Experimental investigation on physical and chemical properties of solid products from co-pyrolysis of bituminous coal and semi-coke

Semi-coke is a low-volatile solid carbonaceous fuel, which is quite difficult to combustion individually. Co-processing semi-coke with bituminous coal has the potential for efficient and clean utilization of powdery semi-coke, while the co-pyrolysis is an important step and the physical-chemical properties of residual solid products yield great influences on subsequent combustion characteristics and NOx formation. However, less work, if any, has aimed at the co-pyrolysis of bituminous coal and semi-coke, and the synergistic mechanisms on physical and chemical properties of solid products have yet to be fully understood. Even limited oxygen may generate remarkable influences on co-pyrolysis behaviors. In addition, limited oxygen is possibly present during pyrolysis process, which has been rarely paid attention to. In this work, the physicochemical properties of solid co-pyrolysis products of bituminous coal and semi-coke were investigated experiment, while the effects of multiple atmosphere composition were also emphasized, including CO2/N-2 atmosphere, N-2 atmosphere with limited O-2, and CO2/N-2 atmosphere with a little O-2. The results indicate that the dehydrogenation and poly-condensation of bituminous aromatics are observed over 700 degrees C. The semi-coke and bituminous coal have the synergistic effect in the co-pyrolysis process. In N-2 atmosphere with little oxygen, the pore development mainly occurs as the O-2 concentration is below 3%. The residual char is over-ablated with the further increasing oxygen content. When the atmosphere contains O-2, a small number of nitrogen oxides are formed. The present work can provide a scientific guidance for the utilization of semi-coke in large-scale and the design of power plant co-fired with semi-coke. This work is also beneficial to improve combustion reactivity of blended fuel, determine the optimal blending ratio and control NOx emissions.