Abstract:
A pump assembly to move water past a reverse osmosis membrane, the pump assembly having a first pump and a second pump each including a bore having a longitudinal axis and surrounding a chamber. First and second partition members extend longitudinally of the chamber. The second partition is moveable relative to the first partition member, and divides the chamber into a first sub chamber and a second sub chamber. A shaft is attached to the second member to cause angular movement thereof about the axis to change the volumes of the sub chambers. End caps are fitted to ends of each chamber to contain pressure, and ducting is provided to provide for the flow of water. The shaft of the first pump is coupled to the shaft of the second pump so that the first pump second partition angularly oscillates in phase with the second pump second partition.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is an U.S. national phase application under 35 U.S.C. §371 based upon co-pending International Application No. PCT/AU2008/000675 filed on May 14, 2008. Additionally, this U.S. national phase application claims the benefit of priority of co-pending International Application No. PCT/AU2008/000675 filed on May 14, 2008 and Australia Application No. 2007902705 filed on May 21, 2007. The entire disclosures of the prior applications are incorporated herein by reference. The international application was published on Nov. 27, 2008 under Publication No. WO 2008/141361. 
     TECHNICAL FIELD 
     The invention relates to reverse osmosis systems and, more particularly, provides a novel device to reduce the energy requirement in comparison to conventional reverse osmosis methods. 
     BACKGROUND OF THE INVENTION 
     Reverse osmosis is a phenomenon that was first considered in the 1950&#39;s as a method for separating the components of a solution. Since that time the process has been highly developed and refined and is now one of the primary methods of producing desalinated water from saline water. 
     In the reverse osmosis process the solution to be separated is passed under high pressure past a reverse osmosis membrane enclosed within a higher pressure chamber. The reverse osmosis membrane allows a certain percentage of the solution to pass through the membrane as potable water, while rejecting the various impurities within the water, including salt. 
     Although reverse osmosis can be used for many sorts of separation it is most commonly used for desalination of salt or brackish water, especially sea water. Accordingly, for convenience, throughout this specification the feed stock or saline water to be desalinated will be described generally as “feed water” the desalinated water produced as “product water” and the feed water which has had the product water extracted from it, as “brine” and reverse osmosis as “RO”. 
     In a conventional RO system, from 10% to 40% of the feed water is recovered as potable water, but regardless of the recovery rate, 100% of the feed water passing through the system must be brought to operating pressure by the high pressure pump. To bring the feed water to the necessary pressures required for the RO operation, conventional systems require significant amounts of energy. Various ways have been explored to reduce the energy required. 
     Among the ways that have been tried are energy recovery methods but if energy is being recovered, then more energy than needed is being supplied. Furthermore, these methods are unable to recover all the energy being lost by conventional methods. 
     Disclosed in U.S. Pat. No. 5,462,414 is a pump employed in reverse osmosis systems. The pump is a dual chamber pump, each chamber having a piston with the pistons linearly reciprocated alternatively pumping feed water towards the reverse osmosis membrane of the desalination system. 
     The ram and piston assembly is caused to move by the supply of feed water to one end of the hydraulic unit. The forward movement of the ram at this end causes the ram and piston at the other end to move at the time and at the same rate. Feed water at this end is contained within a closed loop either side of the piston, said closed loop also includes a RO membrane. 
     As the piston moves feed water is driven from one side of the piston to the other via the RO membrane. As the feed water enters the side of the piston containing the ram, the pressure of the water is intensified by the volume of the ram. This intensified pressure of the feed water causes the RO process to take place. 
     This device is far superior to those that had preceded it but still has drawbacks in that it has a large number of parts and a fixed recovery rate, making it unfit to alter the volume recovery rate. It is also unsuitable to be retro fitted to existing systems. 
     Disclosed in U.S. Pat. No. 6,491,813 are two pumps similar to that as described in U.S. Pat. No. 5,462,414. The first solution offered in this patent, is the same as the above. The second solution provides for pressure intensification by the use of a high pressure pump. This system still has its drawbacks due to a large number of parts and the use of non return valves. 
     OBJECT OF THE INVENTION 
     It is the object of the present invention to overcome or substantially ameliorate at least one of the above disadvantages. 
     SUMMARY OF THE INVENTION 
     There is disclosed herein a pump assembly to move water past a reverse osmosis membrane, said pump assembly having a first pump and a second pump, each pump including: 
     a bore having a longitudinal axis and surrounding a chamber; 
     a first partition member extending longitudinally of the chamber; 
     a second partition member also extending longitudinally of the chamber and moveable relative to the first partition member, and dividing said chamber into a first sub chamber and a second sub chamber; 
     a shaft attached to said second member to cause angular movement thereof about said axis to change the volumes of said first and second sub chambers; and 
     ducting communicating with said first and second sub chambers to provide for the flow of water with respect thereto as the volumes are varied; and wherein 
     the shaft of said first pump is coupled to the shaft of said second pump so that the first pump second partition angularly oscillates in phase with the second pump second partition. 
     There is further disclosed herein, the above pump assembly in combination with a reverse osmosis membrane, with the pump assembly being employed to pass feed water past the membrane to desalinate the water. 
     Preferably, said membrane is part of a reverse osmosis assembly having a feed water inlet, with each pump being operable to deliver feed water to said inlet, and said combination includes a further pump to deliver feed water to said feed water inlet. 
     Preferably, said assembly includes an outer housing within which the first and is second pumps are located with said outer housing being provided to be internally pressurised. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings wherein: 
         FIG. 1  is a schematic isometric view of one of the cylinders, excluding end caps, in the pump system to be used with a reverse osmosis membrane; 
         FIG. 2  is a schematic top plan view of the pump of  FIG. 1 ; 
         FIG. 3  is a schematic top plan view of a modification of the pump of  FIG. 1 ; 
         FIG. 4  is a schematic sectioned side elevation of a still further pump; 
         FIG. 5  is a schematic diagram illustrating a drive system for a reverse osmosis system; 
         FIG. 6  is a schematic diagram illustrating a closed loop drive system for a reverse osmosis system; 
         FIG. 7  is a schematic diagram of a reverse osmosis system during a first cycle; 
         FIG. 8  is a schematic diagram of the system of  FIG. 7  during a second cycle; and 
         FIG. 9  is a schematic modification of the pump of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIGS. 1 and 2  of the accompanying drawings there is schematically depicted a pump  10  to be used in a reverse osmosis membrane system, and more particularly but not exclusively to a system when used to produce desalinated water. 
     The pump  10  has a cylinder  11  having an internal generally cylindrical bore  12  surrounding a chamber  14 . The chamber  14  has a longitudinal axis  13 . 
     Mounted so as to extend longitudinally of the axis  13  is a shaft  15 , while fixed to the cylinder  11  and extending to the shaft  15  is a first partition member  16 . In this embodiment the partition member  16  is fixed so as to be stationary relative to the cylinder  11 . 
     Fixed to the shaft  15  is a second partition member  17  that divides the chamber  14  into a first sub chamber  18  and a second sub chamber  19 , with the volumes of the sub chambers  18  and  19  being varied by angular movement of the member  17  about the axis  18 . 
     Operatively associated with the sub chamber  19  is a duct  20  that provides for the flow of water to and from the sub chamber  19 . Operatively associated with the sub chamber  18  is a duct  21  that provides for the flow of water with respect to the sub chamber  18 . 
       FIG. 3  illustrates a pump  10  that is a modification of the pump of  FIGS. 1 and 2 . In this embodiment there are two “fixed” first partition members  16 , and two “movable” second partition members  17  that are angularly oscillated in unison about the longitudinal axis  13  by the angular movement of the shaft  15 . Accordingly there are two sub chambers  18  and two sub chambers  19 , and two chambers  14 . Other variations of the design are to divide the one cylinder into four or more equal number of compartments with corresponding changes in the number of partition members  17 . 
     Typically the pump  10  in  FIGS. 1 and 2  would be part of a pump assembly  20  ( FIG. 4 ), the assembly  20  consisting of two pumps  10 , with the two shafts  15  linked so as to rotate in unison. 
     The chambers  14  are sealed at their ends by end caps  21  and a central cap  22  within which bearings  23  are mounted to support the shafts  15  for angular movement about the longitudinal axis  13 . Seals  24  are also provided. 
     In use of the above described pump  10 , the pump  10  would be coupled to a low pressure feed pump  30  ( FIG. 5 ) (by valve not illustrated) so that feed water at low pressure was delivered to the sub chamber  18  via duct  21 . For example, when water at low pressure is delivered to the sub chamber  18 , rotation of partition member  17  occurs and brine in the sub chamber  19  is delivered to the outlet duct  20  and thus to waste. 
     In  FIG. 6  there is schematically depicted a desalination system  30 . The system  30  employs the pump  10  as well as a reverse osmosis membrane assembly  31  employing a membrane  32  that provides for the delivery of product water to an outlet  33 . The assembly  31  has an inlet  34  to which feed water is delivered under pressure due to operation of the pump  35 . 
     The high pressure pump  35  receives a supply of feed saline water and delivers it to the pump  10  and therefore membrane  31 . 
     The pump  10  is connected to the inlet  34 , as well as an outlet  36  from which the pump  10  receives water having passed the membrane  32 . In this present example, as the volume of the sub chamber  19  decreases, the volume of the sub chamber  18  increases by the same amount. As the pump  35  is a high pressure pump, it delivers extra supply of feed water at the pressure necessary for the reverse osmosis process to occur. This additional pressure is delivered to the closed loop of the assembly  31  that incorporates the pump  10 . The water delivered to the loop is equivalent to the volume of product water forced through the membrane  32  and delivered to the outlet  33 . The volume of water delivered to sub chamber  18  is the same as the volume delivered from the sub chamber  19 . 
     In  FIGS. 7 and 8 , there is depicted the full desalination system  30 . In this example, two pumps  10  are labelled pump  10 A and pump  10 B. 
     System  30  includes a further pump  58  that delivers low pressure feed water to the pumps  10 A and  10 B, as well as the pump  35  that delivers feed water at high pressure to the assembly  31 . 
     The pumps  10 A and  10 B are interconnected via conduits to the pumps  35  and  58  as well as the assembly  31  by means of a spool valve  37  to form a full desalination system. The spool valve  37  in particular coordinates operation of the pumps  10 A and  10 B. In that regard reference is made to  FIG. 4  where the pump assembly  20  is more fully depicted, with the shafts  15  coupled so as to be driven in unison. Accordingly in  FIGS. 7 and 8  the movable partition members  17 A and  17 B angularly oscillate in unison. The members  17 A and  17 B have the same swept volumes. 
     In  FIG. 7 , the spool valve  37  is configured so that feed water at low pressure is delivered from the pump  58  to the ports  45  and therefore port  47  to the duct  21 A so that feed water at low pressure is delivered to the sub chamber  18 A to drive the member  17 A. Accordingly brine in the sub chamber  19 A is delivered to the port  46 , then port  38  for delivery to the outlet (drain)  50 . As the feed water under low pressure being delivered to the sub chamber  18   a  drives the member  17 A, the member  17 B is accordingly driven. Thus the volume of the sub chamber  19 B is decreased and the volume of the sub chamber  18 B increased. Feed water in the sub chamber  19 B is delivered to the inlet  34  via the ports  20 B,  48  and  43 . During this cycle, feed water supplied by the further pump  58  is delivered to the high pressure pump  35 , which in turn delivers a volume of high pressure feed water into the closed loop of pump  10 B and assembly  31 . Product water (desalinated water) of the same volume as supplied by pump  35  is delivered to the outlet  33 , with the remaining water (brine) exiting from the outlet  36  and being delivered to the sub chamber  18 B via ports  41 ,  49  and  21 B. 
     In  FIG. 8  the spool valve  37  is configured so that the pump  58  is connected to the ports  42  and  48  so that feed water is delivered to the sub chamber  19 B via port  20 B. Accordingly the partition member  17 B is angularly driven to reduce the volume of the sub chamber  18 B and the brine in this chamber from the previous cycle is sent to drain  50  via ports  21 B,  49  and  40 . The partition member  17 A is driven by the rotation of  17 B to reduce the volume of the sub chamber  18 A so that feed water is delivered to the inlet  34  via ports  21 A,  47  and  44 . At the same time feed water supplied by pump  58  is delivered to high pressure pump  35 , which in turn delivers a volume of high pressure feed water into the closed loop of pump  10 A and assembly  31 . Product water of the same volume as supplied by pump  35  is delivered to outlet  33 . With the remaining water (brine) exiting from the outlet  36  and being delivered to the sub chamber  19 A via ports  39 ,  46  and  20 A. 
     Accordingly by moving the spool valve  37  cyclically between the configurations of  FIGS. 7 and 8 , the system  30  operates to provide desalinated product water at the outlet  33 . 
     In  FIG. 9  there is schematically depicted a modification of the pump  20 . In this embodiment the pumps  10 A and  10 B are encapsulated in a sealed outer housing  51 . In this embodiment, the outer housing  51  provides the “pressure vessel” with passages  52 ,  53  and  54  providing for a balance of pressure in the voids between the outside surfaces of pumps  10 A and  10 B and the pressure vessel  51 , thereby transferring the major pressure containment to the outer housing  51 . More particularly the outer housing  51  has end “dome” portions  55  joined by a cylindrical sleeve  56 . Additionally, shafts  15  of pumps  10 A and  10 B are hollow and are provided with passages  57  to provide for a balance of pressure. The above construction enables metal thicknesses employed in the cylinders  11  and end walls  21  to be reduced and for the shafts  15  to be of a lighter construction. 
     The above described preferred embodiments provide a number of advantages. 
     Substantially less energy is required to operate the system by comparison with conventional systems. 
     The device is simple and has a small number of parts. 
     The system is very versatile and adaptable by comparison to a system with a fixed recovery/volume ratio. In addition, all conventional systems can easily be adapted to the device by simply down sizing the output of the high pressure pump. All other components i.e. the pre-filter system, the membrane, booster pump and control circuit are unaffected by the addition of the device. 
     The output of the high pressure pump  35  can be precisely metered to match the production capacity of the membrane/s, the output can be precisely controlled and over production, which is detrimental to the membranes, is avoided. As a consequence no pressure regulating valve is needed, as is the case in conventional systems. 
     Another consideration is the adaptability of the pump  10 . By controlling the number of oscillations per minute of the partition members  17  with a speed control metering valve or by selection of pump capacity, one size device can be used for a number of different RO system sizes. Additionally by being able to independently control the volume of water supplied by the low pressure pump  58  and also the high pressure pump  35 . 
     Since the recovery/volume ratio can be varied, the device, in addition to RO sea water desalination can also be used in brackish water, nanofiltration and ultrafiltration systems. All systems will benefit from considerable power savings.