Analysis of corrosion and tower blockage issues associated with the desulfurization of coke oven gas using complexed iron

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This post was last edited by Steven_p0kTk on 2025-8-26 09:26. I. Regarding corrosion: As for the issue of corrosion, corrosion does occur in the HPF desulfurization units for coke oven gas, regardless of the catalyst used; it is mainly caused by chemical corrosion resulting from by-products and sulfur. When complexed iron catalysts are used in HPF units, the concern regarding corrosion is actually mainly related to the electrochemical corrosion that free iron may cause to carbon steel equipment (not to stainless steel), whereas complexed iron itself does not cause electrochemical corrosion to carbon steel equipment. The electrochemical corrosion caused by complexed iron is primarily due to the instability of the catalyst, which leads to some of the iron in the complexed iron becoming free; in the form of iron ions or iron hydroxide colloids, this causes electrochemical corrosion to carbon steel equipment. Early complexed iron catalysts were used on-site by combining solid powder with liquid; due to factors such as the mixing ratio and handling procedures, their stability was low, which led to many cases of severe corrosion resulting from the use of these catalysts. Currently, the Guolitong GLT chelated iron catalyst has been upgraded to the fifth generation. This type of catalyst is in a fully liquid form; during production, iron is mixed with the chelating agent in the right proportions to ensure better chelation, eliminating the need for on-site mixing. Its stability far exceeds that of traditional chelated iron catalysts. This type of catalyst has been used in HPF units for over two years and exhibits good corrosion resistance. II. Regarding tower blockage: The use of combined iron in HPF desulfurization units leads to frequent tower blockage, which is a major concern for various companies. Apart from the conventional reasons, there are mainly two factors that cause tower blockage: first, the catalyst concentration is not designed properly; the concentration of complexed iron needs to be determined based on the sulfur capacity of the plant, and this varies from one plant to another. Especially when the concentration of complexed iron is much higher than the designed level, it is easy for S8 to form inside the desulfurization tower, leading to tower blockage. Secondly, some units require adaptive modifications for complexed iron, especially those with two-stage series desulfurization. The characteristic of a two-stage series desulfurization unit is that the absorption load of the first desulfurization tower reaches over 90%, while that of the second stage is less than 10%. The use of complexed iron for desulfurization improves efficiency, and the difference in load between the two stages becomes even greater. At this time, since the two stages of desulfurization liquid belong to the same system, for the second stage of desulfurization, the catalyst concentration mentioned in point \"1\" above is inevitably higher than the designed value. Additionally, due to the low load in the second stage, the lean liquid after regeneration contains a high amount of oxygen; both of these factors contribute to the easy conversion of S (sol) into S8 within the desulfurization tower. This is also why the second tower in a two-stage series desulfurization unit tends to get clogged. In addition to the above two reasons, in the application of some complexed iron, no attention was paid to the cumulative accumulation of salts, oils, and sulfur in the system, which led to an imbalance in the system’s components. As a result, the desulfurization density and viscosity increased, causing blockages. Therefore, when applying complexed iron catalysts in HPF units, it is necessary, on the one hand, to design the catalyst concentration appropriately based on the unit’s processing load and capacity, rather than using a one-size-fits-all approach ； On the other hand, necessary modifications are made as required based on the characteristics of the device, since after all, the HPF device was not designed using complexed iron. Finally, no matter how it is operated, it is necessary to ensure that the system reaches a state of material balance.