Abstract:
An apparatus and method for reversing the flow in a reverse osmosis system is described utilizing a single unitary valve. The improved system and method provides a means to reduce operating costs, maintenance and down time associated with a reverse osmosis system by providing a reliable and robust means to reverse the flow of fluid thereby flushing filter membranes.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to fluid treatment systems, and more particularly to a system and method for the continuous cleansing of reverse osmosis membranes contained within the system. 
       SUMMARY OF THE INVENTION 
       [0002]    The reverse osmosis membrane is well suited to, and accepted for, purifying a variety of liquids, including sea water, ground water, and the like. However, the input surface of the membrane against which the pressurized input fluid to be purified is forced against and through becomes clogged of solid materials which have been filtered out to produce product liquid. As the deposit on the input surface of the membrane increase, efficiency of the membrane decreases rapidly. 
         [0003]    A number of U.S. patents attempt to address the issue of cleansing of the filter or reverse osmosis membrane either during use or in conjunction with the interruption of the purifying process. However, none of these disclose the present system or method, nor do these references approach the relatively high efficiency achieved with the present system, both in terms of being devoid of downtime, as well as the unique and highly efficient means to accomplish cleansing of the membrane. 
         [0004]    The successful implementation of reverse osmosis technology requires long term reliable operation. With clean inlet water, the systems will function without disruption. However, inlet water is rarely clean, and requires pretreatment steps to remove silt, turbidity and fouling species. Because pretreatment systems are also rarely 100% efficient in the removal of foulants, over time reverse osmosis membrane arrays can lose efficiency due to plugging of the flow passages. 
         [0005]    Foulants can include scale, inorganic and/or biological slimes which either originate in the raw inlet water, or can grow in the intake structures of the desalination plant. The problem is well known and has been the target of much research and innovation. 
         [0006]    It is therefore an object of this invention to provide a fully automatic self-cleaning reverse osmosis liquid purification system which continually functions to both produce product liquid and to cleanse the membranes simultaneously. 
         [0007]    It is another object of this invention to provide a method of cleansing clogged reverse osmosis membranes utilizing a solenoid operated or hydraulically operated valve to reverse the flow of product liquid. 
         [0008]    In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with reference to the accompanying drawings 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a simplified schematic view of a prior art reverse osmosis system. 
           [0010]      FIG. 2  is a simplified schematic view of a prior art reverse osmosis system having discrete valves for flow reversal. 
           [0011]      FIG. 3  is a simplified schematic view of an embodiment of the invention. 
           [0012]      FIG. 4  is a simplified schematic view of a spool valve in Position A in accordance with an embodiment of the invention. 
           [0013]      FIG. 5  is a simplified schematic view of a spool valve in Position B in accordance with an embodiment of the invention. 
           [0014]      FIG. 6  is a simplified schematic view of a spool valve in Transition Position in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Referring first to  FIG. 1 , which depicts a reverse osmosis system  10  for filtering water in accordance with the prior art. Pretreated water  12  is supplied to a traditional liquid pump  14  where the pressure of the flow is increased accordingly. In the traditional reverse osmosis membrane array  15 , the flow is uni-directional whereby high pressure saline liquid  16  enters the membrane array  15  disposed in a pressure vessel  22 , and the first membrane element  18  of each pressure vessel  22  and then the next filter element such that at the point where the flow exits the array  15  from the last membrane element  20  the discharge flow has been converted from saline water  16  to very saline water  24 , and a fresh water flow  26  has also been established. Because the flow passages of membrane elements are small, the first element  18  in the pressure vessel  22  is typically subject to more foulants that have survived the pretreatment process  12  than the last membrane element  20 . Over time, the membrane array  15  will suffer from reduced flow and will require higher pressures to operate, both of which can damage the membrane array  15 . 
         [0016]    The current mechanism for addressing this is to use chemical cleaning techniques. This requires that the membrane array  15  be shutdown, and various chemicals are recirculated through the membrane array  15  to restore flow and pressure characteristics to an acceptable level. This process requires additional cost, additional equipment, process downtime and additional cost for the operator. Where inlet water has difficult characteristics or where problems exist with the pretreatment system, membrane fouling can render plants unusable, so there is great interest in design improvements that reduce the requirement for membrane cleaning. 
         [0017]    As one skilled in the art can quickly see, one of the primary problems with the membrane arrays  15  is the uni-directional flow. If the flow could be reversed, then foulants that impinge in the leading membrane elements could be removed because the flow would be away from the element instead of into the element. By altering the flow into the membrane array  15  from the front to the rear, and then back again, the tendency of foulants to remain in the membrane array  15  is reduced because the flow will carry debris out of the element from time to time instead of always into the array in the same direction. 
         [0018]    Referring now to  FIG. 2 , which depicts another reverse osmosis filtering system  10  which employs the use of discrete valves, denoted as V 1 , V 2 , V 3  and V 4  in order to reverse the flow of fluid to flush and clean the filter array  15 . This technique is already known, as noted by Japanese Patent JP6079142 to HIDEO, which is incorporated herein by reference. However, from a practical perspective the reversal of flow requires a number of discreet two way valves to achieve the flow reversal, and this added complexity detracts from the implementation of the technique. 
         [0019]    The prior art for achieving flow reversal in a membrane array  15  consists of a number of discreet valves (V 1 , V 2 , V 3 , V 4 ) that interrupt and redirect flow such that the inlet and outlet to the membrane array  15  alternate. It is desirable to keep the system online during this process, and therefore the valve timing must be very precise in order to avoid water hammer or pump dead heading. Because of these issues and the cost implications, the implementation of HIDEO is not found in the reverse osmosis industry. 
         [0020]    As shown in  FIG. 2 , saline inlet water is directed from the pretreatment system  12  to the high pressure pump  14 . The pump raises the pressure such that the membrane array  15  will separate the saline inlet water into a highly saline flow stream  24  and a fresh water stream  26 . The high pressure saline water  16  can be directed to membrane pressure vessel  22  if either V 1  or V 2  is open or closed. For the purposes of this description we will assume that V 1  is open and V 2  is closed. In this way, high pressure inlet water  16  is directed to the membrane pressure vessel  22  and membrane element  18  is the leading element and membrane element  20  is the last element in the pressure vessel  22 . Note that the pressure vessel may consist of may consist of one vessel containing a single element or multiple elements arranged within the vessel in series, and there may be a single vessel, or multiple membrane pressure vessels in parallel. 
         [0021]    Still referring to  FIG. 2 , V 3  is closed and V 4  is open. In this configuration, flow will pass from inlet  16  through V 1  to pressure vessel  22 . Membrane element  18  in this case is the first element and membrane element  20  is the last. Highly saline water exits the vessel  22  at conduit  30  and is directed to outlet  24  through open valve V 4 . Fresh water is provided from vessel  22  through outlet  26 . Outlet  24  may be connected to an additional process for further treatment, a waste stream or energy recovery system, as well known in the art. 
         [0022]    To reverse flow through the membrane vessel  22  or array  15  using this prior art design, it is necessary to actuate the various valves. Similar to our example case previously described, inlet water is directed from the pretreatment system  12  to the high pressure pump  14  which creates pressure and flow for the process at  16 . While previously the flow was directed through open valve V 1  to the membrane pressure vessel  22 , in order to reverse flow, V 1  is now closed and V 2  is open. Flow and pressure are therefore directed through V 2  and through conduit  30  to pressure vessel  22 . Membrane element  20  is now the first element and membrane element  18  is the last element. With valve V 4  closed and valve V 3  open, saline water is directed through conduit  30  and the membrane elements  20  through  18  separate the water into highly saline water which exists through conduit  28  and through valve V 3  which is open to outlet  24 . 
         [0023]    Note that in one configuration conduits  30  and  28  have flow in one direction and in the other configuration conduits  30  and  28  have flow in the other direction. The result of this design is that the membrane vessel  22  is subject to reversing inlet and outlet flow whereby membrane elements  18  and  20  alternately are the first and last filter element as defined by the inlet and outlet conditions of the process. While this system is functional, practically, the implementation of this arrangement requires precise valve timing and costly valves. If for instance valves V 1  and V 2  are closed at the same time during the transition, even briefly, between each aforementioned state, then pump  14  will be deadheaded resulting in water hammer, and similarly if valves V 1  and V 2  are closed at the same time during the transition, even briefly, the membrane array  15  will lose pressure. In addition, if valves V 2  and V 3  are open at the same time, the system will not function properly. All of these traits can be damaging and highly undesirable. 
         [0024]    The current invention addresses this complexity, and provides for a single simple device and method for flow reversal in a reverse osmosis membrane array. The invention provides for an improved method of reversing flow in a membrane array. The invention replaces a quantity of valves as required to achieve reversing flow as described previously in the prior art with a single unitary device. 
         [0025]    Referring now to  FIG. 3 , which depicts a simplified schematic diagram in accordance with an embodiment of the invention  100 , where like numerals have similar function and purpose, a pretreated fluid  12  is in fluid communication with a high pressure pump  14  as previously discussed. An embodiment of the valve device  32  would have four process connections, the inlet  16  from the high pressure pump  14 , a first bi-directional hydraulic conduit process connection  30  to the membrane array  15 , a second bi-directional hydraulic conduit process connection  28  to the membrane array  15 , and an exhaust outlet  24 . During operation, all process connections are at high pressure relative to atmospheric conditions. Note that conduits  28  and  30  would be subject to reversing flow direction conditions whereby conduit  16  would be an inlet only and outlet  24  would be an outlet only. The flow into the valve device  32  would equal the flow out of the valve device  32  at outlet  24  plus the flow out of the membrane array at  26 . It is preferable that the membrane array  15  be able to withstand reversing flow. 
         [0026]    Referring now to  FIG. 4 , which depicts a simplified layout of the valve  32  in accordance with an embodiment of the invention, whereby the valve  32  is in a position denoted as Position A. A conduit  34  suitably sized for the capacity and pressure of the system is provided whereby one distal end  36  of the conduit  34  is blocked and located at the other distal end of conduit  34  is mounted with a reciprocating actuating device  38  which may be for example an electrically operated solenoid or reciprocating hydraulic actuator. The actuating device  38  may be a reciprocating valve that is actuated by an electronic solenoid, a linear electronic actuator, a cam, an air piston, or a hydraulic actuator. The actuating device  38  could also be a rotary actuating device. The conduit  34  is arranged such that there are six apertures  39   a - 39   e  which are suitably sized for the filtration process. These apertures  39   a - 39   e  are hydraulically connected via conduits to the desalination process system and consist of inlet  39   b  from high pressure pump  16 , outlet  39   e,  membrane array connection  39   c  and  39   a  which are hydraulically connected together at connection  42 . 
         [0027]    The actuating device  38  is connected via a shaft  44  to a plurality of separation devices or lands  46 ,  48  and  50  which are spaced in a predetermined fashion to direct the flow of fluid through the valve  32 . The lands  46 ,  48  and  50  are configured to sealingly and slidingly separate the conduit  34  and apertures  39   a - 39   e  into chambers. Preferably, the lands  46 ,  48  and  50  are configured to minimize or eliminate leakage between the chambers. Preferably, conduit  34  is substantially at the same pressure in all chambers, excepting flow losses. This reduces the driving force required by actuating device  38  which saves cost, weight and complexity. 
         [0028]    With this configuration, flow enters the device at inlet  16  and is directed to various apertures depending on the position of the actuating device  38 . Similarly, flow enters and exits the device  32  at connection  40  and connection  42  depending on the position of the actuating device  38 . 
         [0029]    Referring still to  FIG. 4 , with the valve  32  in Position A, whereby flow is directed from the high pressure pump through aperture  39   d  into conduit  34 . In this configuration, flow is blocked by lands  48  and  50  and fluid flow is directed to aperture  39   c  through connection  42  to the membrane array as shown by arrow  41 . Returning flow is directed to the device through connection  40  through aperture  39   b  and exhausts through aperture  39   e  and outlet  24  as shown by arrow  43 . 
         [0030]    Referring now to  FIG. 5 , (where like numerals have like meaning) which shows valve  32  in Position B, whereby flow is directed from the high pressure pump through aperture  39   d  into conduit  34 . Flow is blocked by lands  48  and  50  and is directed to aperture  39   b  through connection  40  to the membrane array as shown by arrow  52 . Returning flow is directed to the valve  32  through connection  42  through aperture  39   a , disposed between lands  46  and  48  to exhaust through aperture  39   e  as shown by arrow  54 . 
         [0031]    Referring now to  FIG. 6 , (where like numerals have like meaning) which shows valve  32  in a Transition State in which the actuating device  38  is transitioning between Position A and Position B, and vice versa. Flow is directed from the high pressure pump through aperture  39   d  into conduit  34 . Flow is blocked by lands  48  and  50  and is directed to both apertures  39   c  and  39   b  through outlet  42  and outlet  40  to the membrane array. In this transition state, whereby the separation devices  46 ,  48  and  50  are slidingly and sealingly transferring via the actuation device  38  through shaft  44  from Position A to Position B or vice versa, there is no position where inlet flow from the high pressure pump at aperture  39   d  is blocked. 
         [0032]    The invention is constructed such that lands  46 ,  48  and  50  are fixed to the shaft  44  and the dimensional relationship between  46 ,  48  and  50  and apertures  39   a - 39   e  are such that in Positions A and B and during transition between those two positions, the apertures are correctly closed or open as required to reverse the flow and improve the filtering process with no down time or damage to the equipment. This configuration also ensures the flow paths from  16  to  40  or  42 , and  40  or  42  to  24  are never interrupted even during transition from Position A to B and B to A. It should be noted that the frequency of the transition can be easily tailored to meet the needs of the particular application. 
         [0033]    Optionally, during this transition, to reduce any process impacts, the high pressure pump  14  can be turned down to below membrane osmotic pressure prior to transition, and then turned up again after transition. 
         [0034]    As can be clearly seen, the invention is relatively low cost to manufacture due to the balanced design and provides for the reduction of foulants in the membrane array due to flow reversal. Another benefit of the invention is the reduction of bio-fouling due to the salinity change whereby the first element is initially subject to saline water inlet, but on reversal is subject to highly saline water, and vice-versa for the last elements in the membrane array. The changing and variable salinity eliminates steady state conditions that biological activity prefers which may restrict or eliminate biomass growth within the system. 
         [0035]    In addition to these benefits, the invention may also reduce the requirement for the pretreatment process to provide very clean water to the membrane array which will reduce the pretreatment costs associated with a particular application. 
         [0036]    Although an exemplary embodiment of the invention has been shown and described, many changes, modifications, and substitutions may be made by one having ordinary skill in the art without necessarily departing from the spirit and scope of this invention.