Posted by NINGBO INNO PHARMCHEM CO.,LTD.

In the realm of industrial emission control, Selective Catalytic Reduction (SCR) technology plays a vital role in mitigating nitrogen oxides (NOx). However, a critical secondary reaction within SCR systems is the oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3). This SO2/SO3 conversion has significant implications for the performance of the SCR catalyst itself, as well as the overall operational efficiency and longevity of industrial equipment. For businesses looking to purchase SCR catalysts, understanding this conversion is key to making informed decisions.

The primary function of an SCR catalyst is to facilitate the reaction between NOx and a reducing agent like ammonia to produce nitrogen and water. However, many common SCR catalysts, particularly those containing vanadium pentoxide (V2O5), also possess catalytic activity for the oxidation of SO2 to SO3. This SO2/SO3 conversion is generally considered an undesirable side reaction. The degree of conversion can vary significantly based on catalyst composition, flue gas temperature, SO2 concentration, and catalyst structure. Typically, SCR catalysts are designed to achieve a SO2/SO3 conversion rate of less than 1%, but this can fluctuate.

The consequences of excessive SO2/SO3 conversion can be substantial. SO3 reacts readily with moisture in the flue gas to form sulfuric acid (H2SO4). This acidic compound can condense on cooler surfaces downstream of the SCR reactor, such as air preheaters, economizers, and ductwork, leading to severe corrosion. This corrosion necessitates costly repairs and can significantly shorten the lifespan of expensive equipment. Furthermore, SO3 can react with ammonia slip (unreacted ammonia from the SCR process) to form ammonium bisulfate [(NH4)HSO4] and ammonium sulfate [(NH4)2SO4]. These compounds are sticky and can deposit on surfaces, causing fouling and blocking of catalyst channels, air preheaters, and filter bags. This buildup increases system pressure drop, reduces heat transfer efficiency, and ultimately lowers the overall performance of the industrial process.

Therefore, controlling the SO2/SO3 conversion rate of the SCR catalyst is a critical aspect of SCR system design and operation. Factors that influence this conversion include:

  • Catalyst Composition: Catalysts with higher V2O5 content tend to have higher SO2/SO3 conversion rates. Promoters like MoO3 can help suppress this conversion.
  • Flue Gas Temperature: Higher flue gas temperatures within the SCR operating range generally increase the SO2/SO3 conversion rate.
  • SO2 Concentration: While higher SO2 concentrations can theoretically reduce the conversion percentage, the absolute amount of SO3 produced can still be significant.
  • Catalyst Structure: The surface area and pore structure can influence the reaction kinetics.

For companies looking to buy SCR catalysts, it is essential to partner with manufacturers like NINGBO INNO PHARMCHEM CO.,LTD. who understand the delicate balance required. By carefully selecting catalyst formulations and optimizing operating conditions, industries can minimize SO2/SO3 conversion, thereby protecting their equipment, reducing operational costs, and ensuring efficient and compliant emission control.