The Combustion of Forest Humus Blended with Low-Rank Coal: Effects of Oxygen Ratio and Blending Ratio

In this study, the combustion characteristics of pine needles, pine needle humus, and the co-combustion of these two types of biomass with coal were compared. In addition, the optimization of the combustion performance of coal/humus was assisted through the following studies: (i) the combustion performance of coal/pine needle humus was studied under four different oxygen concentrations (N-2, 10%O-2/90%N-2, 20%O-2/80%N-2, and 40%O-2/60%N-2); (ii) the synergistic effect between the humus and coal during combustion was also investigated by adjusting the blending ratio and oxygen content; (iii) the mechanisms of the optimized combustion processes were expounded by kinetics and thermodynamics discussion. The results demonstrated that the combustion characteristics of the coal/humus blends were found to be higher than those of the coal/pine needle blends. The coupling interactions of the oxygen content and blending ratio contributed to the significant synergistic effect between the two fuels, and the synergistic effect showed a nonlinear variation with an increased oxygen concentration. The synergistic effect in a rich oxygen environment (O(2)40%/N(2)60%) is 5.1 times greater than that in the synthetic air (O(2)20%/N(2)80%) and 13.8 times greater than that in the oxygen-poor environment (O(2)10%/N(2)90%). Hence, the blending ratio could be adjusted to maintain the intensity of the synergistic effect in an oxygen-rich atmosphere.