Abstract:
A reverse osmosis system and method for operating the same includes a pressure tank having a first end and a second end, the pressure tank has a first volume adjacent to the first end and a second volume adjacent to the second end and a third volume between the first volume and the second volume and a fluid passage fluidically coupling the second volume to the first volume. The reverse osmosis system also includes a plurality of membranes disposed within the third volume generating permeate and a permeate manifold receiving permeate from the membranes and fluidically communicating permeate out of the pressure tank. A feed line couples feed fluid into the pressure tank. A first pump pressurizes the feed line. A second pump is disposed within the tank and circulates brine fluid from the second volume through the fluid passage.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. application Ser. No. 12/706,811 filed on Feb. 17, 2010. The disclosure of the above application is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to reverse osmosis systems, and, more specifically, to a batch operated reverse osmosis system that may be operated as a continuous process. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Reverse osmosis systems are used to provide fresh water from brackish or sea water. A membrane is used that restricts the flow of dissolved solids therethrough. 
     A reverse osmosis system involves pressurizing a solution with an applied pressure greater than an osmotic pressure created by the dissolved salts within the solution. The osmotic pressure is generally proportional to the concentration level of the salt. The approximate osmotic pressure in pounds-per-square-inch is the ratio of the salt mass to water mass times 14,000. A one-percent solution of salt would have an osmotic pressure of about 140 psi. Ocean water typically has a 3.5 percent concentration and an osmotic pressure of 490 psi. 
     Water extracted from a reverse osmosis system is called permeate. As a given batch of saline solution is processed by the reverse osmosis membrane, the concentration of the solution is increased. At some point, it is no longer practical to recover permeate from the solution. The rejected material is called brine or the reject. Typically, about 50% of recovery of permeate from the original volume of sea water solution reaches the practical limit in standard seawater RO systems. 
     Reverse osmosis systems typically have several components that are under very high pressures that may exceed 1,000 psi. These components include membrane housings, brine tanks, pumps and interconnecting pipes. Providing reinforced components increases the cost of the reverse osmosis system. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     The present disclosure provides a system that reduces the number of components that must be reinforced to withstand pressures compared to prior known systems. 
     In one aspect of the invention, a reverse osmosis system includes a pressure tank having a first end and a second end, the pressure tank has a first volume adjacent to the first end and a second volume adjacent to the second end and a third volume between the first volume and the second volume and a fluid passage fluidically coupling the second volume to the first volume. The reverse osmosis system also includes a plurality of membranes disposed within the third volume generating permeate and a permeate manifold receiving permeate from the membranes and fluidically communicating permeate out of the pressure tank. A feed line couples feed fluid into the pressure tank. A first pump pressurizes the feed line. A second pump is disposed within the pressure tank and circulates brine fluid from the second volume through the fluid passage. 
     In another aspect of the invention, a method of performing reverse osmosis in a system that includes a pressure tank having a first end and a second end, the pressure tank has a first volume adjacent to the first end, a second volume adjacent to the second end and a third volume between the first volume and second volume and a fluid passage fluidically coupling the second volume to the first volume includes communicating feed fluid to the pressure tank, increasing the pressure within pressure tank with a pump disposed within the inner chamber, generating permeate at a plurality of membranes disposed within the third volume, fluidically communicating the permeate out of the pressure tank and circulating brine from the membranes from the second volume to the first volume using a circulation pump. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a cross-sectional view of a first embodiment of a reverse osmosis system according to the present disclosure. 
         FIG. 2  is a radial cross-sectional view of the tube sheet of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a second embodiment of the present disclosure. 
         FIG. 4  is a schematic view of a turbocharger for use in an alternative configuration of  FIG. 1 . 
         FIG. 5  is a cross-sectional view of an eductor according to the present disclosure. 
         FIG. 6  is an electromagnetic pump that may be used in place of the recirculation pump of  FIG. 1 . 
         FIG. 7  is a cross-sectional view of a third embodiment of the reverse osmosis system. 
         FIG. 8  is a cross-sectional view of a fourth embodiment of the present disclosure. 
         FIG. 9  is a cross-sectional view of a fifth embodiment of the reverse osmosis system according to the present disclosure. 
         FIG. 10  is a cross-sectional view of a sixth embodiment of the reverse osmosis system according to the present disclosure. 
         FIG. 11  is a cross-sectional view of a seventh embodiment of the reverse osmosis system according to the present disclosure. 
         FIG. 12  is a cross-sectional view of an eighth embodiment of the reverse osmosis system according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     Referring now to  FIG. 1 , a first embodiment of a reverse osmosis system  10  is illustrated. The reverse osmosis system  10  includes a pressure tank  12  that includes a housing  14  and a cover  16 . The housing  14  may be a cylindrical housing having a longitudinal axis  18 . A cover  16  is securely fastened to the housing  14  during the reverse osmosis process to maintain a pressurized condition therein. The cover  16  may be opened for servicing components within the pressure tank  12 . The pressure tank  12  may have a longitudinal axis  18  should the system be cylindrical. 
     The pressure tank  12  may be divided into three different volumes that include a first volume  26  (adjacent to a first end of the pressure tank  12 , as illustrated in  FIG. 1 ), a second volume  28  (adjacent to the second end of the pressure tank  12 ) and a third volume  30  (between the first volume  26  and the second volume  28 ). The first volume  26  is separated from the second volume  28  by the third volume  30 . 
     A fluid passage  34  may communicate fluid between the second volume  28  and the first volume  26 . The fluid communication process will be further described below. The fluid passage  34  may be formed by a pipe between the first volume  26  and the second volume  28 . 
     A plurality of membranes  40  are disposed in the third volume  30 . The membranes  40  may be arranged away from a first end  42  of the third volume near a second end  44  of the inner chamber  30 . The membranes  40  may be disposed within a membrane housing or tube  46 . The membranes  40  allow permeate to pass therethrough. Permeate is collected in a collection pipe  48  which is disposed in each of the membrane housings  46 . Only one collection pipe  48  for one membrane  40  is illustrated for simplicity. Each membrane has a collection pipe  48 . Each permeate collection pipe  48  is in fluid communication with a permeate manifold  50 . The permeate manifold  50  fluidically communicates the permeate out of the pressure tank  12  using a permeate outlet pipe  52 . 
     The membrane housings  46  may be secured by one or more tube sheets. In this example, a first tube sheet  54  and a second tube sheet  56  are used. The tube sheets  54 ,  56  may be formed from various lightweight material since differential pressures acting on the tube sheets are low. The tube sheets  54 ,  56  may, for example, be formed from a sheet metal, plastic or other lightweight material. The tube sheet  56  may be sealed to or against the wall of housing  14 . The tube sheet  54  may not extend across to housing  14 . At least one tube sheet  54 ,  56  separates and prevents the flow of brine directly between the second volume  28  and third volume  30 . The sheets  54 ,  56  ensure the brine passes through tubes  46 . In this embodiment, the tube sheets  54 ,  56  orient the housings  46  in a direction parallel with the longitudinal axis  18  of the pressure tank  12 . A number of housings  46  and thus a number of membranes  40  may be disposed within the pressure tank  12 . As will be illustrated below, sixteen housings  46  and thus sixteen membranes  40  are disposed. Various numbers of membranes  40  may be used. 
     A circulation pump  62  is used to circulate fluid from the second volume  28  to the first volume  26 . The movement of fluid from the second volume  28  circulates through the fluid passage  34  to the first volume  26  and ultimately into the third volume  30 . The direction of circulation is illustrated by arrows  64 . 
     The circulation pump  62  may be driven by a motor  66 . The motor  66  may be a submersible motor  66 . The motor  66  may be located at various locations within the second volume  28  or within the third volume  30  including directly adjacent to the pump or included as part of the circulation pump  62 . The motor  66  may be coupled to the pump  62  by a shaft  68  extending therebetween. The circulation pump  62  may be located in other places within the pressure tank  12  including within the first volume  26 . 
     A low-pressure supply pipe  70  may be used for supplying low-pressure feed fluid into the pressure tank  12 . More specifically, the feed pump  72  may communicate low-pressure feed fluid through the housing  14 . The feed pump  72  may be in fluid communication with the supply pipe  70 . The feed pump  72  may increase the pressure of the low-pressure fluid. The feed pump  72  may be coupled to a feed motor  74 . The feed motor  74  may be a submersible motor used for driving the feed pump  72 . The feed pump  72  may have an output in fluid communication with a feed manifold  76 . The feed manifold  76  may have a plurality of feed manifold outlets  78 . The feed manifold outlets  78  may be disposed adjacent to or near an end of the membrane housings  46  nearest the first end  42 . Thus, fresh feed fluid is thus provided near the membranes and reduce mixing with the increased salinity fluid within the pressure tank is achieved. 
     The pump  72 , the motor  74 , the feed manifold  76  and the feed manifold outlet  78  may all be disposed within the third volume  30 . 
     A distribution plate  80  may be disposed across pressure tank  12 . The distribution plate  80  may be mechanically coupled to the inner wall  14  of the pressure tank  12 . Various fastening means may be used. Removable fasteners allow access to the membranes after the cover is removed. The distribution plate  80  may have vanes  82  used for evenly distributing the fluid that is recirculated through the fluid passage  34  and minimizing the turbulence and mixing of the elements within the third volume  30 . 
     In operation, low-pressure feed fluid is provided through the feed pipe  70 . The pump  72  increases the pressure of the feed and also increases the pressure within the pressure tank  12 . The feed fluid is communicated adjacent to the membranes  40 . After pressure has risen above the osmotic pressure, permeate from the permeate collection tube  48  is removed from the pressure tank  12  by the permeate manifold  50 . The circulation pump  62  circulates brine fluid in the second volume  28  through the fluid passage  34  to the first volume  26 . The recirculated brine fluid from the first volume then enters the third volume  30  through the distribution plate  80 . Fluid then passes through membrane  40  to second volume  28 . 
     Referring now to  FIG. 2 , a cross-sectional view of a tube sheet  56  taken in a direction perpendicular to the longitudinal axis  18  is set forth. As is illustrated, a plurality of membrane housings  46  are illustrated. In this embodiment, sixteen membrane housings are illustrated. However, various numbers of membrane housings including only one membrane housing may be provided. The tube sheet  54  may also be configured in a similar manner. The tube sheet  56  forces brine fluid to pass through the housing  46  and the brine fluid not converted into permeate is routed into the second volume  28 . The tube sheet  54  allows fluid to enter the membrane housing  46  from the third volume  30 . 
     Referring now to  FIG. 3 , a second embodiment of a reverse osmosis system  10 ′ is illustrated. In this embodiment, the motor  74  of  FIG. 1  is replaced with motor  174  and a shaft seal  176  in the housing  14  of the pressure tank. The motor  174  is located outside of the pressure tank  12  and may provide a lower cost and high-efficiency motor than the submersible motor  74  illustrated in  FIG. 1 . A shaft seal  176  seals the motor shaft  178  from leakage from the pressure tank  12 . 
     A non-submersible recirculation motor  150  may also be provided in place of the recirculation motor  50 . The recirculation motor  150  may also have a shaft  152  that is sealed in the exterior wall of the pressure tank  12  by a shaft seal  154 . The motor  150  is coupled to the recirculation pump  62  that operates is described in the description of  FIG. 1 . The remaining elements and the operation of the second embodiment of the reverse osmosis system  10 ′ is the same as described above with respect to  FIG. 1 . 
     Referring now to  FIG. 4 , the circulation pump  62  and the recirculation motor  50  of  FIG. 1  may be replaced by a turbocharger  210 . The turbocharger  210  may include a pump portion  212  and a turbine portion  214 . A common shaft  216  may be used to rotate the pump  212  in response to the rotation of the turbine  214 . 
     The turbine  214  may be in fluid communication with the pipe  76  and outlet  78 . The feed flow through the pipe  76  rotates the turbine which in turn rotates the pump  212  to generate a recirculation current or flow within the pressure tank  12 . 
     Referring now to  FIG. 5 , the outlets  78  may include an eductor  230 . The eductor  230  induces brine circulation. The brine flow from the feed pump  72  is expelled at higher pressure due to the energizing effect of the high-feed flow velocity from the feed pump  72 . The outlet  232  of the eductor  230  receives the feed fluid from the pump  72  which is mixed with brine fluid  236  and thus the combined fluid  238  may not flow through a manifold  76  as described above. 
     Referring now to  FIG. 6 , an electromagnetic pump may replace the pump  62  and motor  66  illustrated in  FIG. 1 . The electromagnetic pump  260  may also replace the motor  150  and pump  62  illustrated in  FIG. 3 . Power lines  262  provide power to the electromagnetic pump to create electric currents and magnetic fields to provide a pumping action in the highly conductive brine fluid. The electromagnetic pump  260  has no moving parts and thus has increased reliability. 
     Referring now to  FIG. 7 , another embodiment of the reverse osmosis system  10 ″ similar to  FIG. 1  is illustrated having a recharging arrangement  310 . The recharging arrangement  310  allows continuous operation in a single-batch tank by purging of the brine with fresh feed once a maximum concentration has been reached in the pressure tank  12 . Brine is depressurized as it leaves the tank and incoming feed is pressurized before entering the tank. A turbocharger  312  may be used to recover some of the energy lost in the process. The turbocharger  312  includes a pump portion  314  and a turbine portion  316 . The turbine portion  316  provides brine fluid through brine pipe  318 . The brine pipe  318  may provide brine fluid to the turbine portion  316  through a valve  320 . The pump portion  314  may inject feed fluid under high pressure through a check valve  322 . In addition to the increase in pressure from the pump portion  314 , a charge pump  330  may be used to increase the pressure in the feed fluid. The feed fluid for the pump  330  may be provided from a feed tank  350 . The feed tank  350  may also provide feed fluid to the pump  72 . 
     The charge pump  330  may be operated by a motor  362 . The motor may be controlled by a controller  364 . The controller  364  may be a variable frequency drive that is operated in response to a pressure sensor  366 . The charge pump  330  operates during the recharge process. When the batch process has reached a final brine concentration, the pump  330  is energized and the valve  320  is opened allowing the brine to be drawn in from the first volume  26  through pipe  318 . The brine from the first volume  26  is at a high pressure and thus the turbine portion  316  is rotated which in turn rotates the pump portion  314  to increase the pressure in the feed from the feed tank  350 . The check valve  322  opens when the pressure is sufficient to overcome the pressure tank pressure and allow the feed into the pressure tank within the second volume  28 . When providing the feed into the inlet  370 , flow within the pressure tank  14  is opposite to the arrows  64 . The combination of the reversal of flow and the high rate of input from the fresh feed from the feed tank through the feed inlet  370  may reduce scale and foulants from the membrane which may be carried out through the pipe  318  during the process. The inlet may be at various locations including in the center of the lower surface of the pressure tank. Feed fluid from the pipe  370  may also travel up the membrane housings to reduce and remove the foulants from the membrane  40 . The speed of the pump  330  may be controlled by the controller  364  which controls the speed of the motor  362 . Fluid from the pipe  318  that passes through the turbine  360  may be input to a drain  374  at a reduced pressure. 
     The fluid that enters the drain  374  has a significantly lower pressure than the fluid from the pipe  318  as reduced by the turbine portion  316 . 
     Referring now to  FIG. 8 , another embodiment of the reverse osmosis system  10 ′″ similar to that of  FIG. 7  is illustrated having the motor  74  and pump  72  removed and controlled by the charge pump  330  and motor  362 . In this embodiment the charge pump  330  is provided directly after the feed tank  350 . After the charge pump  330 , fluid may flow into the fluid manifold or into the turbocharger  312 . A valve  410  may be provided between the charge pump  330  and the turbocharger  312  to selectively control the input to the pump portion  322 . During recharge the valve  410  is opened to allow feed fluid to flow from the feed tank  350  through the charge pump  330  and into the pressure tank  312  as described above. In this embodiment, the additional pump within the third volume  30  is removed. Valves  410  and  320  are closed during batch operation and opened during recharge operation. 
     Referring now to  FIG. 9 , another embodiment of the reverse osmosis system  10 ″″ similar to  FIG. 7  is illustrated. In this embodiment, a work exchanger  510  replaces the turbocharger  312 . The work exchanger  510  is used to receive high-pressure fluid from the first volume  26  through the valve  320  which is open during the recharge process and convert the work to useful energy (to pressurize the feed fluid into the pressure tank  12 ). Feed fluid is provided into the pressure tank  12  using a booster pump  572  that is coupled to a booster motor  514 . The recharge process uses the flow work exchanger  510  to inject fresh feed into the pressure tank while removing an equal volume of concentrate through the pipe  318 . The booster pump  572  is used to make up for pressure loss in the piping and the work exchanger  510 . During the recharge process, the valve  320  is opened and the pump  512  is energized using motor  514 . The pump  72  may continue to operate during the recharge process and thus the permeate production continues without interruption. 
     Referring now to  FIG. 10 , an embodiment of a reverse osmosis system  10 ′″″ similar to  FIG. 1  is illustrated. In this embodiment, an additional tank  410  is fluidically coupled to the pressure tank  12 . The tank  410  may have an inlet pipe  412  that fluidically communicated fluid from the first volume of the pressure tank  12  into the fluid tank  410 . Fluid is provided from the fluid tank  410  through an outlet pipe  412 . The outlet pipe  412  may fluidically couple fluid into the third volume of the pressure tank  12 . A valve  414  may be used to control the flow out of the tank  410 . The tank  410  increases the amount of feed that can be processed by a batch. 
     Referring now to  FIG. 11 , another embodiment similar to  FIG. 1  is illustrated. In this embodiment, the pressure tank  12 ′ is increased in length to increase the amount of fluid volume within the tank to insure a sufficiently long batch run. When the feed total dissolved solids (TDS) is high then additional tank volume may be needed to insure a sufficiently long batch run. When the total dissolved solids are low, the smaller tank volume may be more appropriate. A tank extender  450  with seals  452  may be used to increase the length of the tank  12 ′. Mechanical fasteners or the like may be used to mechanically couple the extender  450  to the housing  14  of the previous embodiments. The fluid passage  34 ′ may also be extended so that fluid from the second volume  28  may be communicated to the first volume  26 . 
     Referring now to  FIG. 12 , another embodiment similar to  FIG. 1  is provided. In this example, easy access so that the membranes  40  may be easily replaced is provided. In this embodiment, the membrane tubes  46  extend through the second tube sheet  56 . Brine fluid from the membrane tubes  46  still enters the second volume  28 . 
     A plurality of covers  510  is secured within the housing  14 . The covers  510  are adjacent to the membranes  40  so that the membranes may be easily removed from within the pressure tank  12 . The covers  510  may be coupled to the bottom of the housing  14  by various methods, including, but not limited to, bolting, snap rings, or other suitable methods. In this embodiment, the permeate manifold  50 ′ is located outside of the pressure tank  12 . The collection tubes  48 ′ extend through the covers  510 . To access the membrane elements, the covers  510  are removed. Prior to removal of the covers  510 , the collection tubes  48 ′ may be disassembled to allow disassembly of the covers  510 . 
     A spacer  512  may be used to allow brine fluid exiting from the membrane to flow to the fluid passage  34 . The spacer  512  may be a separate structure or mechanically coupled to the covers  510 . 
     It should be noted that the various components of the disclosure for each of the figures may be interchanged. For example, either or both motors may be located outside the pressure tank or within the pressure tank  12 . Likewise, the recharging systems illustrated in  FIGS. 7-12  may also be interchanged with themselves or the other components. The alternative components of  FIGS. 4-6  may be individual in any embodiment separately or in combination. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.