Hello - I am looking for a little guidance on calculating a relief load on a distillation tower during reboiler tube rupture. Ill preface by saying that I am by no means performing the "official" calculations. I just have some doubts about the existing calculations and want to check their validity. I also dont perform a lot of relief valve calculations so please excuse me if this has been covered ad nauseum.
The condensed question is: can I take credit for the overhead condenser during a reboiler tube rupture scenario?
In more detail:
The tower normally runs at 29 inHg vacuum. We are separating a mixutre of specialty amines that have a latent heat ~200 Btu/lb. We supply 225 psig steam to a control valve then to the reboiler.
Without going into great detail about determining the steam flow across the ends of the tube ruptures, can we use the condenser to reduce the required relief load? If so, do we also need to add the normal reboiler duty? Or do we simply use the volumetric displacement from the steam?
The existing calculations have taken credit for the condenser and there are some assumptions that bother me. The heat transfer coefficient during normal operating conditions is ~30 Btu/hrft2F. The heat transfer coefficient during relief conditions is closer to 90 Btu/hrft2F. The LMTD is also much larger at reflief conditions. The composition is also largely steam in these calculations. This has led to a condenser credit that is almost 10 times the normal operating duty of the condenser. It just doesnt seem right that the condenser can be given this much credit, completely negating the need for a PSV for this scenario.
Does anyone have an article they can reference or provide guidance on normal practice? API 521 doesnt provide guidance as far as I can tell.
Thanks in advance,
Jamie