Pyrolysis of low-rank coal under a CH4-rich atmosphere and combustion characteristics of derived char

The CH 4 atmosphere exerts a significant impact on the pyrolysis characteristics of low-rank coal and the structural evolution of the resulting char. Thermogravimetric analysis–mass spectrometry (TG‑MS) was employed to characterize the evolution of volatile components during low‑rank coal pyrolysis under a CH 4 ‑rich atmosphere. The changes in chemical functional groups and the carbon microstructure of char were evaluated through infrared spectroscopy (FTIR), CO 2 adsorption, X-ray diffraction (XRD) and micro-Raman spectroscopy (MRS). Thermogravimetric analysis was employed to characterize the combustion reactivity of the char. The results show that the CH 4 -rich atmosphere accelerated the pyrolytic conversion of raw coal prior to approximately 760 °C, enhancing the reactivity of CH• and H• radicals, which facilitates the formation of CH 4 and H 2 . Conversely, CH 4 atmosphere suppresses the cleavage of carbonyl and carboxyl functional groups, thereby decreasing the generation of CO 2 and CO. The CH 4 ‑rich atmosphere facilitates aromatization and ordering of the char, increasing the degree of graphitization ( I G / I All ratios rising from 12.11% to 13.55% as CH 4 concentration increases from 20% to 80%), while inhibiting pore development (specific surface areas declining from 360.8 to 293.4 m 2 /g). With increasing CH 4 concentration, the volatile matter content decreases, the carbon structure becomes more ordered, and the pore structure remains underdeveloped, leading to a reduction in the combustion reactivity of char-CH 4 (comprehensive combustion index S values are 4.05, 3.89, and 2.68 (10 −9 ), respectively). The char produced under CH 4 -rich pyrolysis conditions fulfills the grindability standards for blast‑furnace injection coal and the mechanical strength specifications for ferroalloy production