Distribution Study - Packed Bed

A limitation to gamma scanning is that the scan measurements are “static”. They measure density at a specific point (the path that the radiation is currently passing through) at that particular moment in time. Gamma-ray scanning determines changes in density from which we draw certain conclusions, for example liquid maldistribution. However, there may be cases where there is maldistribution, but the density change is so small that it can not be detected by gamma scanning. For instance, if the packing normally holds 3 lbs/ft³ of liquid and an additional 1 lb/ft³ effects bed performance such that it is flooded and the dry density of the packing is 10 lbs/ft³, then the change in the average density is from 13 to 14 lbs/ft³, which is only a 7.6 % increase. If this is occurring in only a portion of the bed, then the apparent density change might be only a few percent in the scan. With liquid maldistribution, the liquid may be traveling faster down one side of a column than the other. Another example is if there is a vapor maldistribution flowing up a tower that can not be detected by gamma scanning due to its very small change in overall density throughout the packed bed. In these and other cases, a TRACERCO Diagnostics™ Distribution Study can be employed to effectively measure and quantify a particular maldistribution problem.

A TRACERCO Diagnostics™ Distribution Study involves the injection of a very small volume of short lived radiotracer material that will closely follow the process material phase under investigation. Low voltage detectors are positioned on the external walls of the process at specific locations and detect the quantity of radiotracer passing by. Analysis of each detector response allows flow dynamics to be determined including cross sectional distribution, velocity, and residence time.

In any tracer study it is imperative that the correct radiotracer type and purity is used. In all tracer projects Tracerco uses its 50 years of applications experience to ensure the selected radiotracer fully matches the project design and the process system under investigation.