Centrifugal compressor achieving high pressure ratio

Abstract

Compressors achieve in a single stage a high-pressure ratio (r) of greater than or equal to 2.5:1 on a process fluid having a molecular weight of 12-20, such as natural gas. Two or more of the compressor stages are combined serially to increase overall pressure ratio. Each single-stage includes respective inlet and outlet passages and an unshrouded, centrifugal impeller that includes a plurality of impeller blades. Process fluid is discharged from trailing edges of the impeller blades at a rotational velocity greater than or equal to 1400 feet/second into a diffuser passage of the outlet. Dimension ranges of the annular diffuser passage, the centrifugal impeller, and the diffuser vanes vary as a function of pressure ratio (r) and/or the flow coefficient (φ) of the process fluid flowing between the inlet and the outlet.

What is claimed is: 
     
         1 . A compressor comprising:
 a housing having: an inlet defining an inlet passage; and an outlet defining an annular diffuser passage, respectively configured to receive and flow a process fluid there between and therethrough, the process fluid in the inlet passage having an inlet pressure (P 1 ) and the process fluid discharged from the annular diffuser passage having a discharge pressure (P 2 ) greater than the inlet pressure, such that a pressure ratio (r) of the discharge pressure divided by the inlet pressure is greater than unity;   a rotary shaft, defining a shaft axis, in the housing between the inlet and the outlet thereof;   an unshrouded centrifugal impeller mounted about the rotary shaft between the inlet and the outlet of the housing, and in fluid communication with process fluid flowing there between, the centrifugal impeller having: a hub with an axial length (A x ) extending axially along the shaft axis of the rotary shaft, and a hub outer diameter (D 2 ) extending radially at a radius (R 2 ) relative to the shaft axis; a plurality of impeller blades projecting outwardly from the hub, each of the impeller blades having: a leading edge facing the inlet passage of the housing at a blade sweep angle (θ), a trailing edge facing the annular diffuser passage at a back sweep angle (β) and having a tip width (b 2 ), and a blade tip having a radius of curvature (R C ), which defines an outer periphery of the centrifugal impeller; the impeller blades configured to impart energy to the process fluid, upon rotation of the rotary shaft and, to discharge the process fluid therefrom at a flow angle (α) into the annular diffuser passage;   the annular diffuser passage having: a shroud wall and a hub wall which define a diffuser passage height (b 3 ) there between; a plurality of diffuser vanes in the annular diffuser passage to receive process fluid discharged by the centrifugal impeller and convert the energy imparted therein by the centrifugal impeller, in order to raise pressure thereof by the pressure ratio and cause actual volumetric flow therethrough at a flow coefficient (φ), the respective diffuser vanes extending axially from the shroud wall towards the hub wall thereof and having a vane height (b 3R ), and circumferentially disposed about the periphery of the centrifugal impeller, each diffuser vane respectively defining: curved, opposing vane pressure and vane suction sides, a vane leading edge proximate the periphery of the centrifugal impeller at a radial distance (R 3 ) relative to the shaft axis and conjoining the suction side, a vane trailing edge facing the outlet and conjoining the suction side, and a vane radial extent between the vane leading and trailing edges, the vane radial extent defining a length (RE); and   wherein: the compressor is configured to impart a pressure ratio (r) of at least 5:1 on the process fluid having a molecular weight of 24-27.99; or at least 4:1 on the process fluid having a molecular weight of 20-24; or at least 3:1 on the process fluid having a molecular weight of 16-20; or at least 2.5:1 on the process fluid having a molecular weight of 10-16; or at least 2:1 on the process fluid having a molecular weight less than 10;   the flow angle (α) is 69-80 degrees;   ratio of the radius of the vane leading edge to the outer hub radius (R 3 /R 2 ) is 1.07-1.15; and   dimension ranges of the annular diffuser passage, the centrifugal impeller, and the diffuser vanes vary as a function of pressure ratio (r); and dimension ranges of the annular diffuser passage and the diffuser vanes vary as a function of flow coefficient (φ) of the process fluid flowing between the inlet and the outlet of the compressor as follows:   
       
         
           
                 
                 
                 
                 
                 
                 
               
                     
                 
                   r 
                   A x /D 2   
                   1/R C   
                   θ 
                   β (angular bandwidth) 
                   RE/R 2   
                 
                     
                 
                   2:1-10:1 
                   0.1-0.4 
                   0.5-0.15 
                   40-85 
                   20-60 to 35-45 
                   0.1-0.5 
                 
                     
                 
             
                
                
                
               
               
                
                
               
            
           
         
       
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   φ 
                   b 3R /b 3   
                 
                     
                     
                 
                     
                      0-0.030 
                   1.0 
                 
                     
                   0.030-0.050 
                   0.5-1.0 
                 
                     
                   0.050-0.110 
                   0.3 
                 
                     
                     
                 
             
                
                
                
               
               
                
                
                
                
               
            
           
         
       
     
     
         2 . The compressor of  claim 1 , comprising a single-stage compressor. 
     
     
         3 . A two-stage compressor, comprising two of the single-stage compressors of  claim 2  in series, the stages in combination configured to impart a pressure ratio (r) of at least 10:1 on the process fluid having a molecular weight of 24-27.99; or at least 8:1 on the process fluid having a molecular weight of 20-24; or at least 6:1 on the process fluid having a molecular weight of 16-20; or at least 5:1 on the process fluid having a molecular weight of 10-16; or at least 4:1 on the process fluid having a molecular weight less than 10. 
     
     
         4 . The two-stage compressor of  claim 3 , configured to provide a pressure ratio (r) of greater than or equal to 5:1 on the process fluid having a molecular weight of 12-20, the process fluid comprising natural gas. 
     
     
         5 . The two-stage compressor of  claim 3 , further comprising the two single-stage compressors in series fluid communication, in a common in-line housing, 
     
     
         6 . The two-stage compressor of  claim 5 , configured to provide a pressure ratio (r) of greater than or equal to 5:1 on the process fluid having a molecular weight of 12-20, the process fluid comprising natural gas. 
     
     
         7 . The compressor of  claim 1 , the centrifugal impeller having at least one leading edge of an impeller blade that is not coplanar with the leading edge of at least one other impeller blade. 
     
     
         8 . The compressor of  claim 1 , further comprising a first row of a plurality of diffuser vanes; and
 a second row of a plurality of diffuser vanes whose respective second-row vane leading edges face the vane trailing edges of the diffuser vanes of the first row of said vanes, and whose respective second-row vane trailing edges face the outlet, and terminate at a radial distance (R 5 ) relative to the shaft axis.   
     
     
         9 . The compressor of  claim 1 , the diffuser vanes further comprising a compression-inducing surface formed along the vane leading edge, and configured to generate a shock wave from within the process fluid. 
     
     
         10 . A method for compressing natural gas, having a molecular weight (MW) of 12-20, comprising:
 providing a single-stage, centrifugal compressor with a compressor casing having therein:
 an inlet for receipt of a process fluid; 
 a single, unshrouded, rotatable, centrifugal impeller defining a plurality of impeller blades for imparting kinetic energy into the process fluid, each of the respective impeller blades having a leading edge for receiving process fluid from the inlet and a trailing edge for discharging process fluid therefrom; 
 a diffuser, defining an annular diffuser passage, for receiving the process fluid discharged from the respective trailing edges of the impeller blades in the annular diffuser passage and increasing static pressure of the process fluid therein; and 
 an outlet for receiving process fluid discharged from the annular diffuser passage; 
   introducing a first process fluid, comprising natural gas, having a molecular weight (MW) of 12-20 into the inlet passage of the compressor at an inlet pressure (P 1 );   driving the centrifugal impeller at a rotational speed (N), so that the trailing edges of the respective impeller blades achieve a rotational velocity (U 2 ) of greater than or equal to 1400 feet/second, imparting kinetic energy into the first process fluid;   receiving the first process fluid discharged by the trailing edges of centrifugal impeller in the annular diffuser passage, converting the kinetic energy imparted in the first process fluid by centrifugal impeller into a pressure increase; and   discharging the first process fluid from the annular diffuser passage at a discharge pressure (P 2 ) greater than the inlet pressure (P 1 ) thereof, such that a pressure ratio (r) of the discharge pressure divided by the inlet pressure is greater than or equal to 2.5:1.   
     
     
         11 . The method of  claim 10 , further comprising combining two of the single-stage, centrifugal compressors in series, with the outlet of the first stage coupled to the inlet of the second stage, the stages in combination receiving the first process fluid in the inlet of the first stage thereof, and discharging the first process fluid out of the outlet of the second stage at a throughput pressure ratio (r) of greater than or equal to 5:1. 
     
     
         12 . The method of  claim 11 , comprising configuring and assembling a multi-stage compressor, having 3 or more of the single-stage, centrifugal compressors in series, the stages in combination configured to impart sequentially within the assembled multi-stage compressor a throughput pressure ratio (r) of greater than or equal to 10:1 on the first process fluid. 
     
     
         13 . A method for compressing process fluids, comprising:
 providing a single-stage, centrifugal compressor with a compressor casing having therein:
 an inlet for receipt of a process fluid; 
 a single, unshrouded, rotatable, centrifugal impeller defining a plurality of impeller blades for imparting kinetic energy into the process fluid, each of the respective impeller blades having a leading edge for receiving process fluid from the inlet and a trailing edge for discharging process fluid therefrom; 
 a diffuser, defining an annular diffuser passage, for receiving the process fluid discharged from the respective trailing edges of the impeller blades in the annular diffuser passage and increasing static pressure of the process fluid therein; and 
 an outlet for receiving process fluid discharged from the annular diffuser passage; 
   introducing a first process fluid having a molecular weight (MW) into the inlet passage of the compressor at an inlet pressure (P 1 );   driving the centrifugal impeller at a rotational speed (N), so that the trailing edges of the respective impeller blades achieve a rotational velocity (U 2 ) of greater than or equal to 1400 feet/second, imparting kinetic energy into the first process fluid;   receiving the first process fluid discharged by the trailing edges of centrifugal impeller in the annular diffuser passage, converting the kinetic energy imparted in the first process fluid by centrifugal impeller into a pressure increase; and   discharging the first process fluid from the annular diffuser passage at a discharge pressure (P 2 ) greater than the inlet pressure (P 1 ) thereof, such that a pressure ratio (r) of the discharge pressure divided by the inlet pressure is:   at least 5:1, where the first process fluid has a molecular weight of 24-27.99;   or at least 4:1 where the first process fluid has a molecular weight of 20-24;   or at least 3:1 where the first process fluid has a molecular weight of 16-20;   or at least 2.5:1 where the first process fluid has a molecular weight of 10-16;   or at least 2:1 where the first process fluid has a molecular weight less than 10.   
     
     
         14 . The method of  claim 13 , further comprising combining two of the single-stage, centrifugal compressors in series, with the outlet of the first stage coupled to the inlet of the second stage, the stages in combination receiving the first process fluid in the inlet of the first stage thereof, and discharging the first process fluid out of the outlet of the second stage at a throughput pressure ratio (r) of:
 at least 10:1, where the first process fluid has a molecular weight of 24-27.99;   or at least 8:1 where the first process fluid has a molecular weight of 20-24;   or at least 6:1 where the first process fluid has a molecular weight of 16-20;   or at least 5:1 where the first process fluid has a molecular weight of 10-16;   or at least 4:1 where the first process fluid has a molecular weight less than 10.   
     
     
         15 . The method of  claim 14 , comprising configuring and assembling a multi-stage compressor, having 3 or more of the single-stage, centrifugal compressors in series, the stages in combination configured to impart sequentially within the assembled multi-stage compressor a throughput pressure ratio (r) of greater than or equal to 10:1 on the selected process fluid having a molecular weight of 2.0-27.99, the selected process fluid comprising natural gas.