Does anyone know why there is always a 3 phases separator on the Hysys simulator but not 2 phases separator for decanter? My process is esterification process (Acetic Acid +Ethanol Ethyl Acetate +Water) The feeds pass through reactive distillation column first and reach ternary azeotrope eventually, after a total condenser all vapour forms become liquids, and hence these liquids passing through a decanter to separate heavy liquid and light liquid...and undergo a separation process at the stripper before the product can be obtained. From the literature review, the PFD only showed 2 outlet streams from the decanter but not 3 phases...Can everyone explain for me? Thank you.
The three phase separator is a more generic unit operation by which one gas phase and two liquid phase can be separated. All separation processes in HYSYS are based on phase equilibrium which utilize various EOS models. In case, it is just a decanter separating two liquid phase, the gas phase flow rate from the top of the separator will be negligible/zero.
Mitra said it well. If you indeed use the three phase separator, the flow rate of the gas phase should be zero or thereabouts.
Your gas phase is zero like it was mentioned. Hysys like other software packages use generic icon (one representation) of all the possible cases. Since it is possible to have 3 phase separation and two phase separation, it is easy to have 3 phase separator icon that can result in three phases or two phases (the third phase is zero for this case).
This is also beneficial in somehow (might not be intentional) as you have done. It helps you to make sure your calculations are correct and you are not making mistakes by checking that there is no gas in certain process or no liquid in another process ..
Good luck; (it is a good question and I am answering it since it causes some confusion to users in other software packages as well).
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