3 replies to this topic

My company recently purchased UniSim Design (formerly Hysys) from Honeywell and I am trying to use it to model a vacuum steam stripping column separating hydrotreated oils. I have spent about six weeks and tried various column templates, thermodynamic models, and increased the number of hypocomponents.

My problem is, I cannot get my simulation to match the field data at all. I should be getting around 18% overheads and I am only getting 8%. The simulator does not seem to be capturing the interaction between the superheated steam and the oil, which lowers the partial pressures and makes everything boil at a lower temperature.

I have characterized my oil feed with ASTM D2887 simulated distillation data as well as API gravity and viscosity at 100 F and 200 F.

Does anyone have any advice on making this work?

[Milutin]

Hi iwilson

Such problem pointing more on your input data then on simulation software.
You should check your plant data and feed characterization.

How close is column mass balance, does pressure and temperature measurement are ok?
If you are not sure in feed characterization you can go backward - construct feed from products mass balance and product lab analysis.

Regards,

Milutin

[Zauberberg]

Hi Wilson,

Characterizing heavy oils is a tricky job - you will not get an impressive pseudocomponent breakdown, based only on D2887 and SG/visosity inputs. To get more into the problem, you may want to compare TBP vs 2887 results, and I bet it's going to be a big surprise for you.

Thermodynamic package could be an issue, but I doubt; you are having pure hydrocarbon stream at moderate or high temperatures and low pressure - PR or SRK should do the job.

I think Milutin is on the right trail: get as much data from your plant products and blend them as new feed to the vacuum tower. Please confirm column temperature and pressure profile and run the simulation again.

Regards

[Milutin]

Hi Zauberberg

Generally for vacuum services is recommended Esso tabular or Braun K10 thermodynamic packages, but I agree it is not main problem here.

Regards