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?
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#1
Posted 20 January 2022 - 04:26 AM
#2
Posted 20 January 2022 - 04:56 AM
Hi ,
Using PR EOS I have similar result.
Is this the right equation to use ?
Breizh
#3
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
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
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
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....
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