Use Downcomer Gamma Scans to Troubleshoot Your Process

Downcomer scanning can provide valuable information to diagnose your tower. In particular, these scans are useful for determining the mechanism of flooding — one of the most common problems encountered in distillation columns. Follow these guidelines to avoid pitfalls.

Gamma scanning is one of the most powerful diagnostic techniques available for distillation and absorption towers and has been successfully used to troubleshoot tens of thousands of towers over more than five decades. Although gamma scans are typically shot through the active areas of column trays, valuable information can be obtained by gamma scanning column downcomers. However, the narrow width of downcomers makes downcomer scanning trickier than active-area scanning. It is important to pay attention to the pitfalls, so you do not end up with a misleading diagnosis.

An earlier CEP article discussed the basic principles of quantitative gamma scanning tray active areas, provided recommendations for applying the technique, and introduced a graphical tool called the Kistergram that can be used to display the data (1). A follow-up article focused on unique applications of quantitative gamma scanning to high-capacity trays with truncated downcomers (2). This article focuses on gamma scanning of downcomers, discusses how downcomer scans should be performed, and provides guidelines for avoiding some of the pitfalls. It also presents several case studies in which downcomer gamma scanning was key to successfully diagnosing a tower problem.