Abstract:
An improved pressure exchange apparatus having elongated ports that are defined by a swept area of the bores of an internal rotor, thereby increasing throughput and providing for improved sealing.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to pressure exchangers for transfer of energy from one liquid flow to another. More specifically, this invention relates to pressure exchangers for the transfer of energy from one liquid stream to another using a rotating rotor.  
           [0003]    2. Summary of the Prior Art  
           [0004]    The present invention provides a device which can be appropriately described as an engine for exchanging pressure energy between relatively high and relatively low pressure fluid systems, which the term fluid being defined here as including gases, liquids and pumpable mixtures of liquids and solids. The engine for pressure energy exchange of the present invention is a highly efficient device with well over 90% of the energy of pressurization in a pressurized fluid system being transferred to a fluid system at a lower pressure. The device employed for achieving this highly efficient transfer has a long and trouble free operating life which is not interrupted by the plugging and fouling of valves, or the binding or freezing of sliding pistons or the like.  
           [0005]    In processes where a liquid is made to flow under pressure, only a relatively small amount (about 20%) of the total energy input is consumed in pressurizing the liquid, the bulk of the energy being used instead to maintain the fluid in flow under pressure. For this reason, continuous flow operation requires much greater energy consumption than non-flow pressurization.  
           [0006]    In some industrial processes, elevated pressures are required only in certain parts of the operation to achieve the desired results, following which the pressurized fluid is depressurized. In other processes, some fluids used in the process are available at high pressures and others at low pressures, and it is desirable to exchange pressure energy between these two fluids. As a result, in some applications, great improvement in economy can be realized if pressure exchange can be efficiently transferred between two liquids or between pumpable slurries of liquid-solid mixtures.  
           [0007]    By way of illustration, a specific process of this type is the exchange crystallization process for effecting desalination of sea water, or other saline aqueous solutions. In this process, a slurry of ice and an exchange liquid, such as a hydrocarbon, is placed under extreme pressure in order to reverse the order of freezing so that the ice crystals melt, and the exchange liquid is partially frozen. Following this step of the desalinization process, the water from the melting of the ice is separated from the hydrocarbon, which is in the form of a slurry of solid hydrocarbon particles with the liquid hydrocarbon, and the separated phases are then depressurized to near atmospheric pressure. The economy with which the exchange crystallization desalination process can be practiced is directly dependent upon the efficiency with which the energy input to the process upon pressurization of the ice-exchange liquid system can be recovered after separation of the water-exchange liquid phases.  
           [0008]    Another example where a pressure exchange engine finds application is in the production of potable water using the reverse osmosis membrane process. In this process, a feed saline solution is pumped into a membrane array at high pressure. The input saline solution is then divided by the membrane array into super saline solution (brine) at high pressure and potable water at low pressure. While the high pressure brine is no longer useful in this process as a fluid, the pressure energy that it contains has high value. A pressure exchange engine is employed to recover the pressure energy in the brine and transfer it to feed saline solution. After transfer of the pressure energy in the brine flow, the brine is expelled at low pressure to drain.  
           [0009]    Accordingly, pressure exchangers of varying design are well known in the art. U.S. Pat. No. 3,431,747 to Hashemi et al. teaches a pressure exchanger for transfer of pressure energy from a liquid flow of one liquid system to a liquid flow of another liquid system. This pressure exchanger comprises a housing with an inlet and outlet duct for each liquid flow, and a cylindrical rotor arranged in the housing and adapted to rotate about its longitudinal axis. The cylindrical rotor is provided with a number of passages or bores extending parallel to the longitudinal axis and having an opening at each end.  
           [0010]    A ball is inserted into each bore for separation of the liquid systems. The ball movement is limited due to the use of a seat at each end of the passages. The seats cause a reduction in cross-area of the bores and are susceptible to wear and eventual failure. A more significant problem with this invention however, is that the bores of the cylindrical rotor line up with respective outlet ports for a very limited time. In this arrangement, fluid flow is not continuous, but is rather shut off and on as the cylindrical rotor spins. This results in very low efficiency as well as increased mechanical wear of the various parts due to pressure transients in the system.  
           [0011]    In an attempt to improve the overall efficiency of this type of pressure exchanger, a modified pressure exchanger for liquids can be found in U.S. Pat. No. 4,887,942 to Hauge. Similar to the pressure exchanger found in Hashemi, a cylindrical rotor is spun inside a housing for the communication of pressure energy between a low and high pressure liquid source. Located in the rotor is an array of longitudinally running passages for the communication of the flowing liquid to inlet and outlet ports. The inlet and outlet ports of the Hauge pressure exchanger however is comprised of two semi-circular shaped ducts that allow for the almost continuous flow of liquid from the passages to the ducts. Allowing for the almost continuous, uninterrupted flow of liquid increases the pressure exchanger efficiency as well as reduces wear and tear on the mechanical components connected to the device.  
           [0012]    Referring to FIG. 1 which shows a cross-sectional view of the Hauge invention, a major drawback of the Hauge invention is the reduction in sealing surface-area between the inlet and outlet ports. The two semi-circular ducts are separated by a very thin wall, thereby requiring extremely tight fitting components to ensure an acceptable level of sealing and the prevention of pressure loss between the high and low pressure ports. Leakage between these two ports results in reduced efficiency of the pressure exchanger, and as the tight tolerances of the mechanical components begin to wear, leakage between the ports will only increase and require costly maintenance.  
           [0013]    There therefore is a need for a pressure exchanger which provides both smooth and uninterrupted fluid exchange as well as enhanced sealing capability thereby reducing the amount of leakage that occurs between the high and low pressure ports.  
         SUMMARY OF THE INVENTION  
         [0014]    The primary objective of the present invention is to provide a device for efficiently transferring the energy of pressurization from a pressurized fluid to a second fluid at a lower pressure.  
           [0015]    Another object of the present invention is to provide a device for efficiently transferring the energy of pressurization from a pressurized fluid to a second fluid at a lower pressure which exhibits enhanced sealing properties between the two pressurized fluids.  
           [0016]    Yet another object of the present invention is to provide a pressure exchanger that allows for an almost continuous flow of fluids thereby increasing overall efficiency as well as reducing deleterious transients within the pressure exchanger.  
           [0017]    Still another object of the present invention is to provide a pressure exchanger that has reduced maintenance costs and an increased usable life.  
           [0018]    Yet another object of the present invention is to provide a device that allows for the exchange of pressure energy between two fluids with the use of conventional in line valving.  
           [0019]    In addition to the described objects and advantages of the present invention, additional objects and advantages will become apparent as the following detailed description of the invention is read in conjunction with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a cross-sectional view of a pressure exchange apparatus in accordance with the prior art;  
         [0021]    [0021]FIG. 2 is a simplified cross-sectional view of the present invention;  
         [0022]    [0022]FIG. 3 and FIG. 4 are isometric views of rotors in accordance with the present invention;  
         [0023]    [0023]FIG. 5 and FIG. 6 are sectional views through the closure plates showing various configurations of the inlet and outlet ports superimposed over the example rotor duct shapes;  
         [0024]    [0024]FIG. 7 is an isometric view of a closure plate showing the circular ports.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    Referring first to FIG. 2, a preferred embodiment 10 of the pressure exchange apparatus in accordance with the present invention is generally shown. A solid cylindrical rotor  11  which has a pair of spaced end faces  12  and  14 . Extending through the rotor  11  in an axial direction is at least one bore. In the preferred embodiment, and not by limitation, the bore is cylindrical, but could be of almost any shape. In FIG. 2, two of the axially extending bores are depicted, and are designated by reference numeral  16  and  18 . As shown, the bores  16  and  18  each open at their opposite ends in the two end faces  12  and  14 .  
         [0026]    Pressed into the two ends of each of the bores  16  and  18  are stops. The stops at the opposite ends of the elongated, axially extending bore  16  are designated  20  and  22 , and those at the opposite ends of the axially elongated bore  18  are designated by numerals  24  and  26 . A small cylinder or separator  28  is slidably mounted in axial bore  16 , and a similar small cylinder or separator  30  is slidably mounted in the bore  18 . In the preferred embodiment, the separators  28  and  30  may be constructed of any hard, rigid and wear resistant material. The separators  28  and  30  are not necessarily required, and can be removed depending on the process requirements and the liquids employed in the system.  
         [0027]    Surrounding and enclosing cylindrical rotor  11  in a circumferential manner is a cylindrical housing  32 . The cylindrical housing  32  has a radially inner cylindrical wall  32   a  which is preferably positioned closely adjacent but out of contact with the outer peripheral wall  11   a  of the rotor  11 . A pair of generally cylindrical, relatively thick closure plates  34  and  36  are secured by axially extending fasteners  37  to cylindrical housing  32 . Rotor  11  is thus rotatably and sealing contained in cylindrical housing  32  and closure plates  34  and  36 .  
         [0028]    The closure plate  34  is provided with a central counter bore  38  in which is mounted an annular bearing  40  for journaling a portion of a central shaft  42  which is provided coaxially to rotor  11 . Intermediate the other distal end of the shaft  42  is another bore  38 ′ in closure plate  36  in which is mounted another annular bearing  40 ′ for journaling another portion of the central shaft  42 . A keyway  41  and key  41 ′ is provided between the shaft  42  and the rotor  11  for the transmission of torque from the shaft  42  to the rotor  11 . A seal  50  is provided in closure plate  36  around shaft  42  for the prevention of fluid leakage. The extending and exposed portion of the shaft  42  is adapted to be connected to a suitable source of power such as an electric motor or the like (not illustrated).  
         [0029]    An elongated low pressure fluid inlet passageway  52  extends through the closure plate  36  in a predetermined direction in relation to bore  16  and is directed to a single circular port  100   d . As shown in FIG. 2, a second high-pressure discharge passageway  72  is provided in the closure plate  36 , disposed 180 degrees from the passageway  52 , also directed to a single circular port  100   c . Similarly, a low pressure fluid discharge passageway  96  and a high pressure fluid inlet passageway  98  are provided in closure plate  34 . Each of these passageways are also directed to a single circular port  100   a  and  100   b  respectively for connection of a hose or the like (not shown).  
         [0030]    It will be noted that the open ports or passageways  52  and  72  (in the case of closure plate  36 ), and the open ports or passageways  96  and  98  (in the case of closure plate  34 ) are located so as to be in alignment with the axially extending bores  16  and  18  through the rotor  11  when the rotor is in the position depicted in FIG. 2. Of course, as the rotor  11  is driven in rotation by power applied to the shaft  42 , the axial bores  16  and  18  are moved out of alignment with the respective passageways. The openings to each end of each axially extending bore  16  and  18  are disposed on the same circular paths or at the same radius from the shaft  42  as the passageways in closure plates  34  and  36 . Thus, the high pressure and low pressure fluid inlet and fluid discharge passageways which are provided through the closure plates  34  and  36  are successively brought into alignment with the axially extending bores  16  and  18 . Through the rotor  11  at such time as the rotor is driven in rotation.  
         [0031]    Still referring to FIG. 2., the operation of the pressure exchange apparatus in accordance with the present invention will now be described. Let&#39;s assume that two process fluids which will be called fluid A and fluid B are available in an industrial process at pressures P 2  and P 1 , respectively. Let it be assumed that the pressure P 1  of fluid B is substantially greater than the pressure P 2  of fluid A.  
         [0032]    With a source of fluid A at pressure P 2  available, this source is connected to the low pressure fluid inlet passageway  52  in closure plate  36  so that fluid A at pressure P 2  may enter this passageway. The passageway  96  through the closure plate  34  is connected to a relatively low pressure zone. The high pressure inlet passageway  98  is connected by a pipe (See FIG. 2 a ) or other suitable means to a source of high pressure fluid B which is maintained at pressure P 1 . Finally, the high pressure discharge passageway  72  is connected to suitable fluid confining means which can retain a fluid under pressure, and can permit fluid under pressure to be pumped thereinto from the high pressure fluid discharge passageway  72 .  
         [0033]    With these connections made to the several fluid passageways through the closure plates  34  and  36 , the depicted structure can be utilized for efficiently transferring substantially all of the pressure energy from the high pressure fluid B to the relatively low pressure fluid A. Having set the rotor  11  in rotational motion by energizing a motor or other suitable prime mover connected to shaft  42 , the axial bores  16  and  18  formed in the rotor  11  are, in consecutive sequence, brought into axial alignment with passageways  52  and  96 , and then  72  and  98  formed in the closure plates  34  and  36 .  
         [0034]    Thus, at the instant in the operation of the apparatus which is represented by the positions of the elements shown in FIG. 2, the rotor has been rotated to a position in which the axially extending bore  16  is aligned with the passageways  52  and  96 . Concurrently, the bore  18  has aligned with the passageways  72  and  98 . At this time, the relatively low pressure fluid A at pressure P 2  enters the bore  16  to the right of separator  28  via the low pressure fluid inlet passageway  52 . At the same time, some of fluid B which has been previously entrapped in the part of bore  16  to the left of the separator  28  is placed in communication with a vent or low pressure environment and can be discharged through discharge passageway  96  as the separator  28  is displaced to the left in bore  16  by the impress of the relatively low pressure fluid A entering the right side of this bore.  
         [0035]    In the case of the axially extending bore  18 , as shown in FIG. 2, relatively high pressure liquid B at pressure P 1  is entering the left side of this bore from the high pressure inlet passageway  98 , and drives the separator  30  toward the right. This displaces the entrapped fluid A which is disposed in the right side of the bore  18  as a result of its entry into this bore at a previous time when the bore  18  occupied the position shown as occupied by bore  16  in FIG. 2. This occurred of course, at a time earlier in the rotational movement of rotor  11 . Continued communication of the high pressure fluid B upon the left side of the separator  30  eventually drives separator  30  to the right side of the bore  18 , and completely displaces the relatively low pressure fluid A from this bore at a pressure which is only slightly less than that of the high pressure fluid B.  
         [0036]    It may thus be seen that as rotor  11  continues to rotate, the net effect is that, in being depressured from its elevated pressure P 1 , to atmospheric pressure, the high pressure fluid B is made to transfer efficiently its energy of pressurization to the relatively low pressure fluid A. The transfer is highly efficient due to the minimum energy required to displace the separators  28  and  30  in their respective bores without the use of valving which may choked or clogged. Thus, relatively thick slurries of high solids content can be successfully passed through the pressure exchange apparatus.  
         [0037]    Referring to FIGS. 3 and 4, rotor  11  is provided with cylindrically shaped axial bores  58  or substantially arc-segment shaped axial bores  59 . The present invention contemplates all such shapes of bores for fluid transmission through rotor  11 . Naturally, if required, separators  28  and  30  would be formed to slidably engage and seal the axial bores.  
         [0038]    Referring to FIGS. 5 and 6, the high pressure discharge port elongated passageway  72  extending through the closure plate  36  in a direction substantially parallel with the bore  16  is shown. Also shown is the low-pressure inlet passageway  52  disposed diametrically opposed from the passageway  72 . As shown, the passageways  52  and  72  are essentially swept areas of the bores  16  or  18  located in rotor  11 . In this configuration, more than a single bore in rotor  11  is in fluid communication with a respective passageway. This increases overall apparatus efficiency as well as reduces pressure transients that occur as a result of starting and stopping the flow of liquids.  
         [0039]    These elongated passageways would also need to be provided in closure plate  34  so that the fluids may be equally communicated through the plurality of axial bores in rotor  11 .  
         [0040]    An increased sealing surface as shown by hatched area  60  is provided between the high pressure discharge passageway  72  and the low pressure inlet passageway  52 . This increased sealing surface substantially reduces or eliminates fluid leakage between the ports and increases apparatus efficiency.  
         [0041]    Referring now to FIG. 7, the closure plate  36  is shown isometrically to reveal the relationship of the passageways  52  and  72  with the circular ports  100   d  and  100   c  respectively. As shown in the figure, fluid entering passageway  52  is directed to flow through circular port  100   d , which provides an easy means for securing a typical cylindrical member such as a hose or a tube to the apparatus. Similarly, fluid in passageway  72  is directed to circular port  100   c  for further communication to a hose or the like.  
         [0042]    It is to be understood that the invention is not limited to the illustrations described herein, which are deemed to illustrate the best modes of carrying out the invention, and which are susceptible to modification of form, size, arrangement of parts and details of operation. For example, more than one elongated passageway at a different radius could be provided to increase the throughput of the apparatus. Variations and modifications of the passageway locations and sizes are fully contemplated by the present invention. The invention is intended to encompass all such modifications, which are within its spirit and scope as defined by the claims.