15 replies to this topic

[jatinder]

Dear All,

 

I have a question about flash calculation. I got confused after performing the calculation and now I am still in the state of confusion. I have performed a very simple basic flash calculation.

 

So, I have the crude oil composition with me with some hypo components. The flash needs to be performed at standard conditions 

T = 15.6C

P = 1 bar

Molar flow is 6848 kgmol/hour

 

So I have two streams now from the flash Separator:

 

Upper Stream - Vapor Stream 

T = 15.6 C

P = 1 bar 

molar flow = 5920 kgmol/hr

St. gas flow = 118.6 MMSCFD

St. Liquid Vol. flow = empty

 

Bottom Stream - Oil Stream

 

T = 15.6 C

P = 1 bar 

Molar flow = 927 kgmol/hr

St. gas flow = 18.6 MMSCFD

St. Liquid Vol. flow = 31400 barrel/day

 

Now I wanted to mix both streams to get a one stream. Therefore, I have used mixer and added both Vapor and oil stream to get single output stream "dry crude stream"

 

Now, when I see the results in the properties under my Standard liquid volume flow, it says 100046 barrels/day which seems to be very wrong because in the begening I only had 31400 barrels/day.

 

Where is the rest of 68646 barrels/day coming from when my bottom oil stream shows only 31400 barrels/day?????

 

Thank you so much in advance 

[thorium90]

Its possible you have the same problem as before. Perhaps the fluid package you chose has problems calculating the correct VLLE. Tried other fluid packages? Could be due to all those hypo components too...

[jatinder]

Its possible you have the same problem as before. Perhaps the fluid package you chose has problems calculating the correct VLLE. Tried other fluid packages? Could be due to all those hypo components too...

Thanks again for quick respone. Could you please tell me any other fluid package that I can use instead of peng Robison to do the flash calculation and gas lift calcuations?

[thorium90]

Not knowing all the components inside, I'm gonna make guesses. If it is highly non ideal, PR might not be too suitable. Activity models would be better and it might also help since you have 2 liquid phases. Typically NRTL and UNIQUAC. Perhaps you can choose NRTL with PR for vapor phase. However you have hypo components, which you likely do not have binary parameters. Not sure how well that might work...

Edited by thorium90, 21 February 2013 - 11:02 AM.

[shan]

Hysys converts your vapor flow 118.6 MMCFD to liquid flow 68664 bbl/d in the Overall Property Column.  If you check the Liquid Property Column the flow should still be 31400 bbl/d.

[Profe]

Hi Jatinder.

If you review the material ballance (Kgmol/hr)in = (Kgmol/hr)vap + (Kgmol/hr)liq

we have: (6848 kgmol/hr)in = (5920 kgmol/hr)vap + (927 kgmol/hr)liq a little bit difference for decimals.

the mass balance agree.

Don't worry about de volume because the material balance is Ok.

 

If you review the bottom stream this steam has some gas flow 18.6 MMSCFD, this gas is included in the 927 kgmol/hr

 

I think that will be useful

[jatinder]

Shan:

 

PERFECT........

 

This is what I was looking for !!

 

Thank you so much for your response.

[jatinder]

Profe:

 

Exactly Sir..

 

Its all clear to me now and I would like to thank you for your response...

 

Once again, Thank you so much

[jatinder]

Thorium90:

 

Thank you so much for the response Sir. Its all clear to me 

[kkala]

I am not accustomed to Hysys and a clarification would be useful for my understanding (if I do not miss something).

Vapor flow is 118.6 MMSCFD (or MMCFD?).

1 barrel (bbl) = 42 USgal = 42x231 in3 = 5.6146 ft3

So vapor flow 118.6/5.6146 = 21.123 MMbarrel/day = 21 123 000 barrel/day (at 1 bara, 15.5 oC)

How is this vapor flow converted to 68664 barrel/day of liquid?

Edited by kkala, 22 February 2013 - 07:25 AM.

[shan]

Hysys does not just do a volum conversion.  I think, not confirmed with Hysys, the calculation is:  118.6 MMSCFD/379 SCF/Mol = 3,129,288 mol/day,  Mol Density = 0.022 bbl/mol,  3,129,288 bbl/day * 0.0219 bbl/mol = 68664 bbl/day.

 

Make sense?

[jatinder]

Are there any confusions again? 

[thorium90]

Mol Density = 0.022 bbl/mol?

Attached Files

•  Wierd calc.jpg   35.38KB   20 downloads

Edited by thorium90, 22 February 2013 - 08:43 AM.

[shan]

While, frankly speaking, 0.022 bbl/mol is my back calculation based on the results (kind of cheating probably).  I just want to show you the calculation logic and do not intend to define any specific numbers.

[kkala]

Thanks to all of you for the clarifications on the question of post no 10 (by kkala). I have tried it more, considering shan's assumption that  gas is supposed to be totally condensed to 68664 bbl/day (measured at some reference state).

Molar volume = 379 scf/lbmol (60 oF, 1 Atma), so vapor quantity = 312929 lbmol/day = 5914 kgmol/h, quite close to 5920 kgmol/h reported by Hysys (post no 1).

68664/312929=0.2194 bbl/lbmol, corresponding to liquid density of about 4.56 lbmol/bbl = 13.0 kgmol/m3. The latter seems possible, if vapor is rich in C3H8 - C2H6.

Irrespectively of it, can you  see whether input stream (being liquid) is roughly 68664+31400+(68664/118.6)*18.6 ~ 110000 bbl/day? This could be a verification of the above.

[chengineer]

I am using  VLE flash iOS app which allows me to do basic Vapor-Liquid Equilibrium Calculation of

Multi-Components System .I suggest every one to try it.

 

iphone version: https://itunes.apple...68616?ls=1&mt=8

 

ipad version: https://itunes.apple...d684155871?mt=8