New Frontiers in Quantitative Analysis of Packed Tower Gamma Scans

A new method of analyzing gamma scans can guide smarter troubleshooting by identifying liquid holdup in packed tower vapor spaces crowded by distributor parting boxes or complex piping.

Qualitative gamma scanning has been used to successfully troubleshoot tens of thousands of packed towers for over five decades. Scan data have traditionally been analyzed visually to detect flooding, damage, plugging, foaming, and liquid maldistribution. Such qualitative analysis has at times been challenging because the gamma rays are simultaneously absorbed by the packing metal, the liquid held in the packing, and solids like polymer or coke. Difficulty in decoupling these from each other begets misinterpretation, subjectivity, and incorrect diagnostics.

A relatively recent breakthrough by Pless (1, 2) pioneered packing quantitative analysis that successfully decouples the packing metal absorptions from the liquid absorptions and from absorptions due to plugging. This method of quantitative analysis of packed beds is simple, inexpensive, and can be incorporated into any scan.

A remaining unresolved challenge is to identify liquid accumulation in the vapor space between distributor parting boxes or where complex piping exists. In such regions, there is no telling whether the gamma ray absorptions are due to the parting boxes, the pipes, or liquid in the vapor space. Scanning contractors often avoid the issue altogether and make no comment about whether liquid is present in such regions.

This article describes a breakthrough that extends the quantitative gamma scan analysis to vapor spaces containing parting boxes or pipes. In the same way that quantitative analysis can decouple liquid holdup absorptions in a packed bed from the packing metal and solids, this new quantitative technique can decouple parting box absorptions and pipe absorptions from absorptions due to liquid holdup in the vapor spaces...