What are the causes of blockage at the top of the stripper?
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The diesel hydroprocessing unit uses a thermal hydrotreating process, and the hydrogen sulfide removal stripping tower relies on steam for stripping. The unit was temporarily shut down in August without any maintenance work being carried out. It was restarted at the end of September as arranged by the company; however, sulfur compounds clogged the top of the stripping tower during operation (the exact composition is unknown, but 70% of it is sulfur). The unit was shut down again to clean the vapor line at the top of the tower, and it was restarted after cooling. Have any of you encountered similar problems? What is the mechanism behind this phenomenon?
It should be ammonia hydrosulfide or ammonium chloride crystals
Water is added before parking; the crystals may be ammonium hydrogen sulfide and ammonium chloride
During our maintenance work, we replaced the entire vaporization line and air cooling system of the degassing tower. A large amount of loose black substance (which I suspect is FeS) was attached to the walls of the removed vaporization line pipes, and the diameter of these pipes had decreased significantly.
I have encountered this situation before; the reason was that the temperature control of the air cooling at the top of the tower during winter was too low, there was less light component in the feed, and there was a deviation in flow within the air cooling tube bundles at the top of the tower, which led to blockages caused by ammonia salt crystallization in those two sets of tube bundles
It’s likely that ammonium salt crystals are causing the blockage; didn’t you take any action after shutting down the operation?
Is there water injection in the reaction system? How much water is to be poured in? What is the N content of the feed? Ammonium salts should not be taken into the stripping tower.
Water is injected into the reaction; normal ammonium salts shouldn’t reach the top of the stripping tower, right?
This post was last edited by crazymoonman on 2015-10-24 at 11:47. The substance in our pipeline is yellow in color; more than 70% of it consists of sulfur. The exact molecular structure is unknown, which makes it difficult to determine the formation mechanism.
This post was last edited by uyouu1 on 2015-10-27 at 11:13. If it’s yellow, that’s correct; it’s caused by ammonium sulfide/hydrosulfide deposits. Of course, the possibility of corrosion beneath those ammonium salts (resulting in loose black substances) cannot be ruled out. If it’s ammonium chloride, it will be white. Since sulfur has been detected, it makes no sense not to be able to determine whether it’s an ammonium salt as well. Rust presence can also be detected; by rubbing the scale with a tool, the ammonium smell can be easily identified.