Pyrolysis behavior of low-rank coal in an H2-containing atmosphere and combustion properties of the prepared chars

The H2 atmosphere exerts an important influence on both the pyrolysis behavior of low-rank coal and the efficient application of the resultant char. Thermogravimetry-mass spectrometry in conjunction with the Fourier transform infrared was applied to examine the pyrolytic properties of low-rank coal in an H2-containing atmosphere. The coal chars’ carbon chemical structure, surface morphology, pore structure, and combustion reactivity were subjected to characterization by Raman spectroscopy, scanning electron microscopy, CO2 adsorption, and thermal analysis, respectively. The results indicate that the H2-atmosphere enhanced the volatiles release during the pyrolysis stage of low-rank coal. H2-containing atmosphere accelerated the synthesis of H2O through the transformation of the hydroxyl group in coal during coal pyrolysis; the H2 and CH4 production was increased through the chemical interaction of active hydrogen group with aromatic or aliphatic C–H groups; CO2 and CO evolution reduced owing to the dissociation inhibition of carbonyl groups and functional groups containing oxygen. H2-containing atmosphere enhanced the order of carbon structure (as the proportion (20–60%) of H2 contained in the pyrolysis atmosphere increases, the IG/IAll (12.72, 13.14, and 14.03%, respectively) of char-H2 increased), which was not conducive to the pore structure (the specific surface area are 373.7, 364.6, and 357.9 m2 g−1, respectively) development of char-H2. Lower volatile content as well as ordered carbon structure reduced the combustion reactivity of chars-H2 (S are 2.27 and 2.04, respectively). Similarly, lesser development of pore structure also reduced the combustion reactivity of chars-H2 (S is 1.81). Char-H2 (pyrolysis atmosphere with H2 ratio of 20, 40%) meets the grindability index requirements of blast furnace coal injection and char-H2 (pyrolysis atmosphere with H2 ratio of 60%) meets the strength requirements of ferroalloy smelting.