JP6414528B2 - Water desalination method and apparatus - Google Patents

Description

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

  Various methods for desalinating seawater using a semipermeable membrane are known, but the reverse osmosis method that forcibly permeates water through a semipermeable membrane by applying a pressure higher than the osmotic pressure to seawater has been mainly developed. It was. 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. A method using a combination of ammonia and carbon dioxide as the volatile gas has already been developed (Patent Document 1).

  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. The resulting diluted salt solution is sent to a distillation tower to obtain fresh water, and a mixed gas containing ammonia, carbon dioxide and water is separated, the mixed gas is cooled and regenerated into a salt solution, and then a semipermeable membrane. It is a method of returning to the original room.

  As shown in FIG. 3, the apparatus used in this method includes a seawater supply pump 22, a forward osmosis (FO) membrane module 24, a pump 28, an attraction solution separation means 32, a fresh water separation means 36, a compressor 42, an attraction solution regeneration means. 44. Seawater supplied by the seawater supply pump 22 enters the FO membrane module 24 and makes countercurrent contact with the attracting solution through the FO membrane. In the meantime, due to osmotic pressure, water in the seawater passes through the FO membrane and moves to the attracting solution, and the concentrated seawater concentrated thereby exits the FO membrane module 24 from the flow path 26. On the other hand, the diluted attraction solution diluted by the movement of water from the seawater leaves the FO membrane module 24 and enters the attraction solution separating means 32. In the attracting solution separating means 32, the attracting solution is heated to decompose ammonium carbonate into ammonia and carbon dioxide, and the generated ammonia and carbon dioxide are compressed by the compressor 42 through the gas flow path 40 and attracted solution regenerating means 44. to go into. On the other hand, the water remaining after the ammonia and carbon dioxide are decomposed by the attracting solution separating means 32 is sent to the fresh water separating means 36 through the flow path 34, and part of the water passes through the flow path 46 and is attracted solution regenerating means 44. It is used as the moisture of the attracting solution regenerated in The remaining water is taken out from the flow path 38 as fresh water. The attraction solution regenerated by the attraction solution regeneration means 44 is returned to the FO membrane module 24 through the flow path 30 by the pump 28.

  On the other hand, what uses the sensitive substance which has the lower critical temperature which is a temperature sensitive chemical | medical agent for this attraction solution is also known (patent document 2). This temperature sensitive substance is a compound of alcohol or fatty acid and ethylene oxide.

  Furthermore, a method has been developed in which an inorganic salt such as magnesium sulfate is used as an osmotic pressure agent for increasing the osmotic pressure in the attracting solution, and a temperature sensitive agent such as a copolymer of polyethylene oxide and polypropylene oxide is combined with this. (Patent Document 3). As shown in FIG. 4, the apparatus used in this method includes a forward osmosis membrane unit 230, a first separation tank 250, a heat exchanger 256, a second separation tank 253, and a purification apparatus 261. The seawater 210 enters the forward osmosis membrane unit 230 and makes countercurrent contact with the osmotic agent solution 240 via the FO membrane 212. In the meantime, due to osmotic pressure, the moisture 211 in the seawater passes through the FO membrane and moves into the osmotic agent solution, and the concentrated seawater 220 concentrated thereby exits from the forward osmosis membrane unit 230. On the other hand, the diluted osmotic pressure agent solution 245 diluted by the movement of water from the seawater exits the forward osmosis membrane unit 230 and is mixed with the temperature sensitive drug solution 260 returned from the second separation tank 253 and the like, and diluted osmotic solution. The water in the pressure agent 245 moves to the temperature sensitive drug solution 260. This mixed liquid 246 is sent to the first separation tank 250. The first separation tank 250 is divided into a phase of the osmotic agent solution 240 and a phase of the temperature sensitive drug solution 252 by gravity sedimentation, and the osmotic agent solution 240 is returned to the forward osmosis membrane unit 230. On the other hand, the dilution temperature sensitive drug solution 252 is sent to the heat exchanger 256, heated above the cloud point of the temperature sensitive drug, and sent to the second separation tank 253. The second separation tank 253 is separated into a phase of crude fresh water 257 and a phase of a temperature-sensitive drug aggregation liquid 255 by gravity sedimentation, and the crude fresh water 257 is processed by a purification device 261 equipped with a reverse osmosis membrane 262 to become fresh water 258. . On the other hand, the temperature-sensitive drug concentrated liquid 259 separated by the purification device 261 is merged with the temperature-sensitive drug aggregation liquid 255 separated by the second separation tank 253, cooled, and regenerated into the temperature-sensitive drug solution 260. Then, the diluted osmotic pressure agent solution 245 flowing out from the forward osmosis membrane unit 230 is returned to the first separation tank 250.

US Patent No. 8,021,549B2 JP 2014-1000069 A2 US Pat. No. 8,852,436B2

  However, the performance of such an apparatus (water membrane permeation rate: filtration rate) varies depending on the water to be treated supplied to the FO membrane module, the concentration of the attracting solution, the flow rate, and the state of the membrane (clogging, etc.). Unless the operating conditions are adjusted optimally, a desired amount of fresh water cannot be obtained.

  For example, when the salt concentration of treated water increases due to water quality fluctuations, the average osmotic pressure on the treated water side increases in the FO membrane module, and the permeation serving as the driving force for membrane filtration when the amount of attracted solution supplied is constant. The pressure difference decreases, and the water membrane permeation rate (filtration rate) decreases. In such a case, the amount of fresh water is less than the set value.

  An object of the present invention is to solve such a problem, and an attracting solution according to changes in the water to be treated supplied to the FO membrane module, the concentration, flow rate, and membrane state (clogging, etc.) of the attracting solution. It is intended to provide a means for optimally adjusting the flow rate.

  As a result of intensive studies to solve the above problems, the present inventor has considered as follows.

  When the amount of the attracting solution (DS) supplied to the forward osmosis (FO) membrane is increased by increasing the inflow rate, the membrane permeation rate immediately increases due to the effect of suppressing the DS dilution by the membrane permeated water. However, since the DS flow rate circulating in the system increases in this case, the sedimentation tank residence time for phase-separating the diluted DS diluted with FO membrane permeated water is reduced, and the temperature sensitive agent used as the osmotic agent is a cloud point. A phenomenon such as an increase in pressure loss of the heat exchanger that heats occurs as described above, causing problems such as a decrease in separation efficiency and an increase in pump power. Therefore, the control based on the DS inflow rate is controlled within a small deviation, for example, 10%, of the influence of the residence time and pressure loss on the performance and cost, and the DS separation temperature is changed when exceeding the deviation. When the separation temperature is increased, the DS concentration flowing into the FO membrane is increased, so that the membrane permeation rate is increased as in the case where the DS inflow amount is increased. However, this effect causes a time delay until the DS temperature in the sedimentation basin reaches the control value after the change in control of the separation temperature and the DS concentration after separation reaches a steady value.

  Therefore, the amount of water produced is detected by the difference in the DS flow rate before and after the membrane, and the amount of DS inflow is increased when the amount of fresh water is lowered, and is decreased when the amount of fresh water is raised. For example, when the deviation from the set value of the DS inflow amount is within 10%, the above operation is performed. When the deviation exceeds 10%, a method and apparatus for changing the DS separation temperature together with the DS inflow amount have been devised.

The present invention has been made based on such knowledge,
A treated water containing salts and an attracting solution having an osmotic agent dissolved in water and having a higher osmotic pressure than the treated water are brought into contact with each other through a semipermeable membrane, and the water in the treated water is brought into contact with the semipermeable material. Forward osmosis step of transferring to the attraction solution through a membrane to obtain a diluted attraction solution diluted with water and membrane concentrated water;
A phase separation step of phase-separating the diluted attraction solution into a concentrated solution phase mainly composed of an osmotic agent and a dilute solution phase containing a small amount of an osmotic agent;
Circulating the concentrated solution separated in the phase separation step to the forward osmosis step and reusing it as an attracting solution;
A method for desalinating water having a fresh water recovery step for obtaining fresh water from the dilute solution separated in the phase separation step,
When the flow rate of each of the diluted attractant solution and the attractant solution is measured and the flow rate difference between them is lower than a preset value, the flow rate of the attractant solution is increased, and the flow rate difference is preset. If higher than the set value, the water desalting method characterized by reducing the flow rate of the attracting solution;
The osmotic agent is a temperature sensitive agent having a lower critical temperature, and the phase separation step has a heating step of heating the dilution attraction solution to a temperature above the cloud point of the attraction solution; and When the flow rate difference between the diluted attracting solution and the attracting solution is lower than a preset value, the flow rate of the attracting solution is increased and the heating temperature in the warming step is increased. When the flow rate difference is higher than a preset set value, the flow rate of the attracting solution is decreased, and the heating temperature in the heating step is decreased. When,
The osmotic agent is an inorganic salt, and has a temperature sensitive drug mixing step in which a temperature sensitive drug having a lower critical temperature is mixed with the dilution attraction solution before the phase separation step, and is separated in the phase separation step. A fresh water recovery step for obtaining fresh water from the diluted solution is a heating step for heating the diluted solution to a temperature equal to or higher than the cloud point of the attracting solution, and a temperature mainly comprising a temperature-sensitive drug following the heating step. Having a second phase separation step of phase separation into a sensitive drug solution phase and a fresh water phase mainly containing fresh water and containing a small amount of temperature sensitive drug;
And when the flow rate difference between the diluted attracting solution and the attracting solution is lower than a preset value, the flow rate of the attracting solution is increased and the heating temperature in the warming step is increased. When the flow rate difference is higher than a preset value, the water desalting is characterized in that the flow rate of the attracting solution is decreased and the heating temperature in the heating step is decreased. Processing method,
An apparatus according to these methods is provided.

  According to the present invention, the concentration of the water to be treated and the attracting solution supplied to the FO membrane module, the flow rate, the flow rate of the attracting solution, and the heating temperature in the phase separation step are adjusted according to the state of the membrane. A stable operation of the salt treatment apparatus can be performed.

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

  The water desalination method of the present invention comprises a forward osmosis step, a phase separation step, a circulation step, and a fresh water recovery step.

Forward osmosis step In the forward osmosis step, the water to be treated containing salts is brought into contact with an attracting solution having an osmotic agent dissolved in water and having a higher osmotic pressure than the water to be treated through a semipermeable membrane. Water in the treated water is transferred to the attraction solution through the semipermeable membrane to obtain a diluted attraction solution and membrane concentrated water diluted with water.

  The water to be treated may be water containing salts, but for example, seawater, lake water, river water, factory wastewater, and the like.

  The attracting solution is obtained by dissolving an osmotic agent in water, and a temperature-sensitive drug and an inorganic salt can be used as the osmotic agent.

  A temperature-sensitive drug is hydrophilic and well soluble in water at low temperatures. be called. When this temperature is reached, a hydrophobized temperature-sensitive drug is precipitated, resulting in white turbidity or phase separation. When gradually warming, there are those that become cloudy by the drug but not phase-separated, those that become cloudy and then further heated and phase-separated, and those that phase-separate without passing through the cloudy state, the drug used in the present invention Means that the phases are separated, and the lower critical temperature here means the temperature at which the phases are separated.

  This temperature-sensitive agent is used as various surfactants, dispersants, emulsifiers, and the like. For example, alcohols, alkyl groups, glycols, or fatty acid and ethylene glycol compounds (water-soluble polyalkylene glycol derivatives, Polyoxyethylene polyoxypropylene alkyl ether, polyoxytetramethylene polyoxyethylene glycol, polyoxyethylene polyoxypropylene trimethylolpropane, polyoxyethylene polyoxypropylene glyceryl ether, polyoxyethylene polyoxypropylene pentaerythritol ether, etc.) alkyl group Or fatty acid and propylene oxide compound, acrylamide and alkyl group compound, ethylene glycol fatty acid ester, glycerin fatty acid ester, sorbi Fatty acid ester ethylene oxide adduct, amino acids and derivatives thereof, glycols such as butyl glycol and hexyl glycol, preferably a block or random copolymer of polyethylene glycol and polypropylene / polybutylene glycol, glycerol ethoxylate butoxylate, And trimethylolpropane ethoxybutoxylate. As the temperature-sensitive drug 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. Therefore, a method is adopted in which the lower critical temperature is adjusted to the above range by combining a nonionic surfactant having an HLB value of 10 or more and a nonionic surfactant having a lower HLB value, a fatty acid or an alcohol. You can also.

  The concentration of the temperature-sensitive drug must be adjusted so that the osmotic pressure of the attracting solution is sufficiently higher than the osmotic pressure of the water to be treated.

  The inorganic salt only needs to have a solubility capable of making the osmotic pressure higher than that of the water to be treated. Sodium carbonate, sodium silicate, sodium sulfate, sodium phosphate, lithium sulfate, ammonium sulfate, ammonium carbonate, ammonium carbamate, zinc sulfate, copper sulfate, Various materials such as iron sulfate, magnesium sulfate, aluminum sulfate, disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium carbonate, and manganese sulfate can be used. Preferred are magnesium sulfate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. The concentration of the inorganic salt must also be adjusted so that the osmotic pressure of the attracting solution is sufficiently higher than the osmotic pressure of the water to be treated.

  When an inorganic salt is used as the osmotic pressure agent, a means for separating water from the dilution attraction solution is necessary, and a temperature sensitive drug is preferably used as the means. Since this results in two stages of phase separation, this is called a double loop method.

  The semipermeable membrane used in the forward osmosis membrane treatment apparatus that performs the forward osmosis step 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 water to be treated flows into one chamber partitioned by this semipermeable membrane, and the other chamber is filled with water. An attracting solution can be flowed, and a known semipermeable membrane device can be used, and a commercially available product can also be used.

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

  The inlet of the chamber through which the attracting solution flows is connected to the fresh water separator's attracting solution regeneration side, and the outlet is connected to the fresh water separator's inlet, thereby forming a circulation line of the attracting solution.

  A chamber where treated water flows into the attracting solution through the semipermeable membrane due to the difference in osmotic pressure when the treated water is brought into contact with the attracting solution through the semipermeable membrane in the forward osmosis process. From the membrane concentrate and from the chamber into which the attraction solution flows, the dilute attraction solution flows out.

  The diluted attraction solution that flows out is phase-separated into a concentrated solution phase mainly composed of an osmotic agent and a dilute solution phase containing a small amount of osmotic agent in a phase separation step. Hereinafter, the case where a temperature-sensitive drug is used as the osmotic agent and the case where an inorganic salt is used will be described separately.

A. When a temperature-sensitive drug is used as an osmotic pressure agent Heating process In the forward osmosis process, water is transferred from the water to be treated, and the dilution-induced solution diluted with the temperature-sensitive drug is heated to a temperature above the lower critical temperature. Agglomerate at least a portion of the temperature sensitive drug. This aggregation is a phase separation of a concentrated solution of the temperature sensitive drug.

  The heating means in the heating step is not limited, but a heating tank equipped with a heater or a heat exchanger can be used.

  The heating temperature in the heating step can be controlled, for example, by adjusting the flow rate of the heat medium introduced into the heat exchanger.

  It is preferable to use the sensible heat of the concentrated solution separated in the next phase separation step as the heat source for this heating step.

Phase separation step The solution is separated by gravity sedimentation into a concentrated solution phase mainly composed of a temperature-sensitive drug separated in the heating step and a dilute solution phase mainly composed of water and containing a small amount of the temperature-sensitive drug. This gravitational separation can be performed by standing in a phase separation tank at a liquid temperature equal to or higher than the lower critical temperature.

  When the heated dilution-inducing solution is put into the phase separation tank, if the specific gravity of the temperature sensitive drug is heavier than water, the fine droplets of the concentrated solution will settle quickly and the droplets will coalesce. A concentrated solution phase is formed. On the other hand, when the specific gravity of the temperature sensitive drug is lighter than water, for example, when butyl glycol or hexyl glycol is used as the temperature sensitive drug, the concentrated solution phase becomes the upper phase and the diluted solution phase becomes the lower phase.

Circulation step The circulation step is a step in which the concentrated solution separated in the phase separation step is circulated to the forward osmosis step and reused as an attraction solution. A pump and piping are used for this circulation means. The concentrated solution separated in the phase separation step is first cooled to a temperature lower than the lower critical temperature of the attracting solution to be dissolved in water and regenerated into the attracting solution. Although this temperature can be employed in a wide range, considering the economy, a temperature of room temperature or higher is preferable. As this cooling heat source, it is preferable from the viewpoint of efficient use of energy to use the water to be treated or the dilution attraction solution obtained in the forward osmosis step. If this cooling is insufficient, the concentration is lowered by the water moving from the water to be treated in the forward osmosis process, so that the lower critical temperature is developed and phase separation occurs, and the osmotic pressure is lost.

  The regenerated attractant solution is directly recycled to the forward osmosis process.

Fresh Water Recovery Step On the other hand, the dilute solution separated in the phase separation step is subjected to membrane filtration with a nanofiltration membrane or a reverse osmosis membrane to remove the temperature sensitive drug remaining there. Membrane filtrate is fresh water and can be used for drinking water and the like. Since the membrane-concentrated water remaining without being membrane-filtered contains a temperature-sensitive drug, it should be circulated in the phase separation step. Alternatively, it can be concentrated and returned directly to the forward osmosis process as an attractant solution.

  On the other hand, since the membrane concentrated water obtained in the forward osmosis process contains a high concentration of salt, it can be concentrated by precipitating the salt and separating it for effective use.

B. When an inorganic salt is used as the osmotic agent On the other hand, when an inorganic salt is used as the osmotic agent, phase separation does not occur even when the dilution attraction solution is heated. A temperature sensitive drug mixing step is provided for mixing a temperature sensitive drug having a lower critical temperature.

Temperature-sensitive drug mixing step The temperature-sensitive drug may be selected from those described above. In the mixing step, it is necessary for the temperature-sensitive drug to absorb fresh water from the dilution attraction solution and concentrate the dilution attraction solution. Therefore, it is necessary to set the concentration and amount of the temperature sensitive drug so that the osmotic pressure of the temperature sensitive drug after water absorption exceeds the osmotic pressure of the concentrated attractant solution.
As the temperature-sensitive drug mixed in this step, the temperature-sensitive drug solution separated in the second phase separation step in the fresh water recovery step when an inorganic salt is used as the osmotic agent is usually circulated.

Phase Separation Step A liquid in which a temperature-sensitive drug is mixed with a dilution attraction solution is separated into a concentrated solution phase mainly composed of an inorganic salt and a dilute solution phase mainly composed of a temperature-sensitive drug by gravity sedimentation. In general, a temperature-sensitive drug has a cloud point lowering in the presence of salt, and therefore, in this phase separation step, the temperature-sensitive drug aggregates without heating. However, depending on the combination of the inorganic salt and the temperature sensitive agent, a clear phase separation may not be performed at room temperature. When magnesium sulfate, sodium dihydrogen phosphate, or disodium hydrogen phosphate is used as the inorganic salt, the layers are separated at room temperature in many cases. In other cases, heating is required for layer separation. There is also. Since this temperature varies depending on the type and concentration of the temperature-sensitive agent of the inorganic salt, it must be determined experimentally separately.
This gravitational separation can be performed by standing in a phase separation tank.

Fresh water recovery process When an inorganic salt is used for the osmotic pressure agent, the diluted solution separated in the phase separation process is a liquid mainly composed of a temperature sensitive drug. The phases are separated and the phases are separated in the second phase separation step.

Heating process The dilute solution mainly composed of a temperature-sensitive drug separated in the phase separation process is heated to a temperature equal to or higher than the lower critical temperature of the temperature-sensitive drug to agglomerate at least a part of the temperature-sensitive drug. . The heating temperature is controlled, for example, by adjusting the flow rate of the heat medium introduced into the heat exchanger.

Second phase separation step A temperature-sensitive drug solution phase mainly composed of the temperature-sensitive drug phase-separated in the heating step and a fresh water phase mainly composed of water and containing a small amount of the temperature-sensitive drug are separated by gravity sedimentation. This gravity separation can be left in the phase separation tank at a liquid temperature equal to or higher than the lower critical temperature.

  The fresh water containing a small amount of the temperature-sensitive drug separated in the second phase separation step is subjected to membrane filtration with a nanofiltration membrane or a reverse osmosis membrane to remove the temperature-sensitive drug remaining there. Membrane filtrate is fresh water and can be used for drinking water and the like. Since the membrane-concentrated water remaining without being membrane-filtered contains a temperature-sensitive drug, it is preferable to circulate it in the second phase separation step.

Circulation step The circulation step is a step in which the concentrated solution separated in the phase separation step is circulated to the forward osmosis step and reused as an attraction solution. A pump and piping are used for this circulation means.

C. The present invention relates to a method for controlling the flow rate of the attracting solution and the heating temperature. In such a method for desalinating water, the flow rate of each of the diluted attracting solution and the attracting solution is measured and the difference between the flow rates is set in advance When it is lower than the value, the flow rate of the attracting solution is increased, and when the flow rate difference is higher than a preset value, the flow rate of the attracting solution is decreased.

  And when the phase separation step or the second phase separation step has a heating step of heating the dilution attraction solution to a temperature above the cloud point of the dilution attraction solution, the dilution attraction solution and the When the flow rate difference of the attracting solution is lower than a preset set value, the flow rate of the attracting solution is increased and the heating temperature in the heating step is increased, and the flow rate difference is preset. When the temperature is higher than the set value, the flow rate of the attracting solution is decreased and the heating temperature in the heating step is decreased.

  In the forward osmosis step, the attraction solution is diluted by the water in the for-treatment water moving while in contact with the for-treatment water through the semipermeable membrane. The dilution attraction solution leaving the semipermeable membrane is increased by the amount of water transferred during that time. And the difference of the flow volume of the dilution attraction solution per unit time and the flow volume of the attraction solution becomes this moving water amount. Therefore, when the flow rate difference is lower than the set value, the amount of fresh water is lower than the set value, so that the flow rate of the attracting solution is increased, and when it is higher, the flow rate of the attracting solution is decreased. However, if the flow rate of the attracting solution is increased too much, problems such as a decrease in separation efficiency due to a decrease in residence time in the phase separation tank, an increase in pump power, and an increase in heat exchanger pressure loss in the heating process occur. Therefore, when the flow rate difference exceeds a certain value, in addition to the increase in the flow rate of the attracting solution, the concentration of the attracting solution flowing into the semipermeable membrane is increased by increasing the heating temperature in the heating step.

  The flow rate difference between the dilute attracting solution and the attracting solution should be consistent with the amount of water produced in principle. However, if the amount of water decreases in a subsequent process such as membrane filtration, it is set in consideration of it.

  When the flow rate difference is lower than the set value, the flow rate of the attracting solution is increased. When the flow rate difference is high, the flow rate of the attracting solution is decreased. However, the amount of increase or decrease differs depending on each desalting treatment device. In short, what is necessary is to control the flow rate difference to return to the set value.

  And when the flow rate difference is far from the set value, in addition to controlling the flow rate of the attracting solution, the heating temperature is also controlled in the heating process, but when the combined use of this heating temperature control is started, It depends on the design tolerance of the phase separation tank, liquid feed pump, heat exchanger, etc. In general, the flow control of the attracting solution is preferably controlled so that the deviation from the set value of the flow rate difference is about 5 to 30%, usually about 10 to 20%. The upper limit of the change in the flow rate of the attracting solution is 1.05 to 1.3 times, and the deviation of the flow rate difference from the set value is returned to the range of 5%, preferably to the set value. If control does not return to the set value only by controlling the flow rate of the attracting solution, control of the heating temperature is started. It is preferable that the upper limit of the change in the heating temperature is increased by about 2 to 10 ° C.

  Table 1 shows an example of the control operation when the separation degree is 10%.

Embodiment 1 of the present invention

Embodiment 1 of the present invention is shown in FIG. As shown in the figure, this apparatus includes a forward osmosis membrane treatment apparatus 10, a heat exchanger 7, a heater 12, a phase separation tank 11 and a cooler 13.

  The treated water 1 enters the left chamber of the forward osmosis membrane treatment apparatus 10 from below, the water in the treated water moves to the right chamber through the semipermeable membrane 3, and the concentrated membrane concentrated water 3 is formed. It is discharged from the upper part of the left chamber. The attraction solution 4 enters the right chamber of the forward osmosis membrane treatment apparatus 10 from the upper part, contacts the water to be treated 1 through the semipermeable membrane 3, and the diluted attraction solution 5 is discharged from the lower part of the right chamber. The The dilution attraction solution 5 is measured for flow rate by the dilution attraction solution flow meter 9, heated by the heat exchanger 7, further heated to the cloud point of the temperature sensitive drug by the heater 12, and phase separation tank Enter 11. In the phase separation tank 11, the phase is separated into a concentrated solution phase mainly composed of a temperature-sensitive drug and a dilute solution phase containing a small amount of the temperature-sensitive drug, and the diluted solution 6 is taken out from the upper part, and the remaining temperature-sensitive drug. Is removed to obtain fresh water. On the other hand, the concentrated solution is taken out from the lower part, cooled by the heat exchanger 7, further cooled by the cooler 13, and the flow rate is measured by the attracting solution flow meter 8 as the attracting solution 4. Will be returned.

1. Experimental apparatus The experimental apparatus of FIG. 1 was used.

Water to be treated (FS): NaCl aqueous solution Attracting solution (DS): Temperature sensitive agent (random copolymer of polyethylene glycol and polypropylene) Aqueous forward osmosis (FO) membrane: CTA, membrane area 60 m ² , designed water production 2 .5m ³ / day
Heater: plate type heat exchanger (heat exchange area 7.2 m ² ), heat medium: 100 ° C. silicone oil Cooler: plate type heat exchanger (heat exchange area 4.0 m ² ), heat medium: 5 ° C. cold water phase Separation tank: Cross-flow type precipitation tank (volume 40L)
2. Operating conditions and results (1) RUN1 (normal operation)

表２に通常運転時の運転条件と運転結果を示す。
FS濃度は一般的な海水塩濃度を模擬した。希釈DS分離温度は、工場の冷却器排気等の低温廃熱利用を想定して80℃に設定した。DS濃度は分離温度によって一義的に決まる値であり、本実験に用いたDSの濃度80.2％は海水より充分高い浸透圧を有する。
FSとDSの流量は、予め予備実験を実施し、FSからの淡水の回収率が33％となるように設定した。

Table 2 shows the operation conditions and operation results during normal operation.
FS concentration simulated general sea salt concentration. The dilution DS separation temperature was set at 80 ° C, assuming low-temperature waste heat utilization such as factory cooler exhaust. The DS concentration is a value uniquely determined by the separation temperature, and the DS concentration of 80.2% used in this experiment has a sufficiently higher osmotic pressure than seawater.
Preliminary experiments were conducted in advance to set the flow rate of FS and DS so that the recovery rate of fresh water from FS was 33%.

As a normal amount of fresh water, 2.5 m ³ / day, which is a set value, is obtained. At this time, the diluted DS was heated to 80 ° C. and separated in a sedimentation tank with a residence time of 6.5 minutes, whereby a DS with a concentration of 80.2% was obtained. DS supply is about 2.5 times the amount of fresh water.
(2) RUN2 (high concentration FS1)

表３にＦＳ濃度を３．５ｗｔ％から３．７ｗｔ％に上昇させた場合の運転条件と運転結果を示す。
ＦＳ濃度を３．５ｗｔ％から３．７ｗｔ％に上昇させた場合、ＲＵＮ１と同一の運転条件では造水量が２．３ｍ^３／ｄａｙと８％ほど低下した。ＦＳの浸透圧が上昇したことが原因と考えられる。閉鎖性水域の渇水期などにこのような濃度変化の生じることが想定される。
（３）ＲＵＮ３（ＤＳ流量増加）

Table 3 shows operating conditions and results when the FS concentration is increased from 3.5 wt% to 3.7 wt%.
When the FS concentration was increased from 3.5 wt% to 3.7 wt%, the amount of fresh water was reduced to 2.3 m ³ / day and about 8% under the same operating conditions as RUN1. This is considered to be caused by an increase in the osmotic pressure of FS. It is assumed that such a concentration change occurs during a drought period in a closed water area.
(3) RUN3 (DS flow rate increase)

表４にＤＳ流量を６．３ｍ^３/ｄａｙから６．８ｍ^３／ｄａｙに増やした場合の運転条件と運転結果を示す。

Table 4 shows the operating conditions and operating results when increasing the DS rate from 6.3 m ³ / day to 6.8 m ³ / day.

It could be controlled to a value set as the desalination amount by 8% increase in the flow rate of 6.3 m ³ / day from 6.8 m ³ / day in DS flow. A similar measure can be taken even when a similar decrease in the amount of water produced occurs due to the temperature change of the FS. Since this operation can be obtained immediately by simply changing the pump settings, it is possible to immediately respond to temporary fluctuations in the amount of fresh water. Although the residence time of the precipitation tank decreased from 6.5 minutes to 6.2 minutes, the influence on the separation efficiency was slight, and the DS concentration after separation was 80.1 wt%.
(4) RUN4 (high concentration FS2)

表５にＦＳ濃度を３．９ｗｔ％に増やした場合の運転条件と運転結果を示す。

Table 5 shows operating conditions and operating results when the FS concentration is increased to 3.9 wt%.

As a result of increasing the FS concentration increase range further than RUN2, the amount of fresh water was greatly reduced by 20% of the set value. In such a case, if the DS supply amount is increased, the residence time in the settling tank is significantly reduced, and the separation performance may be lowered. In order to suppress the degradation of the separation performance, it is necessary to take a large margin in the sedimentation tank residence time, which leads to an increase in equipment costs.
(5) RUN5 (Dilution DS separation temperature rise)

表６に希釈ＤＳ分離温度を８０℃から８５℃に上昇させた場合の運転条件と運転結果を示す。

Table 6 shows operating conditions and results when the dilution DS separation temperature is increased from 80 ° C to 85 ° C.

By increasing the dilution DS separation temperature by 5 ° C., the DS concentration increased by 2 points. As a result, the DS flow rate for obtaining the designed water production amount was only slightly increased from the standard values of 6.5 m ³ / day and RUN1.

Embodiment 2 of the present invention

  A control operation when the apparatus of the double loop method shown in FIG. 2 is used will be described.

  In the forward osmosis membrane treatment apparatus 10, the water 1 to be treated is brought into countercurrent contact with the attraction solution 4 using magnesium sulfate as an osmotic pressure agent through the semipermeable membrane 3, thereby being concentrated to become membrane concentrated water 2. Discharged. On the other hand, the diluted attracting solution 5 diluted by the movement of water from the water 1 to be treated is put in the mixing tank 14 and mixed with the temperature sensitive chemical solution 17 circulating from the phase separation tank 11 to be an attracting solution regeneration tank. 15 is sent. The attraction solution 4 using magnesium sulfate separated in the attraction solution regeneration tank 15 as an osmotic pressure agent is returned to the forward osmosis membrane treatment apparatus 10 by a pump. On the other hand, the temperature sensitive drug solution 16 separated in the attracting solution regeneration tank 15 is heated by the 80 ° C. temperature sensitive drug solution 17 coming out of the phase separation tank 11 by the heat exchanger 7 and further heated by the heater 12 at 90 ° C. It is heated by the reduced pressure steam and put into the phase separation tank 11. The temperature sensitive drug solution 17 separated in the phase separation tank 11 is cooled by exchanging heat in the heat exchanger 7, further cooled to 32 ° C. in the cooler 13, put into the mixing tank 14 and circulated. On the other hand, the dilute solution 6 in the phase separation tank 11 is taken out as fresh water.

In such a process, when the amount of water produced decreases, the flow rate of the attraction solution (MgSO ₄ aqueous solution, 15 to 25%) 4 supplied to the forward osmosis membrane treatment apparatus 10 is first increased. Although this operation is effective immediately, the concentration of the attracted solution regenerated is reduced from a predetermined value due to a decrease in the mixing time of the temperature sensitive drug solution 17 and the diluted attracting solution 5 and the separation time in the attracting solution regeneration tank 15. Therefore, the flow rate of the temperature sensitive chemical solution 17 supplied to the attracting solution regeneration tank 15 is increased as the next means. In this case, the movement of fresh water from the dilution attraction solution 5 to the temperature sensitive drug solution 17 is promoted, but there is a limit because the reduction of the mixing time and separation time becomes significant. As a next means, the temperature of the phase separation tank 11 is raised to increase the concentration of the temperature sensitive drug solution 17. Thereby, the movement of the fresh water from the dilution attraction solution 5 to the temperature sensitive drug solution 17 can be promoted without affecting the mixing time and the separation time of the temperature sensitive drug solution 17 and the dilution attraction solution 5.

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

DESCRIPTION OF SYMBOLS 1 Water to be treated 2 Membrane concentrated water 3 Semipermeable membrane 4 Attraction solution 5 Dilution attraction solution 6 Dilute solution 7 Heat exchanger 8 Attraction solution flow meter 9 Dilution attraction solution flow meter 10 Forward osmosis membrane treatment device 11 Phase separation tank 12 Heater DESCRIPTION OF SYMBOLS 13 Cooler 14 Mixing tank 15 Attraction solution regeneration tank 16 Dilution temperature sensitive chemical solution 17 Temperature sensitive chemical solution

Claims (6)

A treated water containing salts and an attracting solution having an osmotic agent dissolved in water and having a higher osmotic pressure than the treated water are brought into contact with each other through a semipermeable membrane, and the water in the treated water is brought into contact with the semipermeable material. Forward osmosis step of transferring to the attraction solution through a membrane to obtain a diluted attraction solution diluted with water and membrane concentrated water;
A phase separation step of phase-separating the diluted attraction solution into a concentrated solution phase mainly composed of an osmotic agent and a dilute solution phase containing a small amount of an osmotic agent;
Circulating the concentrated solution separated in the phase separation step to the forward osmosis step and reusing it as an attracting solution;
A method for desalinating water having a fresh water recovery step for obtaining fresh water from the dilute solution separated in the phase separation step,
When the flow rate of each of the diluted attractant solution and the attractant solution is measured and the flow rate difference between them is lower than a preset value, the flow rate of the attractant solution is increased, and the flow rate difference is preset. If it is higher than the set value, the water desalting method is characterized in that the flow rate of the attracting solution is decreased. The osmotic agent is a temperature sensitive agent having a lower critical temperature, and the phase separation step has a heating step of heating the dilution attraction solution to a temperature above the cloud point of the attraction solution; and When the flow rate difference between the diluted attracting solution and the attracting solution is lower than a preset value, the flow rate of the attracting solution is increased and the heating temperature in the warming step is increased. 2. The water according to claim 1, wherein when the flow rate difference is higher than a preset value, the flow rate of the attracting solution is decreased and the heating temperature in the heating step is decreased. Desalination treatment method. The osmotic agent is an inorganic salt, and has a temperature sensitive drug mixing step in which a temperature sensitive drug having a lower critical temperature is mixed with the dilution attraction solution before the phase separation step, and is separated in the phase separation step. A fresh water recovery step for obtaining fresh water from the diluted solution is a heating step for heating the diluted solution to a temperature equal to or higher than the cloud point of the attracting solution, and a temperature mainly comprising a temperature-sensitive drug following the heating step. Having a second phase separation step of phase separation into a sensitive drug solution phase and a fresh water phase mainly containing fresh water and containing a small amount of temperature sensitive drug;
And when the flow rate difference between the diluted attracting solution and the attracting solution is lower than a preset value, the flow rate of the attracting solution is increased and the heating temperature in the warming step is increased. 2. The method according to claim 1, wherein when the flow rate difference is higher than a preset value, the flow rate of the attracting solution is decreased and the heating temperature in the heating step is decreased. Water desalination method. A treated water containing salts and an attracting solution having an osmotic agent dissolved in water and having a higher osmotic pressure than the treated water are brought into contact with each other through a semipermeable membrane, and the water in the treated water is brought into contact with the semipermeable material. A forward osmosis membrane treatment device that moves to the attraction solution through a membrane to obtain a diluted attraction solution diluted with water and membrane concentrated water;
A phase separation tank for phase-separating the diluted attraction solution into a concentrated solution phase mainly composed of an osmotic agent and a dilute solution phase containing a small amount of an osmotic agent;
A circulating means for circulating the concentrated solution separated in the phase separation tank to the forward osmosis membrane treatment apparatus and reusing it as an attraction solution;
A water desalination apparatus having a fresh water recovery device for obtaining fresh water from a dilute solution separated in the phase separation tank,
The flow rate measuring means for the diluted attracting solution, the flow rate measuring means for the attracting solution, the flow rate difference between the diluted attracting solution and the attracting solution measured by the flow rate measuring means, and the preset flow rate difference setting. An apparatus for desalinating water, comprising flow rate adjusting means for adjusting the flow rate of the attracting solution according to a difference from the value.   The osmotic agent is a temperature-sensitive agent having a lower critical temperature, and has a heating means for heating the dilution attraction solution to a temperature equal to or higher than the cloud point of the attraction solution at the front stage of the phase separation tank. The water desalination apparatus according to claim 4, further comprising a heating temperature adjusting unit that adjusts a heating temperature of the heating unit according to the difference. The osmotic agent is an inorganic salt, and has a temperature-sensitive drug mixing means for mixing a temperature-sensitive drug having a lower critical temperature to the dilution-attracting solution in the previous stage of the phase separation tank, and is separated in the phase separation tank. A fresh water recovery device for obtaining fresh water from the diluted solution, comprising a heating means for heating the diluted solution to a temperature equal to or higher than a cloud point of the attracting solution, and a temperature-sensitive drug in the subsequent stage of the heating means. Having a second phase separation tank for phase separation into a temperature sensitive drug solution phase and a fresh water phase mainly containing fresh water and containing a small amount of temperature sensitive drug;
5. The water desalination apparatus according to claim 4, further comprising a heating temperature adjusting means for adjusting a heating temperature by the heating means in accordance with the difference.

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