Abstract:
A pressure exchange device is provided that utilizes a rotor assembly inside a housing to transfer the pressure of a fluid from one high pressure fluid to another low pressure fluid. The housing may comprise a pressurized fluid contained therein to provide a sealing force to reduce fluid leakage between the spinning rotors and the housing. The sealing force and wear characteristics may be controlled to reduce leakage and wear of the pressure exchange device. The rotor assembly may be driven in either direction and the high pressure ports may be switched with the low pressure ports if desired.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     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 split rotor exhibiting enhanced/proportional sealing and wear adjustment characteristics.  
         [0002]     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.  
         [0003]     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.  
         [0004]     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.  
         [0005]     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 desalination 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.  
         [0006]     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.  
         [0007]     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.  
         [0008]     A separation device may be inserted into each bore for separation of the liquid systems. The movement of the separation device 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.  
         [0009]     Referring to  FIG. 3  which shows a cross-section of the prior art exchanger, a major drawback of the prior art is the reduction in sealing surface-area between the inlet and outlet ports. The two 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 as shown in  FIG. 3 . Attempts have been made to incorporate springs and seals at the ends of the passageways to reduce leakage. Due however to the obvious drawbacks of this approach, the seals eventually wear out and or the springs degrade overtime, both of which require expensive downtime and repair. In addition, seals of this nature function properly only when they are aligned with the housing bores. During a single rotation, alignment of the rotor bore and the housing bore occurs only for a brief moment during the cycle. A seal with intermittent sealing capability is undesirable since leakage of high pressure fluid to the low pressure conduit represents a reduction in efficiency of the device.  
         [0010]     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  
       [0011]     In accordance with a general aspect of the present invention, a pressure exchange apparatus for the transfer of a fluid is provided which consists of a housing having a low pressure inlet located at a first distal end of a housing and a low pressure outlet located at a second distal end of the housing. The low pressure outlet is in alignment with the low pressure inlet, and the housing also has a high pressure inlet located at the second distal end of and a high pressure outlet located at the first distal end of the housing. The high pressure inlet is in alignment with the high pressure outlet.  
         [0012]     A left rotor is rotatably mounted inside the housing, with the left rotor having a first low pressure conduit and a first high pressure conduit running therethrough, both conduits are configured to align with the high pressure outlet and the low pressure inlet concurrently as the left rotor rotates. A right rotor, coaxially aligned with and offset from the left rotor is rotatably mounted inside the housing. The right rotor has a second low pressure conduit and a second high pressure conduit running therethrough, and both conduits are configured to align with the high pressure inlet and the low pressure outlet concurrently as the right rotor rotates.  
         [0013]     A first tube is sealingly placed intermediate the left rotor and the right rotor is configured to communicate fluid between the first low pressure conduit and the second low pressure conduit. A second tube is sealingly placed intermediate the left rotor and the right rotor and is configured to communicate fluid between the first high pressure conduit and the second high pressure conduit. A spring disposed between the left rotor and right rotor is configured to bias the rotors apart thereby maintaining light contact with said housing. A motive force is provided to rotate the left and right rotor. A pressurized fluid is provided inside the housing to maintain sealing contact between the left and right rotor and the housing.  
         [0014]     In accordance with another aspect of the invention, a system for the filtration of contaminated water to produce potable water is provided which has a low pressure pump configured to pump the contaminated water to a high pressure pump. A high pressure pump is provided to receive contaminated water from the low pressure pump and communicate the contaminated water to a filtration device at an elevated pressure. The filtration device is configured to produce potable water and waste water, with the waste water being expelled at an elevated pressure.  
         [0015]     A pressure exchange pump is further provided to receive the waste water from the filtration device and contaminated water from the low pressure pump. The pressure exchange pump has a housing having a low pressure inlet located at a first distal end of the housing and a low pressure outlet located at a second distal end of the housing. The low pressure outlet is in alignment with the low pressure inlet, and the housing also has a high pressure inlet located at the second distal end of and a high pressure outlet located at the first distal end of the housing. The high pressure inlet is in alignment with the high pressure outlet. A left rotor is rotatably mounted inside the housing, with the left rotor having a first low pressure conduit and a first high pressure conduit running therethrough, both conduits are configured to align with the high pressure outlet and the low pressure inlet concurrently as the left rotor rotates. A right rotor, coaxially aligned with and offset from the left rotor is rotatably mounted inside the housing. The right rotor has a second low pressure conduit and a second high pressure conduit running therethrough, and both conduits are configured to align with the high pressure inlet and the low pressure outlet concurrently as the right rotor rotates.  
         [0016]     A first tube is sealingly placed approximately intermediate the left rotor and the right rotor and is configured to communicate fluid between the first low pressure conduit and the second low pressure conduit. A second tube is sealingly placed intermediate the left rotor and the right rotor and is configured to communicate fluid between the first high pressure conduit and the second high pressure conduit. A spring disposed between the left rotor and right rotor is configured to bias the rotors apart thereby maintaining light contact with said housing. A motive force is provided to rotate the left and right rotor. A pressurized fluid is provided inside the housing to maintain sealing contact between the left and right rotor and the housing. This fluid acts on both the left and right sealing surfaces so as to exert a net force on said surfaces in proportion to the pressurized fluid pressure. The control of this pressure can be internal to the mechanism or external depending on system requirements. A controlled method requires an external valve and a feedback method such as a pressure gage.  
         [0017]     In a further aspect of the invention, a pressure exchange apparatus for transferring the energy of pressurization between two fluids is provided, wherein one fluid is at a relatively higher pressure than the other. A first rotatably mounted rotor having a pair of spaced apart planar end faces, having at least one bore extending axially therethrough with each of the bores having an opening at each end thereof with the openings located in the planar end faces. A second rotatably mounted rotor being spaced apart from and coaxially aligned with the first rotor, the second rotor having a pair of spaced apart planar end faces, having at least one bore extending axially therethrough with each of the bores having an opening at each end thereof with the openings located in the planar end faces. A pair of closure plates rigidly affixed in close proximity to a respective end face of the first rotor and the second rotor. The closure plates slidingly and sealingly engaging the respective end face, and each of the closure plate having at least one fluid inlet passageway and at least one fluid discharge passageway, the passageways being positioned so that a fluid inlet passageway in one of the closure plates is aligned with the bore in the rotors at such time during the rotation of the rotors as a fluid discharge passageway in the other closure plates is aligned with the same bore. A pair of tubes slidably inserted axially between the first and second rotor is held in fluid communication with the bores such that fluid flows from a respective bore of the first rotor to a respective bore of the second rotor. A spring is inserted between the first and second rotor which is configured to bias the first rotor apart from the second rotor. A pressurized fluid acting is provided which acts upon a face of the first rotor and the second rotor to increase the sealing contact between the closure plates and the first and second rotors. The bore openings and passageways being positioned in their respective surfaces so that during rotation of the rotors, the openings at the end of each bore are, in alternating sequence, brought into concurrent alignment with an inlet passageway at one end of the respective bore and a discharge passageway at the other end of the respective bore, and then, at a different time, into concurrent alignment with a discharge passageway at one end of the respective bore and an inlet passageway opening at the other end of the respective bore. A motive force for cyclically rotating the rotors relative to the closure plate so that each of the bore openings periodically moves through the same path to repeatedly effect the alternating sequence of alignment of the bores with the passageways.  
         [0018]     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a cross-sectional side view of the pressure exchange device;  
         [0020]      FIG. 2  is a simplified block diagram of a filtration system utilizing the pressure exchange device in accordance with the present invention;  
         [0021]      FIG. 3  is a cross-sectional view of the prior art. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.  
         [0023]     Referring first to  FIG. 2 , which depicts a process flow diagram for a salt water filtration system  200  that uses a reverse osmosis process for the production of potable water which comprises a pressure exchange device  10  in accordance with the present invention.  
         [0024]     A salt water reservoir  201  provides a supply of salt water which is pumped to a high pressure pump  204  by reservoir pump  202 . Typically the reservoir pump  202  supplies salt water to both the high pressure pump  202  and the pressure exchange device  10  at approximately 30 psi pressure at approximately equal flow rates. The high pressure pump  204  boosts the pressure to approximately 1000 psi and supplies the salt water to a filter element  208 . In this particular application, and not by way of limitation, the filter element  208  comprises a reverse osmosis type filter device which removes the impurities from the water and provides a fresh water supply  210 . A pressure drop occurs in the filter element  208  such that a supply of waste water  209  exits the filter element  208  at approximately 980 psi. Rather than dump this waste water  209  at this elevated pressure, the waste water  209  is supplied to a high pressure inlet  104  of the pressure exchange device  10 . This high pressure waste water is thus used to pressurize additional salt water for use in the filtration process. Reuse of this high pressure waste water  209  thus provides for a highly efficient filtration system  200 .  
         [0025]     As mentioned previously, the reservoir pump  202  supplies salt water to a low pressure inlet  100  of the pressure exchange device  10 . The pressure exchange device  10 , as to be discussed in more detail below, is configured to raise the pressure of the salt water supplied to it by the reservoir pump  202  to a pressure equal to the pressure of the waste water  209  supplied to the high pressure inlet  104 .  
         [0026]     A high pressure outlet  106  located on the pressure exchange device  10  is in fluid communication with a boost pump  214 . The waste water  209  from the high pressure outlet  106  is supplied to the boost pump  214  for example at approximately 960 psi and the boost pump  214  raises the pressure to 1000 psi and supplies the waste water to the filter element  208  for further filtration. Thus, a closed loop system is provided that maximizes the use of the waste water and reuses the high pressure waste water to increase system efficiency.  
         [0027]     Referring to  FIG. 1 , the operation of the pressure exchange device  10  will now be discussed in more detail. The pressure exchange device  10  is comprised of a sealed housing  16  having a first and second end plate  12  and  14  respectively affixed thereon. Provided in the first end plate  12  is a low pressure outlet  102  and a high pressure inlet  104 . Provided in the second end plate  14  is a high pressure outlet  106  and a low pressure inlet  100 .  
         [0028]     Referring back to  FIG. 2 , the low pressure outlet  102  is in fluid communication with a waste line  218  which is in fluid communication with a drain  220 . The low pressure inlet  100  is in fluid communication with the reservoir pump  202  and the high pressure outlet  106  is in fluid communication with the boost pump  214 . The high pressure inlet is in fluid communication with the filter element  208  and therefore receives the waste water  209  which is already at an elevated pressure.  
         [0029]     Referring to  FIG. 1 , a left rotor  18   a  and a right rotor  18   b  is rotatably mounted inside the housing  16 . Each rotor has at a minimum two opposing conduits. For ease of illustration in this sectional drawing these shall be referred to as a top conduit  32  and a bottom conduit  30 . These conduits are held in coaxial alignment with each other. A top tube  20   a  and a bottom tube  20   b  is sealingly inserted in a respective conduit between the left and right rotor  18   b  and  18   a  to bridge the gap between the rotors and thereby provide for a continuous passageway from the right rotor  18   a  through the left rotor  18   b . A seal  36  is provided at each end of the top and bottom tubes  20   a  and  20   b  to reduce fluid leakage. With this configuration, when the rotor is in proper alignment with the ports on the end plates  12  and  14 , fluid may flow through the pressure exchange device  10 .  
         [0030]     A spring element  28  is disposed in a step  26  which is formed in the left and right rotor  18   a  and  18   b . The spring element  28  is configured to act against the top and bottom tubes  20   a  and  20   b  and thereby provide a preload force to separate the left and right rotors  18   b  and  18   a  to minimize the gap  24  between a sealing surface  46  and the rotors. It should be noted that the gap  24  as shown in  FIG. 1  is exaggerated for illustration purposes. Thanks in part to the spring element  28 , the gap is actually very small, thereby reducing leakage during the initial start up phase. The sealing surface  46  is a hard coated surface provided on the inside wall of each end plate  12  and  14  to reduce leakage and wear that may occur from the rotors as they spin. The spring elements  28  therefore provide a preload between the sealing surfaces primarily to reduce leakage at the initial start up of the pressure exchange device  10 .  
         [0031]     It should be understood that the location and configuration of the spring elements  28  may easily be modified as to location and type. For example, a single spring may be inserted between the left and right rotors  18   a  and  18   b  to provide the necessary sealing preload. All such modifications are fully contemplated by the present invention.  
         [0032]     A shaft  22  is provided which runs coaxially through both the left and right rotor  18   a  and  18   b . The shaft  22  is configured to provide the force to spin the rotors, but also allows for the left and right rotor to move along the longitudinal axis of the shaft  22  to maintain a proper sealing interface. This configuration may easily be accomplished by providing a spline or a keyway on the shaft  22  that allows the rotors to slide. The shaft  22  exits through a hole  23  in the first end plate  12  and is connected to a motive force such as a motor (not shown). A bearing  25  is provided in the first and second end plates  12  and  14  to support the shaft  22  and increase the overall system efficiency. An optional seal  27  reduces leakage to the environment between the housing end plate  12  and the shaft  22 .  
         [0033]     An optional first separator  38  and second separator  40  may be disposed in the respective top and bottom conduits  30  and  32 . The separators  38  and  40  may be a sphere which is configured to translate back and forth in the respective conduit to aid in the pressure exchange process. The separators  38  and  40  may also be pistons with sealing elements disposed thereon.  
         [0034]     A pressurized fluid  33  is provided internal to the housing  16  which acts to further separate the left and right rotor  18   b  and  18   a  and increase the sealing force acting on the sealing surface  46  and a respective face of the left and right rotors. The net sealing force is proportional to the difference in the pressurized fluid  33  acting to further separate left and right rotor  18   b  and  18   a  and the average force trying to close the left and right rotor  18   b  and  18   a . Since the entire face of the rotor is subject to the pressurize fluid  33  while the sealing face  24  is subject to pressures that average lower than this pressure, there is a net force of separation of the rotors. This force is proportional to the difference in pressure between the pressurized fluid  33  pressure and the average face pressure  24 . The pressurized fluid  33  may be supplied from the working fluid such as the salt water which is to be filtered, or it may be supplied by a unique fluid source such as a pressurized fluid reservoir.  
         [0035]     An orifice  34  is provided between the rotor and the inside of the housing  16  such that pressurized fluid is allowed to enter from the bottom (high pressure) conduit  30  and provide a supply of fluid to help maintain and regulate the pressure of the pressurized fluid  33 . It may also be advantageous to provide a bleed passage  42  which is in fluid communication with the pressurized fluid  33  and the low pressure inlet  100  to further regulate the pressure of the pressurized fluid  33 . A pressure gage  44  may be located on the housing  16  which is configured to measure and indicate the pressure of the pressurized fluid  33 . It would therefore be possible, through the use of dynamically controlled valves and pressure transducers, to provide a regulation system that produces a pressurized fluid that exhibits the optimum sealing force thus maintaining the pressure exchanger at peak efficiency.  
         [0036]     Referring to  FIGS. 1 and 2 , and as previously described, the pressure exchange device  10  operates to transfer the high pressure contained in the waste water  209  (approx. 980 psi) to the low pressure (approx. 30 psi) salt water supplied to the low pressure inlet  100  by the reservoir pump  202 . This is accomplished by spinning the left and right rotors  18   a  and  18   b  in unison such that the top conduit  32  and the bottom conduit  30  intermittently align with a respective inlet and outlet port of the pressure exchange device  10 . A plurality of bores through the rotor is desirable in order to even out the flow through the pressure exchanger and increase throughput.  
         [0037]     For example, with the rotors  18   a  and  18   b  in the position shown in  FIG. 1 , high pressure waste water is allowed to flow into the bottom conduit  30  through the high pressure inlet  104 . This high pressure flow forces separator  34  to push fluid that is already contained in the bottom conduit  30  (from the previous cycle) out the high pressure outlet  106  at the elevated pressure. Thus the low pressure fluid contained in the bottom conduit  30  has now been elevated to the high pressure. At the same time, the top conduit  32  is in alignment with the low pressure inlet  100  and receives low pressure salt water from the reservoir pump  202 . Since the low pressure outlet, as shown in  FIG. 2  is attached to a drain (ie atmosphere), the flow of the low pressure fluid forces the separator  34  to the right and forces the fluid out of the bottom conduit  30  through the low pressure outlet  102  to a drain  220 . It should be noted that the low pressure fluid that just flowed into the bottom conduit  32 , will be the fluid that is pressurized to the higher pressure when the rotor spins 180 degrees and aligns with the high pressure inlet  104 , thereby repeating the pressure transfer all over again. Obviously, a plurality of conduits, of varying cross-sectional shapes and sizes, can be formed in the rotors  18   a  and  18   b  to increase the flow rate and even out the flow of fluid through the pressure exchange device  10 .  
         [0038]     As the rotor assembly spins, the pressurized fluid  33  in the housing  16  acts against the rotor assembly to maintain a sealing pressure between the faces of the rotor assembly and the sealing surfaces  46 . As the two sealing surfaces wear over time, the pressurized fluid  33  maintains the correct sealing pressure such that over time, the efficiency of the pressure exchanger  10  is not substantially degraded and repairs are not required for long periods of time.  
         [0039]     It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims. For example, the fluid pressures discussed herein were used as for illustration purposes only and should not be used to limit the appended claims.