Submersible fuel pump for pumping liquefied fluids

Abstract

The present disclosure relates to a submersible fuel pump for pumping liquefied fluids, particularly a cryogenic submersible fuel pump for pumping liquefied fuels such as liquid natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG), or the like, the pump including a housing (1) having a lower fluid inlet (3') and an upper fluid outlet (3''), the housing including a vertically oriented pump shaft (4), a permanent magnet electric motor (2) having a rotor with a hollow motor drive shaft (22) and a stator (24) around the rotor, and at least one submersible fuel pump (1) mounted on the pump shaft (4) for centrifugally moving the cryogenic fluid from the pump inlet to the pump outlet. The pump contains at least one impeller (85) coaxially provided around the electric motor with a main liquid flow (6) having a main direction from the pump inlet to the pump outlet, and a secondary liquid flow (7) for cooling the electric motor (2) and lubricating bearings (27, 28) in the pump, the secondary flow being a counter liquid flow essentially opposite to the main direction (6) from the region of the pump outlet through the electric motor (2) to a radially central space (7A) above the at least one impeller (5) in the region of the pump inlet (3'), and a filter (71) provided at the inlet of the secondary liquid flow path (7).

Description

[Technical Field]

[0001] The present invention relates to a submersible fuel pump for pumping liquefied fluids, and in particular to a cryogenic submersible fuel pump for pumping liquefied fuels such as liquid natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG), or the like. [Background technology]

[0002] Submersible fuel pumps for liquefied fuels such as LNG are well known in the art.

[0003] WO 2015 / 081314 A2 discloses a cryogenic submersible multi-stage pump assembly including a vertically oriented pump shaft. A permanent magnet electric motor includes a rotor mounted on the pump shaft and a stator disposed around the rotor. A first stage impeller assembly includes a first impeller mounted on 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.

[0004] WO 2015 / 081314 A2 also discloses a hollow permanent magnet rotor to which a pump shaft is attached, the shaft being attached to the hollow rotor at the top by a nut, and below the motor several impellers are attached to the pump shaft. Summary of the Invention [Problem to be solved by the invention]

[0005] To ensure efficient pump performance, it is important that the motor and cryogenic pump do not heat up so much during operation that the liquefied fuel becomes a gas. It is therefore an object of the present invention to provide an improved submersible fuel pump for pumping liquefied fluids, and in particular a cryogenic submersible fuel pump for pumping liquefied fuel that is compact in design and has improved efficiency. [Means for solving the problem]

[0006] In the present disclosure, a submersible fuel pump for pumping liquefied fluids, particularly a cryogenic submersible fuel pump for pumping liquefied fuels such as liquid natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG), or similar liquefied cryogenic dielectric fluids, is described, the pump including a housing having a lower fluid inlet and an upper fluid outlet, the housing including a vertically oriented pump shaft, a permanent magnet electric motor having a rotor with a hollow motor drive shaft and a stator around the rotor, and a pump for centrifugally moving the cryogenic fluid from the pump inlet to the pump outlet. The pump contains at least one shaft-mounted impeller, wherein a primary liquid flow having a primary direction from a pump inlet to a pump outlet is provided coaxially around the electric motor, and a secondary liquid flow for cooling the electric motor and lubricating bearings within the pump, the secondary flow being a counter liquid flow essentially opposite to the primary direction from the region of the pump outlet through the electric motor to a radially central space above the at least one impeller in the region of the pump inlet, and a filter is provided at the inlet of the secondary liquid flow path.

[0007] The present invention provides an efficient and simple solution to providing motor cooling and bearing lubrication in a pump. A first liquid flow is a main liquid flow where pressure is increased from inlet to outlet. A reverse secondary flow is provided due to the pressure difference within the pump such that a small portion of the main flow is reversed in the secondary flow through the motor to cool the motor and lubricate the bearings.

[0008] It has been found to be advantageous in accordance with the present invention to provide a filter at the inlet of the secondary liquid flow path, thereby protecting the motor and bearings from contaminants and thereby extending the life of the pump. It has been found that such a pump can have a very long service life, up to at least 26,000 hours.

[0009] Furthermore, the primary cargo liquid is used to lubricate and cool the pump motor during pump operation without the need to use a separate liquid for these functions. This is particularly advantageous when the cargo is a cryogenic liquid. To ensure proper functioning of the filter, the filter is preferably a cryogenic filter.

[0010] The filter is preferably a lateral flow filter with essentially radial inlet filter flow and axial outlet filter flow, so that counterflow can be established in a simple manner.

[0011] In certain embodiments, the filter is a self-cleaning filter, such as a lateral flow filter, which is advantageous because it improves system cleanliness and the filter may be maintenance-free, or at least have long periods between inspections.

[0012] In a preferred embodiment, the pump shaft extends below the motor shaft and at least one impeller is mounted on the shaft below the motor, allowing for a slim design of the pump. Preferably, multiple impellers are provided on the pump shaft to provide a multi-stage centrifugal pump.

[0013] Preferably, the upper radially central space is about the pump shaft such that the path of the secondary liquid flow exits adjacent the pump shaft above at least one impeller. The impeller generates pressure by rotating and thereby forcing the main flow from the radially central region outward to its periphery. Thus, pressure is lowest in the radially central region of the impeller, and this is utilized to establish the secondary flow.

[0014] In the pump according to the invention, the secondary liquid flow is a subflow of the main flow. In particular, the secondary liquid flow is a small amount of the main flow, preferably at least 15-35 times smaller, such as approximately 30 times smaller. This secondary flow is driven by a lower pressure at the center of the upper side of the impeller than at the pump outlet. The flow path through the motor and bearings is designed and dimensioned such that the flow resistance ensures that only a small amount of the main flow flows back through the pump.

[0015] A plurality of axially oriented flow channels are provided within the stator of the motor for cooling, said channels constituting a substantial portion of the secondary flow path that provides cooling for the motor.

[0016] In some preferred embodiments of the pump, a main bearing is provided at the upper end of the motor shaft to absorb any axial forces provided within the pump, in particular the main bearing is a hybrid bearing, in particular a hybrid ball bearing, said bearing being lubricated by a secondary liquid flow.

[0017] Preferably, a lower bearing is also provided at the lower end of the motor shaft to absorb any radial forces within the pump, this lower bearing being preferably a carbon guide bearing.

[0018] In the pump described in the present disclosure, the housing preferably has an inlet housing portion including several intermediate chambers for accommodating the impeller, a lower flow branch portion, a central motor housing portion, and an upper flow branch portion, and an upper outlet housing portion, and a main flow path is provided through the housing portions. This housing design allows the first flow, i.e., the main flow, to have a coaxial flow path around the motor so that the main flow also provides cooling for the motor.

[0019] In particular, the housing may be provided with a lower flow branch provided with a flow path for diverting the main flow around the motor, the lower flow branch having a central inlet position in fluid communication with the inlet housing portion, i.e., the intermediate chamber, and a radial flow delivery position, the central housing portion being provided with coaxial flow channels at radial positions that are in fluid communication with corresponding flow channels in the lower flow branch, and the upper flow branch being provided with a flow path between a radially outward receiving position and a central outlet flow outlet, the radially outward receiving position being in fluid communication with the coaxial flow channel in the central housing portion. A filter is preferably provided in the upper outlet housing portion. This housing design is advantageous because the lower and upper flow branch portions can be similar or even identical in shape, which facilitates the manufacture of pump parts and assembly. Preferably, the housing portions are provided with outer assembly flanges and are assembled to each other by stay bolts provided around the periphery. This further facilitates easy and simple assembly of the pump.

[0020] The invention will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a side cross-sectional view of a low-temperature submersible fuel pump according to an embodiment of the present invention. [Figure 2] 2 is a side cross-sectional view of the electric permanent magnet synchronous motor of the pump in FIG. 1. [Figure 3] 3 is a cross-sectional view of the electric permanent magnet synchronous motor perpendicular to the viewpoint of FIG. 2. [Figure 4] FIG. 1 is a cross-sectional view of a rotor in an electric permanent magnet synchronous motor with no magnets installed. [Figure 5] FIG. 5 is a detailed view of cross section B in FIG. [Figure 6] FIG. 6 is a detailed view of cross section C in FIG. 5. [Figure 7] FIG. 3 is a side view of a tightening collet for the connection of the motor shaft and the pump shaft shown in FIG. 2. [Figure 8]FIG. 2 is an end view of the clamping collet. DETAILED DESCRIPTION OF THE INVENTION

[0022] In Figure 1 there is shown a cross-sectional view of a submersible fuel pump for pumping liquefied fluids, in particular a cryogenic submersible fuel pump for pumping liquefied fuels such as liquid natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG), or the like. The pump includes a housing 1 having a lower fluid inlet 3' and an upper fluid outlet 3". The pump further includes a vertically oriented pump shaft 4 and a permanent magnet electric motor 2.

[0023] A 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 to provide a multi-stage centrifugal pump, wherein the impellers or vanes 5 centrifugally mounted on the pump shaft 4 move the cryogenic fluid from the pump inlet 3' to the pump outlet 3" as the impellers 5 are rotated by the pump shaft 4.

[0024] This main flow of liquefied fluid constitutes the main liquid flow from the pump inlet 3' to the pump outlet 3", which is indicated in Figure 1 by reference numeral 6. As shown in Figure 1, the main flow 6 is provided coaxially around the electric motor 2.

[0025] As shown in Figure 1, the components of the pump are housed in a housing 1. The housing includes several intermediate chambers 1A, each housing an impeller 5, a lower flow branch portion 1B, a central motor housing portion 1C, and an upper flow branch portion 1D, stacked on top of each other, and an upper outlet housing portion 1E, through which a main flow path 6 is provided.

[0026] The housing sections 1A to 1E are provided with outer assembly flanges and are assembled together by stay bolts 1F provided around the periphery.

[0027] The lower flow branch 1B is provided with a flow path for diverting the main flow 6 around the electric motor 2. The lower flow branch 1B therefore has a central inlet position in fluid communication with the top of the top of the intermediate chamber 1A, and a radial flow delivery position.

[0028] The central housing portion 1C is provided with coaxial flow channels 61 at radial positions (see FIG. 3) that are in fluid communication with corresponding flow channels in the lower flow branch 1B. The upper flow branch 1D is provided with flow channels between radially outward receiving positions and the central outlet flow outlet, said radially outward receiving positions being in fluid communication with the coaxial flow channels 61 in the central housing portion 1C.

[0029] The pump's electric motor 2 is shown in more detail in Figures 2 and 3, and in more detail in Figures 4-6. Housed in a motor housing 21, the electric motor 2 includes a rotor assembly with a rotor body 23 attached to a motor shaft 22, and a plurality of permanent magnetic magnets 231 are provided along the periphery 234 of the rotor body 23. The electric motor also includes a stator 24 having coils arranged concentrically around the rotor assembly. The rotor assembly further includes a mechanical magnet retention system for holding the magnets 231 in place within the rotor body 23. The mechanical magnet retention system includes a plurality of axially oriented slots 232 around the periphery of the rotor body 234 in which the permanent magnets 231 are retained.

[0030] The rotor body 23 is rigidly attached to the motor shaft by any suitable means.

[0031] The motor shaft 22 is hollow and the pump shaft 4 is concentrically mounted within the hollow motor drive shaft 22 as shown in Figure 1. Assembly of the pump shaft 4 and motor shaft 22 is provided by a collet clamp connection to interlock the motor shaft 22 and pump shaft 4 at the upper ends of the shafts 4, 22. The pump shaft 4 is a smooth shaft, preferably a cylindrical elongated shaft having equal diameters.

[0032] The collet clamp connection that attaches the pump shaft 4 to the motor shaft 22 is a collet clamp 41, which is made from a metal alloy, for example an alloy suitable as a low temperature material, such as bronze or stainless steel.

[0033] 1, 2, and further referring to FIGS. 7 and 8, the collet clamp connection includes a clamping collet 41 having a conical outer clamping surface 41A that engages a correspondingly conical inner surface on the end of the hollow motor shaft 22, and a cylindrical inner clamping surface 41B that clamps the collet 41 around the pump shaft 4. The clamping collet 41 is attached to the motor shaft 22 by a clamping nut 29 (see FIG. 2) that is provided with an inner conical surface that engages a conical collar surface 41C on the collet clamp 41. The clamping nut is in threaded engagement with the end of the motor shaft 22, and tightening the clamping nut 29 onto the end of the motor shaft 22 forces the clamping collet 41 into the receiving surface of the motor shaft 22.

[0034] The motor shaft 22 is supported within the motor housing 21 and, consequently, within the pump housing 1 by a main bearing 27 provided at the upper end of the motor shaft 22 to absorb any axial forces that may occur within the pump. In some currently preferred embodiments, the main bearing 27 is a hybrid bearing, particularly 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 within the motor 2 to absorb any radial forces that may occur. 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 that forms a crack-free coating. This can ensure the performance of the motor shaft 22 in low temperature conditions.

[0035] As shown in FIG. 1, a secondary liquid flow 7 is provided to cool the electric motor 2 and lubricate the bearings 27, 28 therein. The secondary liquid flow 7 is a partial flow of the main flow 6. This secondary flow 7 is a counter-flow of liquid from the region of the pump outlet 3″ through the electric motor 2 to a radially central space 7A above the uppermost impeller 5 above the region of the pump inlet 3′.

[0036] A filter 71 is provided in the upper outlet housing portion 1E 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 bearings 27, 28, thereby protecting the motor 2 and bearings 27, 28 and extending the life of these components. The filter 71 is preferably a low temperature filter, and even more preferably, the filter 71 may be a self-cleaning filter, such as a side flow filter.

[0037] The first liquid flow 6 is the main flow whose pressure is increased in the pump from inlet 3' to outlet 3". A reverse secondary flow 7 is provided due to the pressure difference in the pump such 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. The bearings are therefore lubricated by the main fluid flowing through the pump.

[0038] The pressure differential is achieved by providing an outlet for the secondary flow in a radially central space 7A above the uppermost impeller 5 (or the only impeller, in one embodiment of the invention, if the pump is designed with only one impeller 5).

[0039] The secondary liquid flow 7 is a partial flow of the main liquid flow 6. Due to the narrow passage 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 only a small fraction of the main liquid flow 6, such as approximately at least 15-35 times smaller.

[0040] Around the cylindrical periphery of the stator 24 are a plurality of axially oriented flow channels 25 for cooling the electric motor 2, these channels 25 constituting a significant portion of the secondary flow path 7 which provides cooling for the motor.

[0041] As described above, the electric motor is a permanent magnet synchronous motor in which magnets are provided in slots on the rotor. Referring to Figures 4-6, in a mechanical magnet retention system, each slot 232 is provided with a leaf spring member 233 to retain a magnet 231 inserted into the slot 232. The leaf spring member 233 is provided in a shallow recess within the slot 232 and is adapted to provide a force directed radially outward against the magnet 231 when the magnet 231 is inserted into the slot 232 (see Figure 3). The magnet 231 is provided with a cross-sectional shape that fits snugly within the slot 232 over the leaf spring 233.

[0042] The slots 232 are provided coaxially in the rotor 23 and may be open at both ends for the insertion of the magnets 231. In the embodiment shown in Figure 3, a total of twelve slots 232 are provided evenly distributed along the cylindrical surface 234 of the rotor body 23. The magnetic polarity of neighboring magnets on the rotor surface is alternated every two magnets 231 so that the magnets 231 on surface 234 are provided in the configuration NNSSNNSSNNSS.

[0043] In one embodiment, the rotor body 23 is made from a stack of multiple sheets of magnetic steel, in particular electrical steel. The stack of sheets may be thin, such as less than 1 mm thick, preferably 0.35 mm to 0.5 mm thick. In a further embodiment, the leaf springs 233 may be laser cut into the stack and are therefore made from the same material.

[0044] In this disclosure, terms such as "vertical," "horizontal," and the like are used. Such terms are to be understood as relative directional terms between associated elements, flanges, or the like.

[0045] Although the present invention has been described in connection with specific embodiments, it should not be construed as being limited in any way to the examples presented. The scope of the present invention is defined by the appended claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other potential elements or steps. Also, the use of references such as "a" or "an" should not be construed as excluding a plurality. The use of reference signs in the claims for elements shown in the figures should also not be construed as limiting the scope of the invention. Furthermore, individual features recited in different claims can possibly be advantageously combined, and the recitation of these features in different claims does not exclude that combinations of features are not possible and advantageous.

[0046] The present invention is described above in relation to certain presently preferred embodiments of a submersible fuel pump. However, it is recognized that the present invention allows other embodiments and variations to be provided without departing from the scope of the invention as defined in the appended claims.

Claims

1. 1. A submersible fuel pump for pumping liquefied fluids, in particular a cryogenic submersible fuel pump for pumping liquefied fuels such as liquid natural gas (LNG), hydrogen, methanol, ethane, liquefied petroleum gas (LPG) or the like, comprising: a housing having a lower fluid inlet and an upper fluid outlet, said housing comprising: a vertically oriented pump shaft; a permanent magnet electric motor having a rotor with a hollow motor drive shaft and a stator around the rotor; at least one impeller mounted on said pump shaft for centrifugally moving cryogenic fluid from a pump inlet to a pump outlet, at least one impeller coaxially providing a primary liquid flow having a primary direction from the pump inlet to the pump outlet; a secondary liquid flow for cooling the electric motor and lubricating bearings in the pump, the secondary flow being a counter-liquid flow essentially opposite to the main flow direction from the region of the pump outlet through the electric motor to a radially central space above the at least one impeller in the region of the pump inlet, a filter being provided at the inlet of the secondary liquid flow path; Contains a pump.

2. The pump of claim 1 , wherein the pump shaft extends below the motor shaft and the at least one impeller is mounted on the shaft below the motor.

3. 3. A pump according to claim 1 or 2, wherein a plurality of impellers are provided on the pump shaft to provide a multi-stage centrifugal pump.

4. 4. A pump as claimed in any one of claims 1 to 3, wherein the upper radially central space is about the pump shaft such that the path of the secondary liquid flow exits adjacent the pump shaft above the at least one impeller.

5. A pump according to any one of claims 1 to 4, wherein the filter is a lateral flow filter having essentially radial inlet filter flow and axial outlet filter flow.

6. A pump according to any one of claims 1 to 5, wherein the filter is a low temperature filter.

7. A pump according to any one of claims 1 to 6, wherein the filter is a self-cleaning filter.

8. A pump according to any one of claims 1 to 7, wherein the secondary liquid flow is a partial flow of the main liquid flow.

9. 9. A pump according to claim 8, wherein the secondary liquid flow is a small amount of the main liquid flow, such as approximately 30 times smaller, preferably at least 15 to 35 times smaller.

10. A pump according to any preceding claim, wherein the pressure at the central portion of the upper side of the impeller is lower than the pressure at the pump outlet.

11. 11. A pump as claimed in any one of claims 1 to 10, wherein a plurality of axially oriented flow channels are provided in the stator of the motor for cooling, said channels constituting a substantial portion of the secondary flow path that provides cooling for the motor.

12. A pump as claimed in any preceding claim, wherein a main bearing is provided at the upper end of the motor shaft to absorb any axial forces provided within the pump.

13. 13. The pump according to claim 12, wherein the main bearings are hybrid bearings, in particular hybrid ball bearings, and the bearings are lubricated by the secondary liquid flow.

14. A pump according to any one of the preceding claims, wherein a lower bearing is provided at the lower end of the motor shaft to absorb any radial forces.

15. 15. The pump of claim 14, wherein the lower bearing is a carbon guide bearing.

16. 16. A pump as claimed in any one of claims 1 to 15, wherein the housing has an inlet housing portion including one or more intermediate chambers accommodating the impeller, a lower flow branch portion, a central motor housing portion, and an upper flow branch portion, and an upper outlet housing portion, and the main flow path is provided through the housing portions.

17. The lower flow branch includes: a flow path is provided for diverting the main flow around the motor, the lower flow branch having a central inlet location in fluid communication with the inlet housing portion and a radial flow delivery location; the central housing portion is provided with a coaxial flow channel at a radial location that is in fluid communication with a corresponding flow channel of the lower flow branch; 17. The pump of claim 16, wherein the upper flow branch is provided with a flow path between a radially outward receiving location and a central outlet flow outlet, the radially outward receiving location being in fluid communication with the coaxial flow channel of the central housing portion.

18. 18. A pump according to claim 16 or 17, wherein the housing parts are provided with outer assembly flanges and are assembled together by stay bolts provided at the periphery.

19. A pump according to any one of claims 5 and 16 to 18, wherein the filter is provided in the upper outlet housing portion.

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