Investigation on the physicochemical properties of coal char during pressurized pyrolysis and the mineral transformations of coal ash during pressurized O2/N2 and O2/CO2 combustion

Abstract

Physicochemical properties of coal char during pressurized pyrolysis and the mineral transformations of coal ash during pressurized O2/N2 and O2/CO2 combustion were investigated by a pressurized tube furnace with Fourier transform infrared spectroscopy and X-ray diffraction analysis. The results indicated that as the pyrolysis pressure increased, the decompositions of the aromatic ring structure and the hydroxyl hydrogen bonds of char were enhanced and the aromatic ring transformed to the low-substituted single ring. Meanwhile, the aliphatic chain and carboxyl group in the char shortened at elevated pressures. Furthermore, pressurized pyrolysis increased the degree of graphitization of the char, which further influenced the microcrystalline parameters of char. During the pyrolysis process, the decompositions of some low-temperature minerals in the char were inhibited by the elevated pressure. In addition, the effect of the furnace temperature on the mineral transformations of char was more significant than the effect of the furnace pressure. Compared to what observed at atmospheric pressure, the primary minerals in the coal ash remained the same at elevated pressure, but their relative contents changed to some extent. And, the influence of the furnace pressure on the transformations of minerals in the ash was mainly affected by the combustion temperatures of different ignition mechanisms at different pressures. Compared to the O2/N2 mixture, the decompositions of low-temperature minerals and the formations of high-temperature minerals were restrained due to the relatively low combustion temperature in the O2/CO2 mixture. And, the furnace temperature instead of the furnace pressure was the primary factor which influenced the mineral transformations of ash.