I am probably one of the most conservative people around when it comes to PSV calculations and analysis but I won't cost my customer more money then necessary. I see no reason to put in a larger PSV just for the sake of doing so when there are ligitimate and safe ways available to reduce its size. If you were to be using steam as the heating medium, the LMTD between the steam and the boiling liquid can become very small and thus heat transfer is limited). (Nirav, this is when the boiling point of the liquid goes up because of the higher pressure in the tower at relieving conditions. But I would disagree when not taking into account reboiler pinch. I would agree that trying to optimize this type of failure is not the best approach. What specifications should we provide on simulations and what approach should be followed to find the relief rate through simulations? Is it possible to optimize the vapor rate during relieving conditions based on simulations? However, I came across situations wherein a process licensor optimized the vapor flow during reflux failure based on simulation of the column approaching 'reflux rate=0 kg/hr'. Relief load = Vf (feed) + Vr (reboiler) - Vo (vapors out from reflux drum) We deduct the 'normal' vapors going out from reflux drum from above calculated rate (If we want to take credit of condenser, we take 'normal' vapors in column top outlet). So, in normal or conservative manner, we calculate the total vapors coming into the column at the 'relieving' conditions. It is little difficult to predict the heat and mass balance during 'reflux failure'. What should be the best approach for calculating relief load of a distillation column in case of reflux failure?

Relux blk files