2 replies to this topic

[deltaChe]

I would like to ask a very simple and mundane question for professional process engineer about simulating flash scenario through Aspen plus.

Please bear with me.

EO stream : OT=-5C, OP=6barg, a PSV set pressure=24 barg, and will relief to scrubber (O.P.=1 atm)

I tried use Aspen plus to see if any flash will happen when PSV relief, but I encounter some questions in the following.



N1. What is the inlet pressure for flash drum inlet stream in Aspen?

I used 24 barg for flash drum inlet pressure because PSV set pressure is 24 barg, but I wonder if possible I can used the EO stream O.P.=6barg for flash drum inlet.

N2. What is the pressure in the flash drum? I used the Scrubber O.P.=0 barg as flash drum O.P. and heat duty=0(adiabatic condition) in Aspen.

I got the a little EO will flash after running the Aspen (please see the attached file) , and it seems contradict with the No EO will flash result that I found the EO properties in the MSDS.(EO boiling point = 17 C at 1 atm. EO at OT=-5 C will never get flash)



Thank you very much for your kindly help.



My Aspen input variable:

• Thermodynamics properties:SRK,
• Inlet stream : EO flow rate : 500lb/hr. OP=24 barg, OT=-5 C
• flash block : flash specifications : temp : -5 C, heat duty = 0 btu/hr, valid phase: vapor-liquid-free water.

Attached Files

•  Book1.xls   18KB   24 downloads

[MrShorty]

and it seems contradict with the No EO will flash result that I found the EO properties in the MSDS.(EO boiling point = 17 C at 1 atm. EO at OT=-5 C will never get flash)

I'm not sure where this statement comes from, but it seems wrong to me. We have to remember that everything at any temperature has a vapor pressure. "Coincidentally," the vapor pressure of ethylene oxide at -5 C is about 0.5 atm as reported in your flash calculation.

[deltaChe]

and it seems contradict with the No EO will flash result that I found the EO properties in the MSDS.(EO boiling point = 17 C at 1 atm. EO at OT=-5 C will never get flash)

I'm not sure where this statement comes from, but it seems wrong to me. We have to remember that everything at any temperature has a vapor pressure. "Coincidentally," the vapor pressure of ethylene oxide at -5 C is about 0.5 atm as reported in your flash calculation.

I should use 1 atm in flash drum as input insteand -5 C because this is vent to atm.
Thank you.