Harm of oil-containing post-desulfurization gas and preventive measures

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This post was last edited by Steven_p0kTk on 2024-2-5 09:22. The wet oxidation desulfurization unit for coke oven gas is installed after the ammonium sulfate extraction of benzene; the alkali source used in the desulfurization system on a daily basis is added soda ash, which constitutes a post-desulfurization approach. The coke oven gas source after desulfurization treatment is relatively clean, but before desulfurization, benzene is removed from the gas. If a large amount of washing oil from the benzene removal unit enters the desulfurization system along with the gas, it will cause unstable operation of the system. I. Hazards of large amounts of washing oil entering the desulfurization system (1) Washing oil without sulfur foam in the regeneration tank has an antifoaming effect; when large quantities of this washing oil are carried into the desulfurization solution along with the gas, it eliminates the foam. By the time it reaches the area where sulfur foam is present in the regeneration tank, almost no sulfur foam is visible. Meanwhile, the sulfur paste produced by the system contains a significant amount of oil, giving it a black surface. This will severely disrupt the balance of sulfur production in the system, potentially leading to an increase in suspended sulfur in the desulfurization lean liquid and thereby increasing the risk of blockage in the desulfurization tower. (2) Excessive hydrogen sulfide in the purified gas leads to a large amount of oil being carried into the alkaline desulfurization solution; under alkaline conditions, emulsification occurs, forming an oil-water mixture. During the gas-liquid contact process, the oil, being insoluble in the desulfurization solution, forms an oil film at the gas-liquid interface. Both absorption and regeneration are gas-liquid mass transfer processes controlled by this oil film. H2S and oxygen must pass through this liquid film to reach the bulk of the liquid phase in order to participate in the reactions. In such cases, the solubility of H2S and oxygen in the oil film drops sharply, which severely hinders the absorption and regeneration reactions and results in a rapid decrease in the reaction rate of the system. Both absorption and regeneration processes are significantly affected; in other words, the large amount of oil in the desulfurization solution prevents H2S and oxygen from entering the liquid phase, thereby preventing desulfurization and regeneration, and ultimately leading to extremely high levels of H2S in the purified gas produced by the desulfurization system. II. Preventive measures: (1) Strengthen oil control at the upstream stage: If a large amount of washing oil is carried along with the gas due to process-related issues, it is necessary to enhance control over the upstream processes. On one hand, it is important to better control the temperature during the desulfurization process for benzene extraction; in order to reduce the amount of oil in the gas, the temperature of the gas after benzene extraction should be kept as low as possible, with the temperature control ideally set at the lower limit ； On the other hand, it is necessary to strengthen the monitoring of the gas temperature after the benzene washing final cooler, the temperature of the second stage of the oil-poor cooler, as well as the temperature after the benzene washing tower, and to operate strictly in accordance with the specified temperatures. (2) Oil in the gas inevitably increases the amount of oil present in the gas water seal tank; on-site, the frequency of oil skimming operations using the gas water seal can be increased to reduce the risk of oil presence in the system. (3) The regeneration section of the desulfurization system ensures a stable flow rate of regeneration air; the air volume should not be reduced arbitrarily, and overflow should be enhanced to prevent a decline in regeneration capacity. (4) Improve filtration: If conditions permit, it is advisable to replace the foam pump with one that has a higher flow rate and greater head pressure, so that the foam and desulfurization liquid that overflow can be removed promptly. (5) Desulfurization solution replacement: If the solution turns black during operation, it is necessary to replace part of the solution promptly to stabilize the system’s performance.