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TRACERCO Diagnostics™ - Distribution Study

Vapour Distribution Determines Cause of Lost Efficiency

To meet tightened product specifications modifications were made to a key column in a fractionation train. These modifications included repacking the 3 existing packed beds and installing new distributor trays, along with a newly designed deflector plate at the inlet of the vapour return. This plate was orientated at an angle, directly in front of a short vapour sparger, in order to distribute the vapour flow more evenly throughout the entire column. The column was restarted after these modifications were made, but the anticipated improvements in product quality were not observed. In an attempt to improve tower performance changes were made in the column’s operating conditions, including changing the reflux ratio and relocating the feed point.

Distribution study

None of these changes achieved the desired improvement in product separation and the new deflector plate was identified as one possible cause of the poor performance. It was possible that instead of improving vapour distribution, the new plate was causing a maldistribution of the vapour, resulting in a significant reduction in used bed area and a loss of separation efficiency. Before any action could be taken, the refinery needed proof that this was the cause of the problem. Tracerco was asked to perform a vapour distribution study, utilizing advanced radioisotope tracers and sophisticated external detectors. Tracerco injected a gaseous tracer into the vapour return line with detectors placed at various elevations and orientations around the circumference of the vessel. The results showed that there was a significant maldistribution of the vapour flow throughout the tower. The new deflector plate was forcing most of the flow side of the tower opposite the inlet nozzle. The data also indicated that the maldistribution existed all the way through the second packed bed. Only at the third bed did the vapour flow pattern become well distributed throughout each quadrant of the tower. This information provided the engineers with proof that it was necessary to redesign the vapour inlet. The deflector plate was abandoned, and a newly designed vapour sparger was installed. After these modifications were made, the column was restarted, and the resulting product met the more stringent specifications.

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