JP2002054183A - System and method for intake of seawater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system for intake of seawater for reducing clogging of a sand stratum due to the breakage and slit of an biofilm formed in the sand layer as much as possible, and for removing a suspended material or the like deposited on the surface of the sand stratum without much time and labor. SOLUTION: In the system, a conducting tube 10 is buried into a sand stratum 3 in an ocean floor 2, seawater naturally penetrating through the sand stratum 3 is taken in from intake pipes 12 and 14 (an intake part 10a) at the tip of the conducting tube 10. The penetration flow rate of seawater appearing in the sand stratum 3 due to the intake operation of the intake part 10a is set to 1.0-8.0 (m/day). Also, the water depth of the sand stratum 3 where the intake part 10a is formed is set deeper than water depth where sand at the surface- layer part of the sand stratum 3 travels at least for 50 cm and shallower than water depth where the sand travels at least as long as 1 cm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seawater intake system and a seawater intake method in which an intake pipe is buried in a sand layer at the bottom of the sea, and seawater penetrating the sand layer from the sea is introduced into the intake pipe to take water.

[0002]

2. Description of the Related Art A reverse osmosis membrane (RO) is used as a seawater desalination plant for producing seawater such as drinking water by desalinating seawater.
Plants utilizing membranes are known. In this plant, salt dissolved in seawater is removed from seawater by a reverse osmosis membrane to produce freshwater. It is widely practiced because fresh water of very good quality can be obtained. Seawater is pumped through a water intake pipe installed on the seabed, and after adding chemicals such as flocculants,
The filter sand is forcibly permeated through filter sand and is subjected to a large amount of filtration treatment, thereby removing impurities and dust, and performing pretreatment such as sterilization. After purifying seawater to some extent to improve water quality, reverse osmosis membrane (RO membrane)
For desalination. The purpose of purifying seawater in the desalination treatment in this way is to prevent clogging of the reverse osmosis membrane.

[0003]

The seawater desalination plant has the following problems. (1) Since a large amount of seawater is forcibly permeated through the filter sand using a pump and the filtration process is performed, the filter sand is easily contaminated, and a large amount of sludge is generated every day, and the filter sand is frequently washed. Needed. Therefore, a plant for treating the generated sludge is required. (2) Since many chemicals must be added in order to remove bacteria, suspensions, and the like, there is a concern that water quality may be deteriorated by these chemicals. (3) Seawater was forcibly introduced into the intake pipe, causing organisms to adhere and clog the pipe. Therefore, chlorine had to be injected to prevent biofouling and periodic cleaning was required. (4) There are disadvantages such as a great impact on the fishery and a great impact on the natural environment.

[0004] As a system for taking in seawater, there is also a permeated water intake system. In this infiltration water intake system, an intake pipe is buried in a sand layer on the sea floor, and seawater that has naturally penetrated into the sand layer from under the sea is introduced into the water pipe without using a pump to take in seawater. Since the seawater that has been purified by natural permeation through the sand layer is taken in, the seawater with very good water quality can be obtained without organisms adhering to the intake pipe. Another advantage is that the impact on the fishery is small and the impact on the natural environment is small.

[0005] However, this permeation water intake method has a problem that the sand layer is clogged when silt (mud) accumulates on the surface of the sand layer. For this reason, it was hardly adopted in various seawater intake facilities such as a seawater desalination plant because of its unstableness and very poor reliability.

[0006] In view of such circumstances, the present inventor has considered whether a permeated water intake system having many merits can be adopted in a seawater desalination plant or the like. Focusing on the slow filtration method conventionally used in land-based water purification plants,
Taking into account the permeation velocity of seawater into the sand layer, we thought that this slow filtration system would be used for the permeation water intake system. The slow filtration method is a method in which water is filtered by allowing natural permeation through the filter sand, and a biofilm composed of bacteria or the like is formed in the filter sand. Water can be purified. Also,
By this purifying process, it is not necessary to perform a pretreatment using many chemicals to remove suspended matters and kill bacteria and the like.

[0007] However, environmental conditions are completely different between land and the sea, and there are various problems in applying the land-based slow filtration system to the submerged osmotic water intake system. For example, the sand layer may be eroded by 2 to 3 m in the sea overnight due to a large wave or a fast current caused by a typhoon or the like. For this reason, even if a biofilm is formed in the sand layer, it will be destroyed and not only will not be able to obtain the biological filtration function,
The structure itself may be damaged. On land,
Although the work of scraping the surface of the sand layer to remove suspended matter and the like deposited thereon can be easily performed, it is extremely difficult to perform this removal work in the sea.

The present invention has been made in view of such circumstances, and an object of the present invention is to reduce the occurrence of clogging of a sand layer on the seabed that takes in seawater as much as possible, and to improve the filtering action. A seawater intake system that does not destroy the biofilm formed in the sand layer that bears it and that can remove suspended matter etc. deposited on the surface of the sand layer without hassle and ensure stable intake And a method for withdrawing seawater.

[0009]

In order to achieve the above object, in a seawater intake system according to the present invention, an intake section formed by burying an intake pipe in a sand layer at the bottom of the sea passes from the sea through the sand layer. In the system for taking in seawater that naturally penetrates, the seawater permeation flow rate expressed in the sand layer by the water intake action of the water intake section is set to 1.0 to 8.0.
(M / day).

[0010] In the method of drawing seawater according to the present invention, the method of drawing seawater naturally penetrating from the sea through the sand layer by means of a water intake section formed by burying an intake pipe in a sand layer on the sea floor. The seawater infiltration flow rate expressed in the sand layer by the water intake action of the water intake section is 1.0 to
It is 8.0 (m / day).

At this time, the water depth of the sand layer in which the water intake portion is formed is made deeper than the water depth at which the sand of the surface portion of the sand layer moves by 50 cm or more, and shallower than the water depth at which the sand moves by 1 cm or more.

Further, in the sand layer, seawater is filtered by a biofilm.

[0013] The infiltration velocity of seawater in the sand layer is 1.0
The reason for setting to 8.0 (m / day) is as follows. In other words, when the seawater permeation flow rate exceeds 8.0 (m / day), the probability that the silt gets caught in the sand layer increases, and the surface of the sand layer is clogged by the silt being covered with the silt. On the other hand, when the seawater permeation flow rate is lower than 1.0 (m / day), the amount of oxygen supplied to the sand decreases, and the formed biofilm is killed. The film cannot be formed. from these things,
In order to secure a sufficient water intake and minimize the possibility of clogging of the sand layer, and to form a biofilm in the sand layer, the seawater permeation flow rate should be 1.0 to 8.0 (m).
/ Day) is appropriate.

As described above, the infiltration speed of seawater is 1.0 to 8.0.
By setting (m / day), the silt deposited on the surface of the sand layer can be prevented as much as possible from entering the sand layer, and the silt blocks the surface layer of the sand layer as much as possible to cause clogging. Can be reduced. Further, sufficient oxygen can be supplied into the sand layer, and the biofilm formed in the sand layer is not killed. As a result, a sufficient biofilm can be formed, and by the function of the biofiltration function of the biofilm, seawater can be purified at the bacterial level in addition to the physical filtration by the sand layer. This improves the quality of the seawater that has been withdrawn.

Here, there are various ways to develop the seawater permeation flow velocity in the above numerical range by the water intake action of the water intake part. The intake action of the intake section that determines the seawater infiltration velocity is, for example, the equipment area of how large the intake section is to be formed, the burial depth of the intake pipe in the sand layer, the distribution density of the intake pipe, It can be changed and adjusted by various design factors such as the number of buried water pipes, the length of intake pipes, the spacing of intake pipes, the layout of intake pipes, the diameter of intake pipes, etc. By appropriately combining these design elements according to the survey data of the sand layer obtained by conducting an on-site survey of the site, the seawater permeation flow rate to be expressed in the sand layer is set to 1.0 to 8.0 (m / day). Can be done easily.

Here, the water depth of the sand layer where the water intake portion is formed is set to be deeper than the water depth at which the sand at the surface portion of the sand layer moves by 50 cm or more, and shallower than the water depth at which the sand moves by 1 cm or more. The movement of the sand on the surface portion of the sand layer by 1 cm or more means that the sand on the seabed is washed, so to speak, if it is deeper than this water depth, the movement of the sand particles on the surface portion of the sand layer is hardly recognized. On the other hand, the movement of the sand on the surface of the sand layer by 50 cm or more means that the erosion of the sand layer on the seabed is recognized, and if it is shallower than this depth, the sand particles on the surface layer of the seabed move on a large scale. And erosion becomes remarkable. By setting the water depth of the sand layer forming the water intake portion to the above range, the surface of the sand layer is appropriately stirred by waves and currents appearing in the sea, and removes suspended matter such as dust and silt deposited on the surface of the sand layer. And stable water intake can be secured.

Here, terms that define the behavior of the sand layer on the seabed include “surface movement limit water depth” and “complete movement limit water depth”.
It has been known. The "surface movement limit water depth" is roughly
It is said to be the maximum water depth at which sand particles on the sea floor can move to some extent by the target wave. Also, the “complete movement limit water depth” is generally said to be the maximum water depth at which it is confirmed that the sand layer on the seabed is eroded by the action of the target wave. However, the definition of these terms in a strict sense includes various theories and is not uniform. Therefore, in the present specification, such a non-uniform term is not used so as not to raise a doubt, and "water depth at which the sand on the surface portion of the sand layer moves by 50 cm or more" or "water at the surface portion of the sand layer moves by 1 cm or more" Although the water depth of the sand layer was specified by the numerical value "water depth", this specific meaning refers to the above-mentioned water depth of the meaning content described in various theories. That is, the “water depth at which the sand on the surface portion of the sand layer moves by 50 cm or more” corresponds to the above “complete movement limit water depth”, and the “water depth at which the sand on the surface portion of the sand layer moves by 1 cm or more” It is equivalent to "surface movement limit water depth".

[0018]

1 and 2 show an embodiment of a seawater intake system and a seawater intake method according to the present invention. The seawater intake system and the seawater intake method include a land 4 in a sand layer 3 on a seabed 2 in a shallow water near a coast 1.
The water pipe 10 is buried from the side toward the sea 5 side, and the water layer 10a formed in the sand layer 3 by the water pipes 12 and 14 provided at the sea end of the water pipe 10 causes the sand layer on the seabed 2 from the sea. 3 is a system or a method for taking in seawater which naturally penetrates the seawater.

At the front end of the water guide pipe 10 at the sea side, three horizontal intake pipes 12 are arranged in parallel at right angles to the left and right sides in a lateral direction and extend in parallel with each other. Between these three horizontal water pipes 12, a large number of vertical water pipes 14 are provided in parallel at intervals. Each vertical water pipe 14 connects three horizontal water pipes 12 to each other. A number of water intake holes (not shown) communicating with the inside of the pipes are formed through the outer periphery of the horizontal water intake pipe 12 and the vertical water intake pipe 14. The horizontal intake pipe 12 and the vertical intake pipe 14 are buried in the sand layer 3 to function as an intake section 10a, and the seawater that naturally penetrates into the sand layer 3 of the seabed 2 passes through a large number of intake holes to take the horizontal intake pipe. 12 and the vertical water pipe 14 are introduced into each pipe. Then, the seawater is collected from the inside of each of the horizontal intake pipe 12 and the vertical intake pipe 14 to the water conveyance pipe 10 and sent to the water storage tank 16 installed underground on the land 4 side through the water conveyance pipe 10. . Seawater is temporarily stored in the water tank 16 and supplied to a seawater treatment plant such as a seawater desalination plant through a supply line 18.

In this embodiment, these horizontal intake pipes 1
2 and the seawater permeation flow rate generated in the sand layer 3 by the water intake action of the water intake part 10a such as the vertical water intake pipe 14 is 1.0 to 8.0.
(M / day). Here, the seawater permeation flow velocity is the permeation velocity when seawater permeates the sand layer 3. The higher the seawater permeation flow velocity, the more seawater can be taken, but the silt penetrates into the sand layer 3. Otherwise, silt is deposited on the surface of the sand layer 3, which causes clogging of the sand layer 3. On the other hand, if the seawater permeation flow rate is too slow, the amount of water withdrawal will be low and the efficiency of water withdrawal will be extremely low, and sufficient oxygen cannot be supplied into the sand layer 3, resulting in the death of the biofilm. Become.

Therefore, an appropriate seawater infiltration flow rate was determined so as to avoid these problems as much as possible. The particle size of the silt particles is generally approximately 0.005 mm to 0.074.
mm. The flow velocity of the seawater at which the silt does not move, that is, the movement limit flow velocity is obtained. The movement limit flow velocity is a value obtained by multiplying the limit actual flow velocity of the silt particles by the area porosity. In addition,
Here, the area porosity is 0.35. The critical actual flow velocity of the silt particles is shown in Fig. 3 showing the relationship between the particle size and the critical actual velocity (Geotechnical Society of Japan: Geotechnical Engineering Handbook, Hokkodo, p1041, 1999: Measurement results by Kubota and Tanaka). Ask using. From this graph, the critical actual flow rate of the large silt particles having a particle size of 0.08 mm is 0.026 cm /
You can read s. Therefore, the upper limit of the movement limit flow velocity of the silt is 0.026 × 0.35 × 24 × 3600 = 786.
24 (cm / day) ⇒ about 8.0 (m / day).

From this result, in order to prevent clogging due to silt, the maximum permeation flow rate of seawater is 8.0.
(M / day). In order to supply sufficient oxygen into the sand layer 3 so as not to kill the biofilm, at least 1.0 (m /
The seawater infiltration flow rate on the day is required. From these facts, it is best to set the seawater permeation flow rate within the range of 1.0 to 8.0 (m / day). If the seawater infiltration velocity is set in such a range, as shown in FIG.
In the process of natural permeation through the interior at a considerable permeation velocity, the sand layer 3
Contact with a biofilm composed of microorganisms such as nitrifying bacteria formed around the sand particles inside (here, the sand particles in the replacement sand layer),
The biofilm is biofiltered and purified to bacterial levels.

Further, the horizontal intake pipe 12 and the vertical intake pipe 1
The water depth of the sand layer 3 in which the water intake part 10a made of the steel 4 is embedded is set to be deeper than the water depth (X) at which the sand of the surface layer of the sand layer 3 moves by 50 cm or more and shallower than the water depth (Y) at which the sand moves by 1 cm or more. You. These water depths can be obtained not only by numerical calculations but also based on various oceanographic observation data such as, for example, moving observation data of drifting sand using radioactive tracers, wave data, sea bottom surface sediment data, and tidal current analysis data. Can be These water depths vary depending on the sea area.

FIG. 5 schematically shows regions satisfying these conditions. The water intake unit 10a is installed in an area determined based on the above-described data, for example, an area at a water depth of about 11 m. In this area, the surface of the sand layer 3
It is agitated by waves or flows generated about twice. Thereby, suspended matter such as dust and silt deposited on the surface of the sand layer 3 can be removed. Since the surface of the sand layer 3 is not agitated too much, a biofilm or the like in the sand layer 3 is not damaged much.

As described above, according to the seawater intake system and the seawater intake method, the seawater permeation flow rate expressed in the sand layer 3 by the intake action of the intake section 10a is 1.0 to 8.0 (m / m).
Day), it is possible to prevent the sand layer 3 from being clogged by the silt. Further, the biofilm in the sand layer 3 can be maintained. Thus, stable water intake can be ensured, and very good water quality can be obtained.

The sand layer 3 for burying the intake pipes 12 and 14
Is set to be deeper than the water depth (X) at which the sand of the surface portion of the sand layer 3 moves by 50 cm or more, and shallower than the water depth (Y) at which the sand moves by 1 cm or more, so that the surface portion of the sand layer 3 is appropriately adjusted. For example, agitation washing is performed about once or twice a month, and suspended matter and dust accumulated in the sand layer 3 are removed and cleaned, and renewal of the sand layer 3 can be ensured.

In short, in this embodiment, the sand layer 3
The destruction of the biofilm formed therein and the clogging of the sand layer 3 by the silt can be prevented, and the suspended matter and the like deposited on the surface of the sand layer 3 can be removed without trouble.

[0028]

As described in detail in the embodiments of the present invention, according to the seawater intake system and the seawater intake method of the present invention, it is possible to prevent the sand layer from being capped by silt and causing clogging. In addition, sufficient oxygen can be supplied into the sand layer, and the quality of seawater taken can be improved while maintaining the biofilm in the sand layer. Thus, water can be stably taken with a sufficient amount of water.

Further, the washing of the surface layer of the sand layer with stirring is achieved, and the suspended matter, dust and the like accumulated on the surface of the sand layer can be removed, and a stable water intake can be secured.

[Brief description of the drawings]

FIG. 1 is a partially broken perspective view showing an embodiment of a seawater intake system and a seawater intake method according to the present invention.

FIG. 2 is a sectional view showing an embodiment of a seawater intake system and a seawater intake method according to the present invention.

FIG. 3 is a graph showing a relationship between a particle diameter and a critical actual flow velocity.

FIG. 4 is a diagram illustrating a water intake principle of a seawater intake system and a seawater intake method according to the present invention.

FIG. 5 is an explanatory diagram showing an example of an installation location of a water intake unit in the seawater intake system and the seawater intake method according to the present invention.

[Explanation of symbols]

 2 seabed 3 sand layer 4 land 5 sea 10 water pipe 12 horizontal water pipe 14 vertical water pipe 16 water tank

Claims (5)

[Claims] 1. A system for taking in seawater that naturally penetrates from the sea through the sand layer by means of a water intake section formed by burying an intake pipe in a sand layer on the seabed. A seawater intake system characterized in that the developed seawater permeation flow rate is 1.0 to 8.0 (m / day). 2. The water depth of the sand layer where the water intake portion is formed is deeper than the water depth at which the sand of the surface layer of the sand layer moves by 50 cm or more, and shallower than the water depth at which the sand moves by 1 cm or more. Item 2. A seawater intake system according to Item 1. 3. A method for taking in seawater that naturally penetrates from the sea through the sand layer by means of a water intake part formed by burying an intake pipe in a sand layer on the seabed, wherein the water intake part of the water intake part enters the sand layer. A seawater intake method, characterized in that the developed seawater permeation flow rate is 1.0 to 8.0 (m / day). 4. The water depth of the sand layer where the water intake portion is formed is deeper than the water depth at which the sand of the surface layer of the sand layer moves by 50 cm or more, and shallower than the water depth at which the sand moves by 1 cm or more. Item 4. The method for extracting seawater according to Item 3. 5. The seawater intake method according to claim 3, wherein seawater is filtered by a biofilm in the sand layer.