Optimization of internal components in horizontal gravity oil-water separators using response surface methodology

Efficient oil-water separation is crucial in high-water-cut petroleum production to meet stringent environmental discharge standards (e.g., oil content < 300 mg/L). However, designing high-performance separators remains challenging due to complex internal flow dynamics and the interplay of structural parameters. This study presents a systematic optimization framework for horizontal gravity separators, developed by integrating computational fluid dynamics (CFD) simulations with the Box–Behnken experimental design. The effects of key geometric parameters—rectifier–coalesce spacing, lateral offset, and crest–trough distance—on separation efficiency were quantitatively investigated through multiphase flow modeling. Using response surface methodology (RSM), this study identified significant nonlinear interactions among these variables and derived a high-fidelity quadratic prediction model (R² = 0.983, Adj R² = 0.9935, Pred R² = 0.9676). The optimized configuration improved separation efficiency by 53.3%, reducing the oil content in the discharged water from 359.4 mg/L to 167.7 mg/L—well below the typical industrial threshold. This work demonstrates a novel, model-driven approach to the design of separator internals, significantly surpassing conventional trial-and-error methods. The findings provide both practical guidance for enhancing oily wastewater treatment and a generalizable optimization methodology applicable to related separation processes.