REACTION OF CA(OH)(2) WITH SO2 AT LOW-TEMPERATURE

Lime is widely utilized as a sorbent in dry and semidry sulfur removal processes. In this study limestone was calcined at high temperature a nd lime was produced by water vapor steam treatment at low temperature . Experiments were performed at conditions that also cover those usual ly present in coal-fired power plants. The investigation of the reacti on of lime with synthetic flue gas showed that the relative humidity o f the gas has a major impact on the reactivity. Also the presence of o xygen and/or carbon dioxide does not show a significant influence on t he sulfur dioxide removal reaction though some intermediate formation of calcium carbonate cannot be excluded. Mainly calcium sulfite hemihy drate was found to be the reaction product, but some calcium sulfate h emihydrate was also formed when oxygen was present. Four regions with different prevailing reaction mechanisms can be defined: In the beginn ing the formation of a monolayer is mainly determined by the SO2 conce ntration and to some smaller extent also by the relative humidity. Thi s period is followed by the formation of the consecutive product layer s which can initially be determined by a dissolving process of SO2. Af terward this formation is only determined by the relative humidity and most likely by product layer diffusion. Above a conversion of around 9% reaction rate drops significantly which can be due to pore closure.