FIELD OF THE INVENTION

The present invention relates to 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.

BACKGROUND OF THE INVENTION

Submerged fuel pumps for liquidised fuel such as LNG are 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.

WO 2015/081314 A2 also discloses 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.

OBJECT OF THE INVENTION

In order to ensure an efficient pump performance it is important that the motor and cryogenic pump during operation does not gets heated so the liquidised fuel becomes gaseous. Hence, it is an object of the present invention to provide an improved submerged fuel pump for pumping liquidised fluids, in particular a cryogenic submerged fuel pump for pumping liquidised fuel, which is compact in its design and with an improved efficiency.

SUMMARY OF THE INVENTION

In the present disclosure, there is described several embodiments of a submerged 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 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 having a rotor with a hollow motor drive shaft and a stator around said rotor; at least one impeller, which is mounted to the pump shaft, for centrifugally moving cryogenic fluid from a pump inlet to a pump outlet; wherein a main liquid flow having a main flow direction from the pump inlet to the pump outlet is provided coaxially around the electrical motor; and a secondary liquid flow for cooling the electric motor and lubricating bearings in the pump, where said secondary flow is a reverse liquid flow essentially opposite of the main flow direction from the region of the pump outlet through the electrical motor to a radially central space on the upper side of the at least one impeller in the region of the pump inlet, and wherein a filter is provided at the inlet of the secondary liquid flow path.

By the invention, there is provided an efficient and simple solution to providing cooling of the motor and lubrication of the bearings of the pump. The first liquid flow is the main liquid flow where the pressure is increased from the inlet to the outlet. The reverse secondary flow is provided due to the pressure difference in the pump so that a small portion of the main flow is reversed in a secondary flow through the motor to cool the motor and lubricate the bearings.

By the invention it is also found advantageous that the filter is provided at the inlet of the secondary liquid flow path. Hereby the motor and bearings are protected against contaminants and thereby prolongs the lifetime of the pump. It is found that such a pump may have a very long service life of the pump of up to at least 26,000 hours.

Furthermore, the main cargo liquid is used for lubricating and cooling the motor of the pump without any need for using separate liquids for these functions during operation of the pump. This is particularly advantageous and when the cargo is a cryogenic liquid. To ensure a proper functioning of the filter, the filter is preferably a cryogenic filter.

The filter is preferably a side-flow filter having an essentially radial inlet filter flow and an axial outlet filter flow. Hereby, the reverse flow can be established in a simple manner.

In particular embodiments, the filter is a self-cleaning filter, such as a side-flow filter. This improves the system cleanliness and is advantageous as the filter may be maintenance free or at least having a long time between overhauls.

In the preferred embodiments, the pump shaft extends below the motor shaft, where the at least one impeller are mounted to the shaft below the motor. This allows for a slim design of the pump. Preferably, a plurality of impellers are provided on the pump shaft for providing a multistage centrifugal pump.

Preferably, the radially central space on the upper side is around the pump shaft, so that the path of the secondary liquid flow exits adjacent the pump shaft on the upper side of the at least one impeller. The impeller is producing pressure by rotating and thereby forcing the main flow from the radial central region and outwards to its periphery. Thus, the pressure is lowest at the radially central region of the impeller and this is utilised for establishing the secondary flow.

In the pump according to the invention, the secondary liquid flow is a partial flow of the main flow. In particular, the secondary liquid flow is a small amount of the main liquid flow, preferably at least 15-35 times smaller, such as approx. 30 times smaller. This secondary flow is driven as the pressure at the central of the upper side of the impeller is lower than the pressure at the pump outlet. The flow path through the motor and bearings is designed and dimensioned such that the flow resistance ensures that only the small amount of the main flow reverses back through the pump. wherein a plurality of axially oriented flow channels are provided in the stator of the motor for cooling, and wherein said channels constitute a substantial portion of the secondary flow path providing cooling for the motor.

In some preferred embodiments of the pump, a main bearing is provided at the upper end of the motor shaft for absorbing any axial forces is provided in the pump. In particular, the main bearing may be a hybrid bearing, in particular a hybrid ball bearing, wherein said bearing is lubricated by the secondary liquid flow.

Preferably, a lower bearing is also provided at the lower end of the motor shaft for absorbing any radial forces in the pump. This lower bearing may preferably be a carbon guide bearing.

In the pump described in this disclosure, preferably the housing has an inlet housing portion comprising a number of intermediate chambers accommodating the impeller(s), a lower flow branch portion, a central motor housing portion and an upper flow branch portion, and an upper outlet housing portion, and wherein the main flow path is provided through said housing portions. This housing design allows for the first flow, i.e. the main flow, to have coaxial flow path around the motor so that the main flow also provides cooling of the motor.

In particular, the housing may be provided with the lower flow branch, which is provided with a flow path for diverting the main flow around the motor, said lower flow branch having a central entry position in fluid communication with the inlet housing portion, i.e. the intermediate chambers, and a radial flow delivery position; and wherein the central housing portion is provided with flow channels coaxially at a radial position, which are in fluid communication with corresponding flow path of the lower flow branch; and wherein the upper flow branch is provided with flow paths between a radially outward receipt position to a central outlet flow exit, and said radially outward receipt positions are in fluid communication with the coaxial flow channels of the central housing portion. The filter is preferably provided in the upper outlet housing portion. This housing design is advantageous as the lower flow branch portion and the upper flow branch portion may be similar or even identical in shape, which facilitates manufacturing of parts and assembly of the pump. Preferably, the housing portions are provided with external assembly flanges and assembled to each other by peripherally provided stay bolts. This further facilitates easy and simple assembly of the pump.

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 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.