Mass Transfer Behavior of High-Gravity Backwashing for Walnut Shell Filter in Oilfields: Theoretical Frame, Numerical Simulation, and Experimental Study

With the popularization and application of polymer flooding technology in oilfields, many problems have arisen for the walnut shell filter in service, such as poor regeneration of granular media, contamination of the filter bed, and low efficiency of oil/water separation. A new high-gravity backwashing system, based on the perspective of the “field”, has been established. This system primarily uses Bezier curves for parametric modeling of blade cross sections, and a theoretical mathematical model of the high-gravity backwashing velocity gradient G value in the efficient zone has been developed. Meanwhile, the interparticle collision regulation of the high-gravity backwashing process was simulated using the coupled FLUENT-EDEM method. The simulated velocity gradient G values were obtained for different high-gravity values and are in general agreement with the theoretical G values. The optimal high-gravity value for backwashing was determined through numerical simulation and experimental validation. The surface properties of walnut shell filter media before and after backwashing were analyzed using SEM and XPS methods to provide a reference for subsequent high-gravity backwashing studies. The high-gravity backwashing process breaks through the technical bottleneck of backwashing under a gravity field, which will promote technical iteration and upgrading in oilfields.