Extracting LPG

[Mahmoud1984]

I have a case where there is a quantity of natural gas of 50 MMSCFD having the following composition :
N2 0.0988
CO2 0.65
C1 91.2626
C2 6.3481
C3 1.375
IC4 0.1703
NC4 0.0835
NEO C5 0.0005
IC5 0.0068
NC5 0.0022
C6+ 0.0024
Preesure is 55 barg and temperature is -10°C upstream the turbo expander
The question is what is the roughly estimated quantity of LPG and condesate that can be extracted from this mixture?
Taking into consideration that pressure downstream the turbo expander is 25 barg and temperature is -42°C.

 

[georgeverghese]

If you have only a single stage of separation d/s the expander, you can work this out approx by use of the dePriester charts, which, at 25barg and -42degC, indicates y/x for C3 to be approx 0.057 and 0.025 for iC4 and 0.014 for nC4. With these values, I get total condensate to be 83 lbmoles/day, with c3 recovery (in terms of feed rate for component, mole/mole basis ) to be 1.1%, ic4 to be 3.6%, nc4 to be 6.3% and 100% for c5plus. Hope this helps. You can try this out for yourself on a spreadsheet also. dePriester graphical K values can be seen in the chapter on distillation in Perry Chem Engg Handbook.

 

[MortenA]

Yes, get a process engineer to simulate your process using e.g. HYSYS or another process simulation tool.

Best regards, Morten

 

[georgeverghese]

If methane and ethane K values are also taken into account, the total condensate yield at the separator P/T drops to 78 lbmoles/day. Component recoveries are about the same as previous.