Detailed characterization of SA high mineral matter inertinite–rich coals and density fractions and effect on reaction rates with carbon dioxide: macerals, microlithotypes, carbominerites and minerals

Abstract

An investigation was undertaken to determine the distribution of macerals and minerals in South African Highveld coal deposits as well as density fractions derived from a typical deposit. The corresponding effects on carbon dioxide gasification reaction rates were also studied. Detailed chemical, petrographic and mineral analyses, followed by reactivity measurements and reaction rate modeling were carried out. Coal samples from seven different coal mines and five density separated coal fractions (<1.4 g.cm-3 to >2.0 g.cm-3) were examined. It was found that the coal samples have ash contents in the range 21.6 to 38.8 wt. % and inertinite composition in the range 68 to 84 vol. %. The inertinites consist of high concentrations of semifusinites and inertodetrinite which is characteristic of South African Highveld coal deposits. The distribution of macerals and minerals in the different density fractions revealed high concentrations of inert inertodetrinite, carbominerite and ash in the dense fraction. The presence of carbominerites was also found to increase with mineral content within the density range of 1.4 g.cm-3 to 1.8 g.cm-3. The random pore model described the gasification reactivity very well with an increasing intrinsic reaction rate correlating with an increasing density of the coal which is attributed to an increasing pre-exponential factor