Abstract:
Various aspects of the technology provide for reducing noise and vibration in a pressure exchanger for high pressure fluid handling equipment such as a desalination system, by disposing grooves between a seal surface and a port. The groove reduces a hammer effect in moving high pressure fluid to a low pressure port and moving low pressure fluid to a high pressure port. Reduction in the hammer effect, in addition to reducing noise, reduces vibration that can cause deterioration of high pressure fluid handling equipment.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to desalination equipment, and more particularly to pressure exchange devices. 
         [0003]    2. Background 
         [0004]    A pressure exchange device may recover potential energy that is stored in a compressed fluid. A typical application for a pressure exchange device is in a desalination system. For example, seawater may be compressed to a high pressure, and reverse osmosis may be used to extract fresh water from the compressed seawater resulting in a high pressure brine byproduct. If the high pressure brine is discarded then the energy used to compress that volume of concentrate is also wasted. A pressure exchange device may use the high pressure brine to compress seawater for further fresh water extraction. Unfortunately, a pressure exchange device generates substantial noise when the brine and seawater undergo sudden changes in pressure during the pressure exchange. The noise is characteristic of vibration and stress that can degrade the extraction equipment including the pressure exchanger, pipes, manifolds, pumps, turbines, filters, and membranes. 
       SUMMARY 
       [0005]    Noise results from an almost instantaneous change in pressure, or impulse, as a high pressure fluid suddenly comes into contact with a low pressure fluid in a pressure exchanger. The impulse occurs at the edge of a port opening where a previously sealed duct is brought into communication with fluid in the port. For example, high pressure fluid in a sealed duct may be brought into communication with low pressure fluid in a port. In another example, low pressure fluid in a sealed duct may be brought into communication with high pressure fluid in a port. The noise caused at the interface of high pressure and low pressure fluid may be reduced by using a groove extending from the port into the sealing surface to release a small portion of the fluid before all the fluid reaches the edge. The pressure energy stored in the high pressure fluid is applied through the groove to the low pressure fluid to reduce the amount of energy wasted due to noise, turbulence, frictional loses, boundary layer shear, cavitation, flow erosion, and/or the like. The broad groove may extend across a substantial width of the port. The groove may be inclined from the edge of the port into the port similar to a ramp to provide a variable amount of flow through the groove as the duct sweeps across the incline. A width and/or depth of the groove may be varied along the length of the groove to provide a variable amount of flow through the groove as the duct sweeps along the length of the groove. 
         [0006]    Various aspects of an energy recovery apparatus comprises a rotor configured to move a duct containing low pressure fluid into alignment with a high pressure fluid source port for replacement of low pressure fluid in the duct with high pressure fluid. The rotor further is configured to move the duct while containing high pressure fluid into alignment with a low pressure release port for release of the high pressure fluid within the duct to low pressure. A high pressure seal surface adjacent to the low pressure release port may maintain high pressure on fluid in the duct during movement of the duct into alignment with the low pressure release port. A ramp forming a transition between the high pressure seal surface and the low pressure release port may be configured to bleed off pressure from fluid in the duct as the rotor moves the duct over the ramp into alignment with the release port. 
         [0007]    Various embodiments of an energy recovery device comprises a feed-water end cover, and a concentrate end cover. A low pressure feed-water source port may be disposed in the feed-water end cover. A high pressure concentrate source port may be disposed in the concentrate end cover. A duct may be configured to receive low pressure feed-water from the low pressure feed-water source port and high pressure concentrate from the high pressure concentrate source port. A rotor may be configured to position the duct in alignment with the low pressure feed-water source port, and to position the duct in alignment with the high pressure concentrate source port. A high pressure sealing surface may be disposed in a face of the feed-water end cover and adjacent the low pressure feed-water source port. The high pressure sealing surface may be configured for maintaining high pressure on concentrate and/or maintaining a seal between the high and low pressure regions of the ports and the ducts. A groove between the high pressure sealing surface and the low pressure feed-water source port may be configured to release pressure on the concentrate in the duct. 
         [0008]    In various embodiments, a pressure recovery apparatus comprises a rotor including a duct and configured to move the duct and low pressure fluid in the duct to a first position, and to move the duct and high pressure fluid in the duct to a second position. The apparatus further comprises a high pressure input port disposed in the first end cover, the high pressure input port configured to admit high pressure fluid for compressing low pressure fluid and displacing compressed fluid while the rotor is in the first position, and a high pressure output port disposed in the second end cover, the high pressure output port configured to release compressed fluid while the rotor is in the first position. The apparatus further comprises a low pressure output port disposed in a first end cover, the low pressure output port configured to release decompressed high pressure fluid from the duct at low pressure while the duct is at the second position and a low pressure input port disposed in a second end cover, the low pressure input port configured to admit low pressure fluid into the duct to displace decompressed fluid while the duct is at the second position. The first end cover includes a first high pressure seal surface adjacent the low pressure output port and a first groove between the first high pressure seal surface and the low pressure output port. The first groove may be configured to release pressure and decompress high pressure fluid in the duct as the rotor moves the duct over the first groove and into alignment with the low pressure output port. The second end cover includes a second high pressure seal surface adjacent the low pressure input port. A second groove may be disposed between the second high pressure seal surface and the low pressure input port. The second groove may be configured to release pressure and decompress high pressure fluid in the duct as the rotor moves the duct into alignment with the low pressure input port. 
         [0009]    In various embodiments, an energy recovery apparatus includes a rotor configured to rotate a duct containing a fluid and an end cover comprising a low pressure port and a high pressure seal surface adjacent the low pressure port, the high pressure seal surface configured maintain high pressure on fluid in the duct during rotation of the duct. The end cover further includes a release ramp between the high pressure seal surface and the low pressure port. The release ramp may be configured for decreasing pressure on fluid in the duct incrementally as the rotor rotates the duct from the high pressure seal surface over the release ramp into alignment with the low pressure port. The end cover may further include a high pressure port and a low pressure seal surface adjacent the high pressure port, the low pressure seal surface configured maintain low pressure on fluid in the duct during rotation of the duct. The end may also include a pressure ramp between the low pressure seal surface and the high pressure port. The pressure ramp may be configured for increasing pressure on fluid in the duct incrementally as the rotor rotates the duct from the low pressure seal surface over the ramp into alignment with the high pressure port. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows a block diagram illustrating a desalination system including a pressure exchange device, in accordance with various embodiments of the invention. 
           [0011]      FIG. 2A  is a block diagram of a front elevation illustrating an end view of the pressure exchange apparatus of  FIG. 1 . 
           [0012]      FIG. 2B  is a block diagram of a rear elevation illustrating an end view of the pressure exchange apparatus of  FIG. 1 . 
           [0013]      FIG. 2C  is a block diagram of a cross section view of the pressure exchange apparatus of  FIG. 1  along line a-a of  FIGS. 2A and 2B . 
           [0014]      FIG. 3A  is a front perspective of an exploded view of components of the pressure exchange apparatus of  FIG. 2C . 
           [0015]      FIG. 3B  is a rear perspective of an exploded view of components of the pressure exchange apparatus of  FIG. 2C . 
           [0016]      FIG. 3C  shows an end elevation of the rotor and sleeve of  FIGS. 3A and 3B , in accordance with embodiments of the invention. 
           [0017]      FIG. 4A  shows a perspective view of an interior face of the feed-water end cover of  FIG. 2 , in accordance with embodiments of the invention. 
           [0018]      FIG. 4B  shows an interior elevation of the feed-water end cover of  FIG. 4A . 
           [0019]      FIG. 5A  shows a perspective view of an interior face of the concentrate end cover of  FIG. 2 , in accordance with embodiments of the invention. 
           [0020]      FIG. 5B  shows an elevation interior surface of the concentrate end cover of  FIG. 5A . 
           [0021]      FIG. 6A  shows an elevation of the exterior face of the feed-water end cover of  FIG. 2 , in accordance with embodiments of the invention. 
           [0022]      FIG. 6B  shows an elevation of an exterior face of the concentrate end cover of  FIG. 2 , in accordance with embodiments of the invention. 
           [0023]      FIG. 7A  illustrates a groove having a constant hydraulic diameter, in accordance with embodiments of the invention. 
           [0024]      FIG. 7B  illustrates a groove having an increasing hydraulic diameter, in accordance with embodiments of the invention. 
           [0025]      FIG. 8A  is a longitudinal cross section of the groove of  FIG. 4B  taken along line b-b. 
           [0026]      FIG. 8B  is a transverse cross section of the groove of  FIG. 4B  taken along line c-c. 
           [0027]      FIG. 8C  is a longitudinal cross section of the groove of  FIG. 5B  taken along line d-d. 
           [0028]      FIG. 8D  is a transverse cross section of the groove of  FIG. 5B  taken along line e-e. 
           [0029]      FIG. 9A  shows a perspective view of an interior face of an alternative embodiment of the feed-water end cover of  FIG. 4A   2 , in accordance with embodiments of the invention. 
           [0030]      FIG. 9B  shows an interior elevation of the feed-water end cover of  FIG. 9A . 
           [0031]      FIG. 10A  shows a perspective view of an interior face of an alternative embodiment of the concentrate end cover of  FIG. 5A , in accordance with embodiments of the invention. 
           [0032]      FIG. 10B  shows an elevation interior surface of the concentrate end cover of  FIG. 10A . 
       
    
    
     DETAILED DESCRIPTION 
       [0033]      FIG. 1  shows a block diagram illustrating a desalination system  100  including a pressure exchange apparatus  108 , in accordance with various embodiments of the invention. The desalination system  100  further includes a low pressure pump  102  for pumping feed-water into the system  100 . A high pressure pump  104  provides high pressure feed-water to a feed-water separation device or a membrane separation device configured for separating fluids traversing a membrane, such as a reverse osmosis membrane  106 . Concentrated feed-water or concentrate from the membrane separation device  106  may be provided to the pressure exchanger  108 . An example of a concentrate is brine. Pressure in the concentrate may be used in the pressure exchanger  108  for compressing low pressure feed-water to high pressure feed-water. For simplicity and illustration purposes, the term feed water is used in the detailed description and  FIGS. 1-6 . However, fluids other than water may be used in the pressure exchanger  108 . 
         [0034]    The low pressure pump  102  may receive feed-water from a reservoir or directly from the ocean and pump the feed-water at low pressure into the system  100  at position  110 . Low pressure feed-water at position  110  may be provided to the high pressure pump  104  via manifold  114  and to the pressure exchanger  108  via manifold  120 . High pressure feed-water at position  116  may be provided to the membrane separation device  106  via manifold  118 . The membrane may separate fresh water for output to manifold  128  at low pressure. 
         [0035]    Concentrate from the membrane separation device  106  may be provided to the pressure exchanger  108  via manifold  124 . The pressure exchanger  108  may use high pressure concentrate from manifold  124  to compress (or exchange pressure with) low pressure feed-water from manifold  120 . The compressed feed-water may be provided to the membrane separation device  106  via manifold  122 , which is coupled to manifold  118 . The pressure exchanger  108  may output concentrate at low pressure via manifold  126 . Thus, concentrate that has given up pressure to the feed-water may be output from the pressure exchanger  108  at low pressure to manifold  126 . The low pressure concentrate in manifold  126  may be discarded, e.g., released for return to the sea. 
         [0036]    In some embodiments, the high pressure feed-water is output from the pressure exchanger  108  to manifold  122  at a slightly lower pressure than the high pressure feed-water in manifold  118  An optional circulation pump  112  may makeup the small difference in pressure between feed-water in manifold  122  and manifold  118 . In some embodiments, the circulation pump  112  is a turbine. Table 1 provides an example of some typical pressures in a desalination system illustrated in  FIG. 1 . 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 High 
                 Low 
                 High 
                   
                   
               
               
                 Pressure 
                 Pressure 
                 Pressure 
                 High 
                 Low 
               
               
                 Pump- 
                 Feed- 
                 Feed- 
                 Pressure 
                 Pressure 
               
               
                 Membrane 
                 water 
                 water 
                 Concentrate 
                 Concentrate 
               
               
                 Manifold 
                 Manifold 
                 Manifold 
                 Manifold 
                 Manifold 
               
               
                 116 &amp; 118 
                 120 
                 122 
                 124 
                 126 
               
               
                   
               
             
             
               
                 1,000 PSI 
                 30 PSI 
                 965 PSI 
                 980 PSI 
                 15 PSI 
               
               
                   
               
             
          
         
       
     
         [0037]    In the example illustrated by Table 1, the pressure exchanger  108  receives low pressure feed-water at about 30 pounds per square inch (PSI) and receives high pressure brine or concentrate at about 980 PSI. The pressure exchanger  108  transfers pressure from the high pressure concentrate to the low pressure feed-water. The pressure exchanger  108  outputs high pressure (compressed) feed-water at about 965 PSI and low pressure concentrate at about 15 PSI. Thus, the pressure exchanger  108  of Table 1 may be about 97% efficient since the input volume is about equal to the output volume of the pressure exchanger  108  and 965 PSI is about 97% of 980 PSI. 
         [0038]      FIG. 2A  is a front elevation illustrating an end view of the pressure exchange apparatus  108  of  FIG. 2C , in accordance with various embodiments of the invention.  FIG. 2B  is a rear elevation illustrating an end view of the pressure exchange apparatus  108  of  FIG. 2C , in accordance with various embodiments of the invention.  FIG. 2C  is a cross section view of the pressure exchange apparatus  108  of  FIG. 1  along line a-a, in accordance with various embodiments of the invention. The pressure exchanger  108  of  FIGS. 2A and 2B  includes a feed-water plenum  206 , a feed-water end cover  232 , a housing or case  200 , a sleeve  210 , a rotor  202 , a lubrication space  204  between the sleeve  210  and the rotor  202 , a concentrate end cover  230 , and a concentrate plenum  208 . 
         [0039]    High pressure feed-water may flow from the feed-water end cover  232  through the feed-water plenum  206  to the high pressure feed-water manifold  122 . The low pressure feed-water manifold  120  of  FIG. 2A  may be coupled to the feed-water end cover  232  through a feed-water manifold  242 . The dotted line of  FIG. 2A  illustrates an internal portion of the feed-water manifold  242  and shaft  234 . The feed-water manifold  242  is configured to separate low pressure feed-water in the feed-water manifold  242  from high pressure feed-water and shaft  234  in the feed-water plenum  206 . 
         [0040]    Similarly, brine or concentrate may flow from the high pressure concentrate manifold  124  through the concentrate plenum  208  to the concentrate end cover  230 . The low pressure concentrate manifold  126  of  FIG. 2B  may be coupled to the concentrate end cover  230  through a concentrate manifold  240 . The dotted line of  FIG. 2B  illustrates an internal portion of the concentrate manifold  240  and shaft  234 . The concentrate manifold  240  is configured to separate low pressure concentrate in the concentrate manifold  240  from high pressure concentrate in the concentrate plenum  208 . The low pressure concentrate manifold  240  and the low pressure feed-water manifold  242  are illustrated in  FIGS. 2A and 2B  as dividing into two branches. However, the low pressure concentrate manifold  240  and the low pressure feed-water manifold  242  may separate into more or fewer branches. 
         [0041]    The rotor  202  may be suspended within a sleeve  210  and free to rotate. A lubrication space  204  between the sleeve  210  and the rotor  202  is configured to receive a lubrication fluid through a lube port  220  for suspending the rotor  202  within the sleeve  210 . The lubrication fluid may be feed-water or concentrate at high pressure. For example, high pressure concentrate may be bled off from the high pressure concentrate plenum  208  and coupled to the lube port  220 . In various embodiments, high pressure feed-water may be bled off from the high pressure feed-water plenum  206 , or other sources and coupled to the lube port  220 . Similarly, low pressure feed-water may be coupled from low pressure pump  102 , position  110 , low pressure feed-water manifold  120 , manifold  114  and/or other sources to the lube port  220 . A shaft  234  is configured to apply tension for clamping the feed-water end cover  232  and the concentrate end cover  230  to the sleeve  210 . A bore  236  through the rotor  202  may provide a path for the shaft  234  without touching or applying drag to the rotor  202 . 
         [0042]    The rotor  202  includes one or more ducts  218  configured to move feed-water and concentrate at high and low pressures. The ducts  218  extend through the length of the rotor from the feed-water end cover  232  to the concentrate end cover  230 . The ducts are configured to receive low pressure feed-water through the feed-water end cover  232 , and to receive high pressure concentrate from the high pressure concentrate manifold  124 , though the concentrate end cover  230 . The ducts are further configured to provide high pressure feed-water to the feed-water end cover  232 , and to provide low pressure concentrate to the concentrate end cover  230 . Rotation of the rotor  202  moves or rotates the ducts  218  in a circular path around the pressure exchanger  108 . Rotation of the ducts  218  in a circular path between the end covers  230  and  232  is configured to align the ducts between ports in the end covers for receiving low pressure feed-water and high pressure concentrate and providing high pressure feed-water and low pressure concentrate. While two ducts  218  are illustrated in  FIG. 2C , in various embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 18, 20, 24, 30 or more ducts may be used in the rotor  202 . 
         [0043]      FIG. 3A  is a front perspective of an exploded view of components of the pressure exchange apparatus  108  of  FIG. 2 , in accordance with various embodiments of the invention.  FIG. 3B  is a rear perspective of an exploded view of components of the pressure exchange apparatus  108  of  FIG. 2 , in accordance with various embodiments of the invention.  FIG. 3C  shows an end elevation of the rotor  202  and sleeve  210  of  FIG. 2 , in accordance with embodiments of the invention. The feed-water plenum  206 , feed-water manifold  242 , housing  200 , concentrate plenum, and concentrate manifold  240  are omitted for clarity. The feed-water end cover  232  includes one or more low pressure feed-water ports  320  and one or more high pressure feed-water ports  322 . One or more feed-water low pressure seal surface  324  and feed-water high pressure seal surface  326  is disposed on a side facing the rotor  202 . The feed-water low pressure seal surface  324  is configured for maintaining low pressure within a duct  218  during rotation of the duct  218  from a low pressure feed-water port  320  to a high pressure feed-water port  322 . Similarly, the feed-water high pressure seal surface  326  is configured for maintaining a high pressure within a duct  218  during rotation of the duct  218  from a high pressure feed-water port  322  to an adjacent low pressure feed-water port  320 . The low pressure feed-water ports  320  may be circular for coupling to the low pressure feed-water manifold  242 . 
         [0044]    The concentrate end cover  230  includes one or more low pressure concentrate ports  310  and one or more high pressure concentrate ports  312 . One or more concentrate low pressure seal surface  314  and concentrate high pressure seal surface  316  is disposed on a side facing the rotor  202 . The concentrate low pressure seal surface  314  is configured for maintaining a low pressure within a duct  218  during rotation of the duct  218  from a low pressure concentrate port  310  to an adjacent high pressure concentrate port  312 . Similarly, the concentrate high pressure seal surface  316  is configured for maintaining high pressure within a duct  218  during rotation of the duct  218  from a high pressure concentrate port  312  to an adjacent low pressure concentrate port  310 . The low pressure concentrate ports  310  may be circular for coupling to the low pressure concentrate manifold  240 . 
         [0045]    Alignment pins  304  and alignment holes  306  provide for alignment of end covers  232  and  230  in a desired orientation. Three pins distributed asymmetrically about the periphery of the sleeve  210  may provide for a unique alignment. In some embodiments, low pressure feed-water ports  320  and high pressure feed-water ports  322  are partly out of phase with low pressure concentrate ports  310  and high pressure concentrate ports  312 , respectively. Fasteners, such as nuts and washers may be disposed on the shaft  234  and may be used to secure the end covers  230  and  232  to the sleeve  210 . In some embodiments, the fasteners may be to secure the feed-water plenum  206  and the concentrate plenum  208  to the sleeve  210  and end covers  230  and  232 . 
         [0046]    As the rotor  202  spins the open ends of each duct  218  move from alignment with one set of ports through a sealed area and then into alignment with another set of ports (e.g., from a high pressure port to a low pressure port or from a low pressure port to a high pressure port). During operation a duct  218  in the sealed area is under approximately the same pressure as the (low or high) pressure of the previous port it was exposed to. As the duct  218  transitions from the sealed area to the next port the pressure within the duct  218  is brought to that of the next port. For this pressure change to occur, a finite quantity of fluid travels between the duct  218  and the port in the direction of decreasing pressure. The requisite volume of fluid is a function of the compressibility of the fluid, the pressure differential between the duct  218  and the port, and any change in duct volume due to the elastic deformation of the walls of the duct  218 . For isobaric pressure exchanges in seawater, reverse osmosis applications the volume of fluid in question is on the order of 0.3% of the duct volume. 
         [0047]    The movement of fluid into or out of the duct  218  as the fluid becomes exposed to the next port is driven by the pressure difference between the duct  218  and the next port. When the pressure difference is higher than about 100 psi (for example, seawater reverse osmosis operates with around 900 psi difference) a rapid pressure change may occur. The pressure change may be characterized as the magnitude of rate of change of pressure (first derivative of pressure with respect to time—dp/dt) within the duct. The rapid pressure change can create both shock waves and cavitating jets within the device. The shock waves cause undesirable noise and vibration and the cavitating jets can cause wear on the components and additional noise. 
         [0048]    A groove between the sealed area and the next port provide for a partially restricted flow path between the otherwise sealed volume of fluid in the rotor duct and the next port. The physical dimensions of the groove can be varied to set flow rate through the groove to minimize the peak dp/dt in the duct. The dp/dt may be a function of the time available to pressurize or depressurize the duct  218 , the physical space available for the groove, and the volume of fluid that passes through the groove in order to equalize the pressure at a given dp/dt. 
         [0049]    In some embodiments, it is desirable to achieve a relatively constant dp/dt during pressurization/depressurization of the duct  218 . However, as the pressure difference between a duct and a port decreases, the flow through a groove having a constant cross section decreases. The physical dimensions of the groove for a relatively constant dp/dt may be varied (or increased) over the length of the groove to maintain constant flow through the groove. As the duct  218  first engages a groove the differential pressure is high. Thus, a small effective hydraulic diameter of the groove may be used initially to limit flow through the groove. As the duct  218  progresses along the groove and the differential pressure decreases, an increase in the hydraulic diameter may be used to maintain flow about constant and thus, maintain about a constant dp/dt. In some embodiments the width and/or depth of the groove may be varied to provide a desired dp/dt along the length of the groove. 
         [0050]    In various embodiments, the effective hydraulic diameter is a function of the width of the groove, the depth of the groove, the shape of the groove cross section, the number of ducts  218  engaging a groove, and/or the like. Other structures for controlling dp/dt include changing the number of grooves encountered by the ducts  218  as the ducts  218  move from the sealed area to the next port, and creating surfaces within the groove that change size. The effective hydraulic diameter may be changed along the groove in a linear or non-linear fashion. 
         [0051]    The energy in the high pressure fluid moving through the groove toward the low pressure fluid is ultimately dissipated through viscous shear frictional losses into the fluid. Two mechanisms for this to occur include a high velocity jet and boundary layer shear. A high velocity jet may be created, for example, by high pressure moving though a small, roughly square cross section opening into a large open area. The pressure energy is first transferred to kinetic energy of rapidly moving fluid in the high pressure jet, and then to frictional losses in the turbulent eddies created by the jet in the open area. Disadvantages of this a high pressure jet include the high velocity fluid within the jet creating flow erosion, noise and destructive cavitation. 
         [0052]    Laminar flow dissipation of energy may occur through boundary layer shear within the flow channel. In this case a high aspect ratio groove may be used to maximize the wetted perimeter, which is essentially surface area. The increase in wetted perimeter may enhance the shear flow. The relatively low velocities in the boundary layer do not create significant flow erosion, noise, and cavitation. In some embodiments, grooves may be used on end covers at both ends of the rotor  202  to effectively increase the total wetted perimeter. For example, grooves may be disposed between the sealed area and the high pressure port on both the feed-water end cover  232  and the concentrate end cover  230 . The depressurization groove may be eliminated or reduced to one of the end covers (e.g. concentrate end cover  230 ). The slightly higher pressure on the other end cover (e.g., the feed-water end cover  232 ) may be used to reduce cavitation potential. 
         [0053]      FIG. 4A  shows a perspective view of an interior face of the feed-water end cover  232  of  FIGS. 2 and 3A , in accordance with embodiments of the invention.  FIG. 4B  shows an interior elevation of the feed-water end cover  232  of  FIG. 4A . The interior face of the feed-water end cover  232  includes one or more high pressure relief grooves  414  disposed between a high pressure seal surface  326  and a low pressure feed-water port  320 . The high pressure relief grooves  414  are configured to bleed high pressure feed-water gradually from the duct  218  into the low pressure feed-water port  320  as the rotor  202  rotates to move the duct  218  over the high pressure relief grooves  414  from the high pressure seal surface  326  to the low pressure feed-water port  320 . 
         [0054]    The interior face of the feed-water end cover  232  further includes one or more low pressure relief grooves  416  disposed between a low pressure seal surface  324  and a high pressure feed-water port  322 . The low pressure relief grooves  416  are configured to bleed high pressure feed-water gradually from the high pressure feed-water port  322  into the duct  218  containing low pressure feed-water as the rotor  202  rotates to move the duct  218  over the low pressure relief grooves  416  from the low pressure seal surface  324  to the high pressure feed-water port  322 . 
         [0055]      FIG. 5A  shows a perspective view of an interior face of the concentrate end cover  230  of  FIGS. 2 and 3B , in accordance with embodiments of the invention.  FIG. 5B  shows an elevation of the interior surface of the concentrate end cover  230  of  FIG. 5A . The interior face of the concentrate end cover  230  includes one or more impeller surfaces  514  disposed between a high pressure seal surface  316  and a low pressure concentrate port  310 . The impeller surfaces  514  are configured to bias the spin of the rotor  202 . 
         [0056]    The interior face of the concentrate end cover  230  further includes one or more low pressure relief grooves  516  disposed between a low pressure seal surface  314  and a high pressure concentrate port  312 . The low pressure relief grooves  516  are configured to bleed high pressure concentrate gradually from the high pressure concentrate port  312  into the duct  218  as the rotor  202  rotates to move the duct  218  over the low pressure relief grooves  516  from the low pressure seal surface  314  to the high pressure concentrate port  312 . The impeller surface  514  along an edge of the low pressure concentrate port  310  is configured to impart rotation to the rotor  202  in the direction of the arrow. The impeller surface  514  provides torque to the rotor  202  reducing or eliminating a need for an external source to rotate the rotor, such as a motor. Impeller surface  512  may further bias rotor spin in a same direction as impeller surface  514 . Note that the flow direction for low pressure concentrate port  310  is into the page and the flow direction for the high pressure concentrate port  312  is out of the page, and impeller surface  514  and  512  are on opposite sides of their respective ports. Thus, both impeller surfaces  512  and  514  provide torque to the rotor in the same direction, i.e. clockwise. 
         [0057]      FIG. 6A  shows an elevation of the exterior face of the feed-water end cover  232  of  FIG. 2 , in accordance with embodiments of the invention.  FIG. 6A  illustrates circular fittings  602  for the low pressure feed-water ports for coupling to the low pressure feed-water manifold  242 .  FIG. 6B  shows an elevation of an exterior face of the concentrate end cover  230  of  FIG. 2 , in accordance with embodiments of the invention.  FIG. 6B  illustrates circular fittings  600  for the low pressure concentrate ports for coupling to the low pressure concentrate manifold  240 . 
         [0058]      FIG. 7A  and  FIG. 7B  are perspective views of a groove  416  disposed between a low pressure seal surface  324  and a high pressure port  322 .  FIG. 7A  is a perspective view illustrating the groove  416  having a constant hydraulic diameter, in accordance with embodiments of the invention.  FIG. 7B  is a perspective view illustrating the groove  416  having an increasing hydraulic diameter, in accordance with embodiments of the invention. The groove  416  is shallow having a depth substantially less than the width and/or length. This serves to increase the whetted area. The depth of the groove  416  may increase as it approaches the edge of the high pressure feed-water port  322 , that is, the groove  416  in either  FIG. 7A  or  7 B may slope downward toward high the pressure feed-water port  322 , as illustrated elsewhere herein. While the groove  416  is illustrated in  FIGS. 7A and 7B , the shape of the groove  416  may be used for grooves  414 ,  416 , and  516 . The grooves  416  of  FIGS. 7A and 7B  are shown as extending only a portion of the width of the high pressure feed-water port  322 , similar to the grooves illustrated in  FIGS. 9A ,  9 B,  10 A and  10 B (described in more detail below). However, the grooves  416  may extend most or all of the way across the width of the high pressure feed-water port  322 , as illustrated in  FIGS. 4A and 4B , or similar to the grooves illustrated in  FIGS. 5A and 5B . In some embodiments, multiple grooves  416  are disposed along the width of the high pressure feed-water port  322 . 
         [0059]      FIG. 8A  is a longitudinal cross section of the impeller grooves  416 - 418  of  FIG. 4B  taken along line b-b.  FIG. 8B  is a transverse cross section of the groove  416  of  FIG. 4B  taken along line c-c. While  FIG. 8B  illustrates groove  416 , this figure may similarly illustrate groove  414 . While  FIG. 8A  illustrates groove  416  and impeller surface  418 , this figure may similarly illustrate the groove  414 . The groove  416  slopes downward at an angle  802  toward high pressure feed-water port  322 , thus, increasing the effective hydraulic diameter of the groove  416 . The groove  416  is shallow having a depth substantially less than the width and/or length. This serves to increase the whetted area. In various embodiments, the angle  802  is less than about 5, 4, 3, 2, 1, 0.5, 0.2, 0.1 degrees. The impeller surface  418  slopes downward at an angle  804 . In various embodiments, the angle  804  is less than about 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, 0.2 degrees, but greater than the angle  802 . 
         [0060]      FIG. 8C  is a longitudinal cross section of the groove  514  of  FIG. 5B  taken along line d-d.  FIG. 8D  is a transverse cross section of the groove  514  of  FIG. 5B  taken along line e-e. The impeller groove  514  slopes downward at an angle  806  toward the concentrate port  310 , thus, increasing the effective hydraulic diameter of the impeller groove  514 . In various embodiments, the angle  806  is less than about 5, 4, 3, 2, 1, 0.5, 0.2, 0.1 degrees. While  FIGS. 8C and 8D  illustrate the impeller groove  514 , these figures may similarly illustrate the impeller surface  512  and/or groove  516 . 
         [0061]      FIG. 9A  shows a perspective view of an interior face of an alternative embodiment of the feed-water end cover  232  of  FIG. 4A , in accordance with embodiments of the invention.  FIG. 9B  shows an interior elevation of the feed-water end cover  232  of  FIG. 9A , in accordance with embodiments of the invention.  FIGS. 9A and 9B  differ from  FIGS. 4A and 4B , respectively in that  FIGS. 9A and 9B  include multiple grooves  914  along a small portion of the edge of the low pressure feed-water port  320  instead of groove  414  disposed along a substantial or all of the edge of the low pressure feed-water port  320 . Similarly,  FIGS. 9A and 9B  include grooves  916  instead of groove  416  along edge of the high pressure feed-water port  322 . 
         [0062]    The interior face of the feed-water end cover  232  includes one or more high pressure relief grooves  914  disposed between a high pressure seal surface  326  and a low pressure feed-water port  320 . The high pressure relief grooves  914  are configured to bleed high pressure feed-water gradually from the duct  218  into the low pressure feed-water port  320  as the rotor  202  rotates to move the duct  218  over the high pressure relief grooves  914  from the high pressure seal surface  326  to the low pressure feed-water port  320 . 
         [0063]    The interior face of the feed-water end cover  232  further includes one or more low pressure relief grooves  916  disposed between a low pressure seal surface  324  and a high pressure feed-water port  322 . The low pressure relief grooves  916  are configured to bleed high pressure feed-water gradually from the high pressure feed-water port  322  into the duct  218  containing low pressure feed-water as the rotor  202  rotates to move the duct  218  over the low pressure relief grooves  916  from the low pressure seal surface  324  to the high pressure feed-water port  322 . An impeller surface  418  along an edge of the high pressure feed-water port  322  is configured to impart rotation to the rotor  202  in the direction of the arrow. The impeller surface  418  provides torque to the rotor  202  reducing or eliminating a need for an external source to rotate the rotor, such as a motor. 
         [0064]      FIG. 10A  shows a perspective view of an interior face of an alternative embodiment of the concentrate end cover of  FIG. 5A , in accordance with embodiments of the invention.  FIG. 10B  shows an elevation interior surface of the concentrate end cover of  FIG. 10A .  FIGS. 10A and 10B  differ from  FIGS. 5A and 5B , respectively in that  FIGS. 10A and 10B  include multiple grooves  1014  along a small portion of the edge of concentrate port  310  instead of impeller groove  514  disposed along a substantial or all of the edge of the concentrate port  310 . Similarly,  FIGS. 10A and 10B  include grooves  1016  instead of groove  516  along edge of the high pressure concentrate port  312 . 
         [0065]    The interior face of the concentrate end cover  230  includes one or more high pressure relief grooves  1014  disposed between a high pressure seal surface  316  and a low pressure concentrate port  310 . The high pressure relief grooves  1014  are configured to bleed high pressure concentrate gradually from the duct  218  into the low pressure concentrate port  310  as the rotor  202  rotates to move the duct  218  over the high pressure relief grooves  1014  from the high pressure seal surface  316  to the low pressure concentrate port  310 . 
         [0066]    The interior face of the concentrate end cover  230  further includes one or more low pressure relief grooves  1016  disposed between a low pressure seal surface  314  and a high pressure concentrate port  312 . The low pressure relief grooves  1016  are configured to bleed high pressure concentrate gradually from the high pressure concentrate port  312  into the duct  218  as the rotor  202  rotates to move the duct  218  over the low pressure relief grooves  1016  from the low pressure seal surface  314  to the high pressure concentrate port  312 . An impeller surface  518  along an edge of the low pressure concentrate port  310  is configured to impart rotation to the rotor  202  in the direction of the arrow. The impeller surface  518  provides torque to the rotor  202  reducing or eliminating a need for an external source to rotate the rotor, such as a motor. Surface  512  may further bias rotor spin in a correct or desired direction. 
         [0067]    As used in this specification, the terms “include,” “including,” “for example,” “exemplary,” “e.g.,” and variations thereof, are not intended to be terms of limitation, but rather are intended to be followed by the words “without limitation” or by words with a similar meaning. Definitions in this specification, and all headers, titles and subtitles, are intended to be descriptive and illustrative with the goal of facilitating comprehension, but are not intended to be limiting with respect to the scope of the inventions as recited in the claims. Each such definition is intended to also capture additional equivalent items, technologies or terms that would be known or would become known to a person having ordinary skill in this art as equivalent or otherwise interchangeable with the respective item, technology or term so defined. Unless otherwise required by the context, the verb “may” indicates a possibility that the respective action, step or implementation may be performed or achieved, but is not intended to establish a requirement that such action, step or implementation must be performed or must occur, or that the respective action, step or implementation must be performed or achieved in the exact manner described. 
         [0068]    The above description is illustrative and not restrictive. This patent describes in detail various embodiments and implementations of the present invention, and the present invention is open to additional embodiments and implementations, further modifications, and alternative constructions. There is no intention in this patent to limit the invention to the particular embodiments and implementations disclosed; on the contrary, this patent is intended to cover all modifications, equivalents and alternative embodiments and implementations that fall within the scope of the claims. Moreover, embodiments illustrated in the figures may be used in various combination. Any limitations of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.