More Tower Damages Caused by Water-Induced Pressure Surge: Unprecedented Sequences of Events

Three water-induced pressure surge cases in crude towers are presented. Although different and independent, all the cases have a common point: the water induced pressure surge is associated to a pressure relief valve opening event.

In the first case study, a 126.000 bpd crude distillation unit had a significant decrease in one of the atmospheric tower side withdrawals after an emergency shutdown. The light diesel oil production was cut in less than half. A generalized tower temperature profile reduction was observed: 60°F (33°C) temperature decrease in light diesel oil pan; 95°F (53°C) in heavy diesel oil pan and 50°F (28°C) in atmospheric residue withdrawal.

The second case study occurred at another crude distillation unit located at the same refinery of the first one. It was observed a deep reduction in the first side withdrawal (naphtha) yield that was compensated by the other side draw products yields and no loss in total diesel production was noticed. Compared to the second, the damages in the third case were higher and it was observed degradation of products to the bottoms residue. This problem happened at the same tower of the second case, one year after and it was caused by distinct conjugation of facts.

The paper will present the troubleshooting techniques applied to evaluate the different units problems (operational tests, gamma scans surveys, and thermograph readings), the root causes of these incidents and the mitigation actions.

KEYWORDS: PSV, pressure relief valve, troubleshooting, crude tower, atmospheric tower yield, column internals, trays, gamma scan, thermograph reading.