(195b) Troubleshooting Tower Internal Foulings

Tower internals fouling potentials are often overlooked during the design stage. When combined with poor maintenance it can result in capacity shortfall and shorter run lengths.

Case Study #1: A MTBE unit was converted to ETBE production. Since the conversion, ETBE’s catalytic distillation column could not meet the design capacity due premature flooding. Catalytic section trays fouling was suspected as a root cause. As a corrective measure, the licensor recommended certain trays modifications in the catalytic section. However, after the tray modifications and cleanings, the column capacity did not improve. Subsequently the catalysts were completely removed to avoid trays from fouling. Column capacity improved, but premature flooding problem persisted. Thorough column inspection revealed heavy fouling of vapor channels and internal piping that were overlooked previously. After cleaning of all internals, the column design capacity was fully restored.

Case Study #2: Heavy aromatic compounds are purified in a series of distillation columns equipped with high-performance structured packing at elevated temperature and under vacuum. High temperatures and air leakage resulted in coking of the processed hydrocarbons. Coke formation during operation gradually plugged the liquid distributors as well as the structured packings. Ultimately the unit had to be shut down periodically for cleanings with average run lengths of only 3~4 months. Using columns inspection and a series of specialized performance tests, the root cause was attributed to poor liquid distributor designs. Liquid distributors were replaced with anti-fouling & easy maintenance design features. Results from the revamp are: (1) unit run length more than doubled (2) improved product qualities.