Method and theory for optimising ash-fusion characteristics in high-aluminium coal ash via coal blending technology

Abstract

China has abundant resources of high-alumina coal (HAC). However, its application as a raw gasification material is limited owing to high ash-fusion characteristics. For overcoming the limitation, this study employed Xinjiang coal (XJ), having a low ash fusion temperature, to improve the ash fusibility and viscosity of high-alumina Jungar coal (JG). The evolution of Al-containing phases and structures during mixed ash melting were investigated based on XRD, XPS, ²⁷Al NMR, high-temperature stage microscopy (HTSM), and thermodynamic simulations. An increase in the XJ mass ratio resulted in the transformation of gehlenite to anorthite and mullite, producing more amorphous materials at high temperature. These phenomena were manifested at a microscopic imaging as an increase in the number of reaction/melting sites and their area expansion rate, as well as a decrease in ash area shrinkage and melting temperature. Moreover, the introduction of XJ altered the alumina–oxygen network, reducing the binding to the silica-oxygen network and converting some [AlO₆]⁹⁻ to [AlO₄]⁵⁻ as the relative concentration of O²⁻ and O⁻ increases. Consequently, the decrease in the stability of the aluminate structure improves the AFT and viscosity. Based on these results, a mechanism to improve the ash fusion characteristics of HAC based on coal blending is proposed.