Most Crude  unit simulations use "Pseudocomonents" defined by average boilng point and gravity of each cut.  Sulfur content, Nitrogen content and many other contaminants are treated as properties of the cut.  

It is very rare to find a complete analysis of all of the components in a crude oil.  I have seen a few special Mass Spec analysis with  a huge number (well over 1000)  identified compounds once this didn't capture all of the compounds and probably had some error associated with it but it was pretty impressive.  It would not be practical to perform this type of analysis.

If you insist on using some actual S compounds you could include some simple representative compound - Mercaptans and Thiophenes in light cuts, Benzothiophenes, Di and tri Benezothiophenes in the heavy cuts but this approach does not work as well as treating S content (and N content , O contentment metals etc) as properties associated with cuts.   

If you cannot find the sulfur compounds of interest to you in HYSYS electronic library, you can create hypothetical components and add them. HYSYS manual has a step by step procedure of adding a hypothetical component to your system. A few data you need to know about the components of interest such as the chemical structure, molecular weight, boiling point, density, heat of formation, etc.

Professor Yehia Khalil, Yale University, USA

Fellow of the University of Oxford, UK

Thank you for your reply. They are helpful. I am sure that there are not benzothiophenes in  hysys, so maybe I have to add them as pseudocomponents. But do I have to specify in which cut there is every of the sulfur compound or I can add only the different kind of sulfur in hysys and after that they will be distributed in the distillation in the different fractions according to their boiling points? 

You need to ask yourself what the purpose of the model is and build it to achieve that goal.  If the goal is to demonstrate your proficiency using Hysys by using as many of the available features as possible then creating a bunch of  psuedo compounds that boil every 30 C or so might be an effective way to demontrate that and acurately model how sulfur compounds will be distrubuted in a somewhat rigorous way according to their boiling points when you make cuts. 

If the purpose of your program is to provide a usefull tool that accurately matches the sulfur and nitrogen compoundistribution from an assay it is probably more usefull to treat S, N, conradson carbon and metals content etc  as properties that vary smoothly with cut point.

Some academic researchers are very focused on using the more rigorous and technically more correct approach of identifying every compound.  This is usually impractical with petroleum crude simulations because there are too many compounds and you never really have a good enough analaysis to identify every compound.  The most information that you can expect ot have is the SG, and a few physical propries (pour point, Octane, Cetane #, flashpoint, conradson carbon and possibly C,H,S and N content, of 5 to 10 cuts and the total crude.

The other thing that most people don't understand is that "Rigorous" simulation of a distillation unit isn't really rigorous. Distilation unit are typically modelled as a column with 20-40% less trays than the actual equipment has because the "tray efficiency" for comercial units is typically 60-80% (and often lower).  There is not a 1 to 1 correspondence between actual conditions in a real distillation column and the simlation but too parahrase what a very wise man once said  to me  "simulations are never completely  correct but they can still be extremely useful to enhance the understanding of what is happring inside a process unit and how to adjust conditions to improve performance".   It is important to understand what the purpose of your simulation is and taylor it to fit your needs so you can improve your operation.

In a commercial environment the purpose of the tool is usually to design a unit that will meet your processing objectives at several different design points that are representative of the full range of operations for the unit.

In an academic environment there is more of an emphasis on demonstrating to your instructor that you understand what you were taught and know how to use this information and less of an emphasis on practcallity.

 A research environment is somewhere in between there is a need for the tool to be a good representation of the process but there is more of a focus on exploring unique new ways of operating in a new way or improving existing operations and less of an emphasis on how to model day to day operation as unit performance deteriorates over a five year run.

It is important ask yourself and get a clear understanding from your instructor/supervisor what the purpose of your simulation is and build it to fulfill that purpose.   

Hi Panagiotis,

When you simulate crude distillation in Hysys you need to characterize a set of pseudocomponents: you can make it either using program facilities (you provide some assay data like distillation curves, specific gravity, etc. and the system produces a set of pseudocomponents) of specifying directly the boiling ranges as well the properties of each pseudocomponents of the crude.

I guess the goal of your exercise is to understand what is the expected content in Benzotiophenes of column products, maybe to optimize the crude cutting profile.

If you have an idea of the boiling temperatures of the components you are focusing on, you can try to model this creating a user property (Benzotiophenes Content) and to estimate a value for each pseudocomponent. This is approximate because in this way you assume that the VLE behaviour of these components coincides with that of Crude Pseudocomponents in the same boiling range, up to you to decide if this is acceptable or not. The system will automatic calculate the global benzotiophene content of each stream produced by the column.

Hope this helps.

Thank you for both answers! They are helpful!

Panagiotis,

In response to your question, the answer is YES. HYSYS distillation unit operation will distribute the fractions according the boiling points that you entered in the hypothetical components.

Professor Yehia Khalil, Yale University, USA

Fellow of the University of Oxford, UK

If I just use the components that already exist and I add just the composition of these components without specifying what is the composition of sulfur for each cut is it still ok?  I was thinking to add it as separate stream in which I will simply define the composition of different sulfur compounds!!!

You need to add separate stream for the hypothetical components and just enter the composition of each.

Hope this helps answer your question,

Prof. Khalil, Yale University