WO2024047040A1

WO2024047040A1 - An electric motor with permanent magnets and a submerged fuel pump with such motor

Info

Publication number: WO2024047040A1
Application number: PCT/EP2023/073672
Authority: WO
Inventors: Michael Winther
Original assignee: SVANEHØJ Danmark A/S
Priority date: 2022-08-30
Filing date: 2023-08-29
Publication date: 2024-03-07

Abstract

The present disclosure concerns an electrical motor for a pump, such as a submerged fuel pump for pumping liquidised fluids, in particular a cryogenic submerged fuel pump for pumping liquidised fuel, such as liquid natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG) or the like, said motor comprising a rotor with a rotor body mounted on a motor shaft and where a plurality of permanent-magnetic magnets are provided along the periphery of the rotor body, wherein the rotor further comprises a mechanical magnet retention system for holding the magnets in place in the rotor body; a stator having coils arranged concentrically around said rotor; wherein the mechanical magnet retention system comprises plurality of axially oriented slots in the periphery of the rotor body wherein the permanent magnets are retained, and wherein the axially oriented slots are formed with a lateral tangentially extension in the periphery of the rotor body, so that the slot is formed between two radially oriented side webs and a peripheral outer web and the radially inwardly slot side is formed in the rotor body.

Description

AN ELECTRIC MOTOR WITH PERMANENT MAGNETS AND A SUBMERGED FUEL

PUMP WITH SUCH MOTOR

FIELD OF THE INVENTION

The present invention relates to an electrical motor for a pump, such as a submerged fuel pump for pumping liquidised fluids, in particular a cryogenic submerged fuel pump for pumping liquidised fuel, such as liquid natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG) or the like liquidised cryogenic dielectric fluids.

BACKGROUND OF THE INVENTION

A submerged fuel pump for liquidised fuel such as LNG that is powered by a permanent magnet electric motor is well known in the art.

In WO 2015/081314 A2 there is disclosed a cryogenic submerged multi-stage pump assembly including a vertically oriented pump shaft. A permanent magnet electrical motor includes a rotor attached to the pump shaft and a stator disposed about the rotor. A first-stage impeller assembly includes a first impeller attached to the pump shaft, the first impeller configured to move a cryogenic fluid from a first impeller inlet to a first impeller outlet when the pump shaft is rotated by the electric motor. The disclosed pump also comprises a hollow permanent magnet rotor in which the pump shaft is mounted. The pump shaft is mounted to the hollow rotor at the top by a nut, and below the motor, a number of impellers are mounted to the pump shaft.

WO 2015/065699 A2 discloses a rotor assembly for a permanent magnet motor for a pump assembly, including an electric submersible pump. In this rotor assembly, the plurality of permanent magnets are retained by retaining clips in the rotor core. The magnets can be disposed in cavities or recesses in the surface of the rotor. OBJECT OF THE INVENTION

It is an object of the present invention to provide an improved permanent magnet electric motor for a submerged fuel pump for pumping liquidised cryogenic dielectric fluids, where the magnets are provided on the rotor as close to the annular surface thereof in order to improve the efficiency.

SUMMARY OF THE INVENTION

In the present disclosure, there is described several embodiments of an electrical motor for a pump, such as a submerged fuel pump for pumping liquidised fluids, in particular a cryogenic submerged fuel pump for pumping liquidised fuel, such as liquid natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG) or the like liquidised cryogenic dielectric fluids, said motor comprising a rotor with a rotor body mounted on a motor shaft and where a plurality of permanent-magnetic magnets are provided along the periphery of the rotor body, wherein the rotor further comprises a mechanical magnet retention system for holding the magnets in place in the rotor body; a stator having coils arranged concentrically around said rotor; wherein the mechanical magnet retention system comprises plurality of axially oriented slots in the periphery of the rotor body wherein the permanent magnets are retained, and wherein the axially oriented slots are formed with a lateral tangential extension in the periphery of the rotor body, so that the slot is formed between two radially oriented side webs and a peripheral outer web and the radially inwardly slot side is formed in the rotor body.

Using an internal permanent magnet synchronous motor for a submerged cryogenic fuel pump is advantageous due to the high efficiency and compact design. By positioning the magnets in slots and mechanically retaining the magnets therein, the magnets are held in position close to the surface of the rotor so that it is ensured that the magnetic field is as strong as possible and thereby ensuring the efficiency of the permanent magnet electric motor. It is furthermore advantageous when operating in cryogenic conditions that the magnets are mechanically retained rather than e.g. being glued in place as the low temperatures may compromise the structural integrity of the glue. Preferably, each slot may be provided with a system of leaf spring members to retain the magnets inserted in each slot.

To ensure that the permanent magnets are maximum effective it is important to ensure that the magnets are positioned as close to the outer surface of the rotor body. Accordingly, it is found advantageous that the axially oriented slots are formed with a lateral tangentially extension in the periphery of the rotor body, so that the slot is formed between two radially oriented side webs and a peripheral outer web and the radially inwardly slot side is formed in the rotor body. Preferably, the leaf spring members may be provided in shallow depressions in the slots, such as formed in the radially inwardly slot side of the rotor body.

According to an advantageous embodiment, the leaf spring members are provided in shallow depressions in the slots. In addition, the leaf spring members may preferably be adapted to provide radially outwardly directed forces on the magnets, when the magnets are inserted in the slots. This ensures that the magnets are retained in an outwardly position with minimal clearance/play. In the preferred embodiments, the magnets are provided with a cross-sectional shape fitting tightly into the slots over the leaf spring.

In some embodiments of the invention, the coaxial slots in the rotor are open at both ends for the insertion of magnets. Depending on the rotor design and dimensions this may be advantageous and facilitating easy and correct assembly of the rotor. In some embodiment, a total of six slots are provided evenly distributed along the cylindrical surface of the rotor, and wherein the magnetic pole of neighbouring magnets on the rotor surface is altered.

In other embodiments, a total of twelve slots are provided evenly distributed along the cylindrical surface of the rotor. The motor topology may be optimised and selected according to the actual requirements. In some selected embodiments for the present electric motor for cryogenic pumps, the permanent magnets are provided in pairs with the same magnetic pole orientation, such that the magnets on the surface are provided in the configuration N-N-S-S-N-N-S-S-N-N-S-S.

In some preferred embodiments, the rotor body is made by a plurality of sheet laminates made from magnetic steel, in particular electric steel. The sheet laminates are less than 1 mm thick, preferably approx. 0.35 to 0.5 mm in thickness, and bonded together by an adhesive. In an embodiment, the leaf springs may be laser cut into the laminates and are therefore made of the same material.

By the invention, the electric motor is preferably adapted for a cryogenic pump for pumping liquidised fluids with a high capacity, and adapted for operating at a speed of up to 6,000 rpm.

In a preferred embodiment of the electric motor according to the present disclosure, the stator is provided with coaxially disposed cooling channels on its cylindrical exterior surface. Moreover, the stator is mounted inside a cylindrical electric motor housing, so the channels are formed between the stator and the motor housing. Hereby, a compact electric motor is achieved with good cooling properties so that the electric motor is suitable for powering a cryogenic pump.

In another aspect of the invention, there is provided a submerged fuel pump for pumping liquidised fluids, in particular a cryogenic submerged fuel pump for pumping liquidised fuel, such as liquid natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG) or the like, wherein the pump comprises a housing having a lower fluid inlet and an upper fluid outlet and accommodating a vertically oriented pump shaft; a permanent magnet electrical motor as described above; at least one impeller, which is mounted to the pump shaft, for moving cryogenic fluid from an inlet to an outlet; and wherein the pump shaft is concentrically mounted in the hollow motor drive shaft at the top ends of said shafts.

DETAILED DESCRIPTION

The invention is described in the following with reference to the accompanying drawings, in which:

Figure 1 is a cross-sectional side view of a cryogenic submerged fuel pump according to an embodiment of the invention;

Figure 2 is a cross-sectional side view of the electrical permanent magnet synchronous motor of the pump in fig. 1;

Figure 3 is a cross-sectional view of the electrical permanent magnet synchronous motor orthogonal to the view of fig. 2;

Figure 4 is a cross-sectional view of a rotor in the electrical permanent magnet synchronous motor without the magnets installed;

Figure 5 is a detailed view of section B in fig. 4;

Figure 6 is a detailed view of section C in fig. 5;

Figure 7 is a side view of a clamping collet for the connection of the motor shaft and the pump shaft shown in fig. 2; and

Figure 8 is and end-view of said clamping collet.

In figure 1 there is shown a cross-sectional view of a cryogenic submerged fuel pump for pumping liquidised fuel, such as liquid natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG) or the like. The pump comprises a housing 1 having a lower fluid inlet 3' and an upper fluid outlet 3". The pump further comprises a vertically oriented pump shaft 4 and a permanent magnet electrical motor 2.

The pump shaft 4 extends through the electric motor 2. Below the electric motor 2, a plurality of impellers 5 are mounted on the pump shaft 4 for providing a multistage centrifugal pump as the impellers or vanes 5, which is mounted to the pump shaft 4 centrifugally is moving cryogenic fluid from the pump inlet 3' to the pump outlet 3" as the impellers 5 are rotated by the pump shaft 4.

This main flow of liquidised fluid constitutes the main liquid flow from the pump inlet 3' to the pump outlet 3", which in fig. 1 is indicated by the reference number 6. As shown in fig. 1, the main flow 6 is provided coaxially around the electrical motor 2.

As shown in fig. 1, the components of the pump are accommodated in a housing 1. The housing comprises a number of intermediate chambers 1A stacked on top of each other and each accommodating an impeller 5, a lower flow branch portion IB, a central motor housing portion 1C and an upper flow branch portion ID, and an upper outlet housing portion IE, and the main flow path 6 is provided through these housing portions 1A-1E.

The housing portions 1A-1E are provided with external assembly flanges and assembled to each other by peripherally provided stay bolts IF.

The lower flow branch IB is provided with a flow path for diverting the main flow 6 around the electric motor 2. Accordingly, the lower flow branch IB has a central entry position in fluid communication with the top of the uppermost of the intermediate chambers 1A and a radial flow delivery position.

The central housing portion 1C is provided with flow channels 61 coaxially at a radial position (see fig. 3), which are in fluid communication with corresponding flow path of the lower flow branch IB. The upper flow branch ID is provided with flow paths between a radially outward receipt position to a central outlet flow exit, where said radially outward receipt positions are in fluid communication with the coaxial flow channels 61 of the central housing portion 1C.

The electrical motor 2 of the pump is shown in more detail in figures 2 and 3 and details thereof also in figures 4 to 6. Accommodated in the motor housing 21, the electric motor 2 comprises a rotor assembly with a rotor body 23 mounted on a motor shaft 22 and where a plurality of permanent-magnetic magnets 231 are provided in along the periphery 234 of the rotor body 23. The electric motor also comprises a stator 24 having coils arranged concentrically around said rotor assembly. The rotor assembly further comprises a mechanical magnet retention system for holding the magnets 231 in place in the rotor body 23. The mechanical magnet retention system comprises plurality of axially oriented slots 232 in the periphery of the rotor body 234 wherein the permanent magnets 231 are retained.

The rotor body 23 is firmly mounted on the motor shaft by any suitable means.

The motor shaft 22 is hollow and the pump shaft 4 is concentrically mounted in the hollow motor drive shaft 22, as shown in fig. 1. The assembly of the pump shaft 4 and the motor shaft 22 is provided by a collet clamp connection for interlocking the motor shaft 22 and the pump shaft 4 at the top ends of the shafts 4, 22. The pump shaft 4 is a smooth shaft, preferably a cylindrically shaped elongated shaft with an even diameter.

The collet clamp connection mounting the pump shaft 4 to the motor shaft 22 is a collet clamp 41, which is made of an alloy suitable as cryogenic material, such as a metal alloy, for instance bronze or stainless steel.

With reference to figures 1, 2 and also figures 7 and 8, the collet clamp connection comprises a clamping collet 41 having a conical external clamping surface 41A engaging with a correspondingly conical inner surface of the end section of the hollow motor shaft 22 and a cylindrical inner clamping surface 41B clamping the collet 41 around the pump shaft 4. The clamping collet 41 is mounted to the motor shaft 22 by a clamping nut 29 (see fig. 2), which is provided with an inner surface with a conical shape that is engaging the conical collar surface 41C of the collet clamp 41. The clamping nut is in threated engagement on the end section of the motor shaft 22 and by tightening the clamping nut 29 to the end of the motor shaft 22, the clamping collet 41 is forced into the receiving surface of the motor shaft 22.

The motor shaft 22 is supported in the motor housing 21 and consequently also in the pump housing 1 by a main bearing 27, which is provided at the upper end of the motor shaft 22 for taking up any axial forces that may occur in the pump. In some currently preferred embodiments, the main bearing 27 is a hybrid bearing, in particular a hybrid ball bearing, such as a deep groove ball bearing. A lower bearing 28 is provided at the lower end of the motor shaft 22 in the motor 2 for absorbing any radial forces occurring. The lower bearing 28 is a carbon guide bearing. The motor shaft 22 may also be provided with a coating for additional hardness, such as a spray coating forming a crack-free coating. This can ensure the performance of the motor shaft 22 at cryogenic conditions.

As shown in fig. 1, a secondary liquid flow 7 is provided for cooling the electric motor 2 and lubricating the bearings 27, 28 in the motor 2. The secondary liquid flow 7 is a partial flow of the main flow 6. This secondary flow 7 is a reverse liquid flow from the region of the pump outlet 3" through the electrical motor 2 to a radially central space 7A on the upper side of the uppermost impeller 5 above the region of the pump inlet 3'.

A filter 71 is provided in the upper outlet housing portion IE of the housing 1 at the inlet for the secondary flow 7. This filter 71 is provided at the inlet of the secondary liquid flow path 7 so that any contaminants in the main flow 6 are prevented from entering the motor 2 and the bearings 27, 28, thereby protecting the motor 2 and the bearings 27, 28 and prolonging the lifetime of these components. The filter 71 is preferably a cryogenic filter, and even more preferable, the filter 71 may be a self-cleaning filter, such as a side-flow filter.

The first liquid flow 6 is the main flow where the pressure is increased from the inlet 3' to the outlet 3" in the pump. The reverse secondary flow 7 is provided due to the pressure difference in the pump so that a small portion of the main flow 6 is reversed through the electric motor 2 to cool the motor and lubricate the bearings 27, 28. Thus, the bearings are lubricated by the main fluid flowing through the pump.

The pressure difference is achieved by providing the exit of the secondary flow at the radially central space 7A on the upper side of the uppermost impeller 5 (or in one embodiment of the invention the only impeller, if the pump is designed with only one impeller 5). The secondary liquid flow 7 is a partial flow of the main flow 6. Due to the narrow passages through the motor 2 and the bearings 27, 28, the flow resistance in the secondary flow path 7 is quite high. This means that the secondary liquid flow 7 is merely a small amount of the main liquid flow 6, such as approx, at least 15-35 times smaller.

Around the cylindrical outer periphery of the stator 24, a plurality of axially oriented flow channels 25 for cooling the electric motor 2, as these channels 25 constitute a substantial portion of the secondary flow path 7 providing cooling for the motor.

As described above, the electric motor is a permanent magnet synchronous motor where the magnets are provided in slots on the rotor. With reference to figures 4 to 6, in the mechanical magnet retention system, each slot 232 is provided with a leaf spring member 233 to retain the magnets 231 inserted in the slots 232. The leaf spring members 233 are provided in shallow depressions in the slots 232 and are adapted to provide radially outwardly directed forces on the magnets 231, when the magnets 231 are inserted in the slots 232 (see fig. 3). The magnets 231 are provided with a cross-sectional shape fitting tightly into the slots 232 over the leaf springs 233.

The axially oriented slots 232 are formed with a lateral tangentially extension in the periphery of the rotor body, so that the slot is formed between two radially oriented side webs 232a, 232b and a peripheral outer web 232c and the radially inwardly slot side 232d is formed in the rotor body. Moreover, the leaf spring members 233 may be provided in shallow depressions 233a in the slots 232, which is formed in the radially inwardly slot side 232d of the rotor body 23.

The slots 232 are provided coaxially in the rotor 23 and may be open at both ends for the insertion of magnets 231. In the embodiment shown in fig. 3, a total of twelve slots 232 are provided evenly distributed along the cylindrical surface 234 of the rotor body 23. The magnetic pole of neighbouring magnets on the rotor surface is altered for every second magnet 231, such that the magnets 231 on the surface 234 are provided in the configuration N-N-S-S-N-N-S-S-N-N-S-S. In an embodiment, the rotor body 23 is made by a plurality of sheet laminates made of magnetic steel, in particular electric steel. The sheet laminates may be thin, such as less than 1 mm thick, preferably between 0.35 mm to 0.5 mm in thickness. In a further embodiment, the leaf springs 233 may be laser cut into the laminates and are therefore made of the same material.

In the present disclosure, terms are used like "vertical", "horizontal" and the like. Such term are to be understood as relative directional terms between the relevant elements, flanges or the like.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Above, the invention is described with reference to some currently preferred embodiments of a submerged fuel pump. However, by the invention it is realised that other embodiments and variants may be provided without departing from the scope of the invention as defined in the accompanying claims.

Claims

1. An electrical motor for a pump, such as a submerged fuel pump for pumping liquidised fluids, in particular a cryogenic submerged fuel pump for pumping liquidised fuel, such as liquid natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG) or the like liquidised cryogenic dielectric fluids, said motor comprising a rotor with a rotor body mounted on a motor shaft and where a plurality of permanent-magnetic magnets are provided along the periphery of the rotor body, wherein the rotor further comprises a mechanical magnet retention system for holding the magnets in place in the rotor body; a stator having coils arranged concentrically around said rotor; wherein the mechanical magnet retention system comprises plurality of axially oriented slots in the periphery of the rotor body wherein the permanent magnets are retained, and wherein the axially oriented slots are formed with a lateral tangential extension in the periphery of the rotor body, so that the slot is formed between two radially oriented side webs and a peripheral outer web and the radially inwardly slot side is formed in the rotor body.

2. An electric motor according to claim 1, wherein each slot is provided with a system of leaf spring members to retain the magnets inserted in the slot.

3. An electric motor according to claim 1 or 2, wherein the leaf spring members are provided in shallow depressions in the slots, such as formed in the radially inwardly slot side of the rotor body.

4. An electric motor according to any one of the preceding claims, wherein the leaf spring members are adapted to provide radially outwardly directed forces on the magnets, when the magnets are inserted in the slots, so that the leaf springs subject the permanent magnets to a radially outwardly directed retention force for holding the magnets in the slots.

5. An electric motor according to any one of the preceding claims, wherein the magnets are provided with a cross-sectional shape fitting tightly into the slots over the leaf spring.

6. An electric motor according to any one of the preceding claims, wherein the coaxial slots in the rotor are open at both ends for the insertion of magnets.

7. An electric motor according to any one of the preceding claims, wherein a total of six slots are provided evenly distributed along the cylindrical surface of the rotor, and wherein the magnetic pole of neighbouring magnets on the rotor surface is altered.

8. An electric motor according to any one of claims 1-6, wherein a total of twelve slots are provided substantially evenly distributed along the cylindrical surface of the rotor.

9. An electric motor according to claim 8, wherein the permanent magnets are provided in pairs with the same magnetic pole orientation, such that the magnets on the surface are provided in the configuration N-N-S-S-N-N-S-S-N-N-S-S.

10. An electric motor according to any one of the preceding claims, wherein the rotor body is made by a plurality of sheet laminates made of magnetic steel, in particular electric steel.

11. An electric motor according to claim 10, wherein the sheet laminates are less than 1 mm thick, preferably approx. 0.35 to 0.5 mm in thickness.

12. An electric motor according to any one of claims 2 to 5, wherein the leaf springs are laser cut into the laminates and are therefore made of the same material.

13. An electric motor according to any one of the preceding claims, wherein the electric motor is adapted for a cryogenic pump for pumping liquidised fluids, and adapted for operating at a speed of up to 6,000 rpm.

14. An electric motor according to any one of the preceding claims, wherein the stator is provided with coaxially disposed cooling channels on its cylindrical exterior surface.

15. A submerged fuel pump for pumping liquidised fluids, in particular a cryogenic submerged fuel pump for pumping liquidised fuel, such as liquid natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG) or the like, said pump comprising a housing having a lower fluid inlet and an upper fluid outlet and accommodating a vertically oriented pump shaft; a permanent magnet electrical motor according to any of the preceding claims; at least one impeller, which is mounted to the pump shaft, for moving cryogenic fluid from an inlet to an outlet; wherein the pump shaft is concentrically mounted in the hollow motor drive shaft at the top ends of said shafts.