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Assay
Simulator - Use with Crude Quality Monitoring
Data
Many refiners
monitor the properties of the crude they receive.This is usually done
to: 1) detect contamination (spiking), 2) detect trends in crude quality
that may indicate that a new assay is needed, 3) determine if they
are paying too much for the crude, 4) warn refinery planning personnel
that changes are coming. It is not usually possible to put a dollar
value on these evaluations because this requires a fairly complete
assay. Although routine Crude Quality Monitoring may not include all
of the data required for a good assay prediction, it may take only
a few additional tests to make good assay predictions. The property
most often missing from a routine Crude Quality Monitoring program
is the light ends analysis. When pentane and lighter yield data are
added to the existing density and sulfur data, the TBP of the crude
can be quite accurately predicted.
Simulated
distillations are an alternative method for determining the TBP,
but there are several potential problems. The High Temperature Simulated
Distillation (HTSD) required for this is notoriously "touchy".
A laboratory needs to maintain very high standards and process many
samples on a routine basis to get good results. In addition, the
standard HTSD process is not directly connected to the normal distillation
process used to make assays. There are small differences between
the methods that can be seen when the results of many assays are
reviewed. Corrections can be made to adjust for some of these differences
if you have enough assay data (with HTSDs).
The
relative accuracy of Assay Simulator and the HTSD has been compared,
and unless the laboratory data is very good and the SimDist/TBP
corrections are made, the Assay Simulator gave better average results.
Of
course, there are times when the Assay Simulator will not be accurate.
It will not be accurate if a very light and a very heavy crude are
blended together to produce a "dumbell" crude. It will
however detect some or most of the effect of blending condensate
into the crude (due to the pentane and lighter analysis). It will
also not be accurate for synthetic crudes.
If
the crude properties have changed only a small amount from a previous
assay, it may not be appropriate to make corrections using the Assay
Simulator. It might just cause confusing "noise".
The
updating process allows refineries to update their LP input data
based on monitoring data from crude deliveries. Crude representation
to LP models is often a little simplified, partly to acknowledge
that assay representations are not exact.
Although
the base Assay Simulator is designed to update one assay at a time
into the HPI standard format, it can be easily upgraded (by you
or by us) to run a batch process of many crudes based on external
crude monitoring data and output in your propietary format for the
LP, etc.
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