The primary use of the gamma ray scanning technique is to locate mechanical damage and depict process flow characteristics inside distillation columns while they remain in service. Column scans are safe, proven, remain completely external to the process, don't interfere with plant operations, require no plant utilities, and are quickly set up and performed.
The technique is accomplished by positioning a small radioactive source and a sensitive detector along the outside of the column. If the spacing is held constant, the radiation field at the detector is a function of the average density between the two. Or more simply, a dense material (liquid) blocks more radiation from reaching the detector than does a light material (vapor).
In distillation columns,
the source and detector are lowered down opposite sides of the vessel (constant
spacing). Plotting the detector response versus elevation generates
a unique and accurate density profile of the material inside the vessel.
(Liquid responds to the left, vapor to the right). Performance is
then readily evaluated by analyzing the liquid holdup and liquid/vapor
disengagement at each tray level.
Besides locating and identifying problem areas, nuclear scans enable your process and technical people to more fully understand their processes and the nature of instability or poor performance.
Gamma scanning can also eliminate a potential shutdown by showing that tower inefficiencies are not due to internal problems and that process personnel should concentrate their efforts to external causes.
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