration solution moves in an arrow direction10athrough the FO membrane13and flows into the flow path12. Accordingly, energy required to move water from the low concentration solution to the high concentration solution theoretically becomes zero (0).

The connecting flow path140is a pipe connecting a source of the low concentration solution to the connector11a. The connecting flow path141is a pipe connected to the connector11bfor releasing the low concentration solution released from the connector11bout of the water recovery device100.

The connecting flow path150is a pipe connecting a source of the high concentration solution to the connector12a. The connecting flow path151is a pipe connected to the connector12band feeds the high concentration solution released from the connector12binto a DS (draw solution) regeneration device. The DS regeneration device is, for example, an RO membrane device, and recovers water from the high concentration solution and simultaneously sends the concentrated high concentration solution (i.e., a regenerated high concentration solution) back to the source of the high concentration solution.

(Water Recovery Process Using Single Module)

Next, a water recovery process using the water recovery device100is explained.

In this water recovery process, the low concentration solution flows in the flow path11from the connector11a, while the high concentration solution flows in the flow path12for a high concentration solution to the connector12a. Accordingly, water in the low concentration solution flows into the high concentration solution through the FO membrane13. After separating the water, the concentrated low concentration solution is released from the connector11b.

On the other hand, the high concentration solution is less concentrated with water from the low concentration solution, and flows in the same direction as the low concentration solution through the flow path12and is externally released from the connector12b. Then, the high concentration solution is fed into the DS regeneration device, and the DS regeneration device recovers water from the high concentration solution. After recovering the water, the concentrated high concentration solution is sent back to the source of the high concentration solution. Through the above treatment, water in the low concentration solution is recovered.

For example, as shown inFIG. 4, the low concentration solution in a solute concentration (hereinafter simply referred to as ┌concentration┘) of 3.5 mass % flows in the flow path11at a flow rate of 200 m3/day, and the low concentration solution in a concentration solution of 7.0 mass % is released from the flow path11at a flow rate 100 m3/day. A solute used in this embodiment is NaCl. That is, the low concentration solution is sea water. On the other hand, the high concentration solution flows in the flow path12in a concentration of 12.0 mass % at a flow rate of 200 m3/day, and the high concentration solution is released from the flow path12in a concentration of 8.0 mass % at a flow rate of 300 m3/day. A solute in this embodiment is MgCl2, so called polyvalent ions. Accordingly, since water of the low concentration solution at a flow rate of 200 m3/day flows into the high concentration solution at a flow rate of 100 m3/day, recovery efficiency of the water is about 50%. The water flowing into the high concentration solution is recovered by the DS regeneration device.

On the other hand, as shown inFIGS. 1 to 5, the FO membrane shows an ideal blocking rate, that is, 100%, as a simulation result. In other words, water recovery efficiency becomes ideal and may have a small error from actual recovery efficiency. However, the water recovery process according to the embodiment is even actually better than that of the comparative example, and in addition, a person of ordinary skill in the art may realize the process in embodiments and examples.

(Multiple Structure of Water Recovery Device)

When a low concentration solution is massively present, a water recovery device100using the aforementioned single module takes a long time to treat the low concentration solution. Accordingly, a water recovery device using a plurality of modules (multiple modules) may be required for the massive amount of the low concentration solution.

FIG. 5shows an example of a water recovery device using a plurality of modules, for example a water recovery device200. The water recovery device200schematically includes flow paths11,21, and31for a low concentration solution and flow paths12,22, and32for a high concentration solution of a plurality of FO membrane modules10,20, and30, which are coupled in series.

More specifically, the water recovery device200includes FO membrane modules10,20, and30, connecting flow paths240,241,242, and243for a low concentration solution, and connecting flow paths250,251,252, and253for a high concentration solution.

The FO membrane module10has the structure described above.

The FO membrane module20includes a flow path21for a low concentration solution, connectors21aand21bfor a low concentration solution, a flow path22for a high concentration solution, connectors22aand22bfor a high concentration solution, and an FO membrane23.

The FO membrane module30includes a flow path31for a low concentration solution, connectors31aand31bfor a low concentration solution, a flow path32for a high concentration solution, connectors32aand32bfor a high concentration solution, and an FO membrane33. The FO membrane modules20and30have the same function as the FO membrane module10.

The arrows20aand30ain the FO membrane modules20and30indicate a direction in which water moves.

The connecting flow path240is a pipe connecting a source of the low concentration solution to the connector11a, and the connecting flow path241is a pipe connecting the connector11bto the connector21afor the low concentration solution.

The connecting flow path242is a pipe connecting the connector21bto the connector31a.

The connecting flow path243is a pipe connected to the connector31band externally releases the low concentration solution released from the connector31bout of the water recovery device200.

In this way, the flow paths11,21, and31are coupled in series through the connecting flow paths241and242.

In other words, an in-series flow path, that is, an in-series flow path for a low concentration solution, is formed through the connecting flow paths241and242and flow paths11,21, and31. In a water recovery device including a plurality of FO membrane modules like the water recovery device200, the FO membrane modules are counted as first, second, third, . . . from an inlet of an in-series flow path for a low concentration solution, that is, an FO membrane module near the connector11a. In the embodiment as shown inFIG. 5, the FO membrane module10is a first module, and the FO membrane module20is a second module.

The connecting flow path250is a pipe connecting the source of the high concentration solution to the connector12a, and the connecting flow path251is a pipe connecting the connector12bwith the connector22a.

The connecting flow path252is a pipe connecting the connector22bwith the connector32a.

The connecting flow path253is a pipe connected to the connector32band feeds the high concentration solution released from the connector32binto the DS regeneration device. The DS regeneration device has the aforementioned function.

In this way, the flow paths12,22, and32are coupled in series through the connecting flow paths251and252.

In other words, an in-series flow path, that is, an in-series flow path for a high concentration solution, is formed through the connecting flow paths251and252for the high concentration solution and connecting flow paths12,22, and32for the high concentration solution.

(Water Recovery Process Using Multiple Module)

Next, a water recovery process using the water recovery device200, that is, a multiple water recovery process, is illustrated.

In this water recovery process, a low concentration solution flows in an inlet of an in-series flow path for a low concentration solution, that is, from the connector11ato the flow path11, while a high concentration solution flows in an inlet of an in-series flow path for a high concentration solution, that is, the connector12ato the flow path12. Accordingly, water in the low concentration solution flows into the high concentration solution through the FO membrane13. After separating the water, the concentrated low concentration solution is released from the connector11binto the connecting flow path241. The low concentration solution flows into the flow path21from the connector21athrough the connecting flow path241for a low concentration solution.

On the other hand, the high concentration solution is less concentrated by the water from the low concentration solution and flows in the flow path12in the same direction as the low concentration solution and is released from the connector12bto the connecting flow path251. The high concentration solution flows in the connecting flow path251and then flows from the connector22ato the flow path22. Then, the high concentration solution is treated the same in the FO membrane modules20and30as the FO membrane module10.

Finally, the low concentration solution is externally released from the connector31b, and the high concentration solution is externally released from the connector32b. The high concentration solution is fed into a DS regeneration device, and the DS regeneration device recovers water in the high concentration solution. After recovering the water, the concentrated high concentration solution is sent back to the source of the high concentration solution. In this way, water in the low concentration solution is recovered.

For example, as shown inFIG. 5(the comparative example), a low concentration solution in a solution concentration of 3.5 mass % flows in the flow path11at a flow rate of 200 m3/day, and a low concentration solution in a concentration of 7.0 mass % is released from the flow path11at a flow rate 100 m3/day. On the other hand, a high concentration solution in a concentration of 12.0 mass % flows in the flow path12at a flow rate of 200 m3/day, and a high concentration solution in a concentration solution of 8.0 mass % is released from the flow path12at a flow rate of 300 m3/day. Accordingly, water flows from the low concentration solution to the high concentration solution at a flow rate of 100 m3/day. A solute in the low concentration solution and the high concentration solution is the same as inFIG. 4, and the FO membranes13,23, and33are TFC-FO membranes made by HTI Inc. The water flowing in the high concentration solution is recovered by a DS regeneration device. The number of FO membrane modules may be determined by the amount of the low concentration solution. In addition, each FO membrane module may include a plurality of FO membrane devices.

(Problems of Conventional Multiple Water Recovery Process)

In a conventional multiple water recovery process, as the number of steps from an inlet of an in-series flow path for a low concentration solution to an FO membrane module becomes larger, an osmotic pressure difference between low and high concentration solutions in the FO membrane module becomes smaller. The reason is that the low concentration solution module has a higher concentration while the high concentration solution has a lower concentration in the FO membrane as the number of steps from an inlet of an in-series flow path for a low concentration solution to an FO membrane module becomes larger. As an osmotic pressure difference between low and high concentration solutions becomes smaller, less water flows from the low concentration solution to the high concentration solution.

Accordingly, water recovery efficiency in the FO membrane module at a rear end, that is, utilization efficiency (Flux) of the FO membrane is reduced, and furthermore, recovery efficiency over the conventional multiple water recovery process is reduced. In other words, the conventional multiple water recovery process may have equivalent efficiency to that of the embodiment by increasing the size and number of the FO membrane modules.

Attempts to solve this problem have in general used a method of increasing the flow rate of a high concentration solution. However, this method requires a large amount of pump energy to distribute the high concentration solution in a massive amount. In addition, since the high concentration solution in a massive amount is used to recover water, inconvenience of recovering water from the high concentration solution is increased. Accordingly, this method may not fundamentally solve the aforementioned problem.

The present disclosure develops a multiple water recovery device and a multiple water recovery process by repeatedly examining the problem. The water recovery device and water recovery process according to one example embodiment may improve recovery efficiency. Hereinafter, the water recovery device and water recovery process are illustrated in detail.

(Structure of Water Recovery Device)

First, a structure of a water recovery device1according to Embodiment 1 is explained referring toFIG. 1.

The water recovery device1schematically includes a flow path for a high concentration solution in parallel compared with a water recovery device200shown inFIG. 5.

More specifically, the water recovery device1includes FO membrane modules10,20, and30, connecting flow paths40,41,42, and43for a low concentration solution, and connecting flow paths50,51,52,53,54, and55for a high concentration solution.

The FO membrane module10includes a flow path11for a low concentration solution, connectors11aand11bfor a low concentration solution, a flow path12for a high concentration solution, connectors12aand12bfor a high concentration solution, and an FO membrane13. The flow path11is for distributing a low concentration solution, and the low concentration solution is distributed in the flow path11in a parallel direction with the FO membrane13(a rightward direction ofFIG. 1).

Herein, the low concentration solution is a solution including water, that is, an aqueous solution. The low concentration solution to be treated by the water recovery device1may be any solution as long as it includes water. The low concentration solution may be, for example, water from a natural system, for example water obtained from a sea, river, lake, swamp, pond, and the like, for example sea water, blackish water, river water, and the like, industrial drain water, various water drained from homes, and the like.

The connectors11aand11bare respectively an inlet and an outlet for a low concentration solution. In this embodiment, the connector11ais an inlet for the low concentration solution, and the connector11bis an outlet for the low concentration solution. In other words, the low concentration solution flows in from the connector11ainto the flow path11, and is distributed in the flow path11in a rightward direction ofFIG. 1. The low concentration solution is released from the connector11boutside the flow path11.

The flow path12is connected to the flow path11by disposing the FO membrane13therebetween. In other words, the flow path11and the flow path12in the FO membrane module10are partitioned by the FO membrane13.

The flow path12is a flow path for distributing the high concentration solution, and the high concentration solution in the flow path12is distributed in a reverse direction (in the leftward direction inFIG. 1) with the low concentration solution.

In this way, the high and low concentration solutions oppositely flow in the FO membrane module10. Accordingly, an osmotic pressure difference in the FO membrane module10becomes more uniform in a length direction (leftward and rightward directions inFIG. 1) of the FO membrane module10. On the other hand, the high and low concentration solutions may be distributed to flow in parallel (in the same direction). However, the opposite flow may bring about higher water recovery efficiency.

The high concentration solution includes water, that is, an aqueous solution. In addition, the high concentration solution includes a solute in a higher concentration than in the low concentration solution, that is, the osmotic pressure is higher than in the concentration of the low concentration solution. The high concentration solution may also be referred to be as a draw solution (DS).

A kind of a solute dissolved in the high concentration solution is not particularly limited. For example, the solute may include monovalent or polyvalent ions. The polyvalent ions are desirable because they increase osmotic pressure of the high concentration solution. A high concentration solution including the polyvalent ion is referred to be as an MVI (multivalent ion)-based DS.

The MVI may be, for example, calcium chloride, magnesium chloride, magnesium sulfate, magnesium nitrate, and the like. A DS electrolyte including monovalent ions may be, for example, sodium chloride, potassium chloride, potassium nitrate, sodium bicarbonate, and the like.

Other desirable example of the solute may be carbon dioxide, ammonia, and the like. These are gases and thus may be easily removed from the high concentration solution. In other words, water may be easily recovered from the high concentration solution. For example, these solutes may be removed from the high concentration solution by slightly heating the same. The high concentration solution removed of the solutes is substantially water, thereby easily recovering the water. On the other hand, when a solute is a subject (for example, a salt including the aforementioned polyvalent ions), an RO membrane module and the like may be used to recover water from the high concentration solution as described above. Accordingly, a large amount of energy is needed. The solute may be used singularly or in a mixture. For example, when the solute is mixed with ammonia and carbon dioxide, solubility of carbon dioxide may be improved.

The connectors12aand12bare respectively an outlet and an inlet for the high concentration solution. In this embodiment, the connector12bis an inlet for a high concentration solution, and the connector12ais an outlet for the high concentration solution. In other words, the high concentration solution flows in from the connector12binto the flow path12, and is distributed in the flow path12. The high concentration solution is released from the connector12aoutside the flow path12.

The FO membrane13partitions the flow path11and the flow path12. In addition, since the high concentration solution has a higher osmotic pressure than the low concentration solution, water in the low concentration solution naturally flows into the high concentration solution. In other words, the water in the low concentration solution moves in an arrow direction (10a) through the FO membrane13and flows into the flow path12. Accordingly, energy required to move water from the low concentration solution to the high concentration solution is theoretically zero (0).

The FO membrane13may include a conventional semipermeable membrane, for example, an FO membrane, an RO membrane, an NF membrane, and the like without a particular limit. The FO membrane may include, for example, a cellulose3acetate membrane made by Hydration Technologies Inc. (HTI) or a composite membrane (a TFC membrane), but may also include an RO membrane such as a mixed cellulose acetate membrane of 2 acetic acid and 3 acetic acid, CE or CG made by General Electric (GE), SWC series or CTA series as a polyamide-based composite membrane made by Hydranautics Inc., ESPA series, LFC series, SW series, BW series, HRLE series, XRE series, and the like as a polyamide-based composite membrane made by DOW.

On the other hand, the FO membrane13may be a membrane having high hydrophilicity, to which impurities from the low concentration solution may not be easily attached.

On the other hand, FO membranes having a different permeability coefficient are provided by HTI Inc. These FO membranes may have a permeability coefficient of 9 LMH (L/m2/h) (1 M NaCl vs. distilled water), 20 LMH (L/m2/h) (1 M NaCl vs. distilled water), and the like. The higher permeability coefficient the FO membrane has, the more easily water is passed therethrough.

In the post-described Embodiment 3, FO membranes used in each FO membrane module have different permeability coefficients.

The FO membrane module20includes a flow path21for a low concentration solution, connectors21aand21bfor a low concentration solution, a flow path22for a high concentration solution, connectors22aand22bfor a high concentration solution, and an FO membrane23.

The FO membrane module30includes a flow path31for a low concentration solution, connectors31aand31bfor a low concentration solution, a flow path32for a high concentration solution, connectors32aand32bfor a high concentration solution, and an FO membrane33.

The FO membrane modules20and30have the same function as the FO membrane module10.

The arrows20aand30aindicate a direction in which water moves.

The connecting flow paths40to43for a low concentration solution have the same structure as the connecting flow paths240to243for a low concentration solution described above.

Accordingly, the flow paths11,21, and31for a low concentration solution are coupled in series through the connecting flow paths41and42.

In other words, the connecting flow paths41and42and the flow paths11,21, and31form an in-series flow path, that is, an in-series flow path for a low concentration solution. In addition, FO membrane modules are counted first, second, third, . . . from an FO membrane module closest to an inlet of an in-series flow path for a low concentration solution, that is, a connector11ain the water recovery device1.

InFIG. 1, the FO membrane module10is a first module and the FO membrane module20is a second module.

The present example embodiment shows a device including three modules, but it may include any number of modules of more than two if necessary.

The connecting flow path50is a pipe connecting a source of the high concentration solution with the connector12b.

The connecting flow path51is a pipe connected to the connector12aand feeds the high concentration solution released from the connector12ainto a DS regeneration device.

The DS regeneration device may be any device recovering water from the high concentration solution, but, for example, is an RO membrane device when a solute is a salt including polyvalent ions.

On the other hand, when the solute in the high concentration solution is a gas, the DS regeneration device may be a heating device such as a distillation device and the like.

The connecting flow path52for a high concentration solution is a pipe connecting a source of the high concentration solution and the connector22b.

The connecting flow path53is a pipe connected to the connector22aand feeds the high concentration solution released from the connector22ato the DS regeneration device.

The connecting flow path54is a pipe connecting the source of the high concentration solution and the connector32b.

The connecting flow path55is a pipe connected to the connector32aand feeds the high concentration solution released from the connector32ainto the DS regeneration device.

Accordingly, the connecting flow paths50,52, and54for a high concentration solution are arranged in parallel in Embodiment 1.

In Embodiment 1, the connecting flow paths50,52, and54for a high concentration solution distribute the high concentration solution in the same concentration and simultaneously at the same flow rate.

Accordingly, the high concentration solution in the same concentration and simultaneously at the same flow rate flows in the flow paths12,22, and32.

In addition, an outlet flow rate of the in-series flow path for a low concentration solution is higher than the sum of inlet flow rates of each flow path for a high concentration solution.

Herein, an outlet flow rate of the in-series flow path for a low concentration solution is a flow rate of the low concentration solution released from an outlet of the in-series flow path for a low concentration solution, that is, the connector31b.

In addition, an inlet flow rate of an in-series flow path for a low concentration solution is higher than the sum of inlet flow rates of each flow path for a high concentration solution.

Herein, the inlet flow rate of an in-series flow path for a low concentration solution is a flow rate of the low concentration solution flowing in the inlet of an in-series flow path for a low concentration solution, that is, the connector11a.

In addition, an inlet flow rate of a flow path for a high concentration solution is a flow rate of the high concentration solution flowing in the connectors12b,22b, and32bfor a high concentration solution.

As described above, the high concentration solution is fed into each of the FO membrane modules10,20, and30, for example, by two methods as follows.

First, a flow path from a source of the high concentration solution is branched into the flow paths50,52, and54, and pumps are positioned in the connecting flow paths50,52, and54. These pumps are set to have the same output. Accordingly, each of the connecting flow paths50,52, and54distributes the high concentration solution in the same concentration and simultaneously at the same flow rate.

Secondly, a pump is disposed in a flow path from a source of the high concentration solution, and the path extending from the pump is branched into the connecting flow paths50,52, and54. The output of the pump is set to be three times higher than in the first method, and a valve and the like is used to adjust the flow rate and to uniformly distribute the high concentration solution to each FO membrane module. Accordingly, the high concentration solution is distributed into each of the connecting flow paths50,52, and54in the same concentration and at the same flow rate.

However, there may be another method of distributing the high concentration solution into each of the connecting flow paths50,52, and54in the same concentration and at the same flow rate, other than the two aforementioned methods.

According to the present example embodiment 1, the connecting flow paths50,52, and54are arranged in parallel and simultaneously distribute the high concentration solution in the same concentration and at the same rate. Accordingly, the high concentration solution in the same concentration and simultaneously at the same flow rate flows in the flow paths12,22, and32in Embodiment 1. Accordingly, since each FO membrane module, particularly, each FO membrane module20and30at rear ends maintains a higher osmotic pressure difference than a conventional one, recovery efficiency in these FO membrane modules20and30is remarkably improved.

In addition, since the flow rate of the high concentration solution is very much lower than the flow rate of the low concentration solution, pump energy required for feeding the high concentration solution becomes very small. In addition, inconvenience of recovering water with the high concentration solution is decreased.

On the other hand, as described above, since the high concentration solution in the same concentration is fed in each of the FO membrane modules10,20, and30, a high osmotic pressure difference in each of the FO membrane modules10,20, and30is maintained despite lowering a flow rate of the high concentration solution. In other words, since each of the FO membrane modules10,20, and30maintains a high osmotic pressure difference, the flow rate of the high concentration solution doesn't need to be high.

In addition, since the low concentration solution has an increasing contact area with the high concentration solution, utilization efficiency of the FO membrane is improved. Resultantly, the area of the FO membrane becomes smaller, and simultaneously the number of modules may be decreased.

(Water Recovery Process Using Multiple Module)

Now, a water recovery process, that is, a multiple water recovery process using the water recovery device1, is illustrated. In this water recovery process, while the low concentration solution is made to flow in an inlet of an in-series flow path, that is, in the flow path11from the connector11a, the high concentration solution in the same concentration and at the same flow rate is made to flow in each inlet of flow paths in parallel for a high concentration solution, that is, the connectors12b,22b, and32bto the flow paths12,22, and32for a high concentration solution.

Accordingly, the low concentration solution flows in an in-series flow path for a low concentration solution. In addition, water in the low concentration solution flows in the high concentration solution through the FO membranes13,23, and33. The low concentration solution concentrated by separating the water is released through the flow path43for a low concentration solution.

On the other hand, the high concentration solution in each of the FO membrane modules10,20, and30has a lower concentration due to water from the low concentration solution, flows through the flow paths12,22, and32for a high concentration solution in an opposite direction to the low concentration solution (i.e., reversely), and is released from the connectors12a,22a, and32ainto the connecting flow paths51,53, and55for a high concentration solution. Herein, since the high concentration solution in the same concentration and at the same rate flows in each of the FO membrane modules10,20, and30, an osmotic pressure difference in the FO membrane modules10,20, and30, and in particular, in the FO membrane modules at rear ends20and30, is maintained to be high.

Then, the high concentration solution is fed in a DS regeneration device, and the DS regeneration device recovers water in the high concentration solution. The high concentration solution is concentrated by the water recovery, and then goes back to the source of the high concentration solution.

Through the treatment process, water in the low concentration solution is recovered.

As an example, a low concentration solution having a concentration of 3.5 mass % flows in a flow path11for a low concentration solution at a flow rate of 200 m3/day in the embodiment shown inFIG. 1. A high concentration solution having a concentration of 12.0 mass % flows in each flow path12,22, and32for a high concentration solution at a flow rate of 20 m3/day.

Accordingly, a low concentration solution having a concentration of 7.0 mass % is released from the flow path31for a low concentration solution at a flow rate of 100 m3/day.

Further, a high concentration solution having a concentration of 3.4 mass % is released from the flow path12for a high concentration solution at a flow rate of 70 m3/day.

In addition, a high concentration solution having a concentration of 4.8 mass % is released from the flow path22at a flow rate of 50 m3/day.

On the other hand, a high concentration solution having a concentration of 6.0 mass % is released from the flow path32at a flow rate of 40 m3/day.

In addition, solutes of the low concentration solution and the high concentration solutions are the same as shown inFIG. 4, and FO membranes13,23, and33are TFC-FO membranes made by Hydration Technology Innovations (HTI), LLC.

As is clearly shown in the embodiment, the same recovery efficiency as in a conventional method is obtained by using a high concentration solution in a smaller amount than the conventional method.

On the other hand, as the number of steps from the inlet of an in-series flow path for a low concentration solution to an FO membrane module becomes smaller, the flow rate of a high concentration solution released from the FO membrane module into a DS regeneration device becomes higher, and the concentration thereof becomes lower. The reason is that as the number of steps from the inlet of an in-series flow path for a low concentration solution to the FO membrane module becomes smaller, an osmotic pressure difference in the FO membrane module becomes larger. In other words, as the number of steps from the inlet of an in-series flow path for a low concentration solution to the FO membrane module is smaller, water recovery efficiency is higher. However, as the number of steps from the inlet of an in-series flow path for a low concentration solution to the FO membrane module becomes smaller, the FO membrane is more loaded, and is thus easily deteriorated. Accordingly, the post-described Embodiment 3 provides each of the FO membrane modules10,20, and30having more uniform recovery efficiency to make deterioration of the FO membranes more uniform. Embodiment 3 is now illustrated in more detail.

When also the flow paths for a low concentration solution are arranged in parallel, all of the FO membrane modules10,20, and30are disposed in parallel. Accordingly, when low and high concentration solutions fed into each of the FO membrane modules10,20, and30have the same flow rate as that of the high concentration solution in Embodiment 1, a lesser amount of the low and high concentration solutions are fed into each of the FO membrane modules10,20, and30, causing a concentration polarization problem in both of flow paths for low and high concentration solutions. Herein, the concentration polarization indicates formation of a high concentration area around the FO membrane. On the contrary, when a flow rate of the low concentration solution fed into each of the FO membrane modules10,20, and30becomes equal to that of the low concentration solution according to the present example embodiment, the flow rate increases as much as the number of modules, and in addition, output of pumps prepared for each module needs to be increased, seriously deteriorating energy efficiency.

Accordingly, only the flow paths for a high concentration solution are arranged in parallel in Embodiment 1 to suppress a concentration polarization in each FO membrane module10,20, and30as much as possible. Concentration polarization in the high concentration solution may be suppressed in Embodiment 2. More detail is illustrated later. The concentration polarization may reduce recovery efficiency.

In this regard, a multiple water recovery process according to Embodiment 1 includes inflowing a low concentration solution into an in-series flow path for a low concentration solution including a plurality of flow paths11,21, and31for a low concentration solution coupled in series, and inflowing a high concentration solution having the same concentration into each of the flow paths12,22, and32for a high concentration solution. Accordingly, an osmotic pressure difference in each of the FO membrane modules10,20, and30and particularly the FO membrane modules20and30at rear ends in Embodiment 2 may be maintained to be high. Therefore, recovery efficiency in the FO membrane modules20and30is remarkably improved, and furthermore, overall recovery efficiency in the multiple water recovery process is remarkably improved in Embodiment 1.

In addition, an outlet flow rate of in-series flow paths for a low concentration solution is larger than the sum of inlet flow rates of each flow path for a high concentration solution. In other words, since a flow rate of the high concentration solution is extremely smaller than that of the low concentration solution, pump energy required for feeding the high concentration solution becomes very small. In addition, inconvenience of recovering water with the high concentration solution is lessened.

In addition, an inlet flow rate of the in-series flow path for a low concentration solution is larger than the sum of inlet flow rates of each flow path for a high concentration solution. In other words, since a flow rate of the high concentration solution is extremely smaller than that of the low concentration solution, pump energy required for feeding the high concentration solution becomes extremely small. In addition, inconvenience of recovering water with the high concentration solution is lessoned.

In addition, when sea water is used as the low concentration solution, water, that is, fresh water from the sea water, is recovered with high recovery efficiency.

In addition, an FO method according to the embodiment moves water from the low concentration solution to the high concentration solution and has an advantage of less contaminating a membrane than an RO method of directly recovering water with the low concentration solution.

Herein, a high concentration solution in the same concentration and at the same flow rate is made to flow in each flow path for a high concentration solution in Embodiment 1, but the concentration and flow rate in the flow paths for a high concentration solution may be adjusted unless the purpose of the present example embodiment is changed.

For example, as the number of steps from an inlet of an in-series flow path for a low concentration solution to an FO membrane module is increased, an osmotic pressure difference becomes smaller, since the low concentration solution in the FO membrane module has a higher concentration. Accordingly, as the number of steps from an inlet of an in-series flow path for a low concentration solution to an FO membrane module is increased, at least either one of concentration and flow rate of a high concentration solution in the FO membrane module is made to be higher. However, the purpose of the present example embodiment is to lower a flow rate of a high concentration solution, but the flow rate of a high concentration solution may be increased, as long as the purpose of the present example embodiment is not deviated from. In addition, when the concentration of the high concentration solution is changed, a different source depending on each concentration needs to be prepared. Accordingly, an osmotic pressure difference in the FO membrane modules20and30at a rear end is increased.

(Structure of Water Recovery Device)

Referring toFIG. 2, a structure of a water recovery device2according to Embodiment 2 is explained.

The water recovery device2includes FO membrane modules10-2,20-2, and30-2substituted for the FO membrane modules10,20, and30of the water recovery device1according to Embodiment 1.

The FO membrane modules10-2,20-2, and30-2include flow paths12-2,22-2, and32-2substituted for the flow paths12,22, and32for a high concentration solution of the FO membrane modules10,20, and30.

The flow paths12-2,22-2, and32-2for a high concentration solution are narrower than the flow paths11,21, and31for a low concentration solution. Specifically, the flow paths12-2,22-2, and32-2for a high concentration solution have narrower vertical cross-sections than those of the flow paths11,21, and31for a low concentration solution. Accordingly, the flow paths12-2,22-2, and32-2for a high concentration solution speed up flux of a high concentration solution compared with those of Embodiment 1. Accordingly, a shear force in the high concentration solution is improved, and thus concentration polarization in the high concentration solution is decreased.

In other words, as described above, since a flow rate of the high concentration solution is lower than a flow rate of the low concentration solution, concentration polarization in the high concentration solution may occur. Accordingly, Embodiment 2 increases a flux in the flow paths12-2,22-2, and32-2for a high concentration solution by making the flow paths12-2,22-2, and32-2for a high concentration solution narrower than the flow paths11,21, and31for a low concentration solution. Therefore, since a shear force in the high concentration solution is improved, concentration polarization in the high concentration solution is decreased.

The FO membrane modules10,20, and30may be down-sized in Embodiment 2. The flow path for a low concentration solution is made to be narrow and thus to increase a flux in the flow path for a low concentration solution. However, since the narrow flow path for a low concentration solution is to make each FO membrane module small, the number of FO membrane modules is huge. Accordingly, the water recovery device2according to Embodiment 2 has sharply deteriorated efficiency.

A multiple water recovery process according to Embodiment 2 is the same as that of Embodiment 1 and thus will not be illustrated here.

Example

As shown inFIG. 2, a low concentration solution in a concentration of 3.5 mass % flows in the flow path11at a flow rate of 230 m3/day. On the other hand, a high concentration solution in a concentration of 12.0 mass % flows in each of the flow paths12-2,22-2, and32-2at a flow rate of 20 m3/day. Herein, the vertical cross-section of the flow path for a low concentration solution and the vertical cross-section of the flow path for a high concentration solution have a ratio of 20:1 in each of the FO membrane modules10-2,20-2, and30-2. The FO membrane is the same as that of the example in Embodiment 1. As a result, a low concentration solution in a concentration of 8.1 mass % is released from the flow path11at a flow rate of 100 m3/day.

On the other hand, a high concentration solution in a concentration of 3.0 mass % is released from the flow path12-2at a flow rate 80 m3/day.

A high concentration solution in a concentration of 4.0 mass % is released from the flow path22-2at a flow rate 60 m3/day.

The flow path32-2for a high concentration solution releases a high concentration solution in a concentration of 4.8 mass % at a flow rate of 50 m3/day.

In this way, each of the FO membrane modules10-2,20-2, and30-2shows higher water recovery efficiency than the FO membrane modules of the example in Embodiment 1, and thus concentration polarization has less influence thereon.

Accordingly, since the flow paths12-2,22-2, and32-2for a high concentration solution are narrower than the flow paths11,21, and31for a low concentration solution in the second example, a flux of a high concentration solution in the flow paths12-2,22-2, and32-2for a high concentration solution is improved, and furthermore, concentration polarization in the high concentration solution is lessened.

(Structure of Water Recovery Device)

Referring toFIG. 3, a structure of a water recovery device3according to Embodiment 3 is explained.

The water recovery device3includes FO membrane modules10-3,20-3, and30-3substituted for the FO membrane modules10-2,20-2, and30-2in the water recovery device2according to Embodiment 2.

The FO membrane modules10-3,20-3, and30-3include FO membranes13-3,23-3, and33-3substituted for the FO membranes13,23, and33of the FO membrane modules10-2,20-2, and30-2.

The FO membranes13-3,23-3, and33-3have a higher permeability coefficient, as the number of steps from an inlet of an in-series flow path for a low concentration solution to the FO membrane module is larger. In other words, the FO membrane13-3has the lowest permeability coefficient, and the FO membrane33-3has the highest permeability coefficient. That is, the FO membrane module10passes water with the most difficulty, and the FO membrane module30most easily passes water.

A permeability coefficient difference is provided as a thickness of an FO membrane inFIG. 3. The thicker the FO membrane is, the lower the permeability coefficient it has.

In other words, as described above, as the number of steps from an inlet of an in-series flow path for a low concentration solution to an FO membrane module is smaller, an osmotic pressure difference in the FO membrane module is larger. Specifically, the osmotic pressure difference in the FO membrane module10-3is the largest, and the osmotic pressure difference in the FO membrane module30-3is the smallest. Accordingly, when FO membranes having the same permeability coefficient are used in each FO membrane module as in Embodiment 1, a large amount of water is recovered through the FO membrane module10-3, while a small amount of water is recovered through the FO membrane module30-3compared with the FO membrane module10-3. In addition, an FO membrane in the FO membrane module10-3is highly loaded and easily deteriorated.

Accordingly, a permeability coefficient of the FO membranes13-3,23-3, and33-3is higher as the number of steps from an inlet of an in-series flow path for a low concentration solution to an FO membrane module is larger in Embodiment 3. Accordingly, the amount of water passing the FO membranes13-3,23-3, and33-3, that is, the load of the water, is standardized, and furthermore, a deterioration speed of the FO membranes is standardized. Therefore, each of the FO membrane13-3,23-3, and33-3is exchanged at a standardized time, and thus inconvenience for maintenance and repair is lessened.

The FO membrane13-3may include, for example, an SW series RO membrane made by DOW.

The FO membrane23-3may include, for example, a BW series RO membrane made by DOW.

The FO membrane33-3may include, for example, an HRLE series RO membrane made by DOW.

These RO membranes may be used in an FO membrane mode in the example Embodiments 1 to 3.

A common RO membrane is not mostly optimized for the FO membrane mode and thus may be modified to a have an appropriate module structure for the FO membrane mode. Of course, the RO membrane may be used for the FO membrane without modification.

Example

As an example, in the embodiment shown inFIG. 3, a low concentration solution in a concentration of 3.5 mass % flows in a flow path11at a flow rate of 200 m3/day, and a low concentration solution in a concentration of 7.0 mass % is released from the flow path31for a low concentration solution at a flow rate of 100 m3/day. A high concentration solution in a concentration of 15.0 mass % flows in each flow path12-2,22-2, and32-2at a flow rate of 20 m3/day.

From the flow path12-2, a high concentration solution in a concentration of 5.7 mass % is released at a flow rate of 53 m3/day.

From the flow path22-2for a high concentration solution, a high concentration solution in a concentration of 5.7 mass % is released at a flow rate of 53 m3/day.

From the flow path32-2for a high concentration solution, a high concentration solution in a concentration of 5.7 mass % is released at a flow rate of 53 m3/day.

A solute in the low and high concentration solutions is the same as shown inFIG. 4, and SW30XLE-440i, BW30HR-440i, and HRLE-440i made by DOW are respectively used as FO membranes13-3,23-3, and33-3.

As shown in this embodiment, the amount of water passing each of the FO membranes13-3,23-3, and33-3, that is, the load of the water, is standardized in the present example embodiment.

Hereinbefore, since the FO membranes13-3,23-3, and33-3have a higher permeability coefficient as the number of the FO membranes from an inlet of an in-series flow path for a low concentration solution to an FO membrane module is larger, the amount of water passing the FO membranes13-3,23-3, and33-3, that is, the load of the water, is standardized in Embodiment 3.

Example embodiments of the present disclosure have been illustrated in the accompanying drawings, but it should be understood that the present disclosure is not limited thereto. While various examples have been described, it is to be understood that the present disclosure is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

For example, in the example embodiments, the number of the FO membrane modules is shown as 3, but the present disclosure is not limited thereto. For example, the number of the FO membrane modules may be 2 or may be 4 or more. The number of FO membrane modules is determined, for example, by the amount of the low concentration solution.

DESCRIPTION OF SYMBOLS

1,2,3: water recovery device10,20,30: FO membrane module11,21,31: flow path for a low concentration solution12,22,32: flow path for a high concentration solution40to43: connecting flow path for a low concentration solution50to55: connecting flow path for a high concentration solution