The impact of impurities on system operation during coke oven gas desulfurization

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The most common impurities in the desulfurization process of coke oven gas are oil dust and by-products salts. Oil dust is mainly introduced by gas; generally, a large amount of oil dust enters the desulfurization system due to poor performance or operational failures of the pre-cooling unit and electrostatic tar catcher at the upstream stage ； By-products are formed as a result of side reactions occurring within the desulfurization system itself. I. The impact of oil dust on desulfurization Oil dust, including tar, naphthalene, phenols, and coal dust, enters the desulfurization system and is absorbed by the desulfurization liquid; as a result, the viscosity and density of this liquid increase. This generally has the following effects on the operation of the desulfurization system: (1) It reduces the efficiency of desulfurization: Tar and naphthalene form hydrophobic films on the fillers in the absorption tower, thereby affecting the efficiency of absorption and mass transfer. The desulfurization process involves H2S in the gas phase first entering the liquid phase, where a chemical reaction then takes place. This is a gas film-controlled process, and mass transfer has a significant impact on absorption; a decrease in mass transfer efficiency is immediately reflected in the desulfurization efficiency. (2) Cause filler blockage: Tar and naphtha will adhere to the surface of the filler, blocking the flow channels and causing obstructions. Furthermore, sulfur is oil-soluble; some of the sulfur produced by the system combines with tar and adheres to the surface of the filler, accelerating its clogging. (3) Difficulty in sulfur separation: As with the aforementioned reasons, sulfur blends with tar, making it difficult to float sulfur bubbles; the bubbles become weak, and the quality of the lean liquid is poor. Furthermore, the handling of sulfur during filtration or sulfur melting and separation becomes significantly more difficult; there is an increased likelihood of clogging in the filter cloth or sulfur melting vessels, as well as a greater workload. II. The impact of by-products on desulfurization: The by-products resulting from the side reactions in desulfurization, such as thiocyanates, sulfates, thiosulfates and other sulfur-containing by-products, are substances that cannot be regenerated. When they accumulate to a certain extent, they can have an irreversible effect on the properties of the desulfurization solution. Ultimately, this affects the mass transfer efficiency in desulfurization, leading to a decrease in desulfurization efficiency. When the amount of by-products accumulates significantly, it can cause salt crystallization to block the tower, as well as accelerate corrosion of the equipment and pipelines. Therefore, whether it is oil dust or by-products, their accumulation to a certain level will inevitably have a serious impact on the desulfurization process. The common solution is to replace a large amount of the fresh desulfurization liquid in order to reduce the levels of oil dust and by-products. Today, complexed iron catalysts are being used increasingly widely for the desulfurization of coke oven gas. Early promotions of complexed iron-based desulfurization methods claimed that no liquid waste would be produced; from a theoretical perspective, it is indeed possible to avoid the formation of by-products, thereby achieving no liquid discharge. As the use of complexed iron in the coking industry grows more widespread, we have found that even when optimal conditions are achieved and a sulfur selectivity of over 99% is attained, the amount of by-products remains stable (with only a 1% increase in by-products resulting from minor side reactions, which are carried away along with the sulfur paste). However, the accumulation of oil dust cannot be resolved by catalysts; even when the operating conditions at the front end are optimal, it is not possible to eliminate the effects of oil dust 100%. Therefore, achieving oil balance in the desulfurization system is a major challenge.