Crude-Quality Drift and Flexible CDU Operation: Nile Blend Case Study

Abstract

Atmospheric crude distillation units are often designed for a bounded crude quality envelope, yet mature-field production and blend variability can progressively shift feed properties and degrade yield performance. This study develops an integrated assay-simulation-plant-evidence framework to quantify the impact of Nile Blend crude quality drift on atmospheric crude distillation and to identify practical operating-flexibility levers. Multi-year assays show a decline from 34.81 to 30.58°API between 2006 and 2011, accompanied by a density increase from 850.4 to 872.3 kg/m³, an 80% endpoint increase in measured salt content, and a maximum TAN of 0.59 mg KOH/g. Product-yield variability was operationally significant: naphtha varied by 6.64 percentage points, diesel by 4.15 percentage points, and atmospheric residue by 8.89 percentage points. The Aspen HYSYS model reproduced benchmark product flows with maximum error of 5.32 × 10⁻⁵% and matched TBP-derived yield patterns with MAE of 0.39 vol% and RMSE of 0.74 vol%. Plant comparison revealed average naphtha and kerosene shortfalls of 0.70 and 3.86 wt%, respectively, relative to assay potential. Feed-entry strategy was the strongest modeled lever, increasing naphtha by 15.3 percentage points and reducing residue by 15.3 percentage points across the tested range. Reflux adjustment provided a smaller but field-accessible control lever. The results establish an assay-driven, model-updated surveillance workflow for managing crude quality drift without premature hardware retrofit.