Progressing Cavity Pump (PCP) Behavior in Multiphase Conditions

Abstract

Abstract In operation, the Progressing Cavity Pumps (PCP) boosting gaseous multiphasemixture faces reliability issues that can be summarized as follows: the pumppressure is developed by the stages nearest the discharge, then the highpressure gradient causes heat to build up which commonly results in prematurefailure of the elastomeric stator. This paper first describes our recenttesting program performed with an industrial PCP in multiphase conditions, andthen presents a new analytical model that describes thethermo-hydraulic-mechanic processes which occur when attempting to pumpmultiphase mixtures. The objectives of our program are to:examine the PCPsystem operating at high gas volume fraction,analyze the pumpingperformance (delivered pressure, flow rate, and gas void fraction) and,describe the overheating generated when the gas is compressed. This paper alsodescribes our PCP experimental program and presents resulting experimentaldatas which clearly show the correlation between the pressure distribution andthe heat along the pump. We formally explain this phenomenon by proposing a newanalytical model that evaluates the stator degradation and failure risk. Thispaper should help operators andmanufacturers to design pumps with bettersystem's Mean Time Between Failure (MTBF) performance. Introduction The PCP is a positive displacement pump type that can be used to pump a widerange of multiphase mixtures, including high viscosity fluids with entrainedgas and solid particles in suspension. However, PCP has a reduced ability tohandle high gas-liquid ratio due to limitations of its elastomeric statormaterial required to overcome thermo and mechanical effects. This paper studiesPCP's behavior in multiphase flow conditions with high Gas Volume Fraction(GVF) (i.e., a GVF from 0 to 90%) and liquid (water and viscous oil). Resultsfrom our experimental testing program carried out with industrial pumps, arepresented in this paper. The objectives of this experimental program was to:examine the PCP system operating in multiphase flow conditions,analyzethe pumping performance (delivered pressure, flow rate and gas void fraction),describe the thermo-hydro-mechanical process and overheating generated whenthe gas is compressed and finally deduce the correlation between the pressuredistribution and developed temperature.. Based on the multiphase fluid equations (momentum and mass conservationequations, fluid state function and gas thermodynamic laws), we propose a newanalytical model of pressure-temperature distribution and compare it with dataobtained from the experimental testing program. We find that the pump'sperformance can be predicted using our deduced formulas and that they help topredict more accurately the risk of stator degradation and failure. Also, basedon these results, the pump's design parameters can be better selected to complywith production conditions and increase the pump's performance as well as thepump's reliability. Previous studies dealt with PCP performance in liquid and multiphasemixture. The inventor of this pump system, Moineau [1] have proposed to useHagen-Poiseuille equation for modeling internal slip flow and deduce thedelivered pressure in liquid flow. Recent studies (Vetter [2], Robelloand Saveth [3], and Gamboa [4]) introduce others effects such as rotorrotation, liquid viscosity, rotor-stator gap variation and mechanicalproperties of stator material (elastomer and metal). Experimental work and analytical approache have shown that multiphaseboosting with positive displacement pumps (PCP and twin - screw)isstrongly affected by gas handling (Vetter [2], Wietstock [5], Toma [6], Prang[7]). Extensive experimental studies (Kenyery et al., [8] and [9]) dedicated toPCP's with two-phase flow show the pressure and temperature distribution alongthe pump stator under different sets of variables (gas void fraction, rotational speed and delivered pressure). The objectives of these experimentswere to estimate how flow conditions can be affecting the pump's life and itslift performance.