Subsea Pump Gas Separation via Segmented Canned Motor
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Solution Overview
Problem
Subsea multiphase pump technologies face limitations in handling high gas volume fractions and pressure rises due to rotordynamic constraints and inefficiencies in gas separation, particularly in subsea separator systems where conventional helico-axial and twin screw pumps are ineffective.
Innovation Solution
A multistage centrifugal pump with a canned motor and integral suction gas separation system that separates gas from liquid using axial hydraulics and returns the gas to the main separator, eliminating the need for shaft seals and buffer fluids, allowing operation with high suction gas concentrations and wider pressure ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If helico-axial pump stages are used to achieve high pressure rise, then pressure increase is improved, but gas volume fraction reduction is limited due to rotordynamic constraints on shaft length
Solution Approach 1:
The pump is divided into multiple helico-axial stages stacked in series, with each stage contributing to pressure rise while the segmented configuration allows gas separation between stages. The shaft is divided into multiple segments with gas ports that vent gas from each stage to the annulus, preventing gas accumulation and maintaining reliability with high gas volume fractions.
Solution Approach 2:
The patent introduces a radial dimension for gas removal by creating an annular space between the shaft and pump casing. Gas is removed radially outward through ports in the shaft to the annulus, which then discharges gas axially upward. This dimensional approach to gas management allows the pump to handle high gas volume fractions while achieving high pressure rise through multiple axial stages.
2Quantity of substance
If twin screw pump is used to handle high gas volume fraction, then flow rate is maintained, but viscosity requirements limit effectiveness with low viscosity fluids
Solution Approach 1:
The patent replaces the positive displacement mechanical system of twin screw pumps with a rotodynamic centrifugal pumping system. The helico-axial impellers generate centrifugal force to move fluid, which is effective for low viscosity fluids. Gas separation is achieved through centrifugal forces and pressure differential rather than mechanical sealing, making the system adaptable to low viscosity fluids while maintaining flow rate.
3Reliability
If shaft seals or buffer fluids are used in conventional pumps, then sealing is achieved, but reliability is reduced due to potential failure points
Solution Approach 1:
The patent extracts and eliminates the shaft seal system entirely by using a canned motor design where the motor rotor is hermetically sealed within a can that forms part of the pump casing. The magnetic coupling transfers power through the can wall without mechanical contact, removing the failure-prone shaft seals and buffer fluid systems while maintaining reliable sealing.
4Quantity of substance
If conventional gas separation systems are used, then gas removal is achieved, but device complexity increases with additional separation stages
Solution Approach 1:
The patent merges the gas separation function directly into the pump structure by integrating helico-axial impellers with built-in gas separation capability. The impeller design itself creates pressure differential for gas separation, and the shaft annulus system is integrated within the pump housing. This consolidation achieves effective gas removal without adding separate external separation stages, reducing overall device complexity.
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
The solution enhances flow assurance by reducing gas in the pumped effluent, preventing hydrate formation and enabling stable operation across varying pressures, improving efficiency and reducing the risk of pump failure by eliminating dynamic shaft seals and buffer fluid systems.
Implementation Method 1
The blade and vane geometries are designed to homogenize the gas-oil mixture to prevent separation while increasing the total pressure of the fluid
Implementation Method 2
followed by a diffuser to direct the flow to the next stage
Implementation Method 3
at least one radial hole in the shaft for directing separated gas to the axial hole
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
A combined canned motor-pump operates directly in the process fluid without the need for shaft seals or buffer or lubricating fluids. The pump incorporates an integral gas -separating system that includes gas separating hydraulics and a flow path that returns the gas to the main gas/oil separator. The gas -separating system includes a pump inlet for accepting incoming multiphase flow, at least one blade rotatable about the axis of rotation, an open annulus region for separating gas from liquid in the multiphase flow, at least one radial hole in the shaft for directing separated gas to the axial hole, and a pump outlet for discharging liquid from the pump.