CN113383164A

CN113383164A - Non-lubricated centrifugal compressor

Info

Publication number: CN113383164A
Application number: CN201980074924.7A
Authority: CN
Inventors: E·J·埃切尼克; S·拉博利塔
Original assignee: Smart E Co ltd
Current assignee: Smart E Co ltd
Priority date: 2018-11-19
Filing date: 2019-11-20
Publication date: 2021-09-10
Also published as: MX2021002763A; EP3847372A1; WO2020106879A1; CA3115111A1; US20220049709A1; BR112021009442A2; EP3847372A4; BR112021009442A8; JP2022536225A

Abstract

A compact gas compression device comprising: a) one or more centrifugal compressors; b) high-speed axial-flow type permanent magnet synchronous motor. The motor and compressor are directly coupled to a single shaft and are supported by passive magnetic and electric bearings without lubricant. The device does not use mechanical seals because the rotor is placed inside a pressure vessel of gas. The device does not require auxiliary systems for cooling, filtering, separating or supplying the lubricant.

Description

Non-lubricated centrifugal compressor

Cross Reference to Related Applications

This application claims the benefit of U.S. provisional application 62/769,323 filed on 2018, 11/19, which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to the field of gas compression equipment. More particularly, the present invention relates to a compact electrical device or apparatus that uses a centrifugal compressor to increase air pressure.

Background

At present, the compression of gas by mechanical means is carried out by different techniques, which have been widely spread and tested since a few years ago. Among the most common methods are centrifugal, axial, alternating and screw compressors.

Alternative compressors or piston compressors are similar in construction to internal combustion engines. The piston or plunger is displaced longitudinally in an alternating manner within the cylinder against which a series of seals bear. A set of valves allows gas to enter during the expansion stage of the chamber formed by the cylinder and the plunger, while the plunger returns. When the plunger is advanced again, it reduces the volume of the chamber in which the gas is located, thereby creating the subsequent required pressure increase. Finally, another set of valves allows the escape of high pressure gas. These compressors are widely used in small and medium size applications. They are simple in construction and highly efficient. They have many movable parts, but they move at low speed relative to each other, so they can use conventional lubricants for their seals and bearings. With low speed (about 1000 to 5000rpm) operation, they are typically coupled directly to an electric or internal combustion engine without a transmission assembly.

The main drawback of this technique is that the lubrication system requires extensive maintenance, which is required to ensure the seal between the plunger and the cylinder, the integrity and watertightness of the valve and to avoid bearing damage. With proper maintenance, the alternative compressor can operate properly for many years. However, all of the above components suffer from mechanical wear even when kept under optimal lubricant conditions and should be replaced regularly. The alternative compressor is the largest volume compressor (with lower power coefficient) of the four types mentioned above, due to the large number of mechanisms involved.

Screw compressors and alternative compressors belong to a group of machines called "positive displacement machines", i.e. the variation of the gas pressure is achieved by variation of the volume of the chamber housing it. In a screw compressor, two helical screw shafts arranged in parallel with each other rotate in the same manner one next to the other. Both screws are in a chamber, the chamber wall being very close to its threaded edge, thus forming a mechanical seal with or without a lubricant. Tightening the screws of the chamber creates a sealed isolated volume containing the gas, which gradually decreases as the gas moves from the inlet port to the outlet port.

This type of compressor is generally used for a middle-sized application and shows some advantages such as a reduction in size and an improvement in compression ratio. The mechanical components rotate at moderate speeds (e.g., between 3000 to 10000 rpm), and therefore, they may require a transmission assembly coupled to a generally slow electric motor or internal combustion engine. Instead, they have fewer moving parts than alternative compressors; therefore, mechanical wear is less associated with maintenance. The main disadvantage is the lubrication system requirement, which should be kept free of solid particles and should be constantly cooled. Lubricants play a critical role by acting as a seal between the screws and as a means of transmitting torque between them without mechanical friction. In addition, the lubricant present in the compression chamber will be mixed with the compressed gas (especially if they are all similar fluids such as hydrocarbons) and should be separated and recycled in a specific set of devices. For these reasons, the reduced size of screw compressors is offset by the large number of auxiliary systems that accompany them.

Centrifugal compressors, together with axial compressors, turbines and centrifugal pumps, belong to the category of turbomachines. In a centrifugal compressor, the increase in gas pressure is achieved indirectly by first increasing the velocity of the gas and then converting this kinetic energy into potential energy. A disk with blades called impellers receives and accelerates the rotation of the gas at low pressure while discharging it to the periphery. Another fixed component, called the diffuser, is responsible for gradually decelerating the rotor, increasing its pressure, as the high velocity gas leaves the rotor.

Centrifugal compressors have some important advantages over positive displacement technology: first, for the same application (flow and pressure), its size is much smaller than alternative or screw compressors (which have high power coefficients). Second, because they do not use seals to form a waterproof chamber, the internal components (e.g., the impeller) are not subject to mechanical wear. The function of the lubricants used in these compressors is to reduce friction on auxiliary components such as external seals and/or bearings.

The problems faced by these compressors are related to their high impeller rotation speed (typically between 20000 and 100000 rpm). Therefore, it is necessary to use a transmission assembly to increase the speed of a drive source such as an electric motor or an internal combustion engine. The transmission assembly becomes a critical component due to its mechanical wear and the implied loss of energy. Another problem that arises with seals is maintaining the process gas isolated from the atmosphere. The seal allows communication between the rotor shaft and the transmission assembly, maintaining high pressure inside the compressor body and low pressure outside. Seals are critical components associated with wear, where lubrication plays a critical role.

The above complexity has limited the use of centrifugal compressors to large applications. However, due to implementation of technologies such as a high-speed electric motor, a centrifugal compressor suitable for medium and small sizes has been recently developed. For example

Companies provide air compressors in which a radial motor is mounted on the same shaft as the compressor rotor. In this way, no gearing assembly is required and the operational difficulties associated therewith are eliminated.

A major drawback that arises when using high-speed radial motors is the presence of a large amount of ferromagnetic material on the stator. High electrical frequencies used at high speeds mean a lot of energy losses in the core, such as parasitic currents and hysteresis. An alternative to this technology is the axial flow motor, which has attracted considerable interest in recent years due to a series of advantageous constructional features.

Firstly, the geometry of the axial flow motor allows to obtain a machine with a higher power coefficient than the radial flow motor. I.e. the axial flow motor requires smaller dimensions than its radial equivalent in order to produce the same power, thus reducing weight and costs. In addition to radial motors, axial motors can also be induction motors and use winding conductors equivalent to a "squirrel cage", or synchronous motors and use permanent magnets. The latter shows the highest power density among all possible configurations.

Secondly, more relevant to the application of the invention, the arrangement of the coils in an axial flow machine requires the use of less ferromagnetic material in the core than in a radial flow machine. In high electrical frequency applications (high rotational speeds), the reduction of ferromagnetic materials means a reduction of energy losses due to hysteresis and parasitic currents, thus significantly improving the performance of the machine and reducing the cooling requirements. Industrial application of axial flow synchronous motors in high speed applications is not well known in the art and it is expected to make important progress in reducing size and improving energy efficiency.

ICR Turbine

Companies (patent publication No. US20140306460) have developed compact brayton cycles that perform multiple compression and expansion stages to improve the overall performance of the system and enhance the radial flow motor coupled with the individual turbines. Each of the compression and expansion stages includes a radial compressor and a radial turbine, both mounted on a single shaft. A small axial flow motor has been installed at the back of each radial compressor, which allows starting the system, driving the rotor to its minimum holding speed. These engines are induction type, comprising a winding stator and a planar squirrel cage rotor.

Additionally, various techniques have been developed to support the rotating components of the electric compressor without the use of lubricating oil, thereby eliminating other complications associated with the high speed operation of these machines. One of these is called "air foil bearing" or simply "foil bearing", in which the same process gas is used as the lubricating fluid. Foil bearings are commonly used in air compressors, for example

In a compressor.

Another more promising technology is a magnetic bearing. In this case, the rotating means are hydrodynamically supported by the magnetic field rather than as before, thus making the system independent of the process fluid. For example,

company supplied for cooling gas

A compressor in which the rotor is suspended by an active magnetic suspension bearing (AMB). The engine-compressor assembly is located in a watertight chamber containing the process gas in such a way that mechanical sealing is not required. Another example of this technology exists in companies

(patent ES2309173), the company developed a large centrifugal compressor in which the engine and compressor are mounted on the same shaft and housed in the same pressure vessel. For the

The bearings are also of the AMB type and use the same process gas to cool the motor.

The complexity exhibited by AMBs is the need for a set of shaft position sensors and an active control electronics system to externally power and command the bearings. If the control system is powered down, the rotating shaft may lose support and come into contact with the stator, which rotates at high speed, causing significant and permanent damage.

Disclosure of Invention

The present invention comprises a compact centrifugal compressor for small and medium-sized applications that does not use lubrication systems, speed multiplication systems or mechanical seals and that generally operates at very high rotational speeds.

The compressor uses axial flow and permanent magnet motors that operate synchronously at high speed and high electrical frequency as drive sources. The machine operates efficiently at high speeds because there are fewer ferromagnetic cores in its stator than an equivalent radial flow machine. In practice, the machine can operate effectively even without a ferromagnetic core in the stator. The compressor wheel is directly coupled to the motor on a single shaft, forming a single movable part of the device. The high efficiency of the axial flow motor and the absence of step-up gearing gives the present invention greater reliability and overall energy efficiency than the prior art.

The motor-impeller rotating assembly is supported by a combination of magnetic levitation radial bearings and electrodynamic thrust (or axial) bearings so that no mechanical contact occurs with the stator. The bearing uses passive permanent magnets and therefore does not require a control system, sensors or an external energy source. This gives the invention greater simplicity and reliability of operation compared to the prior art.

The complete rotor, consisting of the motor-impeller assembly and the magnetic and electric bearings, is located in a waterproof chamber, which is pressure-connected to the stator of the compressor and is filled with the same process gas. In this way, the use of mechanical seals and subsequent frictional wear is avoided, which gives the present invention the feature of requiring less maintenance than other similar prior art devices.

The device of the present invention does not use auxiliary systems to cool, filter, separate or supply lubricant, as there is no need to lubricate bearings, gears or seals. This allows for greater simplicity and smaller size of the present invention compared to other similar devices of the prior art.

Drawings

Fig. 1 is a side view of an embodiment of the present invention showing only the motor-impeller rotating assembly and the stator coils of the motor.

Fig. 2a is a side cross-sectional view of the main components of the axial flow motor.

Fig. 2b is an exploded perspective view of the main components of the axial flow motor.

Fig. 3 is a cross-sectional view of an embodiment of the invention including all components of the device.

Fig. 4 is a complete perspective view and two orthogonal views of an embodiment of the device, the latter being compared to the body shape of an average adult for dimensional reference.

Detailed Description

The present invention is a compact device for gas compression driven by an axial synchronous motor without the use of any type of lubricant.

Fig. 1 shows a single moving part of a motor-impeller rotating assembly (hereinafter referred to as a rotor). The rotor has a centrifugal impeller 1 which is responsible for transferring kinetic energy to the process gas. In the embodiment of fig. 1, only one impeller is shown, but more than one impeller may be used. The impeller is mounted on and fixed to a shaft 5. If multiple impellers are used, all of the impellers may be mounted and fixed on the same shaft.

The axial flow synchronous permanent magnet motor 2 is formed by a stationary stator part and a rotating part. The stator portion of the motor contains the coils, various accessories for support, and may optionally contain a portion of the ferromagnetic core. The portion may be formed by one or more components located between components of the rotating portion. In the embodiment of fig. 1, two stator assemblies 4 are shown between the rotating assemblies 03. In other embodiments, this may be applied to more than two stator assemblies, or only one may be used.

Fig. 2a and 2b show an embodiment of an axial electrical machine, wherein the axial electrical machine comprises a single stator assembly 4. The assembly comprises different parts of the coil 10 and the ferromagnetic core 11. The assembly 4 is placed between two rotating disks 3 containing permanent magnets 12 and may optionally contain another part of a ferromagnetic core 13. These discs form the rotating part 3 of the axial flow motor. The rotating part is mounted on a shaft 5 (see fig. 1) and fixed thereto.

A magnetic flux is established between each pair of opposing permanent magnets 12 arranged in an attracting configuration. The magnetic flux passes through the coil by air or any other means in which the machine is immersed. If the stator assembly contains parts of the ferromagnetic core 11, the magnetic flux will be concentrated through these parts. If the rotor assembly 3 has a ferromagnetic core 13, the flow between the facing surfaces of its adjacent magnets is thereby closed. External electronics monitor the relative position of magnet 12 with respect to coil 10 and activate a series of semiconductors (e.g., Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), Insulated Gate Bipolar Transistors (IGBTs), Solid State Relays (SSRs), etc.) that inject current into the coil. The timing and duration of the current pulses are such that their interaction with the magnetic field induces a force on the permanent magnet, thereby exerting a torque on the shaft 5 (see fig. 1). The stator part of the electrical machine 04 may contain one or more coils 10 which are electrically independent or connected to each other.

As can be seen in fig. 1, the rotating part of the first magnetic-levitation radial bearing 6 is formed by one or more permanent magnets having an annular geometry and is mounted at or near one end of the shaft 5. The rotating part of the second magnetically levitated radial bearing 7 is formed by one or more magnets having a ring-shaped geometry and is mounted at or near the opposite end of the shaft 5. Said rotating part of the radial bearing is part of the rotor. For each bearing, the second stator part is formed by permanent magnets having an annular or cylindrical geometry, which circumferentially surround the rotating part and are fixed to the housing (not shown). As magnets with the same polarity and a high magnetic field strength, by means of the magnetic interaction between each rotating part and its stator counterpart, a magnetic repulsion force is generated which allows radial support of the rotor, avoiding mechanical contact of the rotor with the rest of the device. In the embodiment of fig. 1, two magnetic-levitation radial bearings are shown, one at each end, but three or more bearings may be mounted on different regions of the shaft 5 to make the rotor support more rigid. The radial bearings 6 and 7 are passive and operate without intervention of control systems, sensors or external energy sources. Materials for making high strength passive magnet (e.g., AlNiCo, SmCo, or NdFeB) based magnetic bearings are known in the art and are commercially available.

The mechanical concept of stiffness refers to the ability of an object to resist deformation or displacement caused by external forces. The more rigid the object, the more force it generates against the same degree of deformation. This concept, which is commonly applied to elastic systems such as springs and bearings, is also often used to describe the mechanical properties of active and passive magnetic bearings. When the forces due to the stiffness of the above-mentioned objects tend to compensate for the deformations or displacements originating from them, they are said to have a negative stiffness. In the case of magnetic bearings, positive stiffness refers to the specific behavior of a magnetic bearing, i.e. where the forces generated by displacement tend to increase rather than decrease it. Note that the concept of positive stiffness is useful because it will be used below to explain the function of certain elements of the invention.

The rotor assemblies shown in fig. 1 are supported and stabilized by passive radial bearings because they impart negative stiffness in the radial direction. I.e. if the shaft 5 is moved laterally (radially), the bearings react by generating opposing spring forces that return the shaft to its central position. However, as described by the ensha Theorem (Earnshaw Theorem), such bearings impart positive stiffness in the axial direction. I.e. if the shaft 5 is displaced in its axial direction, said bearings react by generating a force in the same direction and trying to increase the displacement, so that the problem arises that these bearings tend to push the shaft 5 axially out of its position. Thus, the great advantage of these bearings, deriving from their completely passive nature, consists of the drawback of exhibiting an axial positive stiffness, so that they cannot be used as a single rotary connection of the assembly. To counteract this effect, an additional mechanism should be applied to operate by a physical principle that is different from the interaction between the permanent magnets and fixes the position of the shaft 5 in the axial direction. After various tests with different types of restraining connections in the axial direction, the best results were obtained by using an electric thrust bearing.

As can be seen in fig. 1, the rotating part of the electrical thrust bearing 8 is formed by two discs with permanent magnets and a ferromagnetic core. The rotating part is mounted on the shaft 5 and fixed to the shaft 5, thus forming part of the rotor. Solid or perforated conductor discs 9 are located between the rotating discs and form the stator part of the thrust bearing, which is connected to a housing (not shown). Relative movement between the magnets of the rotating portion and the conductor material of the stator portion induces a current on the stator portion that generates a repulsive force against the magnets. In the arrangement shown in fig. 1, the repulsive force imparts a negative stiffness in the axial direction. Thus, if the shaft 5 is moved in the axial direction, the electric thrust bearing will generate a force in the opposite direction that attempts to restore the original position.

The electric thrust bearing operates in a completely passive manner and does not require an auxiliary control system. However, this function is only produced when there is relative movement between the components, i.e. only when the rotor is rotating. Above the minimum rotational speed, the electric thrust bearing provides sufficient axial negative stiffness for the rotor to offset the axial positive stiffness of the magnetic levitation radial bearing. It is possible to arrange the magnet support disc 8 as the rotating part and the conductor disc 9 as the stationary part, or vice versa. In the embodiment of fig. 1, only one thrust bearing is shown, but two or more thrust bearings may be stacked to provide higher axial stiffness to the rotor. In applications where the rotor is oriented non-horizontally, some or all of its axial component of weight may be offset by the same positive stiffness of the magnetic bearings. Thus, the electric thrust bearing must only provide negative stiffness to the assembly and cannot be used to support its weight.

The combination of the magnetic levitation radial bearing and the electric thrust bearing allows the rotor to be fully supported in its axial and radial positions above a certain minimum rotational speed, thereby avoiding mechanical contact of the rotor with the rest of the device. In contrast to Active Magnetic Bearings (AMB), the combination of passive components in the present invention ensures its function even in the event of a complete interruption of the power supply without requiring external energy or control. This novel combination allows the device to be rotated at the required speed by the impeller of the centrifugal compressor without suffering any wear, since there are no friction forces that would generate a lot of heat and stop the energy.

Fig. 3 shows an embodiment of the invention in which the above-mentioned rotor is placed horizontally and distributed in a body forming the fixed structure of the device (hereinafter referred to as stator). The orientation of the rotor may be horizontal, vertical or any other orientation than that shown in this embodiment. The flange connection or any other type of connection 15 allows low pressure process gas to enter the watertight chamber formed by the main stator wall 16 and other components sealed thereto (e.g. the high pressure collector 17 or the shaft end cover 21). The number and arrangement of the components forming the watertight chamber may be different from those shown in fig. 3, but they are generally contained inside the entire rotor, so the watertightness of the gas can be ensured by static seals such as gaskets, O-rings, etc.

The low-pressure-low-temperature gas passes through the region where the axial flow motor 2 is located, which is shown in fig. 3 as a stack of 4 stator assemblies, and is the respective rotating part. This airflow allows acting as a coolant to remove heat generated in the electric machine. The gas then enters the first compression stage formed by the impeller 1 and its corresponding diffuser. In the embodiment of fig. 3, the rotor comprises a second impeller 14 which is traversed by the gas immediately after the first impeller. At each compression stage, the gas increases its pressure and temperature until it enters the high pressure accumulator 17 and is directed to the exhaust of the stator. Other embodiments of the invention may incorporate more or fewer impellers, and more or fewer components forming an axial flow motor, depending on each particular application.

In the embodiment shown in fig. 3, the gas temperature at the inlet is low enough to act as a coolant for the power electronics for controlling the motor. A series of power electronics 19 are arranged outside the pneumatic container 16 and thermally connected thereto. The electronic components are cooled with the same process gas by the thermal conductivity of the metal forming the pressure vessel. Finally, the cover 18 covers the power electronics from the outside to protect them from dust and ambient moisture. Other embodiments of the invention may position the electronic components directly within a pressure vessel filled with process gas. In the case of extremely high gas temperatures at the compressor inlet, other different embodiments may use other conventional and independent methods to cool the power electronics.

Fig. 4 shows an isometric view of an embodiment of the invention with the rotor oriented horizontally. The view shows a flange inlet connection for gas arranged coaxially with a rotor, which is not visible within the pressure vessel. In this embodiment, the high-pressure gas discharge port is arranged transversely and perpendicularly to the rotor shaft. Fig. 4 also shows a side view and another front view of the compressor and the general human body shape in order to visualize representative dimensions of the device. Other embodiments of the invention may vary in size and proportions, and the gas inlet and outlet connections may be arranged in other orientations, e.g. both coaxial with the rotor axis or both transverse, etc.

The innovative technical characteristics of this device include:

1. it uses a synchronous electric axial-flow motor with permanent magnets as the driving force, the motor being mounted on the same shaft as the impeller of the centrifugal compressor. This type of motor is more efficient and has a higher power density than high speed radial motors, which impart superior overall performance and smaller physical dimensions to the device than current technology.

2. It uses passive magnetic bearings and passive electric bearings that do not require any energy supply, auxiliary systems or monitoring or control systems. This characteristic imparts a high operational reliability to the device even in the event of an unexpected power failure. In addition, the omission of the control assistance system contributes to its compact size.

3. It does not use mechanical seals because the rotor assembly is completely located within the same pressure vessel as the process gas. Mechanical seals wear due to friction and require frequent maintenance, particularly in high speed applications. The omission thereof imparts to the device a feature that requires less maintenance than other prior art devices. Furthermore, the absence of mechanical seals helps to improve the overall energy efficiency of the device.

4. It does not use any type of lubricant for the seals, transmission or bearings. This feature thus contributes to reducing the maintenance requirements and size of the apparatus, since no auxiliary systems (such as coolers, filters, separators or pumps) are required to handle the lubricant.

5. Under normal conditions, the assembly rotates at the same speed as the compressor wheel without experiencing any mechanical wear, thanks to the new non-contact rotary bearing system.

Claims

1. A compact gas compression device comprising a rotating electric machine-impeller assembly consisting of one or more centrifugal compressor impellers (1) and an electric machine (2), wherein said one or more compressor impellers are directly coupled to the electric machine (2) on a single shaft (5), wherein the electric machine (2) is a synchronous axial flow permanent magnet electric machine.

2. The compact gas compression device according to claim 1, wherein the shaft (5) of the rotating motor-impeller assembly is supported by more than two magnetically levitated radial bearings (6,7) to fix the radial position of the shaft (5) and by one or more passive electrical thrust bearings (8,9) to fix the axial position of the shaft, wherein said magnetically levitated radial bearings (6,7) and said one or more electrical thrust bearings (8,9) operate completely without lubricant and auxiliary control systems.

3. The compact gas compressing apparatus of claim 1, wherein each of the one or more electric motors (2) is formed by one or more stator assemblies (4) located between one or more rotating assemblies (3) fixed to the shaft (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 compressing apparatus of claim 4, wherein the one or more stator assemblies (4) further comprise a portion of a ferromagnetic core (11).

5. The compact gas compression device according to claim 3, wherein some of the one or more rotating assemblies (3) have a ferromagnetic core (11).

6. The compact gas compression device of claim 3, wherein the one or more coils receive current pulses activated by control electronics (19) monitoring the position of the magnet (12).

7. The compact gas compression device according to claim 3, wherein the control device (19) comprises a semiconductor, in particular comprising the group of metal oxide semiconductor field effect transistors, insulated gate bipolar transistors, solid state relays.

8. The compact gas compression device according to claim 2, wherein each of the magnetic levitation radial bearings (6,7) is formed by a rotating part comprising one or more permanent magnets with annular geometry fixed to the shaft (5) and a stator part also formed by one or more permanent magnets with annular or cylindrical geometry and circumferentially surrounding the rotating part, wherein the two parts are separated by elastic magnetic repulsion forces.

9. The compact gas compression device according to claim 2, wherein each of the electrical thrust bearings (8,9) is formed by a rotating part fixed to the shaft (5) and formed by two or more discs (8) containing permanent magnets and ferromagnetic cores, and a stationary part fixed on the device housing and formed by a solid or perforated electrically conductive disc (9) located between two rotating discs (8) and containing electrically conductive material, wherein the relative movement between the rotating discs (8) and the electrically conductive material induces an electric current that generates a repulsive force acting on the magnets.

10. The compact gas compression device as recited in claim 2, wherein each of said electric thrust bearings is formed by a stationary part fixed to a device housing and formed by two or more discs containing permanent magnets and ferromagnetic cores, and a rotating part fixed to a rotating shaft of said device and formed by solid or perforated electrically conductive discs located between said stationary discs and comprising an electrically conductive material, wherein relative movement between said stationary discs and said electrically conductive material induces thereon an electric current that generates a repulsive force acting on said magnets.

11. The compact gas compression device according to claim 1 or 2, wherein the rotating electric machine-impeller assembly, the magnetic levitation radial bearings (6,7) and the electrodynamic thrust bearings (9,10) are arranged within a pressure vessel of process gas (16), within a fully water-tight vessel without mechanical seals.

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

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

14. The compact gas compression device as recited in claim 1, wherein the device is free of auxiliary systems for cooling, filtering, separating, or supplying any kind of lubricant.

15. The compact gas compression device as claimed in claim 1, wherein the device comprises a compressor wheel (1) and an electric motor (2).

16. The compact gas compression device according to claim 1, wherein the device comprises more than two compressor wheels (1) and one electric motor (2).

17. The compact gas compression device according to claim 2, wherein the motor-impeller rotating assembly is mounted on a shaft (5) supported by two magnetic-levitation radial bearings (6,7) and one passive electric thrust bearing (9, 10).

18. The compact gas compression device according to claim 2, wherein the motor-impeller rotating assembly is mounted on a shaft (5) supported by two magnetically levitated radial bearings (6,7) and more than two passive electric thrust bearings (9, 10).

19. The compact gas compression device according to claim 2, wherein the motor-impeller rotating assembly is mounted on a shaft (5) supported by more than two magnetic levitation radial bearings (6,7) and more than two passive electric thrust bearings (9, 10).