Crude cutting

Within planning and scheduling tools the basic representation of a crude distillation train consists of a single set of data per crude describing the distiller product yields and the product properties. The crude assay in this context represents a model of the crude distillation. Process Model Manager Reference Manual uses the ECP/SI (Effective Cut Point / Separation Index) as a model for distillation units. This model is tuned to simulate the actual performance of individual CDU trains. Using the ECP/SI mechanism allows Process Model Manager Reference Manual to produce sets of crude data which are different from standard commercial assays. These sets of crude data (assay tables) include cuts which represent the actual product streams where separation between cuts is not perfectly sharp. Swing cuts are also used between adjacent products to represent the potential to change product cut points "Swing Cuts" below ). When produced using the same cut point and ECP/SI tuning, crude assays for different grades are additive and each set of assay dat represents how an individual crude will be split when processed in a mixture with other crudes.

If there are instances of blocked out operations which are significantly different to normal operations, for example during lube oil production, then it is necessary to define additional modes of operation. In this case a crude is represented by multiple sets of assay tables, each representing a specific type of column operation. Similarly when additional distillation trains perform differently in terms of sharpness of separation or cut points, then separate assay tables for each crude on each of the different CDU trains are needed.