Petroleum coke facilitate the upgrade of lignite under microwave irradiation for slurryability improvement

To remarkably reduce moisture and volatile content of lignite for the preparation of lignite water slurry (LWS) with high solid concentration, different additions of petroleum coke (PC) were used to increase the heating rate of microwave irradiation. After that the physical and chemical property changes of upgraded lignite were investigated through X-ray photoelectron spectra (XPS) and low temperature N2 adsorption method. The results show that: the coal rank increased, the oxygen-containing functional groups decreased remarkably, the specific surface area and pore volume increased, the average pore diameter decreased, and the macropores gradually transformed to mesopores and micropores. Furthermore, these changes of upgraded lignite reached their maximum when 10 wt% PC was added to facilitate microwave pyrolysis. The maximum solid concentration increased from 51.60 wt% to 66.87 wt% and further increased to 67.51 wt% when the 10 wt% PC was mixed with upgraded lignite to prepare LWS. The LWSs prepared from upgraded lignite showed a weaker shear-thinning characteristic and lower static stability.