Modelling Crude Distillation Units for Production Optimization and Scheduling

Crude distillation unit models for real time optimization are rigorous tray to tray models, predicting accurately product distillation curves and other bulk properties (e.g. sulfur, density, etc.) by using approx. 10k to 20k of nonlinear equation, which enables predictions within 1% to 2% of the actual equipment performance.  On the other hand, models used for planning and scheduling ae much simpler (e.g. swing cut model) but they provide a significantly lower accuracy.

In this work, we present methodology for development of hybrid models of crude distillation units.  The goal is to achieve accuracy on par with detailed tray to tray models and to have much smaller number of equations.  In addition, the model needs to be linear or nearly linear to make it easy to include it in the overall plant model for production planning and for scheduling.   The work removes commonly made assumption that the front end/back end of the adjacent product from the CDU are equidistant from the crude distillation curve.  Model performance is demonstrated on a crude unit consisting of a preflash tower, atmospheric tower, and of vacuum tower.  Model predictions are within 1% to 2% of the rigorous tray to tray model which has been used as a surrogate for the plant.  The model is suitable for use in production planning and production scheduling optimization.