Corrosion-prone areas in coking units and preventive measures
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What are the parts of a coking unit that are prone to corrosion? What measures are generally taken?
The anti-corrosion measures for coking units depend first on the properties of the residue oil being processed – specifically its acid value. Anti-corrosion is particularly important in areas such as the top of the distillation tower, the large end caps of heat exchangers, the elbows of heating furnace tubes, the coke tower, as well as in the absorption and stabilization and desulfurization systems (where there is a high amount of acidic gases), as well as in low-temperature, high-pressure pipelines
The tops of the coke tower and the distillation tower are the areas most susceptible to sulfur corrosion; the preventive measure is to use materials resistant to sulfur corrosion when selecting materials. It seems that there is no effective way to avoid sulfur corrosion during normal production. Since the raw materials are often uncontrollable, the residue oil coming out of the upstream vacuum distillation tower must be used for coking downstream; there is no way to be picky. Also, low-temperature dew point corrosion, which is a type of sulfur corrosion, tends to occur on the flue gas side of air preheaters. The way to avoid this is by raising the temperature at the low-temperature end; the air can be heated ； Another option is to use gas that has been desulfurized. The flue gas temperature must not be lower than the corrosion temperature at the low-temperature dew point.
Our workshop has dedicated tanks for corrosion inhibitors. Generally, in addition to focusing on the materials used in the top of the distillation tower and the absorption and stabilization towers, corrosion inhibitors are also added before air cooling at the outlet of the distillation tower top, as well as before air cooling after the rich gas passes through the compressor. Normally, not much corrosion inhibitor is added; water is used for the most part.
There is corrosion at high temperatures as well as at low temperatures; corrosion occurs both at the top and bottom of the distillation tower!