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I have laboratory ASTM D7169 data for Vacuum residue of Vacuum unit & Clarified slurry oil from FCC. I want to use them in simulation. As per literature information it is mentioned that for Vacuum residue ASTM D7169 data can be used as True boiling point data in Wt% & i have seen it is giving ok type of match for simulated properties. However, for FCC Clarified Slurry oil (cracked stream) when i input (in simulator) as TBP wt% then even there is lot of mismatch in density itself. Can you please tell me whether for cracked stream is it appropriate to use ASTM D7169 data as TBP wt%? if no, then how to model it in a simulator like Aspen plus?
 
Answers
09/05/2013 A: keith bowers, B and B Consulting, kebowers47@gmail.com
ASTM D7169 is an excellent test and correlation developed for use with virgin residues. Even these 'resids' have side chains that keep the molecules from stacking tightly together.
However, 'FCC Slurry' has been thermally de-alkylated (cracked) and is highly 'aromatic', which results in substantially tighter molecule stacking--and higher density than 'virgin' residues of similar volatility as measured by D 7169.
You might try consulting with Dr. Sheldon Cramer, who is the principle researcher for collecting and validating much of the content of the API Data Book.
The volatility and other relevant characteristics of these high boiling hydrocarbons are not easy to characterize. This is one reason so many 'deep cut vacuum distillation' revamps failed to meet expectations--often with very adverse consequences.
There is a firm in Houston--with history of excellent results--- which Specializes in 'deep-cut' distillation consulting , design, and troubleshooting.
If you are considering making modifications to the process or equipment, you're strongly encouraged to seek out their assistance.
09/05/2013 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
If you are simulating the cat main fractionator, you are probably adding each stream from the unit to construct the feed to the column, and using known data for the clarified oil stream in this summation. It is not unusual for the resulting simulation results to fail to replicate the clarified oil properties, even if you have carefully used the physical properties of the clarified oil in the preparation of the feed composition.
Even when simulating the crude vacuum column, some K and H data combinations will not check well with the observed vacuum column flash zone temperature in an existing column, and that is important if such data are being used to design a new unit.
In short, simulation results are very useful but have their limitations.