Effect Of CeO₂ Additive On Desulfurization During Coal Combustion

In order to improve the desulfurization efficiency and reduce the Ca/S molar ratio under coal combustion, according to the three coal C₁,C₂ and C₃ with different amount of sulfur which derived from some power plants in western Inner Mongolia, the effect of temperature, Ca/S molar ratio and CeO₂ addition on the Calcium-based desulfurization during isothermal combustion were studied using box electric furnace. The influence mechanism of CeO₂ on the desulfurization and combustion performance was analyzed by XRD, TEM and Thermal Analysis method respectively. The result showed that:The self desulfurization efficiency of the three raw coals decreased with increasing temperature. After doping the sulfur fixing agent CaCO₃, the optimum desulfurization temperatures of the three coals were different, and the temperature increased with the decreasing sulfur content of the three coals. The increasing extent of desulfurization efficiency was wider under low temperature than under high temperature with the increasing Ca/S molar ratio. The promotion of CeO₂ on the desulfurization differed with the coal type and temperature, and the optimum desulfurization temperature changed with the doping of CeO₂.The optimum desulfurization temperature of C₁ coal was 850℃when CeO₂ addition were 1.0% and 1.5%.Under low temperature such as 850℃and 950℃, the effect of CeO₂ on desulfurization was obvious. When Ca/S molar ratio were 2.0 and 2.5, and the CeO₂ additon was 1.0%, the desulfurization efficiency were over 80%After doping CeO₂, when the Ca/S molar ratio was 1.5, the optimum desulfurization temperature of C₂ coal was 850℃, and when Ca/S molar ratio was increased to 2.0 and 2.5, the temperature was 950℃. Compared with the C₂ coal added with CaCO₃ only, the desulfurization efficiency was promoted by CeO₂ under different temperature. The desulfurization efficiency were up to 70～85% under different Ca/S molar ratio and temperature.The optimum desulfurization temperature of C₃ coal was 950℃after doping CeO₂. Compared with the C₃ coal added with CaCO₃ only, promoting effect of CeO₂ was great under low temperature such as 850℃and 950℃, especially at 850℃. When Ca/S molar ratio were 1.5 and 2.0, CeO₂ addition were 1.0% and 1.5%, the desulfurization efficiency were up to 80～95% at 850℃and 950℃.Combining with the XRD and SEM analysis, this paper proposed that the promoting mechanism of CeO₂ on desulfurization was catalyzing the reaction SO₂ to SO₃. TG-DTG-DSC analysis of C₁ coal showed that the doping of CeO₂ improved the coal combustion performance. The ignition point was decreased, and the combustion of volatile and fixed carbon was catalyzed. Desulfurization efficiency would be decreased for the rapid precipitation of sulfur in the coal which was caused by the CeO₂ catalysis on the volatile combustion, however, the promoting effect on combustion was different for various coals. Meanwhile, different coal ash composition influenced the promoting effect of CeO₂ on desulfurization also, so the effect of CeO₂ on desulfurization was different for different coal. CeO₂ additive had the double catalysis action on desulfurization and combustion, and the mechanism could be explained by oxygen transfer theory.