Subsea fluid processing system having a canned fluid-filled stator and cooling mechanism
A subsea fluid processing system includes an electric motor that rotates a shaft on which impellers are fixedly mounted. Diffusors are static and fixed to the pump housing. The electric motor includes a rotor surrounding the shaft and a stator that is filled with a dielectric stator fluid. The stator is sealed or “canned.” The inner surface of the stator which faces the rotor is canned with a canning non-metallic material. The motor, as well as bearings for the rotating shaft are lubricated and cooled with a fluid that in some cases is taken from the process fluid and some alternative source. Alternative sources include: MEG, methanol, treated seawater and untreated seawater.
1. A subsea process fluid processing system, comprising:
a housing having a first inlet, a second inlet, a first outlet and a second outlet;
an elongated impeller shaft disposed within the housing;
a first set of impellers disposed within the housing, wherein the first set of impellers is fixedly mounted to the elongated impeller shaft, and the first set of impellers is configured to rotate to drive a flow of a process fluid through the housing from the first inlet to the first outlet;
a second set of impellers disposed within the housing, wherein the second set of impellers are fixedly mounted to the elongated impeller shaft, and the second set of impellers is configured to rotate to drive a flow of a process fluid through the housing from the second inlet to the second outlet;
a chamber enclosed by an outer sleeve, a first end piece, a second end piece, and an inner canning of non-metallic material, wherein the chamber further comprises a third end piece positioned between the first end piece and the second end piece;
an electric motor coupled to the elongated impeller shaft, wherein the electric motor is configured to drive rotation of the elongated impeller shaft and the first set of impellers about a main longitudinal axis, wherein the flow of the process fluid is internally split within the housing between a first flow path from the first set of impellers to the first outlet and a second flow path from the first set of impellers through the electric motor and in a direction toward the second set of impellers, and wherein the electric motor comprises:
a rotor fixedly mounted to the elongated impeller shaft;
a canned fluid filled stator, dimensioned and positioned to surround the rotor, and being filled with a dielectric stator fluid and sealed at least with the inner canning of non-metallic material on an inner surface facing the rotor, wherein the canned fluid filled stator is positioned in the chamber, and further wherein the canned fluid filled stator includes integrated cooling channels, wherein the integrated cooling channels are oriented parallel to the main longitudinal axis and extend through the stator and are filled with the dielectric stator fluid, and wherein the dielectric stator fluid is circulated by a forced circulation generated by the elongated impeller shaft;
a first pump section comprising the first set of impellers, a first diffuser, the first inlet and the first outlet; and
a second pump section comprising the second set of impellers, a second diffuser, the second inlet and the second outlet;
wherein the pump sections are configured in an arrangement such that an axial force exerted by the first pump section is at least partially offset by an axial force of the second pump section.
2. The system according to claim 1 , wherein the second flow path of the process fluid extends between the inner surface of the canned fluid filled stator and the rotor.
3. The system according to claim 1 , wherein the process fluid comprises sea water.
4. The system according to claim 3 , wherein the sea water is configured to receive treatment via a subsea treatment system, and the subsea treatment system includes at least one of a desalinization system, an oxygen scavenger, or a filtration system.
5. The system according to claim 1 , wherein the process fluid is selected from a group consisting of monoethylene glycol and methanol.
6. The system according to claim 1 , wherein the non-metallic material does not conduct electricity, and the non-metallic material comprises a polymer, a glass fiber material, a ceramic material, or a combination thereof.
7. The system according to claim 1 , wherein the non-metallic material includes fibers of material selected from a group consisting of: aramid, Kevlar, and carbon.
8. The system according to claim 1 , further comprising a pressure compensator configured to adjust the volume of the dielectric stator fluid to pressure compensate the dielectric stator fluid according to environmental fluctuations outside of the system.
9. The system according to claim 1 , wherein the first set of impellers of the first pump section is driven by the electric motor.
10. The system according to claim 1 , wherein the process fluid is a single-phase liquid fluid.
11. The system according to claim 1 , wherein the second flow path of the process fluid extends through the electric motor and then subsequently extends through a return flow path back to an intake for passage through the first set of impellers.
12. The system according to claim 11 , wherein the return flow path either comprises a conduit disposed outside of the housing or extends to a bearing upstream of the first set of impellers, or both.
13. The system according to claim 1 , wherein the subsea fluid processing system comprises a balance piston between the first set of impellers and the electric motor, and the second flow path of the process fluid leaks past the balance piston and then flows through the electric motor.
14. The system according to claim 1 , wherein the second flow path of the process fluid extends through the electric motor to a vent to an external environment of the housing.
15. The system according to claim 1 , further comprising at least one external cooling pipe configured to provide cooling of the dielectric stator fluid.