Numerical modeling of a hydrocyclone for the separation of oil residues in offshore installations

Abstract

This study numerically investigates oil–water separation in a hydrocyclone using the Hsieh  design, selected for its manufacturability and proven experimental database. Computational Fluid Dynamics (CFD) simulations were conducted in ANSYS Fluent 16.1 employing an Eulerian– Lagrangian framework, where the water phase was resolved with the Reynolds Stress Model (RSM) and oil droplets were tracked through the Discrete Phase Model (DPM) under one-way coupling. A mesh independence study confirmed solution stability at 3.16 million cells, and residual convergence was achieved after approximately 1600 iterations, ensuring accurate predictions of velocity, pressure, and air core formation. The numerical results successfully reproduced the characteristic double-vortex flow, axial velocity reversal, and negative static pressure region responsible for air core development, showing strong agreement with published experimental data. Particle tracking demonstrated that separation efficiency strongly depends on droplet size, increasing from approximately 80% for fine droplets (1–5 μm) to a maximum of nearly 90% for larger droplets (≥75 μm), resulting in an overall efficiency close to 90%. However, a fraction of water was entrained in the overflow, revealing design limitations that could be mitigated by modifying the vortex finder or underflow geometries. The validated model provides a robust framework for optimizing hydrocyclone geometry and operating conditions, contributing to enhanced oil–water separation efficiency, reduced water discharge, and improved environmental compliance in offshore production systems.