The vacuum distillation column in a refinery was having trouble producing low metal content fuel oil when processing certain feeds. As a result, it was proving difficult to operate various downstream processes, since they were designed for low metal content. The two most likely causes were increased metals in the feedstock, or internal damage in the column leading to poor separation. A series of laboratory analyses eliminated the feed as being the problem, therefore suggesting the column as the culprit.
The section of the column designed to remove the metals from the fuel oil consisted of several trays and a demister pad. Tracerco performed a Tower Scan of this section during normal operating conditions to ‘see’ what was happening. The scan showed that the trays above the demister pad were holding normal levels of aerated liquid. The trays below the demisted pad were operating drier that expected. The most important observation was the lack of absorption for the demister pad, which appeared to be damaged or dislodged from its correct location. This would result in a high metal content in the fuel oil, since the demister pad was essential in removing the metals from the wash oil section. Based on Tracerco’s scan interpretation, refinery management decided to shut the column down to examine the demister pad. As predicted, the pad was dislodged and damaged. The column was returned to service after a short downtime, since advance preparations had been made. The fuel oil quality is now on specification at various crude rates and compositions.