(120d) Can Vapor Channeling on Trays Induce Premature Foam-Flood?

The lean amine flow rates in the high-pressure (HP) amine absorber in the hydrocracker unit in the Kochi refinery were limited by recurring foamover events. To increase liquid handling capacity, the tower was retrayed by a major tray supplier (Fluor was not involved). The retray was quite standard, using high-capacity valve trays with small fixed valves and push valves and increasing downcomer top area. Surprisingly, higher lean amine flow rates could not be achieved without foamovers. Even at the same amine and gas rates, the frequency of the foamover events jumped from twice per month to once per day. 54 days after the new trays began operation, the bottom line from the pre-knockout drum plugged, causing heavy hydrocarbons entrainment into the amine system, and severely aggravating the foaming issues. This required a reduction in both the amine and gas flow rates. The problem was eventually resolved by replacing the tower by a random packed tower and unplugging the pre-KOD bottom line.

Although the problem was solved, the mystery remained. Why did the revamp trays perform worse than the original trays when they should have performed better? The refinery sought answers from the supplier and the supplier’s tray-rating software, but neither of them were able to provide any clues.

Aware of Fluor’s distillation expertise, the refinery had Fluor join their task force analysing data and performing a “post-mortem”. This joint investigation disclosed a phenomenon that to the best of our knowledge had not been previously reported: tray channeling inducing premature foam-flood. This paper presents our analysis and finding.