Effect of O₂/CO₂ combustion atmosphere on the mineral inter-reaction of blended coal ashes

The mineral inter-reaction of blending coals during O₂/CO₂ combustion was studied. Two coals, Meng coal and Pingqi coal, were blended by certain ratios. The blending coals were burned in a tube furnace with O₂/CO₂ or O₂/N₂. Ash fusion temperature test, XRD, TG/DSC and thermodynamic calculation were employed to examine the melting behavior and mineral reactions of blending coal ashes during O₂/CO₂ and O₂/N₂ combustion in detail. The results show that:there is no a pronounced difference in the blending coal ash fusion temperature between O₂/CO₂ and O₂/N₂ combustion. More CaCO₃ produced during O₂/CO₂ combustion suggests that O₂/CO₂ atmosphere significantly prevents the decomposition of CaCO₃. The changing of atmosphere has an impact on the transformation of Ca-containing minerals, and the reaction between Ca and mullite occurs significantly, which is easier in O₂/CO₂ combustion to produce more low-melting phase that will aggravate the boiler slagging. When the blending ratio of Meng coal in blends with Pingqi coal is 75% or more, less mullite is present in blending coals, and thus the impact of atmosphere on Ca-mullite reaction is weaker. However, the atmosphere has a more impact on Fe-containing minerals and more Fe-glass phase will be formed during O₂/CO₂ combustion, which will aggravate the boiler slagging.