Jump to content



Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

Vertical Tank Selection

New Blog Entry

Low Flow in Pipes- posted in Ankur's blog

3

Cyclohexane + Hydrogen Flash

thermodynamics k-value

5 replies to this topic
Share this topic:
| More

#1 Tummeq

Tummeq

    Brand New Member

  • Members
  • 3 posts

Posted 20 January 2022 - 04:26 AM

I use  ChemCAD software. Recently I found out the following issue in thermodynamic simulation. The cyclohexane (like many other hydrocarbons) does not flash at 50 °C and atmospheric pressure. However, when we add a small amount of hydrogen it starts flashing significantly, which seems incorrect. Have you met any similar issue?



#2 breizh

breizh

    Gold Member

  • Admin
  • 5,381 posts

Posted 20 January 2022 - 04:56 AM

Hi ,

Using PR EOS I have similar result.

Is this the right equation to use ? 

Breizh 



#3 SilverShaded

SilverShaded

    Gold Member

  • Members
  • 147 posts

Posted 20 January 2022 - 12:42 PM

Hydrogen will strip out significant amounts of heavier hydrocarbons.  I tried it with PRSV and PR, PRSV strips out more than PR.  That said if i have 0.01 Mole fraction of H2 in the stream I get 0.011 of total vapour in the stream, which seems to be entirely as expected.



#4 PaoloPemi

PaoloPemi

    Gold Member

  • Members
  • 524 posts

Posted 23 January 2022 - 02:53 PM

vapor pressure at 323.15 K for cyclohexane is 36.50 KPa...
flash below 36.50 KPa to see the vapor phase...
std. Peng Robinson does a good job with vapor pressure for most low/medium Mw HC,
for heavy HC or polar fluids better to use extended versions... 



#5 Tummeq

Tummeq

    Brand New Member

  • Members
  • 3 posts

Posted 19 February 2022 - 07:00 AM

I found out that API SRK (SRK modified by Graboski and Daubert to better reflect mixtures with nonhydrocarbon gases) reduces amount of flashed HC.

I needed it for simulation of existing oil hydrodesulfurization unit and thanks to this modified EoS i managed to construct simulation from PFD and material balance.



#6 PaoloPemi

PaoloPemi

    Gold Member

  • Members
  • 524 posts

Posted 19 February 2022 - 07:58 AM

the usual code for API SRK includes a specific alpha for hydrogen,

however there are not specific correlations for polar fluids etc.

with these better to select a extended EOS with specific alpha functions.... 






Similar Topics