Root Cause Analysis of a Premature Flooded Debutanizer Using Gamma Scanning, Engineering and Installation of a Bypass Line By Hot Tapping

A Debutanizer with two sections, both equipped with two-pass valve trays, in an Ethylene Cracker Unit (ECU) in Germany, flooded prematurely. The column never caused problems during the typical five years turnaround cycles and was at that time in operation for 2.5 years since the last turnaround. A sudden increase of the pressure drop in the bottom and afterwards in the upper section was detected. At the same time the bottom product purity followed by the overhead product purity deteriorated. Consequently, the column was a plant capacity bottleneck, limiting the production to approximately 90%.

A theory was developed by Linde’s Engineering Division that fouling was causing the trays to flood. Gamma scans were performed at different operating conditions and proved the validity of the theory. Following this, a process simulation conducted by Linde’s Engineering Division demonstrated that the desired product specification can still be achieved when bypassing a part of the liquid. Thus, a bypass line was engineered and installed by hot tapping.

Bypassing a part of the liquid solved the capacity limitation and avoided a costly shutdown of the ECU. Severe fouling was found in the bottom section after the column was opened in a later shutdown.

The presentation will cover the troubleshooting which was based on a tray hydraulics rating, the evaluation of field data and gamma scans, the engineering of the bypass line including an explanation of the column simulation as well as the installation by hot tapping.