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 SiO 2 , Al 2 O 3 , CaO, Fe 2 O 3 , 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, Fe 2 O 3 , 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.

The ash fusion temperatures (AFTs) of 21 typical Chinese coal ash samples and 60 synthetic ash samples were measured in Ar and H2 atmospheres. The computer software package FactSage was used to calculate the temperatures corresponding to different proportions of the liquid phase and predict the phase equilibria of synthetic ash samples. Empirical liquidus models were derived to correlate the AFTs under both Ar and H2 atmospheres of 60 synthetic ash samples, with their liquidus temperatures calculated by FactSage. These models were used to predict the AFTs of 21 Chinese coal ash samples in Ar and H2 atmospheres, and then the AFT differences between the atmospheres were analyzed. The results show that, for both atmospheres, there was an apparently linear correlation and good agreement between the AFTs of synthetic ash samples and the liquidus temperatures calculated by FactSage (R > 0.89, and σ < 30 °C). These models predict the AFTs of coal ash samples with a high level of accuracy (SE < 30 °C). Because the iron oxides in coal ash samples fused under a H2 atmosphere are reduced to metallic iron and lead to changes of mineral species and micromorphology, the AFTs in a H2 atmosphere are always higher than those with an Ar atmosphere.