(4e) Troubleshooting and Solving a Sour Water Stripper Problem

A Sour Water Stripper in a gas processing plant was designed to strip 35 m3/h  (154 gpm) of sour water containing approximately 650 ppmw H₂S to a bottoms purity of less than 5 ppmw. Upon start-up, the column could only achieve a feed flow rate of 20 m3/h (88 gpm). Any increase beyond this would initiate flooding. Several theories were proposed to explain the premature flood.

A systematic investigation combining field testing and hydraulic analysis eliminated about half the theories, leaving foaming and damage as the frontrunners.  A plant test was performed in which the liquid loads were raised at a constant vapor load. The test showed the flood to be vapor-sensitive and liquid-insensitive. When combined with the hydraulic analysis, the test provided strong evidence that supported the column internals damage theory.

The tower was shut down and inspected, and one of the upper trays was found to be damaged. The damage unsealed one of the upper downcomers. Interference of rising vapor with the descending liquid in the unsealed downcomer was proposed as the explanation to the flood. This explanation is consistent with a vapor-sensitive flood. The damage was repaired and the tower achieved design performance.  The most likely cause of the damage was thought to be entry of cold feed water during start-up.

One lesson learned is the importance of using hot feed during start-up of steam-water systems. If cold feed is used, any sudden feed surges or feed temperature drop may cause rapid condensation near the column inlet and consequent column internals damage. Another lesson learned is that contrary to some literature references, Sour Water Strippers are not always foaming. The column investigated was not adequately designed to handle foaming, yet achieved the design capacity after the damage was repaired