Melting Behaviour of Huainan Coal Ash in Reducing Conditions

Abstract

Computer-controlled scanning electron microscope analysis show that the mineral matter in Huainan coals are characterized by higher aluminosilicate clay minerals contents (more than 60 % of the total mineral matter in coal) together with quartz, which accounts for their higher ash flow temperatures, often higher than 1500 ºC. The transformation of mineral matter tested by XRD shows that, as temperature increasing from 1150 to 1450 ºC, quartz phases decrease sharply and anorthite contents show the tendency first increased greatly then decreased. Differences in peak intensity of mullite and anorthite reflect differences in phase concentration of the quenched slag fractions, which contribute to the difference of ash melting temperature. The addition of CaO at a low content around 8 % may increase the melting temperature of HN115 and HN119 coal ashes somewhat. With the increase of its addition, the melting temperature of ash initially decreases gradually, reaching its minimum value at the amount of CaO around 25 % and however increasing again with the further addition of CaO. This phenomenon is consistent with the theoretical thermodynamic equilibrium considerations.