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Title:
CENTRIFUGAL COMPRESSOR WITH SHAFTLESS IMPELLER
Document Type and Number:
WIPO Patent Application WO/2019/199321
Kind Code:
A1
Abstract:
A centrifugal compressor (20), with a shaftless impeller (50), is rotatively mounted on a journal. The journal is incorporated within a stationary journal shaft (40) that spans the impeller hub (52), or in a journal stub (80) that projects into at least one of the axial ends of the impeller hub, or in a pair of opposed, first and second journal stubs (142, 146). A magnetic bearing (60) is interposed between the journal and a hollow hub of the impeller. The journal and magnetic bearing support and position the impeller hub within an impeller cavity of the compressor casing (22). An independent impeller drive (151) rotates the impeller. A drive shaft (150), which is independent of the journal, is coupled to the impeller. Respective drive motor (300), rotor and stator permanent magnets, and/or electromagnetic coils are embedded within the respective, opposing journal and hub.

Inventors:
MOHR, Byron L. (1600 Stardust Lane, Olean, New York, 14760, US)
KUNKEL, Edward (149 Tahattawan Road, Littleton, Massachusetts, 01460, US)
Application Number:
US2018/027507
Publication Date:
October 17, 2019
Filing Date:
April 13, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
DRESSER-RAND COMPANY (500 Paul Clark Drive, Olean, New York, 14760, US)
International Classes:
F04D29/058; F04D17/12; F04D25/06
Domestic Patent References:
WO2015114136A12015-08-06
WO2016193002A12016-12-08
Foreign References:
US20150104335A12015-04-16
RU2458253C12012-08-10
US3938913A1976-02-17
DE202016000085U12017-04-12
Other References:
None
Attorney, Agent or Firm:
MORA, Enrique J. (Siemens Corporation- Intellectual Property Dept, 3501 Quadrangle Blvd. Ste. 230Orlando, Florida, 32817, US)
Download PDF:
Claims:
CLAIMS

What is claimed is:

1. A compressor (20), comprising:

a compressor casing (22), defining a casing longitudinal axis (24) that is circumscribed by an impeller cavity (30);

a journal (40), disposed within the casing, defining a journal central axis (44) that is congruent with the casing longitudinal axis (28);

an impeller (50) disposed within and circumscribed by the impeller cavity, having a hollow hub (52) concentrically aligned with, and configured to rotate about the journal central axis; and

a magnetic bearing (60) interposed between the journal and the hollow hub, for supporting and positioning the impeller within the impeller cavity radially relative to the journal central axis.

2. The compressor of claim 1, the magnetic bearing further comprising:

a first portion (292) coupled to the impeller hub (290), having a first thrust- bearing surface; and

a second portion (282) coupled to the journal (270), having a second thrust- bearing surface opposing the first thrust bearing surface;

wherein, a repulsive magnetic field (FR) generated between the first and second thrust-bearing surfaces of the magnetic bearing orients the impeller hub in the impeller cavity in a single axial position, relative to the journal central axis.

3. The compressor of claim 2, the magnetic bearing further comprising:

the first thrust-bearing surface portion of the magnetic bearing having a first electromagnetic coil (258) or a first permanent magnet (292) coupled to the impeller hub (252, 290); and

the second thrust-bearing surface portion of the magnetic bearing having a second electromagnet coil (234) or a second permanent magnet (94) coupled to the journal (40, 210).

4. The compressor of claim 4, the magnetic bearing further comprising:

the first thrust-bearing surface (334) formed as a female, frusto-conical profile, annular surface within the hollow impeller hub (330); and

the second thrust-bearing surface formed as a male, frusto-conical profile, annular surface (314) on the journal (310) that is captured within the first thrust- bearing surface in opposed and radially spaced relationship.

5. The compressor of claim 4, further comprising the first electromagnet or the first permanent magnet (332) embedded within the first thrust-bearing surface (334); and the second electromagnet (326) or the second permanent magnet embedded within the second thrust-bearing surface (314).

6. The compressor of claim 1, the magnetic bearing further comprising:

a first portion of the magnetic bearing having a first electromagnet coil (258) or a first permanent magnet (62) coupled to the impeller hub (52); and

a second portion of the magnetic bearing having a second electromagnet coil (94) or second permanent magnet coupled to the journal (40);

wherein, a repulsive magnetic field (FR) generated between the first and second portions of the magnetic bearing centers the impeller hub in the impeller cavity (30) in a single radial position, relative to the journal central axis (44).

7. The compressor of claim 6, further comprising the first electromagnet (232) or the first permanent magnet embedded within the impeller hub (222); and the second electromagnet (234) or the second permanent magnet embedded within journal (210).

8. The compressor of claim 1, the journal comprising a journal shaft (40) extending axially through and projecting from first and second axial ends of the impeller hub (52).

9. The compressor of claim 8, further comprising:

a stationary journal shaft (174); and a drive shaft (186) coupled to the impeller (176) independent of the stationary journal shaft, for rotating the impeller about the stationary journal shaft.

10. The compressor of claim 9, further comprising:

a plurality of axially spaced impellers (176A-C) disposed within and circumscribed by a corresponding impeller cavity, each impeller respectively having a hollow hub (178A-C) concentrically aligned with, and configured to rotate about the journal central axis (185) of the stationary journal shaft (174); and

a respective magnetic bearing (180A-C) interposed between the stationary journal shaft and its respective hollow hub, for supporting and positioning the plurality of impellers within their corresponding impeller cavities radially relative to the journal central axis;

each of the respective impellers coupled to a common drive shaft (182, 186), for rotating the impellers about the stationary journal shaft.

11. The compressor of claim 8, further comprising:

a plurality of coupled compressor casings (172) that are axially aligned along a shared, common casing longitudinal axis that is congruent with the journal central axis of the journal shaft (174), each compressor casing respectively having therein:

an impeller cavity that circumscribes the shared, common casing longitudinal axis and the journal shaft;

an impeller (176) disposed within and circumscribed by the impeller cavity, having a hollow hub (178) with first and second axial ends and an inner annular surface formed there between, the journal shaft extending axially through the inner annular surface and projecting from first and second axial ends thereof;

a magnetic bearing (180) interposed between the inner annular surface of the hub and the journal shaft; and

a drive shaft (182, 186) in the coupled casings, coupled to each respective impeller independent of the journal shaft, for rotating all of the impellers about the journal shaft.

12. The compressor of claim 1, further comprising:

the hub (90, 122) having first and second axial ends and an inner annular surface formed there between;

the journal having: a first journal stub (80, 112) coupled to a shroud side (74) of the casing (72) or a hub side (104) of the casing (102), and projecting into at least one of the axial ends and the inner annular surface of the hub; and

a first magnetic bearing (94, 126) interposed between the inner annular surface of the hub and the first journal stub.

13. .The compressor of claim 12, further comprising:

opposed, stationary first (142) and second (146) journal stubs projecting respectively from the shroud side (134) of the casing (132) into the first axial end (164) and the inner annular surface of the hub (158), and the hub side (136) of the casing into the second axial end (166) and the inner annular surface of the hub;

a second magnetic bearing (162) interposed between the inner annular surface of the hub and the second journal stub; and

a drive shaft (150, 152) coupled to the impeller (156) independent of the first and second stationary journal stubs, for rotating the impeller about the first and second journal stubs.

14. The compressor of claim 13, further comprising:

the first (142) and second (146) journal stubs respectively having hollow cores (144, 148) and opposed, axially spaced, first (145) and second (149) distal ends; and the drive shaft (150, 152) oriented within the hollow cores of the respective first and second journal stubs and coupled to the impeller (156) between the respective first and second distal ends of the respective journal stubs.

15. The compressor of claim 12, further comprising:

a plurality of coupled compressor casings (172) that are axially aligned along a shared, common casing longitudinal axis, each respectively having:

an impeller cavity that circumscribes the shared, common casing longitudinal axis; an impeller (176) disposed within and circumscribed by the impeller cavity, having a hollow hub (178) with first and second axial ends and an inner annular surface formed there between;

the journal (174) having a first journal stub coupled to a shroud side of the casing or a hub side of the casing, and projecting into at least one of the axial ends and the inner annular surface of the hub; and

a first magnetic bearing (180) interposed between the inner annular surface of the hub and the first journal stub; and

a drive shaft (186) in the casings, coupled to each respective impeller independent of its respective first stationary journal stub, for rotating all of the impellers about its respective first journal stub.

16. The compressor of claim 1, further comprising:

a first portion of the magnetic bearing (230) having a first electromagnet coil (258) or a first permanent magnet (232) coupled to the impeller hub (222); and

a second portion of the magnetic bearing having a second electromagnet coil (234) or second permanent magnet coupled to the journal (210);

a controller (242) operably controlling distribution of electrical energy by an electrical power source (240) to each respective first and/or second electromagnets (234), for selectively varying repulsive magnetic field generated between the first and second portions of the magnetic bearing, for orienting the impeller hub in the impeller cavity in a desired radial and/or axial position, relative to the journal central axis (208).

17. The compressor of claim 1, further comprising:

a stationary journal (270) extending axially into a first and/or second axial end of the impeller hub (290);

an electric motor (340), interposed between the journal and the impeller hub, axially offset from the magnetic bearing (292, 294), having:

a rotor having rotor coils or permanent rotor magnets (304) embedded within a first recess formed in the impeller hub; and a stator having stator coils (302A-C) embedded within a second recess (318, 320) formed in the journal;

the rotor and stator coils configured to generate a magnetic field (F@) for rotating the rotor and the impeller that is coupled thereto about the stationary journal.

18. A method for aligning and supporting a rotatable impeller in a compressor, comprising:

supporting an impeller (50), having a hollow hub (52), by interposing a magnetic bearing (60) in the hollow hub, the magnetic bearing circumscribing a stationary journal (40) disposed within an impeller cavity (30) of a compressor casing (22), the stationary journal defining a journal central axis (44) that is congruent with a casing longitudinal axis (28), with both axes circumscribed by the impeller cavity; energizing at least one electromagnet of the magnetic bearing, generating a repulsive magnetic field in the bearing that radially (FR) and/or axially (FA) positions the journal and hub relative to each other along the journal central axis; and

selectively aligning the impeller and the stationary journal relative to each other by varying energization of the electromagnet.

19. The method of claim 18, further comprising rotating the impeller with a drive shaft (150, 186) coupled thereto, without rotating the stationary journal (40).

20. The method of claim 18, further comprising rotating the impeller (290, 330) with an electric motor (300, 340) having stationary stator coils (302, 342) embedded within the stationary journal (270, 310), which are axially offset from coils (282, 284, 326, 328) of the electromagnet that are also embedded within the stationary journal (270, 310); and rotor coils (304, 344) embedded within the impeller hub (290, 330), which are axially offset from coils of the electromagnet (292, 294, 332, 336) that are also embedded within the impeller hub;

energizing coils (292, 294, 332, 336) of the electromagnet to align the impeller hub and the stationary journal relative to each other; and

energizing the rotor and stator coils, driving the impeller with the electric motor.

Description:
CENTRIFUGAL COMPRESSOR WITH SHAFTLESS IMPELLER

TECHNICAL FIELD

[0001] The invention relates to centrifugal compressors. More particularly, the invention relates to shaftless impeller mounting in centrifugal compressors, where the impeller supported and positioned by a journal and rotates on magnetic bearings interposed between the journal and an impeller hub. In some embodiments, the impeller is driven by an electric motor, whose stator is embedded in the journal and whose rotor is embedded in the impeller hub.

BACKGROUND

[0002] Centrifugal compressors typically incorporate a shaft-mounted impeller in the compressor casing or housing. The impeller is rigidly affixed to the compressor shaft; the shaft provides multiple mechanical functions. First, the shaft supports and aligns the impeller within the impeller cavity of the compressor casing. Second, the shaft rotates the impeller with a driver, such as an electric motor or an engine. The compressor shaft is in turn rotationally mounted in the compressor housing by bearings that are axially offset from the impeller, so that it can support and rotate the impeller. Some known compressors have“center-mounted” impellers, where ends of the compressor shaft extend from both axial ends of the impeller hub, and are supported in film-lubricated, rolling element or magnetic bearings. Other known compressors have“overhung” impeller, where the shaft extends from only one axial end of the impeller hub. The portion of the shaft that extends from the hub is supported in a film-lubricated, rolling element or magnetic bearing, where the impeller is supported by the shaft in cantilever-like fashion.

[0003] Shafts with offset bearing mounts require use of compressor casings of sufficient axial length to retain one or more shaft-mounted impellers and the associated bearings/bearing mounts. These shafts require sufficient cross-sectional area and strength to resist shear and bending stresses associated with the axially offset impeller loads and their bearing supports.

SUMMARY OF INVENTION

[0004] Exemplary embodiments of centrifugal compressors described herein comprise shaftless impellers, rotatively mounted on journals. In some embodiments, the journal is stationary. In some embodiments, the journal is incorporated within a stationary journal shaft that extends axially from both axial ends of the impeller. Both ends of the journal shaft are coupled to the compressor casing. In other embodiments, the journal is a journal stub, one end of which is coupled to compressor casing and the other end of which projects into at least one of the axial ends of the impeller hub, in cantilever-like fashion. In yet other embodiments, a pair of opposed, first and second journal stubs project respectively from a shroud side of the casing into a first axial end of the impeller hub, and from a hub side of the casing into a second axial end of the impeller hub. One or more magnetic bearings are interposed between the journal and a hollow hub of the impeller. The journal and magnetic bearing support and position the impeller within an impeller cavity of the compressor casing. In some embodiments, first and second, opposing, magnetically repulsing portions of the magnetic bearing are embedded in the journal and the impeller hub, respectively. For example, permanent magnets or electromagnetic coils are embedded in the impeller hub, and opposing permanent magnets or electromagnetic coils are embedded in the journal.

[0005] The impeller is rotated with a driver, in order to compress working fluids flowing through the compressor. In some embodiments, a drive shaft, which is independent of the journal, is coupled to the impeller and rotates the impeller about the journal shaft. In other embodiments, respective permanent magnets or electromagnetic coils of a drive motor are embedded in the impeller hub and the opposing journal, eliminating the need for an external impeller drive. [0006] Other exemplary embodiments of the invention feature a compressor, having a compressor casing that defines a casing longitudinal axis. An impeller cavity circumscribes the casing’s longitudinal axis. A journal is disposed within the casing; it defines a journal central axis that is congruent with the casing longitudinal axis. An impeller is disposed within and is circumscribed by the impeller cavity. The impeller has a hollow hub that is concentrically aligned with, and configured to rotate about the journal central axis. A magnetic bearing is interposed between the journal and the hollow hub, for supporting and positioning the impeller within the impeller cavity radially relative to the journal central axis.

[0007] Additional exemplary embodiments of the invention feature a method for aligning and supporting a rotatable impeller in a compressor, having a hollow hub. The impeller is supported by interposing a magnetic bearing in the hollow hub. The magnetic bearing circumscribes a stationary journal disposed within an impeller cavity of a compressor casing. The stationary journal defines a journal central axis that is congruent with a casing longitudinal axis; both axes circumscribed by the impeller cavity. At least one electromagnet of the magnetic bearing is energized. This generates a repulsive magnetic field in the bearing that radially and/or axially positions the journal and hub relative to each other along the journal central axis. Selectively energizing the at least one electromagnet aligns the impeller and the stationary journal relative to each other by varying energization of the electromagnet.

[0008] The respective features of the exemplary embodiments of the invention that are described herein may be applied jointly or severally in any combination or sub- combination.

BRIEF DESCRIPTION OF DRAWINGS

[0009] The exemplary embodiments of the invention are further described in the following detailed description in conjunction with the accompanying drawings, in which: [0010] FIG. 1 is an axial cross-sectional, schematic view of a centrifugal compressor, in accordance with an embodiment described herein, where the impeller is rotatively mounted on a stationary journal shaft;

[0011] FIG. 2 is an axial cross-sectional, schematic view of a centrifugal compressor, in accordance with an embodiment described herein, where the impeller is rotatively mounted on a stationary journal stub that is coupled to the shroud side of the compressor casing;

[0012] FIG. 3 is an axial cross-sectional, schematic view of a centrifugal compressor, in accordance with an embodiment described herein, where the impeller is rotatively mounted on a stationary journal stub that is coupled to the hub side of the compressor casing;

[0013] FIG. 4 is an axial cross-sectional, schematic view of a centrifugal compressor, in accordance with an embodiment described herein, where the impeller is rotatively mounted on a pair of opposed, axially spaced, stationary first and second journal stubs, which are respectively coupled to the shroud side, and the hub side of the compressor casing, and driven by a drive shaft that is independent of the journal stubs;

[0014] FIG. 5 is an axial cross-sectional, schematic view of a centrifugal compressor, in accordance with an embodiment described herein, where a plurality of axially spaced impellers are disposed within and circumscribed by the impeller cavity; each impeller respectively having a hollow hub concentrically aligned with, and configured to rotate about the journal central axis of a stationary journal shaft;

[0015] FIG. 6 is a fragmented, axial cross-sectional, schematic view of a centrifugal compressor, in accordance with an embodiment described herein, where opposed portions of the magnetic bearing respectively is embedded within the journal and the impeller hub; [0016] FIG. 7 is an axial cross-sectional, schematic view of an impeller, in accordance with an embodiment described herein, an electromagnetic coil of an electromagnetic bearing is embedded in the impeller hub;

[0017] FIG. 8 is a plan view schematic of a journal that incorporates embedded electromagnetic coils for radial support, electromagnetic bearings, and for a stator of an embedded drive motor, in accordance with an embodiment described herein; and

[0018] FIG. 9 is a plan view schematic of a journal that incorporates embedded electromagnetic coils for electromagnetic thrust and radial support bearings, and for a stator of an embedded drive motor, in accordance with an embodiment described herein.

[0019] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale.

DESCRIPTION OF EMBODIMENTS

[0020] Exemplary embodiments of centrifugal compressors described herein comprise shaftless impellers, rotatively mounted on journals. In some embodiments, the journal is stationary. In some embodiments, a drive shaft, which is independent of the journal, is coupled to the impeller and rotates the impeller about the journal shaft. In some embodiments, the journal is incorporated within a stationary journal shaft that extends axially from both axial ends of the impeller. Both ends of the journal shaft are coupled to the compressor casing. In other embodiments, the journal is a journal stub, one end of which is coupled to compressor casing and the other end of which projects into at least one of the axial ends of the impeller hub, in cantilever-like fashion. In yet other embodiments, a pair of opposed, first and second journal stubs project respectively from a shroud side of the casing into a first axial end of the impeller hub, and from a hub side of the casing into a second axial end of the impeller hub. One or more magnetic bearings are interposed between the journal and a hollow hub of the impeller. The journal and magnetic bearing support and position the impeller within an impeller cavity of the compressor casing. In this way, the journals, magnetic bearings and the impeller hub interfaces support the impeller rotatively within compressor casing. The impeller is driven rotatively by a driver, to compress a working fluid flowing through the compressor. In some embodiments, a drive shaft that is independent of the journal or journals rotates the impeller. In other embodiments, the impeller is directly driven by a motor whose respective rotor and stator permanent magnets and/or electromagnetic coils are directly embedded within the journal and impeller hub.

[0021] FIG. 1 shows, schematically, a fragmentary view of a compressor 20, having a compressor casing 22. The compressor casing 22 is split vertically into a shroud side 24 and a hub side 26 with a diffuser channel 36. In other embodiments, the casing is split horizontally into upper and lower halves along a casing longitudinal axis 28. An impeller cavity 30 within the casing circumscribes the casing longitudinal axis 28. Process fluid F enters the impeller cavity 30, via an inlet 31, and flows there through, within a path bounded by a shroud surface 32 and a hub surface 34 of the compressor casing 22, and exits via a diffuser 36 (not shown). A journal 40, having an outer surface 42 is disposed within the casing 28. The journal outer surface 42 is concentric with a journal central axis 44 that is congruent with the casing longitudinal axis 28. An impeller 50 is disposed within and circumscribed by the impeller cavity 30. The impeller 50 has a hollow hub 52 that is concentrically aligned with, and configured to rotate about the journal central axis 44. A magnetic bearing 60 is interposed between the journal 40 and the hollow hub 52, for supporting and positioning the impeller 50 within the impeller cavity 30 radially relative to the journal central axis 44. The magnetic bearing has a first portion 62 that is retained within or otherwise coupled to the hub 52 and a second portion 64 that is coupled to the outer surface 42 of the journal 40. As the impeller 50 rotates, supported by the magnetic bearing 60, its impeller blades 54 accelerate the process fluid F through the diffuser 36.

[0022] In FIG. 1, the journal 40 is part of a journal shaft that extends axially through both axial ends of the impeller hub 52 coupled to both the shroud side 24 and the hub side 26 of the compressor casing 22. In the embodiment of FIG. 1, the journal 40 is stationary and does not rotate within the compressor casing 22. In other embodiments, the journal is free to rotate within the compressor casing 22.

[0023] The fragmentary views of FIGs. 2-6 show other impeller-supporting journal, impeller hub, and magnetic bearing embodiments for centrifugal compressors. Impeller rotation and acceleration of process fluid F through these compressor embodiments is functionally equivalent to the compressor 20 of FIG. 1.

[0024] In FIG. 2, the compressor 70 has a compressor casing 72 with shroud side 74 of the casing defining a casing longitudinal axis 76 and an impeller cavity 78. A journal stub 80 has a first end 82 that is coupled to the shroud side 74 of the casing 72, and a second end 84 projecting away from the shroud side in cantilever-like fashion, and an outer surface 86. The impeller 88 has an impeller hub 90. A shroud-side axial end 92 of the inner annular surface of the impeller hub 90 receives the second end 84 of the journal stub 80. In some embodiments, the journal stub 80 projects through both axial ends of the impeller hub 90 (not shown). A magnetic bearing 94 is interposed between the inner annular surface of the impeller hub 90 hub and the outer surface 86 of the journal stub 80.

[0025] In FIG. 3, the compressor 100 has a compressor casing 102 with hub side 104 of the casing defining a casing longitudinal axis 108 and an impeller cavity 110. A journal stub 112 has a first end 114 that is coupled to the hub side 104 of the casing 102, and a second end 116 projecting away from the hub side in cantilever-like fashion, and an outer surface 118. The impeller 120 has an impeller hub 122. A hub- side axial end 124 of the inner annular surface of the impeller hub 122 receives the second end 116 of the journal stub 112. In some embodiments, the journal stub 112 projects through both axial ends of the impeller hub 122 (not shown). A magnetic bearing 126 is interposed between the inner annular surface of the impeller hub 122 hub and the outer surface 118 of the journal stub 112. [0026] The compressor 130 of FIG. 4 has a compressor casing 132, with a shroud side 134, a hub side 136, and a casing longitudinal axis 138. An impeller cavity 140 within the casing 132 circumscribes the casing longitudinal axis 138. The compressor 130 has a pair of opposed, mutually spaced, concentrically aligned first 142 and second 146 journal stubs. The first journal stub 142 has a first end 143 coupled to the shroud side 134 of the casing 132; it defines a first hollow cavity 144 and a distal end 145. The second journal stub 146 has a first end 147 coupled to the hub side 136 of the casing 132; it defines a and second hollow cavity 148 and a distal end 149. The impeller 156 has an impeller hub 158 that straddles the opposed, respective distal ends 145 and 149 of the first 142 and second 146 journal stubs. A first magnetic bearing 160 is interposed between the inner annular surface of the impeller hub 158 on its shroud end 164 and the first journal stub 142. A second magnetic bearing 162 is interposed between the inner annular surface of the hub 158 on its hub end 166 and the second journal stub 146. The impeller 156 is supported by, and rotates about, the respective first 142 and second 146 journal stubs and the respective first 160 and second 162 magnetic bearings.

[0027] The impeller-supporting journal, impeller hub, and magnetic bearing embodiments for centrifugal compressors support and align the rotating impeller radially and/or axially relative to the journal central axis, but they do not impart driving torque on the impeller. Thus, the impellers are driven by drive systems that are independent from the journal/impeller hub/magnetic bearing interface. In FIG. 4, a drive shaft 150 and a driver 151 (e.g., an electric motor or a gas turbine engine) are coupled to and rotate the impeller 156 independent of the first 142 and second 146 stationary journal stubs. The drive shaft 150 passes through the respective first 144 and second 148 hollow cavities of the first 142 and second 146 stationary journal stubs, where it mates to the impeller hub 158 via a flanged, drive shaft coupling 152. In FIG. 5, a multi-stage compressor 170 is driven by a drive shaft 186 and a driver 188 (e.g., an electric motor or a gas turbine engine) that are coupled to and rotate an impeller stack 176, independent of the stationary journal shaft 174. [0028] Describing further the multi-stage compressor 170 of FIG. 5, a compressor casing 172, or a plurality of coupled compressor casings that are axially aligned, retains a journal shaft 174 that extends axially through and projecting from both ends of an impeller stack 176. This journal shaft 174 and impeller stack 176 construction is similar to the single-stage compressor 20 construction of FIG. 1. Each of the respective impellers 176A-C in the impeller stack 176 is circumscribed by its own impeller cavity (not shown). One or more impeller cavities are defined in a common compressor casing, or distributed among separate, coupled compressor casings. Each of the respective impellers 176A-C incorporates a respective impeller hub 178A-C. Respective magnetic bearings 180A-C are interposed between the stationary journal shaft 174 and its respective hollow impeller hub 178A-C, for supporting and positioning the plurality of impellers within the impeller cavity of the compressor casing 172, radially relative to the journal central axis 185.

[0029] In FIG. 5, One or more tie rods 182 rigidly couple the impeller hubs 178A-C axially and radially relative to each other, to form the unitized impeller stack 176. In this embodiment, a plurality of tie rods 182 is circumferentially spaced about the respective impeller hubs 178A-C. One of the axial ends of the tie rods 182 are coupled to a tie rod flange 184, which is in turn, coupled to the drive shaft 186 and the drive 188. A central axis 190 of the drive shaft 186 is congruent with the journal central axis 185, but in other embodiments, those respective axes are not congruent— for example, when a gearbox is interposed between the tie rod flange 184 and the drive 188. While three impellers are shown in FIG. 5, other embodiments of multi- stage compressors comprise two or more than three impellers. The multi-stage compressor 170 has a journal shaft 174 that passes through both axial ends of the impeller stack 176 and projects axially there from; both projecting axial ends of the journal shaft 174 are coupled to the compressor casing 172. In other embodiments, the journal shaft 174 is replaced by a journal stub, similar to any of the journal stubs 80, 112, 142, 146 of FIGs. 2-4.

[0030] Various compressor embodiments of FIGs. 1-5 incorporate magnetic bearings 60, 94, 126, 160, 162, and 180A-C. As was previously described, the bearing 60 of FIG. 1 has a first portion 62 coupled to the impeller hub 52 and an opposed, second portion 64 coupled to the journal 40. A repulsive magnetic field generated between the first 62 and second 64 portions of the magnetic bearing 60 orients the impeller hub 52 in the impeller cavity 30 in a single radial and/or axial position, relative to the journal central axis 44 and the congruently aligned, casing longitudinal axis 28. In various embodiments, the repulsive magnetic field is generated in the magnetic bearing 60 by pairs of permanent magnets, or pairs of electromagnets, or a pairing of an electromagnet and a permanent magnet. Various compressor embodiments of FIGs. also 2-5 incorporate magnetic bearings 94, 126, 160, 162, and 180A-C, which have first and second portions that generate respective, repulsive magnetic fields.

[0031] In the fragmentary view of FIG. 6, the compressor 200 has a compressor casing 202, with a shroud side casing 204 and a hub side casing 206 that collectively define a casing longitudinal axis 208. Journal shaft 210 has an outer surface 212 and an annular recess 214. A centrifugal impeller 220, with an impeller hub 222 circumscribes the journal shaft 210. The impeller hub 222 defines an internal annular recess 224. A magnetic bearing 230 is interposed between the journal shaft 210 and the impeller hub 222, for orienting the impeller hub in a single axial position, relative to the journal central axis 208 and the congruently aligned, casing longitudinal axis 208. More specifically, a first portion 232 of the magnetic bearing 230 is retained within the annular recess 224 of the impeller hub 222 and a second portion 234 of the magnetic bearing is retained within the annular recess 214 of the journal shaft 210. The first portion 232 of the magnetic bearing is a permanent magnet. The second portion 234 of the magnetic bearing is an electromagnet whose conductive coils (not shown) are within the annular recess 214. Coil leads 236 and 238 feed current from a power source 240. Controller 242 regulates power supplied to the coils in the second portion 234 of magnetic bearing 230; this selectively varies the repulsive magnetic field generated between the first 232 and second 234 portions of the magnetic bearing. The electromagnetic bearing power source 240 and the controller 242 are of known construction. The controller 242 incorporates a processor 244 accesses and executes a non-transient instruction set, resident in software modules that are stored in a non volatile memory device 246. [0032] While reference to an exemplary controller 242 platform architecture and implementation by software modules executed by the processor 244, it is also to be understood that exemplary embodiments of the invention may be implemented in various forms of hardware, software, firmware, special purpose processors, or a combination thereof. Preferably, aspects of the invention embodiments are implemented in software as a program tangibly embodied on the program-storage memory device 246. The program may be uploaded to, and executed by, a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units (CPU), a random access memory (RAM), and input/output (I/O) interface(s). The computer platform also includes an operating system and microinstruction code. The various processes and functions described herein may be either part of the microinstruction code or part of the program (or combination thereof) which is executed via the operating system. In addition, various other peripheral devices may be connected to the computer/controller platform.

[0033] It is to be understood that, because some of the constituent system components and method steps depicted in the accompanying figures are preferably implemented in software, the actual connections between the system components (or the process steps) may differ depending upon the manner in which the exemplary embodiments are programmed. Specifically, any of the computer platforms or devices may be interconnected using any existing or later-discovered networking technology; all may be connected through a larger network system, such as a corporate network, metropolitan network or a global network, such as the Internet.

[0034] In the embodiment of FIG. 7, the shrouded impeller 250 has an impeller hub 252 with an impeller recess 254. A first portion 256 of an electromagnetic bearing, including its electromagnetic coils 258 are embedded in the impeller recess 254. Coil leads 260 and 262 feed current from the power source 240. The controller 242 regulates power supplied to the coils 258. [0035] In the embodiments of FIGs. 8 and 9, conductive coils of electromagnetic bearings are embedded within recesses formed within the journal; some embodiments also have conductive coils embedded within the hub. In some embodiments, conductive coils are embedded in both the journal and the hub, for orienting the impeller hub in the impeller cavity in a desired radial and/or axial position, relative to the journal central axis. In other embodiments, respective conductive coils of the rotor and/or stator of an electric drive motor are embedded in the journal and/or the hub, or within both of them. In both of these respective figures, journal shafts 270 and 310 are shown in fragmentary elevational view. Their respective hubs 290 and 330 and their respective, related structures are shown in dashed line phantom view, but they are substantially similar to those of FIGs. 1-7. Electromagnetic bearings in FIGs. 8 and 9 function as those in the embodiments described in FIGs. 6 and 7.

[0036] In FIG. 8, compressor 268 has a stationary journal shaft 270 that extends axially into both axial ends of an impeller hub 290, similar to the construction shown in FIG. 1. In other embodiments (not shown), the journal extends only into one of the first and/or second axial end of the impeller hub, in cantilever-like fashion, similar to the constructions shown in FIGs. 2-4. In other embodiments, the stationary journal shaft 270 is incorporated into a multi-stage compressor, such as the one shown in FIG. 5. An outer surface 272 of the journal shaft incorporates recesses 274, 276, 278 and 280. Respective conductive coils 282A-C of a first electromagnetic journal bearing is wound about a projecting stub formed between the recesses 274 and 276. Respective coils 284 A-C of a second electromagnetic journal bearing are wound about projecting stub formed between the recesses 278 and 280, axially offset from the coils 282A-C of the first electromagnetic bearing. The hub 290 incorporates coils of a first electromagnetic hub bearing 292 and a second electromagnetic hub bearing 294 in opposed axial and radial relationship, respectively with the corresponding coils 282A- C of the first electromagnetic journal bearing and the corresponding coils 284A-C of the second electromagnetic journal bearing. Electrical energy supplied to the opposing electromagnetic bearing coils (such as by the power source 240 and controller 242 of FIG. 6) generates repulsive electromagnetic forces between them. Repulsive electromagnetic forces FR, generated radially between the opposing journal and hub electromagnetic coils center the hub concentrically with the central axis of the journal 272. Centrifugal compressors generate axial thrust loads that are parallel to the central axis of the journal 272. Known centrifugal compressors often incorporate balancing pistons to generate counter-active axial thrust loads on the impeller shaft, to maintain the impeller in a desired axial orientation within the impeller casing.

[0037] The compressor 308 of FIG. 9 incorporates electromagnetic thrust bearings to support axial loads imparted on its impeller. Journal shaft 310 incorporates opposed orientation, frusto-conical profile, first 314 and second 316 annular surfaces, separated by the cylindrical surface 312. The hub 330 incorporates opposing, female, frusto-conical profile first 334 and second 338 annular surfaces. The electromagnetic coils, similar to those of FIG. 8 are embedded within recesses on the opposing frusto- conical surfaces. When the coils are energized (such as by the power source 240 and controller 242 of FIG. 6), they generate repulsive electromagnetic forces FR in the radial direction and FA in the axial direction. Hence, the bearings in the journal shaft 310 and the hub 330 are also thrust bearings; they eliminate the need for a separate balancing piston assembly. Other embodiments incorporate other profiles of thrust bearing surfaces that generate the electromagnetic repulsive forces FR in the radial direction and FA in the axial direction. Respective conductive coils 326A-C of a first electromagnetic journal bearing is wound about a projecting stub formed between the recesses 318 and 320. Respective coils 328 A-C of a second electromagnetic journal bearing are wound about projecting stub formed between the recesses 322 and 324. The hub 330 incorporates coils of a first electromagnetic hub bearing 332 and a second electromagnetic hub bearing 336 in opposed axial and radial relationship, respectively with the corresponding coils 326A-C of the first electromagnetic journal bearing and the corresponding coils 328A-C of the second electromagnetic journal bearing.

[0038] The compressors 268 and 308 of FIGs. 8 and 9 also respectively incorporate integral electric motors 300 and 340 for driving the compressor impeller, eliminating the need for external drive motors and related driving shafts. The compressor 268 incorporates stator coils 302A-C circumferentially embedded about the journal shaft 270 between the recesses 276 and 278, and a corresponding permanent or electromagnetic rotor 304 embedded in a recess within the hub 290. Similarly, the compressor 308 incorporates stator coils 342A-C circumferentially embedded about the journal shaft 310 between the recesses 320 and 322, and a corresponding permanent or electromagnetic rotor 344 embedded in a recess within the hub 330. The rotor and stator of the respective motors 300 and 340 are configured to generate a magnetic field Fg, for rotating the rotor and its corresponding impeller hub 290, 330. Stator coils 302A-C and 342A-C are selectively energized by a known motor drive and drive control, in order to rotate the respective corresponding hubs 290 and 330.

[0039] An impeller, having a hollow hub, is supported and aligned by interposing a magnetic bearing in the hollow hub, according to methods disclosed herein. The magnetic bearing circumscribes a stationary journal disposed within an impeller cavity of a compressor casing. The stationary journal defines a journal central axis that is congruent with a casing longitudinal axis, with both axes circumscribed by the impeller cavity. At least one electromagnet of the magnetic bearing is energized with a power source; this generates a repulsive magnetic field in the bearing that radially and/or axially positions the journal and hub relative to each other along the journal central axis. When practicing this method, the impeller and the stationary journal are selectively aligned relative to each other by varying energization of the electromagnet with the power source. In some method embodiments, coils of the electromagnet are embedded in the stationary journal. The impeller is driven, rotatively, with a drive shaft coupled thereto, without rotating the stationary journal.

[0040] In other method embodiments, the impeller is rotated with an electric motor having stationary stator coils embedded within the stationary journal, which are axially offset from coils of the electromagnet that are also embedded within the stationary journal. In some embodiments, rotor coils are embedded within the impeller hub, which are axially offset from coils of the electromagnet that are also embedded within the impeller hub. Coils of the electromagnet are energized, to align the impeller hub and the stationary journal relative to each other. In other embodiments, which incorporate integral drive motors in the impeller and the journal, with embedded electromagnetic coils, the impeller is driven by energizing the rotor and stator coils.

[0041] Although various embodiments that incorporate the invention have been shown and described in detail herein, others can readily devise many other varied embodiments that still incorporate the claimed invention. The invention is not limited in its application to the exemplary embodiment details of eonstaiction and the arrangement of components set forth in the description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. In addition, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms“mounted”,“connected”,“supported”, and“coupled” and variations thereof are to he interpreted broadly; they encompass direct and indirect mountings, connections, supports, and couplings. Further,“connected” and“coupled” are not restricted to physical, mechanical, or electrical connections or couplings.