Ash melting behavior under coal gasification conditions

The results of this study show that CaCO3 additives are an efficient fluxing element for the control of ash melting, more particularly Al2O3-rich ash melting. The minimum values of the hemispherical temperatures of the ash-additive mixtures were 50-500 K lower than those of parent coal ashes. Empirical equations have been derived to relate ash fusion temperatures to ash composition. X-ray diffraction studies of the mixtures at elevated temperature (up to 1773 K) showed some light on the phase transformations that the mineral systems undergo. Interaction between the components of the coal ashes and the additive proceeds within the system SiO2-Al2O3-CaO. A knowledge of the original mineralogical composition can be of assistance in interpreting both the high temperature phases formed and the ash melting behavior. From FT-IR data, melted glass phase containing CaO was depolymerized relative to the parent coal glass and had a higher pozzolanic reactivity (supplementary cementing material). (C) 1997 Elsevier Science Ltd.