3 replies to this topic

[Downes99]

Hi,
I'm currently trying to simulate a ethanol water distillation column on hysys. I started with a short cut distillation column, but i keep getting the same error " A minimum reflux ratio below zero has been calculated for yoru distillation". the compositions I'm using are, 0.15 water in distillate and 0.0091 ethanol in the bottoms. Can anyone provide any help?
Cheers

[breizh]

Consider this resource it may help to understand the issue

http://www.chemsof.com/vle/vle.htm

then Data ; Y=f(x)


Breizh

Edited by breizh, 24 February 2012 - 07:11 AM.

[Downes99]

Thanks for the link, it showed me how many stages I needed. I used this and went back to hysys, this time with the actual distillation column and it is giving me the error that it doesnt converge?

[PaoloPemi]

there could be many reasons why your simulator cannot find a suitable solution even for a binary mixture, for example a set of unfeasible specifications or wrong models for VLE or enthalpy etc. you may start with a model as Wilson or NRTL for VLE, check that the proper BIPs are available, differently you may use a predictive model as UNIFAC.
For the column do not specify a component's fractions or a purity, you may instead specifiy a reflux and a flow (bottom or top), you may change the flows if the solver is unable to find a solution (since you have two components to separate).
Once you have found a solution you may modify reflux, flows etc. in order to reach the desired separation.