Discussion on measures to ensure that the sulfur content in the flue gas from catalytic cracking units is within acceptable limits!

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The current environmental compliance standard for sulfur content in the flue gas of the waste heat boilers in catalytic units is that, when the unit’s load is at least 80%, the SO2 concentration should not exceed 850 mg/m3. However, given the current production conditions in China, it is difficult to meet this standard even under the designed conditions for the raw materials; moreover, most units use low-quality raw materials with high sulfur content. So what measures can be taken in such situations? Of course, reducing the sulfur content in the raw materials is the ultimate solution, but it seems impractical. Currently, two methods are commonly used (we won’t discuss the unconventional methods for passing inspections). 1. Install a desulfurization unit; this involves subsequent handling and disposal of alkaline slag, may require additional staff positions, and entails high initial investment, but it provides a permanent solution. 2. Use sulfur transfer agents, which require low upfront investment but demand ongoing costs. The mechanism behind these agents is to transfer the sulfur that would otherwise end up in the flue gas into the product (mainly dry gas). If the desulfurization unit has the necessary capabilities, and considering the economic benefits, this approach can be quite effective. However, since catalytic regeneration differs depending on whether oxygen levels are high or low, the agents used also need to be appropriate for such conditions. Currently, domestically produced agents work well for regeneration under high-oxygen conditions, but their performance under low-oxygen conditions is not ideal, so imported agents are mainly relied upon. (My views on additives are personal; please feel free to point out any mistakes from those in the same field.) Regarding the mechanism of sulfur transfer agents, these agents utilize a specific chemical mechanism that enables the following reactions to take place in the riser and regenerator. In the regenerator, these agents capture SOx, which is then released as H2S in the riser. These agents help to oxidize SO2 into SO3, which is subsequently absorbed by the agents as sulfates. Later, under the reducing atmosphere in the riser of the catalytic unit, it is released as H2S, as shown in the following reaction equations. Regenerator: S + O2 → SO2; 2SO2 + O2 → 2SO3; SO3 + MeO → MeSO4. Reactor: MeSO4 + 4H2 → MeO + H2S + 3H2O; MeSO4 + 4H2 → MeS + 4H2O. Stripper: MeS + H2O → MeO + H2S. This can be considered a lecture by someone who claims to be an expert in this area, but it’s hardly a proper lecture – it’s more of a discussion aimed at mutual improvement. I am also very interested in knowing which companies use sulfur transfer agents in their catalytic units (whether they are domestic or imported, and what the efficiency of removal is like), as well as which companies have installed flue gas desulfurization systems in their catalytic units and how well those systems are performing Everyone is welcome to join the discussion!