Investigation of the Role of Silica Additive in Thermal Transformation of Zhundong Coal High-calcium Fly Ash by DSC

In order to study the influence of the particle size and ratio of silica additive on the prevention and control of slagging and fouling of Zhundong coal, a differential scanning calorimeter(DSC) was used to measure blended samples of a Zhundong coal high-calcium fly ash with two different sizes of silica, and the heat flux characteristics were investigated during heating process. X-ray diffraction was used to analyze phase transformation of the heated samples. The results shows that the significant thermal transformation of the calcium- containing phases in Zhundong coal fly ash and the effect of the silica additive both occur at temperatures above 810℃. The additive promoted the conversion of gehlenite in the high-calcium fly ash thermal product to anorthite. The prevention effect of 2000-mesh silica is better than that of 100-mesh silica. With a silica- ash ratio of 1: 9, 2000-mesh silica can delay the temperature at which the fly ash reaches the DSC endothermic valley by 50℃, effectively slowing down the formation of molten matter in fly ash. However, when the silica-ash ratio is increased to 1: 1, the additive role in slowing the generation of fly ash molten material is not more significant. In engineering practice of using silicon oxide additives to prevent slagging and fouling of Zhundong coal, selecting additives with smaller particle size may be more effective than increasing the amount of additives. © 2020 Chin. Soc. for Elec. Eng.