Premature Flooding in Column Internals

Flooding is an undesirable but common enough occurrence in the industrial distillation process. It happens when liquid accumulates in the column caused by excessive upward vapor flow. This results in massive entrainment that restricts the liquid down flow in the column. Flooding can end up causing excessive pressure drops, decreased separation efficiency, and instability. The causes of flooding are complicated. Below we will share a recent flooding investigation on distillation columns at a refinery that revealed some surprising results in regard to the column’s internals.**

Cause of Premature Flooding in Column Internals

The aforementioned investigation took place in an atmospheric crude tower with severe corrosion in the top pumparound and upper fractionation trays. The corrosion was caused by small quantities of water entering the tower that also damaged the 410 stainless-steel trays. Flooding also occurred in the TPA trays, the fractionation trays below, and the upper trays in the fractionation section. These upper trays were found to be clean but missing most of the valve floats. This resulted in increasing the open area on the trays, and flooding occurred near the end of that run but did not occur in earlier runs. It caused investigators to question if the lost valve floats promoted flood in these trays?

Other possible causes for the premature flooding include:

  • Uneven float removal on two-pass trays that changes the vapor and liquid flows.
  • Dry tray pressure drop reduction upon valve pop-out.
  • Unbolted tray manways when loads are high and the conditions favor channeling.
  • Towers operated at high loads and under conditions conducive to channeling.

Explanation of Premature Flooding in Column Internals

The investigation showed that loss of valves or open manways could lead to channeling and ultimately premature flooding. Channeling can result in flooding depending on operating rates and tray geometry. In this case, valve loss led to vapor cross-flow channeling and eventually flooding. However, valve float loss is unlikely to cause flood unless the loads are high combined with channeling. Their work showed that two-pass trays that lose an even number of valves on both tray panels do not lead to flooding if there is no channeling. Uneven loss can cause the panel closer to flood.

One of the most impressive findings in this case was that combining gamma scans and field data with maldistribution and hydraulic analysis was highly effective for diagnosing problems in columns. It successfully diagnosed conditions such as channeling, maldistribution in the multipass tray, unexpected efficiency loss at turndown, and uneven fouling.

AMACS is a leading process internal manufacturer, specializing in trays and packing. Contact us with your tower internal needs for a quick response, an experienced staff, and the highest quality process internals.

**To read the full case study, “An Investigation of Premature Flooding in a Distillation Column”,  Click Here.