Load-sharing in parallel fluid pumps

Abstract

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 (Ta) and a monitored differential pressure value (DPa) of the first pumping unit, identifying the minimum allowable torque value (Ta) of the first pumping unit corresponding to the monitored differential pressure value (DPa) 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 (Tb) and a monitored differential pressure value (DPb) of the second pumping unit, identifying the minimum allowable torque value (Tb) of the second pumping unit corresponding to the monitored differential pressure value (DPb) of the second pumping unit, and regulating the rotational speed of the first and second pumps such that Ta/Tb equals Tb/Tb.