Abstract:
An submersible desalination unit composed of a structure containing a water intake system for acquiring sea water, a sea water pre-filtration system for removing lager contaminants and debris, a reverse osmosis system for the purification of the water, a permeate transfer system to carry the water to where it will be used, a power source for powering the equipment used in the process and a control system that operates and monitors the equipment and process of removing salt from the water and transferring the desalinated water to other use and returning the brine solution to the sea.

Description:
RELATED APPLICATIONS 
       [0001]    The present application is related to U.S. Pat. No. 3,456,802, issued Jul. 22, 1969, included by reference herein. 
         [0002]    The present application is related to U.S. Pat. No. 4,125,463, issued Nov. 14, 1978, included by reference herein. 
         [0003]    The present application is related to U.S. Pat. No. 5,229,005, issued Jul. 20, 1993, included by reference herein. 
         [0004]    The present application is related to U.S. Pat. No. 6,800,201, issued Oct. 5, 2004, included by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0005]    The present invention relates to an apparatus and method for desalination of salt water and, more particularly, to an apparatus and method for desalination of salt water by reverse osmosis. 
       BACKGROUND OF THE INVENTION 
       [0006]    The increasing demand for water among households, industry, the environment, and especially agriculture is making global water scarcity a perilous possibility. However, salt or brackish water is readily available in many areas of the world. In fact, 97 percent of the surface water of the earth is salt water. 
         [0007]    Much of the projected increase in water demand will occur in developing countries, where population growth and industrial and agricultural expansion will be greatest. The world&#39;s thirst for water is likely to become one of the most pressing resource issues of the 21st Century. 
         [0008]    One-quarter of the world&#39;s population lives in areas where water is physically scarce, while about one-sixth of humanity—over a billion people—live where water is economically scarce. Declining groundwater supplies, pollution, flooding and drought could well worsen poverty in many areas. 
         [0009]    Irrigation already accounts for about two thirds of water use worldwide. As rivers and lakes are dammed, dried up, or polluted, and as food demand grows in the next 50 years, farmers will become increasingly dependent on ground water for irrigation. 
         [0010]    Nearly one third of all humanity relies almost exclusively on groundwater for drinking, including the residents of some of the largest cities in the developing world. Today water tables are falling on every continent. The depletion of aquifers is a new problem, one that has emerged only in the half past century or so, because it is only in this period that we have had the pumping capacity to quite literally deplete aquifers. 
         [0011]    Desalination of sea water has been practiced for over half a century and is a well known means of water supply in many countries. 
         [0012]    Evaporation and reverse osmosis are two common methods to produce fresh water from sea water. Evaporation methods involve heating the sea water, condensing the vapor produced and isolating the distillate. 
         [0013]    Reverse osmosis is a membrane separation process in which the water from a pressurized saline solution is separated from the dissolved material by flowing through a membrane. 
         [0014]    In U.S. Pat. No. 3,456,802, osmotic membranes units are submerged at great depths in the sea, 3,000 to 4,000 feet, to take advantage of the hydrostatic pressure of the ocean for supplying the necessary differential pressure to the osmotic membranes. 
         [0015]    U.S. Pat. No. 4,125,463 discloses a reverse osmosis apparatus placed in a well hole and using the head pressure of the salt water to supply the necessary differential pressure to the osmotic membranes. 
         [0016]    In U.S. Pat. No. 5,229,005, a reverse osmosis apparatus is lowered into the ocean by means of lines attached to pulleys, then raised to the surface to remove the fresh water produced. The invention also uses hydrostatic pressure of the ocean for supplying the necessary differential pressure to the osmotic membranes. 
         [0017]    U.S. Pat. No. 6,800,201 discloses a large open top metal cylinder anchored to the sea floor with several units of osmotic membranes attached to the side of the cylinder. Due to the pressure differential, freshwater passes through the membranes by reverse osmosis. The brine is disposed back to the ocean by gravity through an opening in the bottom of the cylinder. 
         [0018]    Energy costs for desalination of prior inventions is still high, and one of the main drawbacks to the use of reverse osmosis systems as used by the prior art is the pumping energy required for raising the sea water to the pressures necessary for osmotic separation. These pressures are typically in the neighborhood of 800 to 1000 psi. The problem is amplified by the increasing cost of energy and the ongoing decreasing supply of available energy resources. 
         [0019]    The above cited prior art inventions have attempted to save pumping energy by using the hydrostatic pressure of the ocean to desalinate seawater by reverse osmosis, but none of them have proved to be practical or economically viable since they all require the invention to be placed at great depths above 3,000 feet in order to obtain the required pressure of 800 to 1000 psi for osmotic separation. The amount of energy saved by such a process is offset by installation and maintenance costs since it requires working in extremely deep waters. Furthermore the important head requires substantial energy to pump the fresh water to the surface. 
         [0020]    The present invention is distinguishable from the above prior art in that it can be located at much lower depth, as low as 70 feet. It combines the use of the ocean hydrostatic pressure and the sea currents renewable energy to supply the necessary differential pressure to the osmotic membranes. 
         [0021]    It is an object of the present invention to reduce the pumping energy required for the desalination process. 
         [0022]    Another object of this invention is the use of renewable energy for the three following pumping processes, contributing to the protection of our environment: pumping to raise the feed water pressure to reverse osmosis operational pressure above 800 PSI, pumping the brine back to the ocean, and pumping the product water to an onshore storage tank and the distribution network. 
         [0023]    Another object of this invention is to eliminate the feed water and pre-filtration pumping processes by using exclusively the hydrostatic pressure of the ocean. 
         [0024]    Another object of this invention is the discontinued use of land and building facilities for the desalination process. Land leasing, construction and contractor costs can therefore be avoided, reducing substantially the initial capital costs of the project. Only the product water storage will be required onshore. 
         [0025]    Another object of this invention is to keep the desalination system unseen from shore, avoiding obnoxious noise and visual impact on the shoreline. Therefore, this invention is submerged at a sufficient depth to allow free maritime traffic over the operating area. 
         [0026]    Another object of this invention is to facilitate an increased amount of output of desalinated water without the need to upgrade existing equipment. The vessels of this invention are stand alone and turnkey units, providing a modular plant design that can be easily upgraded and modified. The expansion of present facilities is only limited by the offshore operating area granted by the local authorities. 
         [0027]    Another object of this invention is to reduce maintenance and installation cost issues by placing the invention into shallow waters less than 1200 feet, and regular maintenance is possible from the surface without the requirement of divers or submersible maintenance equipment to work on, repair, or maintain the system. 
         [0028]    Another object of this invention is to provide the means to be rapidly moved to an alternate location in order to optimize the use of renewable energy resources and/or relocate the location of a source of intake water and the discharge of brine. 
         [0029]    Another object of this invention is to produce large quantities of fresh water in locations distant from any public water distribution network or grid power source. 
         [0030]    Another object of this invention is to reduce the accumulation of concentrated brine released by conventional desalination plants. Conventional desalination plants release their brine through pipelines laid on the seabed a few miles from shore. In absence of sufficient currents or water mixing at the disposal spot, the accumulation of concentrated brine could be harmful for the sea flora and fauna. This invention is designed to release the brine in the middle of strong sea currents at mid-depth, thus providing a rapid dispersion with minimal impact on the environment. 
         [0031]    Another object of this invention is to reduce the risk of sea life impingement through the feed water intake system. Conventional desalination plants use single spot intake systems with particularly strong suction flows, while the modular configuration of this invention allows an efficient dispersion of the suction effect, as the desalination vessels are kept at a specific distance from each other. 
         [0032]    Additional features of this invention will be apparent with the following description and accompanying drawings. 
       SUMMARY OF THE INVENTION 
       [0033]    In accordance with the present invention, there is provided an submersible desalination unit composed of a structure containing a water intake system for acquiring sea water, a sea water pre-filtration system for removing larger contaminants and debris, a reverse osmosis system for the purification of the water, a permeate transfer system to carry the water to where it will be used, a power source for powering the equipment used in the process and a control system that operates and monitors the equipment and process of removing salt from the water and transferring the desalinated water to other use and returning the brine solution to the sea. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when considered in conjunction with the subsequent, detailed description, in which: 
           [0035]      FIG. 1  is a schematic view of a submersible reverse osmosis desalination apparatus; 
           [0036]      FIG. 2  is a left perspective view of a general view of the desalination unit in operating mode. The vessel is secured inside the main cradle secured to the seabed with 3 vessels anchor lines and concrete blocks. The sea current power converter can rotate freely to position itself to face sea currents for the greatest effect, while the body or frame is kept in a static position to remain permanently connected to the secondary flexible pipeline; 
           [0037]      FIG. 3  is a left perspective view of a hoisting system. The hoisting system is designed to provide the vessel with a vertical 45 degrees travel angle for surfacing and immersion without disconnecting the secondary flexible pipeline. The hoisting pulley line can be retrieved from the surface by the maintenance team. Once the docking arm is released from the main cradle, the entire vessel can be hoisted to the surface by acting on the hoisting pulley line from the maintenance barge using an electric winch (not shown); 
           [0038]      FIG. 4  is a left perspective view of a multi-vessel configuration in operating mode. The vessels are secured inside their respective main cradle, each secured to the seabed with 3 vessels anchor lines and concrete blocks. The hoisting pulley lines are set in operating mode, parallel to the main flexible pipeline. The maintenance mooring lines are fully retracted and the mooring line ring and its buoy are in idle mode; 
           [0039]      FIG. 5  is a left perspective view of a multi-vessel configuration in pre-hoisting mode. For any vessel requiring maintenance, its maintenance barge mooring line and the hoisting pulley line are retrieved from the surface up to the maintenance barge using the mooring line ring. The fully extended mooring line is then secured to the maintenance barge, while the hoisting pulley line is connected to an electric winch mounted on the maintenance barge (not shown), ready for the vessel hoisting operation; and 
           [0040]      FIG. 6  is a left perspective view of a multi-vessel configuration in hoisting mode. The vessel requiring maintenance is first released from its main cradle. In a second step, the maintenance barge electric winch (not shown) acts on the hoisting pulley line to surface the vessel and bring it underneath the maintenance barge, then through the maintenance barge&#39;s opening designed to host the top of the vessel. Maintenance can then be done from the maintenance barge pontoon all around the top of the vessel. Once maintenance is completed, the vessel is immersed then secured in its main cradle following the inverse procedure as for surfacing. It is to be noted that the secondary flexible pipeline is never disconnected from the vessel during hoisting operation. 
       
    
    
       [0041]    For purposes of clarity and brevity, like elements and components will bear the same designations and numbering throughout the Figures. 
       DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0042]    Referring now to  FIG. 1 : The apparatus is comprised of equipment necessary for the seawater reverse osmosis contained in a main body or frame  10  removably attached and made of materials not overly subject to the problems of salt or brackish water such as a fiber reinforced plastic intended to be immersed into the marine medium at a depth of less than 1200 ft. A main flexible pipeline  62  and a secondary flexible pipeline  64  which both include a permeate pipeline  12  made of a flexible material substantial enough to withstand sustained external pressures of greater than 34 PSI, a seawater resistant power line  14  such as a WPI Burton Engineering Underwater Power Cable and an air pipeline  16  made of a flexible material substantial enough to withstand sustained external pressures of greater than 34 PSI which therefore connects the apparatus to shore. 
         [0043]    Pre-filtration is provided by a set of submerged hollow fiber membranes known as the pre-filtration hollow fiber membrane set  20  commercially available such as a Zenon Zeeweed 500/1000 Reinforced Membranes, located in a pre-filtration membrane housing  22  set at ambient hydrostatic pressure of the ocean. An air blower  18  pump connected to the air pipeline  16  provides the required air flow across the pre-filtration hollow fiber membrane set  20 . 
         [0044]    The pre-filtered seawater pipes  24  are connecting the pre-filtration hollow fiber membrane set  20  outlet to the pre-filtered water inlets of the main high pressure pump  26 , commercially available in the form of a Danfoss Nessie APP 10.2, and the Pressure exchanger energy recovery exchanger  38  commercially available such as a ERI PX Exchanger Pressure Energy Recovery Device—PX 220/180. Pre-filtered water flux is generated by a simultaneous suction effect from the main high pressure pump  26  and the Pressure exchanger energy recovery exchanger  38  pre-filtered water inlets. Therefore the entire pre-filtration process doesn&#39;t require water pumping energy. 
         [0045]    Prior to entering the reverse osmosis membrane  32 , commercially available in the form of a Dow Filmtec SW30XLE-400i, pre-filtered water is pressurized to above 800 PSI by the main high pressure pump  26 , the Pressure exchanger energy recovery exchanger  38  and its Pressure exchanger booster pump  42 . 
         [0046]    A plurality of reverse osmosis membranes is installed inside a pressure vessel  34 , commercially available in the form of a Codeline 8″ “High-Flow” series 80H Membrane Housing. Pre-filtered feed water pressure buildup inside the pressure vessel  34  provides the required pressure and flow across the reverse osmosis membranes for the seawater reverse osmosis desalination process. The present invention can operate in a multiple pressure vessels configuration. 
         [0047]    The Reverse osmosis main feed high pressure pipes  28  are connecting the main high pressure pump  26  and the Pressure exchanger booster pump  42  pre-filtered water outlets to the pressure vessel  34  pre-filtered water inlet. 
         [0048]    The Pressure exchanger reverse osmosis feed high pressure pipe  40  connects the Pressure exchanger energy recovery exchanger  38  pre-filtered water outlet to the Pressure exchanger booster pump  42  pre-filtered water inlet. 
         [0049]    The hydrostatic pressure of the pre-filtered water allows constant feed water pre-charging for the main high pressure pump  26  and the Pressure exchanger energy recovery exchanger  38 . This design eliminates the need of pre-charging the feed water of main high pressure pump  26  which represent an additional source of energy consumption. 
         [0050]    The main high pressure pump  26  the Pressure exchanger booster pump  42  and the air blower  18  are removably coupled to the drive shaft  46  of a driving motor such as a sea current powered motor, not shown, which provides the pumping energy. This design allows the entire desalinization process to run on renewable energy using sea currents as the main power source. In an absence of sea currents, the desalination process can also be powered by an optional electric high pressure pump  30  connected to the grid via the power line  14 . The electric high pressure pump  30  is commercially available such as a Danfoss Nessie APP 10.2 pump powered by a Reliance Rockwell CLC submersible motor, optional for grid power systems only. 
         [0051]    Permeate pumping to shore via the permeate pipeline  12  is powered by throttling the permeate pressure through the reverse osmosis membrane  32  in order to obtain the necessary pressure to overcome the ambient hydrostatic head and the friction loss in the permeate pipeline  12 . This design eliminates the need of an additional pumping station for permeate transfer. 
         [0052]    The brine rejected by the reverse osmosis membrane  32  is recovered by the Pressure exchanger energy recovery exchanger  38 , which uses the brine residual pressure to pressurize part of the pre-filtered feed water flow required by the reverse osmosis membrane  32 . The Reverse osmosis brine exit high pressure pipe  36  is connecting the pressure vessel  34  brine outlet to the Pressure exchanger energy recovery exchanger  38  brine inlet. 
         [0053]    The Pressure exchanger booster pump  42  compensates the brine&#39;s trans-membrane pressure loss, the ambient ocean hydrostatic pressure as well as the small friction loss incurred through the Pressure exchanger energy recovery exchanger  38 . The depressurized brine exiting the Pressure exchanger energy recovery exchanger  38  is set at a pre-determined pressure in order to overcome the ambient ocean hydrostatic pressure. 
         [0054]    The Pressure exchanger brine exit low pressure pipe  44  is connecting the Pressure exchanger energy recovery exchanger  38  brine outlet to the sea current power converter  48  fins. 
         [0055]    The brine is expelled through the fins the sea current power converter  48  in order to enhance the mixing with ambient sea water. This design eliminates the need of an additional pumping station for brine disposal. 
         [0056]    A person skilled in the art will notice that the entire process is powered by the main high pressure pump  26  and in a much lesser degree by the Pressure exchanger booster pump  42  avoiding the need of numerous auxiliary pumping services required in a traditional onshore desalination plant. 
         [0057]    Referring now to  FIG. 2 ; the main body or frame  10  is connected to the sea current power converter  48  via the drive shaft  46  and is maintained in suspension in the water by three vessel anchor lines  50 , each one secured by a concrete block  52  laid on the sea floor. Foam inserts are placed inside the main body or frame  10  in order to provide the vessel  90  with light negative buoyancy. The three vessel anchor lines  50  and their respective concrete blocks are disposed in a triangular layout on the ocean floor. The top extremities of the three vessel anchor lines  50  are secured to the main cradle  54  in order to give the mooring system a pyramidal shape. The main cradle  54  includes the docking arm hydraulic locking system  56 , the hoisting system  60  as well an embedded buoy  58  filled with synthetic foam which provides strong positive buoyancy. 
         [0058]    A vessel  90  is the combination of the main body or frame  10  and the sea current power converter  48 . 
         [0059]    In a multi-vessel  90  configuration, the main cradle  54  also includes a connection ring on its side (not shown) to host and guide the main flexible pipeline  62  comprised of a plurality of pipelines and power cable, across the array of multiple vessel  90  (s) positioned on a single row layout. 
         [0060]    The main body or frame  10  is permanently connected to a secondary flexible pipeline  64  comprised of a plurality of pipelines and power cable and maintained in a static position, the secondary flexible pipeline  64  is connected to the main flexible pipeline  62  while the sea current power converter  48  connected under the main body can rotate freely to position itself to face sea currents for the greatest effect. 
         [0061]    The objective of the present invention is also to facilitate access for maintenance. The main body or frame  10  and the sea current power converter  48  can be surfaced without disconnecting any pipeline. The length of the secondary flexible pipeline  64  must at least equal the head distance in order to keep the connection (in a vertical position) with the main flexible pipeline  62  when the vessel  90  is surfaced. When the vessel  90  is submerged and secured in the main cradle  54 , the secondary flexible pipeline  64  runs parallel to the main flexible pipeline  62 . Therefore the junction point between the secondary flexible pipeline  64  and the main flexible pipeline  62  must be located at an equal distance required for surfacing away from the main body. 
         [0062]    A person skilled in the art will notice that in order to surface the system without disconnecting the pipelines, the vessel  90  must travel in a vertical angle of 45 degrees, and the minimum distance to keep between vessels in a multi-vessel  90  configuration represents approximately the head distance. 
         [0063]    Referring now to  FIG. 3 ; the hoisting system  60  provides the vessel  90  with a vertical 45 degrees travel angle. It includes a closed loop hoisting pulley line  66  which is guided by two hoisting pulley guides  68  mounted on the main cradle  54 . The hoisting pulley line  66  is also linked to the docking arm  70  of the sea current power converter  48  so that the entire vessel  90  can be hoisted to the surface by pulling on one end of the hoisting pulley line  66 . 
         [0064]    The vessel&#39;s docking arm  70  has a shape of a rudder and is designed to fit exactly the female aperture (not shown) in the main cradle  54 . This design ensures vertical and horizontal stability under strong sea currents. The docking arm hydraulic locking system  56  integrated in the main cradle  54  secures the vessel&#39;s docking arm  70  to the main cradle  54 . It can be remotely operated from shore via a servo motor (not shown). 
         [0065]    Referring now to  FIG. 4 ; in normal operation mode, the vessel&#39;s docking arm  70  is secured in the main cradle  54 . The hoisting pulley line  66  is positioned horizontally along the main flexible pipeline  62  leading to a neighboring vessel  90 . A maintenance barge mooring line  74  is linked with a snap hook  76  to the opposite end of the hoisting pulley line  66 , away from the main cradle  54 . The snap hook  76  is also hooked to a mooring line ring  78  equipped with a small mooring line buoy  80  on its top. 
         [0066]    The maintenance barge mooring line  74  is used by the maintenance barge  72  to maintain a static position at the surface of the ocean. It is running through the main static line ring  82  mounted on the main static line  84  running parallel to the main flexible pipeline  62  and linking each cradle in a multi-vessel  90  array configuration. The maintenance barge mooring line  74  has a mooring line stopper  86  at its end extremity opposite to the snap hook  76 , preventing the line to exit the main static line ring  82 . In normal operation mode, the maintenance barge mooring line  74  is also maintained under tension by an elastic cable  88  secured to the next vessel  90  of the array. 
         [0067]    Referring now to  FIG. 5 ; whenever the vessel  90  needs to be surfaced for maintenance, the docking arm  70  is first disengaged from the main cradle  54 . A long pole (not shown) lowered from the maintenance barge  72  is used to hook the mooring line ring  78  and bring it to the surface. 
         [0068]    As the mooring line ring  78  is hooked to the snap hook  76 , it will pull along the extremities of the maintenance barge mooring line  74  and the hoisting pulley line  66  to the surface. 
         [0069]    An alternate method to bring the maintenance barge mooring line  74  to the surface would be to use a remote controlled electric winch (not shown) mounted on the main cradle  54 . The maintenance barge mooring line  74  is mounted on the electric winch (not shown) which has full control on the released length of the maintenance barge mooring line  74 . 
         [0070]    Once the mooring line ring  78  is surfaced, the maintenance barge mooring line  74  extremity is unhooked from the snap hook  76  and secured to the maintenance barge  72 . The hoisting pulley line  66  is also unhooked from the snap hook  76  and installed in a power wheel (not shown) driven by an electric motor (not shown). 
         [0071]    As a consequence, the maintenance barge mooring line  74  is kept in a vertical position and the hoisting pulley line  66  at an angle of 45 degrees between the main cradle  54  and the maintenance barge  72 . 
         [0072]    Referring now to  FIG. 6 ; The vessel  90  can then be surfaced or submerged by acting on either side of the hoisting pulley line  66  from the maintenance barge  72  (using an electric motor not shown), without disconnecting any pipeline. In order to facilitate maintenance, the maintenance barge  72  is designed with an open area in its center (not shown) to host the main body of frame once it is surfaced. This allows the maintenance team to work all around the desalination unit with better access to its main components. 
         [0073]    A person skilled in the art will notice that the maintenance barge  72  is actually using the mooring infrastructure of two vessels to maintain its static position at the surface. This design can guarantee smooth operational conditions even under strong surface currents. 
         [0074]    Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to the example chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention. 
         [0075]    Having thus described the invention, what is desired to be protected by Letters Patent is presented in the subsequently appended claims.