GB2453313A

GB2453313A - Compressor bearing arrangement

Info

Publication number: GB2453313A
Application number: GB0715336A
Authority: GB
Inventors: Richard R Shultz
Original assignee: Waukesha Bearings Ltd
Current assignee: Waukesha Bearings Ltd
Priority date: 2007-08-04
Filing date: 2007-08-04
Publication date: 2009-04-08
Anticipated expiration: 2027-08-04
Also published as: GB2453313B; GB0715336D0

Abstract

A motorized compressor comprises a compressor component 20, and a drive component 10, 11 coupled together with a unitary, one-piece transmission component 10A, preferably a drive shaft. The drive component 10, 11 is typically a hydraulically, electrically or pneumatically driven motor, which, by means of said transmission component 10A, rotationally drives the compressor component 20. All the components are integrated within a common pressure housing which includes an entry port and exit port by means of which the fluid to be compressed enters and exits said housing. The compressor is characterized in that the compressor component 20, drive component 10, 11 and said transmission component 10A are rotatably mounted in three magnetic bearings 2, 6, a pair of said bearings 6 being disposed at remote ends of said transmission component 10A, and a third bearing 2 being disposed between said drive component 10, 11 and said compressor 20 component, the stator 14 of the third bearing 2 being split so as to enable easier assembly of the compressor unit. A pair of auxiliary bearings 9 may be provided at each end of the shaft 10A, and a there may be provided a single primary thrust bearing 8.

Description

1 2453313 Motor Compressor This invention relates to a motorized compressor, and in particular a compressor driven by an electric, pneumatic, hydraulic or other motor and which is adapted for the compression of fluids, particularly but not exclusively natural gas.

BACKGROUND

Centrifugal compressors are used to increase the pressure of gas streams. Natural gas compression is a typical application for these types of machines, either boosting the flow pressure along a pipeline or boosting pressure at a natural gas well head. The high-speed centrifugal compressors are typically driven by either gas turbines or electric motors. For natural gas applications gas turbines are used in the majority of the applications to drive the compressor. In recent years electric motor drives have increased in popularity and at the current time, it is expected that this trend will continue into the future.

The majority of gas turbines, motors, and compressors in service in the world today utilize fluid film lubricated bearings for rotating shaft support. In recent years magnetic bearings have replaced fluid film bearings in many applications, especially in electric motor drives and compressors. The most successful rotating machines employing such bearings are of a bespoke design which encompasses the various working and physical characteristics of the bearing to be used in the device. Initially, it was considered that magnetic bearings might be retro-fitted within an established rotating machine configuration that was originally designed with and for fluid film bearings, but this approach has been shown to produce unsatisfactory results. Accordingly, the more contemporary thinking is that unique rotating machine design characteristics may leverage the benefits of magnetic bearings, and increase the reliability and performance of the machine as a whole.

The conventional electric motor/compressor machine is essentially comprised of two segregated machines, the electric motor (and the associated drive produced thereby) being the first, with the compressor being second and connected to the first machine by means of a coupling. This configuration of two separate machines contained in separate housings connected with a coupling is known as a standalone configuration. The compressors in the standalone configuration require seals to segregate the high pressure gas within the compressor casing from the fluid film bearings and the outside world. To accomplish this segregation function, the majority of compressors use a device called a dry gas seal for this high pressure seal requirement. The dry gas seal is a very large reliability improvement compared to the former oil type seals that they replaced, but the dry gas seal remains as one of the least reliable components of standalone compressor systems.

In terms of most relevant known prior art, W097/1 3986 discloses a rotodynamic machine for conveying a fluid, like a turbo-machine or a centrifugal pump, with at least one drive and bearing device in the form of an electric motor with a stator and a magnetic-bearing rotor, in which the windings generating the torque and the magnetic bearing force are arranged together in the stator, the rotor forms a section of the shaft of the turbo-machine and there is a control device controlling one of the two windings, in such a way that a magnetic bearing force acting on the rotor can be generated by the first winding in order contactlessly to hold the shaft radially and a torque acting on the rotor can be generated by the second winding.

EP1074746 discloses a turbocompressor having an electric motor, a multistage radial turbocompressor and a common shaft, part of which forms the rotor of the electric motor and another the rotor of the radial turbocompressor. A housing consists of several sub-housings rigidly connected together, with the electric motor and radial turbocompressor each mounted in a separate sub-housing. The rotors can be connected to a common shaft via coupling between the rotor of the electric motor and the compressor wheel.

Accordingly, it is an object of this invention to provide a more reliable, effective and inexpensive standalone motor compressor configuration.

It is a further object of this invention to provide a motorized compressor which incorporates magnetic bearings.

SUMMARY OF THE INVENTION

According to the present invention there is provided a motorized compressor comprising a compressor component, and a drive component coupled together with a unitary, one-piece transmission component, said drive component being typically a hydraulically, electrically or pneumatically driven motor, which, by means of said transmission component, rotationally drives the compressor component, said components being integrated within a common pressure housing which includes an entry port and exit port by means of which the fluid to be compressed enters and exits said housing, Characterized in that said compressor component, drive component and said transmission component are rotatingly mounted in three magnetic bearings, first and second bearings being disposed remotely from one another around said transmission component, and a third bearing being disposed between said drive component and said compressor component and intermediate said first and second bearings, and further characterized in that the stator of the third bearing is split.

By usplitn is meant that the stator of the third bearing is circumferentially discontinuous, consisting of at least two separate parts, which may be hingedly connected to one another, such that the bearing can be easily fitted around the transmission component in a desired location without needing to be slid over one or other end of said transmission component. For instance, without the split stator for the mid-span bearing, assembly of the machine is a whole machine is either wholly impractical or impossible, because a conventional bearing with circumferentially continuous stator would not fit over the compressor impeller wheels, which may be integrally formed with the transmission component.

In a preferred arrangement, the drive component is an electric motor having a stator, and said transmission component is a shaft, one portion of which is disposed within said motor and acts as rotor therein, another remote portion of said shaft additionally providing a mounting for said compressor component.

In a most preferred arrangement, said shaft is provided with at least four rotor portions, one each for each of said magnetic bearings, and one for said electric motor.

In a further preferred embodiment, a pair of auxiliary bearings is provided at either end of said shaft.

In a yet further preferred embodiment, the compressor includes only one primary thrust bearing against which axial shaft forces can react.

Magnetic bearings have fewer physical limitations that fluid film bearings, such as the need for effective sealing, and as such are therefore more suitable for use in the pressurized or compressed gas environments. For example, the combination of placing the electric drive motor, compressor and the magnetic bearings within a common pressure housing allows elimination of all the dry gas seals. This design, including the hermetically sealed motor compressor, increases the reliability of the overall motor compressor because it eliminates the dry gas seals, and it also has the advantage of eliminating even the small amount of leakage of gas to the environment that the dry gas seals allow. The increased reliability and improved environmental impact due to the lack of process gas leakage provides the hermetically sealed motor compressor designs distinct competitive advantages over the standalone configuration.

The new design for a hermitically sealed motor compressor also takes advantage of some of the technological possibilities of magnetic bearings to make a simpler and more robust motor compressor design. In this new design, the motor and compressor are built onto a common one-piece shaft. The design uses three radial magnetic bearings and one axial magnetic bearing. Three bearings can be used with the one piece shaft if the middle bearing stator is split. The split bearing provides significant cost advantage compared to a split shaft design.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic drawing of a hermetically sealed motor compressor machine, according to the present invention, and Figures 2A, B, C -5A, B, C show various stages in the assembly of a hermitically sealed motor compressor.

Figure 1 shows a integrated, common pressure machine compressor indicated generally at 20 having a rotor and stator identified at 10 and 11 respectively.

Within a housing of the machine indicated at 15, radial magnetic bearings consisting of rotor sleeves 1, 6, and stators 2, 5 respectively are provided to lend support to the rotor 10. or more particularly a shaft IOA which passes through or forms an integral part of said rotor 10, and add itionally axial bearings 7 and 8 are provided at one end of the housing; auxiliary bearings are indicated by reference 9, and the cooperating compressor parts, e.g. impellers and cavities, are identified generally at 3 and 4.

A motor stator 11, 12 is provided which surrounds the shaft rotor 10, and the housing is closed by means of pressure containment cap 13 and a cover 17. Additionally, the compressor component is provided with a pressure containment barrel housing 15 and a compressor end cap housing 16. A ring housing 14 covers the stator 1 of the centrally disposed magnetic bearing 1, 2.

Figure 2 shows the first stages of assembling the new type hermitically sealed motor compressor. Typically the motor rotor elements would be added to the shaft 1 OA first.

Before the compressor impellers 3 are put into place, the rotor sleeve 2 of the mid-span magnetic bearing is installed. This rotor sleeve can be of sufficient diameter to fit over a feasible compressor shaft diameter with the compressor impellers not yet fitted. The compressor impellers 3 can then be installed on the shaft. The completed rotor is inserted into the motor stator 11, 12, and the motor end radial magnetic bearing stator 5, the motor end radial auxiliary bearing 9, and pressure containment cap 13 and over housings 17 are inserted into the motor barrel housing 12.

Figure 3 shows the progression of assembly with the upper and lower split halves of the mid-span magnetic bearing stator sections IA, lB assembled into place. A ring housing 14 is then fitted over the stator halves.

Figures 4 and 5 show the further progression of assembly, with the diffuser elements of the compressor 4, which are also typically split, assembled around the compressor impellers. The compressor pressure containment barrel housing 15 is then installed.

The compressor end radial magnetic bearing stator 5 and axial magnetic bearings stator 7 are installed into the barrel housing. The axial magnetic bearing collar 8 is mounted on the shaft. The axial magnetic bearing outboard stator 7 and compressor end auxiliary bearing stator 9 are mounted on the compressor end cap housing 16 and this housing is installed in the end of the barrel housing. The compressor housing end cover 17 provides pressure containment and removal of this cover enables access to the auxiliary bearing.

The new design has the added feature of only using two radial auxiliary bearings. For the mid-span location, there is only a radial magnetic bearing, and in some cases, a mid-span bumper. With auxiliary bearings only at the ends of the machine, the maintenance process to replace the auxiliary bearings is greatly facilitated.

One of the important design elements of the hermetically sealed motor compressor units is the overall design arrangement of the motor, the compressor, and the magnetic bearings. The typical standalone (prior art) motor or compressor machines have two radial bearings and one thrust bearing to support the rotor of each component, such rotors generally being mechanically coupled together. Accordingly, the total bearing requirement is four radial bearings and two thrust bearings.

Alternatively, existing hermetically sealed motor compressors may have a typical design feature of an axially rigid coupling between the motor and compressor that allows elimination of one thrust bearing from the assembly. The axially stiff coupling allows thrust loads from either component part of the machine, that is, the motor or the compressor, to be reacted by the single thrust bearing.

In the present invention however, three primary radial magnetic bearings are employed and disposed around opposite, or remote portions of a unitary, one-pIece shaft, a portion of which acts as rotor within an electric motor, and a further portion of which provides mounting support for the compressor impeller vanes. Importantly, the middle magnetic bearing employs a split stator to allow simpler assembly of the turbocompressor unit as a whole.

In summary therefore, a motorized compressor is disclosed comprising a compressor component, and a drive component coupled together with a unitary, one-piece transmission component. The drive component is typically a hydraulically, electrically or pneumatically driven motor, which, by means of said transmission component, rotationally drives the compressor component. All the components are ideally integrated within a common pressure housing which includes an entry port and exit port by means of which the fluid to be compressed enters and exits said housing. The compressor is characterized in that the compressor component, drive component and said transmission component are rotatingly mounted in three magnetic bearings, a pair of said bearings being disposed at remote ends of said transmission component, and a further bearing being disposed between said drive component and said compressor component. Most preferably, the stator of the further bearing is axially split so as to enable easier assembly of the compressor unit.

Claims

CLAIMS: 1. A motorized compressor comprising a compressor component, and a drive component coupled together with a unitary, one-piece transmission component, said drive component being typically a hydraulically, electrically or pneumatically driven motor, which, by means of said transmission component, rotationally drives the compressor component, said components being integrated within a common pressure housing which includes an entry port and exit port by means of which the fluid to be compressed enters and exits said housing, Characterized in that said compressor component, drive component and said transmission component are rotatingly mounted in three magnetic bearings, a first pair of said bearings being disposed at remote ends of said transmission component, and a third bearing being disposed between said drive component and said compressor component, and further characterized in that the stator of the third bearing is split.
2. A compressor according to claim 1 wherein the drive component is an electric motor having a stator, and said transmission component is a shaft, one portion of which is disposed within said motor and acts as rotor therein, another remote portion of said shaft additionally providing a mounting for said compressor component.
3. A compressor according to claim 2 wherein said shaft is provided with at least four rotor portions, one each for each of said magnetic bearings, and one for said electric motor.
4. A compressor according to any preceding claim wherein a pair of auxiliary bearings is provided at either end of said shaft.
5. A compressor according to any preceding claim wherein the compressor includes only one primary thrust bearing against which axial shaft forces can react.