LUBRICATION-FREE CENTRIFUGAL COMPRESSOR

Abstract

A gas compression compact device comprised of: a) one or more centrifugal compressors; and b) a high speed axial flow permanent magnet synchronous electric motor. The electric motor and the compressor are directly coupled on a single axis and supported by passive magnetic and electrodynamic bearings, free of lubrication. The equipment does not use mechanic seals since the rotor is placed inside the pressure containment of the gas. The equipment does not require auxiliary systems for cooling, filtration, separation or feeding of lubricant fluids.

Claims

1. A compact gas compressing device comprising a rotating motor-impeller assembly formed by one or more centrifugal compressor impellers (1) and an electric motor (2), in which the one or more compressor impellers are coupled directly and on a single axis (5) to the electric motor (2), wherein said electric motor (2) is a synchronous, axial flow and permanent magnet motor.

2. The compact gas compression device in accordance with claim 1, wherein the axis (5) of the rotating motor-impeller assembly is supported by two or more magnetic radial bearings (6, 7) to fix the radial position of the axis (5), and one or more passive electrodynamic thrust bearings (8, 9) to fix the axial position of the axis, and wherein the magnetic radial bearings (6, 7) and the one or more electrodynamic thrust bearings (8, 9) operate totally free of lubricants and of auxiliary control systems.

3. The compact gas compression device in accordance with claim 1, wherein each one of said one or more electric motors (2) are formed by one or more stator assemblies (4) located between one or more rotating assemblies (3) which are fixed to the axis (5); and wherein the stator assemblies (4) contain one or more coils (10) and the rotating assemblies (3) contain one or more pairs of permanent magnets (12).

4. The compact gas compression device in accordance with claim 4, wherein the one or more stator assemblies (4) further comprise part of the ferromagnetic core (11).

5. The compact gas compression device in accordance with claim 3, wherein some of the one or more rotating assemblies (3) have ferromagnetic cores (11).

6. The compact gas compression device in accordance with claim 3, wherein said one or more coils receive current pulses activated by a control electronic device (19) which monitors the position of magnets (12),

7. The compact gas compression device in accordance with claim 3, wherein said control device (19) comprises semiconductors of the group including, among others: mosfet, IGBT, SSR.

8. The compact gas compression device in accordance with claim 2, wherein each one of the magnetic radial bearings (6, 7) is formed by a rotating section comprising one or more permanent magnets with ring geometry fixed to the axis (5) and a stator section also formed by one or more permanent magnets with ring or cylinder geometry and that circumferentially surround the rotating section; and wherein both sections are separated by an elastic force of magnetic repulsion.

9. The compact gas compression device in accordance with claim 2, wherein each one of said electrodynamic thrust bearings (8, 9) is formed by a rotating section fixed to the axis (5) and formed by two or more discs (8) that contain permanent magnets and ferromagnetic cores; and a static section fixed to the housing of the device and formed by a solid or perforated conducting disc (9) which is located between both rotating discs (8) and which comprises the conducting material; and wherein the relative movement between the rotating discs (8) and said conducting material induces electrical currents that generate repulsion forces against said magnets.

10. The compact gas compression device in accordance with claim 2, wherein each one of said electrodynamic thrust bearings is formed by a static section fixed to housing of the device and formed by two or more discs that contain permanent magnets and ferromagnetic cores; and a rotating section fixed to the rotating axis of the device and formed by a solid or perforated conducting disc placed between said static discs and comprising conducting material; and wherein the relative movement between static discs and said conducting material induces electric currents thereon that generate repulsion forces against said magnets.

11. The compact gas compression device in accordance with claim 1 or 2, wherein said rotating motor-impeller assembly, said magnetic radial bearings (6, 7) and said electrodynamic thrust bearings (9, 10) are placed inside the pressure containment of process gas (16), in a totally water tight container which is free of mechanical seals.

12. The compact gas compression device in accordance with claim 1 or 2, wherein the same process gas is used as a coolant for said electric motor (2) and said magnetic radial bearings (6, 7) and said electrodynamic thrust bearings (8, 9).

13. The compact gas compression device in accordance with claim 1, wherein the same process gas is used as a coolant for the power electronics (19) driving the electric motor.

14. The compact gas compression device in accordance with claim 1, wherein the device is free of auxiliary systems for cooling, filtration, separation or feeding of any kind of lubricants.

15. The compact gas compression device in accordance with claim 1, wherein the device comprises a compressor impeller (1) and an electric motor (2).

16. The compact gas compression device in accordance with claim 1, wherein the device comprises two or more compressor impellers (1) and one electric motor (2).

17. The compact gas compression device in accordance with claim 2, wherein the motor-impeller rotating assembly is mounted on an axis (5) supported by two magnetic radial bearings (6, 7) and a passive electrodynamic thrust bearing (9, 10).

18. The compact gas compression device in accordance with claim 2, wherein the motor-impeller rotating assembly is mounted on an axis (5) supported by two magnetic radial bearings (6, 7) and two or more passive electrodynamic thrust bearings (9, 10).

19. The compact gas compression device in accordance with claim 2, wherein the motor-impeller rotating assembly is mounted on an axis (5) supported by more than two magnetic radial bearings (6, 7) and two or more passive electrodynamic thrust bearings (9, 10).

Description

BRIEF DESCRIPTION OF FIGURES

[0024] FIG. 1 is a side view of an embodiment of the invention which shows only the motor-impeller rotating assembly and the stator coils of the motor.

[0025] FIG. 2a is a cross-sectional side view of the main components of the axial flow motor.

[0026] FIG. 2b is an exploded perspective view of the main components of the axial flow motor.

[0027] FIG. 3 is a cross-sectional view of an embodiment of the invention including all the components of the device.

[0028] FIG. 4 is a full perspective view of an embodiment of the device and two orthogonal views of same, being the latter compared to the silhouette of an average adult for dimensional reference.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention is a compact device for gas compression driven by an axial flow synchronous electric motor with no use of any kind of lubricants.

[0030] FIG. 1 shows the single mobile piece of the motor-impeller rotating assembly (hereinafter, the rotor). Said rotor has a centrifugal impeller 1 in charge of delivering kinetic energy to the process gas. In the embodiment of FIG. 1 only one impeller is shown but more than one may be used. Said impeller is mounted on an axis 5 and fixed thereto. If more than one impeller is used, all of them may be mounted on and fixed to the same axis.

[0031] An axial flow synchronous and permanent magnet electric motor 2 is formed by a stationary stator section and a rotating section. The stator section of said motor contains the coils, different auxiliary pieces for support and may optionally contain part of the ferromagnetic core. This section may be formed by one or more assemblies located between assemblies of a rotating section. In the embodiment of FIG. 1, two stator assemblies 4 are shown located between rotating assemblies 03. In other embodiments this could be applied to more than two stator assemblies or only one may be used.

[0032] FIGS. 2a and 2b show an embodiment of the axial electric motor in which it is comprised of a single stator assembly 4. Said assembly contains coils 10 and different portions of the ferromagnetic core 11. The assembly 4 is placed between two rotating disks 3 that contain the permanent magnets 12 and may optionally contain another part of the ferromagnetic core 13. These discs form the rotating section 3 of the axial flow motor. Said rotating section is mounted onto the axis 5 (see FIG. 1) and fixed thereto.

[0033] The magnetic flow is established between each opposing pair of permanent magnets 12, which are placed in an attraction configuration. Said magnetic flow passes through the coils through air or any other means in which the motor is immersed. If the stator assembly contains portions of ferromagnetic core 11, the magnetic flow is concentrated through these. If a rotor assembly 3 has a ferromagnetic core 13, the flow between opposite faces of its adjacent magnets is closed therethrough. An external electronic device monitors the relative position of magnets 12 as regards the coils 10 and activates a series of semiconductors (for example: mosfet, IGBT, SSR, etc.) that inject current to the latter. The moment and the duration of current pulses is such that their interaction with the magnetic field induces a force over the permanent magnets resulting in a torque applied onto the axis 5 (see FIG. 1). The stator section of the motor 04 may contain one or more coils 10 either electrically independent or linked to each other.

[0034] In FIG. 1 it may be seen that the rotating section of a first magnetic radial bearing 6 is formed by one or more permanent magnets with ring geometry and is mounted on one end or near to an end of the axis 5. The rotating section of a second magnetic radial bearing 7 is formed by one or more magnets with ring geometry and is mounted on one the opposite end or near to the end opposite end of the axis 5. Said rotating sections of radial bearings are part of the rotor. For each bearing, a second stator section is formed by permanent magnets with ring or cylinder geometry that circumferentially surround the rotating sections and are fixed to the housing (not shown). Being the magnets of the same polarity and great field intensity, by means of the magnetic interaction between each rotating section and its stator counterpart, magnetic repulsion forces are developed that allow radially supporting the rotor avoiding its mechanical contact with the rest of the device. In the embodiment of FIG. 1 two magnetic radial bearings are shown, one at each end, but three or more bearings could be mounted on different zones of the axis 5 in order to make the rotor support more rigid. Radial bearings 6 and 7 are passive and operate with no intervention of control systems, sensors or external energy sources. The materials for the manufacturing of magnetic bearings based on high intensity passive magnets such as AlNiCo, SmCo, or NdFeB are well known in the art and are available in the market.

[0035] The concept in mechanics of rigidity refers to the capacity of an object to resist a deformation or displacement due to external forces. The more rigid the object, the higher force it generates against the same degree of deformation. This concept, typically applied to elastic systems such as springs and bearings, is also frequently used to describe the mechanical properties of active and passive magnetic bearings. When the forces due to the rigidity of the above mentioned object are such that they tend to compensate the deformation or the displacement that origins them, it is said to have negative rigidity. In the case of magnetic bearings, positive rigidity refers to a particular behavior of these in which the forces originated by a displacement tend to increase it, instead of being opposite. It is useful to note the concept of positive rigidity since this will be used below to explain the functioning of some elements of this invention.

[0036] The rotor assembly shown in FIG. 1 is supported and stabilized by the passive radial bearings since they give negative rigidity in the radial direction. That is, if axis 5 is displaced laterally (radially), said bearings react by generating an opposite elastic force returning the axis to its central position. However, as stated by the Earnshaw Theorem, this type of bearing gives positive rigidity in the axial direction. That is, if axis 5 is displaced along its axial direction, said bearings react by generating a force in the same direction and attempting to increase the displacement, therefore the problem arises that these bearings tend to push axis 5 out of its position in the axial direction. Thus, the great advantage of these bearings, originated from their completely passive nature, involves the disadvantage of showing a positive axial rigidity, therefore they cannot be used as single rotating links of the assembly. To counteract this effect, an additional mechanism should be implemented to operate by physical principles that are different to the interaction between permanent magnets and that fix the position of axis 5 in the axial direction. After various tests with different types of restriction links in the axial direction, the best results have been obtained by using the electrodynamic thrust bearing.

[0037] In FIG. 1 it may be seen that the rotating section of an electrodynamic thrust bearing 8 is formed by two disks having permanent magnets and ferromagnetic cores. Said rotating section is mounted on axis 5 and fixed thereto, thus forming part of the rotor. A solid or perforated conductor disc 9 is located between said rotating discs and forms the stator section of the thrust bearing, linked to the housing (not shown). The relative movement between the magnets of the rotating section and the conductor material of the stator section induces electric currents on the latter that generate repulsion forces against said magnets. In the arrangement shown in FIG. 1, said repulsion forces give negative rigidity in the axial direction. This way, if axis 5 is displaced in the axial direction, the electrodynamic thrust bearing generates a force in the opposite direction attempting to reestablish the original position.

[0038] The electrodynamic thrust bearing works in a completely passive manner and does not require auxiliary control systems. However, said functioning only happens if there is relative movement between parts, that is, only if the rotor is spinning. Above a minimum rotation speed, the electrodynamic thrust bearing provides the rotor with enough negative axial rigidity to counteract the positive axial rigidity of magnetic radial bearings. It is possible to arrange the magnet supporting discs 8 as the rotating section and the conductor disc 9 as the static section, or vice versa. In the embodiment of FIG. 1, only one thrust bearing is shown, but two or more could be stacked to provide higher axial rigidity to the rotor. In applications where the rotor is not horizontally oriented, part of or the whole axial component of its weight may be offset by the same positive rigidity of magnetic bearings. This way, the electrodynamic thrust bearing must only provide negative rigidity to the assembly but it is not used to support its weight.

[0039] The combination of magnetic radial bearings with electrodynamic thrust bearings allows the rotor to be completely supported in its axial and radial position, above a specific minimum spinning speed, thus avoiding its mechanical contact with the rest of the device. In opposition to active magnetic bearings (AMB), the combination of passive components in this invention assures its functioning with no external energy or control requirements, even with total interruptions of electric supply. This novel combination allows the device to spin at the required speed by the impeller of the centrifugal compressor without suffering any wear, due to the absence of friction force that would generate a great amount of caloric and stopping energy.

[0040] FIG. 3 shows an embodiment of the invention in which the above mentioned rotor is positioned horizontally and allocated inside the body forming the fixed structure of the device (hereinafter, the stator). The orientation of the rotor may be horizontal, vertical or any other orientation different from what is shown in this embodiment. A flanged connection or any other type of connection 15 allows the entering of low pressure process gas to a water tight chamber formed by the main stator walls 16 and other components sealed against them, such as a high pressure collector 17 or an axis end cap 21. The number and arrangement of the components that form said water tight chamber may be different from the ones represented in FIG. 3 but they always contain inside the whole rotor, thus assuring the water tightness character of the gas by means of static seals such as gaskets, O-rings, etc.

[0041] The zone where the axial flow motor 2 is located, shown in FIG. 3 as the stacking of 4 stator assemblies and is corresponding rotating sections, is crossed by the low pressure-low temperature gas. This gas flow allows removing the heat generated in the motor, acting as a coolant. Then, the gas enters a first compression stage formed by an impeller 1 and its corresponding diffuser. In the embodiment of FIG. 3, the rotor contains a second impeller 14 immediately crossed by the gas after the first one. At each compression stage the gas increases its pressure and temperature until it enters a high pressure collector 17 and is conducted to a discharge connection of the stator. Other embodiments of the invention may contain more or fewer impellers, as well as more or fewer assemblies forming the axial flow motor, according to each specific application.

[0042] In the embodiment shown in FIG. 3, the gas temperature at the entrance is low enough to act as a coolant of the power electronics in charge of commanding the electric motor. A series of power electronic components 19 is placed out of the gas pressure containment 16 and is thermally linked thereto. Said electronic components take advantage of the thermal conductivity of metal forming the pressure containment to be cooled with the same process gas. Finally, a cap 18 externally covers the power electronics to protect it from dust and ambient moisture. Other embodiments of the invention may locate said electronic components directly inside the pressure contention, flooded by the process gas. Other different embodiments may use other conventional and independent methods to cool the power electronics in case the gas temperature at the entrance of the compressor is extremely high.

[0043] FIG. 4 shows an isometric view of an embodiment of the invention in which the rotor is oriented horizontally. Said view shows a flanged entrance connection for gas co-axially disposed with the rotor, being the latter out of sight inside the pressure containment. In this embodiment, the high pressure gas discharge is placed laterally and perpendicularly to the above mentioned rotor axis. FIG. 4 also shows a side and another front view of the compressor along with the average human figure in order to visualize a representative size of the device. Other embodiments of the invention may vary in size and proportions and may place the entrance and exit connections for gas in other orientations such as, for example, both coaxial with the rotor axis or both lateral, etc.

[0044] Innovative technical characteristics of the present device include:

[0045] 1. It uses an electric, synchronous, axial flow motor with permanent magnets as driving force mounted on the same axis as the impellers of the centrifugal compressor. This type of motor is more efficient and has higher power density than high speed radial flow motors, which gives this device a superior global performance and a smaller physical size compared to the current art.

[0046] 2. It uses passive magnetic bearings and passive electrodynamic bearings that do not require any energy supply, auxiliary system or monitoring or control system. This characteristic gives the device a high operating reliability, even in case of sudden electric supply fault. Additionally, the absence of control auxiliary systems contributes to its compact size.

[0047] 3. It does not use mechanical seals since the rotor assembly is placed totally inside the same pressure containment as the process gas. The mechanical seals suffer from wear by friction and require frequent maintenance, especially in high speed applications. Its absence gives this device the feature that it requires less maintenance than other prior art equipment. Additionally, the absence of mechanical seals contributes to the global energy efficiency of the equipment.

[0048] 4. It does not use any kind of lubricants for seals, gears or bearings. This characteristic contributes to the low maintenance requirement of the equipment and also to its reduced size, since there is no need of auxiliary systems for treatment of lubricant, such as coolers, filters, separators, or pumps.

[0049] 5. Under normal conditions, due to the novel contact-free rotating support system, the assembly rotates at the same speed as the impeller of the compressor without suffering any mechanic wear.