JP6028645B2 - Water treatment equipment - Google Patents

Description

  The present invention relates to an apparatus for producing fresh water, for example, seawater using a semipermeable membrane.

  Various methods for desalinating seawater using a semipermeable membrane are known, but a reverse osmosis method for forcibly permeating water by applying a pressure higher than the osmotic pressure to seawater has been mainly developed. Since this method requires pressurization to a high pressure, there is a problem that the equipment cost and operation cost are high. On the other hand, if a salt solution having a higher concentration than seawater is present through the semipermeable membrane, water can be transferred to the salt solution by osmotic pressure without applying pressure. If a solution in which a volatile gas is dissolved is used as the salt solution, fresh water can be obtained by evaporating and separating the volatile gas by distilling the salt solution. As this forward osmosis method, a method using a combination of ammonia and carbon dioxide as a volatile gas has already been developed (Patent Documents 1 and 2).

  In the method of Patent Document 1, a salt solution obtained by dissolving ammonia and carbon dioxide is passed through a semipermeable membrane on the side opposite to seawater, and water in the seawater is passed through the semipermeable membrane into the salt solution. This is a method in which the diluted salt solution obtained is transferred to a distillation tower to obtain fresh water, and a mixed gas containing ammonia, carbon dioxide and water is separated, and the mixed gas is returned to the original chamber of the semipermeable membrane. .

  As shown in FIG. 2, the apparatus used in this method includes a first chamber 52, a semipermeable membrane 56, a second chamber 58, a third chamber 62, and a fourth chamber 64. Raw water 50 such as seawater flows into the first chamber 52 and comes into contact with the semipermeable membrane 56, and water in the raw water 50 passes through the semipermeable membrane 56 and enters the second chamber 56. Concentrated liquid 54 having increased salt concentration due to moisture permeation exits first chamber 52. On the other hand, in the second chamber 58 in contact with the opposite side of the semipermeable membrane 56, there is a salt solution obtained by dissolving ammonia and carbon dioxide and having a salt concentration higher than that of the raw water. The third chamber 62 is diluted with the water that has passed through the first chamber 62. Salt is precipitated in the third chamber, and the salt 68 separated by precipitation is returned to the second chamber 58. The liquid from which the salt has settled and separated in the third chamber 62 enters the fourth chamber 64, which is a distillation column, and is heated to decompose the remaining salt into its constituent components. Will be returned. Fresh water 66 left by the decomposition and removal of the salt is taken out from the fourth chamber.

  In the method of Patent Document 2, a salt solution obtained by dissolving ammonia and carbon dioxide is passed through a semipermeable membrane on the side opposite to seawater, and water in the seawater is passed through the semipermeable membrane into the salt solution. The obtained diluted salt solution is separated into ammonium ion and carbonate ion separately using an ion exchange membrane or distillation tower to obtain fresh water, and the separated ammonium ion and carbonate ion are dissolved to dissolve the semipermeable membrane. It is a method to return to the original room.

US Patent Application Publication No. 2005 / 0145568A1 JP 2011-83663 A

  Technology that performs seawater desalination and wastewater treatment by the forward osmosis method (FO method) does not require energy to apply hydraulic pressure that overcomes the osmotic pressure of raw water before treatment, such as the reverse osmosis method (RO method). In addition, it is necessary to separate the permeated water, which has been permeated into the high osmotic pressure induction solution on the opposite side of the raw water through the FO membrane, from the salt.

  Distillation and filtration methods are generally used for the separation process of the induction solution and the permeated water, but in order to reduce the size of the membrane filtration device, the throughput is increased by using a high concentration induction solution. Therefore, there is a problem that the energy of the induction solution separation process increases and the processing cost (cost for the amount of permeated water) increases.

  An object of the present invention is to provide means for increasing the ability of a forward osmosis device by increasing the efficiency of osmosis without increasing the concentration of the induction solution.

  In the water treatment method using an FO membrane, when raw water permeates the membrane, the salt concentration in the raw water is concentrated in the membrane or the induced solution is diluted in the membrane with the permeated water, and only a few percent of the osmotic pressure difference can be used as the driving force for filtration. . Therefore, a method of increasing the amount of permeated water by adding a small amount of hydraulic positive pressure or negative pressure that works independently of the liquid concentration (osmotic pressure) (1/10 or less of the general RO method) can be considered. After a certain period of time, the concentration of the raw water in the membrane and the dilution of the induction solution in the membrane become more prominent, so that the brake is applied and the effect of increasing the amount of permeate is reduced. Therefore, it has been found that the brake is eliminated by releasing the applied pressure for a certain period of time, and it is possible to obtain a high permeated water amount by repeating the pressure application and release.

  The present invention has been made based on these findings. An apparatus that applies a hydraulic positive pressure to the raw water side of a device (membrane module) loaded with an FO membrane or applies a negative pressure to the permeate side is provided. It is characterized by changing the pressure.

That is, in the present invention, a liquid whose solvent is water is brought into contact with an induction solution having a higher osmotic pressure than the liquid through a semipermeable membrane, and water in the liquid is passed through the semipermeable membrane to the induction solution. Forward osmosis means for movement, fresh water separation means for separating fresh water from a dilution induction solution diluted with water obtained by the forward osmosis means, and the induction from the dilution induction solution from which fresh water has been separated by the fresh water separation means In a water treatment apparatus having an induction solution regeneration means for regenerating a solution, intermittently pressurizing means for intermittently pressurizing the liquid supplied to the forward osmosis means and / or the diluted induction solution flowing out from the forward osmosis means as well as a pressure reduction means for reducing the pressure in the induction solution is induced solution temperature-sensitive material was prepared by dissolving in water having a lower critical temperature, the fresh water separating means, the dilute draw solution Warming, there is provided a water treatment apparatus which comprises a heating tank for precipitating and hydrophobized at least part of the temperature sensitive material.

  According to the present invention, the forward osmosis membrane device can be operated efficiently and the amount of permeated water can be increased.

It is a block diagram which shows an example of a structure of the apparatus of this invention. It is a block diagram which shows an example of a structure of the conventional apparatus.

  The liquid (raw water) used for obtaining fresh water in the present invention may be water as long as the solvent is used. Examples thereof include seawater, lake water, river water, and factory waste water.

Forward osmosis means The forward osmosis means brings the raw water, which is the liquid, into contact with the induction solution having a higher osmotic pressure through the semipermeable membrane, and moves the water in the liquid to the induction solution through the semipermeable membrane. A semipermeable membrane device is used.

  The induction solution only needs to have an osmotic pressure higher than that of the raw water, but the solute is preferably volatile in view of the separability of fresh water from the diluted induction solution diluted by the movement of water. An aqueous ammonium carbonate solution produced by dissolving a fixed amount of ammonia and carbon dioxide in water is preferred. The predetermined amount is an amount that makes the concentration of the water to be purified to a concentration that allows the water to pass through the semipermeable membrane to the induction solution and is higher than the salt concentration of the raw water. The upper limit of the concentration is determined so that a salt of ammonia and carbon dioxide, that is, ammonium carbonate, ammonium hydrogen carbonate, ammonium carbamate, etc. does not precipitate on the semipermeable membrane surface or in the distillation tower, and this can be obtained by experiment. . One of the methods for confirming whether or not precipitates are generated on the semipermeable membrane surface or in the distillation column is a method of judging whether stable operation is possible by operating for a long time. The molar ratio of ammonia to carbon dioxide is about 1.5-3. This molar ratio is also taken into consideration so that the salt of ammonia and carbon dioxide does not precipitate on the semipermeable membrane surface or in the distillation column. As the volatile solute, in addition to a salt of ammonia and carbon dioxide, alcohols such as tert-butanol and ketones can be used.

  In addition, a temperature-sensitive substance having a lower critical temperature can also be used as a solute. That is, forward osmosis membrane treatment is performed using a high osmotic pressure induction solution prepared by dissolving a thermosensitive substance having a lower critical temperature in water, and the obtained dilution induction solution is heated to the lower critical temperature or higher. Then, by partially hydrophobizing and precipitating the temperature-sensitive substance and separating it, fresh water can be obtained easily and inexpensively from seawater or the like with less energy.

  For example, when polyoxyethylene alkyl ether having a lower critical temperature of 40 ° C. is used as an inducer, the thermosensitive substance exhibits hydrophilicity and dissolves in the solution in a normal temperature (5 to 25 ° C.) dilution induction solution. ing. When this is heated to 40 ° C., the thermosensitive substance becomes hydrophobic and aggregates. Since the solution becomes cloudy at this time, it is generally known as a cloud point phenomenon. The cloud point is determined visually as the temperature at which the solution becomes cloudy. The cloudy temperature-sensitive substance is eventually separated into a thick layer and a dilute layer due to the difference in specific gravity. Using this property, it is desirable to perform gravity separation first. However, even if the size of the agglomerated particles cannot be visually confirmed as cloudiness at a temperature slightly below the cloud point, the agglomeration reaction proceeds and the number of molecules apparently decreases due to the aggregation of molecules together. To drop. When the solution in which the temperature sensitive substance is aggregated is filtered through a UF membrane or NF membrane, the temperature sensitive substance is easily removed by the membrane, and pure water is obtained as a filtrate. The membrane concentrate is an induction solution in which the hydrophobized thermosensitive substance is aggregated. When this is cooled to 30 ° C., the temperature sensitive material is redissolved and the induction solution is regenerated. In the regeneration-inducing solution in which the temperature-sensitive substance is redissolved, the concentration of the inducing substance is increased and a predetermined high osmotic pressure is obtained. By introducing the regenerated induction solution into the semipermeable membrane device and bringing it into contact with the water to be treated through the membrane, pure water can be repeatedly obtained from the water to be treated.

  This thermosensitive substance is used as various surfactants, dispersants, emulsifiers, and the like. For example, alcohol or fatty acid and ethylene oxide compound, alcohol or fatty acid and propylene oxide compound, acrylamide and alkyl group Compounds, glycerin fatty acid esters, sorbitan fatty acid ester ethylene oxide adducts, amino acids and derivatives thereof. As the temperature-sensitive substance used in the present invention, those having a lower critical temperature in the range of 30 ° C. to 80 ° C., particularly in the range of 40 ° C. to 60 ° C. are preferable. The concentration of the temperature-sensitive substance contained in the induction solution is preferably as high as possible so as to obtain a high osmotic pressure, and is preferably about 0.1 to 10 mol / L, particularly about 2 to 5 mol / L.

  The semipermeable membrane used in the semipermeable membrane device is preferably one that can selectively permeate water, and a commercially available one, particularly a forward osmosis membrane, can be preferably used. The material is not particularly limited, and examples thereof include cellulose acetate-based, polyamide-based, polyethyleneimine-based, polysulfone-based, and polybenzimidazole-based materials. The form of the semipermeable membrane is not particularly limited and may be any of a flat membrane, a tubular membrane, a hollow fiber, and the like.

  A device for mounting this semipermeable membrane is usually a semi-permeable membrane installed in a cylindrical or box-shaped container, and raw water is allowed to flow in one chamber partitioned by this semipermeable membrane, and an induction solution is introduced into the other chamber. A known semipermeable membrane device can be used, and a commercially available product can be used.

  The entrance of the chamber through which the raw water flows is connected to a raw water reservoir (this may be the sea or river itself, or a tank or the like). The outlet side is usually connected to a concentrate reservoir. A circulation line connecting both pipes can be provided for circulation.

  The inlet of the chamber through which the induction solution flows is connected to the induction solution regenerating unit, and the outlet is connected to the fresh water separation unit, thereby forming a circulation line for the induction solution.

Fresh water separation means The fresh water separation means is a means for separating fresh water from the dilution-inducing solution diluted with water obtained by the forward osmosis means. When the solute is a volatile solute, it is usually a distillation column or heated. In the case of a thermosensitive substance that is hydrophobized by the above, a heating tank or a heat exchanger, a precipitation tank, and a solid-liquid separation device are used.

  A known distillation column may be used, and any type such as a shelf system and a packing system may be used. A heater is provided at the lower part of the distillation tower, and the steam generated by heating the purified water at the lower part is brought into contact with the diluted induction solution falling from the upper part to exchange heat. A reboiler, heat exchange, etc. can be used for a heater. Although the heat source of a heater is not ask | required, the steam before the condensate which comes out of the turbine of a power plant, the hot water collect | recovered from waste heat, etc. can be used. When the temperature of the heat source is 100 ° C. or higher, distillation can be performed at normal pressure, but when it is lower than that, it is necessary to reduce the pressure.

  On the other hand, the heating tank in the case of a temperature sensitive substance may be a box type or a cylindrical one, and a heater and a stirrer are attached. The heater may be provided either inside or outside the tank.

In the heating tank, the diluted induction solution diluted by the movement of water from the raw water is heated to hydrophobize and deposit at least a part of the thermosensitive substance. This precipitation is a phase separation of a concentrated solution of the temperature sensitive substance. The temperature to be heated is preferably a temperature at which a part of the temperature-sensitive substance becomes hydrophobic above the lower critical temperature of the temperature-sensitive substance, and specifically, a range from 1 to 10 ° C. higher than the lower critical temperature. Especially up to 2-5 ° C higher temperatures. Accordingly, heating temperature exceeds the lower critical temperature or it, it is preferable to increase warmed to about 10 ° C. than the lower critical temperature. Incidentally, when the lower limit critical temperature is the cloud point, it is difficult to separate the less than the lower limit critical temperature.
It is preferable to use the sensible heat of the separated liquid separated in the next solid-liquid separation step as the heat source of the heating tank.

  The dilution induction solution heated in the heating tank and depositing the thermosensitive substance separates the deposited thermosensitive substance by solid-liquid separation. This solid-liquid separation means can utilize a nanofiltration (NF) membrane, an ultrafiltration membrane, a filtration device using a microfiltration membrane, a sand filtration device, a filter cloth filtration device, a centrifuge, a sedimentation separation tank, or the like. . Preferred are ultrafiltration membranes, microfiltration membranes, and centrifugal separations because relatively low power and good separation efficiency can be obtained.

  The water separated by the solid-liquid separator can usually be used as it is as fresh water, but is further purified if necessary.

Induction solution regeneration means The induction solution regeneration means is a means for regenerating the induction solution from the diluted induction solution from which fresh water has been separated by the fresh water separation means, and uses a cooler.

  When the solute is a salt of carbon dioxide and ammonia, carbon dioxide obtained from the top of the distillation tower is connected to the top gas cooling and regeneration means via the dilution induction solution temperature control means from the top of the distillation tower, A gas composed of ammonia and water vapor is cooled to form an aqueous solution. Although a cooling means is not ask | required, a heat exchanger can be used. Although it does not specifically limit as a heat source to cool, River water, seawater, air, etc. can be used. The same applies when other volatile solutes are used.

  When the solute is a temperature-sensitive substance, the concentrated solution of the temperature-sensitive substance is cooled to a temperature at which the temperature-sensitive substance becomes hydrophilic, specifically, a temperature at which the white turbidity disappears, and is regenerated into an induction solution. . This temperature can be used in a wide range, but considering the economy, a temperature 5 to 10 ° C. lower than the lower critical temperature is appropriate, and a temperature of room temperature or higher is preferable. As this cooling heat source, it is preferable to use the water to be treated or the dilution induction solution obtained in the forward osmosis step from the viewpoint of efficient use of energy.

  The regenerated induction solution can be recycled as it is.

Pressurizing and Depressurizing Means In the present invention, in such an apparatus, the liquid supplied to the forward osmosis means is intermittently depressurized in the dilution induction solution flowing out from the pressurizing means and / or the forward osmosis means. It is characterized in that a decompression means is installed.

  The degree of pressurization or depressurization to be applied is about 0.01 to 0.5 MPa, usually about 0.05 to 0.2 MPa, and the time for applying one pressurization or depressurization is about 0.5 to 10 minutes. The interval for applying pressurization or depressurization (from the end of pressurization or depressurization to the start of pressurization or depressurization again) is suitably about 0.5 to 10 minutes. This pressurization or depressurization may be performed in one direction, but may be used in combination. A method of performing pressurization or depressurization intermittently using a booster pump for pressurizing a liquid, a vacuum pump or the like for depressurization, and intermittently performing pressurization or depressurization can be performed by opening and closing a valve.

  A configuration of an apparatus according to an embodiment of the present invention is shown in FIG.

  This apparatus comprises a membrane module 1 equipped with a forward osmosis membrane 2, a salt solution storage tank 4, and a salt separation device 3.

  A raw water supply pump 21 and a pressurizing device 23 for pressurizing the raw water are provided on the inlet side of the raw water 11 of the membrane module 1. A booster pump is used for the pressurizing device 23. A pressure recovery device 24 is attached to the outlet side of the concentrated water 12 concentrated by moving water through the forward osmosis membrane 2 to the induction solution side in the membrane module 1. As this pressure recovery device, a pressure energy recovery device such as a Pelton turbine type or a cylinder piston type, which is generally used for an RO membrane device or the like, is used.

  The induction solution 14 flows into the opposite chamber partitioned by the forward osmosis membrane 2 in the membrane module 1, and a hydraulic positive pressure 31 is induced on the flow side of the raw water 11 of the forward osmosis membrane 2. Hydraulically, negative pressure 32 is applied to the flow side of the solution 14.

  The dilution induction solution diluted by the movement of water from the raw water in the membrane module 1 enters the salt solution storage tank 4 through the negative pressure device 25. A vacuum pump is used for the negative pressure device 25.

  The dilution induction solution 15 is sent from the salt solution storage tank 4 to the salt separation device 3 where the fresh water 13 is separated and taken out. On the other hand, the induction solution 16 separated and concentrated from fresh water is returned to the salt solution storage tank 4 and sent to the induction solution chamber of the membrane module 1 by the salt solution supply pump 22.

  The pressurization pattern and filtration rate when the filtration rate when not pressurized is 100% are shown in the following table.

  According to the present invention, since fresh water can be efficiently produced from seawater or the like, the present invention can be widely used in an apparatus for producing fresh water from seawater or the like.

1: membrane module 2: forward osmosis membrane 3: salt separation device 4: salt solution storage tank 11: raw water 12: concentrated water 13: treated water (fresh water)
14: induction solution 15: dilution induction solution 16: induction solution 21: raw water supply pump 22: salt solution supply pump 23: pressurization device 24: pressure recovery device 25: negative pressure device 31: hydraulic positive pressure 32: water Negative pressure

Claims (1)

Forward osmosis means for bringing a liquid whose solvent is water into contact with an induction solution having a higher osmotic pressure than the liquid through a semipermeable membrane, and moving water in the liquid to the induction solution through the semipermeable membrane; A fresh water separation means for separating fresh water from a diluted induction solution diluted with water, obtained by the forward osmosis means, and an induction solution for regenerating the induction solution from the diluted induction solution from which fresh water has been separated by the fresh water separation means In a water treatment apparatus having a regeneration means,
A pressurizing means for intermittently pressurizing the liquid supplied to the forward osmosis means and / or a decompression means for intermittently reducing the dilution induction solution flowing out from the forward osmosis means ;
The induction solution is an induction solution prepared by dissolving a thermosensitive substance having a lower critical temperature in water,
The water treatment apparatus , wherein the fresh water separation unit includes a heating tank that warms the dilution induction solution to hydrophobize and deposit at least a part of the thermosensitive substance .

Images