FR3113303A1 - Multi-stage centrifugal compressor - Google Patents

Abstract

Multi-stage centrifugal compressor (1), comprising: - a rotary electric motor (2) inside a motor housing (3) and coupled to a motor shaft (4); - two radial compression stages (5, 6) comprising back-to-back compression impellers (50, 60); - an outlet manifold (7) in communication with second exhaust streams; - at least one interstage flow path (10) comprising:- a main pipe (11) passing through the crankcase and opening onto a first side face of the crankcase; - an intermediate pipe (12) in sealed communication with the main pipe and passing through a spacer (64) inserted between a second side face of the engine casing and a second cover; and - a secondary pipe (13) formed in the second cowl and opening opposite a second bladed compression wheel. Abstract Figure: Figure 4

Description

Multi-stage centrifugal compressor

The invention relates to a multi-stage centrifugal compressor, the function of which is to compress a gaseous fluid in at least two successive compression stages.

It relates more particularly to a multi-stage centrifugal compressor comprising:
- a rotary electric motor arranged inside a motor housing;
- A motor shaft driven in rotation by the rotary electric motor and having a first section and an opposite second section extending on either side of the rotary electric motor and of the crankcase;
- A first radial compression stage comprising a first bladed compression wheel coupled in rotation to the first section of the motor shaft and having a first upstream end in communication with a gaseous fluid inlet and a first downstream end;
- a second radial compression stage comprising a second compression impeller rotatably coupled to the second section of the motor shaft and having a second upstream end, where the first compression impeller and the second compression impeller are arranged in a back-to-back configuration;
- An outlet manifold secured to the crankcase and in communication with the second downstream end of the second compression impeller;
- At least one gaseous fluid inter-stage flow path placing the first downstream end of the first compression vaned wheel of the first stage in communication with the second upstream end of the second compression vane wheel.

Thus, in operation, a gaseous fluid is introduced into the first stage via the gaseous fluid inlet, and this gaseous fluid is sucked axially at the first upstream end of the first compression bladed wheel, to be pressurized and then evacuated radially at its first downstream end. The inter-stage flow path of gaseous fluid brings this gaseous fluid compressed by the first stage at the level of the second stage, and more precisely at the level of the second upstream end of the second compression impeller, in order to be sucked axially at this second upstream end of the second compression bladed wheel, to be pressurized again and then evacuated radially at its second downstream end. The gaseous fluid, thus compressed in two successive stages, is then evacuated at the level of the outlet manifold.

Such a multi-stage centrifugal compressor is known in particular from document EP1749992, where an intermediate volute-type collector is provided which surrounds the first downstream end of the first compression bladed wheel to recover the compressed gaseous fluid at the outlet of the first stage, and a volute type outlet manifold which surrounds the second downstream end of the second compression vane wheel to recover the compressed gaseous fluid at the outlet of the second stage. Furthermore, the gaseous fluid interstage flow path is in the form of an external pipe which connects the volute type intermediate manifold to a second cowl facing the second upstream end of the second blade wheel of compression, in order to provide an axial injection of the gaseous fluid at this second upstream end.

A drawback of the compressor known from document EP1749992 is its size, due to the use of an external pipe, located outside the engine casing.

Moreover, during the compression of the gaseous fluid at the level of the first stage, the temperature will increase, thus reducing its density and increasing the volume flow rate and therefore the necessary passage sections. In a multi-stage centrifugal compressor, it is therefore preferable to cool the gaseous fluid between two compression stages, to limit the final temperature of the gaseous fluid and thus be able to reduce the size of the components and the energy consumption, and to be able to improve the performance.

Also, in a compressor equivalent to that of document EP1749992, it is possible to use an external heat exchanger between the external pipe and a cold source, which again affects the size of the compressor.

The invention proposes to solve all or part of the aforementioned drawbacks, by providing a multi-stage centrifugal compressor having an architecture with improved compactness.

Another object of the invention is to provide a solution for cooling the gaseous fluid between two compression stages, without harming the size and preferably in an economical manner.

To this end, the invention proposes a multi-stage centrifugal compressor, comprising:
- A rotary electric motor arranged inside a motor housing having two opposite side faces, namely a first side face and a second side face;
- A motor shaft driven in rotation along a motor axis by said rotary electric motor and having a first section and a second opposite section extending on either side of the rotary electric motor and the two respective side faces of the motor housing;
- a first radial compression stage comprising a first compression impeller coupled in rotation to the first section of the motor shaft and having a first upstream end in communication with a gaseous fluid inlet and a first downstream end facing the side of the first side face of the engine casing;
- a second radial compression stage comprising a second compression impeller coupled in rotation to the second section of the motor shaft and having a second upstream end and a second downstream end facing the side of the second lateral face of the motor casing, such that the first compression impeller and the second compression impeller are arranged in a back-to-back configuration;
- An outlet manifold secured to the crankcase and in communication with the second downstream end of the second compression impeller;
- A first cover covering the first radial compression stage;
- A second cover covering the second radial compression stage; And
- At least one inter-stage gaseous fluid flow path placing the first downstream end of the first compression impeller in communication with the second upstream end of the second compression impeller;
in which this inter-stage flow path of gaseous fluid has the following successive pipes:
- A main pipe passing through the crankcase and provided with a main inlet orifice opening onto the first side face of the crankcase and in communication with the first downstream end of the first compression bladed wheel;
- An intermediate pipe in leaktight communication with the main pipe and passing through a spacer inserted between the second side face of the engine casing and the second cover; And
- A secondary pipe formed in the second cowl and which is in leaktight communication with the intermediate pipe, where said secondary pipe has a secondary outlet orifice opening out facing the second upstream end of the second compression vane wheel.

Thus, the invention proposes to put the compressed gaseous fluid at the outlet of the first stage into communication with the inlet of the second stage, by passing through the engine casing, thus avoiding the use of an external pipe. To do this, the gaseous fluid interstage flow path, or each of the gaseous fluid interstage flow paths, comprises:
- the main pipe which recovers the gaseous fluid at the outlet of the first compression bladed wheel (at the level of its first downstream end), and which sends this gaseous fluid to the other side of the crankcase (passing through it );
- the intermediate pipe, which extends the main pipe in a leaktight manner, to cross a spacer which makes it possible to reach the second cowl while being isolated from the second downstream end of the second compression impeller; And
- the secondary pipe which extends the intermediate pipe in a sealed manner and which is provided in the second cowl to redirect the gaseous fluid towards the center of the second compression impeller, at its second upstream end, so as to enter the second stage compression.

In operation, the gaseous fluid (such as for example a gas or a gaseous mixture, such as air) is introduced into the first stage via the gaseous fluid inlet, and this gaseous fluid is sucked axially at the level of the first upstream end of the first bladed compression wheel, to be pressurized and then evacuated radially at its first downstream end. This gaseous fluid (which is compressed for the first time) then enters the main pipe of the or each of the gaseous fluid interstage flow paths, crosses the crankcase, and reaches the intermediate pipe to cross the spacer ( without communication with the second downstream end of the second bladed compression wheel), then to access the secondary pipe provided in the second cowl in order to be injected at the level of the second stage, and more precisely at the level of the second upstream end of the second bladed compression wheel, in order to be sucked axially at this second upstream end of the second bladed compression wheel, to be pressurized again and then to be evacuated radially at its second downstream end. The gaseous fluid is finally collected by the outlet manifold.

According to one embodiment, a first diffuser surrounds the first downstream end of the first bladed compression wheel and is provided with first fins distributed around said first downstream end of the first bladed compression wheel, where the first blades are separated by first exhaust streams, and in which the main inlet of the main pipe opens into a first exhaust stream, between two first fins of the first diffuser.

Thus, the or each of the gaseous fluid inter-stage flow paths takes the gaseous fluid at the level in a first exhaust stream of the first diffuser, at the outlet of the first stage, this first diffuser (also called stationary blading) filling a straightening function, by slowing down the gaseous fluid at the outlet of the first compression vane wheel (at its first downstream end).

In a first embodiment, the first fins of the first diffuser are secured to the first side face of the engine casing, and the first cowl bears against these first fins.

In a second embodiment, the first fins of the first diffuser are integral with the first cover, and the first fins bear against the first side face of the engine casing.

In a third embodiment, the first fins of the first diffuser are independent of the first cowl and of the engine casing, being interposed between the first cowl and the first side face of the engine casing.

In particular, the spacer (or each of the spacers) is:
- Attached to the second lateral face of the crankcase, and the second cover bears against the spacer; west
- Secured to the second cowl, and the spacer bears against the second side face of the crankcase; west
- Independent of the crankcase and the second cover, being interposed between the second side face of the crankcase and the second cover.

In a particular embodiment, a second diffuser surrounds the second downstream end of the second bladed compression wheel and is provided with second fins distributed around said second downstream end of the second bladed compression wheel and interposed between the second side face of the crankcase and the second cowl, where the second fins are separated by second exhaust streams, and in which the intermediate pipe is provided through one of the second fins which thus forms the spacer.

Thus, at the outlet of the main pipe of the or each of the gaseous fluid interstage flow paths, the gaseous fluid passes through a second fin (forming a spacer) of the second diffuser, which makes it possible to pass through the second diffuser while being isolated from the second veins of this second diffuser.

In a first embodiment, the second fins of the second diffuser are secured to the second side face of the engine casing, and the second cowl bears against the second fins.

In a second embodiment, the second fins of the second diffuser are integral with the second cover, and the second fins bear against the second side face of the engine casing.

In a third embodiment, the second fins of the second diffuser are independent of the crankcase and of the second cover, being interposed between the second side face of the crankcase and the second cover.

According to one possibility, the crankcase is in one piece and the main pipe passes through the crankcase.

Alternatively, the crankcase comprises an inner sleeve and an outer sleeve fitted into one another and the main pipe passes through the crankcase in an interface zone between the inner sleeve and the outer sleeve.

In this variant, the main pipe is provided on an outer peripheral face of the inner sleeve and/or on an inner peripheral face of the outer sleeve. This variant is advantageous for reasons of cost and simplicity of manufacture.

According to another possibility, the second cover is in one piece and the secondary pipe is provided in the second cover.

As a variant, the second cover comprises an internal part and an external part assembled on one another and the secondary pipe is provided in the second cover in an interface zone between the internal part and the external part.

In this variant, the secondary pipe is provided on an outer face of the inner part and/or on an inner face of the outer part. This variant is advantageous for reasons of cost and simplicity of manufacture.

According to one characteristic, the multi-stage centrifugal compressor further comprises a cooling circuit provided in the crankcase for circulation of coolant inside the crankcase.

In this way, the gaseous fluid circulating in the main pipe of the or each of the gaseous fluid interstage flow paths, which is heated at the outlet of the first stage, can be cooled by heat exchange with this cooling circuit. Indeed, thanks to the invention, this or these main pipes are provided in the engine casing, in heat-conducting material, and therefore the surfaces offered by the main pipe or pipes and the circulation of water in the cooling circuit allow to evacuate the heat. In other words, the invention makes it possible to use this cooling circuit for a dual purpose, namely to cool the rotary electric motor and cools the gaseous fluid passing from the first compression stage towards the second compression stage, which is interesting to from a compact and also economical point of view.

According to one possibility, the cooling circuit has one or more sections contiguous to the main pipe of the gaseous fluid interstage flow path or of one of the gaseous fluid interstage flow paths.

In a particular embodiment, several interstage flow paths of gaseous fluid are provided.

According to one possibility, the main pipes of the various gaseous fluid interstage flow paths open into separate first exhaust streams.

According to another possibility, the first diffuser comprises N first fins separated by N first exhaust veins where N is an integer greater than 2, and there are provided N inter-stage flow paths of gaseous fluid with N main pipes which open in the respective first N exhaust veins.

According to one characteristic, the intermediate pipes of the various gaseous fluid interstage flow paths pass through separate spacers.

According to another characteristic, the intermediate pipes of the various gaseous fluid interstage flow paths pass through separate second fins (which, as a reminder, form spacers).

Advantageously, the second diffuser comprises N second fins where N is an integer greater than 2, and N inter-stage flow paths of gaseous fluid are provided with N intermediate pipes which pass through the respective N second fins.

According to one characteristic, the main pipe of the gaseous fluid interstage flow path or of one of the gaseous fluid interstage flow paths extends in an axial direction parallel to the motor axis or substantially parallel to the motor axis; being understood by “substantially parallel” a maximum inclination between this axial direction and the motor axis of 10 degrees.

According to another characteristic, the main pipe of the gaseous fluid interstage flow path or of one of the gaseous fluid interstage flow paths has a variable section along the motor axis.

Such a variation of the cross-section is advantageous for going from a main inlet orifice of suitable shape and dimensions to emerge on the first side face of the engine casing (and in particular in a first exhaust stream), until reaching the intermediate pipe which passes through the corresponding spacer (which can be a second fin) and which can therefore be of suitable shape and dimensions to pass through such a spacer (or second fin).

In a particular embodiment, the secondary pipe of the gaseous fluid interstage flow path or of one of the gaseous fluid interstage flow paths has a curved section between the corresponding intermediate pipe and its orifice secondary output.

Such a curved section is advantageous for bringing the gaseous fluid leaving the intermediate pipe concerned (in a direction more or less parallel to the motor axis), towards the center and in an opposite direction facing the second upstream end of the second compression impeller.

According to one possibility, the curved section of the secondary pipe has an angular amplitude of between 150 and 180 degrees, to define a reversal of the flow in said secondary pipe.

According to another possibility, the second cowl is closed, without an orifice for introducing gaseous fluid opening into an outer face to introduce a gaseous fluid from the outside into the second stage of radial compression.

In other words, insofar as the gaseous fluid passes from the first stage to the second stage through the crankcase, then inside the second cover, then this second cover does not have to have a shaped orifice to introduce from the outside a gaseous fluid in the second stage of radial compression. However, it remains possible to provide at least one orifice passing through the second cover for another function, for example for a sealed passage for a cable or a sensor.

According to a variant, the second cover is fixed to the engine casing or to the outlet manifold.

According to a variant, the outlet manifold has an outlet volute in communication with the second downstream end of the second compression bladed wheel (and where applicable with the second exhaust veins of the second diffuser).

In an advantageous embodiment, the second diffuser comprises an annular body having two opposite annular planar faces, one of which forms the front face of the second diffuser and the other forms a face from which the second fins protrude.

Other characteristics and advantages of the present invention will appear on reading the detailed description below, of a non-limiting example of implementation, made with reference to the appended figures in which:

is a schematic side view of a multi-stage centrifugal compressor according to the invention;

is a schematic rear perspective view of part of the multi-stage centrifugal compressor of Figure 1, without the outlet manifold, the second compression impeller and the second shroud;

is a schematic exploded front perspective view of the multi-stage centrifugal compressor of Figure 1;

is a schematic view in axial section of the multi-stage centrifugal compressor of Figure 1.

With reference to the figures, a multi-stage centrifugal compressor 1 according to an exemplary embodiment of the invention comprises a rotary electric motor 2 arranged inside a motor casing 3, where the rotary electric motor 2 comprises a stator 20 arranged inside a housing of the motor casing 3, and a rotor 21 rotatably mounted in the stator 20 along a motor axis AM. The motor casing 3 has sealed holes 30 for the passage of electrical power supply and control cables to the rotary electric motor 2.

The motor casing 3 has two opposite side faces, namely a first side face 31 and a second side face 32 which are transverse to the motor axis AM, as well as a peripheral face 33 extending around the rotary electric motor 2 and of the AM motor axis. The sealed orifices 30 are provided in the peripheral face 33. Feet 34 are also provided on the peripheral face 33 in order to be able to anchor the motor casing 3 and thus the multi-stage centrifugal compressor 1 to a frame, for example by screwing, bolting, welding or other equivalent fastening means.

The multi-stage centrifugal compressor 1 also comprises a motor shaft 4 driven in rotation along the motor axis AM by the rotary electric motor 2. This motor shaft 4 has two axial end sections, namely a first section 41 and a second opposite section 42 extending on either side of the rotary electric motor 2 and the motor housing 3. The first section 41 extends beyond the first side face 31 of the motor housing 3, and the second section 42 s extends beyond the second side face 32 of the engine casing 3.

Furthermore, a cooling circuit 36 is provided in the crankcase 3 for circulation of cooling liquid inside the crankcase 3, around the rotary electric motor 2, with an inlet 37 and an outlet 38 leading to the peripheral face 33 for fluid communication of the cooling circuit 36 with a source of coolant (not shown).

The multi-stage centrifugal compressor 1 comprises a first radial compression stage 5 and a second radial compression stage 6 configured to successively compress a gaseous fluid, and arranged on either side of the rotary electric motor 2 and the crankcase 3.

The first radial compression stage 5 comprises a first compression impeller 50 (also called impeller or impeller) coupled in rotation to the first section 41 of the motor shaft 4 to be driven in rotation along the motor axis AM. This first compression vane wheel 50 has:
- A first upstream end 51 in communication with a gaseous fluid inlet 80; And
- a first downstream end 52 surrounded by a first diffuser 53.

The first downstream end 52 is turned towards the side of the first lateral face 31 of the engine casing 3 so that, along the engine axis AM, the first upstream end 51 is more distant from the engine casing 3 compared to the first downstream end 52.

The multi-stage centrifugal compressor 1 comprises a first cowl 8 covering the first radial compression stage 5 and fixed to the first side face 31 of the engine casing 3. This first cowl 8 has in its center an inlet opening forming a gaseous fluid 80, placed facing the first upstream end 51 of the first compression impeller 50. This gaseous fluid inlet 80 is centered on the motor shaft AM.

The first bladed compression wheel 50 is of increasing diameter from the first upstream end 51 to the first downstream end 52, and it has blades (also called blades) which define between them compression channels which are, on the one hand, hand, open at the first upstream end 51 for an inlet of the gaseous fluid and, on the other hand, open at the first downstream end 52 for an outlet of the compressed gaseous fluid.

The function of the first diffuser 53 is to straighten and slow down the compressed gaseous fluid at the outlet of the first compression vane wheel 50. To do this, the first diffuser 53 is provided with first fins 54 distributed around the first downstream end 52 of the first compression bladed wheel 50 and separated by first exhaust veins 55. These first exhaust veins 55 thus form spaces between the first fins 54, and they are in communication with and in the extension of the compression channels of the first compression impeller 50.

Furthermore, the first diffuser 53 is secured to the first side face 31 of the engine casing 3. Thus, the first fins 54 are secured to the first side face 31 of the engine casing 3, for example by being formed in one piece with this first side face 31. The first fins 54 protrude from the first side face 31, and can for example be of triangular or polygonal shape in general.

In a variant not shown, the first diffuser 53 is integral with the first cowl 8 and is pressed against the first side face 31 of the engine casing 3. In other words, in this variant, the first fins 54 are integral with and protrude from the first cowl 8, for example by being formed in one piece with this first cover 8, and they are pressed against the first side face 31 of the engine casing 3.

The second radial compression stage 6 comprises a second impeller compression wheel 60 (also called impeller or impeller) coupled in rotation to the second section 42 of the motor shaft 4 to be driven in rotation along the motor axis AM. This second compression impeller 60 has:
- a second upstream end 61; And
- a second downstream end 62 surrounded by a second diffuser 63 secured to the second side face 32 of the engine casing 3.

The second downstream end 62 is turned towards the side of the second lateral face 32 of the engine casing 3 so that, along the engine axis AM, the second upstream end 61 is more distant from the engine casing 3 compared to the second downstream end 62. Thus, the first compression impeller 50 and the second compression impeller 60 are arranged in a back-to-back configuration. Such a back-to-back assembly is advantageous for subtracting the forces of the two compression vane wheels 50, 60 on the motor shaft 4, the resulting force then being less and easier to compensate for increasing the life of the compressor. multi-stage centrifugal 1.

The second bladed compression wheel 60 is of increasing diameter from the second upstream end 61 to the second downstream end 62, and it has blades (also called blades) which define between them compression channels which are, on the one hand, hand, open at the second upstream end 61 for an inlet of the gaseous fluid and, on the other hand, open at the second downstream end 62 for an outlet of the compressed gaseous fluid.

The function of the second diffuser 63 is to straighten and slow down the compressed gaseous fluid at the outlet of the second compression vane wheel 60. To do this, the second diffuser 63 is provided with second fins 64 distributed around the second downstream end 62 of the second compression bladed wheel 60 and separated by second exhaust veins 65. These second exhaust veins 65 thus form spaces between the second fins 64, and they are in communication with and in the extension of the compression channels of the second compression impeller 60.

The second fins 64 are integral with the second side face 32 of the engine casing 3, for example by being formed in one piece with this second side face 32. The second fins 64 protrude from the second side face 32, and can by example be triangular or polygonal in general.

The second diffuser 64 also has an annular body 66 (or annular ring) having two opposed flat annular faces 67, 68, one of which 67 forms a front face and the other 68 forms a dorsal face from which the second fins protrude. 64. Thus, these second fins 64 extend between the second lateral face 32 and the dorsal face 68 of the annular body 66, and the second downstream end 62 of the second compression impeller 60 is housed inside the second diffuser 64 to be surrounded by the second fins 64.

The multi-stage centrifugal compressor 1 comprises a second cover 9 covering the second radial compression stage 6 and fixed to the outlet manifold 7. This second cover 9 comprises an internal face (turned towards the engine casing 3 and the second stage of radial compression 6) on which is provided an annular bearing face 90 which bears against the front face 67 of the second diffuser 64. This second cover 9 comprises an external face 91, opposite to the internal face, and which is turned on the outside.

In a variant not shown, the second diffuser 64 is integral with the second cover 9, so that the second fins 64 are integral with and protrude from the second cover 9, for example by being formed in one piece with this second cover 9, and they are pressed against the second side face 32 of the engine casing 3.

The multi-stage centrifugal compressor 1 comprises an outlet manifold 7 integral with the engine casing 3, which has an outlet volute 70 in communication with the second exhaust veins 65 of the second diffuser 63. This outlet manifold 7 is fixed on a annular flange 35 provided on the peripheral face 33 of the engine casing 3, so that the outlet volute 70 surrounds the second diffuser 63 and its second exhaust veins 65.

The multi-stage centrifugal compressor 1 comprises several inter-stage flow paths of gaseous fluid 10 communicating:
- The first downstream end 52 of the first bladed compression wheel 50, and in particular the first exhaust veins 55 of the first diffuser 53 of the first radial compression stage 5;
with
- the second upstream end 61 of the second compression impeller 60.

Each gaseous fluid interstage flow path 10 comprises at least:
- a main pipe 11 made through the engine casing 3 and provided with a main inlet 111 opening into a first exhaust stream 55, between two first fins 54 of the first diffuser 53, so as to open into the first lateral face 31 of the engine casing 3 to be in communication with the first downstream end 52 of the first compression impeller 50;
- an intermediate pipe 12 in sealed communication with the main pipe 11 and passing through a second fin 64 of the second diffuser 63 to emerge on the front face 67 of the second diffuser 63, this second fin 64 thus forming a spacer inserted between the second side face 32 of the engine casing 3 and the second cowl 9, where this intermediate pipe 12 is provided with a main outlet orifice 112 opening into the front face 67;
- a secondary pipe 13 formed in the second cover 9 which is pressed against the front face 67 of the second diffuser 63, this secondary pipe 13 comprising a secondary inlet orifice 131 opening into the annular bearing face 90 of the second cover 9 and in communication with the main outlet orifice 112 of the intermediate pipe 12, and a secondary outlet orifice 132 opening into the internal face of the second cowl 9 opposite the second upstream end 61 of the second compression bladed wheel 60 to form all or part of a gaseous fluid inlet within the second compression stage 6.

Thus, the gaseous fluid is introduced into the multi-stage centrifugal compressor 1 via the gaseous fluid inlet 80 formed in the first cowl 8, then it is compressed in the first compression impeller 50 to come out at its first end. swallows 52, and then the compressed gaseous fluid is straightened in the first exhaust veins 55 of the first diffuser 53, and it enters inside the main pipes 11, then it passes through the intermediate pipes to cross the second fins 64 of the second diffuser 63 (without being in communication with the second exhaust streams 65) to enter the secondary pipes 13, which will allow the compressed gaseous fluid to come out opposite the second upstream end 61 of the second compression bladed wheel 60, and thus this compressed gaseous fluid is compressed in the second compression impeller 60 to emerge at its second downstream end 62, and the fluid The compressed gas thus compressed twice is collected in the outlet manifold 7.

In this way, between the first stage of radial compression 5 and the second stage of radial compression 6, the interstage flow paths of gaseous fluid 10 do not exit on the outside of the multistage centrifugal compressor 1, but are provided entirely inside the crankcase 3, the second fins 64 of the second diffuser 63 and the second cover 9.

It should be noted that the secondary pipes 13 do not open into the external face 91 of the second cover 9, but only open into its internal face at the level of their secondary inlet orifices 131 and their respective secondary outlet orifices 132.

It should also be noted that, in the particular embodiment where the second fins 64 are integral with the engine casing 3, then the main pipe 11 and the intermediate pipe 12 together form a single and same channel. On the other hand, in the variant where the second fins 64 are integral with the second cover 9, then the secondary pipe 13 and the intermediate pipe 12 together form a single and same channel.

In addition, to spare the main pipes 11 through the crankcase 3, it is possible to have a crankcase 3 comprising two parts, namely:
- an internal sleeve inside which the rotary electric motor 2 is arranged, and
- an outer sleeve fitted contiguously around the inner sleeve;
where the main pipes 11 are provided in a peripheral interface zone between the inner sleeve and the outer sleeve.

In other words, the main pipes 11 are formed on an outer peripheral face of the inner sleeve and/or on an inner peripheral face of the outer sleeve.

Similarly, to spare the secondary pipes 13 in the second cover 9, it is possible to have a second cover 9 comprising two parts, namely:
- an internal part turned on the side of the second radial compression stage 6, and
- An outer part assembled contiguously on the inner part and turned on the outside;
where the secondary pipes 13 are arranged in an interfacing zone between the internal part and the external part.

In other words, the secondary pipes 13 are provided on an outer face of the inner part and/or on an inner face of the outer part.

Furthermore, the cooling circuit 36, provided in the crankcase 3, has one or more sections contiguous to the main pipes 11, which has the advantage of cooling the compressed gaseous fluid leaving the first stage of radial compression 5, before enter the second radial compression stage 6. Such cooling of the gaseous fluid between the two radial compression stages 5, 6 makes it possible to increase the density of the gaseous fluid and thus to reduce the sections of the main pipes 11. In addition, the cooling of the gaseous fluid between the two radial compression stages 5, 6 makes it possible to limit the final temperature of the gaseous fluid and therefore the energy consumption, and thus to improve the performance of the multistage centrifugal compressor 1.

It is conceivable that the first diffuser 53 comprises N first fins 54 separated by N first exhaust veins 55 where N is an integer greater than 2 (for example an integer greater than or equal to 10), the second diffuser 63 comprises N seconds fins 64, and N inter-stage flow paths of gaseous fluid 10 are provided with N main pipes 11 which open into the N respective first exhaust streams 55 and N associated intermediate pipes 12 which pass through the respective N second fins 64 . Thus, N secondary pipes 13 are provided in the second cover 9, and moreover the main pipes 11 open into first separate exhaust streams 55 and the N intermediate pipes 12 pass through second separate fins 64.

Each main pipe 11 extends in an axial direction parallel to the motor axis AM or substantially parallel to the motor axis AM, being understood by "substantially parallel" a maximum inclination between this axial direction and the motor axis AM of 10 degrees.

Furthermore, the shape and dimensions of the main inlet orifices 111 depend on the shape and dimensions of the first exhaust veins 55, and likewise the shape and dimensions of the main outlet orifices 112 depend on the shape and dimensions of the second fins 64. Also, insofar as the first exhaust veins 55 do not have the same shapes and dimensions as the second fins 64, then the main inlet orifices 111 do not have the same shapes and dimensions than the main outlet orifices 112. Therefore each main pipe 11 has a variable section between its main inlet orifice 111 and the main outlet orifice 112.

Each secondary pipe 13 has a curved section between its secondary inlet orifice 131 and its secondary outlet orifice 132, according to an angular amplitude comprised between 150 and 180 degrees, to define a reversal of the flow in the secondary pipe 13. Indeed, as each secondary pipe 13 only opens into the inner face of the second cover 9 at its secondary inlet orifice 131 and its secondary outlet orifice 132, the secondary pipe 13 causes the fluid to make a sort of U-turn compressed gas. The secondary outlet orifices 132 are provided at the level of the center of the second cover 9. Deflector flaps 92 can be provided on the second cover 9, opposite the secondary outlet orifices 132 of each secondary pipe 13, in order to deflect the gaseous fluid leaving the secondary pipes 13 in the direction of the second downstream end 62 of the second compression impeller 60.

It should also be noted that the second cover 9 is closed, without an orifice for introducing gaseous fluid opening into its external face 91 to introduce a gaseous fluid from the outside into the second stage of radial compression. In other words, the only gaseous fluid entering the second stage of radial compression is that coming from the secondary pipes 13. It is of course possible to provide an orifice passing through the second cover 9, for example for a sealed passage of a cable or a sensor, but not for introducing a gaseous fluid from the outside into the second stage of radial compression.

Claims (23)

Multi-stage centrifugal compressor (1), comprising:
- a rotary electric motor (2) arranged inside a motor casing (3) having two opposite side faces (31, 32), namely a first side face (31) and a second side face (32);
- a motor shaft (4) driven in rotation along a motor axis (AM) by said rotary electric motor (2) and having a first section (41) and a second section (42) opposite each other extending on either side of the rotary electric motor (2) and of the two respective side faces (31, 32) of the motor casing (3);
- a first radial compression stage (5) comprising a first compression impeller (50) coupled in rotation to the first section (41) of the motor shaft (4) and having a first upstream end (51) in communication with a gaseous fluid inlet (80), and a first downstream end (52) facing the side of the first side face (31) of the motor casing (3);
- a second radial compression stage (6) comprising a second compression impeller (60) coupled in rotation to the second section (42) of the motor shaft (4) and having a second upstream end (61) and a second downstream end (62) facing the side of the second side face (32) of the motor casing (3) so that the first compression impeller (50) and the second compression impeller (60) are arranged in a back configuration -to-back;
- an outlet manifold (7) integral with the engine casing (3) and in communication with the second downstream end (62) of the second compression impeller (60);
- a first cover (8) covering the first radial compression stage (5);
- a second cover (9) covering the second radial compression stage (6); And
- at least one gaseous fluid inter-stage flow path (10) communicating the first downstream end (52) of the first compression impeller (50) with the second upstream end (61) of the second impeller compression (60);
wherein said gaseous fluid interstage flow path (10) has the following successive pipes (11, 12, 13):
- a main pipe (11) passing through the crankcase (3) and provided with a main inlet orifice (111) opening onto the first side face (31) of the crankcase (3) and in communication with the first downstream end (52) of the first compression impeller (50);
- an intermediate pipe (12) in sealed communication with the main pipe (11) and passing through a spacer (64) inserted between the second side face (32) of the engine casing (3) and the second cover (9); And
- a secondary pipe (13) formed in the second cover (9) and which is in sealed communication with the intermediate pipe (12), where said secondary pipe (13) has a secondary outlet orifice (132) opening opposite the second upstream end (61) of the second compression impeller (60). Multi-stage centrifugal compressor (1) according to Claim 1, in which a first diffuser (53) surrounds the first downstream end (52) of the first compression impeller (50) and is provided with first vanes (54) distributed around of said first downstream end (52) of the first compression bladed wheel (50), where the first vanes (54) are separated by first exhaust veins (55), and in which the main inlet port ( 111) of the main pipe (11) opens into a first exhaust stream (55), between two first fins (54) of the first diffuser (53). A multi-stage centrifugal compressor (1) according to claim 2, wherein the first vanes (54) of the first diffuser (53) are:
- Attached to the first side face (31) of the engine casing (3), and the first cover (8) bears against said first fins (54); where are
- integral with the first cowl (8), and the first fins (54) bear against the first side face (31) of the engine casing (3); where are
- independent of the first cover (8) and the crankcase (3), being interposed between the first cover (8) and the first side face (31) of the crankcase (3). Multi-stage centrifugal compressor (1) according to any one of claims 1 to 3, in which the spacer (64) is:
- Attached to the second side face (32) of the engine casing (3), and the second cover (9) bears against the spacer (64); west
- integral with the second cover (9), and the spacer (64) bears against the second side face (32) of the engine casing (3); west
- independent of the crankcase (3) and the second cover (9), being interposed between the second side face (32) of the crankcase (3) and the second cover (9). Multi-stage centrifugal compressor (1) according to any one of claims 1 to 4, in which a second diffuser (63) surrounds the second downstream end (62) of the second compression impeller (60) and is provided with second fins (64) distributed around said second downstream end (62) of the second compression bladed wheel (60) and interposed between the second lateral face (32) of the engine casing (3) and the second cowl (9), where the second fins (64) are separated by second exhaust veins (65), and in which the intermediate pipe (12) is provided through one of the second fins (64) which thus forms the spacer. A multistage centrifugal compressor (1) according to claim 5, wherein the second vanes (64) of the second diffuser (63) are:
- Attached to the second side face (32) of the engine casing (3), and the second cover (9) bears against the second fins (64); where are
- Attached to the second cover (9), and the second fins (64) bear against the second side face (32) of the engine casing (3); where are
- independent of the crankcase (3) and the second cover (9), being interposed between the second side face (32) of the crankcase (3) and the second cover (9). Multi-stage centrifugal compressor (1) according to any one of claims 1 to 6, in which:
- the crankcase (3) is in one piece and the main pipe (11) crosses the crankcase (3), or
- the engine casing (3) comprises an internal sleeve and an outer sleeve fitted into one another and the main pipe (11) passes through the engine casing (3) in an interface zone between the internal sleeve and the sleeve external. Multi-stage centrifugal compressor (1) according to any one of claims 1 to 7, in which:
- the second cover (9) is in one piece and the secondary pipe (13) is provided in the second cover (9), or
- the second cover (9) comprises an internal part and an external part assembled on one another and the secondary pipe (13) is provided in the second cover (9) in an interface zone between the internal part and the outer part. Multi-stage centrifugal compressor (1) according to any one of Claims 1 to 8, further comprising a cooling circuit (36) provided in the motor casing (3) for circulation of cooling liquid inside the casing engine (3). A multi-stage centrifugal compressor (1) according to claim 9, wherein the cooling circuit (36) has one or more sections contiguous to the main line (11) of the gaseous fluid interstage flow path (10) or one of the gaseous fluid interstage flow paths (10). A multi-stage centrifugal compressor (1) according to any one of claims 1 to 10, wherein a plurality of gaseous fluid inter-stage flow paths (10) are provided. Multi-stage centrifugal compressor (1) according to Claims 2 and 11, in which the main pipes (11) of the various inter-stage flow paths of gaseous fluid (10) open into first separate exhaust streams (55) . Multi-stage centrifugal compressor (1) according to claim 12, in which the first diffuser (53) comprises N first fins (54) separated by N first exhaust veins (55) where N is an integer greater than 2, and N inter-stage flow paths of gaseous fluid (10) are provided with N main pipes (11) which open into the respective N first exhaust streams (55). Multistage centrifugal compressor (1) according to any one of claims 11 to 13, in which the intermediate pipes (12) of the different interstage flow paths of gaseous fluid (10) pass through separate spacers (64). Multistage centrifugal compressor (1) according to claims 5 and 14, in which the intermediate pipes (12) of the different interstage flow paths of gaseous fluid (10) pass through separate second fins (64). A multistage centrifugal compressor (1) according to claim 15, wherein the second diffuser (63) comprises N second vanes (64) where N is an integer greater than 2, and there are N interstage flow paths of gaseous fluid (10) with N intermediate pipes (12) passing through the respective N second fins (64). A multistage centrifugal compressor (1) according to any of claims 1 to 16, wherein the main line (11) of the interstage gaseous fluid flow path (10) or one of the inter-stage flow of gaseous fluid (10) extends in an axial direction parallel to the motor axis (AM) or substantially parallel to the motor axis (AM). A multistage centrifugal compressor (1) according to any of claims 1 to 17, wherein the main line (11) of the interstage gaseous fluid flow path (10) or one of the interstage flow of gaseous fluid (10) has a variable section along the motor axis (AM). A multistage centrifugal compressor (1) according to any one of claims 1 to 18, wherein the branch line (13) of the interstage gaseous fluid flow path (10) or of one of the inter-stage flow of gaseous fluid (10) has a curved section between the corresponding intermediate pipe (12) and its secondary outlet orifice (132). Multi-stage centrifugal compressor (1) according to claim 19, wherein the curved section of the secondary pipe (13) has an angular amplitude comprised between 150 and 180 degrees, to define a reversal of the flow in said secondary pipe (13 ). Multi-stage centrifugal compressor (1) according to any one of Claims 1 to 20, in which the second cover (9) is closed, without an orifice for introducing gaseous fluid opening into an outer face (91) to introduce from the outside a gaseous fluid in the second stage of radial compression (6). Multi-stage centrifugal compressor (1) according to any one of Claims 1 to 21, in which the second cover (9) is fixed to the motor casing (3) or to the outlet manifold (7). A multi-stage centrifugal compressor (1) according to any one of claims 1 to 22, wherein the outlet manifold (7) has an outlet volute (70) in communication with the second downstream end (62) of the second impeller compression vane (60).