JPH04108590A - Desalination of seawater - Google Patents

Abstract

PURPOSE:To obtain a fresh water of good quality at a substantially low production cost by a method wherein a container which has its surface formed of a semipermeable membrane and whose exterior and interior parts are isolated from each other is sunk into seawater to such a depth as to be able to obtain the pressure not lower than the osmotic pressure of the seawater. CONSTITUTION:A semipermeable membrane tube 2 is attached to the tube plate of a sealed container part in a water permeating device 1 to define a sealed container together with the water permeating device 1. The bottom of a space part within the sealed container 3 forms a water reservoir part for receiving the fresh water passing through the semipermeable membrane. The sealed container part is so constructed as to fully withstand the pressure differing between the interior and exterior not lower than a water permeating pressure. The water permeating device 1 is sunk from a base 9 into the natural current of seawater having a depth required to obtain fresh water and the water permeating device is supplied with a required utility from a mooring through a utility supply line 10 and supplies the water to the mooring through a water conveying pipe 5. The water permeating device 1 is lifted to be brought back to the base when its maintenance is required.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for obtaining fresh water from shrubs, in particular.

It concerns the method of obtaining fresh water from seawater.

In recent years, in Japan, the demand for water has been increasing due to the development of various industries accompanying economic growth, the concentration of urban population, and improvements in living standards. Furthermore, recently, the development of new water resources has been desired for greening projects, which have a large impact on the increase in carbon dioxide gas, which is a major cause of global warming.

(Problems that conventional technology and inventions have tried to solve) As methods for obtaining fresh water from shrubs, many research and developments have been carried out such as evaporation method, electrodialysis method, freezing method, and hydrate method. There are many problems both economically and technologically.
It is no exaggeration to say that it has not yet been put into practical use except for special uses.

Among these methods, the present invention relates to reverse osmosis, which consumes relatively little energy and is expected to be developed.

In the reverse osmosis method, which uses a semipermeable membrane to obtain fresh water from shrubs, the brine that has been pretreated to remove harmful substances is first raised to a pressure higher than the osmotic pressure using a pump, etc. A common method is to supply fresh water to the surface of a semipermeable membrane at a pressure of The disadvantage of such a method is that
It is necessary to use power to raise the pressure of the raw brine above the osmotic pressure, and the power cost accounts for a large portion of the cost of producing fresh water, and there is a problem in that the equipment cost is high. The raw material water supply power is determined by the amount and pressure of the supplied salt water, but the supply water pressure to obtain fresh water must be greater than the osmotic pressure of the semipermeable membrane. However, it is well known that the osmotic pressure increases as the concentration of brine increases, and as the concentration of raw brine increases, the required pressure also increases. When collecting fresh water using a semi-permeable membrane, the concentration of water increases as the fresh water permeates, making it necessary to further increase the supply pressure, which increases the economic and technical difficulties. In addition, the salt concentration in the obtained fresh water increases as the salt concentration in the raw brine increases, and an increase in the salt concentration in the brine is not preferable since it deteriorates the quality of the fresh water product. In order to minimize the increase in the concentration of cancer water due to water permeation, it is possible to increase the amount of raw material water relative to the amount of fresh water obtained, but increasing the amount of supplied cancer water requires pretreatment. There are economic and technical constraints as this results in an increase in volume and supply power, as well as an increase in brine supply equipment.

Contamination of the semipermeable membrane surface due to adhesion of impurities in the brine is also greatly influenced by the flow conditions of the brine on the brine side membrane surface.
The faster the flow and the more vigorous the agitation, the less likely it is to be contaminated, but in order to achieve this type of brine flow, it is generally necessary to increase the supply amount. However, as mentioned above, it is generally difficult to increase the amount of raw brine supplied because of the pre-treatment and supply power of the raw brine, and the complexity of the equipment due to devising the flow path. be. Attempts have been made to recover part of the power required to supply raw brine by recovering energy from the high discharge pressure of concentrated brine after fresh water has been extracted, but this approach has the disadvantage of requiring complex and expensive equipment. In addition, brine is highly corrosive, and it is often difficult to handle large amounts of brine under high pressure.

(Means for Solving the Problems) The present invention aims to eliminate these drawbacks and obtain fresh water from shrubs.As a result of various studies, the present invention uses a semi-permeable membrane to allow water to pass through. When obtaining fresh water, the pressure necessary for water permeation is obtained by using the static pressure of the raw brine, preferably by using the naturally existing static pressure and the circulation phenomenon of the brine. It was discovered that the above object can be achieved without adding artificial energy. This is the gist of the present invention.

As mentioned above, if it were possible to supply a large amount of raw material water to the semipermeable membrane surface without requiring a large amount of power or with any special restrictions, it would not only be possible to reduce the required power, but also to provide fresh water with a low salt concentration. It is preferable to obtain high-quality fresh water and to prevent contamination of the semipermeable membrane surface, and the cost of producing high-quality fresh water can be significantly lowered.

As a means to achieve such a state, the present inventor has developed a container whose surface is partially or entirely composed of a semipermeable membrane to isolate the outside from the inside, by increasing the brine concentration on the surface of the semipermeable membrane. By submerging the water in brine with a natural flow that prevents water from occurring, the pressure difference between the inside and outside of the semipermeable membrane is greater than the osmotic pressure of the brine. The present invention provides a method for supplying a large amount of raw brine to a semipermeable membrane surface by using a method for obtaining fresh water without using much power for supplying brine.

As a method for taking out the fresh water obtained in the closed container, it is possible to collect the container below the brine surface and take out the fresh water, or to take out the fresh water continuously from a position at a depth where fresh water can be obtained using a pump or the like.

In either case, the power required per amount of fresh water to extract fresh water from below the water surface to above the water surface is almost constant regardless of the amount of raw water supplied, and there are few problems such as corrosion.

In the present invention, underground shrubs or seawater are suitable as the raw brine.

The usual method of utilizing the static pressure of raw brine is to submerge a permeator in seawater with a natural flow, for example, at the depth necessary to obtain fresh water.

Transmission sampling of freshwater. In this case, it is necessary to install the water permeator at a location where collecting fresh water will not increase the salt concentration of the surrounding seawater.

In order to speed up the flow of brine on the permeable membrane surface, minimize the difference in brine concentration with the surrounding brine concentration, and to bring the brine flow on the membrane surface to a flow rate in a turbulent region, we It is desirable to attach a water supply machine, this water supply machine is
Unlike conventional brine supply pumps, it is not used to obtain osmotic pressure, but simply requires a head that corresponds to the flow resistance to send brine to the membrane surface, and its power consumption is extremely low. First, an embodiment of the present invention, which has a simple structure and may be a propeller-type water conveyor, for example, will be described below with reference to the drawings.

A specific example of a water permeator will be explained according to FIGS. 1 and 2. Figure 1 shows a cross-sectional view of a permeator in which the inner surface of the cylindrical semi-permeable membrane is in contact with the shrub, and Figure 2 is a cross-sectional view of the permeator in which the outer surface of the cylindrical semi-permeable membrane is in contact with the shrub. It shows a constructed cylindrical water-permeable surface.

The semipermeable membrane tube 2 in the figure is glued to the tube plate of the sealed container part 1 in the figure, and the bottom of the space inside the sealed container 3 in the figure forms a sealed container together with 1 in the figure. This is the storage area for fresh water that flows through the membrane. It is of course necessary that the closed container part has a structure that can sufficiently withstand the differential pressure between the inside and outside that is higher than the water permeability pressure. Another preferred method is to fill the inside of the closed container with a porous material such as sintered metal. This is a water pump. This prevents the salt concentration from increasing due to water permeation on the semi-permeable membrane surface, reduces the permeation resistance of fresh water by making the flow state of brine water turbulent, and reduces the thickness of the liquid layer on the semi-permeable membrane surface. This is preferable because it prevents the adhesion of contaminants as much as possible. In addition, this water conveyor can maintain brine with almost the same concentration of brine around the permeator, which is maintained at a constant salt concentration by the natural flow of brine, at the water permeator outlet, which is preferable. The pressure required to supply brine is several hundred times lower than the pressure required for supply using conventional methods, and the required power is minimal. The fresh water that passes through the semipermeable membrane and collects at 3 in the figure is supplied to necessary locations by a pump 4 and a water pipe 5 in the figure.

A common method of utilizing the static pressure of raw brine is to submerge a water permeator in the sea with a natural current, for example, at a depth necessary to obtain fresh water.

FIGS. 3 to 5 show examples of how the water permeator is used. Figure 3 shows how to submerge a water permeator from the base 9 in the figure into seawater with a natural flow to a depth necessary to obtain fresh water, and install the IO anchorage and utility supply line in the figure. This is an example of an embodiment in which the necessary utility is supplied by 5 and water is obtained by 5 in the figure. The water filter is.

Figure 4 shows the depth of the soil so that when it is filled with brine, the pressure of the brine at the bottom exceeds the permeability pressure. A method of digging a hole, filling the hole with shrubs, installing a permeator at the bottom, sending brine from the brine source to the permeator using pump 6 and pipe 8, and circulating it to the brine water source via pipe 9. This is an example. This method is also effective when the water permeator is submerged in the sea and a drop in seawater temperature becomes a problem. Figure 5 shows a system in which brine is circulated by connecting a brine source with a brine supply pump 6 and a water supply/drainage pipe 8.9° to a water permeator installed at the bottom of a hole deep enough to obtain permeability pressure. This is an example.

In this case, the required head of the pump 6 is only required by the flow resistance of the brine in the water supply and drainage pipes and the permeator, and the resistance due to the difference in specific gravity of the brine resulting from the temperature difference between the upper and lower parts of the brine, and is compared to conventional brine supply pumps. Much less power consumption is required.

[Brief explanation of the drawing]

Figure 1.21 shows a cross-sectional view of the permeator, Figures 3.4 and 5.
The ゜ figure is a diagram showing an example of how a water permeator is used. l is water permeator,
2 is a semi-permeable membrane, 3 is a reservoir for permeated fresh water, 4 is a fresh water pump, 5 is a water pipe for collecting fresh water, 6 is a pump for supplying brine to the permeator, 7 is a base, and 8 is a pump for supplying fresh water to the permeator. A brine supply pipe, 9 a brine drainage pipe, and 10 a connection between the permeator and the base and a utility supply line.

Claims (3)

[Claims] (1) A container (hereinafter referred to as a water permeator) whose surface is partly or entirely composed of a semi-permeable membrane to isolate the outside from the inside is heated to a depth where a pressure higher than the osmotic pressure of brine can be obtained. A brine desalination device and method that obtains fresh water inside a water permeator by submerging it in brine. (2) The method for desalinating brine according to claim 1, wherein the fresh water that has flowed into the water permeator is discharged by a pump, and the differential pressure inside and outside the water permeator is maintained at a level higher than the osmotic pressure. (3) The brine desalination apparatus according to claim 1, characterized in that brine is fed by a water feeder so that the flow of brine on the surface of the semipermeable membrane becomes a turbulent region.