Patent Publication Number: US-2009223881-A1

Title: Reverse Osmosis System with Dual Water Intake

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a reverse osmosis system with increased filtration efficiencies. More particularly, the present invention relates to a multi stage reverse osmosis system with dual water inlets. 
     2. Description of the Background Art 
     Governments and municipalities are increasingly turning to reverse osmosis separation processes to meet rising demands for fresh water. Reverse osmosis processes are widely known for use in removing salt and other minerals from seawater or brackish water. The result is a purified naturally occuring water that can be readily used in a variety of applications. 
     Seawater reverse osmosis is typically carried out over a number of stages. These stages may, for example, include an intake stage, a pre-treatment stage, a high pressure pump stage, one or more membrane stages, a re-mineralization and pH adjustment stage, and finally a disinfection stage. 
     Salt and other minerals are separated from water in the membrane stages. As is known in the art, this involves forcing seawater through a series of semi-permeable membranes. This creates a higher solute concentration on the upstream side of the membrane stages and a lower solute concentration on the downstream side. The high pressure pump is employed in pressurizing the upstream seawater to overcome inherent osmotic pressures. For most seawater applications, pressures of between 600 to 1000 psi are utilized. This pressure decreases as the water travels downstream through sequential membranes. 
     Although the above described reverse osmosis system is sufficient to generate pure water, it has inherent inefficiencies. Namely, as the seawater traverses the various membranes it gradually loses pressure. As a consequence, there is a considerable drop in the velocity of the water traversing the membranes and a commensurate drop in filtration efficiency. This, in turn, means that most of the impurities are removed by the initial membranes of the series and that very little purification is carried out in the final membranes. 
     Various efforts have been made over the years to compensate for inefficiencies in the reverse osmosis process. For instance, U.S. Pat. No. 5,207,916 to Goheen et al. discloses a single RO membrane having a double-pass design using two banks of membranes in series. Liquid is initially pumped into a first bank of RO membranes. On the downstream side of the first bank of membranes, the liquid is conducted into a hydraulic turbocharger to re-elevate the pressure of the liquid prior to entering the second bank of membranes. 
     The use of multiple pumps in an reverse osmosis system is also known. For instance, U.S. Pat. No. 4,160,727 to Harris, Jr. discloses a method for purifying and dispensing water that utilizes staged RO membranes. The method pumps water into a first RO membrane. The permeate from this first RO membrane is then routed to a second pump, sending the liquid into a second RO membrane. Two feed water supplies are included for the two RO membranes. 
     Likewise, U.S. Pat. No. 4,808,287 to Hark discloses a water purification process which includes a two stage RO process, wherein water is initially pumped into a first RO unit, then pumped into a second RO unit. The system also maintains proper osmotic pressure relative to the discharge pressure and flow pressure of the first pump. 
     Finally, U.S. Pat. No. 6,139,740 to Oklejas discloses an apparatus for improving the efficiency of an RO system which utilizes a hydraulic turbocharger to increase the pressure of water between a first RO chamber and a second RO chamber. It is also disclosed that the turbine can be utilized for recovering energy from the process. 
     Although some of the above referenced inventions may enjoy slightly increased filtration efficiencies, none contemplate achieving increased pressurization and filtration efficiency via the addition of a secondary water inlet. 
     SUMMARY OF THE INVENTION 
     It is therefore one of the objectives of this invention to provide for increased filtration efficiency in a multi stage reverse osmosis process by providing an additional water inlet at a point intermediate the first and last membranes. 
     It is another object of this invention to increase the supply of water to a multi stage reverse osmosis system to thereby maintain increased pressurization throughout the various stages. 
     It is still yet another object of this invention to provide a computer control to a multi stage reverse osmosis system, wherein variations in the amount of purified water created can be compensated for by increasing the amount of water added downstream between first and final reverse osmosis stages. 
     The foregoing has outlined rather broadly the more pertinent and important features of the present invention in order that the detailed description of the invention that follows may be better understood so that the present contribution to the art can be more fully appreciated. Additional features of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which: 
         FIG. 1  is a schematic view of the reverse osmosis system of the present invention. 
         FIG. 2  is an alternative embodiment of the reverse osmosis system of the present invention. 
     
    
    
     Similar reference characters refer to similar parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention relates to an improved multi-stage reverse osmosis system with dual water inlets for improving filtration efficiency. More specifically, the system includes a pressure vessel with a series of semi permeable membranes. A water inlet is included at both a first end of the vessel and at an intermediate location. By re-supplying water at the intermediate location, a minimum water pressure is maintained throughout the entire length of the vessel and increased efficiencies are realized. 
     One embodiment of the reverse osmosis system  20  of the present invention is illustrated in  FIG. 1 . As is typical, system  20  includes an elongated pressure vessel  22  with first and second ends ( 24  and  26 , respectively). Water is delivered to the first end  24  of vessel  22  via a first sea water intake  28  with the resulting purified being likewise removed from the first end  24  via an axial conduit  30 . The water used in the system will be seawater or perhaps brackish water. Solute, containing the salt and other minerals removed from the seawater, are extracted via the second end  26  of vessel  22 . 
     System  20  achieves seawater filtration via a series of semi-permeable membranes ( 40   a ,  40   b ,  40   c ,  40   d ,  40   e ,  40   f ,  40   g , and  40   h ) positioned within pressure vessel  22 . As is known in the art, these membranes ( 40   a ,  40   b ,  40   c ,  40   d ,  40   e ,  40   f ,  40   g , and  40   h ) can be radially disposed in a concentric fashion about the axial conduit  30 . This construction allows seawater to pass inwardly toward the axial conduit  30  in a radial direction. The result is that the purified and de-mineralized water is delivered to the axial conduit  30  and is extracted from first end  24 . 
     In order to ensure that the seawater delivered via first intake  28  is sufficiently pressurized, a high pressure pump  32  is provided. In the preferred embodiment, pump  32  ensures that the seawater supplied via intake  28  is pressurized to between approximately 600 to 1000 pounds per square inch. Pressurizing first intake  28  is necessary to ensure proper operation of the downstream membranes as well as to overcome the inherent osmotic pressure of the system. 
     In accordance with the present invention, a second water intake  34  is included along the intermediate extent of vessel  22 . In the embodiment depicted in  FIG. 1 , a total of eight membranes ( 40   a ,  40   b ,  40   c ,  40   d ,  40   e ,  40   f ,  40   g , and  40   h ) are included within vessel  22 , and the second water intake  34  is included at a midpoint between the membranes (i.e. after  40   d  but before  40   e ). More specifically, second intake  34  feeds into an intermediate chamber  36  of vessel  22 . 
     A second high pressure pump  38  is likewise provided for pressurizing the second seawater intake  34 . In the preferred embodiment, pump  38  pressurizes the seawater to between approximately 600 to 1000 pounds per square inch. 
     It has been discovered that by providing this additional intake  34  at a downstream location, the pressure of the water can be more uniformly maintained throughout the entire length of vessel  22 . By contrast, without an additional intake, the pressure and velocity of water within vessel  22  would quickly diminish across the multiple membranes. In the preferred embodiment, a balanced flow is achieved by ensuring that the volume of water supplied at the second input  34  is equal to the amount of fresh water extracted from conduit  30 . 
     In accordance with a further embodiment of the present invention, this balanced flow is maintained via flow meters and a controller. This embodiment is depicted in  FIG. 2 . Flow meters  42  are associated with conduit  30  and second intake  34 . Specifically, a first flow meter  42   a  is operatively coupled to the fresh water conduit  30  and a second flow meter  42   b  is operatively coupled to the second high pressure pump  38  and second intake  34 . The first flow meter  42   a  monitors the volume of water leaving vessel  22  as fresh water, and the second flow meter  42   b  monitors the volume of water supplied to the second intake  34 . 
     A controller  44  is operatively associated with the flow meters ( 42   a  and  42   b ) and pump  38  and is used in maintaining an equilibrium between the freshwater generated by system  20  and the amount of seawater supplied to the second intake  34  via pump  38 . 
     The present disclosure includes that contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention