JP2022129708A - Forward osmosis water treatment device and method - Google Patents

Abstract

To provide means to stably perform an operation of a factory regardless of the variation of the water production amount of fresh water and the like by a forward osmosis method by using factory waste heat for a heat source to heat a diluted temperature sensitive agent aqueous solution to a cloud point or higher.SOLUTION: A forward osmosis water treatment device comprises: a forward osmosis membrane module 3 moving water in water 1 to be treated to a temperature sensitive agent aqueous solution 12 having a cloud point; heating means 6 heating a diluted temperature sensitive agent aqueous solution 5 flown out from the forward osmosis membrane module to the cloud point or greater; a gravity separation tank 7 where a concentrated solution phase and a diluted solution phase phase-separated by heating are layer-separated; a recovery membrane filter 15 obtaining fresh water by the membrane filtration of a diluted solution 8; cooling means 18 cooling a concentrated solution 9 to the cloud point of the temperature sensitive agent aqueous solution or lower; circulation means where the cooled concentrated solution is returned to the forward osmosis membrane module and reused as the temperature sensitive agent aqueous solution; and a line where a heating medium 23 heated by the heat exchange of a factory cooling system is supplied to the heating means and the heating medium 25 discharged from the heating means is returned to the cooling system.SELECTED DRAWING: Figure 1

Description

The present invention relates to an apparatus and method for removing salts from seawater, wastewater, etc. by forward osmosis.

Various methods for producing fresh water from seawater using a semipermeable membrane are known, but the reverse osmosis method, in which a pressure higher than the osmotic pressure is applied to seawater to forcibly permeate the seawater, has been mainly developed. However, since this method requires high pressure, there is a problem that equipment costs and operating costs increase. Therefore, seawater and a solution with a higher concentration than seawater are brought into contact with each other through a semipermeable membrane as a suction liquid, and the water in the seawater is moved to this solution by osmotic pressure without pressurization, and the freshwater is separated and recovered. A manufacturing forward osmosis method has been developed.

In this forward osmosis method, a solution in which ammonia and carbon dioxide are dissolved in water has been used as a suction liquid. We have been focusing on the development of methods using

In the forward osmosis method using this temperature sensitive agent, a forward osmosis step of bringing seawater and an aqueous solution of a temperature sensitive agent into contact with each other through a semipermeable membrane to move moisture in the seawater through the semipermeable membrane to the aqueous solution of the temperature sensitive agent; a heating step of heating the dilute aqueous solution of the temperature-sensitive agent diluted with water to a cloud point or higher to separate the layers into a concentrated solution mainly composed of the temperature-sensitive agent and a dilute solution mainly composed of water; It consists of a gravitational separation process and a cooling/circulation process in which the separated concentrated solution is cooled to below the cloud point and is circulated as an aqueous thermosensitive agent solution that is brought into contact with seawater.

In order to use this dilute solution as fresh water, it is also known that a recovery membrane filtration step is provided to remove the temperature-sensitive agent remaining therein by membrane treatment (Patent Documents 1 to 3).

This representative process is shown in FIG. As shown in the figure, this apparatus comprises a forward osmosis module 3, a heat exchanger 6, a gravity separation tank 7, a heat exchanger 11, a membrane filtration device 15, a heat exchanger 18 and a boiler 19. Seawater 1 is supplied to a forward osmosis module 3 by a seawater supply pump 2, contacts an aqueous solution of a temperature sensitive agent 12 through a semipermeable membrane 4 in the module, and the water in the seawater moves toward the aqueous solution of a temperature sensitive agent due to osmotic pressure. Moving. The dilute thermosensitive agent aqueous solution 5 diluted by the movement of water is first heated in the heat exchanger 18 by exchanging heat with the concentrated solution 9 separated in the gravity separation tank 7. Since the recovered sensible heat alone is insufficient in the amount of heat, it is further heated to a predetermined temperature by the heat exchanger 6 and put into the gravity separation tank 7 . A heat source such as a boiler 19 is used to make up for the shortage of heat. The temperature sensitive agent dilute solution 8 separated in the gravity separation tank 7 is sent to the membrane filtration device 15 by the pump 14 to separate the temperature sensitive agent and the like, and fresh water is taken out as recovered membrane filtered water 16 . The recovered membrane concentrated water 17 remaining without passing through the membrane is returned and added to the dilute temperature sensitive agent aqueous solution 5 flowing out from the forward osmosis module 3 . On the other hand, the concentrated solution 9 of the temperature sensitive agent separated in the gravity separation tank 7 is cooled by exchanging heat with the diluted aqueous solution of the temperature sensitive agent 5 in the heat exchanger 18, and is further cooled in the heat exchanger 11 to a temperature appropriate for the forward osmosis process. and returned to the forward osmosis module 3 as an aqueous temperature sensitive agent solution 12 .

JP 2015-54292 A JP 2017-56424 A JP 2017-148734 A

By the way, in the forward osmosis method using a thermosensitive agent, the process that consumes the most energy is the process of heating the diluted thermosensitive agent aqueous solution to above the cloud point. It's a big problem. In this regard, Patent Document 2 describes that it is preferable to use the sensible heat of the concentrated solution separated in the gravity separation process as the heat source, and in its examples, low-temperature waste such as factory cooler exhaust Assuming heat utilization. However, the heat medium discharged from the heat exchanger that cools the concentrated solution cannot be used to heat the diluted thermosensitive agent aqueous solution unless it is further heated. There is no explanation about. In addition, there is no explanation at all about how to utilize low-temperature waste heat such as factory cooler exhaust.

The present inventors considered using the waste heat of the factory as a heat source for separating the thermosensitive agent in water treatment by the forward osmosis method. A system to stabilize both operations has not been established.

The object of the present invention is to use waste heat from a factory as a heat source for heating a diluted thermosensitive agent aqueous solution above the cloud point in water treatment by the forward osmosis method. To provide means for stably operating a factory irrespective of fluctuations in temperature.

The present inventors have made intensive studies in order to solve the above problems, and installed a connection line between the heating means for the diluted thermosensitive agent aqueous solution in the forward osmosis water treatment apparatus and the cooling system of the factory, and the heat exchange. The line can be switched according to the operation status of the factory and the water treatment by the forward osmosis method, thereby stabilizing both the operation of the factory and the water treatment by the forward osmosis method.
That is, the present invention
A forward osmosis membrane module for moving water in the water to be treated containing salts to an aqueous temperature-sensitive agent solution having a cloud point; a heating means, a gravity separation tank for separating the heated and phase-separated dense solution phase and the dilute solution phase by gravity, and the diluted solution discharged from the gravity separation tank after layer separation is filtered through a membrane to remove fresh water. cooling means for cooling the concentrated solution discharged from the gravity separation tank to a temperature below the clouding point of the temperature-sensitive agent aqueous solution; In a forward osmosis water treatment apparatus having a circulation means for returning and reusing as the temperature sensitive agent aqueous solution,
A line is provided for supplying a heat medium heated by heat exchange in a factory cooling system to the heating means and for returning the heat medium discharged from the heating means to the cooling system. a forward osmosis water treatment device;
A forward osmosis step of moving the water in the water containing salts to be treated to an aqueous temperature-sensitive agent solution having a cloud point; a gravity separation step of separating the warmed and phase-separated thick solution phase and the dilute solution phase by gravity; a recovery membrane filtration step of obtaining fresh water by membrane filtration of the layer-separated dilute solution; a cooling step of cooling the layer-separated concentrated solution to a temperature below the cloud point of the aqueous temperature-sensitive agent solution; In a forward osmosis water treatment method comprising the steps of:
A heat medium heated by exchanging heat in a factory cooling system is supplied to the heating process, and the heat medium discharged from the heating process is returned to the cooling system to cool the object of the cooling system. To provide a forward osmosis water treatment method characterized by:

According to the present invention, both the operation of the factory and the water treatment by the forward osmosis method are stabilized, and the waste heat of the factory is used as the heat source for heating the dilute thermosensitive agent aqueous solution above the cloud point in the forward osmosis method. , the cost of desalination by the forward osmosis method can be greatly reduced.

It is a figure which shows the state which connected the cooling system of the factory in one Embodiment of this invention, and the forward osmosis water treatment apparatus. It is a figure which shows an example of the cooling system of the conventional factory. It is a figure which shows schematic structure of the conventional forward osmosis water treatment apparatus.

The water to be treated by the method of the present invention is a solution containing salts in water as a solvent, such as seawater, brackish water, and wastewater.

Forward Osmosis Membrane Module The forward osmosis membrane module brings the water to be treated, which has been filtered if necessary, and a high osmotic pressure aqueous solution in which a thermosensitive agent is dissolved in water, into contact with each other through a semipermeable membrane. It is an apparatus for obtaining a water-diluted temperature-sensitive agent aqueous solution and a forward osmosis membrane-concentrated water by moving the temperature-sensitive agent solution through a permeable membrane.

A thermosensitive agent is a substance that is hydrophilic at low temperatures and dissolves well in water, but becomes hydrophobic at a certain temperature or higher, and its solubility decreases. be called. When this temperature is reached, the hydrophobized thermosensitive agent agglomerates to cause white turbidity.

This thermosensitive agent is used as various surfactants, dispersants, emulsifiers, and the like. compounds of groups, glycerin and compounds of ethylene oxide and/or propylene oxide, pentaerythritol and compounds of ethylene oxide and/or propylene oxide, hexylene glycol and both ethylene oxide and propylene oxide Or a compound with one side, and the like. The temperature sensitive agent used in the present invention preferably has a cloud point in the range of 30°C to 80°C, particularly 40°C to 60°C.

The concentration of the aqueous temperature-sensitive agent solution must be adjusted so that the osmotic pressure of the aqueous temperature-sensitive agent solution is sufficiently higher than the osmotic pressure of the liquid to be treated. %, preferably about 70 to 95% by mass, more preferably about 75 to 95% by mass.

The semipermeable membrane is preferably one capable of selectively permeating water, and is preferably a forward osmosis membrane, but a reverse osmosis membrane can also be used. Although the material is not particularly limited, examples include cellulose acetate, polyamide, polyethyleneimine, polysulfone, and polybenzimidazole. The form of the semipermeable membrane is also not particularly limited, and may be a flat membrane, a tubular membrane, a hollow fiber membrane, or the like.

A device equipped with this semipermeable membrane usually has a semipermeable membrane installed in a cylindrical or box-shaped container, and the water to be treated flows into one chamber partitioned by this semipermeable membrane, and flows into the other chamber. An aqueous solution of a temperature sensitive agent can be flowed through, and a known semipermeable membrane device can be used, and a commercially available product can also be used.

When the water to be treated in the forward osmosis membrane module is brought into contact with the aqueous solution of the temperature-sensing agent through the semipermeable membrane, the difference in osmotic pressure causes the water in the water to move through the semi-permeable membrane to the aqueous solution of the temperature-sensing agent, resulting in dilution. The warm water solution is formed, and the remaining water to be treated is concentrated by the movement of water and discharged as forward osmosis membrane concentrated water.

In addition, since the forward osmosis membrane concentrated water obtained here contains salts at a high concentration, it can be concentrated to precipitate and separate the salts for effective use.

Heating Means Means for coagulating at least part of the temperature-sensitive agent by heating the dilute aqueous solution of the temperature-sensitive agent, which has been diluted by moving water from the water to be treated in the forward osmosis membrane module, to a temperature equal to or higher than the cloud point. . The agglomerates are separate concentrated solutions of the temperature sensible. A heat exchanger or the like can be used as the heating means as long as it can heat the diluted thermosensitive agent aqueous solution. The heating temperature in the heating means can be controlled, for example, by adjusting the flow rate and temperature of the heat medium introduced into the heat exchanger.

As a heat source for this heating means, it is preferable to use sensible heat of the concentrated solution separated in the following gravity separation tank. Further, if the sensible heat of the dilute solution separated in the gravity separation tank is also used as the heat source of the heating means, the energy efficiency is further improved, which is more preferable. A heat source such as a boiler compensates for the insufficient heat of the heating means due to the sensible heat recovered from the concentrated solution and the diluted solution, and the waste heat from the factory is used as described later.

Gravity Separation Tank Gravity separation is performed into a thick solution layer mainly composed of the temperature-sensitive agent phase-separated by the heating means and a dilute solution layer mainly composed of water and containing a small amount of the temperature-sensitive agent. This gravitational separation can be carried out at a liquid temperature equal to or higher than the cloud point while standing still or continuously flowing. At that time, when the concentrated solution of the temperature sensitive agent aggregated by the heating means is put into the gravity separation tank, the fine droplets of the concentrated solution quickly settle, and the droplets are united to the lower part of the gravity separation tank. A thick solution layer is formed at

The concentration of the temperature sensitive agent in the dilute solution separated by gravity is about 0.01 to 2.0% by mass, usually about 0.1 to 1.0% by mass. is in suspension.

The concentration of the thermosensitive agent in the concentrated solution is about 70-95 mass %, usually about 75-85 mass %.

Recovery Membrane Filtration Apparatus The dilute solution separated in the gravity separation tank is subjected to recovery membrane filtration using a nanofiltration membrane, a reverse osmosis membrane, or the like to remove mainly dissolved and remaining temperature sensitive agent. The recovered membrane filtered water is fresh water and can be used as drinking water. Since the collected membrane concentrated water remaining without membrane filtration contains the temperature sensitive agent, it can be combined with the diluted temperature sensitive agent aqueous solution flowing out from the forward osmosis membrane module, or can be combined with the temperature sensitive agent aqueous solution. .

Cooling Means The concentrated solution separated in the gravity separation tank is cooled to a temperature lower than the cloud point of the aqueous thermosensitive agent solution, thereby dissolving it in water and regenerating the aqueous thermosensitive agent solution. This temperature can be used in a wide range, but in consideration of economy, room temperature or higher is preferred. A heat exchanger or the like can be used as the cooling means. As the cooling heat source, it is preferable to use the water to be treated or the dilute thermosensitive agent aqueous solution obtained in the forward osmosis process from the viewpoint of efficient use of energy.

Circulation Means This means circulates the regenerated temperature-sensitive agent aqueous solution as it is to the forward osmosis membrane module for reuse.

By the way, in the forward osmosis method of the present invention using an aqueous temperature-sensitive agent solution, the concentrated solution separated from the dilute solution by heating above the cloud point is circulated and used as the aqueous temperature-sensitive agent solution in the forward osmosis process. It is necessary to cool the concentrated solution to a temperature suitable for the temperature, while the aqueous solution of the temperature sensible agent diluted by the movement of water in the water to be treated needs to be warmed above the cloud point in order to separate the water from it. There is As described above, the forward osmosis water treatment apparatus uses a large amount of energy for heating and cooling, and its management is important.

As a heat source for heating the diluted thermosensitive agent aqueous solution above the cloud point, it is desirable to preferentially use the heat in the system from the viewpoint of operational stability as well as energy saving. First, the sensible heat of the concentrated solution discharged from the gravity separation tank should be used for heating. Furthermore, a dilute solution can also be used as a heat source for heating the diluted thermosensitive agent aqueous solution. However, since the heat exchanger cannot recover all of the sensible heat, it is necessary to make up for the shortage of heat.

The present invention is characterized in that waste heat from the factory is used for heating the dilute thermosensitive agent aqueous solution, which consumes the most thermal energy, in the forward osmosis water treatment.

In the heating means, the dilute aqueous solution of the temperature-sensitive agent may be heated to a cloud point or higher, but the concentration of the temperature-sensitive agent decreases as the temperature of the dilute solution phase-separated by heating increases. In the subsequent recovery membrane filtration apparatus, the lower the concentration of the temperature-sensitive agent, the less the load, so it is better to increase the temperature of the heating means as much as possible. Therefore, the temperature of the diluted thermosensitive agent aqueous solution in the heating means is preferably about 60 to 95.degree. C., preferably about 80 to 90.degree.

Therefore, the waste heat of the factory used in the forward osmosis water treatment equipment is heat-exchanged in the cooling system, and the temperature is raised to about 5 to 50°C, usually about 20 to 40°C, higher than the above temperature. preferably in the form The heat medium may be one commonly used such as water or oil. When the heat medium is used above its boiling point, the heat exchanger and piping must be pressure resistant.

The factory to be used may be any factory that can obtain the required amount of such waste heat, and examples include oil refineries and thermal power plants. An example of a refinery cooling system is shown in FIG. The produced hot fluid such as gasoline and light oil is sent to the heat exchanger 21 at, for example, 150° C., where it is cooled to, for example, 35° C. in the heat exchanger 26 of the cooling tower 22 with a heat medium 23 such as cooling water. For example, it is cooled to 50° C. and taken out as a product. The cooling water is brought to a temperature of, for example, 120° C. (2 atm) by the heat exchanger 21 and circulated to the heat exchanger 26 of the cooling tower 22 .

In the present invention, such a heat medium in the factory is used as a heat source for heating the diluted thermosensitive agent aqueous solution. The heat exchanger for heating with the heat medium in the factory may be newly installed, but if the heat medium is the same, it can be used as an existing heat exchanger for heating with a boiler or the like. In addition, in order to cool the forward osmosis water treatment device with factory cooling water, a heat exchanger for exchanging heat between the dilute thermosensitive agent aqueous solution and the concentrated solution of the forward osmosis water treatment device and the osmosis membrane module It is also preferred to be able to supply a heat exchanger for further cooling of the concentrated solution with cooling water from the cooling tower on the plant side.

By using the heating medium in the factory as a heating means for the forward osmosis water treatment device, the cooling system in the factory has two systems, one for cooling by the diluted thermosensitive agent aqueous solution and the other for cooling by cooling water. Therefore, if the forward osmosis water treatment equipment is operating at full capacity and the cooling capacity required by the factory is satisfied with the diluted thermosensitive agent aqueous solution, the cooling on the factory side will be performed with the diluted thermosensitive agent aqueous solution, and the forward osmosis water treatment equipment will be cooled. It can be done with factory cooling water. If the operation rate of the forward osmosis water treatment device is low and the cooling at the factory cannot be sufficiently performed with only the diluted temperature-sensing agent aqueous solution, the lack of cold heat can be supplemented with the cooling water from the factory.

FIG. 1 shows a state in which the factory cooling system and the heating means of the forward osmosis water treatment apparatus are connected in one embodiment of the present invention. This embodiment utilizes the conventional forward osmosis processing apparatus shown in FIG. 3 in combination with the refinery cooling system shown in FIG.

Specifically, a heat medium supply line 27 that newly supplies the heat medium 23 to the heat exchanger 6 (heating means) of the forward osmosis water treatment device, and a heat medium 25 discharged from the heat exchanger 6 are sent to the factory. A heat medium return line 28 is provided for return to the cooling system. Then, each line is provided with a valve, and in addition to circulating hot water and steam, which are the heat medium of the factory cooling system and the boiler 19 of the forward osmosis water treatment device, through each conventional line, the factory cooling The heat medium 23 of the system can also be switched to be supplied to the heat exchanger 6 for replenishing and heating the diluted thermosensitive agent aqueous solution 5 . The heat medium 23 may be supplied to the heat exchanger 6 entirely or partially. In this example, the heat medium 23 of the cooling system of the factory and the heat medium 20 of the boiler are both water, so the heat exchanger 6 is not added and is used as both.

The heat medium 25 discharged from the heat exchanger 6 is returned to the factory cooling system through a heat medium return line 28 . Then, the heat medium 25 returned to the cooling system of the factory is supplied to the heat exchanger 26, cooled to a predetermined temperature, and supplied to the heat exchanger 21 again.

In this way, by supplying the heat medium 23 (steam) heated by heat exchange in the heat exchanger 21 in the cooling system of the factory to the heat exchanger 6 of the forward osmosis water treatment device as needed, the boiler 19 It is possible to reduce the load.

The cooling tower 22, which is a cooling medium (cold water) source for the heat exchanger 26, also serves as a cooling medium (cold water) source for the heat exchanger 11 of the forward osmosis water treatment apparatus. (A and B in the figure)
By using the heat exchanger 26 and the heat exchanger 11 with the cooling tower 22 as the cooling medium (chilled water) source, the cooling of the factory and the forward osmosis water treatment apparatus can be balanced.

INDUSTRIAL APPLICABILITY The present invention can be widely used for production of fresh water from seawater by forward osmosis, desalination of wastewater, and the like, which are installed in factories.

1 seawater (water to be treated)
2 Seawater supply pump 3 Forward osmosis membrane module 4 Forward osmosis membrane 5 Diluted temperature sensitive agent aqueous solution 6 Heat exchanger 7 Gravity separation tank 8 Dilute solution 9 Concentrated solution 10 Temperature sensitive agent aqueous solution pump 11 Heat exchanger 12 Temperature sensitive agent aqueous solution 13 Positive Osmotic membrane concentrated water 14 Pump 15 Recovery membrane filtration device 16 Recovery membrane filtered water 17 Recovery membrane concentrated water 18: Heat exchanger 19: Boiler 20: Heat medium (steam, hot water)
21: Heat exchanger 22: Cooling tower 23: Heat medium (steam, hot water)
25: Heat medium (steam, hot water)
26: Heat exchanger 27: Heat medium supply line 28: Heat medium return line

Claims (4)

A forward osmosis membrane module for moving water in the water to be treated containing salts to an aqueous temperature-sensitive agent solution having a cloud point; a heating means, a gravity separation tank for separating the heated and phase-separated dense solution phase and the dilute solution phase by gravity, and the diluted solution discharged from the gravity separation tank after layer separation is filtered through a membrane to remove fresh water. cooling means for cooling the concentrated solution discharged from the gravity separation tank to a temperature below the clouding point of the temperature-sensitive agent aqueous solution; In a forward osmosis water treatment apparatus having a circulation means for returning and reusing as the temperature sensitive agent aqueous solution,
A line is provided for supplying a heat medium heated by heat exchange in a factory cooling system to the heating means and for returning the heat medium discharged from the heating means to the cooling system. Forward osmosis water treatment equipment. The heating means is provided between the gravity separation tank and a heat exchanger that exchanges heat between the dilute temperature-sensitive agent aqueous solution flowing out of the forward osmosis membrane module and the concentrated solution discharged from the gravity separation tank. a heat exchanger for further heating the diluted temperature-sensitive agent aqueous solution, and the line further heats the diluted temperature-sensitive agent aqueous solution with the heat medium heated by heat exchange in the cooling system of the factory. 2. The forward osmosis water treatment system of claim 1, wherein the forward osmosis water treatment system is connected in supply to a heat exchanger. The cooling means is provided between the forward osmosis membrane module and a heat exchanger that exchanges heat between the diluted thermosensitive agent aqueous solution flowing out of the forward osmosis membrane module and the concentrated solution discharged from the gravity separation tank. 3. A circulation line for supplying cooling water from the cooling system of the factory is connected to the heat exchanger for further cooling the concentrated solution. of forward osmosis water treatment equipment. A forward osmosis step of moving the water in the water containing salts to be treated to an aqueous temperature-sensitive agent solution having a cloud point; a gravity separation step of separating the warmed and phase-separated thick solution phase and the dilute solution phase by gravity; a recovery membrane filtration step of obtaining fresh water by membrane filtration of the layer-separated dilute solution; A cooling step of cooling the layer-separated concentrated solution to a temperature below the cloud point of the aqueous temperature-sensitive agent solution, and a circulation of returning the cooled concentrated solution to the forward osmosis step for reuse as the aqueous temperature-sensitive agent solution. In a forward osmosis water treatment method comprising the steps of:
A heat medium heated by exchanging heat in a factory cooling system is supplied to the heating process, and the heat medium discharged from the heating process is returned to the cooling system to cool the object of the cooling system. A forward osmosis water treatment method characterized by:

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