Cat reformate's characterisation

[RadovanB]

I tried to predict RVP, RON and P/N/A of heavy and light platformate with Hysys using ASTM distillation and density @ 15C, but got pretty bad results, i.e. bad match with experimental data.

What I did:

took PR from fluid packages, entered oil environment, defined my steam by its standard density in bulk properties and entered ASTM D 86 data, picked auto calculate for light ends,calculated assay, installed oil as blend, defined the stream in simulation environment, and got cold properties form tools menu.

In case of light platformate, I got the folowing deltas:

RVP: 30%
RON: 11%
P: 73%
N: 850%
A: 73%

and I am not very happy with them.

I outlined above what I did in case I made some procedural mistake. If I did, somebody please point out. If not, can somebody advise how to obtain better results, if that's at all posible.

Also, if Hysys is inadequate for this, please advise on more appropriate method.

Best Regards,

B.Radovanovic

 

[epoisses]

Hi,
I think you may want to double check the values and units you quoted, as they don't seem to make any sense. RVP should be a pressure, RON should be dimensionless and close to 100. PNA should add up to 100%.

I'd tend to think that deriving these data from density and D86 only cannot be very accurate, but I'm not a modelling expert.

 

[RadovanB]

Eppoises,

Data are OK. I also agree that deriving data from density and D86 only cannot be very accurate, and that is exactly what I was asking: what else shall I put when defining a stream in order to obtain better results?

 

[EmmanuelTop]

Radovane, nesreco

Using ASTM D86 is (probably) the most inaccurate way of stream characterization. Even when these are coupled with density, you should not take Hysys outputs for serious.
What I can recommend, is to find a few books from vast petroleum ChE/refining theory and practice (Nelson, Jones, Perry) and try to establish a correlation between certain properties and RVP - but forget about D86. Another soulution could be to go for complete individual compounds analysis in platformate, but this is expensive and time-consuming job.

Epoisses' comments are right on place, so please check your data. How can you have 850% Naphthenes in 100% of sample volume (or mass)?

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[RadovanB]

I pointed out in my original message that what i wrote are deltas, or maybe better known as relative errors (|Xexp-Xcalc|)/Xexp*100) so they don't quite sum to 100%.

Data:
Paraffins [mol%] 75,Naphthas [mol%] 2.9, Olefins [mol%] 1.1 Aromatics [mol%] 21

Hysys:
Paraffins [mol%] 66.9177,Naphthas [mol%] 27.5596,Aromatics [mol%] 5.5227

 

[epoisses]

OK it's already quite important to know if the percentages quoted are weight, volume or mole. Remains RVP (should be a pressure) and RON (should be dimensionless and close to 100).
However these Hysys data are so far off, the stream might as well be platformer feed, not platformate.
What if, alternatively, you sent a sample out to a lab for PIONA analysis which is relatively easy/cheap? With these data, would you be able to determine more accurate RVP and RON?

 

[RogerH]

RadovanB
I guess you already came to the same conclusion as many before you have done, i.e. representing reformate needs a full GC analysis to be able to get proper values. Octane on the other hand is even more difficult than this. Blending indices are needed, so good correlations or a load of statistical data is a must to get RON/MON correctly.

Thermodynamical packages (like PR) are not tuned for all different possible blends of hydrocarbons and cannot give a correct octane. Even in the case of isomerate where one only has parraffines inkluding cycloparaffines will not be able to get a proper octane. Such a calculation can only give indications of the direction, i.e. better or worse but thats as far as it gets.
RogerH

 

[RadovanB]

RogerH,

Thanx. I came to a more or less the same conclusion myself.

RadovanB