Effect of coal ash composition on ash fusion temperatures

The ash fusion temperatures (AFTs) of coal mineral matter at high temperature are important parameters for all gasifiers. Experiments have been conducted in which mixtures of selected coal ashes and SiO₂, Al ₂O₃, CaO, Fe₂O₃, and MgO were subjected to the standard test for ash fusibility. The computer software package FactSage has been used to calculate the liquidus temperatures of coal ash samples and the proportions of the various phases present as a function of temperature. The results show that the AFTs of coal ash samples first decrease with increasing CaO, Fe₂O₃, and MgO contents, then reach a minimum value, before increasing once more. However, for the effect of S/A ratio, its AFTs are always increased with increasing S/A ratios. The measured AFTs all show variations with mixture composition that correlated closely with liquidus temperatures for the appropriate pseudoternary phase diagrams. The liquidus and AFTs generally showed parallel compositional trends but are displaced from each other because of the influence of additional basic components in the coal ash. The liquidus temperatures of coal ash samples are always higher than its AFTs.