JP2014097483A - Water treatment method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment method and an apparatus capable of desalinating sea water, etc. inexpensively and easily with tenuous energy consumption.SOLUTION: The provided problem-solving method comprises: a forward osmosis step of contacting, via a semi-permeable membrane, a body of treatment target water and a leading solution obtained by dissolving a specified quantity of tert-butanol into water so as to mobilize water within the treatment target water into the leading solution via the semi-permeable membrane and obtain not only a diluted leading solution diluted with water but also membrane-concentrated water; a distillation step of feeding the diluted leading solution into a distillation column so as to obtain a tert-butanol vapor and obtain purified water; and a cooling regeneration step of regenerating the leading solution by cooling and condensing the vapor. An apparatus used for the same is also provided.

Description

  The present invention relates to a water treatment method and apparatus for desalinating and treating seawater, brine, and the like.

  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, purified water can be obtained by evaporating and separating the volatile gas by distilling the diluted salt solution by moving water. A method using a combination of ammonia and carbon dioxide as the volatile gas has already been developed (Patent Documents 1 and 2).

  As schematically shown in FIG. 4, the method of Patent Document 1 is a salt solution obtained by dissolving ammonia and carbon dioxide on the opposite side of seawater (treated water) through a semipermeable membrane (FO membrane) ( And water in seawater is moved to the salt solution through the semipermeable membrane, and the obtained diluted salt solution is sent to a distillation tower to obtain water, and ammonia, carbon dioxide and water are In this method, the mixed gas is separated and the mixed gas is returned to the original chamber of the semipermeable membrane.

  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 ions and carbonate ions individually using an ion exchange membrane or distillation tower to obtain purified water, and the separated ammonium ions and carbonate ions 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

In the methods of Patent Documents 1 and 2, regeneration of the inducer (for example, ammonium carbonate) is performed by evaporation. However, the latent heat of vaporization of ammonia and accompanying water is enormous and energy is required. In addition, the cost is high. Furthermore, the size of the evaporation facility is extremely large, and is not suitable for producing a large amount (for example, 100,000 m ³ / day) of drinking water. Moreover, since the input energy is large, the size of the heat exchanger is also large, which is not suitable for mass processing. When using the evaporation method, volatile substances such as ammonium carbonate must be used. However, when ammonium carbonate is used, the inducer that leaks into the environment due to backflow from the FO film contains nitrogen. Causes nutrition.

  The present invention has been made to solve these problems, and an object of the present invention is to provide a water treatment method and apparatus that can be easily desalted with low energy from seawater or the like at low cost.

  The present invention has been made to solve the above-mentioned problems, and tert-butanol as an inducer can easily obtain a high osmotic pressure and can efficiently move water from the water to be treated to the induction solution side. In addition, the present inventors completed the present invention by finding that water and the inducer can be easily separated with less energy by distilling the diluted induction solution obtained by moving water.

  That is, in the present invention, the water to be treated and an induction solution in which a predetermined amount of tert-butanol is dissolved in water are brought into contact with each other through a semipermeable membrane, and the water in the water to be treated passes through the semipermeable membrane and the induction solution And a forward osmosis step for obtaining a dilution induction solution diluted with water and membrane concentrated water, a distillation step for feeding the dilution induction solution to a distillation tower to obtain tert-butanol vapor and obtaining purified water, The present invention provides a water treatment method having a cooling regeneration step of regenerating the induction solution by cooling and condensing the steam, and an apparatus therefor.

In the present invention, by using an induction solution in which tert-butanol is dissolved in water, a high osmotic pressure difference is obtained between the water to be treated and water in the water to be treated is efficiently moved to the induction solution side. By distilling the diluted induction solution thus obtained, water and tert-butanol can be efficiently separated, and purified water can be efficiently produced at low cost. In addition, tert-butanol has a molecular weight of 74, which is larger than 17 of NH ₃ , and therefore, the permeation rate of the FO membrane is small and the leakage to the concentrated water is small. Does not pollute the environment.

It is the figure which showed one embodiment of this invention typically. It is the figure which showed the other embodiment of this invention typically. It is the graph which showed the relationship between the molecular weight of an inducer, and the reverse flow rate which passes through the FO membrane. It is the figure which showed typically the method of desalting by the conventional forward osmosis method.

  The treated water to be treated by the method of the present invention is water containing salt, such as seawater and waste water. The drainage water includes shale gas, oil sand, CBM (coal bed methane), accompanying water from a well for mining oil and the like.

Accompanying water is water that is discharged along with the object to be mined from the well, and includes salt, organic matter, suspended matter, and the like. Concentrations of pollutants include, for example, evaporation residues (mainly Na ⁺ , K ⁺ , Ca ²⁺ , Cl ⁻ , SO ₄ ^2−, etc.) of 1,000 to 100,000 mg / L, organic substances (such as oil and added chemicals) Is contained in a range of 10 to 1,000 mg / L as TOC and suspended material in a range of 100 to 10,000 mg / L.

  Although the accompanying water separation means is not limited, for example, oil-water separation is performed by sedimentation or the like.

When the accompanying water is treated water, the accompanying water is first filtered. This filtration treatment is performed with a filter using a microfiltration membrane, and a normal membrane used as a microfiltration membrane can be used as the filtration membrane. For example, in addition to cellulose acetate, polytetrafluoroethylene, polysulfone, polyvinyl chloride, etc., ceramic membranes and porous glass membranes can also be used. In the micromembrane filtration treatment, membrane filtrate water that has passed through the microfiltration membrane and membrane concentrated water remaining without passing through the membrane are obtained.
In addition to precision membrane filtration, filtration treatment such as ultramembrane filtration and sand filtration is used. The material of the ultrafiltration membrane is the same as that of the microfiltration membrane.

Forward osmosis process The forward osmosis process is a process in which water to be treated is brought into contact with an induction solution in which tert-butanol is dissolved in water through a semipermeable membrane, and water in the treated water is transferred to the induction solution through the semipermeable membrane. And a dilution induction solution diluted with water and membrane concentrated water.

  As the induction solution, a solution obtained by dissolving tert-butanol in water is used. Tert-butanol is used for disinfection and has high safety to the human body. It is also excellent in that it has a small influence on membrane materials such as polyacrylamide and polysulfone.

FIG. 3 shows the molecular weight of the induction solution and the mass flux of the induction solution that moves to the treated water side through the semipermeable membrane. The larger the molecular weight, the more difficult it is to permeate the semipermeable membrane. The permeation mass flux of tert-butanol having a molecular weight of 74 is as small as about 5% of NH ₃ having a molecular weight of 17.

  The concentration of tert-butanol contained in the induction solution is preferably as high as possible so that a high osmotic pressure can be obtained. For example, the volume of water to be treated with a salt concentration of 35,000 mg / L is ½ with the FO membrane device. In the case of concentrating in the solution, the tert-butanol concentration of the induction solution is preferably 2.6 to 10 mol / L, particularly preferably 4.5 to 10 mol / L. The lower the distillation temperature, the higher the tert-butanol concentration because the entrainment of water vapor is suppressed, but the upper limit is 10 mol / L from the ratio of the vapor pressure at 82 ° C., which is the boiling point of tert-butanol.

  The semipermeable membrane is preferably one that can selectively permeate water, and is preferably a forward osmosis membrane, but a reverse osmosis membrane can also be 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 membrane filtered water flows into one chamber partitioned by this semipermeable membrane, and the other chamber is filled with water. The induction solution can be flowed, and a known semipermeable membrane device can be used, and a commercially available product can be used.

  When the water to be treated is brought into contact with the induction solution through the semipermeable membrane in the forward osmosis step, the water in the water to be treated moves to the induction solution through the semipermeable membrane due to the difference in osmotic pressure.

  The temperature for forward osmosis is preferably about 5 to 40 ° C.

Distillation step In the distillation step, the dilution induction solution diluted by the movement of water in the permeation step is adjusted to a predetermined temperature, and then sent to the distillation column to obtain a gas composed of tert-butanol and water vapor from the top of the column. This is a process for obtaining purified water from the bottom of the tower.

In the present invention, tert-butanol is used as the inducer in place of conventional ammonia, but the latent heat of vaporization is NH ₃ : 1,300 J / g, tert-butanol: 500 J / g. Much smaller.

In addition, in the case of ammonium carbonate, the concentration of ammonium carbonate in the evaporation gas could not be 4.5 mol / L or more in order to prevent precipitation, but in the case of butanol there is no such restriction, so that the concentration can be increased to 10 mol / L. It is. Heating energy can be reduced because entrained water vapor during evaporation is reduced. When viewed as a system, the heating energy can be greatly reduced to NH ₃ : 450 MJ / m ³ and butanol: 250 MJ / m ³ . This is a trial calculation in the application of the accompanying water treatment.

  The dilution induction solution is distilled in a distillation column to separate tert-butanol from water.

  By distillation, a gas composed of tert-butanol and water vapor is obtained from the top of the distillation tower, and purified water is obtained from the bottom of the tower. The purified water taken out from the bottom of the tower has a tert-butanol content of about 10 ppm or less, and water with a content of 1 ppm or less can be obtained depending on the distillation conditions.

  The mixed gas of tert-butanol and water vapor generated by distillation can be used as a heating source by exchanging heat with the water to be treated or the dilution induction solution fed into the distillation column.

Cooling regeneration step The cooling regeneration step is a step of regenerating the induction solution by cooling a gas composed of tert-butanol and water vapor taken from the top of the distillation column.
The regenerated induction solution is sent to the semipermeable membrane for circulation.

Membrane concentrated water evaporation step The membrane concentrated water evaporation step is a step of evaporating and concentrating the membrane concentrated water to precipitate salts contained in the evaporated concentrated water, and a known evaporator can be used for concentration. The steam generated here can be used as condensed water. By the way, in the forward osmosis process, butanol slightly reversely flows from the semipermeable membrane to the concentrated accompanying water. This can prevent leakage to the environment by introducing the water vapor generated here into the distillation column of butanol. The evaporated liquid crystallizes out. For the crystallizer, a sealed normal crystallizer can be used. The slurry taken out from the crystallizer is separated into solid and liquid, and the mother liquor containing crystals and organic substances is disposed of as industrial waste or used as a snow melting agent when it contains almost no environmental contaminants such as heavy metals and organic substances. It can also be used.

  In the above water treatment method, the water to be treated and an induction solution obtained by dissolving a predetermined amount of tert-butanol in water are brought into contact with each other through a semipermeable membrane, and the water in the water to be treated is guided through the semipermeable membrane. A forward osmosis means for obtaining a diluted induction solution diluted with water and membrane concentrated water; a distillation column for distilling the diluted induction solution to obtain tert-butanol vapor and purified water; and the tert-butanol vapor. This is carried out using a water treatment device having a cooling and regenerating means for regenerating the induction solution by cooling and condensing, and an evaporator for evaporating the membrane concentrated water.

Forward osmosis means The forward osmosis means is a means for bringing the water to be treated and the induction solution into contact with each other through the semipermeable membrane and moving the water in the water to be treated to the induction solution through the semipermeable membrane. Use.

  The semipermeable membrane used in the semipermeable membrane device is as described above. A device for mounting this semipermeable membrane is usually a semi-permeable membrane installed in a cylindrical or box-shaped container, and water to be treated flows into one chamber partitioned by this semipermeable membrane, and the other chamber is filled with water. The induction solution can be flowed, and a known semipermeable membrane device can be used, and a commercially available product can be used.

  The entrance of the chamber through which the water to be treated flows is connected to a water tank to be treated (this may be the sea or the well itself). The outlet side is usually connected to a membrane concentrated water tank by piping. A circulation line connecting both the pipes can be provided to circulate the water to be treated.

  The inlet of the chamber through which the induction solution flows is piped to the cooling regeneration means, and the outlet is piped to the distillation column, thereby forming a circulation line for the induction solution.

Distillation Tower A known distillation column may be used, and any of a shelf system, a packing system, and the like 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, a heat exchanger, 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.

Cooling regeneration means Pipe connection is made from the top of the distillation tower to the tower top gas cooling regeneration means, and the gas comprising tert-butanol and water vapor obtained from the tower top 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.

Evaporating means The evaporating means is means for heating and evaporating the membrane concentrated water obtained by the forward osmosis means, and a normal evaporator or evaporator can be used.

  The apparatus shown in FIG. 1 was used.

The well-accompanying water was used as the water to be treated, and the accompanying water at 30 ° C. was introduced at a flow rate of 2.5 L / min into a semipermeable membrane device equipped with a 67 m ² polyamide composite flat membrane FO membrane. A 50 v / v% aqueous tert-butanol solution at 30 ° C. was introduced as an induction solution into the chamber on the opposite side of the semipermeable membrane device at a flow rate of 0.5 L / min. In the apparatus, the accompanying water dilutes the induction solution through the FO membrane, and the diluted induction solution having a tert-butanol concentration of 10 v / v% flows out of the semipermeable membrane apparatus at a flow rate of 2.5 L / min. .

  The dilution induction solution was sent to a distillation tower and distilled at 82 ° C. and atmospheric pressure. The distillation tower was fed with water vapor containing 0.6 v / v% of tert-butanol obtained by evaporating the accompanying water with an evaporator as an aqueous solution. Vapor containing tert-butanol as an aqueous solution at 50 v / v% was discharged from the top of the distillation column, and this was cooled and condensed to 30 ° C. by a coagulator and returned to the semipermeable membrane device. Nearly all of tert-butanol was circulated.

  Purified water flowed out from the bottom of the distillation column at a flow rate of 2.0 L / min. The tert-butanol concentration in this water was 1 mg / L.

  On the other hand, the concentrated accompanying water further concentrated by the evaporator was put into a crystallization can (not shown), cooled and crystallized, and the deposited salt crystals were separated.

FIG. 2 shows an apparatus flow when the vapor generated in the evaporator is condensed and then supplied to the distillation tower together with the dilution induction solution.
In this flow, the diluted induction solution having a tert-butanol concentration of 13 v / v% is combined with condensed water and sent to the distillation column.
Vapor tert-butanol from the top of the column rises to 70 v / v% due to the difference in the vapor pressure of butanol and water, which is a feature of distillation. That is, when compared at the same temperature, butanol having a high vapor pressure is gasified and rises upward. On the other hand, water with low vapor pressure falls down and is separated in the tower. Therefore, the concentration of butanol in the vapor from the top of the tower is increasing.

  As a result, it is possible to efficiently produce purified water from well-associated water at low cost, and even a slight induction solution that leaks from the semipermeable membrane to the concentrated water can be evaporated with water evaporated by the evaporator or its condensation. It was possible to recover the water by distilling again in the distillation column.

  The method of the present invention can be widely used for production of fresh water from seawater, treatment of associated water from a well, and the like.

Claims (6)

  The water to be treated is brought into contact with the induction solution in which a predetermined amount of tert-butanol is dissolved in water through a semipermeable membrane, and the water in the water to be treated is transferred to the induction solution through the semipermeable membrane, A forward osmosis step for obtaining a diluted dilution induction solution and membrane concentrated water, a distillation step for feeding the dilution induction solution to a distillation column to obtain tert-butanol vapor and obtaining purified water, and cooling and condensing the vapor. A water treatment method comprising: a cooling regeneration step for regenerating the induction solution.   The water treatment method according to claim 1, wherein the membrane concentrated water is heated and evaporated to recover salts in the water to be treated, and the generated steam or condensed water thereof is supplied to the distillation tower.   The water according to claim 1 or 2, wherein the temperature of the dilution induction solution fed to the water to be treated and / or the distillation column is adjusted by heat exchange with the tert-butanol vapor. Processing method.   The water to be treated is brought into contact with the induction solution in which a predetermined amount of tert-butanol is dissolved in water through a semipermeable membrane, and the water in the water to be treated is transferred to the induction solution through the semipermeable membrane, Forward osmosis means for obtaining a diluted dilution induction solution and membrane concentrated water, a distillation column for distilling the dilution induction solution to obtain tert-butanol vapor and purified water, and cooling and condensing the tert-butanol vapor. A water treatment device having cooling and regeneration means for regenerating the induction solution.   5. The apparatus according to claim 4, further comprising: an evaporation unit that heats and evaporates the membrane concentrated water obtained by the forward osmosis unit; and a unit that supplies the vapor generated by the evaporation unit or condensed water thereof to the distillation column. The water treatment apparatus as described.   6. The water treatment apparatus according to claim 4, further comprising a heat exchange means for the water to be treated and / or the dilution induction solution and the tert-butanol vapor.

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