SUBSEA PUMP SYSTEM WITH PROCESS LUBRICATED BEARINGS

Abstract

The invention provides a subsea pump system, comprising a subsea centrifugal pump with a motor compartment and a process compartment, wherein the motor compartment is separate from the process compartment and comprises an electric motor or stator driving a motor shaft, wherein the process compartment comprises a pump arranged on a pump rotor, an inlet for fluid and an outlet for pressure boosted fluid, and wherein the motor shaft via a coupling preferably drives the pump rotor. The subsea pump system is distinguished in that it further comprises a liquid phase separator arranged downstream to the pump or downstream to at least one pump impeller, the liquid phase separator comprising: an inlet receiving the pressure boosted fluid, an outlet delivering a majority, or a minor part, of the pressure boosted fluid, and a liquid phase outlet, a liquid recirculation line, a flow mixer arranged on the inlet side of the pump, wherein the liquid recirculation line is arranged from the liquid phase outlet to the flow mixer, and a liquid lubricant line arranged from a location containing pressure boosted fluid to one or more process compartment bearings, directly or via other equipment, for lubricating said process compartment bearings.

Claims

1. A subsea pump system comprising: a subsea centrifugal pump with a motor compartment and a process compartment; wherein the motor compartment is separate from the process compartment and comprises an electric motor or stator driving a motor shaft; wherein the process compartment comprises a pump arranged on a pump rotor, an inlet for fluid and an outlet for pressure boosted fluid; and a liquid phase separator arranged downstream to the pump or downstream to at least one pump impeller, the liquid phase separator comprising: an inlet receiving the pressure boosted fluid; an outlet delivering a majority, or a minor part, of the pressure boosted fluid; and a liquid phase outlet; a liquid recirculation line; a flow mixer arranged on the inlet side of the pump, wherein the liquid recirculation line is arranged from the liquid phase outlet to the flow mixer; and a liquid lubricant line or -conduit arranged from a location containing pressure boosted fluid to one or more process compartment bearings, directly or via other equipment, for lubricating the process compartment bearings.

2. The subsea pump system according to claim 1, comprising a liquid lubricant impeller arranged on the pump rotor.

3. The subsea pump system according to claim 1, comprising a second stage liquid separator, arranged in the liquid recirculation line, for conditioning the recirculated liquid further for service as liquid lubricant, wherein the liquid lubricant line is arranged from the second stage separator to the process compartment bearings, directly or via other equipment.

4. The subsea pump system according to claim 1, further comprising an inlet for methanol, glycol or other liquid feasible for bearing lubrication, coupled to the liquid lubricant line or directly to the process compartment, for delivering the methanol, glycol or other liquid for bearing lubrication, and/or for maintaining a motor compartment overpressure.

5. The subsea pump system according to claim 4, wherein the inlet is connected to a line for liquid injection for flow assurance.

6. The subsea pump system according to claim 1, wherein the pressure booster comprises a magnetic coupling and a separation wall arranged between magnetic coupling parts, the separation wall separating the motor compartment hermetically from the process compartment while the motor shaft is magnetically coupled to drive the pump rotor through the separation wall.

7. The subsea pump system according to claim 1, comprising: wherein the pump is a subsea centrifugal multiphase pump; wherein liquid for process compartment bearing lubrication is separated out from the pressure boosted multiphase fluid in two stages, the liquid phase separator and the second stage liquid separator, respectively; and wherein the liquid is supplied via a liquid lubricant line from the second stage liquid separator.

8. The subsea pump system according to claim 1, wherein the liquid for lubricating the bearings is directed from the liquid lubricant line or a liquid lubricant impeller, to bearings in the process compartment.

9. A method for lubricating the bearings in a process compartment of a subsea pump system comprising a subsea centrifugal pump with a motor compartment and a process compartment, the method comprising: separating out a liquid phase in a liquid phase separator arranged downstream to the pump or downstream to at least one pump impeller; discharging the separated-out liquid into a liquid recirculation line or -conduit, arranged from a liquid phase outlet from the liquid phase separator to a flow mixer arranged on the inlet side of the pump; and directing a flow of liquid fluid as lubricant to at least one process compartment bearing, via a liquid lubricant line arranged from the liquid recirculation line or conduit.

10. (canceled)

11. The subsea pump system of claim 1, wherein the motor shaft via a coupling drives the pump rotor.

12. The subsea pump system of claim 5, wherein the line for liquid injection for flow assurance comprises an umbilical flow bore or a separate line arranged to subsea field equipment for ensuring flow assurance by preventing hydrate formation.

13. The method of claim 9, wherein the directing is via a second stage liquid separator upstream to the liquid lubricant line.

14. The method of claim 13, wherein the directing is via a liquid lubricant impeller on the downstream side of the liquid lubricant line.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0041] FIG. 1 illustrates an embodiment of a subsea pump system of the invention.

[0042] FIG. 2 illustrates an embodiment of a liquid lubricant impeller in a subsea pump system of the invention.

[0043] FIG. 3 illustrates an embodiment of a subsea pump system of the invention.

[0044] FIG. 4 illustrates a further embodiment of a subsea pump system of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0045] Reference is made to FIG. 1, illustrating a subsea pump system 1 embodiment of the invention.

[0046] The subsea pump system 1 comprises a subsea pump 2, such as a subsea multiphase pump, with a motor compartment 3 and a process compartment 4. The motor compartment 3 is separate from the process compartment 4 and comprises an electric motor 5 driving a motor shaft 6. The process compartment 4 comprises a multiphase pump 7 arranged on a pump rotor 8, an inlet for process fluid 9 and an outlet 10 for pressure boosted fluid. The motor shaft drives the multiphase pump rotor via a magnetic coupling 22. A liquid phase separator 11 is arranged downstream to the multiphase pump, the liquid phase separator comprising: an inlet 12 receiving the pressure boosted multiphase fluid; an outlet 13 delivering a majority of the pressure boosted multiphase fluid; and a liquid phase outlet 14 delivering a part of the pressure boosted liquid into a liquid recirculation line 15. A flow mixer 16 is arranged on the process fluid inlet side of the multiphase pump, wherein the liquid recirculation line is arranged from the liquid phase outlet to the flow mixer, via a second stage liquid separator 19. A liquid lubricant line 17 arranged from the liquid recirculation line for directing a flow of liquid fluid as lubricant to at least one process compartment bearing 18.

[0047] A liquid lubricant impeller 20, arranged with respect to flow direction between the liquid lubricant line and the at least one process compartment bearing, is illustrated. In the illustrated embodiment the liquid lubricant impeller 20 is arranged on the multiphase pump rotor 8.

[0048] The liquid lubricant impeller can be arranged on the pump rotor in the distal end or the near end relative to the motor compartment. The liquid lubricant line 17 can be arranged to the pump compartment in the distal or the near end from the motor compartment or be divided or be double lines arranged to each ends/sides of the pump compartment/pump rotor.

[0049] Further, an inlet 21 for methanol, glycol or other flow assurance liquid, surprisingly also feasible for bearing lubrication, is for redundancy coupled to the liquid lubricant line for delivering said methanol, glycol or other liquid for bearing lubrication, as illustrated.

[0050] Dependent on the bearings of the pump compartment of the pump system of the invention, the liquid of the liquid lubricant is one of water, oil, glycol, methanol and any mixture thereof. A practical achievable minimum of particle contents is preferred in said liquid or mixture. Bearings under development are expected to tolerate gas in a limited period of time, when such bearings become available the liquid can also include gas within the tolerable time periods for the bearings.

[0051] The magnetic coupling 22 couples the motor shaft 6 to the pump rotor 8. A static separation wall 23, between two rotating magnetic coupling parts, separates the motor compartment hermetically from the process compartment. No external supply of barrier fluid is required through a long pressure-controlled supply chain, since the motor compartment is designed for operation throughout the lifetime with prefilled lubricant/coolant, while the separated liquid is lubricant for bearings and seals of the process compartment. Preferably, also a hydraulic variable speed drive (not illustrated) is arranged between the motor and the magnetic coupling. An external variable speed drive, VSD, can thereby be eliminated.

[0052] Process fluid enters the subsea pump system via process inlet 24 and pressure boosted process fluid exits the subsea pump system via process outlet 25. The valve 26 between said inlet and outlet is usually closed.

[0053] Reference is made to FIG. 2 illustrating in more detail an embodiment of a liquid lubricant impeller 20 in a subsea pump system of the invention. The impeller 20 is arranged on the pump rotor 8. Lubricant is received from the liquid lubricant line 17. Arrows indicate the flow direction from an end cover 28 into the impeller 20. From the impeller, lubricant flows in several conduits, lubricating bearings, more specifically thrust bearings 18t and radial bearing 18r, as well as seals s. In the illustrated embodiment, a suction cover 29, at the main inlet to pump impellers, are also illustrated. The lubricant delivered from the liquid lubricant line 17 is preferably directed into an inflow lubricant channel coaxial to the rotational axis of the pump rotor 8, as illustrated by arrow 17. Preferably, similar arrangement is provided at both ends of the rotor. The arrow 30 radially outwards from the static end cover 28 illustrate that part of the pressurized lubricant is directed to the further bearings at or towards the opposite end of the rotor 8. In addition to bearing lubrication 18, the lubricant delivered from the liquid lubricant line preferably also lubricates, cools and provide hydrodynamic stabilization of the process compartment side of the preferable magnetic coupling 22, also illustrated by the arrow 30 radially outwards from the static end cover 28. Alternatively, the liquid lubricant line or -conduit is divided or two liquid lubricant lines/-conduits are arranged, and liquid lubricant is directed to bearings at both ends of the pump rotor. However, only details essential for the understanding of the present invention are illustrated, not to scale, and not including full details or the whole pump, for increased clarity.

[0054] FIG. 3 illustrates an embodiment of a subsea pump system of the invention, illustrating in more detail. A control valve 27 in the liquid recirculation line 15 can ensure a minimum recirculation flow of liquid, for sufficient cooling and lubrication, which can be required for multiphase pumps. The liquid phase separator 11, and also the second stage liquid separator 19, are in the illustrated embodiment combined cyclonic and gravity-based separators. The outlet 14 from the liquid phase separator 11 is arranged low towards the major flow part outlet 13, but not lowermost or outermost, to avoid liquid rich in sand content.

[0055] Further reference is made to FIG. 4, illustrating an embodiment of the pump system of the invention for which the liquid lubricant line 17 is arranged directly from a liquid filled part of the liquid separator 11 to the pump compartment.

[0056] The subsea pump system of the invention, and the method of the invention, can include any feature or step as here described or illustrated, in any operative combination, each of which operative combinations are an embodiment of the present invention.