5 replies to this topic

[psuche03]

I am trying to determine the vapor pressure of a blend of two different crudes at varying percentages.  Does anyone have any knowledge of how to achieve this?  I'm doubting that the blend is linear, so I'm trying to determine what type of model is needed.  Unfortunately, I have limited assay data on one of the crudes, and the simulation software I'm using needs more inputs.  I'm stuck at this point and open to suggestions.

[Chellani]

Most of the refinery properties are non-liner and simple method to blend them lineraly is to convert them to index. Oil companies, refineries and process simulation companies have their own correlations from literature and experiments. Find correlation which suits you.

[psuche03]

I was able to get the simulation of this blend working correctly.  At nearly the same time, a co-worker provided a means of calculating this.  Both methods yielded very similar results, so it would appear that these methods are correct.  I'm working on some lab blends to verify.  For the calculation, it is as follows:

 

Vapor Pressure = {sum[(individual blend component^1.25) x component volume fraction]}^0.8

 

For example, a two component blend:

 

Component 1 is 50% with a VP of 1

Component 1 is 50% with a VP of 2

 

Blend VP is [(1^1.25)*0.5+(2^1.25)*0.5]^0.8=1.52

 

Please note that this was done for RVP.  I cannot comment on the accuracy of a TVP blend.  I hope this helps a few others out there.

Edited by psuche03, 15 July 2013 - 07:23 AM.

[Chellani]

Great.

 

It looks like index method except one issue but volume blending seems to be different. Are you sure that it is

 

Vapor Pressure = (sum (individual blend components x component volume fraction)^1.25)^0.8

 

and not

 

Vapor Pressure = (sum {(individual blend components)^1.25 x component volume fraction})^0.8

[Profe]

Hi all

According with Chellani observation and reviewing the "Petroleum Refinery Process Economics" by Robert Maples  pag 366 about blends, Chellani is OK. I attached an Excel file with the Maples example for RVP blends by Chevron Method and copy of Maples table.

 

Good luck

 

Fausto.

Attached Files

•  Blend RVP I.xlsx   12.76KB   233 downloads
•  Maples Example.JPG   37.1KB   47 downloads

Edited by Profe, 10 July 2013 - 02:01 PM.

[psuche03]

Chellani,

 

I looked a little closer, and you are correct.  I got a verbal descriptions of the calculations, and I should have look at the spreadsheet my coworker sent to me.

 

Vapor Pressure = (sum {(individual blend components)^1.25 x component volume fraction})^0.8 is the correct calculation.

 

Good catch.