Statistical results of coal petrographic identification of the B-coal seams in the Xishanyao Formation

4.1.1 Maceral composition and vitrinite reflectanceThe organic constituents of the coal are dominated by inertinite, averaging 69.52%, 70.05%, and 50.73% in the B2, B1, and B0 seams, respectively. Vitrinite is secondary, accounting for 25.76%, 26.43%, and 37.89% in the same seams, with minor liptinite present. The maximum vitrinite reflectance (Romax) of the B2 seam ranges from 0.30% to 0.55% (mean 0.40%); that of the B1 seam ranges from 0.27% to 0.65% (mean 0.39%); and that of the B0 seam ranges from 0.49% to 0.50% (mean 0.50%). Coals from the B2, B1, and B0 seams of the Xishanyao Formation are classified as low-rank. Among the inorganic constituents, clay minerals are overwhelmingly predominant .4.1.2 Industrial characteristics of coalOn an air-dried basis, moisture contents (Mad) in the B2, B1, and B0 seams average 12.59%, 10.75%, and 9.64%, respectively, indicating ultra-low to medium moisture overall. Dry-basis ash yields (Ad) average 10.35%, 9.09%, and 18.92%, spanning ultra-low-ash to high-ash , with low-ash coals predominating. Dry, ash-free volatile matter (Vdaf) averages 33.04%, 32.61%, and 37.70%, corresponding to medium- to high-volatile coals. Dry-basis total sulfur (St,d) averages 0.71%, 0.59%, and 0.64% for B2, B1, and B0, respectively. The mean oxygen uptake capacity (OUC) is 1.01, 1.05, and 0.93 cm³/g for B2, B1, and B0, suggesting an elevated tendency toward spontaneous combustion.4.1.3 Elemental composition of coalOrganic matter represents the principal chemical component of coal, dominated by carbon, hydrogen, nitrogen, and sulfur, with elemental abundances summarized in Table 1. On a dry, ash-free basis, the mean carbon contents (Cdaf) of the B2, B1, and B0 seams are 78.96%, 79.48%, and 76.51%, respectively. The corresponding mean hydrogen contents (Hdaf) are 3.52%, 3.59%, and 3.76%, while mean nitrogen contents (Ndaf) are 0.78%, 0.75%, and 0.84%, respectively.