Investigation on co-combustion of coal gasification fine slag residual carbon and sawdust char blends: Physiochemical properties, combustion characteristic and kinetic behavior

Abstract This study aims to systematically investigate the physiochemical properties, co-combustion characteristic and kinetic behavior of sawdust char and residual carbon in order to guide its combustion as the potential solid fuel in the industrial-scale furnace. The froth flotation process to recycle the residual carbon from coal gasification fine slag increases the higher heating value from 7.81 to 17.70 MJ/kg and upgrade the fuel quality by effectively removing spherical mineral particles. attached to the carbon particles surface or entrained in the pores. The addition of sawdust char into residual carbon could obviously improve the ignitability and combustibility of residual carbon. In the co-combustion process, both synergistic and antagonistic effects (Interaction index x d varies from −3.89 to 13.6) exist between sawdust char and residual carbon, while the synergistic effect was dominant. The first-order chemical reaction (O1) and diffusion-controlled reaction (D3 and D4) are the most effective mechanisms (all the correlation coefficient R2>0.98) for the multi-step co-combustion process. The percentage of sawdust char in blends is recommended to be maintained at 40 wt% because of the lowest combustion total activation energy (105.77 kJ·mol−1) and the strongest synergistic effect (Interaction index x d =13.6). The results provide theoretical reference for realizing the sustainable utilization of coal gasification fine slag and biomass waste resources.