4 replies to this topic

[kenalizer]

Hi there,

 

I am having some problems understanding how flash separation works in HYSYS.

As attached in the picture, I have propylene oxide, propanal, acetone, methanol, water and 3 glycols (listed here in increasing component B.P) in my feed stream. In this flash separation, I want to flash out the lighter components - propylene oxide, propanol, acetone, methanol. The highest boiling point among these components is 64.7C (at 1 atm), from methanol.

 

My feed stream is coming in at 1 bar and 90C and I did not specify any pressure drop across the flash separator.

 

My question is - Why are all the components with boiling point less than 90C NOT vaporised and got separated in the vapour phase?

 

If I further increase the temperature/ decrease pressure, I would vaporise some of the water as well, which is not my intention as I want to get rid of the water downstream.

 

Thank you. 

Attached Files

•  Capture1.PNG   292.02KB   4 downloads
•  Feed Molar Flow.PNG   283.99KB   3 downloads

[Bobby Strain]

You obviously skipped a lot of necessary education before attempting to use HYSYS. You should start with the books.

 

Bobby

Edited by Bobby Strain, 05 February 2014 - 02:04 PM.

[PingPong]

This is not specific for Hysys but for all simulators, or hand calculations.

 

You really should read a book about vapor-liquid equilibria.

 

Then you will understand that if a mixture is flashed at a certain P and T all components will be present in the vapor as well as the liquid phases. You can not expect that a simple single phase flash will result in a sharp separation between light and heavy components.

[Liza Admani]

Dear Kenalizer,

 

Mr.Ping pong is right as i also have not appropriate knowledge in hysys due to this i will suffer so many problems while solving my case in hysys so you must go through to books or can take admission for your basic learning as i have also take online admission in OMESOL.com they provide training according to our need.

[jatinder]

Kenalizer,

 

Just because the equipment is called as "Separator" does not mean it will always separate according to your expected result/desire/wishes. It doesn't work this way.  

 

First thing you must do is; try to gain more knowledge about the base of separation. Study about the vapor-liquid equilbiria.

However, in HYSYS separator, temperature and pressure plays a great role to do separation calcuations. therefore, you need to check these conditions also!