Mineral associations in coal and their transformation during gasification

Abstract

The principle aim of this investigation was to determine the effect that minerals and mineral associations in dense medium coal fractions have on the ash fusion temperature (AFT) of coal, where the mineral matter associated with coal undergoes transformations during gasification. Samples from three coal sources used by Sasol for gasification were acquired and a comprehensive characterisation on all dense medium fractions was conducted, including proximate analyses, AFT, ash oxide analyses, XRD and Mossbauer spectroscopy. From the proximate analyses, the ash content was the highest for the higher density fractions, with an accompanying decrease in fixed carbon content, consistent with the XRD and Mossbauer analyses. From the ash oxide analyses, it was evident that at higher relative densities more Fe2O3 and SiO2 were present than in the lower density samples. From XRD analyses, the low density fractions contained calcite and dolomite. Pyrite and quartz were found in the higher density fractions whereas kaolinite occurred in all density separated fractions. From the different techniques it follows that with the Fe-content high in high density fractions, the AFT was low. When Ca and other basic oxide levels were abundant in low density fractions, the AFT was low and when the SiO2/Al2O3 ratio was high in high density fractions the AFT increased.