Abstract:
A pressure exchanger for transferring pressure energy from a relatively high-pressure fluid stream to another relatively low-pressure fluid stream is provided. A ducted rotor is positioned on a central axle between two end covers inside a pressure vessel with a coaxial inlet and outlet pair that is in communication with a pair of low pressure ports having inclination forming an inlet tangential velocity vector in the direction of rotor rotation and an outlet tangential velocity vector in opposite direction imparting a rotational momentum on rotor. A pair of high-pressure ports is adapted for flow without inclination and imparts no momentum to rotor and flow can be varied without impacting the rotor&#39;s RPM. The end covers have a sloped surface following a flat sealing area that increases the clearance in the direction of rotation causing increased outflow during depressurization and lower duct pressure before duct is exposed to low pressure port and furthermore causing increased inflow during the pressurization phase before duct is exposed to the high pressure port, which will dissipate pressure energy as opposed to producing cavitation or pressure waves with result wear and noise.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to provisional application No. 60/599,760, entitled “Pressure Exchanger” filed Aug. 10, 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to a pressure exchanger for transfer of pressure energy from one fluid flow to another, contained inside a pressure vessel with inlet and outlets for each fluid flow in communication through a rotor with multiple through-going coaxial ducts and arranged for rotation through its longitudinal axis between opposing end covers guiding fluid exchange of a first and second fluid stream within and external of the rotor.  
       BACKGROUND AND DESCRIPTION OF THE RELATED ART  
       [0003]     Commercial pressure exchangers of the above-mentioned category are known to exhibit operational flow limitations due to excessive noise, flow resistance, intermixing and cavitation despite the application of above mentioned patents. Furthermore, the manufacturing of certain parts requires extreme and costly tolerances and limited choice of materials due to asymmetric elastic deformations.  
         [0004]     U.S. Pat. No. 4,887,942 to Hauge, hereby incorporated by reference in its entirety, describes a principle for self-rotation by fluid streams that is based on the so called lift and drag principle, where the rotor duct walls act as hydrofoils. The trailing section of the rotor duct exposed to the exit flow of the low-pressure fluid is under cavitation risk at high flow velocities and therefore a limiting factor for unit flow capacity.  
         [0005]     U.S. Pat. No. 5,988,993 to Hauge, hereby incorporated by reference in its entirety, describes a positioning system of a rotor that requires extremely tight tolerances for the mating of the rotor and the outer bearing sleeve, which makes manufacturing costly. Furthermore, the hydrostatic bearing principle requires high degree of filtration as fluid is bled from the fluid stream under high pressure and passed through the radial rotor/sleeve clearances in a dead-end mode. This may cause silting and blockage of rotor under certain circumstances and applications. The outer sleeve also prevents rotor OD from being sized according to end cover OD or pressure vessel ID, and therefore limits efficiency and capacity further.  
         [0006]     U.S. Pat. No. 6,540,487 to Polizos et al., hereby incorporated by reference in its entirety, describes a pressure transfer mechanism that seeks to avoid the sudden depressurization of the high-pressure fluid and destructive cavitation and noise. However, in reality it is only partially successful as cavitation damage is moved to the connecting channel and away from the exit edge of the end cover port.  
         [0007]     U.S. Pat. No. 6,659,731 to Hauge, hereby incorporated by reference in its entirety, describes returning depressurized fluid through the center of the rotor to induce unnecessary flow resistance with lower efficiency resulting. The pressure vessel described has multiple external seals, which eventually will leak and require replacement causing operational interruption and costly service.  
       SUMMARY OF THE INVENTION  
       [0008]     Thus, there is a need for a pressure exchanger that ameliorates at least some of the above-noted disadvantages of existing pressure exchangers. Thus, at least one objective of the invention is to provide a pressure exchanger that is not encumbered by the aforementioned disadvantages.  
         [0009]     In accordance with at least one embodiment of this invention, a pressure exchanger having increased flow capacity and start momentum is provided. The pressure exchanger according to this embodiment utilizes the one-side unidirectional impulse momentum principle for self-rotation that is less susceptible to cavitation.  
         [0010]     In accordance with at least one embodiment of this invention, a pressure exchanger is configured to exhibit increased flow capacity along with improved operational and manufacturing efficiency. The pressure exchanger according to this embodiment comprises a center axle for rotor positioning along with a full diameter sized rotor.  
         [0011]     In accordance with at least one embodiment of this invention a pressure exchanger having improved depressurization and pressurization of rotor ducts is provided. The pressure exchanger according to this embodiment comprises a geometry controlled decrease of end cover clearance in the direction of rotation for achieving this improved performance.  
         [0012]     In accordance with at least one embodiment of this invention, a pressure exchanger is configured to be less susceptible to substantial or asymmetric deformation of the end cover axle is provided. By complete force balancing through an area exposed to high pressure positioned substantially opposite to the centroid of the separation force of each end-cover. The pressure exchanger according to this embodiment is able to achieve equivalent or improved performance and allow the use of materials other than ceramics and a larger length/diameter ratio for the rotor.  
         [0013]     In accordance with at least one embodiment of this invention, a pressure exchanger having a reduced potential for leakage is provided. The pressure exchanger according to this embodiment comprises a single external seal.  
         [0014]     At least one embodiment of the invention may provide a pressure exchanger for transferring pressure energy from a first fluid flow to a second fluid flow. The pressure exchanger according to this embodiment may comprise a substantially cylindrical-shaped pressure vessel, a pair of end covers located on opposing ends of the pressure vessel, each end cover having at least one passage formed therein, a rotor, disposed inside the vessel, comprising multiple through-going coaxial ducts and arranged for rotation about a longitudinal axis between the pair of opposing end covers, the rotor adapted to guide fluid exchange both within and external to the rotor, a pair of fluid inlets, and a pair of fluid outlets in communication with the fluid inlets to promote a first fluid flow and a second fluid flow through the rotor, wherein the opposing end cover passages on a fluid inlet side are oriented with a degree of inclination to impart a uni-rotational impulse momentum onto the rotor regardless of flow direction of the first and second fluid flows relative to the pressure vessel through an inlet tangential flow vector component in the direction of rotation and an outflow tangential flow vector component in an opposite direction of rotation  
         [0015]     At least one other embodiment according to the invention may provide a bidirectional pressure exchanging device for exchanging pressure from one fluid flow to another fluid flow. The pressure exchanging device according to this embodiment may comprise a pressure vessel, a pair of end covers disposed on opposing ends of the pressure vessel, each end cover having at least one fluid passage formed therein, a rotor, located inside the pressure vessel, comprising multiple through-going coaxial ducts and arranged for rotation about its longitudinal axis between the pair of opposing end covers, the rotor guiding fluid exchange both within and external to the rotor, a first substantially axial fluid flow path perpendicular to a plane of rotor rotation comprising an inlet and outlet communicating through the rotor, and a second fluid flow path that is at least in part parallel to the first fluid flow path through and around the rotor and that comprises an inlet and outlet that are substantially perpendicular to the first fluid flow path, wherein the opposing end cover fluid passages of are oriented on an inlet side with a degree of inclination to impart a uni-rotational impulse momentum onto the rotor regardless of flow direction through an inlet tangential flow vector component in the direction of rotation and an outflow tangential flow vector component in an opposite direction of rotation.  
         [0016]     Yet at least one additional embodiment according to this invention may comprise a reverse osmosis system for desalinating sea water. The system according to this embodiment may comprise a fresh water supply, a sea water supply, a membrane separating the fresh water supply from the sea water supply, wherein the sea water supply is maintained at a pressure against the membrane sufficient to reverse an osmotic tendency of fresh water to flow into the sea water, and a pressure exchanger for increasing a pressure of sea water feed to the reverse osmosis system, the pressure exchanger, comprising a substantially cylindrical-shaped pressure vessel, a pair of end covers located on opposing ends of the pressure vessel, each end cover having at least one passage formed therein, a rotor, disposed inside the vessel, comprising multiple through-going coaxial ducts and arranged for rotation about a longitudinal axis between the pair of opposing end covers, the rotor adapted to guide fluid exchange both within and external to the rotor, a pair of fluid inlets, and a pair of fluid outlets in communication with the fluid inlets to promote a first fluid flow and a second fluid flow through the rotor, wherein the opposing end cover passages on a fluid inlet side are oriented with a degree of inclination to impart a uni-rotational impulse momentum onto the rotor regardless of flow direction of the first and second fluid flows relative to the pressure vessel through an inlet tangential flow vector component in the direction of rotation and an outflow tangential flow vector component in an opposite direction of rotation  
         [0017]     These and other embodiments and advantages of the present invention, which may be employed individually or in selective combination, will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is an external perspective view of a pressure exchanger according to at least one embodiment of the invention;  
         [0019]     FIGS.  2 ( a ) and  2 ( b ) are partial and full cut-away perspective views of the pressure exchanger and components of the pressure exchanger according to the exemplary embodiment illustrated in  FIG. 1 ;  
         [0020]      FIG. 3  is a force vector diagram illustrating the impulse momentum principle for self-rotation;  
         [0021]     FIGS.  4 ( a ) and  4 ( b ) are schematic diagrams illustrating the geometry effecting controlled pressure change in the sealing area of a pressure exchanger according to at least one embodiment of the invention;  
         [0022]     FIGS.  5 ( a ) and  5 ( b ) are partial cut-away perspective views of a pressure exchanger end cover according to at least one embodiment of the invention; and  
         [0023]      FIG. 6  is a force vector diagram illustrating the forces acting on the end covers and the counteracting balancing forces in a pressure exchanger according to at least one embodiment of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     The following description is intended to convey a thorough understanding of the embodiments described by providing a number of specific embodiments and details involving an improved pressure exchanger for transferring pressure energy from one fluid flow to another. It should be appreciated, however, that the present invention is not limited to these specific embodiments and details, which are exemplary only. It is further understood that one possessing ordinary skill in the art, in light of known systems and methods, would appreciate the use of the invention for its intended purposes and benefits in any number of alternative embodiments, depending upon specific design and other needs.  
         [0025]     Referring now to  FIG. 1 , an external embodiment of a pressure exchanger according to at least one embodiment of the invention is illustrated. The pressure exchanger depicted in  FIG. 1  comprises a pressure vessel  1  with a removable end cap or end cover  2  having a low-pressure fluid inlet  4  and secured with a lock ring  3  providing an entrance where an internal assembly may be inserted. In the opposite end a fluid outlet  5  for low pressure is located and additionally fluid inlet  6  and outlet  7  for high pressure fluid flows are aligned essentially normal to pressure vessel  1 .  
         [0026]      FIG. 2   a  shows the different components of the internal assembly, where a rotor  8  with circular shaped ducts  10  uses a hollow central axle  9  with a through going tension rod  11  for positioning, bearing function and mounting. Each end of the tension rod  11  goes through the center face of each end cover  21 ,  22  and is secured with a nut  12  and voucher  13  in a central recess. A bushing  14  fitted in a recess of each end cover and each end of the central axle  9  provides firm center fixation of the rotor assembly.  
         [0027]     The first high-pressure outlet stream  7  communicates directly with and pressurizes the rotor vessel clearance  15 , which is isolated from the second high-pressure inlet stream  6  through an O-ring seal  16 . In various embodiments, the first high pressure outlet stream  7  may be the less contaminating flow, such as feed water in a reverse osmosis (“RO”) plant allowing only feed water to leak into the second low pressure reject stream  5 .  
         [0028]     The various embodiments of the invention may have particular utility in an RO fresh water recovery plant in which salt water is pumped through an osmotic membrane submerged in fresh water at a pressure sufficient to reverse the osmotic effect of fresh water flowing into the salt water.  
         [0029]     Each end cover  21 ,  22  has a balancing area  18  pressurized by the first and second high pressure streams equal to the difference between the center offset low pressure counter area  20  and the full end cover back side area confined by the seal  19  that faces the removal end cap  2  and a fixed end face of the opposing low pressure inlet  4 . The first stream end cover  22  has a low pressure port  23  and a high pressure port  24  and the second stream end cover  21  has a high pressure port  25  and a low pressure port  26 .  
         [0030]      FIG. 2   b  shows an elevated surface  27  that may be incorporated in the end faces of the rotor  8  or end covers  21 ,  22 . If the rotor  8  is made of a brittle material such as ceramic, it is advantageous to keep the material under compression by the high pressure externally. However, this can increase the chance that, due to the counteracting streams through the ducts, the rotor will assume a position where the outer sealing area is brought to a non-parallel contact with the low-pressure side of the opposing end cover. Such a positioning is known to induce asymmetric opposing clearance pressure gradients leading to a force on the rotor normal to the contacting or touched end cover which in turn causes lock-up that prevents start-up rotation. This will induce lower mean pressure in the clearance  28  of the contacting end as the low pressure will creep towards the contact boundary as it provides more resistance to the inward leakage flow. The elevated surface feature  27  will restrict rotor axial movement and avoid touch down between end cover surface and outer rotor rim. Due to external pressurization there are no pressure gradients on the high-pressure side causing potential lock-up.  
         [0031]     Another way of preventing this lock-up potential is to use a rotor material that can be put under tension by a complete external depressurization and hence there will be no pressure gradient at the low-pressure side clearances. Due to the outward leakage flow on the high pressure side, the pressure gradients will seek to center the rotor  8  thereby reducing, and ideally, preventing the potential for lock-up in this configuration.  
         [0032]      FIG. 3  is a force vector diagram illustrating the impulse momentum principle for self-rotation. The diagram illustrates the principle flow arrangement of the first and second stream in a tangential cross-section where a rotor duct  10  has a tangential velocity in the plane of rotation similar to the tangential inlet velocity component of the first incoming low pressure stream. The relationship between the tangential velocity (V r ) and the tangential inlet velocity (V y in ) is characterized in equation 1 below: 
 V r ≈V y in    (1)  
         [0033]     A general concept of the pressure exchanger according to the various embodiments of the invention is to induce the incoming flow through an inclination that essentially induces little or no rotational momentum to the rotor  8 . The coaxial inlet velocity component inside the duct (V x in ) is essentially similar to the duct velocity component (V d ) and is characterized in relation to the duct velocity by equation 2 below: 
 
V x in ≈V d    (2) 
 
         [0034]     The outflow of the second stream (V y out ) through outlet port  25  is essentially responsible for imparting rotational momentum to the rotor  8  as the tangential velocity component is reversed. See equation 3 below: 
 
V y out ≈V y in    (3) 
 
         [0035]     The outflow of the second stream through outlet port  25  is essentially responsible for imparting rotational momentum to rotor  8  as the tangential velocity component is reversed. The rotational momentum is characterized by equation 4, wherein F y t is the impulse in the y direction and [(MV y ) out −(MY y ) in ] is the change in y-directed momentum, 
 
 F   y   t =( MV   y ) out −( MY   y ) in    (4) 
 
 while the tangential velocity component (V x in ) remains unchanged: 
 
V x in ≈V d ≈V x out    (5) 
 
         [0036]     Although the drawings indicate similar inclination of both inflow and outflow low pressure ports, it will be understood that this depends on the relationship that may be required or preferable between the rotor&#39;s RPM and its frictional resistance to rotation.  
         [0037]     It should be appreciated that in various embodiments, and in certain applications, the pressure exchanger high and low pressure sides may be switched. Further, it should be appreciated that the high-pressure flow imparts the rotational momentum through similar port geometry, although this may require additional changes with respect to balancing of the separation force acting between end covers and rotor.  
         [0038]      FIGS. 4   a  and  4   b  show the geometry effecting controlled pressure change in the sealing area of the end cover. Although the figures show the interaction between rotor ducts and port openings at one end, it is envisioned that the particular feature preferably is incorporated with both end covers.  
         [0039]      FIG. 4   a  shows the initial phase of the depressurizing duct  10   a  having entered from the high-pressure port in to the sealing area  29  with its trailing edge  31   a  completely inside of it. Sealing area  29  and  30  have generally flat surfaces with sloped surfaces  33   a  and  33   b,  respectively although slope surface  33   b  is not critical. The leading edge  32   a  is about to enter a sloped surface  33   a  giving increasing clearance as it moves towards the low-pressure port  23 , while maintaining fixed clearance for its trailing edge  31   a . Although the drawing shows the pressurizing duct  10   b  and its trailing and leading edges  31   b,    32   b  entering the sealing area  30  from the low pressure port  23  simultaneously, it may preferably be with a sufficient time difference to avoid resonating pressure pulsations. In various embodiments, this may be arranged through manipulation of the number of ducts or through manipulation of the port angular asymmetry. The remaining sealing area  30  of duct  10   b  may have a slope  33   b  towards the high-pressure port.  
         [0040]     It is important to understand that the depressurization area  33   a  must produce a resistance factor prohibiting cavitation velocities of the exit leakage flow in the clearance while the pressurization area  33   b  is not under a similar constraint.  
         [0041]      FIG. 4   b  shows the second phase of the depressurizing duct  10   a  having entered from the high pressure port in to the sealing area  29  with its trailing edge  31   a  still inside of it while the leading edge  32   a  has entered the sloped surface  33   a  giving increasing clearance as it moves towards the low pressure port  23 , while still maintaining fixed clearance for its trailing edge  31   a.  The pressurization duct  10   b  is shown in a similar position where the fluid is building up pressure in a controlled manner while dissipating pressure energy that otherwise would have produced strong pressure waves and excessive noise when entering the high pressure port.  
         [0042]      FIG. 5   a  shows the rotor of front face of the non-momentum imparting end cover  22  guiding a first or pressure-less stream entering through Inlet  5  to a low pressure port  23  into rotor ducts and obtaining partial high pressure as the duct moves across the sealing area  30  and full pressure at the exit of the sloped area  33   b  to high pressure port  24 . The first stream exits at high pressure without imparting any rotational momentum through outlet  7 . The remaining fluid volume in the duct is partially depressurized while passing sealing area  29  and at complete low pressure upon the duct passes the sloped area  33   a.  The end cover is further equipped with a central bore  34  for a tension rod and a recess  35  for a center bushing.  
         [0043]      FIG. 5   b  shows the back face of end cover  22  where the first stream enters through a central inlet  5  also giving access to the nut and voucher of the tension rod and thereafter flows into the low pressure port  23 . The first stream exits at high pressure from port  24  through the outlet  7 .  
         [0044]     Although the end covers are essentially left and right versions or mirror images of each other, the inventive configuration is not sol limited and it does not preclude individual features of the opposite end covers, such as port wall inclination, to be substantially different from each other in order to satisfy requirements created by other constraints or preferences in the overall design and function of the invention or particular application.  
         [0045]      FIG. 6  shows the dynamics of balancing the separation force between end covers and rotor. The leakage flows between end cover sealing areas and rotor follow a certain pressure gradient as indicated where: A-B indicates a drop from the external rotor clearance space  15  to the low pressure port area  23 ; C-D indicates a pressure increase from low pressure of port area B-C to intermediate pressure in an external groove of the axle  9  while D-E represents the uniform force area created by the clamping force of the nut and voucher on the tension rod; E-F indicates the full pressure increase from the groove and to the high pressure port; and F-G-H represents the uniform high pressure level of port  24  and the external clearance space  15 . The diagram shows the pressure gradient as it is across the symmetry line X-Y and the resulting pressure force from all areas may be substituted by one force F located at the centroid of total force.  
         [0046]     The back side of the end cover is defined by a symmetry line x-y and associated pressure gradient line a-b-c-d and a force balancing area  18  under full high pressure and a low pressure counter area  20  confined by a seal  19  creating a substitute force C, sized and positioned to equalize the opposing separation force F.  
         [0047]     The embodiments of the present inventions are not to be limited in scope by the specific embodiments described herein. For example, although many of the embodiments disclosed herein have been described, in particular configurations, the principles of the invention herein described are equally applicable to other configurations. Indeed, various modifications of the embodiments of the present inventions, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such modifications are intended to fall within the scope of the following appended claims. Further, although some of the embodiments of the present invention have been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the embodiments of the present inventions can be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breath and spirit of the embodiments of the present inventions as disclosed herein.