What is the problem in providing PSVs only on the feed line in a distillation column and not providing any PSV on the overhead line, given the fact that the PSVs on the feed line have been designed for reflux failure case?
Amarjit Bakshi, Refining Hydrocarbon Technologies LLC, firstname.lastname@example.org
Feed line is pumping feed into the column, and will be full of liquid. When the relief condition is reached at the column, it has to relieve vapor volume based on relief design requirements. The feed line being full of liquid, will have to relieve liquid volume equal to vapor volume, which is the normal design when PSV is located at the column overhead line or from column vapor space. The liquid relief equal to vapor relief will require huge PSV size. Additionally it will relieve liquid that would have two-phase flow with slugs making the line and flare header go through major liquid hammer condition and would make the system unsafe.