Formation of SO3 in Flue Gas Under SNCR Conditions

Abstract

Listen

Translate article

AbstractExperimental and numerical studies were conducted to investigate the formation of sulfur trioxide (SO3) during the selective non-catalytic reduction (SNCR) process. The effects of the inlet NH3/NO ratio (RAN), reaction temperature, inlet mole fractions of SO2, O2, CO and H2O were assessed. The experiments were conducted using a perfectly stirred reactor (PSR) and SO3 mole fraction was determined using the sulfur balance method. Corresponding numerical simulation was performed using detailed chemistry developed by Mueller and coworkers. Both experimental and numerical results revealed that the SO3 formation was considerably affected by RAN, SO2 and O2 mole fractions. The experimental results demonstrated that under typical SNCR conditions, 0.5 ~ 1.0% of SO2 was converted into SO3, and SO3 mole fraction was 5–10 ppm. The SO3 formation was noticeably enhanced by the addition of NH3 when RAN < 0.5. The conversion rate decreased as the initial SO2 increased. A small amount of O2 could promote the SO3 formation remarkably, but this effect became much weaker as inlet O2 mole fraction ≥1%. The numerical simulation indicated that the increase of the reaction temperature significantly promoted the SO3 formation when the temperature was above 1173 K. A small amount of CO could significantly enhance the SO3 formation. The H2O addition could inhibit SO3 formation. The detailed chemical kinetic analyses showed that the main reaction paths of the SO3 formation were the oxidization reaction of SO2 with O radical via SO2 + O (+M) → SO3 (+ M) (52.3) and the one of SO2 with NO2 via SO2 + NO2 → SO3 + NO (52.4). The effect of the operational parameters, i.e., RAN, reaction temperature, and SO2, O2, CO, H2O mole fractions, could be well explained by the variation of the reaction rates of Eqs. 52.3) and (52.4).KeywordsSelective non-catalytic reductionAmmoniaSulfur dioxideSulfur trioxide