Patent Publication Number: US-11661949-B2

Title: Interstage capacity control valve with side stream flow distribution and flow regulation for multi-stage centrifugal compressors

Description:
FIELD 
     This disclosure is directed to an interstage capacity control valve for a centrifugal compressor, particularly one providing side stream flow regulation or distribution. 
     BACKGROUND 
     Multi-stage compressors can use single-row or multiple-row, fixed or rotatable return vanes to direct and/or control interstage flow, when operated at full and partial load conditions. These return vans can, at partial load conditions lead to low-momentum zones in return channel passages or adverse pressure gradients that alter the intended side stream injection flow rate, which can lead to compressor instability, reduced system efficiency, and result in narrower operating ranges. 
     SUMMARY 
     This disclosure is directed to an interstage capacity control valve for a centrifugal compressor, particularly one providing side stream flow regulation or distribution. 
     The interstage capacity control valve can simultaneously control flow between stages of a multi-stage compressor while regulating the addition of a side stream flow to that flow between stages. The interstage capacity control valve increases the velocity of the interstage flow where the side stream is added, avoiding stagnant areas of flow. This in turn can improve the stability and efficiency of the compressor at both partial and full load conditions. 
     The axial extension of the interstage capacity control valve further can reduce maintenance issues relating to the complexity of rotatable vane designs for capacity control in centrifugal compressors. 
     Further, embodiments can add the side stream flow at a comparatively low-pressure area in the interstage line, facilitating addition of the side stream and allowing more of the side stream to be successfully introduced. This can avoid cycling and compression of bypass gases 
     In an embodiment, a centrifugal compressor includes a first stage impeller and a second stage impeller. The centrifugal compressor includes a side stream injection port located between the first stage impeller and the second stage impeller, the side stream injection port configured to receive a side stream of a fluid. The centrifugal compressor includes a capacity control valve. The capacity control valve is configured to extend and retract through the side stream injection port. The capacity control valve has a curved surface facing a direction of flow from the first stage impeller to the second stage impeller. The capacity control valve is configured to be extended through the side stream injection port between an open position where the side stream of the fluid can flow through the side stream injection port and a closed position where the capacity control valve obstructs flow of the side stream of the fluid through the side stream injection port. 
     In an embodiment, the capacity control valve has a ring shape. 
     In an embodiment, the centrifugal compressor includes a plurality of the side stream injection ports and a plurality of the capacity control valves. 
     In an embodiment, when in the open position, a tip of the capacity control valve at an end of the curved surface is within the side stream injection port. 
     In an embodiment, the capacity control valve extends and retracts in a direction substantially perpendicular to the direction of flow from the first stage impeller to the second stage impeller. 
     In an embodiment, the centrifugal compressor further includes one or more deswirl vanes between the first stage impeller and the second stage impeller. In an embodiment, the capacity control valve includes one or more notches, the one or more notches each configured to accommodate at least a portion of one of the one or more deswirl vanes. In an embodiment, the one or more deswirl vanes each include one or more notches, the one or more notches each configured to accommodate at least a portion of the capacity control valve. 
     In an embodiment, the capacity control valve has a linear meridional profile on a side opposite the curved surface, the linear meridional profile contacting an edge of the side stream injection port. 
     In an embodiment, a side of the capacity control valve opposite the curved surface is configured such that when the capacity control valve is between the open position and the closed position, the fluid can flow past the capacity control valve on the side of the capacity control valve opposite the curved surface. In an embodiment, the side of the capacity control valve opposite the curved surface includes a second curved surface. In an embodiment, the side of the capacity control valve opposite the curved surface includes one or more channels configured to allow flow of the side stream of the fluid. 
     In an embodiment, a heating, ventilation, air conditioning, and refrigeration (HVACR) circuit includes a centrifugal compressor, a condenser, an expander, and an evaporator. The centrifugal compressor includes a first stage impeller and a second stage impeller. The centrifugal compressor also includes side stream injection port located between the first stage impeller and the second stage impeller. The side stream injection port is configured to receive a side stream of a fluid. The centrifugal compressor further includes a capacity control valve. The capacity control valve is configured to extend and retract through the side stream injection port. The capacity control valve has a curved surface facing a direction of flow from the first stage impeller to the second stage impeller. The capacity control valve is configured to be extended through the side stream injection port between an open position where the side stream of the fluid can flow through the side stream injection port and a closed position where the capacity control valve obstructs flow of the side stream of the fluid through the side stream injection port. 
     In an embodiment, the side stream of the fluid is from the condenser to the side stream injection port. 
     In an embodiment, the HVACR circuit further includes an economizer and wherein the side stream of the fluid is from the economizer to the side stream injection port. 
     In an embodiment, the HVACR circuit further includes an intercooler and wherein the side stream of the fluid is from the intercooler to the side stream injection port. 
     In an embodiment, the capacity control valve has a ring shape. 
     In an embodiment, the capacity control valve has a linear meridional profile on a side opposite the curved surface, the linear meridional contacting an edge of the side stream injection port. In an embodiment, a side of the capacity control valve opposite the curved surface is configured such that when the capacity control valve is between the open position and the closed position, the fluid can flow past the capacity control valve on the side of the capacity control valve opposite the curved surface. 
    
    
     
       DRAWINGS 
         FIG.  1 A  shows a sectional view of a compressor according to an embodiment when a capacity control valve is in a fully open position. 
         FIG.  1 B  shows a sectional view of the compressor shown in  FIG.  1 A  when the capacity control valve is in a high flow position. 
         FIG.  1 C  shows a sectional view of the compressor shown in  FIG.  1 A  when the capacity control valve is in a low flow position. 
         FIG.  1 D  shows a sectional view of the compressor shown in  FIG.  1 A  when the capacity control valve is in a closed position. 
         FIG.  2 A  shows a sectional view of a compressor according to an embodiment when a capacity control valve is in a fully open position. 
         FIG.  2 B  shows a sectional view of the compressor shown in  FIG.  2 A  when the capacity control valve is in a high flow position. 
         FIG.  2 C  shows a sectional view of the compressor shown in  FIG.  2 A  when the capacity control valve is in a low flow position. 
         FIG.  2 D  shows a sectional view of the compressor shown in  FIG.  2 A  when the capacity control valve is in a closed position. 
         FIG.  3 A  shows a heating, ventilation, air conditioning and refrigeration (HVACR) circuit according to an embodiment. 
         FIG.  3 B  shows an economized HVACR circuit  320  according to an embodiment. 
         FIG.  4    shows a sectional view of a centrifugal compressor according to an embodiment along an interstage flow path. 
         FIG.  5    shows a sectional view of a portion of a centrifugal compressor according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure is directed to an interstage capacity control valve for a centrifugal compressor, particularly one providing side stream flow regulation or distribution. 
       FIG.  1 A  shows a sectional view of a compressor  100  according to an embodiment when a capacity control valve is in a fully open position. Compressor  100  can have a cylindrical structure such that the sectional view shown in  FIGS.  1 A- 1 D  be repeated or continuous through 360° of rotation about axis A of the compressor  100 . 
     Compressor  100  is a multi-stage centrifugal compressor according to an embodiment. Compressor  100  includes an inlet guide vane  102  where a core flow of fluid to be compressed is received. Compressor  100  includes a first stage impeller  104  driven by rotation of shaft  106 , a diffuser  108  downstream of the first stage impeller  104 , and a return bend  110  downstream of the diffuser  108 . Compressor  100  further includes one or more deswirl vanes  112  downstream of the return bend  110 . Compressor  100  includes a side stream injection port  114  and a capacity control valve  116 . Compressor  100  includes a second stage impeller  118  downstream of the deswirl vanes  112  and the side stream injection port  114 , with a volute scroll  120  and a discharge conic  122  downstream of the second stage impeller  118 . 
     While compressor  100  is shown in  FIGS.  1 A- 1 D  as a two-stage compressor, compressors according to embodiments can include any number of stages, with the side stream injection port  114  and the capacity control valve  116  are provided in an interstage flow path between any two stages of the compressor. For example, compressor  100  can be a three-stage compressor, with the side stream injection port  114  and capacity control valve  116  disposed between the exhaust of the second stage and the intake of the third stage, or the like. 
     Flow of working fluid into compressor  100  may be controlled using one or more inlet guide vanes  102 . The one or more inlet guide vanes  102  can be configured to obstruct or permit flow of working fluid into the compressor  100 . In an embodiment, each of the inlet guide vanes  102  can be a rotating vane, for example, each rotating vane forming a section of a circle such that when all rotating vanes are in a closed position, the inlet guide vanes  102  obstruct an inlet of the compressor  100 . The one or more inlet guide vanes  102  can be movable between a fully open position and the closed position. In the fully open position the effect of the inlet guide vanes  102  on flow into compressor  100  can be minimized, for example by positioning the inlet guide vanes  102  such that the plane of each vane is substantially parallel to the direction of flow of working fluid into the inlet of compressor  100 . In an embodiment, each or all of the one or more inlet guide vanes  102  can be varied continuously from the fully open position to the closed position, through one or more partially open positions. 
     Compressor  100  includes a first stage impeller  104 . The first stage impeller  104  includes a plurality of blades. The first stage impeller  104  is configured to draw in the working fluid that passes the one or more inlet guide vanes  102  when rotated, and to expel the working fluid towards diffuser  108 . The first stage impeller  104  is joined to shaft  106 . Shaft  106  is rotated by, for example, a prime mover such as a motor. 
     Diffuser  108  receives the fluid discharged from first stage impellers  104  and directs the flow of the fluid towards return bend  110 . Return bend  110  changes the direction of the flow of the fluid such that it travels through the deswirl vanes  112  towards the second stage impeller  118 . 
     One or more deswirl vanes  112  are vanes extending from the return bend  110  towards the second stage impeller  118 . The deswirl vanes  112  are shaped to straighten the flow of the fluid as the flow passes towards the second stage impeller  118 . The deswirl vanes  112  can include notches configured to receive at least a portion of the capacity control valve  116 . 
     Side stream injection port  114  is a port configured to allow a side stream to be introduced into the interstage flow of fluid through compressor  100 . The side stream injection port  114  includes a leading end  124  and a trailing end  126 , with the leading end  124  towards the return bend  110  and the trailing end  126  towards the second stage impeller  118 . Side stream injection port  114  fluidly connects a side stream flow channel  128  with the interstage flow. The side stream flow channel  128  can receive a side stream of fluid from within a fluid circuit including the compressor  100 . The source of the side stream of fluid received by side stream flow channel can be from one or more of a condenser, an economizer, an intercooler, a heat exchanger, or any other suitable source of fluid that is at an intermediate pressure, between the suction pressure and the discharge pressure of the compressor  100 . The side stream injection port  114  can be a ring shape surrounding an intake of the second stage impeller  118 . The side stream injection port  114  can be provided between the return bend  110  and the second stage impeller  118 . 
     Capacity control valve  116  is a valve configured regulate the flow through the side stream injection port  114 . Capacity control valve  116  is configured to be extended axially through the side stream injection port  114  such that it extends substantially perpendicular to a direction of flow of the interstage flow from deswirl vane  110  towards the second stage impeller  118 . Capacity control valve  116  is configured to be able to prohibit flow through side stream injection port  114  in a closed position, for example by including a portion having a thickness corresponding to the width of the side stream injection port  114  from leading end  124  to trailing end  126 . In an embodiment, capacity control valve  116  is controlled in conjunction with inlet guide vanes  102 . In an embodiment, capacity control valve  116  is controlled independently of inlet guide vanes  102 . 
     Capacity control valve  116  includes a leading side  130  facing towards the return bend  110  and a trailing side  132  facing towards an inlet into second stage impeller  118 . Leading side  130  includes curved surface  134  extending towards a tip  136  of the capacity control valve  116 . The curved surface  134  can reduce the cross-sectional thickness of the capacity control valve  116  from a thickness corresponding to the width of the side stream injection port  114  at the base of the curved surface  134  to a smaller thickness at the tip  136 . The change in the cross-sectional thickness of capacity control valve  116  over the length of curved surface  134  towards tip  136  is configured to vary the amount of flow through the side stream injection port based on the extension of the capacity control valve  116 . In the embodiment shown in  FIGS.  1 A- 1 D , trailing side  132  can be, for example, a linear profile in the longitudinal direction of the capacity control valve  116  configured to always be in contact with trailing end  126  of the side stream injection port  114 , such that all flow of the side stream into the interstage flow is over the leading side  130 . 
     Where side stream injection port  114  has a ring shape, the capacity control valve  116  can have a corresponding ring shape. In an embodiment, the capacity control valve is a single ring. In an embodiment, the capacity control valve includes a plurality of ring segments. In an embodiment, the capacity control valve  116  includes one or more notches configured to avoid contact between the capacity control valve  116  and one or more deswirl vanes  112  as the capacity control valve  116  is extended. In an embodiment, the capacity control valve can be moved from a fully open position where the tip  136  is located within the side stream injection port  116  or the side stream channel  128 , and a fully closed position, where the capacity control valve  116  obstructs the side stream injection port  114  from leading end  124  to trailing end  126 . 
     In the fully open position of the capacity control valve  116 , the tip  136  of the capacity control valve  116  does not extend through the side stream injection port  114 . Accordingly, the interstage flow through the deswirl vane  112  is not obstructed, and obstruction of the side stream injection port  114  by the capacity control valve is at a minimum. The side stream fluid passes over the curved surface  134  to join the interstage flow between return bend  110  and second stage impeller  118 . The fully open position can be used when the compressor  100  is operating at or near a full-load capacity. 
     Second stage impeller  118  is used to achieve the second stage of compression. Second stage impeller  118  draws in the combined interstage and side stream flows and expels the fluid towards volute scroll  120 . Second stage impeller  118  can be rotated by shaft  106 , which is also used to rotate first stage impeller  104 . Fluid at the volute scroll  120  can then be discharged from compressor  100  at discharge conic  122 . 
     In an embodiment, the side stream provided through side stream injection port  114  can be received from an economizer, such as the economizer  314  shown in  FIG.  3 B  and described below. The economizer can be a flash-tank economizer, where flash or bypass gas rises and can be directed to the side stream flow channel  128 . The gas from the economizer being directed to the side stream flow channel  128  can reduce or eliminate the presence of gas in the liquid being passed to an evaporator of the HVACR system including compressor  100 . This can in turn improve the absorption of energy at the evaporator without further subcooling by providing more saturated liquid working fluid. In the full load cycle corresponding to the fully open position of capacity control valve  116 , the pressure at the side stream injection port  114  can allow the entrained vapor to be substantially removed from the working fluid in the economizer. 
       FIG.  1 B  shows a sectional view of the compressor shown in  FIG.  1 A  when the capacity control valve  116  is in a high flow position. The high flow position shown in  FIG.  1 B  can be used in a partial load condition where the load is relatively close to full load for the compressor  100 . In the high flow position shown in  FIG.  1 B , the capacity control valve  116  is extended axially such that it partially extends through side stream injection port  114 . The leading side  130  of the capacity control valve  116  partially deflects the interstage flow in compressor  100  due to the projection of the capacity control valve reducing the size of the passage for interstage flow. The capacity control valve  116  restricts flow through the side stream injection port to a greater extent than when in the fully-open position shown in  FIG.  1 A  and described above, with curved surface  134  reducing the orifice size by being closer to the leading end  124  of the side stream injection port  114 . The trailing side  132  of the capacity control valve  116  continues to be in contact with the trailing end  126  of the side stream injection port  114 , and all flow through side stream injection port  114  passes between the leading end  124  of side stream injection port  114  and the leading side  130  of capacity control valve  116 . Optionally, inlet guide vane  102  can be rotated to partially obstruct flow to the first stage impeller  104  of compressor  100 . 
       FIG.  1 C  shows a sectional view of the compressor shown in  FIG.  1 A  when the capacity control valve is in a low flow position. The low flow position shown in  FIG.  1 C  can be used in a partial load condition where the load is below the full load for the compressor  100 , and less than the load where the capacity control valve is in a high flow position such as in  FIG.  1 B . In the low flow position shown in  FIG.  1 C , the capacity control valve  116  is extended axially such that it extends through side stream injection port  114 , extending further than the high flow position shown in  FIG.  1 B . The leading side  130  of the capacity control valve  116  deflects the interstage flow in compressor  100  due to the greater projection of the capacity control valve  116 , further reducing the size of the passage for interstage flow. The capacity control valve  116  restricts flow through the side stream injection port to a greater extent than when in the high flow position shown in  FIG.  1 B  and described above, with curved surface  134  further reducing the orifice size by being even closer to the leading end  124  of the side stream injection port  114 . The trailing side  132  of the capacity control valve  116  continues to be in contact with the trailing end  126  of the side stream injection port  114 , and all flow through side stream injection port  114  passes between the leading end  124  of side stream injection port  114  and the leading side  130  of capacity control valve  116 . Optionally, inlet guide vane  102  can be rotated to further obstruct flow to the first stage impeller  104  of compressor  100  compared to its position in the high flow position shown in  FIG.  1 B . 
       FIG.  1 D  shows a sectional view of the compressor shown in  FIG.  1 A  when the capacity control valve is in a closed position. The closed position shown in  FIG.  1 D  can be used when the compressor  100  is in a partial-load condition at or near a minimum load for the compressor. In the closed position, capacity control valve  116  partially or completely obstructs side stream injection port  114 , from leading end  124  to trailing end  126 . It is appreciated that due to manufacturing tolerances, wear, etc. that there may be some leakage even when the capacity control valve  116  is configured to completely obstruct the side stream and is in the closed position. In an embodiment, capacity control valve  116  is sized such that it does not contact side stream injection port  114  and allows some flow to continue through side stream injection port  114  even in the fully extended closed position. The extension of the capacity control valve  116  into the interstage flow through compressor  100  is at a maximum, reducing the size of the orifice through which the interstage flow passes from return bend  110  towards second stage impeller  118 . Accordingly, this position imparts the greatest additional velocity to the interstage flow, while prohibiting the side stream flow from joining the interstage flow. Optionally, inlet guide vane  102  can be rotated to further obstruct flow to the first stage impeller  104  of compressor  100 , for example by pacing the inlet guide vane  102  in a minimum-flow position. 
       FIG.  2 A  shows a sectional view of a compressor  200  according to an embodiment when a capacity control valve is in a fully open position. Compressor  200  can have a cylindrical structure such that the sectional view shown in  FIGS.  2 A- 2 D  be repeated or continuous through 360° of rotation about axis A of the compressor  200 . 
     Compressor  200  is a multi-stage centrifugal compressor. Compressor  200  includes an inlet guide vane  202  where a core flow of fluid to be compressed is received. Compressor  200  includes a first stage impeller  204  driven by rotation of shaft  206 , a diffuser  208  downstream of the first stage impeller  204 , and a return bend  210  downstream of the diffuser  208 . Compressor  200  further includes one or more deswirl vanes  212  downstream of the return bend  210 . Compressor  200  includes a side stream injection port  214  and a capacity control valve  216 . Compressor  200  includes a second stage impeller  218  downstream of the deswirl vanes  212  and the side stream injection port  214 , with a volute scroll  220  and a discharge conic  222  downstream of the second stage impeller  218 . 
     While compressor  200  is shown in  FIGS.  2 A- 2 D  as a two-stage compressor, compressors according to embodiments can include any number of stages, with the side stream injection port  214  and the capacity control valve  216  are provided in an interstage flow path between any two stages of the compressor. For example, compressor  200  can be a three-stage compressor, with the side stream injection port  214  and capacity control valve  216  disposed between the exhaust of the second stage and the intake of the third stage, or the like. 
     Compressor  200  can include one or more inlet guide vane  202  to control flow of working fluid into the compressor  200 . The inlet guide vanes  202  can be substantially similar to the inlet guide vanes  102  described above and shown in  FIGS.  1 A- 1 D . The one or more inlet guide vanes  202  can be configured to obstruct or permit flow of working fluid into the compressor  200 . In an embodiment, each of the inlet guide vanes  202  can be a rotating vane, for example, each rotating vane forming a section of a circle such that when all rotating vanes are in a closed position, the inlet guide vanes  202  obstruct an inlet of the compressor  200 . The one or more inlet guide vanes  202  can be movable between a fully open position and the closed position. In the fully open position the effect of the inlet guide vanes  202  on flow into compressor  200  can be minimized, for example by positioning the inlet guide vanes  202  such that the plane of each vane is substantially parallel to the direction of flow of working fluid into the inlet of compressor  200 . In an embodiment, each or all of the one or more inlet guide vanes  202  can be varied continuously from the fully open position to the closed position. 
     Compressor  200  includes a first stage impeller  204 . The first stage impeller  204  is driven by shaft  206 . Shaft  206  is rotated by, for example, a prime mover such as a motor. The first stage impellers  204  are configured to draw in the working fluid that passes the one or more inlet guide vanes  202  when rotated, and to expel the working fluid towards diffuser  208 . 
     Diffuser  208  receives the fluid discharged from first stage impellers  204  and directs the flow of the fluid towards return bend  210 . Return bend  210  changes the direction of the flow of the fluid such that it travels through the deswirl vanes  212  towards the second stage impeller  218 . 
     One or more deswirl vanes  212  are vanes extending from the return bend  210  towards the second stage impeller  218 . The deswirl vanes  212  are shaped to straighten the flow of the fluid as the flow passes towards the second stage impeller  218 . The deswirl vanes  212  can include notches configured to receive at least a portion of the capacity control valve  216 . 
     Side stream injection port  214  is a port configured to allow a side stream to be introduced into the interstage flow of fluid through compressor  200 . The side stream injection port  214  includes a leading end  224  and a trailing end  226 , with the leading end  224  towards the return bend  210  and the trailing end  226  towards the second stage impeller  218 . Side stream injection port  214  fluidly connects a side stream flow channel  228  with the interstage flow. The side stream flow channel  228  can receive a side stream of fluid from within a fluid circuit including the compressor  200 . The source of the side stream of fluid received by side stream flow channel  228  can be from one or more of a condenser, an economizer, an intercooler, a heat exchanger, or any other suitable source of fluid that is at an intermediate pressure, between the suction pressure and the discharge pressure of the compressor  200 . The side stream injection port  214  can be a ring shape surrounding an intake of the second stage impeller  218 . The side stream injection port  214  can be provided between the return bend  210  and the second stage impeller  218 . 
     Capacity control valve  216  is a valve that configured regulate the flow through the side stream injection port  214 . Capacity control valve  216  is configured to be extended axially through the side stream injection port  214  such that it extends substantially perpendicular to a direction of flow of the interstage flow from deswirl vane  212  towards the second stage impeller  218 . Capacity control valve  216  is configured to be able to prohibit flow through side stream injection port  214  in a closed position, for example by including a portion having a thickness corresponding to the width of the side stream injection port  214  from leading end  224  to trailing end  226 . In an embodiment, capacity control valve  216  is controlled in conjunction with inlet guide vanes  202 . In an embodiment, capacity control valve  216  is controlled independently of inlet guide vanes  202 . 
     Capacity control valve  216  includes a leading side  230  facing towards the return bend  210  and a trailing side  232  facing towards an inlet into second stage impeller  218 . Leading side  230  includes curved surface  234  extending towards a tip  236  of the capacity control valve  116 . The curved surface  234  can cause the distance between capacity control valve  216  and leading end  224  of side stream injection port  214  to be varied as capacity control valve  216  is axially extended or retracted. 
     Trailing side  232  includes one or more passages  238  configured to allow the side stream flow from side stream flow channel  228  to pass through the side stream injection port  214  and be introduced into the interstage flow on the trailing side  232  of the capacity control valve  216 . In an embodiment, passage  238  includes one or more channels having openings on the trailing side  232  of the capacity control valve  216 . In an embodiment, passage  238  is a cutout or scalloping formed in the trailing side  232 , such that in some positions of capacity control valve  216 , a gap exists between the trailing side  232  and the trailing end  224  of the side stream injection port  214 . 
     In the fully open position of the capacity control valve  216 , side stream flow passes from the side stream flow channel  228  through side stream injection port  214 , between the leading end  224  of the side stream injection port  214  and the leading side  230  of the capacity control valve  216 . Tip  236  of the capacity control valve  216  is located within the side stream injection port  214  or retracted into the side stream flow channel  228 , and capacity control valve  216  does not substantially affect the interstage flow passing from return bend  210  to second stage impeller  218 . Optionally, in the fully open position shown in  FIG.  2 A , inlet guide vane  202  can be in an open position where it provides little to no resistance to flow into the first stage impeller  204 . The fully open position shown in  FIG.  2 A  can be used, for example, when compressor  200  is being operated at or near full load capacity. In the embodiment shown in  FIG.  2   , when in the fully open position shown in  FIG.  2 A , some or all of the side stream flow passing through side stream injection port  214  can pass over the leading side  230  of capacity control valve  216 . 
     Second stage impeller  218  is used to achieve the second stage of compression. Second stage impeller  218  draws in the combined interstage and side stream flows and expels the fluid towards volute scroll  220 . Second stage impeller  218  can be rotated by shaft  206 , which is also used to rotate first stage impeller  204 . Fluid at the volute scroll  220  can then be discharged from compressor  200  at discharge conic  222 . 
     In an embodiment, the side stream provided through side stream injection port  214  can be received from an economizer, such as the economizer  314  shown in  FIG.  3 B  and described below. The economizer can be a flash-tank economizer, where flash or bypass gas rises and can be directed to the side stream flow channel  228 . The gas from the economizer being directed to the side stream flow channel  228  can reduce or eliminate the presence of gas in the liquid being passed to an evaporator of the HVACR system including compressor  200 . This can in turn improve the absorption of energy at the evaporator without further subcooling by providing more saturated liquid working fluid. In the full load cycle corresponding to the fully open position of capacity control valve  216 , the pressure at the side stream injection port  214  can allow the entrained vapor to be substantially removed from the working fluid in the economizer. 
       FIG.  2 B  shows a sectional view of the compressor shown in  FIG.  2 A  when the capacity control valve  216  is in a high flow position. The high flow position shown in  FIG.  2 B  can be used in a partial load condition where the load is relatively close to full load for the compressor  200 . In the high flow position shown in  FIG.  2 B , capacity control valve  216  is extended such that tip  236  projects into the path for interstage flow from return bend  210  to the second impeller  218 , partially obstructing the path for the interstage flow. In the high flow position of the embodiment shown in  FIG.  2 B , a first gap exists between the leading end  224  of the side stream injection port and the leading side  230  of the capacity control valve  216 , and a second gap exists at passage  238  between the trailing side  232  of the capacity control valve  216  and the trailing end  226  of the side stream injection port  214 . Each of the first and second gaps allow some of the side stream flow to join the interstage flow. The portion passing through the second gap experiences less of the pressure exerted by the interstage flow due to its introduction on the trailing side  232  of the capacity control valve  216 . Optionally, in the high flow position shown in  FIG.  2 B , inlet guide vane  202  can be in a high flow position where the inlet guide vane  202  provides increased resistance to flow into the first stage impeller  204  compared to the fully open position shown in  FIG.  2 A , but less resistance to flow than the low flow or closed positions shown in  FIGS.  2 C and  2 D , respectively. In the high-flow position shown in  FIG.  2 B , flow through side stream injection port  214  can include both flow over the leading side  230  and past the trailing side  232  of the capacity control valve. 
       FIG.  2 C  shows a sectional view of the compressor shown in  FIG.  2 A  when the capacity control valve  216  is in a low flow position. The low flow position shown in  FIG.  2 C  can be used in a partial load condition where the load is below the full load for the compressor  200 , and less than the load where the capacity control valve is in a high flow position such as in  FIG.  2 B . In the low flow position shown in  FIG.  2 C , capacity control valve  216  is extended further into the interstage flow from return bend  210  to second impeller  218 . The capacity control valve  216  thus provides even greater resistance to the interstage flow when compared to the high flow position shown in  FIG.  2 B . In the low flow position of the embodiment shown in  FIG.  2 C , a first gap exists between the leading end  224  of the side stream injection port and the leading side  230  of the capacity control valve  216 , and a second gap exists at passage  238  between the trailing side  232  of the capacity control valve  216  and the trailing end  226  of the side stream injection port  214 . Compared to the first and second gaps shown of the high flow position shown in  FIG.  2 B , in the low flow position of  FIG.  2 C , the second gap is relatively larger compared to the first, and a greater proportion of the side stream flow passes through the second gap to join the interstage flow relative to the amount of the side stream flow passing through the first gap. Optionally, in the low flow position shown in  FIG.  2 C , inlet guide vane  202  can be in a low flow position where the inlet guide vane  202  provides increased resistance to flow into the first stage impeller  204  compared to the high flow position shown in  FIG.  2 B , but less resistance to flow than the closed positions shown in  FIG.  2 D . In the low-flow position shown in  FIG.  2 B , flow through side stream injection port  214  can primarily or entirely be past the trailing side  232  of the capacity control valve. The shape of the leading side  230  and of passage  238  can each or both be selected to control the relative amount of flow being introduced on either the leading side  230  or trailing side  232  of the capacity control valve  216 , and how those relative amounts vary with the position of capacity control valve  216  from the fully open position through the closed position as shown in  FIGS.  2 A- 2 D . 
     In an embodiment, side stream flow channel  228  can receive the side stream flow from an economizer, such as economizer  314  shown in  FIG.  3 B  and described below. Providing passage  238  in capacity control valve  216  can allow capacity control valve  216  to not only control the quantity of flow being introduced, but the particular point at which the side stream is introduced in side stream injection port  214 , and the pressure at the point of introduction. Controlling the position of the point of introduction of side stream flow can provide control over the relationship between core flow and side stream flow in the compressor. Control of the point of introduction can improve economizer effectiveness across different load conditions. The low flow position shown in  FIG.  2 C  can be used when compressor  200  is operated at part load. When the compressor  200  is operated at part load, the static pressure at the side stream injection port  214 , particularly between leading end  222  of the side stream injection port  214  and the leading side  232  of the capacity control valve  216 , can be relatively elevated. The pressure within the economizer is a function of the static pressure at the injection location in compressor  200 , in addition to pipe losses and fixed orifice pressure drops for the system. The elevated pressure at side stream injection port  214  can therefore lead to an elevated pressure at the economizer, reducing effectiveness in removing flash or bypass gas from the fluid contained within. Passage  238 , by being on an opposite side of the capacity control valve  216  from leading side  232  that is facing the interstage flow within compressor  200 , is subject to a reduced pressure in comparison to the pressure on the leading side  232 , or the static pressure at the side stream injection port  114  in the embodiment shown in  FIG.  1 C . The reduced pressure at such an injection point can correspondingly lower the pressure within the economizer as described above, improving the release of flash or bypass gas from liquid in the economizer and its removal from the stream of working fluid passing to the evaporator. This improves the heat transfer at the evaporator and can also reduce recompression losses in the system including compressor  200  having capacity control valve  216  including passages  238 . 
       FIG.  2 D  shows a sectional view of the compressor shown in  FIG.  2 A  when the capacity control valve  216  is in a closed position. The closed position shown in  FIG.  2 D  can be used when the compressor  200  is in a partial-load condition at or near a minimum load for the compressor. In the closed position, capacity control valve  216  partially or completely obstructs side stream injection port  214 , from leading end  224  to trailing end  226 . It is appreciated that due to manufacturing tolerances, etc., there may be some possible leakage even when capacity control valve  216  is in the closed position. In an embodiment, capacity control valve  216  may be sized such that it does not contact side stream injection port  214 , and allows some flow through the gap between the side stream injection port  214  and the capacity control valve  216 . Any features of capacity control valve  216  configured to allow the introduction of the side stream flow on the trailing side  232  of the capacity control valve  216  such as passage  238  can be configured such that they do not permit such flow when capacity control valve  216  in the closed position. For example, as shown in  FIG.  2 D , a scalloped portion on the trailing side  232  forming passage  238  in this embodiment is sized and positioned such the trailing side  232  contacts the trailing end  226  of side stream injection port  214  when the capacity control valve  216  is extended into the closed position. The extension of the capacity control valve  216  into the interstage flow through compressor  200  is at a maximum, reducing the size of the orifice through which the interstage flow passes from return bend  210  towards second stage impeller  218 . Accordingly, this position imparts the greatest additional velocity to the interstage flow, while prohibiting the side stream flow from joining the interstage flow. Optionally, inlet guide vane  202  can be rotated to further obstruct flow to the first stage impeller  204  of compressor  200 , for example by pacing the inlet guide vane  202  in a minimum-flow position. 
       FIG.  3 A  shows a heating, ventilation, air conditioning and refrigeration (HVACR) circuit according to an embodiment. HVACR circuit  300  includes compressor  302 , condenser  304 , expander  306 , and evaporator  308 . 
     Compressor  302  is a centrifugal compressor, for example compressor  100  shown in  FIGS.  1 A- 1 D  or compressor  200  shown in  FIGS.  2 A- 2 D  and described above. 
     Condenser  304  receives working fluid from compressor  302  and allows the working fluid to reject heat, for example to air or another heat exchange medium. In an embodiment, a fluid line from the condenser  304  can convey some of the working fluid of HVACR circuit  300  back to compressor  302 , as the side stream flow provided to the side stream flow injection port of the compressor  302 , such as side stream injection ports  114  or  214  described above and shown in  FIGS.  1 A- 2 D . Condensed working fluid from condenser  304  can then pass to expander  306 . 
     Expander  306  expands the working fluid passing through as the fluid passes through HVACR circuit  300 . Expander  306  can be any suitable expander for the working fluid within the HVACR circuit  300 , such as, for example, an expansion valve, one or more expansion orifices, or any other suitable expansion device for use in an HVACR circuit. 
     Evaporator  308  is a heat exchanger where the working fluid of HVACR circuit  300  absorbs heat, for example from an ambient environment or a fluid to be cooled such as water in a water chiller HVACR system. The evaporator  308  can be, for example, an indoor coil of an air conditioner or a heat exchanger configured to cool water used in an HVACR system including the HVACR circuit  300 . 
     HVACR circuit  300  can further include an intercooler  310 . Intercooler  310  is a heat exchanger where working fluid from the HVACR circuit exchanges heat with the interstage flow within compressor  302 . The working fluid that exchanges heat with the interstage flow in intercooler  310  can be sourced from, for example, evaporator  308 , between expander  306  and evaporator  308 , or between the evaporator  308  and the compressor  302 . Some or all of the working fluid that exchanges heat with the interstage flow can then be reintroduced into HVACR circuit  300  downstream of where the working fluid is sourced. In an embodiment, at least some of the working fluid from intercooler  310  can be directed to a side stream flow channel of compressor  302  instead of returning to the ordinary flow path through HVACR circuit  300 . The side stream flow channel can be, for example, side stream flow channel  128  or side stream flow channel  228  of the compressors  100  and  200  described above and shown in  FIGS.  1 A- 1 D and  2 A- 2 D . 
       FIG.  3 B  shows an economized HVACR circuit  320  according to an embodiment. In  FIG.  3 B , compressor  302 , condenser  304  and evaporator  308  are included as in HVACR circuit  300  described above and shown in  FIG.  3 A , with compressor  302  being a multi-stage compressor in this embodiment. HVACR circuit  320  includes a first expander  312  and a second expander  314 . Each of first expander  312  and second expander  314  can be any suitable expander for the working fluid within the HVACR circuit  320  such as, for example, an expansion valve, one or more expansion orifices, or any other suitable expansion device for use in an HVACR circuit. Economizer  314  can be disposed between first and second expanders  312 ,  314 , such that working fluid of HVACR circuit  320  is at an intermediate pressure at the economizer  314 . The economizer  314  can be used as a source for the side stream introduced into compressor  302 , for example through a side stream flow channel such as side stream flow channel  128  or side stream flow channel  228  as described above and shown in  FIGS.  1 A- 1 D and  2 A- 2 D . 
       FIG.  4    shows a sectional view of a centrifugal compressor according to an embodiment along an interstage flow path. Centrifugal compressor  400  includes compressor housing  402 . Compressor housing  402  in part defines an interstage flow path  404 . The interstage flow path includes deswirl vanes  406  radially distributed around the interstage flow path  404 . Capacity control valve ring  408  extends into interstage flow path  404 , upstream of following stage inlet  410 . Capacity control valve ring can  408  be, for example, capacity control valve  116  or capacity control valve  216  as described above and shown in  FIGS.  1 A- 1 D and  2 A- 2 D . Capacity control valve ring  408  can be a single continuous ring or composed of a plurality of ring segments that combine to provide the ring shape. Following stage inlet  410  receives flow passing the capacity control valve ring  408  and allows the flow to enter into the following stage impeller  412 . 
       FIG.  5    shows a sectional view of a portion of a centrifugal compressor according to an embodiment. In the view of centrifugal compressor  500 , the interaction between the deswirl vanes  502  and the capacity control valve ring  504 . Deswirl vanes  502  can be any of the deswirl vanes shown in  FIGS.  1 A- 1 D,  2 A- 2 D , or  4 . Capacity control valve ring  504  can be any of the capacity control valves shown in  FIGS.  1 A- 1 D,  2 A- 2 D , or  4 . Capacity control valve ring includes notches  506 , each of notches  506  configured to accommodate one of the deswirl vanes  502  such that the capacity control valve ring  504  can be extended into a flow path including the deswirl vanes  502  without mechanically interfering with the deswirl vanes  502 . In an embodiment, notches corresponding to notches  506  can instead be included on each of the deswirl vanes  502  such that the deswirl vanes  502  do not contact the capacity control valve ring  504  as it is extended. In an embodiment, notches  506  are provided along with corresponding notches on the deswirl vanes  502 . In this embodiment, the notches  506  can have a depth that is less than an entire height of the area where capacity control valve ring  504  could contact deswirl vanes  502 , and the notches in the deswirl vanes have a depth such that they accommodate any portion of capacity control valve ring  504  that would otherwise contact the deswirl vanes  502  in the absence of said notches. 
     Aspects: 
     It is understood that any of aspects 1-12 can be combined with any of aspects 13-19. 
     Aspect 1. A centrifugal compressor, comprising: 
     a first stage impeller; 
     a second stage impeller; 
     a side stream injection port located between the first stage impeller and the second stage impeller, the side stream injection port configured to receive a side stream of a fluid; and 
     a capacity control valve, the capacity control valve configured to extend and retract through the side stream injection port, wherein: 
     the capacity control valve has a curved surface facing a direction of flow from the first stage impeller to the second stage impeller; and 
     the capacity control valve is configured to be extended through the side stream injection port between an open position where the side stream of the fluid can flow through the side stream injection port and a closed position where the capacity control valve obstructs flow of the side stream of the fluid through the side stream injection port. 
     Aspect 2. The centrifugal compressor according to aspect 1, wherein the capacity control valve has a ring shape. 
     Aspect 3. The centrifugal compressor according to any of aspects 1-2, comprising a plurality of the side stream injection ports and a plurality of the capacity control valves. 
     Aspect 4. The centrifugal compressor according to any of aspects 1-3, wherein in the open position, a tip of the capacity control valve at an end of the curved surface is within the side stream injection port. 
     Aspect 5. The centrifugal compressor according to any of aspects 1-4, wherein the capacity control valve extends and retracts in a direction substantially perpendicular to the direction of flow from the first stage impeller to the second stage impeller. 
     Aspect 6. The centrifugal compressor according to any of aspects 1-5, further comprising one or more deswirl vanes between the first stage impeller and the second stage impeller. 
     Aspect 7. The centrifugal compressor according to aspect 6, wherein the capacity control valve includes one or more notches, the one or more notches each configured to accommodate at least a portion of one of the one or more deswirl vanes. 
     Aspect 8. The centrifugal compressor according to any of aspects 6-7, wherein the one or more deswirl vanes each include one or more notches, the one or more notches each configured to accommodate at least a portion of the capacity control valve. 
     Aspect 9. The centrifugal compressor of any of aspects 1-8, wherein the capacity control valve has a linear meridional profile on a side opposite the curved surface, the linear meridional profile contacting an edge of the side stream injection port. 
     Aspect 10. The centrifugal compressor of any of aspects 1-9, wherein a side of the capacity control valve opposite the curved surface is configured such that when the capacity control valve is between the open position and the closed position, the fluid can flow past the capacity control valve on the side of the capacity control valve opposite the curved surface. 
     Aspect 11. The centrifugal compressor according to aspect 10, wherein the side of the capacity control valve opposite the curved surface includes a second curved surface. 
     Aspect 12. The centrifugal compressor according to any of aspects 10-11, wherein the side of the capacity control valve opposite the curved surface includes one or more channels configured to allow flow of the side stream of the fluid. 
     Aspect 13. A heating, ventilation, air conditioning, and refrigeration (HVACR) circuit, comprising: 
     a centrifugal compressor; 
     a condenser; 
     an expander; and 
     an evaporator, 
     wherein the centrifugal compressor includes: 
     a first stage impeller; 
     a second stage impeller; 
     a side stream injection port located between the first stage impeller and the second stage impeller, the side stream injection port configured to receive a side stream of a fluid; and 
     a capacity control valve, the capacity control valve configured to extend and retract through the side stream injection port, 
     the capacity control valve has a curved surface facing a direction of flow from the first stage impeller to the second stage impeller; and 
     the capacity control valve is configured to be extended through the side stream injection port between an open position where the side stream of the fluid can flow through the side stream injection port and a closed position where the capacity control valve obstructs flow of the side stream of the fluid through the side stream injection port. 
     Aspect 14. The HVACR circuit according to aspect 13, wherein the side stream of the fluid is from the condenser to the side stream injection port. 
     Aspect 15. The HVACR circuit according to aspect 13, further comprising an economizer and wherein the side stream of the fluid is from the economizer to the side stream injection port. 
     Aspect 16. The HVACR circuit according to aspect 13, further comprising an intercooler and wherein the side stream of the fluid is from the intercooler to the side stream injection port. 
     Aspect 17. The HVACR circuit according to any of aspects 13-16, wherein the capacity control valve has a ring shape. 
     Aspect 18. The HVACR circuit according to any of aspects 13-17, wherein the capacity control valve has a linear meridional profile on a side opposite the curved surface, the linear meridional surface contacting an edge of the side stream injection port. 
     Aspect 19. The HVACR circuit according to any of aspects 13-17, wherein a side of the capacity control valve opposite the curved surface is configured such that when the capacity control valve is between the open position and the closed position, the fluid can flow past the capacity control valve on the side of the capacity control valve opposite the curved surface. 
     The examples disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.