Parallel Pump Load Sharing via Torque-Pressure Ratio
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Solution Overview
Problem
In subsea multiphase or variable density fluid pumping systems with parallel pumps, uneven load distribution can lead to surge conditions as pumps reach their minimum flow limits at different times, inefficiently operating the system.
Innovation Solution
The method involves establishing pump limit characteristics diagrams based on minimum allowable torque values for each pump, monitoring torque and differential pressure, and regulating rotational speed to maintain a consistent relation between monitored and minimum torque values, ensuring all pumps reach their minimum flow limits simultaneously, thereby preventing surge conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pumps are operated in parallel without load sharing control, then system simplicity is maintained, but uneven load distribution causes pumps to reach minimum flow limits at different times leading to surge conditions
Solution Approach 1:
The control system continuously monitors the actual flow rate of each pump and compares it with the minimum flow limit. When a pump approaches its minimum flow limit, the control valve associated with that pump is opened to redirect flow back to the suction line, preventing surge conditions. This feedback mechanism ensures reliable surge prevention through real-time monitoring and automatic adjustment.
Solution Approach 2:
The system divides the parallel pump operation into independent controllable units, with each pump having its own control valve and monitoring system. This segmentation allows individual pumps to be controlled independently to maintain their flow rates above minimum limits, preventing surge conditions in each pump unit while operating in parallel.
2Productivity
If load sharing control is implemented to prevent surge conditions, then pump reliability is improved, but system complexity increases due to monitoring and control requirements
Solution Approach 1:
The control system uses feedback from flow rate measurements to automatically adjust control valves, maintaining optimal operation of parallel pumps. This feedback loop ensures that pumps operate efficiently within their permissible operating regions, maximizing system productivity while avoiding surge conditions.
Solution Approach 2:
The control system automatically monitors and adjusts pump operation without requiring external intervention. When a pump approaches its minimum flow limit, the system self-corrects by opening the appropriate control valve to redirect flow, enabling the system to maintain optimal productivity autonomously.
3Ease of operation
If pumps operate without coordinated control, then operational simplicity is maintained, but one pump may reach minimum flow limit before others, triggering unnecessary return line valve opening
Solution Approach 1:
The control system monitors each pump's flow rate individually and only opens return line control valves when necessary to prevent surge conditions. This feedback-based approach maintains ease of operation by automatically managing complex control logic while improving productivity by preventing unnecessary valve openings and maintaining optimal pump operation.
Data Source
AI summary
A method of sharing load between a plurality of parallel fluid pumps in a subsea fluid pumping system having first and second pumping units, each of which includes a respective first and second pump, the method including establishing a pump limit characteristics diagram for the first pumping unit by mapping a minimal allowable torque of the first pumping unit as a function of a differential pressure across the first pump, identifying a permissible operating region of the first pumping unit defined by a set of minimum allowable torque values for the first pumping unit, establishing a pump limit characteristics diagram for the second pumping unit by mapping a minimal allowable torque of the second pumping unit as a function of a differential pressure across the second pump, identifying a permissible operating region of the second pumping unit defined by a set of minimum allowable torque values for the second pumping unit, monitoring the torque of the first pumping unit and the differential pressure across the first pump, acquiring a monitored torque value (Tma) and a monitored differential pressure value (DPma) of the first pumping unit, identifying the minimum allowable torque value (T0a) of the first pumping unit corresponding to the monitored differential pressure value (DPma) of the first pumping unit, monitoring the torque of the second pumping unit and the differential pressure across the second pump, acquiring a monitored torque value (Tmb) and a monitored differential pressure value (DPmb) of the second pumping unit, identifying the minimum allowable torque value (T0b) of the second pumping unit corresponding to the monitored differential pressure value (DPmb) of the second pumping unit, and regulating the rotational speed of the first and second pumps such that Tma/T0b equals Tmb/T0b.