Design And Development Of Electric Submersible Pumps For Large Capacities

Abstract

A submerged electric (SE) pump has been designed and analyzed for high flow applications. The challenges when designing a high power density SE pump are torsional and lateral dynamics and hydraulic stability. The case discussed in this paper is a single-stage pump rated for 7000 m3/h (31,000 gpm) with a mixed flow impeller and differential head of 65 mlc (213 ft). The increased flow design means that the impeller/motor inertia ratio increases compared to smaller designs. It is therefore important to review the torsional vibrations during start up when having direct online start. In this case the fundamental torsional critical was much higher than the main excitation frequency during start up, hence the response can be regarded as quasistatic. The main challenge with the lateral analysis was related to rotordynamic coefficients for the fluid filled clearances in the motor and impeller. The first bending mode was related to the motor itself, but with satisfactory separation margin from the operation speed.in addition, the response was highly damped. The impeller/diffuser interaction was analyzed with regard to flow stability. The diffuser can be a source for rotating stall that again can affect both vibrations and performance. Numerical flow simulations (computational fluid dynamics, CFD) were used to analyze the performance and flow at off-design. No sign of propagating recirculation around the circumference was detected. Additionally, casing/bearing house vibration analysis showed low vibration values and stable blade passing frequencies, confirming no blade stall interaction and corresponding diffuser instability in the flow domain of interest.