Abstract

This paper presents a model of the thermo-hydraulic behavior of twin screw multiphase pumps, including effects of gradual opening of the last chamber and fluid recirculation between suction and discharge of the pump and different working fluids (water-air and oil-gas). Giving pump geometry and operational conditions, it is possible to calculate the most important pump performance parameters, such as, volumetric efficiency, suction flow, back-flow, power consumption and pressure and temperature distribution. The model was developed based on mass and energy balances and geometry variation of the pump chambers due to operation. Its implementation was made in C++. Simulation results showed that pumps with recirculation decrease their volumetric efficiency and increase their discharge temperatures. In the case of the opening effects of the discharge chamber, there are important variations on pressure distribution and volumetric efficiency of the pump, and these effects are more important in short screw pumps

Introduction

The twin screw multiphase pumping technology is still considered a relatively new technology, the first prototype was presented at the end of 80s, result of research projects supported mainly by the German government (World pumps, 2009). During the last years, multiphase pumps have gained greater acceptance, especially in the field of petroleum production, for its applications in offshore oil and its capacity of replacing conventional equipment, with simple and economical one. The increasing requirements on their performance combined with those related to a higher operational availability of such systems, as well as operating conditions with pressure increase of about 150 bar, highlights the importance of developing accurate mathematical models to predict the performance behavior of these equipment.

For this reason new features were implemented in a thermo-hydraulic model (Nakashima et al, 2004) to account for the effects of the gradual discharge chamber opening and the direct fluid recirculation between suction and the discharge of the pump caused by the use of recirculation channels in some pump assemblies. In the first case, it was developed equations to represent the variation of the geometry of the flank clearance with the pump rotor rotation. In the second one, energy and mass balances were applied to model the flow in the channel between its suction and its discharge.

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