Patent Publication Number: US-2007104588-A1

Title: Rotary pressure exchanger

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation of international patent application no. PCT/EP2005/004606, filed Apr. 29, 2005, designating the United States of America, and published in German on Dec. 8, 2005 as WO 2005/116456, the entire disclosure of which is incorporated herein by reference. Priority is claimed based on Federal Republic of Germany patent application no. DE 10 2004 025 289.0, filed May 19, 2004. 
    
    
     BACKGROUND OF THE INVENTION  
      The present invention relates to a rotary pressure exchanger for transferring pressure energy from a liquid flow of one liquid system to a liquid flow of another system.  
      U.S. Pat. No. 3,431,747 discloses the general principle of a rotary pressure exchanger, the rotor of which is provided with passageways in the form of cylindrical bores and having a ball disposed in each passageway. These balls, which act as sealing members, cause energy losses and are mechanically complex to manufacture. In addition, the abrupt impact of the balls on their spherical seats has the disadvantage that it causes damage due to cavitation. Published German patent application no. DE 37 81 148, which discloses a pressure exchanger without ball valve function in the passageways of the rotor, attempts to avoid this.  
      U.S. Pat. No. 5,988,993 (=DE 695 12 089 T2) relates to the hydrostatic bearing principle of the rotating rotor. This solution avoids the arrangement of a shaft carrying the rotor and the corresponding bearing within the housing, but the shaftless configuration of the rotor is quite complex and expensive to manufacture. The production costs for the precision manufacture of a ceramic rotor and the associated ceramic bearing shell are considerable.  
      U.S. Pat. No. 6,540,487 attempts to solve the problem of noise in pressure exchangers of this type caused by the alternating opening and closing of the passageways and the concurrent cavitation. Two sealing areas are provided on the housing end faces opposite the end faces of a rotor and between an inlet and outlet port on the housing side. During the respective pressure exchange processes taking place in the passageways of the rotor, these sealing zones ensure an external blocking of the passageways. They also prevent a short circuit flow between the inlet and the outlet port of the housing. As the openings of the passageways travel across the sealing zones, the alternating opening and closing of the passageways causes a considerable amount of noise, and destructive cavitation phenomena occur. The attempt to avoid the latter through connecting channels that are formed in the sealing zones to equalize the pressure between two zones of different pressure levels, however, reduces the efficiency of a pressure exchanger of this type and has limited effectiveness.  
     SUMMARY OF THE INVENTION  
      It is an object of the invention to provide an improved pressure exchanger comprising a rotor disposed within a housing and having a plurality of passageways therethrough.  
      Another object of the invention is to provide a rotary pressure exchanger which operates with greatly reduced force loading of the rotor.  
      A further object of the invention is to provide a rotary pressure exchanger with improved cavitation characteristics.  
      An additional object of the invention is to provide a rotary pressure exchanger which operates with a reduced noise level.  
      These and other objects are achieved in accordance with the present invention by providing a pressure-surge-reducing secondary flow zone or afterflow zone at the transition between a housing-side inlet port and a housing-side sealing zone and/or at the transition between the end face openings of the passageways disposed in the rotor and the sealing webs of the rotor arranged therebetween.  
      The sudden loading of a rotor occurs primarily when a column of liquid flowing into a passage is abruptly cut off. An abrupt cutoff of a column of liquid flowing into a passage results in substantial pressure surges. This causes overloading of the rotor material, usually a ceramic, even to the point of fractures in the rotor wall. It also causes cavitation phenomena in the flowing liquid column with the known detrimental effects. This solution is independent of the driving method used for such a rotor. It works both in rotors where the rotary movement is produced by a pulse of the inflowing liquid and in rotors rotated by an external drive via a shaft.  
      One embodiment of the invention provides that while a passage opening is blocked by the sealing zone or starts to be covered by the sealing zone and the following sealing web, the afterflow zone blocks the volumetric flow into the passageway in a time delayed manner. This prevents abrupt blocking of the volumetric flow and the resulting disadvantages.  
      A closing process of a passageway is commenced when a first or preceding sealing web of a passageway as seen in moving direction reaches the edge of a sealing zone. From this point in time onward the cross section of an opening is progressively reduced by the sealing zone, which acts as a cover. With continued rotational movement of the rotor, a second or following sealing web of this opening approaches the edge of the sealing zone. An end face opening of a rotor passageway is generally enclosed between respective preceding and following sealing webs, which as a rule extend radially. If the following sealing web reaches the edge of the sealing zone, the flowing liquid column is blocked abruptly in view of the peripheral speed of the rotor, causing the detrimental effects. This is prevented by the arrangement of an afterflow zone in the area of the intersection of the following sealing web and the start or the edge of the sealing zone. The afterflow zone causes a gradual reduction of the flowing liquid column over time.  
      According to other embodiments, an afterflow zone disposed on the housing at the transition between the inlet port and the sealing zone as viewed in the direction of rotation of the rotor has a cross section which decreases toward the sealing zone. On the other hand, an afterflow zone disposed on the rotor at the transition between adjacent openings of passageways and a sealing web has an increasing cross section in the direction of rotation of the rotor. In this solution, afterflow zones disposed at the sealing webs of the rotor again block the volumetric flows flowing into the passageways in a time delayed manner. This prevents an abrupt blocking of the volumetric flow in the form of a flowing fluid column and the resulting drawbacks.  
      Depending on the structural dimensions of a pressure exchanger, the width of a sealing zone at a housing end face, the width of the sealing webs at the rotor end face between adjacent openings of the passageways formed in the rotor, and the cross-sectional shape of the passageway, the afterflow zone can be disposed so as to be stationary in the housing, rotating in the rotor and/or on both components. In combinations of such rotating afterflow zones, a stationary afterflow zone on the housing may be used. Depending on the number of inlet ports, a corresponding number of afterflow zones is also arranged in or on the housing.  
      An advantageous aspect of the invention is the configuration according to which, as seen in the direction of rotation of the rotor, an afterflow zone is disposed at that location of the pressure exchanger which is blocked by the respective opening edge of a passageway at the latest possible moment of an inflow or filling process of a liquid column into the rotor.  
      The advantage of creating the afterflow zone is the resulting gradual slowing down of the liquid column flowing into a passageway of the rotor. This is a very simple way of preventing overloading of the material of the passageways in the rotor caused by pressure surges and pressure pulses. Since rotors of this type are predominantly ceramic components, their structural durability is substantially improved as a result.  
      In accordance with yet another embodiment, the measurable width of a sealing zone between an end of the afterflow zone and a beginning of an outlet port corresponds to at least the width of an end face opening of a passageway and the width of a sealing web. This solution ensures a reliable seal of a passageway at the sealing zone in any event by at least one half of the sealing web width to prevent a type of continuous short circuit line between the inlet port and the outlet port. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be described in further detail hereinafter with reference to illustrative preferred embodiments shown in the accompanying drawing figures, in which:  
       FIG. 1  shows a three-dimensional view of a transition area between an inlet port and the passageways of a rotor;  
       FIGS. 2 and 3  are diagrams of the pressure pattern during a filling process of a passageway;  
       FIGS. 4   a  to  4   c  show different cross-sectional shapes of the afterflow zone in the stator, and  
       FIGS. 5   a  to  5   c  show different embodiments of the sealing webs. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       FIG. 1  is a perspective view of the end face of a rotor of a pressure exchanger with passageways arranged therein and opposite inlet and outlet ports on the housing side. Those surfaces which are uniformly distributed on one end face of the rotor and around its axis of rotation in an annular plane enclosing the axis of rotation between the openings of passageways are referred to as sealing webs because of their shape. However, they are actually only a part of the entire sealing surface on the end face of the rotor, which adjoins an opposite housing surface and forms a minimal sealing gap.  
      The volume of the gap defined by the dotted lines in the figure does not correspond to the actual volume but was selected in the shape depicted due to computational considerations.  
      The housing surface has an inlet port and an outlet port. The fluid under pressure flows through the inlet port into the passageways in the form of a column of liquid. Within the passageways, the pressure is transferred to the liquid, which then flows out of the passageways into an outlet port of the housing. This occurs alternately in the area of the two end faces of the pressure exchanger.  
      A rotor of this type and the opposite housing surfaces are formed of a ceramic material, which is sensitive to alternating pressure loading. An afterflow zone, which is depicted here on the housing side, prevents an abrupt cutoff of a liquid column flowing into a passageway. According to the invention it was recognized that an abrupt cutoff of a flowing liquid column causes pressure peaks or surges and thus peak stresses that are destructive of the material. The afterflow zone makes it possible, for the completion of a blocking process of a passageway to be sealed, to gradually reduce a volumetric flow flowing into a passageway. A characteristic curve relative to the average flow rate occurring at the site of the blockage conforms to the zero line over time.  
      In the diagram of  FIG. 2  along a time axis t, the dotted line represents a pressure curve p and the solid line a flow velocity v of a conventional pressure exchanger at the instant when a passageway in a rotor is blocked. The two lines illustrate how a fluid column flows into a passageway of a rotor at a constant velocity v and a constant pressure p. At the instant t z , the sealing zone abruptly blocks the opening of the passageway and the flow velocity v drops almost instantly to zero. This disadvantageous blocking or closing process generates a pressure surge that produces a shock front in the blocked passageway of the rotor. This shock front oscillates in the blocked passageway at a very high pressure level and thereby causes excessive loading of the rotor material. In the worst case, this can lead to the destruction of the rotor.  
       FIG. 3  shows a similarly structured diagram illustrating the effect of an afterflow zone. When the afterflow zone is reached at instant t N1 , the flow velocity v is gradually reduced over a time span t NZ  and completed at instant t N2 . Shortly before instant t N2  is reached, the solid curve of flow velocity v reaches a turning point. This has the result that a fluid column flowing into a passageway is slowed down gently. As a consequence, when a passageway is fully closed, a pressure fluctuation still occurs within it but is much smaller than the aforementioned pressure surge. As a result, the shock front within a passage way is substantially weakened, as clearly indicated by the dotted line. Thus, the fatigue loading of a rotor is significantly reduced, and the operational reliability of the rotor is increased several fold.  
       FIGS. 4   a  to  4   c  illustrate different longitudinal sections of the afterflow zones taken in flow direction. The afterflow zones NZ, which are stationary here, are distinguished in that they have a cross-sectional characteristic between the inlet port  1  and the sealing zone  2  of the housing extending perpendicularly to the drawing plane which causes a gradual deceleration of a flowing liquid column. This characteristic can be wedge-shaped, stepped, rounded, or the like. The important aspect is the resulting gradual blocking of a passageway that occurs over a time span t NZ .  
       FIGS. 5   a  to  5   c  show different longitudinal sections of afterflow zones NZ taken in flow direction. In this example, the afterflow zones are disposed on the sealing webs  3  between the individual passageways  4  of a rotor  5 . The arrow indicates the direction of rotation of the rotor whose end faces are seated against the housing and its sealing zones  2  so as to form a seal. These rotatingly disposed afterflow zones NZ are also distinguished in that they cause a cross-sectional characteristic between the inlet port  1  and the sealing zone  2  extending perpendicularly to the drawing plane, such that a gradual deceleration of a flowing fluid column is obtained. This characteristic can be wedge-shaped, stepped, rounded, or the like. The important aspect is the resulting gradual blocking of the passageways to be filled, which occurs over a time span t NZ .  
      Depending on the flow volumes to be processed and the size of a pressure exchanger, the afterflow zones can be disposed only on the housing, only on the rotor, or in combination.  
      The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations within the scope of the appended claims and equivalents thereof.