Changes in gas H2S load during the desulfurization of coke oven gas using complexed iron, and corresponding adjustments

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This post was last edited by Steven_p0kTk on 2024-5-7 09:00. The changes in the H2S load in gas involve two aspects: one is the change in the amount of gas, and the other is the change in the H2S content in the gas. In the coke production process, the amount of gas generated is related not only to the type and quality of coal used in the coke oven, but also to the operating conditions of the coke oven, such as its operating temperature and pressure, as well as the amount of coal fed into it ； The changes in the H2S content in gas are mainly related to the types of coal used in the coke oven production process as well as the sulfur content in those coals. In the actual production process, changes in the H2S content in the gas are inevitable. Sometimes these changes are caused by variations in the types of coal used; other times, they result from adjustments in coke production based on production needs and market conditions. In most cases, production capacity for coke decreases to varying degrees as a result of market forces, which in turn leads to changes in the amount of gas produced according to production demands. When the H2S load in the gas changes, when operating a wet oxidation desulfurization unit for coke oven gas using complexed iron as a catalyst, it is necessary to make appropriate adjustments to the operation of the unit based on the reaction characteristics of the complexed iron catalyst and the actual load conditions, in order to avoid adverse situations associated with complexed iron-based desulfurization, such as an increase in pressure drop in the desulfurization tower or a rapid increase in the amount of by-products in the desulfurization solution. 1. Effects of reducing the H2S load in gas and adjustment measures. As the H2S load in the gas decreases, the amount of sulfur that needs to be removed through complexed iron desulfurization also drops. Generally speaking, this improves the operational stability of the desulfurization system; it is an effective solution, especially for desulfurization units operating under high pressure and high load conditions. However, even with a reduced H2S load in the gas, appropriate adjustments to the coke oven gas iron-complexed desulfurization system are still required. (1) As the sulfur content in the system decreases, the regular dosage of the iron-based catalyst used for complexation should be reduced according to the actual sulfur level and the requirements of the plant. In the case of a long-term reduction in the sulfur load in the gas, it is also advisable to gradually lower the concentration of the catalyst in the desulfurization solution to the design value corresponding to that sulfur load, if possible. (2) Under two-stage or multi-stage series desulfurization, the reduction in the H2S load in the gas inevitably leads to an imbalance in the sulfur absorption load within the two-stage or multi-stage desulfurization towers. To meet the operating requirements of the complexed iron catalyst, it is necessary to adjust the absorption load to achieve balance, for example by adjusting the opening degree of the gas valves between the stages in order to regulate the H2S load in each stage of desulfurization and thus achieve balance in the absorption loads across the stages. (3) If the H2S load in the gas decreases significantly, when using multiple towers in series or parallel for desulfurization, technical calculations can be carried out by taking into account the reaction properties of the iron-based catalyst, the mass transfer requirements in the packed tower during desulfurization, as well as the needs for catalyst regeneration. In this way, it is possible to reduce the operation time of one of the towers while ensuring that the H2S content in the purified gas remains within acceptable limits, thereby helping the company to save energy and reduce consumption. (4) In post-desulfurization using sodium alkali, it is also necessary to consider reducing the daily alkali consumption as the sulfur content in the gas decreases. 2. Effects of increased H2S load in gas and adjustment measures. (1) As the H2S load in the gas increases, the amount of sulfur in the system inevitably rises; it is therefore necessary to enhance the production of sulfur foam to prevent sulfur accumulation in the system. At the same time, it is essential to verify and adjust the actual daily sulfur production accordingly. (2) An increase in the H2S load in the gas is likely to cause the H2S content in the purified gas to exceed the specified limits. It is necessary to promptly assess the absorption and mass transfer processes in the desulfurization system, as well as the air requirements for regeneration. In cases of insufficient mass transfer, this should be reported immediately; whereas in cases of inadequate regeneration, measures such as increasing the amount of air supplied should be taken to enhance regeneration, thereby preventing a rapid increase in the by-products contained in the desulfurization solution due to an unbalanced regeneration load. (3) An increase in sulfur content leads to an increase in catalyst loss; therefore, the amount of catalyst added on a daily basis should be increased based on the actual sulfur content in the gas. At the same time, one-time catalyst replenishments should be carried out according to the requirements of the plant, in order to maintain the appropriate catalyst concentration and meet the plant’s load requirements. (4) Under certain conditions, an imbalance reoccurs in the absorption and regeneration loads between the desulfurization towers in multi-stage desulfurization; therefore, adjustments to balance the absorption and regeneration loads required for complex iron-based desulfurization are also necessary. (5) Similarly, in post-combustion sodium-alkali desulfurization, it is necessary to consider increasing the daily alkali consumption as the sulfur content in the gas increases.