JP2003001253A - Apparatus for producing water and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing water, that can attain a higher recovery ratio when raw water is subjected to membrane treatment to obtain permeate and to provide an apparatus therefor. SOLUTION: The apparatus has a freezing means to freeze raw water, a thawing means to thaw frozen raw water, a membrane separation means with a reverse osmosis membrane and/or a nanofiltration membrane for treating thawed water and a pump for pressurizing thawed water and supplying it to the reverse osmosis membrane and/or nanofiltration membrane. Raw water is frozen and thawed using the equipment to selectively draw thawed water having a lower concentration of impurities than the raw water and the thawed water is treated the reverse osmosis membrane and/or nanofiltration membrane to obtain treated water having a lower concentration of impurities than the thawed water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a desalination apparatus and a desalination apparatus capable of realizing a high recovery rate in obtaining treated water having a lower impurity concentration than raw water by using a reverse osmosis membrane or a nanofiltration membrane. Regarding the water method.

[0002]

2. Description of the Related Art In recent years, a technique for obtaining fresh water such as industrial water or drinking water from seawater has been developed, and a membrane separation method using a reverse osmosis membrane has been attracting attention in place of the evaporation method which has been generally used conventionally. It is supposed to collect. Since this membrane separation method requires less energy for operation and can obtain high quality fresh water, it is expected to be used in various fields.

In carrying out this membrane separation method, the focus of the technology is how to produce water at low cost, so efforts are made to increase the rate of recovering fresh water from seawater (recovery rate). However, if the operation is performed at a high recovery rate of 60% or more, the concentration of solute components on the concentrated water side of the reverse osmosis membrane will increase, and scale components with low solubility in water will precipitate, resulting in reduced membrane life and permeated water quality. It caused problems such as doing.

Therefore, a method has been developed in which the seawater supplied to the reverse osmosis membrane is pretreated in advance to remove the scale component to some extent, thereby increasing the recovery rate. For example, Japanese Unexamined Patent Publication No. 8-206460 discloses a device in which reverse osmosis membranes are arranged in multiple stages and operation is performed at a high recovery rate.
However, in this device, in order to increase the overall recovery rate, the recovery rate in the pretreatment process must be increased, and in the end, scale components are precipitated in the pretreatment step, increasing the total recovery rate. There was a problem that it was not possible. In order to solve this, Japanese Patent Laid-Open No. 9-1412
Japanese Patent Laid-Open No. 60 proposes to use a nanofiltration membrane (hereinafter abbreviated as NF membrane) that removes only sulfate ions in order to prevent precipitation of calcium sulfate, which is a main scale component. However, according to this method, there is less concern about scale deposition in the pretreatment even if the recovery rate is increased, but such a membrane generally has a low salt removal rate and lowers the osmotic pressure of the reverse osmosis membrane. Since it is less effective, it is necessary to operate the reverse osmosis membrane at a very high pressure when operating at a high recovery rate. As a result, the recovery rate of the reverse osmosis membrane cannot be increased, and the recovery rate of the entire plant is 6%.
It was difficult to raise it to 0% or more.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned conventional problems and to obtain high-purity water by membrane treatment of raw water such as seawater having a high impurity concentration such as salt concentration. An object of the present invention is to provide a realistic desalination method and a desalination apparatus capable of achieving operation with a high recovery rate.

[0006]

Means for Solving the Problems The present invention for achieving the above object is to thaw frozen raw water and then selectively thaw the thawed water having an impurity concentration lower than that of the raw water, and then reverse osmosis the thawed water. It is characterized by a method for producing water by treating with a membrane and / or a nanofiltration membrane to obtain treated water having an impurity concentration lower than that of deicing water.

At this time, it is preferable that the deicing water is subjected to ultrafiltration and / or microfiltration to pass through the reverse osmosis membrane and / or the nanofiltration membrane. Further, it is preferable to freeze the raw water while flowing it down, to freeze the raw water by using night power, and to freeze the raw water while circulating the raw water. It is also preferable that the frozen raw water is thawed by using heat generated by a pump, and that the thawed water is used as a cold heat source of the air conditioning equipment. Further, it is also preferable to use any of seawater, industrial wastewater and domestic wastewater as raw water, and to set the recovery rate of the reverse osmosis membrane and / or the nanofiltration membrane to 50% or more.

Further, the present invention for achieving the above object comprises a freezing means for freezing raw water, and a thawing means for selectively thawing the frozen raw water to obtain thawed water having an impurity concentration lower than that of the raw water. A membrane separation means provided with a reverse osmosis membrane and / or a nanofiltration membrane for treating the deicing water to obtain treated water having an impurity concentration lower than that of the deicing water; Alternatively, it is characterized by a water producing device provided with a pump for supplying to the nanofiltration membrane.

Here, it is preferable to provide an ultrafiltration means and / or a microfiltration means between the deicing means and the membrane separation means. In addition, the freezing means includes a heat exchange pipe and a heat source that changes the temperature of the heat exchange pipe, and freezes the raw water while flowing it down from above the heat exchange pipe. It is preferably frozen. Furthermore, it is also preferable that the deicing means uses the heat generated by the pump as an energy source and that the deicing means is provided with an energy recovery means of the defrosting water.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing water of the present invention, raw water is passed through a freezing means to selectively freeze-separate only fresh water components from which impurities such as salt have been removed. Defrosted water with a lower concentration of impurities than the raw water is selectively extracted, and the extracted deiced water is treated with a reverse osmosis membrane or nanofiltration membrane to obtain treated water with a lower concentration of impurities than the deiced water. Is what you get.

A desalination apparatus for achieving this is shown in FIG.
As shown in, intake pump 1 for taking raw water such as seawater
Membrane separation including a freezing means 22 for freezing the taken raw water, a deicing means 25 for defrosting the frozen raw water, and a reverse osmosis membrane and / or a nanofiltration membrane for treating the thawed defrosted water And means 23.

The freezing means 22 is, for example, a raw water tank 2 which also serves as a non-freezing water recovery tank, a cold heat source, and a heat exchange pipe 4.
And a brilliantler 3 equipped with a circulation pump 53 for circulating a cold heat source, a sprinkler 6 for sprinkling raw water from above the heat exchange pipe 4, a hopper 24 for receiving non-frozen water, and sprinkling raw water including non-frozen water. Circulation pump 7 for supplying water to the vessel 6
And so on. The freezing means 22 is not particularly limited to the above embodiment, but the raw water is made to flow down in the form of a liquid film from the upper part of the heat exchange pipe 4 through which the refrigerant flows, and is frozen around the heat exchange pipe 4, so-called downflow. A liquid film type is particularly preferable. In the falling liquid film type, as the raw water flows downward from above the heat exchange pipe 4, only the pure water of the raw water becomes ice and adheres to the surface of the heat exchange pipe 4, and concentrated water in which impurities are concentrated Since it flows downward, it is possible to obtain a large amount of ice with high purity (for example, 90% or more of raw water) by circulating the concentrated water that has flowed downward and repeatedly flowing it down. Further, the falling liquid film type has high efficiency at the time of thawing described later. It is preferable that the freezing unit 22 uses nighttime electric power of 22:00 to 8:00, which is relatively inexpensive, in order to reduce running costs.

The defrosting means 25 is, for example, a heat exchange pipe 4, a heat source capable of circulating a fluid of 0 ° C. or more flowing in the heat exchange pipe 4, a circulation pump 53 for circulating the heat source, A hopper 24 for receiving frozen water, and a sprinkler 6 for circulating the deicing water 9 and the resulting deicing water to sprinkle water from above the heat exchange pipe 4, and a circulation pump 51 for circulating the deicing water. ing. The heat exchange pipe 4, the circulation pump 53, the sprinkler 6, the hopper 24, and the like are the same as those of the freezing means 22, and therefore, in order to regulate the water flow in each process, before and after the sprinkler and the hopper 2.
4, valves 60 to 63 are provided on the downstream side, and a valve 65 is provided on the downstream side of the circulation pump 51 for circulating the deicing water.
Is provided with a valve 64 for supplying the thawed water to the membrane separation means 23 described later without circulating it. Heat exchange pipe 4
In addition to the one that circulates a heat source inside to increase the temperature, the one that raises the temperature on the outer surface side of the pipe may be used.
At this time, the high-pressure pump 1 provided in the membrane separation means 23 in the subsequent stage
It is also useful to use the exhaust heat of 0 to change the temperature of the heat exchange pipe 4 to thaw it. Further, the present invention can be suitably used for desalination of seawater in an area where the temperature is relatively high and air conditioning is required.
In that case, the energy recovery means 52 is provided in the circulation path 50 of the deicing water so that the deicing water can be used as a cold heat source or the like of the refrigerant of the air conditioning equipment of the building structure such as the accommodation facility or the office. It is preferable because energy can be effectively used and the total running cost can be reduced.

Then, a plurality of sets of the freezing means 22 and the deicing means 23 are prepared, the cycles of the freezing step and the deicing step are sequentially adjusted, and the whole system is operated as a continuous system to continuously connect to the membrane separation means 23. It is also preferable to allow water flow.

The membrane separating means 23 is provided with at least one of a separation reverse osmosis membrane and a nanofiltration membrane for separating the sent deicing water into permeated water having a low impurity concentration and concentrated water having concentrated impurities. The high-pressure pump 10 for pressurizing and releasing the deicing water is provided in the front stage of the membrane separation unit 23, and the energy recovery unit 13 for the concentrated water is provided in the rear stage.

The reverse osmosis membrane is preferably one using a cellulose acetate polymer, one using a polyamide, one having an asymmetric structure or one having a composite structure, and further a hollow fiber membrane form. It is possible to use any of those having a flat film form and those having a flat film form. Among them, the reverse osmosis membrane using a cellulose acetate polymer having an asymmetric structure and the reverse osmosis membrane using a polyamide having a composite structure have a high impurity removal rate. In addition to the ratio, the amount of permeated water obtained is large, which is preferable.

As the nanofiltration membrane, a polyamide-based, particularly piperazine-based polyamide membrane having a large amount of permeated water to be obtained is preferable. In addition, as the membrane structure, those having an asymmetric structure or those having a composite structure,
As the sowing form, any of the one having a hollow fiber membrane form and the one having a flat membrane form can be used.

Whether to use a reverse osmosis membrane or a nanofiltration membrane is determined according to the application. That is, it is preferable to use a reverse osmosis membrane when the concentration of impurities in the deicing water is high or when it is necessary to make highly pure permeate. On the other hand, if the concentration of impurities in the deicing water is low, or if the requirement for the purity of the permeated water is not so strict, a nanofiltration membrane may be used. When the concentration of minerals such as calcium and magnesium in the deicing water is high, it is preferable to use a nanofiltration membrane and a reverse osmosis membrane together, as described later.

If these reverse osmosis membranes and nanofiltration membranes are flat membranes, they may be wound around the water collecting pipe together with the permeate flow passage material and the raw water flow passage material to form a spiral element or a tubular element. , Plate-and-frame type element, and U for hollow fiber membrane
The elements are bundled into a letter shape or an I shape and placed in a housing. Then, one or more of these elements are housed in a pressure vessel and used as a module. The number of elements loaded in the module is preferably between 4 and 8 in order to satisfy the processing capacity and the reduction of the equipment occupation area in a well-balanced manner. Furthermore, in order to increase the processing capacity in the same occupied area,
It is also preferable to arrange a plurality of series of these modules in parallel to form a module unit.

Furthermore, in order to produce water more economically and efficiently, especially when fresh water is obtained from seawater, the above-mentioned modules or module units should be arranged in multiple stages to constitute the membrane separation means 23. Is preferred. For example, when arranging modules or module units in two stages before and after, a concentrated water two-stage method in which the concentrated water obtained in the preceding stage is pressurized to be feed water to the latter stage and permeated water (fresh water) is obtained from each of the preceding and following stages Alternatively, the permeated water two-stage method for obtaining high-quality permeated water (fresh water) by using the permeated water in the former stage as the feed water to the latter stage can be applied. Of course, these are not limited to the two-stage arrangement, and a multi-stage configuration of three or more stages can be used if necessary.

When a concentrated water multi-stage method such as a concentrated water two-stage method is used, the concentrated water obtained from the latter stage has a high pressure energy, and therefore is recovered using a recovery turbine or the like to defrost water. It is preferable to use it as energy for pressurizing.

As the high pressure pump 10, various types of pumps such as a centrifugal pump, a turbine pump and a plunger pump can be used.

Further, in order to prevent or reduce the contamination of the membrane surface of the membrane separating means 23 in advance, the membrane separating means 23 is provided with:
It is preferable to provide an ultrafiltration unit or a microfiltration unit equipped with a filtration membrane, a filter cloth, sand filter or the like. These may be provided individually or may be installed together and may be determined according to the quality of the deicing water.

In the apparatus constructed as described above, water is produced as follows.

Raw water such as seawater is supplied by the intake pump 1.
Water is fed batchwise to the raw water tank 2 of the freezing means 22.
The raw water stored in the raw water tank 2 is supplied to the water sprinkler 6 by the circulation pump 7, and is supplied from above to the outer circumference of the heat exchange pipe 4 through which the cold heat source flows. The sprinkled raw water flows down in the form of a liquid film along the heat exchange pipe 4, so that the pure water component freezes and adheres to the outer periphery of the heat exchange pipe 4, and the concentrated water that has not frozen has a slight impurity concentration. Flows downwards with rising. The raw water that has not been frozen, that is, the concentrated water, flows down and moves downward, and the pure water component further freezes on the outer peripheral surface of the heat exchange pipe 4 to sequentially form ice. Then, the concentrated water that has not frozen until it flows down to the bottom of the heat exchange pipe 4 is collected by the hopper 24 and stored in the raw water tank 2 which also serves as a non-frozen water recovery tank, and then the circulation pump 7 Is again supplied to the sprinkler 6 and is repeatedly used for the above steps. At this time, the valves 61 and 63 are closed, and the valves 60 and 6 are
2 is open.

This is repeated until, for example, 80 to 90% of the raw water supplied batchwise to the raw water tank 2 adheres to the heat exchange pipe 4 as ice. Of course, raw water tank 2
The freezing step may be continued until all the raw water supplied to the freezing step is frozen, but it is economically preferable that the end point of the freezing step is at a concentration of 5 to 10 times.

Subsequently, the cold heat source inside the heat exchange pipe 4 is switched to a hot heat source capable of circulating fluid at 0 ° C. or higher, the valves 60, 62 and 65 are closed, and the valves 61 and 6 are closed.
3, 64 are opened, the ice frozen on the outer surface of the heat exchange pipe 4 is thawed, and the thawed water is stored in the thawed water tank 9. When a certain amount of deicing water is obtained, the deicing water is supplied to the sprinkler 6 using the circulation pump 51, and the sprinkler 6
By sprinkling water from above the heat exchange pipe 4, it is possible to shorten the time for the thawing process. At this time, the deicing water is passed through the energy recovery means 52 provided in the circulation path 50, and the energy of the defrosting water is provided to the cold heat source etc. of the refrigerant of the air conditioning equipment of the building structure such as the accommodation facility or the office, It is preferable to raise the temperature of ice water. Note that, in addition to the above, the ice-melting step may be carried out by stopping the supply of the cold heat source inside the heat exchange pipe 4 and raising the temperature on the outer surface side of the pipe, even if it is natural ice-melting. , The heat exchange pipe 4 using the exhaust heat of the high-pressure pump 10 provided in the membrane separation means 23 in the latter stage.
It is also useful to change the temperature of the ice to thaw it. Such an ice-melting step is continued until all the ice frozen and adhered to the outer surface of the heat exchange pipe 4 is thawed, and the ice-melting water is finally stored in the ice-melting water tank 9.

Thereafter, the valve 64 is closed and the valve 65 is opened, and the deicing water stored in the deicing water tank 9 is pressurized by the high pressure pump 10 and sent to the membrane separating means 23. The delivered defrosted water is separated by a reverse osmosis membrane or a nanofiltration membrane into permeated water having a lower impurity concentration than concentrated defrosted water and concentrated water having an increased impurity concentration.

Thus, according to the present invention, the raw water is frozen,
After the thawing treatment, it is subjected to membrane treatment with a reverse osmosis membrane or nanofiltration membrane, which enables practical water production with low cost and high recovery rate. In other words, the concentration of impurities such as salt can be reduced before the membrane separation step by the freeze and thaw steps, and as a result, the osmotic pressure in the membrane separation step can be reduced and operation at a lower pressure is possible. Becomes
This not only enables downsizing of the high-pressure pump 10 and reduction of power cost and equipment cost, but also leads to an increase in recovery rate, and further consolidation of the reverse osmosis membrane and the nanofiltration membrane. Can be prevented and the life of the reverse osmosis membrane and the nanofiltration membrane can be extended, that is, the frequency of element replacement can be reduced.

Specifically, the present invention can be particularly suitably carried out when the raw water is water having a salt concentration of 0.2% by weight, such as seawater or brackish water, but for example, the salt concentration (that is, total evaporation residue concentration) When seawater with a TDS of 3.5% by weight is desalinated, scale components in the raw water that precipitate on the membrane surface of the reverse osmosis membrane or the nanofiltration membrane along with chlorine ions, sodium ions, etc. by the freezing and thawing steps, It is possible to obtain thawed water having a salt concentration in the range of 1.5% by weight to 0.1% by weight, from which most of sulfate ions, calcium ions, magnesium ions and the like have been removed. Therefore, even if this thawed water is treated with a reverse osmosis membrane or a nanofiltration membrane under a high recovery condition of, for example, 60% or more, or even 70% or more, scale generation is suppressed and major ions such as chloride ions. Since it is also removed and the salt concentration is reduced, it is possible to perform membrane separation with reduced pressure, that is, with reduced energy consumption.

When seawater is treated, the concentrated water that has not been frozen contains a large amount of minerals. Therefore, it can be used to produce natural salt, or to use a high-mineral content liquid. It is also preferable to manufacture the above and use the high-mineral content liquid for health food, drinking water, cosmetics, pharmaceuticals and the like.

Further, the present invention can be applied not only to desalination of seawater and brackish water but also to treatment of factory wastewater and domestic wastewater. In treating these raw water, rough impurities, mud and microorganisms, inorganic substances, algae, etc. contained in the raw water can be removed in advance by sand filtration, coagulated sand filtration, ultrafiltration membrane or microfiltration membrane filtration. preferable.

In the present invention, the impurity concentration is the total evaporation residue concentration (TD) when seawater or brackish water is used as raw water.
In S), when factory wastewater or domestic wastewater is used as raw water, TDS and total organic matter (TOC) are used.

In the freezing step, impurities in the raw water are pushed out to the outer surface layer of water drops during freezing, and the freezing proceeds preferentially from the fresh water component. Therefore, by discarding the deicing water obtained at the initial stage of the defrosting, it is possible to obtain defrosting water having a higher purity. In addition, the raw water is circulated slowly and slowly, preferably 2 to 4 mm per hour in the heat exchange pipe 4.
It is possible to further improve the purity of frozen water by freezing at the speed at which ice is made with the thickness of. When freezing, the air contained in the raw water is discharged to the outer surface of the water droplets,
When freezing progresses slowly, the amount of air exhaled is small, and the exhaled air diffuses and thins. However, when the freezing rate is high, the amount of air discharged exceeds the amount of diffusion. As a result, as freezing progresses, air is contained in the water in a supersaturated state, and the air gathers and freezes with impurities as nuclei. Therefore, by selecting conditions so that the freezing rate is low, it is possible to prevent impurities from being taken up by ice, and to improve the purity of frozen water. It is possible to reduce the amount of ice water, and in some cases it becomes unnecessary to discard the amount of ice water.

In the freezing process, by using the nighttime electric power of 22:00 to 8:00, which is inexpensive in Japan,
The running cost can be reduced.

Further, both the freezing step and the thawing step are carried out in a batch system, but the cycle is adjusted between a plurality of freezing means and thawing means, and the whole system is operated as a continuous system for membrane separation. It is preferable to allow continuous water flow to the process.

In the membrane separation step, which of the reverse osmosis membrane and the nanofiltration membrane is to be used or both membranes are to be used is determined by the degree of the impurity concentration of the frozen water and the defrosting water. . For example, when trying to obtain water of higher purity from seawater, a nanofiltration membrane that removes scale components (multivalent ions such as sulfate ions, calcium ions, and magnesium ions) mainly from seawater in the first stage. In the latter part, a reverse osmosis membrane that removes mainly monovalent ions such as sodium ions and chlorine ions in seawater is placed in the latter stage, and membrane separation is performed. However, at this time, even in the nanofiltration membrane in the previous stage, sodium ions,
Since monovalent ions such as chlorine ions can be removed to some extent, it is sufficient to remove the remaining monovalent ions in the subsequent reverse osmosis membrane. Therefore, the load on the reverse osmosis membrane in the subsequent stage can be reduced, scale generation can be prevented even if the recovery rate is increased, and operation with a high recovery rate becomes possible.

In order to reduce the cost of water production, the membrane separation step is preferably operated so that the recovery rate in the membrane separation means 23 is 50% or more, and is preferably 60% or more. Particularly preferred. The recovery rate is the membrane separation means 23.
It is defined as the ratio of the total amount of permeated water recovered from the total amount of water supplied to the. The membrane separating means 23 may be supplied with all or only a part of the deicing water obtained in the previous stage, or may be supplied with the deicing water mixed with other raw water. . In the present invention, as described above, it is possible to prevent scale generation even when treated under a high recovery condition, and since the main ions such as chlorine ions are also removed, the salt concentration is reduced, Membrane separations with low pressure or energy consumption are possible.

When the raw water contains a large amount of fine particles and solid impurities, and the frozen water and the defrosted water also contain a large amount of fine particles and solid impurities, a filtration membrane or the like is used before the membrane separation step. It is preferable that the deiced water is subjected to ultrafiltration or microfiltration.

[0040]

EXAMPLES <Example> Water was produced using the water producing apparatus shown in FIG.

As raw water, salt concentration (concentration of total evaporation residue:
TDS) used 3.5% by weight of seawater, and
A heat exchange pipe that is filtered through a microfiltration membrane with 0 liters and a pore size of 0.1 μm and put into the raw water tank 2 and sprinkles water from the raw water tank 2 at 10 liters per minute, a part of which flows at a temperature of -10 ° C. The outer surface of No. 4 was frozen. At the same time, the concentrated water that flows down to the bottom of the coil without freezing is collected in the raw water tank 2 that also serves as a non-frozen water tank, and the circulation pump 7 is used to sprinkle the sprinkler 6
It was sprinkled with water. The amount of water in the raw water tank 2 is 1
It continued until it reached 0 liters.

Next, by stopping the supply of the fluid of minus 10 ° C. into the heat exchange pipe 4 and leaving it as it is,
The frozen water on the outer surface of the heat exchange pipe 4 was naturally thawed and the defrosted water was stored in the treated water tank. At this time, the amount of thawed water was 90 liters, and TDS was 0.55% by weight.

Subsequently, one spiral type element incorporating a polyamide reverse osmosis membrane (UT80 membrane manufactured by Toray Industries, Inc.) having a membrane area of 2 m ² was housed in a pressure vessel to form a reverse osmosis membrane module (membrane separation means 23). Then, the reverse osmosis membrane module was configured as a single stage and the deicing water was supplied.

As a result, the pressure was 1.5 MPa and the recovery rate was 60.
%, It was possible to obtain permeated water having a water amount of 0.8 m ³ / day and a salt concentration of 0.028% by weight.

In the reverse osmosis separation, both the permeated water and the concentrated water are returned to the deicing water tank for 120 minutes immediately after the start of the operation, and the operation is performed with the impurity concentration of the deicing water being kept constant to achieve stable operation. After the start of operation, which is assumed to have reached 120
The time was measured at 1 minute for 1 minute. Further, during this period, the temperature of the defrosting water was maintained at 25 ° C. by the temperature control equipment. <Comparative example> Pore size of 0.1 without freezing and thawing seawater
An attempt was made to produce water in the same manner as in Example 1 except that the reverse osmosis membrane module was supplied to the reverse osmosis membrane module just after being filtered through a microfiltration membrane of μm.

As a result, permeated water could not be obtained at a pressure of 1.5 MPa, and desalination of seawater could not be performed.

Next, when the pressure was increased to 5.5 MPa, the recovery rate was 30%, the water amount was 0.5 m ³ / day, and the TDS was 30%.
A permeated water of 0.034% by weight could be obtained.

[0048]

INDUSTRIAL APPLICABILITY According to the present invention, the deicing water in which the concentration of impurities such as salts in the raw water is reduced by freezing and deicing is selectively taken out and the deicing water is treated with a reverse osmosis membrane or a nanofil and a ration membrane. Therefore, the osmotic pressure in the reverse osmosis membrane or the nanofil and the ration membrane can be reduced. As a result, even when seawater having a high impurity concentration such as TDS of 3.5% by weight is used as raw water, high-purity water can be obtained by operation at low pressure and high recovery rate. In addition, it is possible to reduce the power cost and equipment cost by downsizing and labor saving of the high-pressure pump. Furthermore, it is possible to prevent consolidation of the reverse osmosis membrane and the nanofiltration membrane and reduce the frequency of membrane exchange. it can.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a fresh water generator according to an embodiment of the present invention.

[Explanation of symbols]

1: Water intake pump 2: Raw water tank 3: Blinchler 4: Heat exchange pipe 6: Sprinkler 7: Circulation pump 9: Deicing water tank 10: High pressure pump 13: Energy recovery means 22: Freezing means 23: Membrane separation means 24: Hopper 25: Defrosting means 50: Circulation path 51: Circulation pump 52: Energy recovery means 53: Circulation pump 60: Valve 61: Valve 62: Valve 63: Valve 64: Valve 65: Valve

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01D 61/16 B01D 61/16 61/58 61/58 C02F 1/22 C02F 1/22 C F24F 5/00 102 F24F 5/00 102K F term (reference) 4D006 GA03 GA06 GA07 HA01 HA21 HA41 HA61 JA56A JA66A JA67A JA70A KA01 KA15 KA52 KA53 KA54 KA55 KA57 KA67 KB30 MA01 MA02 MA03 MC18 MC54 PA01 PB03 PB08 CA03 AA 21 A03 AA 21 A03

Claims (15)

[Claims] 1. Defrosting water after freezing the raw water to selectively take out deicing water having an impurity concentration lower than that of the raw water, treat the deicing water with a reverse osmosis membrane and / or a nanofiltration membrane, and defrost water A method for producing water, characterized in that treated water having an impurity concentration lower than that of the above method is obtained. 2. The method for producing water according to claim 1, wherein the defrosted water is subjected to ultrafiltration and / or microfiltration to pass through the reverse osmosis membrane and / or the nanofiltration membrane. 3. The method of freezing while allowing raw water to flow down.
Alternatively, the water production method described in 2. 4. The method for producing water according to claim 1, wherein the raw water is frozen by using nighttime electric power. 5. The method of freezing while circulating raw water.
The method for producing water according to any one of to 4. 6. The method for producing water according to claim 1, wherein the frozen raw water is thawed by utilizing heat generated by a pump. 7. The desalination method according to claim 1, wherein the deicing water is used as a cold heat source for air conditioning equipment. 8. The method for producing water according to claim 1, wherein any one of seawater, factory drainage and domestic drainage is used as raw water. 9. The recovery rate in a reverse osmosis membrane and / or a nanofiltration membrane is 50% or more, 1 to 8.
The method for producing water according to any one of 1. 10. Freezing means for freezing raw water, deicing means for thawing the frozen raw water to selectively take out thawed water having an impurity concentration lower than that of the raw water, and treating the thawed water for more than thawed water. Further, a membrane separation means having a reverse osmosis membrane and / or a nanofiltration membrane for obtaining treated water having a low impurity concentration, and a pump for pressurizing the deicing water to supply the reverse osmosis membrane and / or the nanofiltration membrane. A desalination apparatus comprising: 11. The desalination apparatus according to claim 10, further comprising an ultrafiltration means and / or a microfiltration means between the deicing means and the membrane separation means. 12. The freezing means comprises a heat exchange pipe and a heat source for changing the temperature of the heat exchange pipe, and freezes the raw water while flowing the raw water downward from above the heat exchange pipe. 11. The water producing apparatus according to item 11. 13. The method for producing water according to claim 10, wherein the freezing means freezes while circulating the raw water. 14. The method for producing water according to claim 10, wherein the deicing means uses heat generated by a pump as an energy source. 15. The method for producing water according to claim 10, wherein the deicing means includes an energy recovery means for defrosting water.