Crude Vacuum Tower Wash Bed Optimization Based on Tomography Gamma-Scans

The crude unit of today’s modern refinery is where it all starts. Good, clean fractionation from the Crude Atmospheric and Crude Vacuum Towers sets the tone for all the downstream operations.
The Wash Bed in the Crude Vacuum Tower is one of those evil necessities. When it operates well it does not seem to garner much attention but when things go wrong all hell can break loose downstream. Refinery operators are constantly trying to minimize wash oil loss versus keeping the wash bed from coking.
Packed columns are widely used in distillation, absorption and stripping processes. It is well known that liquid maldistribution can severely reduce column efficiency and operability. For packed towers a grid-scan, 3 or 4 equal-distant scans would be done to diagnose macro problems of severe liquid maldistribution. But more subtle patterns of maldistribution can be better diagnosed by a more comprehensive method.
The most prevalent use of tomography is still in medical applications, for instance the Computerized Tomography (CT) device that is used for non-destructive examination of the human body. Gamma-ray tomography takes advantage of the penetrating properties of high-energy gamma radiation to generate a cross sectional density profile through a packed bed.
This paper presents a case study describing gamma-ray computer-aided tomography (CAT-Scan) to monitor the density distribution profile through a Vacuum Column Wash Bed enabling this refiner to correlate operation data to the inevitable wash bed coking and to optimize tower assets.