EP1988292B1 - Rotating machine comprising a passive axial balancing system - Google Patents

Description

The present invention relates to the field of rotating machines intended to be traversed by a main flow of liquid, such as for example suction pumps or turbines for generating an electric power. If the rotating machine is a pump, then the main flow of liquid is the aspirated liquid, whereas if the rotating machine is a turbine, the main flow of liquid is the liquid injected into the turbine.

The rotating machine generally comprises an electrical member consisting of a rotor and a stator, said member being an electric motor when the machine operates as a pump, and said member being an electric generator when the machine operates in a turbine.

Such a rotating machine is often intended to be arranged vertically, that is to say that its axis of rotation extends generally vertically, so that one can define the "bottom" and the "top" of the pump with reference to such a vertical axis.

The terms "axial", "radial" and "tangential" are also defined with reference to the axis of the machine.

Due to the large mass of some of the rotating elements of this rotating machine, in particular that of the electrical member and the rotation shaft attached to the rotor of the electric member, it is understood that the gravitational force which tends to move these elements down is important.

In addition, when the machine is operating as a pump, the counter-reaction due to pumping induces a pulling force which pulls down the machine rotation shaft and the elements attached thereto.

This additional force is added to the force of gravity so that the rotation shaft undergoes significant forces directed axially down the machine.

As a result, the bearings provided to guide the rotational shaft in rotation are highly stressed axially by these forces, which affects their service life.

To overcome this drawback, such rotating machines generally comprise an active axial balancing system, such as that described in the document US 4,538,960 or in the document GB 17268 which describes the preamble of claim 1, to compensate all or part of these efforts, exerting a force of axial recovery on the shaft in a direction opposite to that of the force of gravity.

It is understood that it seeks to obtain an axial recovery force whose intensity is substantially equal to the intensity of the forces to be compensated, the latter being constituted by the force of gravity and the tensile force.

In practice, the intensity of the forces to be compensated can fluctuate, for example due to a fluctuation of the flow rate of the main flow of liquid, so that the intensity of the axial recovery force can suddenly become greater than the intensity of the forces. forces to compensate, thus causing the shaft to move towards the top of the machine.

In the absence of an active axial balancing system, such axial thrust on the shaft would lead to fatigue the bearings, which would adversely affect their service life.

In an active axial balancing system, the intensity of the axial return force depends on the displacement of the rotation shaft relative to the housing. This makes it possible to regulate the intensity of the axial recovery force.

Thus, the intensity of the axial return force decreases if the intensity of the axial return force becomes greater than the intensity of the forces to be compensated and, conversely, the axial recovery force increases if the intensity of the axial return force increases. the axial recovery force becomes less than the intensity of the forces to be compensated. In other words, the intensity of the axial recovery force is slaved to the displacement of the rotation shaft.

It is therefore understood that thanks to the active axial balancing system, the intensity of the axial return force is actively regulated.

• un arbre monté rotatif par rapport à un carter de la machine tournante,
• un système d'équilibrage axial actif apte à exercer une première force de reprise axiale sur l'arbre.

The present invention thus relates to such a rotating machine according to claim 1 intended to be traversed by a main stream of liquid, comprising:

• a shaft rotatably mounted relative to a housing of the rotating machine,
• an active axial balancing system capable of exerting a first axial return force on the shaft.

Nevertheless, it has been found that in certain situations, the intensity of the axial recovery force exerted by the active axial recovery system is not sufficiently large.

An object of the present invention is to provide a rotating machine having improved axial recovery capability.

The invention achieves its object by the fact that the rotating machine according to the present invention further comprises a circuit for a secondary flow of liquid taken from the main flow of liquid, and a passive axial balancing system capable of exerting a second force. of axial recovery on the shaft, said passive axial balancing system being fed by the circuit of the secondary flow of liquid.

Within the meaning of the invention, the passive axial balancing system differs from the active axial balancing system in that the intensity of the second force is not slaved to the displacement of the shaft relative to the housing.

In other words, the intensity of the second force is constant regardless of the displacement of the rotation shaft relative to the housing.

Moreover, like the first axial return force, the second axial return force has a direction opposite to that of the gravitational force, when the machine is arranged vertically.

When the rotating machine according to the invention is a pump, the second axial recovery force has a direction opposite to that of the tensile force mentioned above.

The passive axial balancing system, distinct from the active axial balancing system, therefore provides an additional axial return force, namely the second axial return force, as a result of which, the intensity of the overall axial recovery force exerting itself on the rotation shaft is advantageously increased.

According to the invention, the flow rate of the secondary liquid flow is substantially lower than that of the main flow of liquid.

Also, according to the invention, the flow of secondary liquid flowing in the circuit during operation of the machine, advantageously feeds the passive axial balancing system, that is to say that the secondary flow of liquid provides the energy necessary for the operation of the passive axial balancing system.

Advantageously, the passive axial balancing system comprises an annular passage between the shaft and the housing, through which the secondary liquid flow is intended to flow, said passage axially defining an upstream fluid chamber of a downstream fluidic chamber. such that the pressure in the upstream fluid chamber is greater than the pressure in the downstream fluid chamber.

The terms "upstream" and "downstream" are here considered with reference to the direction of flow of the secondary flow of liquid.

The pressure difference between the two chambers is due to the fact that the annular passage constitutes a flow restriction for the secondary flow of liquid.

Advantageously, the annular passage is defined between a disk attached to the shaft and the housing.

Preferably, the annular passage is defined radially between the outer periphery of the disc and an inner surface of the housing.

Also, the disc preferably extends radially from the axis of the rotation shaft, so that it defines axially the upstream chamber of the downstream chamber. The second axial recovery force, resulting from the pressure difference between the upstream and downstream chambers, is exerted on the rotation shaft via the disc.

Advantageously, the disk comprises at its periphery an annular labyrinth seal.

The annular passage is thus defined radially between the labyrinth seal and the inner surface of the housing.

Particularly advantageously, the passive axial balancing system further comprises means for calibrating the flow rate of the secondary liquid flow.

Indeed, the flow of the secondary flow of liquid must not be too high because otherwise it would reduce the efficiency of the machine.

Thanks to the present invention, the flow rate of the secondary liquid flow is calibrated so that a sufficient second axial recovery force is obtained without greatly reducing the efficiency of the rotating machine.

Advantageously, the means for calibrating the flow rate of the secondary liquid flow comprise said annular passage.

In other words, the annular passage participates both in the generation of the second axial recovery force, and in the calibration of the flow rate of the secondary liquid flow.

Advantageously, the annular passage has a predetermined radial extension in order to calibrate the flow rate of the secondary flow of liquid.

Preferably, the radial extension corresponds to the radial clearance existing between the disk and the casing.

Advantageously, the secondary flow of liquid is also used to cool a rotating element of the machine.

Thus, the secondary stream of liquid is a flow of coolant. In this case, this flow of coolant is advantageously calibrated so that the cooling of the rotating element is sufficient.

Within the meaning of the invention, a rotating element is an element of which at least one component is rotated by the shaft.

Preferably, the rotating element is a bearing, a motor and / or an electric generator. The machine according to the invention may comprise a plurality of rotating elements chosen from the abovementioned elements.

As the rotating element heats up during operation of the machine, it is necessary to cool it.

Thanks to the invention, the same flow of liquid is used to cool the rotating element and to feed the passive axial balancing system. It is therefore not necessary to provide separate circuits, which allows to advantageously simplify the structure of the machine.

According to a first variant, the rotating machine is a pump.

According to a second variant, the rotating machine is a turbine.

• la figure 1 est une vue en coupe d'une machine tournante selon la présente invention, cette dernière étant une pompe ;
• la figure 2 est une vue de détail de la machine tournante de la figure 1 , représentant le système d'équilibrage axial passif selon l'invention.

The invention will be better understood and its advantages will appear better on reading the detailed description which follows, of an embodiment indicated by way of non-limiting example. The description refers to the accompanying drawings in which:

• the figure 1 is a sectional view of a rotating machine according to the present invention, the latter being a pump;
• the figure 2 is a detail view of the rotating machine of the figure 1 , representing the passive axial balancing system according to the invention.

The figure 1 represents an example of a rotary machine 10 according to the present invention, this rotating machine 10 being intended preferentially but not exclusively to pumping fluid such as liquefied gas. It can advantageously be used to empty the tanks of a LNG carrier.

The example shown on the figure 1 is not limiting, the rotating machine according to the invention may also be a turbine in which circulates a liquid driving a generator that provides an electric power.

In the description which follows, the adjectives "axial", "tangential" and "radial" are defined with respect to the axis of rotation A of the machine 10.

Since the rotating machine 10 is generally intended to be arranged vertically, the adjectives "low" and "high" are defined with reference to the vertical direction.

Considered according to the suction direction of the main flow of liquid shown schematically by the arrows referenced F1, the machine 10 successively comprises a suction stage 12, a centrifugal wheel 14 and an annular duct 16 for discharging the aspirated liquid.

The suction stage 12 comprises a rotary inductor 18 driven in rotation by a rotation shaft 20 of the machine 10, the rotation shaft 20 being driven by a rotating element consisting of an electric motor 22.

The electric motor 22 comprises a rotor 24 fixed to the shaft 20 and a stator 26 fixed to a housing 28 of the machine 10.

As we see on the figure 1 , the rotation shaft 20 is rotatably mounted on the housing 28 via a low bearing 30 located between the centrifugal wheel and 14 and the motor 22, and a high bearing 32 located between the motor 22 and a discharge sleeve 34.

The rotation shaft 20 comprises a shoulder 36 coming into axial abutment against an inner ring 38 of the low bearing 30.

The machine 10 being arranged vertically, it is understood that the low bearing 30 supports the weight of the rotation shaft, the centrifugal wheel 14, the rotor 24 and the inductor 18, weight plus the tensile force undergone by the inductor 18 during the suction of the liquid.

To take back at least partly the resultant of the efforts mentioned above, the machine 10 further comprises an active axial balancing system 40, well known elsewhere, capable of exerting on the shaft 20 a first axial recovery force R1 .

This recovery effort is achieved through the first axial resumption force R1 opposite to the resultant efforts mentioned above.

In known manner, the active axial balancing system 40 further allows the regulation of the intensity of the first axial recovery force R1. More precisely, the regulation depends on the axial displacement of the shaft 20 relative to the casing 28.

In practice, if the intensity of the first axial take-up force R1 is greater than that of the resultant of the forces to be resumed, the active axial balancing system 40 operates a regulation by decreasing the intensity of the first axial recovery force. R1.

It has been found that the active axial balancing system 40 is not sufficiently efficient when the flow rate of the main fluid flow F1 pumped is low. More specifically, it has been found that the regulation means do not work correctly for low flow rates.

To remedy this drawback, the rotating machine 10 also comprises, in a particularly advantageous manner, a passive axial balancing system 42, better visible on the figure 2 Which is capable of exerting on the shaft 20 a second axial take-up force R2.

This axial balancing system 42 is passive, that is to say that, unlike the active axial balancing system, the second axial recovery force R2 is independent of the axial displacement of the shaft 20 relative to the housing 28. .

Using the figure 2 it can be seen that the passive axial balancing system 42 comprises a disk 44 fixed to the upper end of the shaft 20.

This disk 44 is able to slide in a bore 47 made in the casing 28.

Preferably, the high bearing 32 is mounted between the disk 44 and a shoulder 45 of the shaft 20.

Preferably, the disc 44 has at its periphery an annular labyrinth seal 46. However, other types of joints may be provided.

According to the invention, the passive axial balancing system 42 is fed by a circuit of a secondary flow of liquid F2 which is taken from the main flow of liquid F1, in this case thanks to a radial passage 49 formed in an inner surface 51 of the annular pipe 16.

As we see on the figure 1 this secondary flow F2 passes through the gap 48 of the motor 22, whereby the motor is advantageously cooled.

Using the figure 2 it can be seen that the secondary flow of liquid F2 then passes through the high bearing 32, thus advantageously allowing cooling of said high bearing, before entering an upstream fluid chamber 50 arranged axially upstream of the disk 44.

The secondary flow of liquid F2 then flows through an annular passage 52 defined radially between the outer periphery of the disc 44 and the casing 28, then flows in a downstream fluidic chamber 54 arranged axially downstream of the disc 44. This downstream fluidic chamber is preferably connected to a discharge orifice 56 to allow the discharge of the secondary liquid flow F2 towards the outside of the rotating machine 10. The terms "upstream" and "downstream" are considered here in relation to in the direction of flow of the secondary flow of liquid F2.

As shown on the figure 2 the annular passage 52 defines axially the upstream fluid chamber 50 of the downstream fluidic chamber 54.

As already mentioned, the annular passage 52 forms a flow restriction for the secondary flow of liquid F 2, so that the pressure in the upstream fluid chamber 50 is greater than the pressure in the downstream fluidic chamber 54.

It follows that it exerts on an upstream side face 58 of the disk 44 a pressure greater than that which is exerted on a downstream side face 60 of the disk 44. This pressure difference thus generates the second axial recovery force R2 which is exerted on the shaft 20 via the disk 44.

It is furthermore understood that the intensity of this second axial recovery force R2 depends on the radial clearance between the disk 44 and the casing 28 and not on the displacement of the shaft 20 with respect to the casing 28.

For this reason, the "axial" balancing system 42 is termed "passive". Consequently, the overall axial recovery force R acting on the shaft 20 is the sum of the first and second axial recovery forces R1, R2 .

Particularly advantageously, the passive axial balancing system 42 further comprises calibration means for calibrating the flow rate of the secondary liquid flow F2. In this case, these calibration means comprise the annular passage 52.

In this case, the annular passage 52 has a radial extension e predetermined to calibrate the flow of the secondary liquid flow F2.

This radial extension e is defined between the outer periphery of the disk 44 and the casing 28.

As has been seen above, the secondary flow of liquid F 2 is also advantageously used for cooling rotary elements of the machine 10, in this case the motor 22 and the bearing 32.

It is advantageous to calibrate the flow rate of this coolant flow because too low a flow rate would not sufficiently cool the rotating elements, while a too high flow rate would reduce the efficiency of the machine, which output is a function of the flow of the main flow of F1 liquid . It is understood that if we take a secondary flow of liquid F2 too large, the main flow F1 is reduced accordingly.

In other words, thanks to the invention, the flow rate of the engine cooling flow is calibrated in a constant manner, whatever the axial position of the rotor 24.

As already mentioned above, the rotating machine according to the invention can also be a turbine. In this case, the main flow of liquid has a direction of flow opposite to that of the main flow of liquid F1 of the machine operating as a pump. On the other hand, the secondary flow of liquid in the turbine has the same direction of flow as that of the secondary flow of liquid F2 circulating in the pump.

Claims (13)

1. A rotary machine (10) for passing a main liquid stream (F1), the machine comprising:

   - a shaft (20) mounted to rotate relative to a casing (28) of the rotary machine;

   - an active axial balancing system (40) suitable for exerting a first axial take-up force (R1) on the shaft, the intensity of the first axial take-up force depending on the displacement of the shaft relative to the casing; and

   - a centrifugal impeller (14) mounted on the shaft:

   said machine being characterized in that it further comprises a circuit for a secondary liquid stream (F2) taken from the main liquid stream (F1), and a passive axial balancing system (42) that is distinct from the active axial balancing system and from the centrifugal impeller, and that is suitable for exerting a second axial take-up force (R2) on the shaft (20), said passive axial balancing system (42) being fed by the circuit for the secondary liquid stream (F2), and the second axial take-up force not being servo-controlled to the displacement of the shaft relative to the casing.
2. A rotary machine according to claim 1, characterized in that the passive axial balancing system has an annular passage (52) between the shaft (20) and the casing (28) through which the secondary liquid stream (F2) is to flow, said passage axially separating an upstream fluidic chamber (50) from a downstream fluidic chamber (54) in such a manner that the pressure in the upstream fluidic chamber is greater than the pressure in the downstream fluidic chamber.
3. A rotary machine according to claim 2, characterized in that the downstream fluidic chamber (54) is connected to a discharge orifice (56).
4. A rotary machine according to claim 2 or claim 3, characterized in that the annular passage (52) is defined between the casing (28) and a disk (44) secured to the shaft (20).
5. A rotary machine according to claim 4, characterized in that the disk (44) is secured to one end of the shaft (20).
6. A rotary machine according to claim 4 or claim 5, characterized in that the disk (44) includes at its periphery an annular labyrinth seal (46).
7. A rotary machine according to any one of claims 1 to 6, characterized in that the passive axial balancing system (42) further comprises means (52) for calibrating the flow rate of the secondary liquid stream (F2).
8. A rotary machine according to claims 2 and 7, characterized in that the means for calibrating the flow rate of the secondary liquid stream comprise said annular passage (52).
9. A rotary machine according to claim 8, characterized in that the annular passage presents a predetermined radial extent (e) for the purpose of calibrating the flow rate of the secondary liquid stream (F2).
10. A rotary machine according to any one of claims 1 to 9, characterized in that the secondary liquid stream (F2) is also used for cooling a rotary element (22, 32) of the machine.
11. A rotary machine according to claim 10, characterized in that the rotary element is a bearing (32), a motor (22), and/or an electricity generator.
12. A rotary machine (10) according to any one of claims 1 to 11, characterized in that it is a pump.
13. A rotary machine (10) according to any one of claims 1 to 11, characterized in that it is a turbine.

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