U.S. patent application number 14/347499 was filed with the patent office on 2014-08-14 for seawater infiltration method and water infiltration intake unit.
This patent application is currently assigned to NAGAOKA CORPORATION. The applicant listed for this patent is Hironari Arai, Takayuki Inoue, Hitoshi Mimura, Kiyokazu Mukai, Hideyuki Niizato. Invention is credited to Hironari Arai, Takayuki Inoue, Hitoshi Mimura, Kiyokazu Mukai, Hideyuki Niizato.
Application Number | 20140224746 14/347499 |
Document ID | / |
Family ID | 47994982 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140224746 |
Kind Code |
A1 |
Niizato; Hideyuki ; et
al. |
August 14, 2014 |
SEAWATER INFILTRATION METHOD AND WATER INFILTRATION INTAKE UNIT
Abstract
To clean sediments and the like trapped not only in a top layer
of a sand filtration layer, but also in intermediate layers. A
seawater infiltration method which uses a water infiltration intake
unit which is formed in advance and provided with a water intake
pipe embedded in a gravel layer which forms a deep layer of the
sand filtration layer, and a backwashing pipe embedded in a sand
layer which forms an intermediate layer and a surface layer of the
sand filtration layer, and a water suction pipe which is disposed
above the sand layer. A desired number of water infiltration intake
units are combined to form a sand filtration layer at an
installation site on an ocean floor, and they intake seawater from
the sea which has undergone natural infiltration in the sand
filtration layer and this is introduced into the water intake pipe.
The seawater infiltration rate is set at less than 400 m/day. Water
or air is injected from the backwashing pipe to agitate and blow
upward from the surface layer living organisms or sediments trapped
in intermediate layers of the sand filtration layer, and the
agitated water is sucked in by a suction pipe and recovered. The
seawater infiltration rate can be maintained as high as possible
under 400 m/day.
Inventors: |
Niizato; Hideyuki; (Osaka,
JP) ; Inoue; Takayuki; (Osaka, JP) ; Arai;
Hironari; (Osaka, JP) ; Mukai; Kiyokazu;
(Osaka, JP) ; Mimura; Hitoshi; (Osaka,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Niizato; Hideyuki
Inoue; Takayuki
Arai; Hironari
Mukai; Kiyokazu
Mimura; Hitoshi |
Osaka
Osaka
Osaka
Osaka
Osaka |
|
JP
JP
JP
JP
JP |
|
|
Assignee: |
NAGAOKA CORPORATION
Izumiotsu-shi, Osaka
JP
HITACHI ZOSEN CORPORATION
Osaka-shi, Osaka
JP
|
Family ID: |
47994982 |
Appl. No.: |
14/347499 |
Filed: |
August 6, 2012 |
PCT Filed: |
August 6, 2012 |
PCT NO: |
PCT/JP2012/070002 |
371 Date: |
March 26, 2014 |
Current U.S.
Class: |
210/747.5 ;
210/170.11 |
Current CPC
Class: |
B01D 2311/04 20130101;
C02F 1/441 20130101; B01D 61/04 20130101; B01D 2311/04 20130101;
C02F 1/004 20130101; E03B 3/04 20130101; B01D 2311/2649 20130101;
C02F 2103/08 20130101; Y02A 20/131 20180101; B01D 2311/2649
20130101 |
Class at
Publication: |
210/747.5 ;
210/170.11 |
International
Class: |
E03B 3/04 20060101
E03B003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2011 |
JP |
2011-217388 |
Claims
1. A seawater infiltration method which uses water infiltration
intake units combined to form a sand filtration layer at an
installation site on an ocean floor, wherein each of the water
infiltration intake units comprises a water intake pipe embedded in
a gravel layer which forms a deep layer of the sand filtration
layer, and a backwashing pipe embedded in a sand layer which forms
an intermediate layer and a surface layer of the sand filtration
layer, and intakes seawater from the sea which has undergone
natural infiltration in the sand filtration layer and been
introduced into the water intake pipe, comprising: setting a
seawater infiltration rate at less than 400 m/day, and injecting
water or air from the backwashing pipe to agitate and blow upward
from the surface layer living organisms or sediments trapped in
intermediate layers together with living organisms accumulated in
the surface layer, thereby preventing clogging of the sand
filtration layer.
2. The seawater infiltration method according to claim 1, wherein
the water infiltration intake units are further provided with
suction pipes disposed above the sand layer, and are combined to
form a sand filtration layer at an installation site on an ocean
floor, the method further comprising: injecting water or air from
the backwashing pipe to agitate and blow upward from the surface
layer living organisms or sediments trapped in intermediate layers
together with living organisms accumulated in the surface layer,
after which the agitated water containing the living organisms or
sediments is sucked in by the water suction pipes, thereby
preventing clogging of the sand filtration layer.
3. The seawater infiltration method according to claim 2, further
comprising using a difference in settling rates of the living
organisms or sediments blown above the sand filtration layer when
sucking in the agitated water by the water suction pipes according
to a timing at which the substances which are to be sucked in
settle in the sand filtration layer.
4. The seawater infiltration method according to claim 1, wherein
the water infiltration intake units are further provided with water
discharge pipes disposed above the sand layer, and are combined to
form a sand filtration layer at an installation site on an ocean
floor, the method further comprising: injecting water or air from
the backwashing pipe to agitate and blow upward from the surface
layer living organisms or sediments trapped in intermediate layers
together with living organisms accumulated in the surface layer,
after which the agitated water containing the living organisms or
sediments is injected by the water discharge pipes to discharge it
to outside of the sand filtration layer, thereby preventing
clogging of the sand filtration layer.
5. The seawater infiltration method according to claim 4, further
comprising using a difference in settling rates of the living
organisms or sediments blown above the sand filtration layer to
inject water from the water discharge pipes according to a timing
at which the substances which are to be discharged to outside of
the sand filtration layer.
6. A water infiltration intake unit used in the seawater
infiltration method according to claim 4, wherein the water
discharge pipe injects water in a direction other that in which the
water infiltration intake units are adjacent, and the angle of
injection of the water is in a range of 30-60.degree. with respect
to a horizontal plane.
7. A seawater infiltration method which uses a water intake pipe
embedded in a deep layer of a sand filtration layer and a
backwashing pipe which injects water or air and which is embedded
in the intermediate layers of the sand filtration layer, and
intakes seawater from the sea which has undergone natural
infiltration in the sand filtration layer and been introduced into
the water intake pipe, the method comprising: setting a seawater
infiltration rate at less than 400 m/day, and injecting water or
air from the backwashing pipe to agitate and blow upward from the
surface layer living organisms or sediments trapped in intermediate
layers together with living organisms accumulated in the surface
layer, thereby preventing clogging of the sand filtration
layer.
8. The seawater infiltration method according to claim 7, wherein a
water suction pipe is further installed above the surface layer of
the sand filtration layer, and water or air are injected from the
backwashing pipe to agitate and blow upward from the surface the
living organisms or sediments trapped in the intermediate layers of
the sand filtration layer together with living organisms or
sediments accumulated on the surface of the sand filtration layer,
after which the agitated water containing the living organisms or
sediments is sucked in by the water suction pipe, thereby
preventing clogging of the sand filtration layer.
9. The seawater infiltration method according to claim 7, wherein a
water discharge pipe is further installed above the surface layer
of the sand filtration layer, and water or air are injected from
the backwashing pipe to agitate and blow upward from the surface
the living organisms or sediments trapped in the intermediate
layers of the sand filtration layer together with living organisms
or sediments accumulated on the surface of the sand filtration
layer, after which water is injected from the water discharge pipe,
thereby preventing clogging of the sand filtration layer.
Description
TECHNICAL FIELD
[0001] The present invention relates to a filtration method
employed for intake of seawater which infiltrates through a sand
layer on an ocean floor, and a water infiltration intake unit for
implementing the filtration method which has a backwashing pipe or
the like which prevents clogging by removing living organisms or
sediments which accumulate in a surface layer of the sand layer and
which become trapped in intermediate layers.
BACKGROUND ART
[0002] As shown in FIG. 14, as an example of a present seawater
intake method, a direct water intake method is used in which
seawater is taken in from a water intake orifice 1 via a water
conduit 2 provided on the ocean floor. In FIG. 14, Reference
Numeral 3 is a pump for taking in the seawater, and Reference
Numeral 4 is a reverse osmosis membrane system.
[0003] However, when employing the direct water intake method,
debris, sediments, and living organisms are all taken in at the
same time together with seawater, and thus there are cases in which
water intake has to be stopped, for example, when there is abnormal
adhesion of jellyfish or algal blooms, oil spill accidents, and
increased turbidity due to high waves. Moreover, when employing the
direct water intake method, it is necessary to perform periodic
cleaning, to add chemicals (e.g., chlorine) to prevent adhesion, or
to increase the diameter of pipes when living organisms becoming
attached to the entire length of the pipes are taken into
consideration, because the adhesion of sea life such as barnacles
and mussels can be significant. In addition, when intake seawater
is treated by reverse osmosis in the direct water intake method, a
sand filtration system must be installed for filtering seawater to
which a coagulant has been added, and thus there is a need to
install a system for treating sludge which accumulates in the sand
filtration system.
[0004] Accordingly, in recent years, attention has been focused on
indirect water intake methods which take in seawater from a sand
layer 5 (referred to below as a sand filtration layer) on the ocean
floor, as shown in FIG. 15, without using chemicals such as
coagulants to pre-treat the intake seawater.
[0005] As illustrated in FIG. 16, an indirect water intake method
is a method which involves excavation of an ocean floor at an
offshore site several hundred meters from a shoreline and at a
depth of several tens of meters, forming a sand filtration layer 5
from supporting gravel layers 5a and 5b, and a filtration sand 5c,
and implementing backfilling up to the same ocean floor surface to
install an intake pipe 6 in the supporting gravel layer 5a, from
which seawater which is purified by filtration is taken in.
Although none of the problems of the direct water intake method
arises when this indirect water intake method is employed, there
are problems such as initial high cost and reduced water intake
volume due to clogging at the infiltration surface, and
consequently, this method has been slow in achieving widespread
use.
[0006] A method is disclosed in Patent Reference 1 for achieving a
stable water intake using a seawater infiltration intake method,
which makes it possible to reduce as much as possible clogging of
the sand filtration layer which takes in seawater on the ocean
floor, and which makes it possible to remove sediments which
accumulate on the surface of the sand filtration layer without a
lot of labor.
[0007] The seawater infiltration intake method disclosed in Patent
Reference 1 is characterized in that the seawater infiltration rate
achieved in the sand filtration layer on the ocean floor is set at
1-8 m/day, and it is also characterized in that the water depth of
the sand filtration layer is greater than the critical water depth
for total sediment movement at which sand in the surface layer
portion of the sand filtration layer travels at least 50 cm, and
less than the critical water depth for surface layer movement at
which the sand travels at least 1 cm.
[0008] However, in the seawater infiltration intake method
disclosed in Patent Reference 1, a large surface area is needed for
the intake of a large volume of seawater in a short period of time,
because the seawater infiltration intake rate of 1-8 m/day is a
very slow infiltration rate, and therefore requires a large-scale
construction (Problem 1).
[0009] In addition, in the seawater infiltration intake method
disclosed in Patent Reference 1, it is necessary to install the
filtration intake system in the ocean area where the optimum flow
of seawater is obtained, so as to prevent clogging of the sand
filtration layer by silt (or sludge) which accumulates in the
surface layer, thereby limiting it to sites where seawater is moved
by waves (Problem 2).
[0010] Accordingly, in order to solve Problem 1 described above,
the present applicant proposed a seawater infiltration method which
increases the seawater infiltration intake rate to thereby greatly
reduce the infiltration surface area and significantly reduce the
scale of construction. However, the upper limit for the intake rate
that could be realistically implemented was 400 m/day.
[0011] In addition, the present applicant proposed a seawater
infiltration intake method which prevents clogging by manually
removing living organisms or sediments which become trapped in the
surface layer of the sand filtration layer. The present applicant
also proposed a device for preventing clogging, which involved
installing some type of a water-jet device such as a mechanical
type or pneumatic type, for example, for removing the sediments
trapped in the surface layer of the sand filtration layer. This
made it possible to install a sand filtration layer in a calm ocean
area where water is not moved rapidly by currents or waves, for
example.
[0012] According to the seawater infiltration method proposed by
the present applicant, the volume of intake water can be increased
in a short period of time, and the water intake surface area can be
reduced in comparison with the prior art, by setting the seawater
infiltration rate as high as possible under 400 m/day. Furthermore,
if a device for preventing clogging is installed in the surface
layer of the sand filtration layer, there is no longer a need to
install the infiltration intake system in the ocean area where the
optimum seawater flow is obtained, thus making it possible to take
in water near a seawater desalination plant. It is therefore
possible to greatly reduce the scale of construction and the scale
of the water intake system, and it is also possible greatly
mitigate effects on the surrounding environment during
construction.
[0013] However, in a method which utilizes the movement of
seawater, or in the case of a method which injects water and the
like from a clogging prevention device installed on the surface of
the sand filtration layer, it is only possible to remove sediments
which accumulate in the surface layer of the sand filtration layer,
and it is not possible to remove living organisms and sediments
trapped in intermediate layers which are deeper than the surface
layer of the sand filtration layer. In particular, in cases where
the seawater infiltration rate is set as high as possible under 400
m/day, clogging readily progresses in the intermediate layers of
the sand filtration layer as well, so clogging occurs more
frequently.
[0014] Accordingly, there is a possibility that the seawater
infiltration rate will drop if only the sediments which accumulate
in the surface layer of the sand filtration layer are removed.
[0015] In addition, in the seawater infiltration intake method
disclosed in Patent Reference 1, the construction involved in
installation is on a large scale, because the supporting gravel
layer 5a is formed in the excavated portion of the ocean floor and
the intake pipe 6 is buried therein, and the supporting gravel
layer 5b and the filtration sand 5c are formed on top of the
supporting gravel layer 5a, while implementing backfilling up to
the same ocean floor surface, and all of this is done on site on
the ocean floor. Moreover, if a defect occurs in a part of the
intake pipe 6 after the system starts operating, the surface of the
ocean floor will have to be excavated again to repair a
malfunctioning part of the intake pipe 6. Patent Reference 1:
Japanese Patent No. 3899788
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0016] The problems which the present invention aims to solve are
that the prior art seawater infiltration intake method relies on
washing by the movement of seawater or by means of the clogging
prevention device installed on the surface of the sand filtration
layer and this is not able to remove living organisms or sediments
trapped in the intermediate layers of the sand filtration layer,
and there is a possibility of a reduced seawater infiltration rate.
In addition, in the prior art method, installation involved
large-scale construction. In the event that a defect occurs in a
part of the intake pipe after the system starts operating, the
surface of the ocean floor has to be excavated again to repair a
malfunctioning part.
Means for Solving this Problem
[0017] The present invention has as its object to solve the
above-described problems, and to provide a seawater infiltration
method and a water infiltration intake unit which is able to remove
not only living organisms and sediments which accumulate in the
surface layer of a sand filtration layer, but also to remove living
organisms and sediments which are trapped in intermediate layers,
and the unit can be installed on an ocean floor with construction
on a small scale, and it can be easily maintained.
[0018] The seawater infiltration method according to the present
invention uses water infiltration intake units combined to form a
sand filtration layer at an installation site on an ocean floor.
Each of the water infiltration intake units comprises a water
intake pipe embedded in a gravel layer which forms a deep layer of
the sand filtration layer, and a backwashing pipe embedded in a
sand layer which forms an intermediate layer and a surface layer of
the sand filtration layer, and intakes seawater from the sea which
has undergone natural infiltration in the sand filtration layer and
been introduced into the water intake pipe. The method
comprises
[0019] setting a seawater infiltration rate at less than 400 m/day,
and
[0020] injecting water or air from the backwashing pipe to agitate
and blow upward from the surface layer living organisms or
sediments trapped in intermediate layers together with living
organisms accumulated in the surface layer, thereby preventing
clogging of the sand filtration layer.
[0021] According to the present method described above, living
organisms or sediments trapped in intermediate layers of a sand
filtration layer are agitated by air or water injected from a
backwashing pipe, and these are blown above the sand filtration
layer together with sediments present in the surface layer. The
sediments which were blown upward in the sea above the sand
filtration layer are dispersed to outside of the sand filtration
layer by the movement of seawater produced by currents or
waves.
[0022] The present invention described above makes it possible to
easily form a sand filtration layer, by combining water
infiltration intake units which were formed in advance and
arranging them at an installation site on an ocean floor. In the
event that a defect occurs in a part of the intake pipe after the
system starts operating, the water infiltration intake unit which
includes a malfunctioning part such as a pipe can be separated and
replaced as a unit module, without needing to excavate the surface
of the ocean floor to repair the malfunctioning part.
[0023] In the present invention described above, if the sand
filtration layer is installed in a calm ocean area where water is
not moved rapidly by currents or waves, clogging of the sand
filtration layer may be prevented by forming water infiltration
intake units in advance, being also equipped with a water suction
pipe and installed on the upper portion of the sand filtration
layer, and combining a desired number of these water infiltration
intake units at the installation site on the ocean floor, injecting
water or air from the backwashing pipe to agitate and blow upward
from the surface layer living organisms and sediments trapped in
intermediate layers together with living organisms and sediments
accumulated in the surface layer, after which the agitated water
containing the living organisms and sediments is sucked in by the
water suction pipe.
Advantageous Effects of the Invention
[0024] According to the present invention, clogging can be
prevented by removing living organisms or sediments accumulated in
the surface layer and trapped in the intermediate layers of the
sand filtration layer, and continuous high-speed filtration can be
achieved, by maintaining the seawater infiltration rate as high as
possible under 400 m/day. Moreover, when water infiltration intake
units of the present invention are combined to form the sand
filtration layer, the scale of construction during installation in
greatly reduced. In addition, it becomes easy to maintain the
system, because after the system starts operating, a water
infiltration intake unit with a problem can be separated and
replaced as a unit module.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a drawing illustrating an example of a water
infiltration intake unit used in the seawater infiltration method
of the present invention, in a case where the unit is of a size
that can be mounted on a truck. FIG. 1(a) is a sectional view along
the line A-A' of a planar view; FIG. 1(b) is a sectional view along
the line B-B' of a planar view; and FIG. 1(c) is a drawing viewed
from a planar direction.
[0026] FIG. 2 is a drawing illustrating the various pipes of the
water infiltration intake unit of the present invention viewed from
a planar direction. FIG. 2(a) is a planar view of the water suction
pipe; FIG. 2(b) is a planar view of the backwashing pipes; and FIG.
2(c) is a planar view of the water intake pipe.
[0027] FIG. 3 is a drawing illustrating examples of arrangement of
water intake pipes of the water infiltration intake units of the
present invention. FIG. 3(a) illustrates an arrangement in a case
where water intake pipes in 5 blocks are connected in a bus-type
arrangement, and FIG. 3(b) illustrates an arrangement in a case
where intake pipes in 5 blocks are connected to respective pump
pits.
[0028] FIG. 4 is a drawing illustrating an example of the
connection of backwashing pipes of the water infiltration intake
units of the present invention. FIG. 4(a) illustrates the
connection of a pump when a construction is used in which water is
injected, and FIG. 4(b) illustrates the connection to an air
compressor when a construction is used in which air is
injected.
[0029] FIG. 5 is a drawing illustrating examples of the dimensions
and arrangement of the water infiltration intake units of the
present invention. FIG. 5(a) illustrates an example when the water
intake volume is set at 100,000 t/day, and FIGS. 5(b) and (c)
illustrate an example when the water intake volume is set at
400,000 t/day, and another example.
[0030] FIG. 6 is a drawing illustrating an example of a water
infiltration intake unit of the present invention which uses a
water discharge pipe. FIG. 6(a) is a sectional view along line A-A'
of a planar view; FIG. 6(b) is a sectional view along the line B-B'
of a planar view; and FIG. 6(c) is a drawing viewed from a planar
direction.
[0031] FIG. 7 is a drawing illustrating another example of a water
infiltration intake unit of the present invention which uses a
water discharge pipe. FIG. 7(a) is a drawing of a backwashing pipe
viewed from a planar direction, and FIG. 7(b) is a schematic
drawing of a branch pipe of a water discharge pipe viewed from a
cross-sectional direction, and the drawing illustrates the angle of
injection of water from a water discharge pipe.
[0032] FIG. 8 is a drawing illustrating an example of the
arrangement of water intake pipes and backwashing pipes in the
direction of height within a unit module of a water infiltration
intake unit of the present invention.
[0033] FIG. 9 is a drawing illustrating an example of a water
infiltration intake unit of the present invention which is not
provided with water suction pipes or water discharge pipes. FIG.
9(a) is a sectional view along the line A-A' of a planar drawing;
FIG. 9(b) is a sectional view along the line B-B' of a planar
drawing; and FIG. 9(c) is a drawing viewed from a planar
direction.
[0034] FIG. 10 is a drawing illustrating an experimental flow of a
seawater infiltration method.
[0035] FIG. 11 is a graph showing experimental results. FIG. 11(a)
is a graph showing turbidity data, and FIG. 11(b) is a graph
showing silt density index (SDI) data.
[0036] FIG. 12 is a graph showing the relationship between the
passage of time and the loss of pressure in the case of total
blockage and in the case of standard blockage.
[0037] FIG. 13 is a drawing illustrating the seawater infiltration
method of the present invention.
[0038] FIG. 14 is a schematic drawing illustrating a direct
seawater intake method of the prior art.
[0039] FIG. 15 is a schematic drawing illustrating an indirect
water intake method of the prior art.
[0040] FIG. 16 is a schematic structural diagram of ocean floor
filtration elements.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0041] According to the present invention, the object of preventing
clogging of the sand filtration layer to maintain the seawater
infiltration rate as high as possible under 400 m/day is achieved
by agitating the living organisms or sediments trapped in the
intermediate layers of the sand filtration layer and blowing them
upward from the surface layer by means of water or air injected
from a backwashing pipe, together with the living organisms or
sediments accumulated in the surface layer, in order to continually
implement high-speed filtration.
[0042] It desirable that clog-causing substances which are
contained in the living organisms and sediments which are blown
above the sand filtration layer are recovered by a water suction
pipe provided at the top of the sand layer, so that these
substances do not have a negative effect on the environment
surrounding the sand filtration layer.
[0043] In the case of ocean areas where there is relatively little
need to protect the environment, there are instances in which it is
permitted to discharge into the surrounding area of the sand
filtration layer, clog-causing substances including the living
organisms and sediments which are blown above the sand filtration
layer. In cases where a sand filtration layer is installed in such
an ocean area, one of the configurations described below should be
selected, depending on the flow rate of the seawater.
[0044] If installation is done in an ocean area where the flow of
seawater is slow, a structure is used whereby clog-causing
substances are manually discharged by means of a discharge pipe
provided above the sand layer. On the other hand, if installation
is done in an ocean area where the flow of seawater is rapid,
clog-causing substances are dispersed by the movement of seawater
produced by currents or waves, so a structure may be employed which
is not provided with water suction pipes or water discharge
pipes.
EXAMPLES
[0045] An embodiment of the present invention is described in
detail below, using FIG. 1 to FIG. 13.
[0046] FIG. 1 is a drawing illustrating an example of a water
infiltration intake unit 11 used in the seawater infiltration
method of the present invention.
[0047] In FIG. 1(a) and FIG. 1(b), Reference Numeral 12 is a water
intake pipe embedded in a gravel layer 13 which forms a deep layer
of a sand filtration layer on the ocean floor. The water intake
pipe 12 is formed from a main pipe 12a and a plurality of branch
pipes 12b which branch in a direction crossing the main pipe 12a.
Embedded in a sand layer 15 formed from intermediate layers 15b and
15c and a surface layer 15a of a sand filtration layer is a
backwashing pipe 14 formed from a main pipe 14a and a plurality of
branch pipes 14b which branch in a direction crossing the main pipe
14a.
[0048] In FIG. 1(c), Reference Numeral 16 is a water suction pipe
formed from a main pipe 16a and a plurality of branch pipes 16b. As
shown in FIG. 1(a), the main pipe 16a is constructed between
mutually facing side surfaces 17a and 17c of a frame 17. As shown
in FIG. 1(b), the end portions of the plurality of branch pipes 16b
which branch in a direction crossing the main pipe 16a are
supported by side surfaces 17b and 17d of the frame 17. According
to such a configuration, the water suction pipe 16 is installed
above the sand layer 15, being spaced by a distance from the upper
surface of the sand layer 15.
[0049] The water infiltration intake unit 11 of the present example
is constructed with the frame 17 which measures, for example, 10 m
in length.times.2.5 m in width.times.2.5 m in height, and which
houses the water intake pipe 12 embedded in a central position in
the direction of height of the gravel layer 13 which has a height
of 0.5 m, the backwashing pipe 14 embedded in an upper portion of
in the direction of height of the sand layer 15 which has a height
of 2.0 m, and the water suction pipe 16 disposed above the upper
surface of the sand layer 15. Accordingly, the water infiltration
intake unit 11 can be transported on a truck having a platform on
which a load of the above-described size can be mounted, making it
easy to transport on land. An optimal material for the frame 17 may
be selected from FRP, concrete, metal, or the like, depending on
the water quality in the ocean area where the sand filtration layer
is installed, and depending on the components of the substances
contained in the seawater.
[0050] FIG. 2 is a drawing illustrating the various pipes of the
water infiltration intake unit 11, as viewed from a planar
direction. The lower portion of the drawing is a land side where a
seawater desalination plant is provided, and the upper portion of
the drawing is an ocean side.
[0051] As shown in FIG. 2(a), there are provided in the branch
pipes 16b of the water suction pipe 16 a plurality of suction holes
16ba and 16bb arranged in rows on the land side and on the ocean
side. In the present example, the suction holes 16ba on the land
side and the suction holes 16bb on the ocean side open parallel to
a lengthwise direction of the main pipe 16a, and when installed on
site, they are oriented so that the blowing angle of the blow holes
are oriented parallel to the horizontal direction. The land side of
the main pipe 16a is connected to a water collection pump of the
seawater desalination plant. Turbid water sucked in by the suction
holes 16ba and 16bb is collected in the main pipe 16a from the
branch pipes 16b, and recycled to the seawater desalination
plant.
[0052] As shown in FIG. 2(b), a plurality of blow holes 14ba are
arranged in rows in the branch pipes 14b of the backwashing pipe 14
in a position on the side facing upward when installed on site. In
the present example, the blowing angle of the blow holes 14ba is
90.degree. with respect to the horizontal position. The land side
of the main pipe 14a is connected to a water supply pump or an air
compressor of the seawater desalination plant. Water or air fed
from the main pipe 14a to the branch pipes 14b is blown from the
blow holes 14ba upwardly in a perpendicular direction. In the
present example, the blow holes 14ba are provided in a direction
facing upward when installed on site, for instance, but the blow
holes 14ba of the backwashing pipe 14 may be configured so as to
face downward when installed on site.
[0053] The branch pipes 12b of the water intake pipe 12 are
provided with a plurality of water intake holes on the entire
surface area (not shown in FIG. 2(c)). The land side of the main
pipe 12a is connected to a water collection pump of the seawater
desalination plant. Seawater which has undergone natural
infiltration in the sand filtration layer is introduced into the
branch pipes 12b by the water intake holes, and taken into the
seawater desalination plant via the main pipe 12a.
[0054] The seawater infiltration method according to the present
invention uses the above-described water infiltration intake units
11 which are built on land in advance, and a certain number of
water infiltration intake units 11 are combined to form a sand
filtration layer at an installation site on an ocean floor.
Seawater which has undergone natural infiltration in the sand
filtration layer in the ocean is introduced into the water intake
pipe 12, and the seawater infiltration rate is set at less than 400
m/day. Living organisms or sediments trapped in the intermediate
layer 15b, which is above the backwashing pipe 14, are agitated by
blowing water or air from the blow holes 14ba of the backwashing
pipe 14 upward at an angle of +90.degree. or downward at an angle
of -90.degree. with respect to a horizontal plane, thereby blowing
them upward in the ocean above the sand filtration layer, together
with living organisms accumulated in the surface layer of the sand
filtration layer. After that, the agitated water containing the
living organisms or sediments is sucked in by the water suction
pipe 16 installed above the surface layer of the sand filtration
layer. By operating in this manner, the living organisms or
sediments which are blown upward above the sand filtration layer
are recovered without accumulating again on the surface of the sand
filtration layer, thereby making it possible to reliably prevent
clogging of the sand filtration layer.
[0055] The living organisms or sediments which are blown upward
above the sand filtration layer not only contain clog-causing
components such as silt, but also contain substances with a
particle diameter suitable for supporting the seawater filtration
effect in the sand filtration layer.
[0056] Accordingly, in this example, using a difference in settling
rates of the living organisms or sediments blown upward by water or
air blown from the backwashing pipe 14 into the seawater above the
sand filtration layer, the agitated water is sucked in by the water
suction pipe 16 according to a timing at which the clog-causing
substances settle in the sand filtration layer. It is therefore
possible in this example to leave in the sand filtration layer
substances which serve to support the filtration effect by sucking
out only those clog-causing substances.
[0057] Following is a specific example of a method of installing
and connecting the water infiltration intake units 11 of the
present invention, with regard to the size of a water intake area
formed by assembling a water infiltration intake block 110.
[0058] FIG. 3 is a drawing illustrating examples of arrangement of
water intake pipes 12 of the water infiltration intake units 11. In
this example, a water intake pipe block 120 is formed by arranging
horizontally 7 water intake pipes 12. In the case of such a
configuration, the water intake pipe blocks 120 may be connected to
a water collection pump which integrates 5 of the water intake pipe
blocks 120 into a single unit by using a shared pipe 18, as shown
in FIG. 3(a). Alternatively, each of the water intake pipe blocks
120 may be separately connected to a water collection pump set
19.
[0059] FIG. 4 is a drawing illustrating an example of the
connection of backwashing pipes 14 of the water infiltration intake
units 11. In this example, a backwashing pipe block 140 is formed
by arranging 7 backwashing pipes 14 in parallel in a row. In the
present invention, water or air may be injected from the
backwashing pipes 14, in order to agitate living organisms or
sediments accumulated in the surface layer of the sand filtration
layer and trapped in intermediate layers and to blow them into the
sea above the sand filtration layer. If a structure is used for
injecting water, the backwashing pipe block 140 is connected to a
water supply pump 20, as shown in FIG. 4(a). On the other hand, if
a structure is used for injecting air, then the backwashing pipe
block 140 is connected to an air compressor 21.
[0060] FIG. 5 is a drawing illustrating examples of the dimensions
and arrangement of the water infiltration intake units 11 of the
present invention. In the example shown in FIG. 5(a), the structure
consists of water infiltration intake blocks 110 constructed with 8
or 9 water infiltration intake units 11 which are each 10 m in
length in the lengthwise direction of the main pipes 12a, 14a, and
16a and are arranged in parallel in a row. Then, four of these
water infiltration intake blocks 110 are arranged in parallel in a
row to form a water intake area 1100 having a size 10 m.times.105 m
(not including the sheet thickness of the frame).
[0061] In the present invention, the seawater infiltration rate is
set at less than 400 m/day, and if the seawater infiltration rate
is set at 100 m/day, and if the infiltration surface area is set at
30 m.sup.2 per each unit module of the water infiltration intake
units 11, then the amount of water collected would be 3,000
m.sup.3/day per each unit module of the water infiltration intake
units 11. In a case where the water intake area 1100 is formed from
about 35 water infiltration intake units 11, as in the example
shown in FIG. 5(a), the total amount of water collected would be
about 100,000 t/day. This is about the scale of water intake at the
"Mamizu Pia" seawater desalination facility in Fukuoka Prefecture,
Japan.
[0062] If the daily water intake volume needs to be increased to
400,000 t/day, for example, then four water intake areas 1100 of
FIG. 5(a) may be arranged as illustrated in FIG. 5(b) and FIG.
5(c). In this case, it is possible to obtain a water intake volume
of 400,000 t/day using a water intake area of 25 m.times.ca 270 m
in the example of FIG. 5(b), and 210 m.times.ca 25 m in the example
of FIG. 5(c), and these are much smaller than in the conventional
osmotic water intake method.
[0063] In the present invention, the water intake pipe 12, the
gravel layer 13, the backwashing pipe 14, the sand layer 15, and
the water intake pipe 15 are formed into a unit, and an optimal
arrangement can be selected according to the topology of the ocean
area where installation takes place. It is also possible to
accommodate a required daily water intake volume by varying the
number of units combined as described above.
[0064] According to the present invention, if damage occurs in some
of the water infiltration intake units 11, the system as a whole
affected little, because it is necessary to replace only the
damaged water infiltration intake units 11. Moreover, the
maintenance construction is on a small scale, and the maintenance
can be reduced, because there is no need to excavate the surface of
the ocean floor when replacing the water infiltration intake units
11.
[0065] FIG. 6 is a drawing illustrating an example of a water
infiltration intake unit of the present invention in a case where a
water discharge pipe is used as a means to remove living organisms
or sediments which are blown upwards in the ocean. In the
description given below, only the items which are different from
the construction of example of FIG. 1 which uses the water suction
pipe 16 are explained.
[0066] In FIG. 6, Reference Numeral 22 is a water discharge pipe
formed from a main pipe 22a and a plurality of branch pipes 22b. As
shown in FIG. 6(a), the main pipe 22a is constructed crosswise
between the opposite side surfaces 17a and 17c of the frame 17.
Moreover, as shown in FIG. 6(b), the end portions of the plurality
of branch pipes 22b which branch in a direction crossing the main
pipe 22a are supported by side surfaces 17b and 17d of the frame
17. According to such a configuration, the water discharge pipe 22
is installed above the sand layer 15, being spaced apart by a
distance from the upper surface of the sand layer 15.
[0067] The branch pipes 22b are provided with a plurality of
injection holes on the ocean side (these are not depicted in FIG.
2(b) because the drawing is viewed from the land side). The
injection holes open in parallel in a lengthwise direction of the
main pipe 22a, and when installed on site, they are oriented so
that the suction angle of the suction holes are oriented parallel
to the horizontal direction. The land side of the main pipe 22a is
connected to a water supply pump of the seawater desalination
plant. Water fed to the branch pipes 22b by the main pipe 22a is
injected from the injection holes in a horizontal direction to the
ocean side.
[0068] Accordingly, in this example, living organisms or sediments
trapped in the intermediate layers of the sand filtration layer are
agitated by water or air injected from the backwashing pipe 14 and
blown upward above the surface layer, together with living
organisms accumulated in the surface layer, after which they are
dispersed to outside of the sand filtration layer by water injected
from the water discharge pipe 22.
[0069] FIG. 7 is a drawing illustrating another example of a water
infiltration intake unit of the present invention which uses a
water discharge pipe, wherein the water discharge pipe 23 is viewed
from a planar direction. The right side of the drawing is the land
side where a seawater desalination plant is installed, and the left
side of the drawing is the ocean side (in the direction of the
arrows). In this example, there are no other water infiltration
intake units adjacently disposed on the ocean side.
[0070] As shown in FIG. 7(a), a plurality of injection holes 23bb
are arranged in rows only on the ocean side in the branch pipes 23b
of the water exhaust pipe 23. FIG. 7(b) is a schematic drawing of a
branch pipe 23b of a water discharge pipe 23 viewed from a
cross-sectional direction, and the drawing illustrates the angle of
injection .theta. of water from an injection hole 23bb. In this
example, the angle of injection .theta. can be variably set within
a range of 30-60.degree. with respect to a horizontal plane by
installing a nozzle at the injection hole 23bb. The land side of
the main pipe 23a is connected to a water supply pump of a seawater
desalination plant. For example, if the angle of injection of the
injection hole 23bb is set at 45.degree., then water fed from the
main pipe 23a to the branch pipe 23b is injected upward from the
injection hole 23bb on the ocean side at a 45.degree. angle with
respect to a horizontal plane.
[0071] Accordingly, in this example, the water discharge pipe 23 is
formed so as to inject water in a direction other than the
direction in which the water infiltration intake units are
adjacent, and the angle of injection of the water is in a range of
30-60.degree. with respect to a horizontal plane.
[0072] Therefore, in this example, clog-causing sediments and the
like which are discharged by the discharge pipe 23 do not settle on
top of the sand filtration layer of other water infiltration intake
units. Moreover, in the present example, water injected from the
injection hole 23bb forms a parabolic curve, thereby making it
possible to discharge to a greater distance the clog-causing
sediments and the like.
[0073] Incidentally, if the living organisms or sediments which
accumulate on the ocean floor are unnecessarily discharged into the
surrounding area, they can affect the surrounding natural
environment in some manner.
[0074] Accordingly, in this example, using differences in settling
rates of the living organisms or sediments blown upward by water or
air blown from the backwashing pipe 14 into the seawater above the
sand filtration layer, water is injected from the water discharge
pipe 23 according to a timing at which the clog-causing substances
settle in the sand filtration layer. Thus, in the present example,
it is possible to have very little effect on the surrounding
natural environment.
[0075] FIG. 8 is a drawing illustrating an example of the
arrangement of the water intake pipes 12 and the backwashing pipes
14 in the direction of height within a unit module of a water
infiltration intake unit 11 of the present invention. In the
present invention, the water infiltration intake unit 11 should not
be too far from a bottom surface 17e of the frame 17 of the water
infiltration intake unit 11, so as not to reduce the filtration
capacity. Specifically, if the outer diameter of the water
infiltration intake unit 11 is set at D, the COP (center of pipe)
height of the water intake pipe 12 should be in a range of 0.75 D
to 1.25 D above the bottom surface 17e.
[0076] The backwashing pipe 14 is advantageously installed at a
position as deep as possible, so as to achieve a broad range of
backwashing of the sediments accumulated in the surface layer or
trapped in the intermediate layers of the sand filtration layer.
However, if the installation position is too deep, a high water
pressure is required, so consideration must be given to balancing
these two. Specifically, if the outer diameter of the backwashing
pipe 14 is set at d, the COP (center of pipe) height of the
backwashing pipe 14 is in a range of 1.0 d to 5.0 d below a surface
15d of the sand layer of the sand filtration layer.
[0077] FIG. 9 is a drawing illustrating an example of a water
infiltration intake unit of the present invention which uses the
movement of seawater as a means for removing living organisms or
sediments blown upward in the seawater. Except for the fact that
there is no water suction pipe 16 or no water discharge pipe 22,
the structure of FIG. 9 is identical to that of the example of FIG.
1. In this example, the living organisms and sediments trapped in
the intermediate layers of the sand filtration layer are blown
upward from the surface layer by water or air injected from the
backwashing pipe 14, together with the living organisms and
sediments accumulated on the surface of the sand filtration layer,
and dispersed to outside of the sand filtration layer by the
movement of seawater produced by currents or waves.
[0078] Following is an explanation of the reason why the seawater
infiltration rate is set at under 400 m/day in the seawater
filtration method of the present invention.
[0079] FIG. 10 is a diagram illustrating an experimental flow of a
seawater infiltration method of the present invention. In FIG. 10,
Reference Numeral 31 is a water intake pump immersed at a position
50 cm from the ocean floor and 3.3 m from the surface of the water.
Reference Numeral 32 is a raw water tank which holds seawater which
is drawn up by the water intake pump 31. The seawater held in the
raw water tank 32 is drawn up by a raw water pump 33, and fed to a
column device 34. The column device 34 is provided with a
filtration layer formed from a sand layer 34a and a gravel layer
34b, and filtered water which has passed through this filtration
layer is guided to a treated water tank 35.
[0080] In the experimental flow shown in FIG. 10, there are
provided a reverse conduit pipe 37 which sends back the filtered
water from the treated water tank 35 to the column device 34 using
an interposed reverse-direction pump 36. An overflow pipe 38 is
also provided to guide the seawater fed to the column device 34 to
the treated water tank 35 so it does not overflow.
[0081] The turbidity and silt density index SDI of the filtered
water are measured after the seawater is taken in by the water
intake pump of the experimental flow device and filtered through a
filtration layer of the column device. The filtration layer used in
this measurement consists of a 0.45 mm diameter sand layer
(thickness 900 mm), a 2-4 mm diameter gravel layer (thickness 75
mm), a 4-8 mm gravel (thickness 75 mm), and a 6-12 mm gravel
(thickness 150 mm).
[0082] The results of measurement are given in FIG. 11. To the raw
water for which turbidity data is obtained is added in advance a
quantity of silt such that the turbidity is that for a water
infiltration intake rate of 0 m/day shown in FIG. 11(a). If the
seawater infiltration rate is set at 50-400 m/day, the turbidity
and silt density index SDI do not change from the conventional case
where the seawater infiltration rate is set at 1-8 m/day, which
confirms that the same treatment capacity was indicated.
[0083] Incidentally, in the invention disclosed in Patent Reference
1, the seawater infiltration rate occurring in the sand filtration
layer on the ocean floor is set at 1-8 m/day, and the sand
filtration layer is set at a depth greater than the critical water
depth for total sediment movement at which sand in the surface
layer portion of the sand filtration layer travels at least 50 cm,
and less than the critical water depth for surface layer movement
at which the sand travels at least 1 cm.
[0084] Following is an explanation of the reason why the conditions
under which the seawater infiltration rate occurs are such that the
sand filtration layer is set at a depth greater than the critical
water depth for total sediment movement at which sand in the
surface layer portion of the sand filtration layer travels at least
50 cm, and less than the critical water depth for surface layer
movement at which the sand travels at least 1 cm in the invention
disclosed in Patent Reference 1.
[0085] The reason why the sand in the surface of the sand
filtration layer travels at least 1 cm at the critical water depth
for total sediment movement, which is the maximum water depth at
which some degree of sand particle movement resulting from waves
can be observed on the surface of the ocean floor, is that it is
the level at which sand on the ocean floor can be washed, and if it
is at a greater water depth, then there is almost no movement of
sand particles of the surface of the sand filtration layer.
[0086] On the other hand, the reason why sand in the surface of the
sand filtration layer travels at least 50 cm at the critical water
depth for total sediment movement, which is the maximum water depth
at which the sand filtration layer on the ocean floor can be
observed to be eroded by wave action, is because erosion of the
sand filtration layer on the ocean floor is observed.
[0087] Moreover, in Patent Reference 1, the diameter of silt
particles is generally about 0.005-0.074 mm, and the flow rate of
seawater in which silt does not start moving is determined, that
is, the critical flow rate for movement is determined. The critical
flow rate for movement is obtained by multiplying the surface area
porosity (=0.35) by the actual critical flow rate of the silt
particles. According to a graph showing the relationship between
the particle diameter and the actual critical flow rate, the actual
critical flow rate was found to be 0.026 cm/s when the particle
size of silt was 0.08 mm.
[0088] Therefore, the upper limit of the critical flow rate for
movement of silt is 0.026.times.0.35.times.24.times.3600=786.24
cm/day. Based on these results, the maximum seawater infiltration
rate should be 8 m/day, in order to prevent clogging due to silt
blown upward within the sand filtration layer.
[0089] Further, the seawater infiltration rate must be at least 1
m/day, so as to supply sufficient oxygen to the sand filtration
layer to prevent the annihilation of biofilms.
[0090] Accordingly, in the invention according to Patent Reference
1, setting the seawater infiltration rate at 1-8 m/day under the
above conditions makes it possible to remove refuse and sediments
such as silt accumulated in the sand filtration layer by suitable
agitating the surface layer of the sand filtration layer with waves
and currents, thereby making it possible to secure a stable intake
of water.
[0091] The upper limit of the seawater infiltration rate specified
in the invention according to Patent Reference 1 is a condition
which was set in order to prevent penetration or admixture of silt
in the sand filtration layer on the top layer of the ocean floor.
Following up on the 8 m/day limit on silt absorption in Patent
Reference 1, the present inventors confirmed that comparable
treatment performance was exhibited as when the water infiltration
intake rate is 1-8 m/day, for example when the water infiltration
intake rate is 400 m/day, and there is a tendency for silt to be
absorbed.
[0092] In other words, it can be conjectured that if silt is not
agitated or if there is no flow field, and if the water
infiltration intake rate is set at 400 m/day, then the absorption
rate of silt to the sand filtration layer is (water infiltration
intake rate cm/s).times.(porosity resulting from the sand particle
diameter). Therefore, if the water infiltration intake rate is 400
m/day, then the absorption rate of silt into the sand filtration
layer is {40,000 cm/(24.times.3,600)}.times.0.35=0.16 cm/s. In
order to achieve a critical flow rate of at least 1.0 m/day to
supply oxygen, the absorption rate of silt into the sand filtration
layer should be {100 cm/(24.times.3,600)}.times.0.35=0.0004
cm/s.
[0093] In the above computation, if the seawater infiltration
intake rate is set at 400 m/day, it becomes difficult to achieve
washing which is feasible, because silt particles which cause
clogging enter the sand filtration layer at a rate of about 6 m/hr
(about 0.16.times.3,600/100).
[0094] However, when the silt moves together with the water, there
results what is known as a standard blockage type, because the silt
particles are much smaller than the voids in the filtration sand,
so the silt adheres in the vicinity of the surface layer and
remains, since it is detained by the intermolecular forces
(physical adhesion, static electricity) of the filtration sand and
accumulates.
[0095] In the previously described experiment in which silt
components are added, with the results given in FIG. 11(a), under
conditions where the water infiltration intake rate is set at under
400 m/day, after 2 hours, it was observed that most of the silt
accumulated in the surface layer, and there was penetration on the
order of only 1 cm inside the sand filtration layer.
[0096] Unlike total blockage which occurs when the silt particles
are larger than the voids in the filtration sand, standard blockage
occurs such that it takes time for the voids to become smaller due
to adhesion of silt particles, since the particles completely block
the voids, as shown in FIG. 12. This means that even if silt
continues to be removed, infiltration is possible for a long period
of time, because a gradual loss in pressure occurs up to the void
retention threshold value. The amount of time which passes depends
on the condition of the filtration material and the condition of
the seawater (silt density), and is an important factor in
determining the intervals of forced washing.
[0097] Based on the experimental results and findings by the
inventors as described above, the present invention achieves a
significant reduction in the scale of construction and the scale of
water intake facilities by increasing the rate of seawater
infiltration through the filtration material to a rate which had
heretofore been commonly considered taboo.
[0098] According to the results of experiments performed by the
inventors involving subterranean water which has greater
infiltration characteristics than seawater, normal continuous
operation was possible up to an infiltration rate of 600 m/day.
However, if the infiltration rate was set at 700 m/day, the amount
of water needed for cleaning exceeded the water intake volume, so
water could not continuously flow in the sand filtration layer, and
normal water intake was impossible. Therefore, in the present
invention, which employs a filtration method when there is seawater
infiltration intake, the safety factor is set at about 1.5, and the
upper limit for the seawater infiltration rate is set at 400
m/day.
[0099] For the above reason, according to the seawater infiltration
method of the present invention, the seawater infiltration rate is
set at less than 400 m/day, during seawater infiltration intake
when seawater which has undergone natural infiltration in a sand
filtration layer is introduced into a water intake pipe, the
seawater infiltration rate is set at less than 400 m/day.
[0100] In the present invention, when the seawater infiltration
rate is set at 400 m/day, the water intake volume is 50 times that
of the prior art in which the seawater infiltration rate was 8
m/day, thereby making it possible to achieve a water intake surface
area 1/50 that of the prior art. In addition, installation is no
longer necessary in ocean areas in which an optimal flow of
seawater is accelerated. As shown in FIG. 13, a water infiltration
intake facility can be installed in the vicinity of a water
desalination plant 41, thereby making it possible to significantly
reduce the scale of construction and the scale of water intake
facilities, and also making it possible to greatly mitigate effects
on the surrounding environment during construction.
[0101] Moreover, according to the seawater infiltration method of
the present invention, the seawater infiltration rate can be
maintained as high as possible under 400 m/day, and a high-speed
filtration can be implemented continuously, because clogging can be
more reliably prevented by removing living organisms and sediments
not only from the surface layer of the sand filtration layer, but
also by removing living organisms and sediments which are trapped
in the intermediate layers.
[0102] The present invention is not limited to the above-described
examples, and the preferred embodiment may, of course, be
advantageously modified within the scope of the technical ideas
recited in the claims.
[0103] For example, in the example described above, there was
disclosed a case in which the water infiltration intake units 11
were formed in advance, but in the seawater infiltration method of
the present invention, it is also possible to form a sand
filtration layer with the water intake pipe 12 and the backwashing
pipe 14 embedded at the installation site on the ocean floor,
without using the water infiltration intake units 11.
[0104] In detail, the seawater infiltration method comprises
embedding a water intake pipe in a deep layer of a sand filtration
layer, embedding a backwashing pipe, which injects water or air, in
the intermediate layers of the sand filtration layer, and intaking
seawater from the sea which has undergone natural infiltration in
the sand filtration layer and been introduced into the water intake
pipe. The method further comprises
[0105] setting a seawater infiltration rate at less than 400 m/day,
and
[0106] injecting water or air from the backwashing pipe to agitate
and blow upward from the surface layer living organisms or
sediments trapped in intermediate layers together with living
organisms accumulated in the surface layer, thereby preventing
clogging of the sand filtration layer.
[0107] In cases in which water infiltration intake units are not
used, as described above, a water suction pipe is further installed
above the surface layer of the sand filtration layer, and water or
air are injected from the backwashing pipe to agitate and blow
upward from the surface the living organisms or sediments trapped
in the intermediate layers of the sand filtration layer together
with living organisms or sediments accumulated on the surface of
the sand filtration layer. After that, the agitated water
containing the living organisms or sediments is sucked in by the
water suction pipe, thereby making it possible to prevent clogging
of the sand filtration layer without having a negative effect on
the surrounding environment.
[0108] Alternatively, another water discharge pipe is installed
above the surface layer of the sand filtration layer, and water or
air are injected from the backwashing pipe to agitate and blow
upward from the surface the living organisms or sediments trapped
in the intermediate layers of the sand filtration layer together
with living organisms or sediments accumulated on the surface of
the sand filtration layer. After that, water is injected from the
water discharge pipe, thereby making it possible to prevent
clogging of the sand filtration layer, even in calm ocean areas
where there is little movement of the seawater.
[0109] In the above example there was disclosed a structure whereby
the intermediate layers of the sand filtration layer were cleaned
by injecting water or air from the backwashing pipe 14. However, a
structure is also possible whereby the intermediate layers (sand
layers) are cleaned by the backwashing pipe 14, and the deep layers
(gravel layers) of the sand filtration layer are cleaned by
reversing the flow of water at a desired timing with respect to the
water intake pipe 12 and injecting water from the intake holes of
the branch pipe 12b.
[0110] In the above example, an example using the water suction
pipe 16 and an example using the water discharge pipes 22 and 23
were separately described. However, a structure is also possible in
which the function of the water suction pipe and the function of
the water discharge pipe are provided together in a single device,
by switching a water collection and a water feed of a pump
installed in a seawater desalination plant.
[0111] The filtration material used in the gravel layers and the
sand layers of the water infiltration intake units of the present
invention is not limited to natural gravel and sand, regardless of
quality. For example, artificial particulate ceramics or artificial
glass, which have little effect on the environment, may be used as
filter materials in the gravel layers or the sand layers. If such
artificial filtration materials are used, there is generally a
problem of greater cost, but the seawater infiltration method of
the present invention differs from the prior art in that the water
intake surface area can be significantly reduced, thus making it
easier to use artificial filtration materials such as those
described above.
EXPLANATION OF THE REFERENCE SYMBOLS
[0112] 11 Water infiltration intake unit
[0113] 12 Water intake pipe
[0114] 13 Gravel layer
[0115] 14 Backwashing pipe
[0116] 15 Sand layer
[0117] 16 Water suction pipe
[0118] 22 Water discharge pipe
[0119] 23 Water discharge pipe
* * * * *