In boiler flue gas SCR denitration, what is the impact of SO2 in the flue gas on the catalyst, and what are the protective measures? ? ?
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The SCR method is used for flue gas denitration, but the flue gas contains SO2. What are the effects of SO2 in the flue gas on the SCR catalyst? What are the protective measures? ? Thank you all for helping me answer my questions
At low temperatures, SO2 reacts with ammonia to form sulfuric acid, which adheres to the surface of the catalyst, causing blockages in the catalyst’s pores or covering its active surface sites, thereby deactivating the catalyst
In simple terms, sulfur causes the catalyst to become poisoned and inactive; therefore, desulfurization must be carried out first before the flue gas enters the SCR system. It is important to pay attention to the temperature of the flue gas entering the SCR – wet desulfurization takes place at lower temperatures, and usually the temperature of the flue gas needs to be increased before it enters the SCR system. Dry desulfurization, on the other hand, requires dust removal
When using SCR for denitrification, it is not possible to first carry out desulfurization by washing; after desulfurization through washing, the temperature of the flue gas drops significantly. Reheating it to 300 degrees to carry out denitrification results in high energy consumption. Generally, SCR denitrification is performed first, followed by desulfurization by washing. When the flue gas temperature is above 350 degrees, the likelihood of ammonium bisulfate being formed is greatly reduced. Of course, this also depends on the type of catalyst used – it is necessary to select an SCR catalyst that minimizes the oxidation of SO2 to SO3. Ammonium bisulfate is primarily formed as a result of the reaction between SO2 oxidized to SO3 and ammonia； Alternatively, dry or semi-dry desulfurization can be carried out first, followed by SCR denitration; in this way, the flue gas temperature does not drop much after desulfurization, and denitration is still possible
Currently, dry desulfurization is generally used, resulting in little reduction in flue gas temperature, followed by medium- and low-temperature SCR denitration. It helps to save energy consumption, but the problem is that the by-products of dry desulfurization are difficult to handle.