Effect of Ca-based additives on the capture of SO2 during combustion of pulverized lignite

The effect of different Ca-based additives in lignite on the sulfur removal during combustion has been examined using two Polish lignites. After demineralization, the lignite was loaded with Ca using different Ca-based compounds namely: calcium carbonate (CaCO3), calcium hydroxide Ca(OH)2 and calcium acetate Ca(CH3COO)2. Depending on the calcium compound used, the addition of Ca was by mechanical mixing or impregnation. The experiment was carried out in a laboratory scale drop-tube furnace reactor, under different O2 concentration and temperature range of 800–1100 °C. The results showed that Ca added to the lignite strongly suppressed the emission of SO2 under experimental conditions studied. The sulfur capture efficiency appeared to be independent of the calcium compound used and it increased along with the temperature rising up to 1100 °C. This may indicate that poorly dispersed Ca, prepared by mechanical mixing, offers as high efficiency in sulfur removal as Ca in ion-exchangeable form inserted by impregnation. The influence of mineral matter on the retention of SO2 during combustion was also investigated. It was found that some inorganic species inherently present in lignite, particularly calcium in natural form, reduce SO2 pollution.