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Simulated Assay (Low And High Probable Cases)


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#1 Neelakantan

Neelakantan

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Posted 09 October 2015 - 04:46 AM

our company has been contacted by a potential oil refiner (straight run); the client has received assay data for a the expected oil for which contract is being finalised. we have been asked to review the possibility and FEED services for a straight run refinery units based on the assay. so far so good.

 

the crux comes on the assay. it is sent by a major international oil producer; the assay report is a two page document, showing  low probable and high probable cases. The assay is a simulated assay (my understanding is that it is the probable boil cuts based on the chromatograph analysis).

 

now while trying to input the data available on to a hysys simulation case, I have noted the following:

1) there is no definition that it is D86 analysis which is understandable as it is not based on actual D86 equipment

2) but I have seen simulated assays reported as D2887; but in this case it is also not possible, as the yield % are not midpoint values

3) more importantly I find it difficult to comprehend the meaning of these assay results ;

 

the overall crude characterestics are given as 0.817 gm/cc (42.1 api) while cut densities are reported quite differently.

 

3a) in the low probable case, the bulk density of the whole crude is reported as 0.41 gm/cc and 50 % is reported as recovered at 115 deg C (this makes the liquid very light condensate); and the C5-65 cut (the first cut) shows an yield of 2.2%; with upto C4s -light ends- are 1.76% and the cumulative becomes 3.96% while it is mentioned just as 3.1%; i

3b) subsequent individual cuts and cumulative cuts don't add up neatly; and overall distillation yield is reported 50% only (for such a light fluid) at 370 deg C

 

4a) in the high probable case the whole crude density values are all above 1.22 gm/cc and individual cuts all add up to 150% yield value.

 

before inputting these values in a simulator, I would like opinions and explanations from the forum members as to how to interpret these numbers

regards

neelakantan

 

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#2 PingPong

PingPong

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Posted 09 October 2015 - 08:21 AM

This assay is likely based on a TBP distillation (like ASTM D2892), not a simdis like D2887, and certainly not D86.

 

As you noted correctly there is clearly something wrong with the gravities of the fractions, and with the cumulative yields of C5-65 fractions.

 

Note that most other crude properties in the "Whole Crude" column are also wrong.

 

Also very strange is the fact that there are two very different assay tables for the same crude, one with a yield of 29 wt% 370+ and one with only 10 wt% 370+ . An assay stating that the crude probably contains between 10 and 29 wt% 370+ is not very helpful.

 

Do you the official name of this particular crude?

 

You have no choice but to contact the party, who gave you the assay, about those obvious mistakes.


Edited by PingPong, 09 October 2015 - 08:34 AM.





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