Hi,

Can anyone advise on how to calculate relieving rates from a column on reflux failure or overhead condenser failure? I am trying to set HYSYS up to calculate this using steady state mode but it is proving difficult as I am trying to model the reboiler decreaded LMTD due to higher pressure and the lack of reflux.

Regards
Patrick

The easiest way of doing is not to use a simulator. If you already have steady state converged runs for the column, as a worse case scenario u can size the PSV for the total vapors leaving the top tray. If you want to reduce the size of the PSV u can take credit for cooling thru air cooler (if u have any on the reflux circuit). Getting the simulator to converge for higher pressure is diff proposition.

If you're gonna model the reflux failure in steady state, I suggest you to use only simulator to obtain required process data -e.g. mol.weight, temp, pressure, Cp/Cv, etc @ relief condition-. Common practice is to assume vapor load and composition from feed stage or bottom of the column due to there's no rectification.

If you want to get fancy, then switch to dynamic model once you converge the column in stady state and stop reflux.

regards,

C.H. Mondolfi