Evolution of microstructure and combustion reactivity of lignite during high-temperature drying process

Abstract

ABSTRACTThe evolutions of the microstructure characteristics and the combustion reactivity of lignite during high temperature drying process at 600–800°C were addressed in the paper. The information about the oxygen functional groups, carbon skeleton, pore structure, and combustion reactivity of the lignite before and after the drying treatment was obtained by Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller technique, Raman spectroscopy and thermogravimetric analyzer, respectively. The results show that a different evolutionary trend of the chemical structure of the lignite appears at the high drying temperature of 700°C at which the carbonyl, carboxyl, and carboxylate significantly decomposed and the treatment gave a slight elimination of structural imperfections and the formation of new cross-linking structures. Then, at the drying temperature of 800°C, a slight increase of the oxygen functional groups was found. The break of the aromatic ring or heterocycle contributed to the rapid increase of amorphous carbon to some extent. During the drying process, the surface area of the resulted lignite gradually increased until 700°C and then decreased. The evolution may be attributed to the decomposition of organic compounds, shrinkage forces, and thermal relaxation effect. The investigation indicates that the change in chemical nature of the coal had a greater impact on the combustion reactivity than the internal pore structure did. In addition, the combustion intensity and performance of the treated lignite was enhanced by the drying process.