Continuous reforming problem
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Under what conditions does salt formation occur at the top of the debutanization column in a continuous reforming unit, and what is the mechanism behind this salt formation?
The crude oil that enters the reforming unit is usually refined; it goes through pre-hydrogenation to remove pentane, followed by dehydration, so there should be no components that could cause crystallization or scaling. It is estimated that the crude oil at the upstream stage was not refined thoroughly, or that ammonia and sulfides combined to form ammonium hydrosulfide with low sulfur content during the gas-liquid separation process after the pre-hydrogenation reaction. A compositional analysis of the salt in the knot should reveal it.
It is likely that the pre-hydrodenitration of naphtha was not thorough enough; during the reforming reaction, nitrogen was converted into ammonia, which further formed ammonium chloride. Ammonium chloride deposits in areas with lower temperatures, such as at the top of the debutane tower and in the recycle gas. At the same time, it will cause chlorine loss in the reformation reaction system, affecting the water-chlorine balance of the system. I had seen explanations of such abnormal situations in the Process Manual before.
That’s correct; mainly because the refined oil contains nitrogen, which forms ammonium chloride with the chlorine in the reforming reaction system, and this compound precipitates out upon cooling at the top of the distillation column. Currently, there is a technology that involves adding liquid-phase dechlorination before the distillation tower, which can remove impurities such as ammonium chloride and thus protect the distillation tower and the extraction section.