Subsea Pump Lubrication via Liquid Phase Separator
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Solution Overview
Problem
Existing subsea pump systems face challenges in using process fluid as a lubricant due to the variability of multiphase fluid composition, sand content, pressure, and temperature, making reliable and efficient lubrication difficult, especially for centrifugal pumps.
Innovation Solution
A subsea centrifugal pump system with a separate motor compartment and process compartment, featuring a liquid phase separator downstream of the pump impellers, a recirculation line, and a flow mixer, which separates and recirculates a specific intermediate liquid fraction for lubrication, eliminating the need for barrier fluid and allowing for redundant lubrication with methanol or glycol.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If barrier fluid is supplied at controlled overpressure via a long supply chain from topside hydraulic power unit, then bearing lubrication is achieved, but system complexity and supply chain length increase
Solution Approach 1:
The system uses the process fluid itself as the lubricant source, eliminating the need for external barrier fluid supply chains. The liquid phase separator extracts lubricating liquid directly from the process fluid stream, and the recirculation system continuously supplies fresh lubricant to bearings, making the system self-sufficient and removing complex external supply infrastructure
Solution Approach 2:
The process fluid serves dual functions: as the main process material to be pumped and as the source of lubricating liquid for bearings. This multi-functionality eliminates the need for separate barrier fluid systems, reducing overall system complexity while maintaining reliable lubrication
2Reliability
If all liquid is separated out for use as lubricant in multiphase pumps, then bearing lubrication is provided, but productivity and pressure head are limited compared to centrifugal pumps
Solution Approach 1:
Instead of separating all liquid from the multiphase stream, the system selectively separates only a portion of the liquid phase - specifically an intermediate fraction that is free of sand particles and has suitable lubricating properties. The majority of the liquid phase remains in the process stream, maintaining high productivity and pressure head while still providing sufficient lubricant for bearings
Solution Approach 2:
The liquid phase separator is designed to extract only the specific intermediate liquid fraction with optimal lubricating properties, leaving other fractions (lightest and heaviest) in the process stream. This selective separation ensures high-quality lubrication while preserving the overall flow characteristics and productivity of the centrifugal pump
3Reliability
If liquid phase separator separates only an intermediate liquid fraction, then lubrication quality improves, but separation complexity increases
Solution Approach 1:
The liquid phase separator acts as an intermediary device that selectively extracts the intermediate liquid fraction from the multiphase stream. By positioning the separator downstream of the pump where flow conditions are stable, and using simple gravity-based separation principles, the system achieves selective fraction separation without requiring complex multi-stage separation equipment
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution provides a simple, reliable, and efficient lubrication system for subsea pumps, reducing the risk of hydrate formation and maintaining production by using pressure-boosted fluid for lubrication, eliminating the need for a long supply chain and enhancing operational reliability.
Implementation Method 1
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
Implementation Method 2
a liquid recirculation line or -conduit, a flow mixer arranged on the inlet side of the pump, wherein the liquid recirculation line or -conduit is arranged from the liquid phase outlet to the flow mixer
Implementation Method 3
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 said process compartment bearings
Data Source
AI summary
A subsea pump system includes a subsea centrifugal pump with a motor compartment and a process compartment. The subsea pump system further includes a liquid phase separator arranged downstream to the pump or downstream to at least one pump impeller. The liquid phase separator includes 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, and a liquid lubricant line.