LP Modeling - Past, Present and Future

added the critical linkage between upstream changes in pool qualities to the quality
changes in the downstream destinations. Early versions of the DR technique were
slow and difficult to work with. Over the years since then, the technique has become
faster, better, and more reliable. The technique is increasingly popular and is now
widely accepted in the LP modeling systems and refinery models.
Current LP Modeling Practices
As mentioned earlier, there is an infinite variety of modeling techniques currently being
used. However, we can, at least, categorize and discuss current modeling practices in
the various areas of the LP model structure.
Crude Distillation Swing Cuts
Swing cuts are increasing used in LP assay tables to represent the refinery’s flexibility
to alter cut-points for optimization of side-cut yields and properties. When used, swing
cuts have generally replaced the older multiple “mode” type of yields structures. The
Aspen PIMS system, for instance, has provided a Type 4 swing cut in their CRDCUTS
table. The system will then automatically generate the necessary structure for blending
the swing cut up and down. Swing cuts are frequently used for Naphtha/Kerosene,
Kerosene/Diesel cuts and for Gasoil/Bottoms cuts as well as others. A majority of LP
models now employ swing cut architecture in at least some of the crude distillation side-
cuts. In general, the swing cuts are also used along with side-cut property recursion
techniques such that main side-cut yields and properties are impacted by the swing cut
blending.
Crude Assay Recursed Properties
Most crude assay tables now include recursed properties for the various side-cuts.
Typically, the side-cuts in the model now match the physical side-cuts from the “real”
refinery, with the exception of the swing cuts. The individual side-cuts generally have
anywhere from 3 or 4 recursed properties to over 20. The average number of recursed
properties in most models is about 7 to 10. The side-cut recursed properties are not
just used for product blending. The properties are now frequently used as product yield
and property drivers in downstream process units sub-models (e.g. % Naphthenes and
% Aromatics for Reformer sub-models).
Commercial Distillation Properties
LP crude assay data is frequently generated by using one or more of the vendor crude
assay libraries in conjunction with a commercial crude assay system. The assay data
from these libraries is based on laboratory distillation results. In the past, most LP’s
included these laboratory predicted properties, rather than commercial unit properties.
Increasingly, LP modelers are interested in getting the commercial unit distillation
results into the LP. Right now, there are three main techniques that are in common use:
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