The use of gamma ray technology to rapidly identify operational or design problems within distillation towers is well proven. For tray towers it is usual to perform a scan on the “active” tray area of the tray deck, which can be repeated if the trays are more than one ”pass”. (i.e. side-centre downcomers)
However there are cases when more detailed examination of the trays is required in order that the client can fully identify the problem and decide on a solution.
A recent project at a major European refinery required a precise scanning regime when the phenomenon known as “vapour cross-flow channelling” was suspected. This is when the liquid level on the tray is not uniform across its width and is caused when vapour preferentially rises through a region of the tray close to the outlet weir. This can then lead to premature entrainment and flooding.
Clicking on the above graph shows the results from three scans across the trays in a section of the column. The results are shown as density readings, allowing for the different paths lengths of the chords and the variation in wall thickness caused by the curve of the tower. The onset of vapour cross flow channelling is shown by the alternative pattern of the level on trays. For the even trays the level is highest at the outer scan position (blue trace) whilst for the odd trays the level is highest at the inner scan position ( black trace). When compared against the outlet weir / downcomer location then the level on each tray is highest at the locale of the downcomer itself.
This problem is currently being investigated by the clients distillation experts in the USA in conjunction with Henry Kister, probably the worlds leading Distillation expert.