First published in PTQ Q1 2017
Miren Carro-Usle, Technology Team Manager – RDS, FCC & Sweetening Segment, Axens
On the spot market crude oils are traded on short terms. The advantages are the attractiveness of the price as the spot market is influenced solely by supply and demand.
Another characteristic of such a system is the placement of oil for disposal around the world no matter what country it comes from. Therefore, crude oils on the spot market can be unknown for a refinery and have to be evaluated in order to assess the refinery margin that can be obtained and how to process a new crude oil in the refinery.
The planning LP model of the refinery or a less complex LP model adapted to crude evaluation is helpful for such an assessment. The crude assay data will come from a crude assay library. It is important to select the more recent assays in order to have more accurate results.
Prior to the utilisation of a LP model, crude properties should be reviewed using the selected crude assays. Properties such as cut yields, sulphur content, density and TAN (acidity) will allow a comparison of a new crude oil with the usual crude oils processed in the refinery. Then distillation cuts can be calculated using specific software, critical properties for process units feedstock such as sulphur content, mercaptans in kerosene, cetane index in the gasoil cut, metal content in vacuum gasoil can be reviewed as they have an important impact on product properties, metallurgy, catalyst life cycle and so on.
From this first phase of the crude evaluation the conclusion may be that the concerned crude cannot be processed individually but in a blend with other crudes available in the refinery. In this case, a LP model will be able to optimise the crude blend suitable for the refinery while maximising refinery margin.
Regarding process units, the LP model will take into account capacity constraints or other hydraulic limitations as well as operating modes. Ranges of variation on cut points for the specific crude units are also integrated in the LP model.
The main LP model outputs are the optimal refinery margin, routings and unit operating modes when processing the new crude oil (individually or in a blend).
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