Absorption mechanism of SO on various alkaline absorbents in the presence of SO.

Sulfur trioxide (SO) as a condensable particle matter has a significant influence on atmospheric visibility, which easily arouses formation of haze. It is imperative to control the SO emission from the industrial flue gas. Three commonly used basic absorbents, including Ca(OH), MgO and NaHCO were selected to explore the effects of temperature, SO concentration on the SO absorption, and the reaction mechanism of SO absorption was further illustrated. The suitable reaction temperature for various absorbents were proposed, Ca(OH) at the high temperatures above 500°C, MgO at the low temperatures below 320°C, and NaHCO at the temperature range of 320-500°C. The competitive absorption between SO and SO was found that the addition of SO reduced the SO absorption on Ca(OH) and NaHCO, while had no effect on MgO. The order of the absorption selectivity of SO follows MgO, NaHCO and Ca(OH) under the given conditions in this work. The absorption process of SO on NaHCO follows the shrinking core model, thus the absorption reaction continues until NaHCO was exhausted with the utilization rate of nearly 100%. The absorption process of SO on Ca(OH) and MgO follows the grain model, and the dense product layer hinders the further absorption reaction, resulting in low utilization of about 50% for Ca(OH) and MgO. The research provides a favorable support for the selection of alkaline absorbent for SO removal in application.