A new thermogravimetric method to quantify SO2 absorption capacity by limestone

A commercial limestone was used in aqueous suspension to capture SO2 from coal combustion gases in a bench scale system. To evaluate the limestone absorption capacity during the applied process, a new method was developed by thermogravimetry (TG), which quantifies the absorbed SO2, from the gypsum content formed in the residual sulphated limestone after absorption, on the limestone initial mass basis. With the new method the thermogravimetric analyses data needed for the calculations can be obtained in equipment which operate only up to 1000 °C and in a faster way than the methods used previously, which need analyses performed up to 1350 °C, to obtain, after the total anidrous calcium suphate decomposition, the conversion factors of the TG curves to limestone initial mass basis. The new method also allows one to reuse the sample alumina crucible, which is not possible in the previous methods because there was partial melting of the residual oxides when heated up to 1350 °C, which during cooling, adhere on the alumina crucible. A comparative analysis shows that the obtained results with the new method are practically the same of those obtained by the previous methods, applied to the same samples, with a relative error lower than 3%, which shows the importance and much better cost/benefit applicability. The new method is also more cost effective environmentally, because it avoids the release of SO3 during the analysis of the residual sulphated limestone, which needed a banch scale SO2 absorption system, from the gases leaving from the TG equipment, during the analysis.