Corrosion issue of the air-cooling tube bank ahead of the high-pressure separation tank
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Reasons for corrosion in the high-pressure air-cooling tube bundle of hydrogenation units. It is now known that, 1) the amount of water injected is sufficient (it is definitely more than 20% of the feed volume, neither less nor more), and 2) ammonium salt corrosion can be ruled out, as the scale found in the tube bundle is insoluble in water. 3. The flow rate of the tube bundle is unknown; if anyone knows how to calculate it, please let me know (there are no flow meters before and after air cooling: L). I would be very grateful. 4. The salt content in the acidic water discharged also does not exceed the limit. 5. There is some black substance attached to the water injection port, and it has already formed clumps; a small amount of black powder is deposited in the front part of the air-cooling feed tube bundle (it seems to be some kind of substance). 6. The wall thickness of the tube bundles has not decreased; only pitting corrosion occurs. 7. Carbon steel should be suitable for handling CL-, and no CL was detected in the water-
An elemental analysis of the scale that has formed should be conducted to determine what it actually is; otherwise, it’s difficult to make a judgment. It is impossible to determine whether solid impurities are catalyst particles or corrosives without analysis
Is there fluoride in water? Or other chelating agents? Is the level of trivalent iron too high? What does corrosion look like? Pitted pit again?
Fluorine-free; corrosion appears as pit-like spots, in very small numbers – only a few at the inlet pipe opening, with no issues elsewhere
Does the tube bundle have an anti-corrosion coating? The carbon steel pipe bundle should be coated; could it be that there are defects in the coating application?
Do you test for trivalent iron ions and pH value over there?
It has a coating; it’s not known whether there are any defects
Normally, only the pH, COD, and ammonia nitrogen of the wastewater are tested
What are your trivalent iron ion concentrations and pH levels? Are they above the specified values?
Try sending the black residue to a laboratory for burning in a muffle furnace to see how much ash is present; the ash consists of inorganic salts. If the ash content is very low, then the black residue is essentially coke formed; further analysis is needed to determine whether operating conditions with high heat transfer rates contribute to the tendency for coking.
OP, based on your description, salt corrosion is basically ruled out. The black fouling in the air cooler could be heavy aromatics. I’m not sure what type of hydrogenation is being used or what the properties of the feedstock are; when the outlet temperature of the air cooler reaches the freezing point of the heavy aromatics, these substances will condense. Additionally, to calculate the air-cooling flow rate, you need to convert the values related to the amount of circulating hydrogen, the amount of cooling hydrogen, and the anti-surge factor into flow rates under actual conditions; then multiply that value by 1.05, and divide by the number of cooling tubes and the cross-sectional area of each tube. Be sure to take into account the number of tube passes. If you have any further questions, message me privately.