Surge (or hold-up) Time of Sump towers

[liberoSimulation]

I'd like to know the surge requirement of sump tower with thermosyphone reboiler (i.e. time required from LLL to HLL).
The company I'm working with is using about 15 minutes and applying this to all process plants regardless of the plant capacity.

I hope that I can get answers from the experience people in this site as I think it needs so.

Regards
Simulation