JP3016671B2 - Fresh water generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a desalination apparatus using a reverse osmosis apparatus suitable for producing pure water and the like used in a power plant boiler, an electronic parts industry, a chemical industry, and the like. The present invention relates to a desalination apparatus having improved use efficiency of treated water.

[0002]

2. Description of the Related Art Conventionally, as a method of increasing the purity of water, there is a method of subjecting water to be treated to reverse osmosis using a reverse osmosis membrane device. In this method, the water to be treated is treated with a reverse osmosis membrane under high pressure, but silica, calcium,
Hardness components such as magnesium are concentrated by reverse osmosis treatment and precipitate when the concentration exceeds the solubility, which causes clogging of the reverse osmosis membrane, increases differential pressure, and decreases permeation speed Or have a problem. Therefore, conventionally, the concentration ratio is limited within a range in which silica or a hard component is not precipitated, but in this case, there is a problem that water use efficiency (recovery rate) is reduced.

[0003] As a method for solving the problem that the water use efficiency is reduced, Japanese Patent Publication No. 3-66035 discloses that silica-containing water is first passed through a microporous membrane or an ultrafiltration membrane, thereby reducing the silica content. After removing non-soluble silica fine particles that become the nucleus of precipitation, metal such as iron, or fine particles such as oxidizable colloids, by performing reverse osmosis treatment, the silica can be smoothly concentrated even if it is more than the solubility. A method for efficiently recovering purified water is disclosed. Further, there is a method in which a silica dispersant is used when treating silica-containing water with a reverse osmosis apparatus so that pure water can be smoothly recovered even when silica is concentrated to a high concentration. However, in the above-mentioned method, the effect of preventing the precipitation of silica is unstable, and in fact, the precipitation of silica increases the pressure difference between the inlet and the outlet of the reverse osmosis device.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a coating containing a component such as silica or a hardness component, which is a limiting factor of the recovery rate of a reverse osmosis device. It is an object of the present invention to provide a fresh water producing apparatus in which the recovery rate of the water to be treated is improved when the treated water is subjected to reverse osmosis treatment to produce desalinated water.

[0005]

To achieve the above object, the present invention provides a reverse osmosis apparatus for reverse osmosis separation of water to be treated supplied to the reverse osmosis apparatus into reverse osmosis concentrated water and reverse osmosis permeated water. A refrigeration apparatus that cools the reverse osmosis concentrated water to form a mixed phase of an ice phase and a liquid phase, means for separating the formed ice phase and the liquid phase, and melting the separated ice phase A fresh water generator is configured to have a heating device for forming molten water and a means for returning the molten water to the water to be treated supplied to the reverse osmosis device.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, reference numeral 1 denotes water to be treated which is obtained by subjecting raw water such as industrial water or city water to, for example, coagulation filtration and activated carbon treatment. The water to be treated 1 contains hardness components such as silica, calcium and magnesium. Is what it is. Hydrochloric acid 2 is first injected into the water 1 to be treated, the pH is adjusted so as to be about 4 to 6.5, and then sent to the decarbonation tower 3 for decarbonation. The decarbonated water to be treated is then charged with a sodium hydroxide aqueous solution 4 or the like as necessary, and the pH is readjusted. The treated water 1 stored in the raw water tank 5 is then subjected to reverse osmosis (RO)
It is pressurized by the processing pressurizing pump 6 and sent to the reverse osmosis device 7 where the reverse osmosis treatment is performed and the reverse osmosis concentrated water 7a and the reverse osmosis permeated water 7b in which impurities such as silica and hardness components are concentrated.
Thus, permeated water 7b from which impurities such as silica and hardness components have been removed is obtained. At this time, concentrated water 7
The operation is carried out so that the concentration of components such as silica in a does not exceed the solubility and the amount of permeated water is as large as possible. In addition, P1 and P2 are pressure gauges provided on the inlet side and the outlet side of the reverse osmosis device 7. On the other hand, the reverse osmosis concentrated water 7a in which the concentration of the silica and the hardness component is increased is sent to the refrigerating device 8, where it is cooled to form a mixed phase in which an ice phase and a liquid phase are mixed. The cooling means of the refrigeration system 8 may be of any type, for example, liquefied natural gas (LN
It is also possible to use the cold heat of G). When the ice phase is formed, the dissolved impurity components including the silica and the hardness component are hardly taken into the ice phase, so that these components are more unevenly distributed in the liquid phase.

Reference numeral 9 denotes a separating means provided in the refrigerating device 8, for example, composed of a filter. After the formation of the mixed phase is completed, the liquid phase is separated from the ice phase by the separating means 9 and taken out as frozen concentrated water 8a. Is released outside the system.

As a means for separating the liquid phase and the ice phase, for example, a means for allowing the liquid phase to flow out of the system by gravity using a strainer, the above-mentioned filter, or the like, or a means for mechanically separating using a centrifuge or the like. Means and the like can be used. After the liquid phase and the ice phase are separated once, the surface of the ice phase may be washed with, for example, reverse osmosis permeated water to remove impurities adhering to the surface.

On the other hand, the ice phase 8b is sent to a heating device 10, where it is heated and melted into molten water 11, which is then returned by a pump 12 to a raw water tank 5 in which the water to be treated is stored. Reused. In this embodiment, the freezing and the heating are described as being performed by separate devices. However, the freezing device and the heating device may be integrated, and the freezing and the heating may be performed alternately by one device.

As described above, impurities such as silica are more unevenly distributed in the liquid phase. As a result, the concentration of the silica component and the like in the molten water is higher than the concentration in the concentrated water 7a, and further, the solubility of the component is higher. The water is much lower than that of the reverse osmosis device 7 and can be safely reused as the water to be treated in the reverse osmosis device 7 without worrying about the precipitation of silica or the like.

In the above embodiment, the water to be treated was subjected to coagulation filtration and activated carbon treatment. In addition to these treatments, various pretreatments such as coagulation sedimentation, ultrafiltration, and microfiltration (MF) were used. The raw water to be treated is not limited to industrial water and city water, and various kinds of water can be used, and may be variously modified without departing from the gist of the present invention.

Next, changes in the silica concentration in each phase when the concentrated water of the reverse osmosis apparatus is a mixed phase of an ice phase and a liquid phase will be described with reference to an experimental example. (Experimental example) City water (dissolved silica: 21 ppm) was subjected to reverse osmosis treatment to obtain 400 g of reverse osmosis concentrated water (98 ppm of dissolved silica). 400 g of this concentrated water was frozen to obtain a mixture of ice and water. Ice and water are separated by filtration, and the ice is heated to melt 241
g (dissolved silica: 28 ppm). In the present invention, the water recovery rate is improved by returning the molten water having a low silica concentration (28 ppm) to the water to be treated. By the way, the solubility of silica is 100 ppm at room temperature.
It is. Thus, it is clear that the molten water can be reused as the water to be treated in the reverse osmosis device because the silica concentration is much lower than the solubility.

The remaining liquid except for ice in the mixture is 1
48 g, and the dissolved silica concentration was 128 ppm, which was high. (From the mass balance of silica,
The concentration of silica in the residual liquid should be about 220 ppm, but since a part of the silica was precipitated as insoluble silica in the residual liquid, the concentration of dissolved silica was as described above. )

[0015]

According to the present invention, the concentrated water of the reverse osmosis unit is frozen to form an ice phase with a small amount of impurities, which is a limiting factor for the recovery rate of the reverse osmosis unit such as silica, and a liquid phase with the impurities concentrated. A mixed phase is formed, the liquid phase is discharged out of the system, and the ice phase is melted to obtain a molten liquid with a small amount of impurities serving as the limiting factor, which is returned to the water to be treated and reused. The water recovery rate in the entire system is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 treated water 7 reverse osmosis device 7a reverse osmosis concentrated water 8 refrigeration device 9 separation means 10 heating device 11 molten water

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C02F 1/44 C02F 1/22

Claims (1)

(57) [Claims] 1. A reverse osmosis device for reverse osmosis separation of water to be treated supplied to a reverse osmosis device into a reverse osmosis concentrate and a reverse osmosis permeate, and cooling the reverse osmosis concentrate to form an ice phase and a liquid phase. Refrigeration apparatus for forming a mixed phase of: a means for separating the formed ice phase and the liquid phase; a heating apparatus for melting the separated ice phase to obtain molten water; and a reverse osmosis apparatus for applying the molten water to reverse osmosis. Means for returning the water to be supplied to the water to be treated.