Effect of demineralization on pyrolysis characteristics of LPS coal based on its chemical structure

Abstract

The critical issue in developing mature Oxy-Coal Combustion Steam System technology could be the reactivity of demineralized coal which, is closely related to its chemical structure. The chemical structures of Liupanshui raw coal (LPS-R) and Liupanshui demineralized coal (LPS-D) were analyzed by FTIR and solid-state 13C-NMR. The pyrolysis experiments were carried out by TG, and the pyrolysis kinetics was analyzed by three iso-conversional methods. FTIR and 13C-NMR results suggested that the carbon structure of LPS coal was not altered greatly, while demineralization promoted the maturity of coal and the condensation degree of the aromatic ring, making the chemical structure of coal more stable. The oxygen-containing functional groups with low bond energy were reduced, and the ratio of aromatic carbon with high bond energy was increased, decreasing the pyrolysis reactivity. DTG curve-fitting results revealed that the thermal weight loss of LPS coal mainly came from the cleavage of aliphatic covalent bonds. By pyrolysis kinetics analysis of LPS-R and LPS-D, the apparent activation energies were 76 ± 4 to 463 ± 5 kJ/mol and 84 ± 2 to 758 ± 12 kJ/mol, respectively, under different conversion rates. The reactivity of the demineralized coal was inhibited to some extent, as the apparent activation energy of pyrolysis for LPS-D increased by acid treatment.