Patent Publication Number: US-2017350417-A1

Title: Variable area diffuser

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application having Ser. No. 62/345,171, which was filed Jun. 3, 2016. The aforementioned patent application is hereby incorporated by reference in its entirety into the present application to the extent consistent with the present application. 
    
    
     BACKGROUND 
     Reliable and efficient compressors, such as centrifugal compressors, have been developed and are often utilized in a myriad of industrial processes (e.g., petroleum refineries, offshore oil production platforms, and subsea process control systems). Centrifugal compressors may have one or more stages of compression, where each stage may generally include an impeller and a diffuser. Developments in compressor designs have resulted in improved centrifugal compressors with stages of compression capable of achieving higher compression ratios (e.g., 10:1 or greater) for a process fluid having one or more relatively high molecular weight gases. In the high-pressure ratio stages of compression, the process fluid may be discharged from the impeller to the diffuser at increased velocities (e.g., supersonic velocities). Conventional diffusers and designs thereof, however, may not be capable of effectively handling or diffusing the process fluid at the increased supersonic velocities. 
     In view of the foregoing, conventional centrifugal compressors may utilize a pipe diffuser or a similar diffuser to diffuse the process fluid in the high-pressure ratio stages of compression. A conventional pipe diffuser may include an array of pipe-shaped diffuser passages spaced circumferentially about the impeller. The diffuser passages may have a cross-sectional area that may generally increase from an inlet to an outlet thereof to thereby diffuse the process fluid from the impeller. The cross-sectional area of the diffuser passages may at least partially determine the efficacy and efficiency of the pipe diffuser. For example, the relative increase in the cross-sectional area along the diffuser passages may at least partially determine a diffusion rate along the diffuser passages, which may determine the efficiency of the pipe diffuser. 
     Conventional pipe diffusers may often be configured to operate at predetermined or designed operating conditions or operating points of the compressor. For example, the pipe diffusers may be designed to provide increased or optimum efficiency when operating at the designed operating conditions of the compressor. Conventional pipe diffusers, however, may often exhibit a significant decrease in efficiency when the operating conditions of the compressor deviate from the designed operating conditions. For example, the diffuser passages of the pipe diffusers may not be configured to provide optimum diffusion rates when the operating conditions of the compressor deviate from the designed operating conditions. Further, conventional pipe diffuser designs may present a limited ability to control or vary the diffusion rates along the diffuser passages thereof, which may limit the ability to optimize the pipe diffusers over a broad range of operating conditions of the compressor. 
     What is needed, then, are improved pipe diffusers and methods for controlling diffusion rates along the diffuser passages for increased efficiency over a broad range of varying operating conditions of a compressor. 
     SUMMARY 
     Embodiments of the disclosure may provide a diffuser assembly for a compressor. The diffuser assembly may include a diffuser disposable about an impeller of the compressor and configured to receive and compress a flow of process fluid exiting the impeller. The diffuser may include a first stationary wall and a second stationary wall coupled with one another and forming at least in part a volute configured to receive the compressed process fluid from the diffuser. The second stationary wall may define a plurality of stationary wall grooves. The diffuser may also include a moveable wall defining a plurality of moveable wall grooves. The moveable wall may be disposed between the first stationary wall and the second stationary wall such that respective stationary wall grooves and moveable wall grooves form respective flow passages configured to receive the flow of process fluid exiting the impeller. The diffuser assembly may also include an actuator assembly comprising at least one actuator and at least one linkage operatively coupling the at least one actuator and the moveable wall. The actuator assembly may be configured to displace the moveable wall to alter a cross-sectional area of each of the flow passages. 
     Embodiments of the disclosure may further provide a compressor. The compressor may include a casing having an inlet and defining an impeller cavity. The compressor may also include a rotary shaft configured to be driven by a driver, and an impeller fluidly coupled with the inlet and disposed in the impeller cavity. The impeller may be coupled to the rotary shaft and configured to rotate with the rotary shaft to impart energy to process fluid received via the inlet. The impeller may be further configured to discharge the process fluid in at least a partially radial direction. The compressor may further include a diffuser disposed circumferentially about the impeller and configured to receive and compress the process fluid discharged from the impeller. The diffuser may include a first stationary wall coupled with the casing, and a second stationary wall coupled with the first stationary wall and the casing and defining a plurality of stationary wall grooves. The diffuser may also include a moveable wall defining a plurality of moveable wall grooves. The moveable wall may be disposed between the first stationary wall and the second stationary wall such that respective stationary wall grooves and moveable wall grooves form respective flow passages configured to receive the flow of process fluid discharged from the impeller. The compressor may further include a collector formed at least in part by the first stationary wall and the second stationary wall. The collector may be configured to receive the compressed process fluid from the flow passages of the diffuser. The compressor may also include an actuator assembly comprising at least one actuator and at least one linkage operatively coupling the at least one actuator and the moveable wall. The actuator assembly may be configured to displace the moveable wall to alter a cross-sectional area of each of the flow passages. 
     Embodiments of the disclosure may further provide a method for adjusting a cross-sectional area of a flow passage of a diffuser in a compressor. The method may include monitoring one or more operating parameters of the compressor or a process fluid flowing therethrough. The method may also include detecting an operating parameter of the one or more operating parameters outside of a predetermined range. The method may further include axially displacing a moveable wall of the diffuser via at least one actuator operatively coupled with the moveable wall via at least one linkage. The axial displacement of the moveable wall may adjust the cross-sectional area of the flow passage of the diffuser. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is best understood from the following detailed description when read with the accompanying Figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  illustrates an elevated cross-sectional view of a compressor including a diffuser assembly, according to one or more embodiments disclosed. 
         FIG. 2  illustrates an exploded view of the diffuser assembly of  FIG. 1 , according to one or more embodiments disclosed. 
         FIG. 3  illustrates an enlarged cutaway view of a portion of the diffuser assembly including a first stationary wall and a moveable wall, according to one or more embodiments disclosed. 
         FIG. 4  illustrates an enlarged cutaway view of a portion of the diffuser assembly including a second stationary wall, according to one or more embodiments disclosed. 
         FIG. 5A  illustrates an enlarged cross-sectional view of the diffuser arranged to provide flow passages therein having a maximum cross-sectional area, according to one or more embodiments disclosed. 
         FIG. 5B  illustrates an enlarged cross-sectional view of the diffuser arranged to provide flow passages therein having a minimum cross-sectional area, according to one or more embodiments disclosed. 
         FIG. 6  illustrates a flow chart of a method for adjusting a cross-sectional area of a flow passage of a diffuser in a compressor, according to one or more embodiments disclosed. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure; however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the various Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the exemplary embodiments presented below may be combined in any combination of ways, i.e., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure. 
     Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Additionally, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope. Furthermore, as it is used in the claims or specification, the term “or” is intended to encompass both exclusive and inclusive cases, i.e., “A or B” is intended to be synonymous with “at least one of A and B,” unless otherwise expressly specified herein. 
       FIG. 1  illustrates an elevated cross-sectional view of a compressor  100  configured to pressurize a process fluid, according to one or more embodiments of the present disclosure. The compressor  100  may be a direct-inlet centrifugal compressor, such as, for example, a version of a Dresser-Rand Pipeline Direct Inlet (PDI) centrifugal compressor manufactured by the Dresser-Rand Company of Olean, N.Y. In other embodiments, the compressor  100  may be a back-to-back compressor. The compressor  100  may have a center-hung rotor configuration, or the compressor may have an overhung rotor configuration, as illustrated in  FIG. 1 . The compressor  100  may operate in one or more modes or regimes including, but not limited to, a subsonic regime, a transonic regime, a supersonic regime, or any combination thereof. 
     The compressor  100  may be part of a compression system including, amongst other components, a driver (not shown) operatively coupled to a rotary shaft  102  of the compressor  100  via a drive shaft (not shown). The driver may be configured to provide the drive shaft with rotational energy to thereby drive the compressor  100 . In an exemplary embodiment, the drive shaft may be integral with or coupled with the rotary shaft  102  of the compressor  100 , such that the rotational energy of the drive shaft is imparted to the rotary shaft  102 . The drive shaft may be coupled with the rotary shaft  102  via a gearbox (not shown) including a plurality of gears configured to transmit the rotational energy of the drive shaft to the rotary shaft  102  of the compressor  100 , such that the drive shaft and the rotary shaft  102  may spin at the same speed, substantially similar speeds, or differing speeds and rotational directions. 
     The driver may be a motor and more specifically may be an electric motor, such as a permanent magnet motor, and may include a stator (not shown) and a rotor (not shown). It will be appreciated, however, that other embodiments may employ other types of electric motors including, but not limited to, synchronous motors, induction motors, and brushed DC motors. The driver may also be a hydraulic motor, an internal combustion engine, a steam turbine, a gas turbine, or any other device capable of driving the rotary shaft  102  of the compressor  100  either directly or through a power train. 
     The compressor  100  may be a single-stage compressor or a multi-stage compressor (not shown). As illustrated in  FIG. 1 , the compressor  100  is a single-stage compressor capable of providing a compression ratio of at least about 10:1 or greater. While the compressor  100  of  FIG. 1  may be a single-stage compressor capable of generating a 10:1 or greater ratio, it may be appreciated that the compressor  100 , in other embodiments, may include multiple stages of compression including a first stage of compression, one or more intermediate stages of compression, and/or a final stage of compression configured to generate a 10:1 or greater ratio. 
     As shown in  FIG. 1 , the compressor  100  may include a housing  104 . The driver (not shown) may be disposed outside of or within the housing  104 , such that the housing  104  may have a first end, or compressor end, and a second end (not shown), or driver end. The housing  104  may be configured to hermetically seal the driver and the compressor  100  within, thereby providing both support and protection to each component of the compression system. The housing  104  may also be configured to contain the process fluid flowing through one or more portions or components of the compressor  100 . 
     The drive shaft (not shown) of the driver and the rotary shaft  102  of the compressor  100  may be supported, respectively, by one or more radial bearings  106 , as shown in  FIG. 1  in an overhung configuration. The radial bearings  106  may be directly or indirectly supported by the housing  104 , and in turn provide support to the drive shaft and the rotary shaft  102 , which carry the compressor  100  and the driver during operation of the compression system. In one embodiment, the radial bearings  106  may be magnetic bearings, such as active or passive magnetic bearings. In other embodiments, however, other types of bearings (e.g., oil film bearings) may be used. In addition, at least one axial thrust bearing  108  may be provided to manage movement of the rotary shaft  102  in the axial direction. In an embodiment in which the driver and the compressor  100  are hermetically-sealed within the housing  104 , the thrust bearing  108  may be provided at or near the end of the rotary shaft  102  adjacent the compressor end of the housing  104 . The axial thrust bearing  108  may be a magnetic bearing and may be configured to bear axial thrusts generated by the compressor  100 . 
     The housing  104  may form or have an axial inlet  110  defining an inlet passageway  112  through which the process fluid may be drawn into the compressor  100 . Although illustrated as an axial inlet  110  in  FIG. 1 , in one or more other embodiments, the inlet may be a radial inlet. The inlet passageway  112  may be fluidly coupled with an impeller cavity  114  defined in the housing  102  and configured to receive therein an impeller  116 . The compressor  100  further includes a diffuser  118  fluidly coupled to the impeller cavity  114  and the impeller  116 , and a collector  120  fluidly coupled to the diffuser  118 , and an outlet (not shown) formed by or coupled to the housing  104 . As arranged, the inlet passageway  112 , the impeller cavity  114 , the diffuser  118 , and the collector  120  form a fluid passageway through which the process fluid may flow to achieve the desired compression ratio. 
     As shown in  FIG. 1 , the axial inlet  110  defining the inlet passageway  112  of the compressor  100  may include one or more inlet guide vanes  122  of an inlet guide vane assembly configured to condition a process fluid flowing therethrough to achieve predetermined or desired fluid properties and/or fluid flow attributes. Such fluid properties may include flow pattern (e.g., swirl distribution), velocity, mass flow rate, pressure, temperature, and/or any suitable fluid property and fluid flow attribute to enable the compressor  100  to function as described herein. The inlet guide vanes  122  may be disposed within the inlet passageway  112  and may be static or moveable, i.e., adjustable. The inlet guide vanes  122  may be airfoil shaped, streamline shaped, or otherwise shaped and configured to at least partially impart the one or more fluid properties and/or fluid flow attributes on the process fluid flowing through the inlet passageway  112 . 
     The impeller  116  may include a hub  124  and a plurality of blades  126  extending from the hub  124 . In the exemplary embodiment of  FIG. 1 , the compressor includes a shroud  128 , such that the impeller  116  may be covered, thereby functioning as a “shrouded” impeller  116 . In other embodiments, the impeller  116  may be an open or “unshrouded” impeller. The impeller  116  may be at least partially disposed in the impeller cavity  114  and configured to rotate therein to increase the velocity of the process fluid flowing therethrough. For example, the hub  124  of the impeller  116  may be coupled with the rotary shaft  102  configured to rotate the impeller  116  about a center axis  130  (e.g., longitudinal axis) of the compressor  100 . The rotary shaft  102  may rotate the impeller  116  at a speed sufficient to draw the process fluid into the compressor  100  via the inlet passageway  112 . The rotation of the impeller  116  may further draw the process fluid to and through the impeller  116  and accelerate the process fluid to a tip  132 , or periphery, of the impeller  116 , thereby increasing the velocity of the process fluid. The plurality of blades  126  may be configured to raise the velocity and energy of the process fluid and direct the process fluid from the impeller  116  to the diffuser  118  fluidly coupled therewith. 
     In one or more embodiments, the process fluid at the tip  132  of the impeller  116  may be subsonic and have an absolute Mach number less than one. For example, the process fluid at the tip  132  of the impeller  116  may have an exit absolute Mach number less than one, less than 0.9, less than 0.8, less than 0.7, less than 0.6, or less than 0.5. Accordingly, in such embodiments, the compressor  100  discussed herein may be “subsonic,” as the impeller  116  may be configured to rotate about the center axis  130  at a speed sufficient to provide the process fluid at the tip  132  thereof with an exit absolute Mach number of less than one. 
     In one or more embodiments, the process fluid at the tip  132  of the impeller  116  may be supersonic and have an exit absolute Mach number of one or greater. For example, the process fluid at the tip  132  of the impeller  116  may have an exit absolute Mach number of at least one, at least 1.1, at least 1.2, at least 1.3, at least 1.4, or at least 1.5. Accordingly, in such embodiments, the compressor  100  discussed herein may be “supersonic,” as the impeller  116  may be configured to rotate about the center axis  130  at a speed sufficient to provide the process fluid at the tip  132  thereof with an exit absolute Mach number of one or greater or with a fluid velocity greater than the local speed of sound of the process fluid. 
     Looking now at  FIG. 2  with continued reference to  FIG. 1 ,  FIG. 2  illustrates an exploded view of a diffuser assembly  134  including the diffuser  118  shown in  FIG. 1 . The diffuser  118  may be located downstream of the impeller  116  and may be disposed circumferentially about the tip  132  of the impeller  116 . As arranged, the diffuser  118  may be configured to receive the radial process fluid flow exiting the tip  132  of the impeller  116  and to convert kinetic energy of the process fluid from the impeller  116  into increased static pressure. 
     In an exemplary embodiment, the diffuser  118  may include a first stationary wall  136 , a second stationary wall  138 , and a moveable wall  140  disposed therebetween. The first stationary wall  136  may be coupled with or integral with the housing  104  and may be annular in one or more embodiments. The first stationary wall  136  may have a front face  142 , or front side, facing the axial inlet  110  and a rear face  144 , or rear side, axially opposing the front face  142 . The rear face  144  may form at least in part the collector  120  and may be adjacent the second stationary wall  138  as disposed in the compressor  100 . In forming at least in part the collector  120 , a radially inward portion  146  of the rear face  144  may form a helical flowpath  148 . 
     The second stationary wall  138  may be coupled with or integral with the housing  104  and may be annular in one or more embodiments. The second stationary wall  138  may have a front face  150 , or front side, facing the axial inlet  110  and the first stationary wall  136 . In an exemplary embodiment, the front face  150  may form an outer annular ring  152  (most clearly seen in  FIG. 4 ) configured to mate with a radially outward portion  154  of the rear face  144  of the first stationary wall  136  to further form at least in part the collector  120 . Accordingly, as arranged in the compressor  100 , the first stationary wall  136  and the second stationary wall  138  may be coupled with one another and may form at least in part the collector  120  configured to receive the compressed process fluid from the diffuser  118 . 
     As shown in  FIGS. 1 and 2 , the moveable wall  140  of the diffuser  118  may be disposed between the first stationary wall  136  and the second stationary wall  138 . The moveable wall  140  may be annular and may have a diameter less than a diameter of the rear face  144  of the first stationary wall  136 . In an exemplary embodiment, the diameter of the moveable wall  140  may be substantially similar to the diameter of the radially inward portion  146  of the rear face  144  forming the helical flowpath  148 . The moveable wall  140  may have a front annular face  156 , or front annular side, facing the first stationary wall  136  and a rear annular face  158 , or rear annular side, axially opposing the front annular face  156  and facing the second stationary wall  138 . As arranged in the compressor  100 , the front annular face  156  may form a portion of the collector  120 . 
     Turning now to  FIG. 3  with continued reference to  FIGS. 1 and 2 ,  FIG. 3  illustrates an enlarged cutaway view of a portion of the diffuser assembly  134  including the first stationary wall  136  and the moveable wall  140 , according to one or more embodiments disclosed. As illustrated, the moveable wall  140  of the diffuser  118  may define a plurality of moveable wall grooves  160  extending from an inlet end  162  of the diffuser  118  adjacent the tip  132  of the impeller  116  in a tangential orientation about the impeller  116 . In an exemplary embodiment, the moveable wall grooves  160  may be defined in the rear annular face  158  and may extend from the inlet end  162  to a radially outer outlet end  164  of the diffuser  118 . At the outlet end  164 , a portion of the moveable wall grooves  158  may extend axially and fluidly couple the front annular face  156  and the rear annular face  158 , and thus, fluidly couple the moveable wall grooves  160  to the collector  120 . Thus, as arranged, the collector  120  may be axially offset with respect to the diffuser  118 . 
     The moveable wall  140  may further include a plurality of projections  166  extending from the rear annular face  158 . A respective projection  166  of the plurality of projections  166  may be disposed between adjacent moveable wall grooves  160  and may form a generally prismatic shape therebetween. Accordingly, each of the projections  166  may extend from the inlet end  162  adjacent the tip  132  of the impeller  116  in a tangential orientation about the impeller  116 . In an exemplary embodiment, the projections  166  may extend axially outward from the rear annular face  158  and may extend from the inlet end  162  to the radially outer outlet end  164 . At the outlet end  164 , a portion of the each of the projections  166  may extend axially between the front annular face  156  and the rear annular face  158 . 
     Turning now to  FIG. 4  with continued reference to  FIGS. 1-3 ,  FIG. 4  illustrates an enlarged cutaway view of a portion of the diffuser assembly  134  including the second stationary wall  138 . As disclosed above, the rear annular face  158  of the moveable wall  140  and the moveable wall grooves  160  therein may be disposed adjacent the second stationary wall  138 . In an exemplary embodiment, the second stationary wall  138  may define a plurality of stationary wall grooves  168  extending from the inlet end  162  of the diffuser  118  adjacent the tip  132  of the impeller  116  in a tangential orientation about the impeller  116 . In an exemplary embodiment, the stationary wall grooves  168  may be defined in the front face  150  of the second stationary wall  138  and may extend from the inlet end  162  to the radially outer outlet end  164  of the diffuser  118 . At the outlet end  164 , the stationary wall grooves  168  may be fluidly coupled to the collector  120 . 
     The front face  150  of the second stationary wall  138  may further define a plurality of recesses  170 . A respective recess  170  of the plurality of recesses  170  may be disposed between adjacent stationary wall grooves  168  and may form a generally prismatic shape therebetween. Accordingly, each of the recesses  170  may extend from the inlet end  162  adjacent the tip  132  of the impeller  116  in a tangential orientation about the impeller  116 . In an exemplary embodiment, the recesses  170  may extend from the inlet end  162  to the radially outer outlet end  164 . At the outlet end  164 , a portion of the each of the recesses  170  may extend axially along the outer annular ring  152 . 
     In an exemplary embodiment, the stationary wall grooves  168  may be configured in a pattern substantially similar to the moveable wall grooves  160 , such that as disposed in the compressor  100  opposing one another, each of the stationary wall grooves  168  and respective moveable wall grooves  160  form respective flow passages  172  (most clearly seen in  FIGS. 5A and 5B ) in the diffuser  118 . Accordingly, each of the flow passages  172  formed therefrom may extend from the inlet end  162  adjacent the tip  132  of the impeller  116  in a tangential orientation about the impeller  116 . As arranged, the diffuser  118  including the flow passages  172  may be referred to as a pipe diffuser. The flow passages  172  may be configured to receive at the inlet end  162  the process fluid discharged from the tip  132  of the impeller  116  and to discharge the compressed process fluid to the collector  120  at the radially outer outlet end  164 . 
     As arranged in the compressor  100 , each of the projections  166  of the moveable wall  140  may be disposed in respective recesses  170 , thereby defining and forming sidewalls of each of the flow passages  172 . In an exemplary embodiment, a clearance or gap (e.g., 0.005 inches) may be provided between each projection  166  and corresponding recess  170  to allow for movement of the moveable wall  140 . One of ordinary skill in the art will appreciate that the gap may be sized to allow for movement of the moveable wall  140  while minimizing unwanted leakage of the process fluid around the projections  166  at the outlet end  164 . 
     Each of the flow passages  172  may include a throat section  174  (most clearly seen in  FIG. 3 ) adjacent the inlet end  162  of the diffuser  118  and a diffusing cone section  176  disposed downstream from the throat section  174  and upstream of the outlet end  164  of the diffuser  118  and the collector  120 . In an exemplary embodiment, the throat section  174  may have a generally constant or uniform cross-sectional area along at least a portion thereof. For example, the cross-sectional area of the throat section  174  may be generally constant along the length thereof. In at least one embodiment, the cross-sectional area of the diffusing cone section  176  may generally increase in the downstream direction along at least a portion thereof. 
     As illustrated in  FIGS. 1 and 2 , the diffuser assembly  134  may further include an actuator assembly  178  configured to adjust or alter the cross-sectional area of at least one of the flow passages  172  in the compressor  100 . In an exemplary embodiment, the actuator assembly  178  may be configured to increase or decrease the cross-sectional area of at least one of the flow passages  172  via axial displacement of the moveable wall  140  relative to the second stationary wall  138 . To that end, the actuator assembly  178  may include one or more actuators (two are shown  180 ,  182 ) operatively coupled to the moveable wall  140  via one or more linkages (two are shown  184 ,  186 ). 
     In an exemplary embodiment, the actuator assembly  178  may include a first actuator  180  operatively coupled to the moveable wall  140  via a first linkage  184 , and a second actuator  182  operatively coupled to the moveable wall  140  via a second linkage  186 . The first and second actuators  180 ,  182  may be linear actuators configured to axially displace the moveable wall  140  relative to the second stationary wall  138 , thereby increasing or decreasing the cross-sectional area of the respective flow passages  172 . Illustrative actuators may include, but are not limited to, one or more servos, motors, hydraulic cylinders, screw actuators, or any combination thereof. 
     The linkages  184 ,  186 , illustrated as a first linkage  184  operatively coupled to the first actuator  180  and a second linkage  186  operatively coupled to the second actuator  182 , may each include one or more rods or arms  188 ,  190 ,  192 ,  194  operatively coupling the respective first and second actuators  180 ,  182  to the front annular face  156  of the moveable wall  140 . In an exemplary embodiment, the first linkage  184  may include a first rod  188  and a second rod  190  configured to be actuated by the first actuator  180  to axially displace the moveable wall  140 . The first rod  188  and the second rod  190  may be coupled with one another via a u-joint  196 . Correspondingly, the second linkage  186  may include a first rod  192  and a second rod  194  configured to be actuated by the second actuator  182  to axially displace the moveable wall  140 . The first rod  192  and the second rod  194  may be coupled with one another via a u-joint  198 . Each of the second rods  190 ,  194  may extend through respective apertures  200 ,  202  defined by the first stationary wall  136  and may be coupled to the moveable wall  140 . In an exemplary embodiment, the second rods  190 ,  194  may be threadingly attached to the front annular face  156  of the moveable wall  140 , as most clearly seen in  FIG. 3 . 
     The actuator assembly  182  may further include a plurality of seals  204 ,  206  configured to allow for axial movement of the second rods  190 ,  194  while minimizing or prohibiting the leakage of process fluid from the compressor  100 . In an exemplary embodiment, each of the seals  204 ,  206  may be disposed about respective second rods  190 ,  194  of the actuating assembly  182 . The seals  204 ,  206  may be gland style seals disposed about the second rods  190 ,  194  and adjacent the axial inlet  110  of the compressor  100 . 
     In at least one embodiment, the compressor  100  and/or the diffuser assembly  134  may include a control system (not shown) operatively and/or communicably coupled with one or more components thereof. The control system may include one or more sensors (e.g., pressure and/or flow sensors) communicably coupled with one or more components of the compressor  100  and/or the diffuser assembly  134  and configured to monitor one or more operating parameters or conditions thereof. For example, the control system may be configured to monitor a work coefficient, a flow coefficient, a diffusion rate, and/or a diffuser pressure recovery or pressure loss coefficient along one or more sections or regions of the flow passages  172  of the diffuser  118 . The control system may include a programmable logic controller (PLC) (not shown) with inputs from the compressor  100  and/or the diffuser assembly  134  and outputs for controlling the operating conditions of the compressor  100  and/or the diffuser assembly  134 . 
     In one or more embodiments, the control system may be configured to send signals to and/or receive signals from the compressor  100  and/or the diffuser assembly  134  to actuate, adjust, manipulate, and/or otherwise control one or more components of the compressor  100  and/or the diffuser assembly  134 . For example, the control system may send signals (e.g., commands) to the first and second actuators  180 , 182  to thereby axially displace the moveable wall  140  via the first and second linkages  184 ,  186 . Accordingly, the control system may be configured to actuate the moveable wall  140  between a first or extended position (see  FIG. 5A ) and a second or retracted position (see  FIG. 5B ) to vary the cross-sectional area of the flow passages  172 , and correspondingly, the diffusion rate along one or more sections or regions of the flow passages  172 . In at least one embodiment, the control system may be configured to vary the diffusion rate along the flow passages  172  during one or more modes or operating conditions of the compressor  100 . For example, the control system may be configured to vary the diffusion rate along the flow passages  172  to optimize the efficiency of the diffuser  118  for the operating conditions of the compressor  100 . The control system may be integral with the compressor  100  and/or the diffuser assembly  134 , or the control system may be remote. The control system may be communicably coupled via any suitable means including, but not limited to, wired connections and/or wireless connections. 
     The process fluid flow leaving the outlet end  164  of the diffuser  118  may flow into the collector  120 , as most clearly seen in  FIG. 2 . The collector  120  may be configured to gather the process fluid flow from the diffuser  118  and to deliver the process fluid flow to a downstream pipe and/or process component (not shown) via an outlet  208  defined by the second stationary wall  138 . In an exemplary embodiment, the collector  120  may be a volute, such as a discharge volute or specifically, a scroll-type discharge volute. The collector  120  may be further configured to increase the static pressure of the process fluid flow by converting the kinetic energy of the process fluid to static pressure. 
     Referring now to  FIGS. 5A and 5B  with continued reference to  FIGS. 1-4 .  FIG. 5A  illustrates an enlarged cross-sectional view of the diffuser  118  arranged to provide the flow passages  172  therein having a maximum cross-sectional area, according to one or more embodiments disclosed.  FIG. 5B  illustrates an enlarged cross-sectional view of the diffuser  118  arranged to provide the flow passages  172  therein having a minimum cross-sectional area, according to one or more embodiments disclosed. 
     One or more exemplary operational aspects of the compressor  100  will now be discussed with continued reference to  FIGS. 1-5B . In operation and use, a process fluid may be provided from an external source (not shown), having a low pressure environment, to the compressor  100 . As shown in  FIG. 1 , the compressor  100  may include, amongst other components, the impeller  116  coupled with the rotary shaft  102  and the diffuser  118  disposed circumferentially about the rotating impeller  116 . The process fluid may be drawn into the axial inlet  110  of the compressor  100  and through the inlet passageway  112  defined by the axial inlet  110  and across the inlet guide vanes  122  extending into the inlet passageway  112 . The process fluid flowing across the inlet guide vanes  122  may be provided with an increased velocity and imparted with at least one fluid property (e.g., swirl) prior to be being drawn into the rotating impeller  116 . The inlet guide vanes  122  may be adjusted in order to vary the one or more fluid properties imparted to the process fluid. 
     The process fluid may be drawn into the rotating impeller  116  and may contact the impeller blades  126 , such that the process fluid may be accelerated in a tangential and radial direction by centrifugal force and may be discharged via the blade tips of the impeller  116  (cumulatively, the tip  132  of the impeller  116 ) in at least partially radial directions that extend 360 degrees around the rotating impeller  116 . The rotating impeller  116  increases the velocity and static pressure of the process fluid, such that the velocity of the process fluid discharged from the blade tips (cumulatively, the tip  132  of the impeller  116 ) may be supersonic in some embodiments and have an exit absolute Mach number of at least about one, at least about 1.1, at least about 1.2, at least about 1.3, at least about 1.4, or at least about 1.5. 
     The diffuser  118  including the first stationary wall  136 , the second stationary wall  138  and the moveable wall  140  disposed therebetween (see  FIG. 2 ) may be disposed circumferentially about the periphery, or tip  132 , of the impeller  116  and the first stationary wall  136  and the second stationary wall  138  may be coupled with or integral with the housing  104  of the compressor  100 . The radial process fluid flow discharged from the rotating impeller  116  may be received by the diffuser  118  such that the velocity of the flow of process fluid discharged from the tip  132  of the rotating impeller  116  is substantially similar to the velocity of the process fluid entering the inlet end  162  of the diffuser  118 . Accordingly, the process fluid may enter the inlet end  162  of the diffuser  118  with a supersonic velocity having, for example, an exit absolute Mach number of at least one, and correspondingly, may be referred to as supersonic process fluid. 
     The flow passages  172 , most clearly shown in  FIGS. 5A and 5B , may be configured to receive the process fluid from the rotating impeller  116  (see  FIG. 1 ) and convert kinetic energy (e.g., flow or velocity) of the process fluid from the rotating impeller  116  to potential energy (e.g., increased static pressure). As the process fluid enters the diffuser  118 , one or more sensors (not shown) of the control system (not shown) may be communicably coupled with one or more components of the compressor  100  and/or the diffuser assembly  134  and may monitor one or more operating parameters or conditions thereof. For example, the control system may monitor a work coefficient, a flow coefficient, a diffusion rate, and/or a diffuser pressure recovery or pressure loss coefficient along one or more sections or regions of the flow passages  172  of the diffuser  118 . 
     The flow passages  172  may convert the kinetic energy of the process fluid to potential energy by decreasing the flow velocity of the process fluid flowing therethrough. The relative rate in which the flow velocity of the process fluid decreases may be altered or adjusted, at least in part, by the relative increase or decrease in the cross-sectional area along the sections of the flow passages  172 . For example, decreasing the cross-sectional area along a section of the flow passages  172 , such as the throat section  174 , may maintain effective diffusion at lower process fluid flow rates. Correspondingly, increasing the cross-sectional area along a section of the flow passages  172 , such as the throat section  174 , may maintain effective diffusion in the flow passages  172  at higher process fluid flow rates. 
     To that end, if the operation parameter or condition monitored is indicative of a need to decrease the flow rate, the control system may transmit a signal to the first and second actuators  180 ,  182  of the diffuser assembly including instructions to axially displace the moveable wall  140  toward the second stationary wall  138 , thereby decreasing the cross-sectional area of one or more sections  174 ,  176  of the flow passages  172 . The moveable wall  140  may be axially displaced via the first rod  188  and the second rod  190  operative coupled to the first actuator  180  and the first rod  192  and the second rod  194  operative coupled to the second actuator  182 . As shown in  FIG. 5B , the moveable wall may be disposed in a fully extended position providing a minimum cross-sectional area for each of the flow passages  172  to maintain the diffusion of the diffuser  118  at the new lower process fluid flow rate. 
     Correspondingly, if the operation parameter or condition monitored is indicative of a need to increase the flow rate, the control system may transmit a signal to the first and second actuators  180 ,  182  of the diffuser assembly including instructions to axially displace the moveable wall  140  away from the second stationary wall  138 , thereby increasing the cross-sectional area of one or more sections  174 ,  176  of the flow passages  172 . The moveable wall  140  may be axially displaced via the first rod  188  and the second rod  190  operative coupled to the first actuator  180  and the first rod  192  and the second rod  194  operative coupled to the second actuator  182 . As shown in  FIG. 5A , the moveable wall may be disposed in a fully retracted position providing a maximum cross-sectional area for each of the flow passages  172  to maintain the diffusion of the diffuser  118  at the new higher process fluid flow rate. 
     Accordingly, the flow passages  178  may be configured to change or vary flow capacities or flow areas thereof relative to other components of the compressor  100  to thereby allow an optimization of the compression process over a wide or broader range of flow conditions and/or operating parameters of the compressor  100 . The process fluid exiting the diffuser  118  may have a subsonic velocity and may be fed into the collector  120  or discharge volute. The collector  120  may increase the static pressure of the process fluid by converting the remaining kinetic energy of the process fluid to static pressure. The process fluid may then be routed to perform work or for operation of one or more downstream processes or components (not shown) via the outlet  208  defined by the second stationary wall  138 . 
     The process fluid pressurized, circulated, contained, or otherwise utilized in the compression system may be a fluid in a liquid phase, a gas phase, a supercritical state, a subcritical state, or any combination thereof. The process fluid may be a mixture, or process fluid mixture. The process fluid may include one or more high molecular weight process fluids, one or more low molecular weight process fluids, or any mixture or combination thereof. As used herein, the term “high molecular weight process fluids” refers to process fluids having a molecular weight of about 30 grams per mole (g/mol) or greater. Illustrative high molecular weight process fluids may include, but are not limited to, hydrocarbons, such as ethane, propane, butanes, pentanes, and hexanes. Illustrative high molecular weight process fluids may also include, but are not limited to, carbon dioxide (CO 2 ) or process fluid mixtures containing carbon dioxide. As used herein, the term “low molecular weight process fluids” refers to process fluids having a molecular weight less than about 30 g/mol. Illustrative low molecular weight process fluids may include, but are not limited to, air, hydrogen, methane, or any combination or mixtures thereof. 
       FIG. 6  illustrates a flow chart of a method  300  for adjusting a cross-sectional area of a flow passage of a diffuser in a compressor, according to one or more embodiments. The method  300  may include monitoring one or more operating parameters of the compressor or a process fluid flowing therethrough, as at  302 . The method  300  may also include detecting an operating parameter of the one or more operating parameters outside of a predetermined range, as at  304 . The method may further include axially displacing a moveable wall of the diffuser via at least one actuator operatively coupled with the moveable wall via at least one linkage, the axial displacement of the moveable wall adjusting the cross-sectional area of the flow passage of the diffuser, as at  306 . 
     The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.