Abstract:
The present invention is a filtered seawater collection system for installation at seaside locations. This system filters undesirable elements from seawater including garbage, debris, volatile organics and biologics such as toxic algaes. The resulting filtered seawater is then pumped to a desalination plant for de-salting. This system comprises a subterranean reservoir installed at a sheltered location, such as behind a set of dunes. A borehole is created by directional drilling, the borehole breaking through the surf line and into open ocean. A pipe is laid extending from the reservoir out to the open ocean. The pipe ends in an intake, which is overlapped by gravel packets which act as filtration media. The intake receives water filtered through the gravel packets, which is transported through the pipe to the reservoir.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This patent application claims the benefit of United States provisional patent application Ser. No. 60/737,141, filed on Nov. 15, 2005. 
     
    
     TECHNICAL FIELD  
       [0002]     This invention relates to the field of desalination of seawater and more specifically to a system and method for filtering seawater to remove suspended solids, debris and biological material prior to subjecting the seawater to desalination. The system and method of filtering seawater described herein also can be applied to cooling water intakes for power plants.  
       BACKGROUND  
       [0003]     Seawater desalination is becoming-an attractive source of drinking water in coastal states as the costs for desalination decline. A prime consideration for seawater desalination is a source of feed water that is reliable and consistent to sustain operations and produce potable water effectively and efficiently. The amount and quality of feed water entering a desalination plant is greatly dependent upon the placement of the feed water intake. Up to the present time, feed water intakes have been of two basic types, namely: 1) directly from the sea and 2) indirectly from the sea. Each of these types of intakes has significant benefits and significant drawbacks as will be further explained below.  
         [0004]     Open ocean intakes, or direct intakes can be as simple as dredged channels through a nearshore region to draw in seawater. More sophisticated direct intakes involve the construction of pipelines from shore to beyond the nearshore, out to waters deeper than 35 meters. Deeper water is desirable in that the intake is less affected by wave and tidal action, but added pumping costs and pipeline costs limit the depth to which direct intakes can be practically placed. Direct intakes are fairly long lived in that they can have a service life of 30-50 years. They also provide an unlimited supply of seawater to a desalination plant as the seawater is pumped directly to the plant. However, a first drawback of direct intakes is that they are hampered by impingement and entrainment of planktonic organisms that require additional filtration and pretreatment once the seawater arrives at the plant, thereby driving up fresh water production costs. Other common problems associated with direct intakes include biological fouling of intake pipes; trash and other debris in intakes; hydrocarbon products occurring in feed water; and recirculation of discharge to intakes. Additionally, uncertain construction permitting outcomes related to direct intakes in light of modified regulatory practices derived from Section 316(b) of the Clean Water Act plague desalination plant developers.  
         [0005]     Indirect seawater intakes include vertical beach wells, Ranney wells, and infiltration galleries. Common among these indirect seawater intakes is that they are all dependent upon the nearshore zone geology in which they are placed, to provide a filtered seawater product.  
         [0006]     Vertical beach wells are placed near a shoreline, typically very close to the nearshore in order to capture seawater filtering through the local nearshore geology. The beach well is a subterranean reservoir that is sunk with its top portion approximate to sea level, coupled to a pipe that is driven outward from the bottom of the reservoir into the nearshore geology, the pipe having a plurality of through-holes for allowing the flow of seawater into the pipe. The distance that the -pipe can be driven into the surrounding nearshore geology limits the length of pipe. As water flows into the reservoir, it fills the reservoir until the level of water in the reservoir is the same as at sea level. The water is then pumped from the reservoir to the desalination plant to be de-salted. Beach wells are advantageous because they avoid issues related to volatile organic spills and lessen potentially harmful algal blooms. Hence, the water quality provided by beach wells is excellent. However a drawback exists in that the water supply produced by a beach well is totally dependent on hydrogeologic conditions at the site. Furthermore, in comparison to the unlimited seawater supply from direct intakes, beach wells typically provide water volumes in the range of only 400-4000 cubic meters per day.  
         [0007]     A Ranney well employs a plurality of radially arranged collector wells located horizontally beneath a beach. The collector wells channel filtered seawater to a central sunken reservoir from which the seawater is pumped to a desalination plant for de-salting. Ranney wells typically have higher infiltration rates than vertical beach wells, in that they can produce filtered seawater volumes in a range of 8,000-20,000 cubic meters per day. However, like beach wells, they are limited by the nearshore geology. Also, Ranney wells can be hampered by silt buildup and may also influence onshore groundwater resources, so careful evaluation of site characteristics must be employed before a Ranney well can be installed.  
         [0008]     Indirect seawater intakes also suffer from a shorter life span, usually 15-20 years when compared with the 30-50 year life span of direct intakes. Further, the limitation in production capacity limits the use of indirect seawater intakes to only small desalination plants. Also, due to the fact that indirect seawater intakes must be placed in the nearshore region, they are vulnerable to storm damage or damage from beach erosion.  
         [0009]     Present seawater intakes for use with desalination plants require choices and compromises between high volume, long life direct intakes and the low volume, shorter life, but higher water quality provided by indirect intakes. Therefore a need exists for a seawater infiltration system that incorporates the high volume and long life of a direct intake while providing the high water quality of an indirect intake without being limited by surrounding nearshore geology.  
         [0010]     The foregoing reflects the state of the art of which the inventor is aware, and is tendered with a view toward discharging the inventor&#39;s acknowledged duty of candor, which may be pertinent to the patentability of the present invention. It is respectfully stipulated, however, that the foregoing discussion does not teach or render obvious, singly or when considered in combination, the inventor&#39;s claimed invention.  
       SUMMARY OF THE INVENTION  
       [0011]     The inventive filtered seawater collection system provides high quality water without being dependent upon local nearshore geology. The system also provides water volumes much higher than systems that depend upon indirect intakes that are dependent on nearshore geology. The inventive system&#39;s ability to eliminate dependency on local nearshore geology allows it to be placed in coastal areas of the world where the nearshore geology renders indirect intakes an impossibility.  
         [0012]     The inventive system is comprised of a subterranean reservoir in communication with the first end of an intake pipe. The reservoir is buried with its top portion at a level approximate to sea level, so that the inflow of water from the intake pipe occurs until the water in the reservoir reaches sea level.  
         [0013]     The pipe extends from the reservoir out past the nearshore and into the open ocean where it is preferably anchored to the sea floor. The opposite end of the pipe terminates at an intake area where the pipe is perforated with a plurality of openings. Geological materials, preferably gravel, are filled into porous containers and enclosed therein. The containers are then lowered precisely upon the intake so that the porous containers cover the intake openings. The containers then act as a portable geology causing only filtered seawater to enter the pipe. Undesirable suspended elements such as harmful and toxic algae, other suspended biologics and hydrocarbons are either greatly reduced or eliminated altogether by the invention. The placement of the intake of the present invention in the open ocean also allows the invention to produce volumes of water above that of prior art indirect intake designs.  
         [0014]     It is an object of this invention to provide an inventive system and method for filtering seawater that is not dependent upon nearshore geology.  
         [0015]     Another object of the invention is to provide an inventive system and method for filtering seawater, which produces a higher volumetric flow of filtered seawater than existing indirect intake systems.  
         [0016]     Still another object of the invention is to provide an inventive system which allows desalination plants to be located in areas having undesirable nearshore geology for filtering seawater.  
         [0017]     Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention, without placing limitations thereon. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The invention will be more fully understood by reference to the following drawings, which are for illustrative purposes only:  
         [0019]      FIG. 1  is a side view of the inventive filtered seawater collection system shown installed at a coastal location.  
         [0020]      FIG. 2  is a side view of an alternative embodiment of the inventive filtered seawater collection system shown installed at a coastal location.  
         [0021]      FIG. 3  is a top plan view of the inventive system shown without filter media packets installed on the intake portion of the system.  
         [0022]      FIG. 4  is a side cutaway view through a filter media packet of the inventive system.  
         [0023]      FIG. 5  is a top plan view showing the filter media packets arranged around a seawater intake in accordance with the present invention.  
         [0024]      FIG. 6  is a side view of a seawater intake attached to an alternative embodiment seawater filter.  
         [0025]      FIG. 7  is a top plan view of an alternative embodiment of the seawater intake, which employs multiple intakes.  
         [0026]      FIG. 8  is a top plan view of an alternate embodiment fan-shaped intake having multiple pipes for drawing in high volumes of seawater.  
         [0027]      FIG. 9  is a top plan view of an alternate embodiment high-volume intake having a branching configuration.  
         [0028]      FIG. 10A  is a plan view of an alternate embodiment of a filter media container shown anchored to an intake pipe located upon a sea floor.  
         [0029]      FIG. 10B  is a side view of the alternate embodiment of  FIG. 10A .  
         [0030]      FIG. 11A  is a plan view of a further embodiment of a filter media container which inserts over an intake pipe.  
         [0031]      FIG. 11B  is a side view of the alternate embodiment of  FIG. 11A .  
         [0032]      FIG. 12  is an elevated perspective view of a funnel-shaped intake embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     Referring to  FIG. 1 , a preferred embodiment of the filtered seawater collection system  10  is shown. The system  10  is comprised of a subterranean reservoir  12  that is preferably sunk in the ground at an area that is protected from wind, beach erosion, littoral drift, storm surges and other damaging coastal forces. Here, the reservoir  12  is shown sunk behind a first set of dunes  14  adjacent to a beach  16 . The reservoir  12  is connected with a first end  18  of a pipe  20 , and the pipe  20  extends outward from the reservoir  12  through the nearshore  22  and out into the open ocean  24 . The nearshore  22  as shown is a geologic area below the beach  16  and below sea level. In some coastal regions, the nearshore  22  has a porous geology, which allows seawater  28  to filter down free of biological material and debris. However, in other coastal regions the nearshore  22  has an all but impermeable geology. As noted previously herein, the geology of the nearshore  22  is the limiting factor with regard to whether an indirect intake could be used in a seawater pre-filtration system. The inventive system  10  bypasses the nearshore  22  by extending the pipe  20  out through the surf line  30  and into the open ocean  24 .  
         [0034]     The pipe  20  is inserted through a bore  32  drilled into the nearshore geology  22  between the bottom of the reservoir  12  and through the surf line  30 . Directional drilling techniques that have been used in the petroleum recovery arts are applied here to place the pipe in the manner shown and described. Directional drilling can produce a bore  32  several hundred yards long or even up to a half-mile or more. The use of directional drilling allows the reservoir  12  to be placed significantly far out of harms way such that damage to the reservoir  12  from natural coastal forces would be a limited possibility.  
         [0035]     The reservoir  12  is sunk in the ground at a depth where the top portion  34  of the reservoir is approximately at sea level  26  as shown. The top portion  34  of the reservoir  12  is sloped to approximate the slope of the beach  16  which helps prevent sand erosion around the reservoir  12 . Filtered seawater  29  flows into the bottom of the reservoir  12  from the pipe  20  and achieves sea level  26 . A submersible pump  36  placed into the reservoir  12  transfers the filtered water to the desalination plant (not shown) for de-salting.  
         [0036]     The pipe  20  extends past the surf line  30  and out into the open sea  24  a sufficient distance from shore  38  and at a depth to avoid tidal effects. Generally, the placement of pipe  20  is not limited by water depth. The pipe  20  can be mounted  41  to the sea floor  40  as shown in  FIG. 1  or else it could placed in a bore  32  which extends beneath the sea floor  40  and only breaks the sea floor  40  at the intake end  42  as shown in  FIG. 2 . The configuration shown in  FIG. 2  is presented as a lower profile design which is meant to minimally disrupt the ecosystem and also presents a lower profile to avoid contact with sea dredges, bottom trawl nets and other man made activity.  
         [0037]     Referring also to  FIG. 3 , the seawater intake end of the pipe can be one opening or a plurality of openings  44  in the pipe terminus. The openings  44  draw in the filtered seawater  29  which travels up the pipe  20  to the subterranean reservoir  12 . The intake  42  also preferably has an end cap  46  or other access point to periodically clean out and service the pipe intake. Likewise, the reservoir  12  includes a manhole access  48  for regular servicing, as needed.  
         [0038]      FIGS. 4 and 5  demonstrate the filter media portion of the inventive system  10 . In the embodiment of these figures, filter media packets  50  surround the intake end  42  of the pipe  20 . The packets  50  are comprised of a porous container  52  containing a filter media  54 . The filter media  54  must have the characteristics of removing undesired filtration elements including detritus, suspended soil, suspended sediment, planktonic organisms, and biologics such as toxic dinoflagellates and diatoms found in seawater. Additionally, the filter media fosters an environment for microbial communities to effectively remove bioavailable nutrients such as phosphorus and nitrogen compounds. Also, the media  54  must be inexpensive and be able to operate on the intake end  42  in a filtering capacity for a long while before becoming overloaded with undesired filtration elements. Further, it is preferable that upon becoming overloaded the media  54  be able to be cleaned and re-used or else replaced inexpensively. The inventors have found that geologic filtration medias  54  meet these requirements; specific geologic filtration medias  54  include various gravel combinations. As shown in  FIG. 4 , the porous container  52  is filled with gravel media  54  and the container  52  has a flat, mattress-like quality. The containers  52  are made of porous and durable materials including nylon, geotextile fabrics, geo-membranes or other engineered materials. The interiors of the containers are partitioned  56  so that the gravel is placed in separate compartments  58 . This makes the packets  50  easier to handle and less unwieldy. The internal structure provides integrity to the containers. The pliable nature of the media containers allows for encasing the intake end of the pipe. Handling is further eased by the addition of attachment points  60  which can be coupled to a crane cable (not shown) for lowering into the sea and guiding into place over the intake end  42  by a dive crew.  
         [0039]     An example of a filtration media  54  which enables this invention is a sequence of 27% filter sand (typically NSF/ANSI Standard A8071), flint 10.8% (#20 NSF/ANSI Standard A8072), flint 10.8% (¼ to ⅛, NSF/ANSI Standard A8073), flint 10.8% (½ to ¼ NSF/ANSI Standard A8074), anthracite 14.8% (#1, 0.6 to 0.8 mm, NSF/ANSI Standard A8029), and garnet 24.3% (#30 to #40, NSF/ANSI Standard A8037). Site specific factors can augment this recipe.  
         [0040]      FIG. 5  illustrates how the packets  50  are arranged around the intake end  42  of the pipe  20  so as to cover all of the pipe openings  44  in a filtering manner. The packets  50  settle around and form to the pipe intake end  42 , thereby helping to seal off the pipe intake openings  44  from raw seawater  28 . Further, to make sure that the pipe intake openings  44  receive only filtered seawater, the packets  50  can be layered and overlapped to form a sealed geological unit around the pipe intake  42 . The filter media packets  50  provide a filtering geology that can be transported to and adapted to any coastal situation in the world. Therefore, the invention allows nearshore regions  22  having less than optimal filtration characteristics to be bypassed and further allows a more effective filter substrate geology to be installed near any coastline in the world.  
         [0041]      FIG. 6  is an alternative embodiment of the invention, which, instead of enclosing the filtration media in mattress-like containers, encloses the media in filter canisters  66  which can be coupled to the end of a solid pipe  20 . The filter canister  66  shown here would have porous qualities and could be a geologic filter with gravel  54  being the preferred media. The intake end  42  of the pipe would no longer be endowed with a plurality of openings  44 . Instead, the pipe  20  would be solid up to the point of its terminus and would have a coupler  68  on the end of the pipe. The coupler  68  would have a sealing quality to prevent the influx of raw seawater  28 . The coupler  68  could therefore be a threaded arrangement, a gasket arrangement or other known mechanical means, which could achieve the sealing coupling of the filter canister shown.  
         [0042]      FIG. 7  illustrates an alternative embodiment of the intake. This embodiment employs multiple intakes  42 , which feed water to the subterranean reservoir  12  in the manner previously described. The multiple intakes  42  feed into corresponding pipes  20 . A larger pipe  70  functions as a type of bore lining for containing multiple intake pipes  20 . The pipe  70  is preferably sealed with a cover  71  through which penetrate pipes  20 . Cover  71  effectively prevents raw seawater from entering pipe  70  and potentially fouling the filtered seawater  29  contained in reservoir  12 . The bore  32  created by directional drilling can be made to have a diameter of 30″ or greater. As shown in  FIG. 7 , a 30″ or larger bore  32  allows for the placement of the large pipe  70 , so that a plurality of intake pipes  20  can be placed inside of the large pipe  70  and connected to the reservoir  12 . This allows for the filtration of much higher volumes of seawater from the multiple intakes. Also, as desalination needs grow with population growth, this configuration allows for more intake pipes  20  to be added.  
         [0043]      FIG. 8  illustrates a fan-shaped intake  74  having multiple pipes  76  for drawing in high volumes of seawater. This intake  74  would be attached to a pipe  20  having sufficient volumetric capacity to accommodate the large intake of seawater provided by this fan-shaped intake embodiment. The filter media packets  50  (not shown in this view) would be assembled around the multiple pipes  76  in the manner previously described. An impermeable geo-membrane  78  is preferably laid beneath the fan-shaped intake  74  to help prevent the influx of anoxic trace metals, which are especially prevalent in sea floors having high mud or clay compositions. The geo-membrane layer  78  could also be adapted to be laid beneath any of the other pipe intake embodiments described herein.  
         [0044]      FIG. 9  shows another high-volume intake  80  having a branching configuration. The branches represent pipes  82  which can be added as desalination capacity is increased. This configuration can grow along with growing desalination needs.  
         [0045]      FIGS. 10A and 10B  illustrate an embodiment of a filter media container  84  which relies upon the use of polyurethane foam  86  as a filter media. Instead of multiple gravel packets  50 , the container  84  is a large single piece, and bag-like. The length of container  84  would cover intake openings  44  on pipe  20 . The container is anchored  88  to the sea floor  40  to keep container  84  tight over the intake openings  44 . The container remains porous and its polyurethane foam filling results in a malleable assembly which forms itself to the pipe  20  over intake openings  44 .  
         [0046]      FIGS. 11A and 11B  show another filter media container  90  which would preferably employ a foam filter media. It has been found that polyurethane foam  96  operates as a filter media in accordance with the invention. The container  90  is bag-like and is intended to insert over intake end  42  of pipe  20 . Pipe  20  inserts into an inner cavity  92  of container  90 , the inner cavity  92  being lined with porous container material and keeping the intake openings  44  separate from the filter media  96 . The polyurethane foam filter media  96  is injected through a valve opening  94 . This is to allow easy assembly over the end of the pipe by first inserting the pipe  20  into the empty container  90  and then filling the container with filter media  96  through valve  94 . The filter media can be replaced periodically by suctioning it back through the valve and replacing with fresh filter media.  
         [0047]      FIG. 12  offers a funnel-shaped intake embodiment  100  wherein the funnel  102  is filled with different layers  104 ,  106  of gravel filter media. The advantage of a funnel-shaped intake  100  over a pipe intake is that the flow into the intake is significantly slowed while keeping the volume of water entering pipe  20  to a high level. By slowing the water flow rate, biological materials are less likely to be attracted into the funnel.  102 . Also, because the funnel opening  108  extends upwardly from the sea floor  40 , contact with anoxic metal-containing sea muds and clays is significantly reduced. The layers  104 ,  106  of gravel media can be selected according to site-specific water characteristics.  
         [0048]     Finally, although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. This invention may be altered and rearranged in numerous ways by one skilled in the art without departing from the coverage of any patent claims which are supported by this specification.