Discussion on the Corrosion in the Debutanization Tower System of Hydrogenation Units

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In the diesel hydrogenation unit, the inlet filter screen of the butane removal tower bottom circulation pump (reboiler pump) becomes clogged frequently; the solid debris removed from it is flaky in shape, with larger pieces being as big as fingernails and quite hard. The operating conditions of the circulation system are as follows: the temperature at the bottom of the tower is 280 degrees; the fluid is pumped to the reboiler via a circulation pump, with the temperature at the outlet of the reboiler being 310 degrees. From there, it returns to the bottom of the tower to provide heat. The fluid contains trace amounts of water. The materials used for all relevant components (pump inlets and outlets, as well as the furnace tubes) are 20#. Based on the frequent clogging mentioned above, uniform corrosion is suspected, as this phenomenon has persisted for a long time. There are some questions; feel free to discuss them: 1. What are the corrosion products? Chemical analysis revealed that the corrosion product contained no sulfur. 2. Will high-temperature sulfur corrosion occur under these working conditions, and what are the products of sulfur corrosion? 3. The medium at this location shows alkaline properties, with a pH of around 12. Meanwhile, the water-in-water sample from the tower top reflux tank also exhibits alkalinity. What is this alkaline substance? Why does it show alkaline? 4. If corrosion is determined, what is the mechanism of corrosion?