Centrifugal compressor

Abstract

A centrifugal compressor includes a casing, a first compression mechanism and a second compression mechanism. The casing has a first inlet portion, a first outlet portion, a second inlet portion and a second outlet portion. The first compression mechanism includes a first inlet guide vane disposed in the first inlet portion, a first impeller disposed downstream of the first inlet guide vane, a first diffuser disposed in the first outlet portion downstream from the first impeller, and a first motor. The second compression mechanism includes a second inlet guide vane disposed in the second inlet portion, a second impeller disposed downstream of the second inlet guide vane, a second diffuser disposed in the second outlet portion downstream from the second impeller, and a second motor. The first and second motors are arranged to rotate first and second shafts in order to rotate the first and second impellers.

What is claimed is: 
     
         1 . A centrifugal compressor comprising:
 a casing having a first inlet portion, a first outlet portion, a second inlet portion and a second outlet portion;   a first compression mechanism including
 a first inlet guide vane disposed in the first inlet portion, 
 a first impeller disposed downstream of the first inlet guide vane, the first impeller being attached to a first shaft rotatable about a first rotation axis, 
 a first diffuser disposed in the first outlet portion downstream from the first impeller, and 
 a first motor arranged to rotate the first shaft in order to rotate the first impeller; and 
   a second compression mechanism including
 a second inlet guide vane disposed in the second inlet portion, 
 a second impeller disposed downstream of the second inlet guide vane, the second impeller being attached to a second shaft rotatable about a second rotation axis, 
 a second diffuser disposed in the second outlet portion downstream from the second impeller, and 
 a second motor arranged to rotate the second shaft in order to rotate the second impeller. 
   
     
     
         2 . The centrifugal compressor according to  claim 1 , wherein
 rotation speeds of the first and second motors are independently controllable.   
     
     
         3 . The centrifugal compressor according to  claim 2 , further comprising
 a controller programmed to independently control the rotation speeds of the first and second motors.   
     
     
         4 . The centrifugal compressor according to  claim 3 , further comprising
 a first Variable Frequency Drive (VFD) connected to the first motor and the controller to variably control the rotation speed of the first motor; and   a second Variable Frequency Drive (VFD) connected to the second motor and the controller to variably control the rotation speed of the second motor.   
     
     
         5 . The centrifugal compressor according to  claim 1 , further comprising
 a first magnetic bearing rotatably supporting the first shaft; and   a second magnetic bearing rotatably supporting the second shaft.   
     
     
         6 . The centrifugal compressor according to  claim 5 , wherein
 the first and second rotation axes are coincident with each other.   
     
     
         7 . The centrifugal compressor according to  claim 6 , wherein
 the first shaft has a first inlet end with the first impeller mounted thereon and a first remote end with the first motor mounted on the first shaft between the first impeller and the first remote end,   the second shaft has a second inlet end with the second impeller mounted thereon and a second remote end with the second motor mounted on the second shaft between the second impeller and the second remote end,   the first magnetic bearing includes a first impeller side radial magnetic bearing axially disposed between the first impeller and the first motor, and   the second magnetic bearing includes a second impeller side radial magnetic bearing axially disposed between the second impeller and the second motor.   
     
     
         8 . The centrifugal compressor according to  claim 7 , wherein
 the first magnetic bearing includes a first remote side radial magnetic bearing axially disposed on a side of the first motor that is remote from a side where the first impeller is mounted, and   the second magnetic bearing includes a second remote side radial magnetic bearing axially disposed on a side of the second motor that is remote from a side where the second impeller is mounted.   
     
     
         9 . The centrifugal compressor according to  claim 8 , wherein
 the first magnetic bearing includes a first axial thrust magnetic bearing, and   the second magnetic bearing includes a second axial thrust magnetic bearing.   
     
     
         10 . The centrifugal compressor according to  claim 8 , wherein
 the first axial thrust magnetic bearing is axially disposed adjacent to the first remote side radial bearing, and   the second axial thrust magnetic bearing is axially disposed adjacent to the second remote side radial bearing.   
     
     
         11 . The centrifugal compressor according to  claim 6 , wherein
 the first shaft has a first inlet end with the first impeller mounted thereon and a first remote end with the first motor mounted on the first shaft between the first impeller and the first remote end,   the second shaft has a second inlet end with the second impeller mounted thereon and a second remote end with the second motor mounted on the second shaft between the second impeller and the second remote end,   the first magnetic bearing includes a first remote side radial magnetic bearing axially disposed on a side of the first motor that is remote from a side where the first impeller is mounted, and   the second magnetic bearing includes a second remote side radial magnetic bearing axially disposed on a side of the second motor that is remote from a side where the second impeller is mounted.   
     
     
         12 . The centrifugal compressor according to  claim 6 , wherein
 the first magnetic bearing includes at least one first radial magnetic bearing and at least one first axial thrust magnetic bearing, and   the second magnetic bearing includes at least one second radial magnetic bearing and at least one second axial thrust magnetic bearing.   
     
     
         13 . The centrifugal compressor according to  claim 12 , wherein
 the first axial thrust magnetic bearing is axially disposed at the first remote end,   the second axial thrust magnetic bearing is axially disposed at the second remote end, and   the first and second remote ends and the first and second axial thrust magnetic bearings are spaced from each other to form a gap therebetween.   
     
     
         14 . The centrifugal compressor according to  claim 1 , wherein
 the first diffuser is connected to the second impeller such that refrigerant compressed in the first compression mechanism is further compressed in the second compression mechanism.   
     
     
         15 . A chiller system including the centrifugal compressor according to  claim 1 , the chiller system further comprising:
 an evaporator;   a condenser; and   an expansion device,   the compressor, the evaporator, the condenser and the expansion mechanism being connected together to form a refrigerant circuit.   
     
     
         16 . A chiller system according to  claim 15 , further comprising:
 an economizer connected between the first compression mechanism and the second compression mechanism in the refrigerant circuit.