Effects of atmosphere and Si/Al additives on component transformation in high-alkali coal ash

Serious ash-related issues could occur during the combustion of high-alkali coal.Oxy-fuel combustion is a promising combustion technology to deal with the emission reduction of CO₂.However, the influence mechanism of oxy-fuel atmosphere on the transformation of high-alkali coal ash is far away from enough.In addition, the previous study mainly adopted the high-temperature ash composition as the research benchmark, which was difficult to explore the inorganic substances behaviors at low temperature.This study explored the impacts of combustion atmosphere, oxygen content, and additives on the transformation of ash components via FactSage software on the basis of the low-temperature ash composition, also including the element distribution in gas phase.The results showed that the oxy-fuel condition benefited the vaporization of chlorine at 600 ℃.The chlorides and sulfates in the gas phase could condense on the ash particle surface to worsen the fouling and slagging.The oxides of sodium, calcium and aluminum reacted each other to form Na₂Ca₃Al₁₆O₂₈ at 200 ℃ and the Na₂Ca₃Al₁₆O₂₈ was absent with the increasing temperature, which could be put down to the formation of low-temperature eutectic.The oxygen content had little influence on the ash transformation of Wucaiwan coal.The high content of CO₂ could accelerate the carbonation of ash to generate Ca₅Si₂O₇(CO₃)₂ and CaMg(CO₃)₂,but had little influence on the sulfates.In addition, the addition of Al₂O₃ and SiO₂ could reduce the content of CaCO₃ in the ash but exerted little effect on CaSO₄.