WO2012145486A2

WO2012145486A2 - Magnetic bearing system for heavy loaded compressor

Info

Publication number: WO2012145486A2
Application number: PCT/US2012/034212
Authority: WO
Inventors: Pascal Lardy; Jose L. Gilarranz
Original assignee: Dresser Rand Co
Current assignee: Dresser Rand Co
Priority date: 2011-04-20
Filing date: 2012-04-19
Publication date: 2012-10-26
Anticipated expiration: 2013-10-20
Also published as: WO2012145486A3

Abstract

A fluid compression system is disclosed having at least a compressor and a motor (or alternate driver) arranged within a hermetically-sealed housing. The motor rotates a shaft upon which the compressor is disposed, and the shaft is supported within the housing by first and second radial bearings arranged at first and second ends of the shaft, respectively. An intermediate radial bearing is also arranged on the rotatable shaft between the first and second radial bearings. The radial bearings can be active magnetic bearings and controlled by two sets of channels in a bearing control system in order to levitate and control the position of the shaft.

Description

MAGNETIC BEARING SYSTEM FOR HEAVY LOADED COMPRESSOR Background

[0001] This application claims priority to U.S. Patent Application Serial No. 61 /477,518, which was filed April 20, 201 1 . This priority application is hereby incorporated by reference in its entirety into the present application, to the extent that it is not inconsistent with the present application.

[0002] A rotating shaft in a turbomachine, such as a turbo-compressor or turbine, is typically mounted using two radial bearings near the ends of the shaft. Two types of radial bearings that are primarily used are magnetic bearings and oil film bearings. For most turbomachine applications, however, magnetic bearings provide the potential to offer superior performance over oil film bearings, as magnetic bearings provide adequate stiffness, damping, and load capacity, with a reduced power consumption due to reduced viscous and windage losses. Moreover, oil film bearings require lubrication and auxiliary systems such as valves, pumps, filters, coolers, and the like, all of which pose a risk of process contamination.

[0003] Magnetic bearings can be either active or passive. Active magnetic bearings typically include electromagnetic coils surrounding a ferromagnetic shaft, shaft position sensors, and a control system. In response to signals received from the shaft position sensors, the control system adjusts the electrical current supplied to the electromagnetic coils, thereby adjusting a magnetic field that levitates and/or centralizes the ferromagnetic shaft. Passive magnetic bearings, on the other hand, use permanent magnets rather than electromagnets to position and support the shaft and therefore depend heavily on permanent ferromagnetic attraction or repulsion forces. The stiffness and damping of passive magnetic bearings, however, are much less than active magnetic bearings, and they are inherently unstable since it is nearly impossible to stably support a shaft using only passive magnetic bearings. Therefore, in general, active magnetic bearings are usually utilized in addition to the permanent magnet bearings for the axial and radial direction.

[0004] Adequate bearing support for the shaft is crucial to prevent contact between the stationary and rotating components of the turbomachine. Also, appropriate bearing support is required to control the deflection of the shaft throughout the operating speed range of the machine. To increase turbomachine performance, the shaft length can be increased to accommodate more rotating assemblage, such as wheels. However, increasing the shaft length between the radial bearings and adding more wheels places additional strain on the shaft that may result in increased shaft vibration/deflection that potentially damages interior components of the turbomachine.

[0005] Accordingly, there is a need for a magnetic bearing system that provides additional shaft support between the two shaft bearings to provide the capability of implementing more wheels without adversely affecting turbomachine rotordynamics.

Summary

[0006] Embodiments of the disclosure may provide a fluid compression system. In one embodiment, the fluid compression system may include a hermetically-sealed housing, a rotatable shaft having first and second ends and being mounted for rotation within the housing, and a motor arranged within the housing and configured to drive the rotatable shaft. The fluid compression system may further include a compressor arranged within the housing and mounted on the rotatable shaft axially-offset from the motor, and first and second radial bearings positioned proximate the first and second ends of the rotatable shaft, respectively, and configured to support the rotatable shaft and the compressor for rotation. The system may also include an intermediate radial bearing positioned on the rotatable shaft between the first and second radial bearings.

[0007] Embodiments of the disclosure may further provide a method for supporting a rotatable shaft. The method may include positioning the rotatable shaft in a hermetically-sealed housing, the housing having a motor and a compressor positioned therein, wherein the compressor is mounted on the rotatable shaft and the motor is configured to drive the rotatable shaft, and supporting the rotatable shaft proximate a first end with a first radial bearing;. The method may further include supporting the rotatable shaft proximate a second end with a second radial bearing, and supporting the rotatable shaft with an intermediate radial bearing arranged between the first and second radial bearings.

[0008] Embodiments of the disclosure may further provide another exemplary fluid compression system. The exemplary fluid compression system may include a hermetically- sealed housing having a rotatable shaft mounted therein, a motor configured to drive the rotatable shaft, and a compressor arranged within the housing and mounted on the rotatable shaft axially-offset from the motor. The fluid compression system may further include an integrated separator arranged within the housing and axially-spaced from the compressor, and first and second active magnetic bearings arranged at first and second ends, respectively, of the rotatable shaft with the compressor and integrated separator therebetween. The fluid compression system may also include an intermediate active magnetic bearing arranged on the rotatable shaft between the first and second active magnetic bearings, and first and second sets of channels in a bearing control system configured to control the first, second, and intermediate active magnetic bearings.

Brief Description of the Drawings

[0009] The present disclosure is best understood from the following detailed description when read with the accompanying Figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

[0010] Figure 1 illustrates an exemplary fluid compression system, according to one or more embodiments disclosed.

[0011] Figure 2 illustrates another exemplary fluid compression system, according to one or more embodiments disclosed.

[0012] Figure 3 illustrates another exemplary fluid compression system, according to one or more embodiments disclosed.

[0013] Figure 4 illustrates another exemplary fluid compression system, according to one or more embodiments disclosed.

[0014] Figure 5 illustrates another exemplary fluid compression system, according to one or more embodiments disclosed.

[0015] Figure 6 illustrates another exemplary fluid compression system, according to one or more embodiments disclosed.

[0016] Figure 7 illustrates another exemplary fluid compression system, according to one or more embodiments disclosed.

[0017] Figure 8 illustrates another exemplary fluid compression system, according to one or more embodiments disclosed.

[0018] Figure 9 illustrates a flowchart schematic of an exemplary method for supporting a rotatable shaft, according to one or more embodiments disclosed.

Detailed Description

[0019] It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure; however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the various Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the exemplary embodiments presented below may be combined in any combination of ways, i.e. , any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure.

[0020] Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Additionally, in the following discussion and in the claims, the terms "including" and "comprising" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to." All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope. Furthermore, as it is used in the claims or specification, the term "or" is intended to encompass both exclusive and inclusive cases, i.e. , "A or B" is intended to be synonymous with "at least one of A and B," unless otherwise expressly specified herein.

[0021] Figure 1 illustrates an exemplary fluid compression system 100 according to embodiments described herein. The system 100 generally includes a motor 1 02 coupled to a compressor 104 and an integrated separator 1 06 via a rotatable shaft 1 08. In one embodiment, the compressor 1 04 and the integrated separator 106 may be characterized as an integrated separator/compressor assembly, and when the motor 102 operates, it drives both the compressor 104 and the separator 106, generally at the same rotational speed, i.e., without gear reduction between the two components. As will be described in more detail below, however, the integrated separator 1 06 may be omitted from the system 1 00 so that the motor 1 02 drives only the compressor 1 04 during operation. The motor 102 may be an electric motor, but may also be any other type of driver typically used to for rotating compressors, e.g., turbines, engines, etc.

[0022] The motor 102, compressor 104, and integrated separator 106 may each be positioned within a housing 1 10 having a first end, or compressor end 1 1 2, and a second end, or motor end 1 1 4. The housing 1 10 will generally hermetically-seal the motor 1 02, compressor 104, and integrated separator 1 06 (if used) therein, thus providing both support and protection for each component during operation. In at least one embodiment, more than one motor 1 02 may be used to drive the compressor 1 04 and separator 1 06. For example, a second motor (not shown) may be coupled in series with the first motor 1 02, or the second motor may be arranged on the compressor end 1 12 of the housing 1 10 to work in cooperation with the first motor 1 02 and thereby provide more power and torque than could be achieved with the use of a single motor. Such embodiments are shown and described in co-pending application PCT/US1 1 /45270, entitled "Multiple Motor Drivers for a Hermetically-Sealed Motor- Compressor System," filed on July 26, 201 1 , and hereby incorporated by reference in its entirety to the extent these disclosures are consistent with the present disclosure. In yet another embodiment, the motor 1 02 may be arranged outside of the hermetically-sealed housing 1 10, without departing from the scope of the disclosure.

[0023] The shaft 108 may be supported at or proximate each end, respectively, by at least one radial bearing, such as first and second radial bearings 1 16 and 1 1 8 (e.g., the first radial bearing 1 16 supports the first end of the shaft 1 08 and the second radial bearing 1 1 8 supports the second end of the shaft 1 08). The shaft 1 08 is further supported at an intermediate location between the first and second radial bearings 1 1 6, 1 1 8 by at least one intermediate radial bearing 1 20. Each radial bearing 1 16, 1 18, 1 20 may be directly or indirectly supported by the housing 1 1 0 and provide support for the compressor 1 04 and integrated separator 106 as the shaft 108 rotates during system 1 00 operation. In addition, at least one axial thrust bearing 122 may be provided at or near the end of the shaft 1 08 adjacent the compressor end 1 12 of the housing 1 10, and may be configured to bear axial thrusts generated by the compressor 1 04. In one embodiment, the axial thrust bearing 122 may be a magnetic bearing, such as an active magnetic bearing. In other embodiments, however, the axial thrust bearing 1 22 may be a passive magnetic bearing or other type of bearing suitable for rotordynamic damping in high speed turbomachinery.

[0024] The compressor 1 04 may be a multi-stage centrifugal compressor with one or more, in this case three, compressor stage impellers 124 orwheels. However, any number of impellers 1 24 may be implemented or used in the system 1 00 without departing from the scope of the disclosure. The integrated separator 106 may be configured to separate and remove higher- density components from lower-density components contained within a process gas introduced into the system 100. In at least one embodiment, the separator 1 06 may be a rotary drum separator. The higher-density components, i.e., relatively dense gases, liquids, or solids, removed from the process gas are discharged from the system 100, thereby providing a relatively dry process gas to be introduced into the compressor 104. In one embodiment, the separator 1 06 may include a rotatable drum coupled to the shaft 108.

[0025] A balance piston 1 26, including an accompanying balance piston seal (not shown), may be arranged on the shaft 1 08 between the motor 1 02 and the compressor 1 04. Due to the pressure rise developed through the compressor 104, a pressure difference is created such that the compressor 1 04 has a net thrust in the direction of its inlet 128. Arranging the balance piston 1 26 behind the last impeller 124 of the compressor 104 counteracts that force. As can be appreciated, any thrust generated by the compressor 104 that is not absorbed by the balance piston 1 26 may be otherwise absorbed by the thrust bearing(s) 1 22.

[0026] During operation of the system 1 00, the motor 102 drives the shaft 1 08 and simultaneously drives both the compressor 104 and the integrated separator 1 06 (if used). A process gas to be compressed may be introduced into the system 1 00 via the inlet 1 28. The process gas may include, but is not limited to, a mixture of hydrocarbon gas, such as natural gas or methane derived from a production field or via a pressurized pipeline. In other embodiments, the process gas may include air, C0₂, N₂, ethane, propane, i-C , n-C₄, i-C₅, n- C₅, combinations thereof and/or any other process gas(es). In at least one embodiment, especially in subsea oil and gas applications, the process gas may be "wet," having both liquid and gaseous components, or otherwise include a mixture of higher-density and lower-density components. Accordingly, the integrated separator 106 may be configured to receive the process gas via the inlet 1 28 and remove the higher-density components therefrom, thereby generating a substantially dry process gas.

[0027] The compressor 1 04 may be configured to receive the substantially dry process gas from the integrated separator 106 and compress the dry process gas through the successive stages of impellers 124 and thereby produce a compressed process gas. The compressed process gas may then exit the compressor 104 via a process discharge 1 30.

[0028] Returning now to the radial bearings 1 1 6, 1 18, and 120, the present disclosure provides an improved bearing arrangement along the length of the shaft 1 08 that allows the system 100 to increase production by including more stages or impellers 1 24 without adversely affecting shaft 108 rotordynamics. For example, employing the third or intermediate bearing 1 20 between the first and second radial bearings 1 16, 1 18 allows the shaft 108 to be lengthened to accommodate additional impellers 1 24 while simultaneously providing added support and stability to the shaft 1 08, allowing it to have an acceptable rotordynamic behavior. Consequently, the shaft 1 08 may be able to endure higher loads without placing additional strain thereon. As illustrated in Figure 1 , the intermediate bearing 1 20 may be arranged between axially-adjacent impellers 124 of the compressor 104. In other embodiments, however, it is further contemplated herein to place the intermediate bearing 1 20 between the impellers 124 of the compressor 104 and the separator 1 06.

[0029] Each radial bearing 1 16, 1 1 8, and 1 20 may be one of several different types of radial bearings without departing from the scope of the disclosure. For example, the radial bearings 1 16, 1 18, and 1 20 may be magnetic bearings, such as active or passive magnetic bearings, or may be other types of radial bearings, such as roller bearings or oil film bearings. In one embodiment, the first and second radial bearings 1 1 6, 1 18 may be active magnetic bearings controlled either independently by separate channel sets in a bearing control system or jointly by a single set of channels in the bearing control system, and the intermediate bearing 120 may be a passive magnetic bearing or other type of radial bearing besides an active magnetic bearing. In other embodiments, the second and intermediate radial bearings 1 18, 120 may be active magnetic bearings controlled either independently by separate channel sets in a bearing control system or jointly by a single set of channels in the bearing control system, and the first radial bearing may be a passive magnetic bearing or other type of radial bearing besides an active magnetic bearing. It will be appreciated that any combination of radials bearings 1 16, 1 18, 1 20 may be arranged in the system 100 to fit any number of applications without departing from the scope of the disclosure.

[0030] In the embodiment shown in Figure 1 , the first and intermediate radial bearings 1 16, 1 20 may be active magnetic bearings controlled jointly by a first set of channels 1 32 in a bearing control system, and the second radial bearing 1 1 8 may also be an active magnetic bearing but controlled by a second set of channels 1 34 in the bearing control system. It will be appreciated by those skilled in the art that using a reduced number of channels (only two sets 1 32, 134) in the bearing control system to control three active magnetic bearings reduces the amount of electronics required to control the radial bearings 1 16, 1 18, 120, which equates to a cost savings for the system 100.

[0031] Referring now to Figure 2, illustrated is another fluid compression system 200 according to embodiments described herein. The system 200 may be similar in some respects to the system 100 described above and thus may be best understood with reference to Figure 1 , where like numerals designate like components and will not be described again in detail. The system 200 may include an arrangement of bearings 1 16, 1 18, 120 different than that depicted in Figure 1 . For example, the second and intermediate radial bearings 1 18, 120 may be active magnetic bearings controlled jointly by the first set of channels 132 in the bearing control system, and the first radial bearing 1 16 may also be an active magnetic bearing but controlled by the second set of channels 134 in the bearing control system 134.

[0032] Referring to Figures 3 and 4, illustrated are other fluid compression systems 300 and 400, respectively, according to embodiments described herein. The systems 300, 400 may also be similar in some respects to the system 100 described above and therefore may be best understood with reference to Figure 1 where like numerals again designate like components and will not be described again in detail. Similar to the compressor 104 in system 100, the compressor 302 depicted in Figures 3 and 4 may be a centrifugal compressor. However, the compressor 302 may also be characterized as a back-to-back or dual-sided centrifugal compressor and the intermediate bearing 120 may be arranged generally at or near the division wall (not shown) separating the two sides of the compressor 302.

[0033] As with prior described systems 100, 200, the radial bearings 1 16, 1 18, 120 may be any type of radial bearing or arranged in any combination along the shaft 108 without departing from the scope of the disclosure. By way of example, however, Figure 3 depicts the first and intermediate radial bearings 1 1 6, 120 as active magnetic bearings controlled jointly by the first set of channels 132 in the bearing control system, and the second radial bearing 1 18 as an active magnetic bearing controlled by the second set of channels 1 34 in the bearing control system. Moreover, Figure 4 depicts the second and intermediate radial bearings 1 18, 120 as active magnetic bearings controlled jointly by the first set of channels 1 32 in the bearing control system, and the first radial bearing 1 16 as an active magnetic bearing controlled by the second set of channels 134 in the bearing control system. [0034] Referring now to Figures 5 and 6, illustrated are yet other fluid compression systems 500 and 600, respectively, according to embodiments described herein. The systems 500, 600 may also be similar in some respects to the system 100 described above and therefore may again be best understood with reference to the description of Figure 1 where like numerals designate like components and will not be described again in detail. As illustrated, the systems 500 and 600 may omit the integrated separator 106 shown previously in Figures 1 -4, thereby being configured as a more traditional motor-compressor arrangement having only a motor 102 and a compressor 502. Accordingly, the process gas to be compressed may be introduced into the systems 500, 600 via the inlet 1 28 and fed directly into the first impeller 1 24 of the compressor 502 for compression.

[0035] The compressor 502 illustrated in Figures 5 and 6 may be a centrifugal compressor having at least two or more, in this case four, compression stages or impellers 1 24 axially- offset from each other along the shaft 1 08. Again, because of the three-bearing arrangement described herein, the shaft 1 08 may be elongated and more impellers 1 24 may be added to the compressor 502 without departing from the scope of the disclosure and without placing additional strain on the shaft 1 08 that may cause shaft vibration/deformation.

[0036] As with prior described systems 1 00-400, the radial bearings 1 16, 1 18, 120 may each be any type of radial bearing or arranged in any combination along the shaft 1 08 without departing from the scope of the disclosure. By way of example, however, Figure 5 depicts the first and intermediate radial bearings 1 16, 120 as active magnetic bearings controlled jointly by the first set of channels 1 32 in the bearing control system, and the second radial bearing 1 1 8 as an active magnetic bearing controlled by the second set of channels 134 in the bearing control system. Moreover, Figure 6 depicts the second and intermediate radial bearings 1 18, 1 20 as active magnetic bearings controlled jointly by the first set of channels 132 in the bearing control system, and the first radial bearing 1 16 as an active magnetic bearing controlled by the second set of channels 1 34 in the bearing control system.

[0037] Referring to Figures 7 and 8, illustrated are still other fluid compression systems 700 and 800, respectively, according to embodiments described herein. The systems 700, 800 may also be similar in some respects to the system 1 00 described above and best understood with reference to Figure 1 where like numerals once more designate like components and will not be described again in detail. Similar to the compressor 502 shown in systems 500, 600, the compressor 702 depicted in Figures 7 and 8 may be a centrifugal compressor. However, the compressor 702 may also be characterized as a back-to-back or dual-sided centrifugal compressor and the intermediate bearing 1 20 may be arranged generally at or near the division wall (not shown) separating the two sides of the compressor 702.

[0038] As with prior described systems 100-600, the radial bearings 1 16, 1 1 8, 120 may be any type of radial bearing or arranged in any combination along the shaft 108 without departing from the scope of the disclosure. By way of example, however, Figure 7 depicts the first and intermediate radial bearings 1 1 6, 120 as active magnetic bearings controlled jointly by the first set of channels 132 in the bearing control system, and the second radial bearing 1 1 8 as an active magnetic bearing controlled by the second set of channels 1 34 in the bearing control system. Moreover, Figure 8 depicts the second and intermediate radial bearings 1 18, 120 as active magnetic bearings controlled jointly by the first set of channels 1 32 in the bearing control system, and the first radial bearing 1 16 as an active magnetic bearing controlled by the second set of channels 134 in the bearing control system.

[0039] Referring now to Figure 9, illustrated is a flowchart schematic of a method 900 for supporting a rotatable shaft, according to the several embodiments disclosed herein. For example, the method 900 may be descriptive of the systems 1 00-800 described herein. The method 900 may include arranging or otherwise positioning the rotatable shaft within a hermetically-sealed housing, as at 902. The housing may have a motor and a compressor arranged therein and the compressor may be mounted on the rotatable shaft having a plurality of impellers axially-spaced from each other. In at least one embodiment, an integrated separator may also be arranged within the housing and rotatable with the rotatable shaft. In operation, the motor is configured to drive the rotatable shaft, thereby driving the rotation of the impellers and the integrated separator, if used.

[0040] The method 900 further includes supporting the rotatable shaft at a first end with a first radial bearing, as at 904, and supporting the rotatable shaft at a second end with a second radial bearing, as at 906. The shaft can be further supported at a location between the first and second radial bearings with an intermediate radial bearing, as at 908. In one embodiment, the first, second, and intermediate radial bearings can all be active magnetic bearings and can be controlled by one of a first or a second bearing control system. In other embodiments, only one or two of the first, second, or intermediate radial bearings are active magnetic bearings and controlled by either or both of the first and second bearing control systems, while the remaining radial bearing(s) are either passive magnetic bearings or some other type of radial bearing. [0041] The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.

Claims

Claims We claim:

1 . A fluid compression system, comprising:

a hermetically-sealed housing;

a rotatable shaft having first and second ends and being mounted for rotation within the housing;

a motor arranged within the housing and configured to drive the rotatable shaft; a compressor including two or more compressor wheels arranged within the housing and mounted on the rotatable shaft axially-offset from the motor;

first and second radial bearings positioned proximate the first and second ends of the rotatable shaft, respectively, and configured to support the rotatable shaft and the compressor for rotation; and

an intermediate radial bearing positioned on the rotatable shaft between the first and second radial bearings.

2. The system of claim 1 , further comprising a rotating drum separator positioned within the housing on the rotatable shaft and axially-spaced from the compressor.

3. The system of claim 1 , wherein the compressor is a back-to-back compressor having first and second sides separated by a division wall, and the intermediate radial bearing is arranged at or adjacent the division wall.

4. The system of claim 1 , wherein the first and second radial bearings are active magnetic bearings and the intermediate radial bearing is a passive magnetic bearing.

5. The system of claim 4, further comprising a set of channels in a bearing control system to control the first and second radial bearings.

6. The system of claim 4, further comprising a first set of channels in a bearing control system for controlling the first radial bearing and a second set of channels in the bearing control system for controlling the second radial bearing.

7. The system of claim 1 , wherein the second and intermediate radial bearings are active magnetic bearings and the first radial bearing is a passive magnetic bearing.

8. The system of claim 7, further comprising a set of channels in a bearing control system for controlling the second and intermediate radial bearings.

9. The system of claim 7, further comprising a first set of channels in a bearing control system for controlling the second radial bearing and a second set of channels in the bearing control system for controlling the intermediate radial bearing.

1 0. The system of claim 1 , further comprising:

a first set of channels in a bearing control system operatively coupled to one or more of the first, second, and intermediate radial bearings; and

a second set of channels in the bearing control system operatively coupled to one or more of the first, second, and intermediate radial bearings, wherein the first, second, and intermediate radial bearings are all active magnetic bearings.

1 1 . The system of claim 10, wherein the first and intermediate radial bearings are controlled by the first set of channels in the bearing control system and the second radial bearing is controlled by the second set of channels in the bearing control system.

1 2. The system of claim 10, wherein the second and intermediate radial bearings are controlled by the first set of channels in the bearing control system and the first radial bearing is controlled by the second set of channels in the bearing control system.

1 3. A method for supporting a rotatable shaft, comprising:

positioning the rotatable shaft in a hermetically-sealed housing, the housing having a motor and a compressor positioned therein, wherein the compressor includes two or more compressor wheels mounted on the rotatable shaft and the motor is configured to drive the rotatable shaft;

supporting the rotatable shaft proximate a first end with a first radial bearing;

supporting the rotatable shaft proximate a second end with a second radial bearing; and supporting the rotatable shaft with an intermediate radial bearing arranged between the first and second radial bearings.

1 4. The method of claim 13, wherein the first and second radial bearings are active magnetic bearings and the intermediate radial bearing is a passive magnetic bearing, the method further comprising controlling the first and second radial bearings with a common set of channels in a bearing control system.

1 5. The method of claim 13, wherein the second and intermediate radial bearings are active magnetic bearings and the first radial bearing is a passive magnetic bearing, the method further comprising controlling the second and intermediate radial bearings with a common set of channels in a bearing control system.

1 6. The method of claim 13, wherein the first, second, and intermediate radial bearings are active magnetic bearings, the method further comprising:

controlling the first and intermediate radial bearings with a first set of channels in a bearing control system; and

controlling the second radial bearing with a second set of channels in the bearing control system.

1 7. The method of claim 13, wherein the first, second, and intermediate radial bearings are active magnetic bearings, the method further comprising:

controlling the second and intermediate radial bearings with a first set of channels in a bearing control system; and

controlling the first radial bearing with a second set of channels in the bearing control system.

1 8. A fluid compression system, comprising:

a hermetically-sealed housing having a rotatable shaft mounted therein;

a motor configured to drive the rotatable shaft;

a compressor including two or more compressor wheels arranged within the housing and mounted on the rotatable shaft axially-offset from the motor; an integrated separator arranged within the housing and axially-spaced from the compressor;

first and second active magnetic bearings arranged at first and second ends, respectively, of the rotatable shaft with the compressor and integrated separator

therebetween;

an intermediate active magnetic bearing arranged on the rotatable shaft between the first and second active magnetic bearings; and

first and second sets of channels in a bearing control system configured to control the first, second, and intermediate active magnetic bearings.

1 9. The system of claim 18, wherein the first and intermediate active magnetic bearings are controlled by the first set of channels in the bearing control system and the second active magnetic bearing is controlled by the second set of channels in the bearing control system.

20. The system of claim 18, wherein the second and intermediate active magnetic bearings are controlled by the first set of channels in the bearing control system and the first active magnetic bearing is controlled by the second set of channels in the bearing control system.