| This study was undertaken to understand the superior coking properties of the high volatile bituminous rank Lower Block Coal Member. Coals of this low rank are normally considered to be non-coking partly because coking parameters calculated from predictive models give poor results. Previous studies on selected Indiana coals have demonstrated that high volatile bituminous coals do not conform to coking models derived from higher-rank coals and that these models most likely do not provide accurate predictions of coking properties in low-rank coals. Pilot scale coke oven tests have shown that the Lower Block coal possesses a wide plastic range and high fluidity, along with strong contraction properties, all of which are unexpected for a coal of high volatile bituminous rank. In order to determine the reasons for these unusual coking properties, the whole coal and individual maceral chemistries of the Lower Block Coal Member and the similar rank, non-coking Danville Coal Member, both from the eastern part of the Illinois Basin, were compared via the application of a variety of analytical techniques including proximate and ultimate analyses, coal petrology, electron microprobe and Fourier Transform Infrared Spectroscopy, along with heating experiments to investigate changes in chemistry as the coal is carbonized. Overall, vitrinites of the Danville and Lower Block coals proved to be similar in elemental composition, in both unaltered and thermally altered form, with the exception of samples exposed to 375°C. At this temperature, Lower Block coal vitrinites exhibited higher reflectance, higher carbon content, lower oxygen content, and a greater contribution of aromatic hydrogen, all of which indicate molecular re-arrangement in the form of increasing aromaticity. As vitrinites from the Lower Block coal are almost indistinguishable from those of the Danville coal at all other experimental temperatures as well as in unaltered coal, the changes observed at 375°C must be the result of influence from other macerals, particularly liptinites. Breakdown of these dispersed liptinites widens the plastic range and improves the overall fluidity of the vitrinites, allowing for better development of aromatic structures. The high proportion of liptinite in the Lower Block Coal Member and their properties appear to be the primary controls on the coking behavior of this high volatile bituminous coal. |
