Investigation on the structure evolution and combustion behavior of residual carbon from entrained-flow coal gasification fine slag after oxidation

Direct combustion of residual carbon (RC) from coal gasification fine slag (CGFS) is an effective way of energy recycling. Improving the combustion reactivity of RC is crucial for large-scale treatment of CGFS. In this study, the RC was modified by mild oxidation, and the evolution mechanism of the structures of RC in the oxidation process was analyzed, and the essential relationship between the structural characteristics and combustion behaviors of the oxidized RC was revealed. The research results show that the combustion behavior and structural characteristics of the oxidized RC are obviously improved. The combustion temperature range of some oxidized RC is significantly compressed, the time required for complete combustion is shorter than that of RC, and the activation energy of the combustion reaction decreases. Compared with air or CO₂ oxidation, air–steam shows a stronger oxidation effect on the structure of RC, while the oxidation effect of CO₂-steam is weakened. The structural characteristics of the oxidized RC collectively determine its combustion reactivity. The RC oxidized by steam presents disordered carbon microcrystalline structure, well-developed pore structure and a high proportion of active groups, corresponding to the best combustion reaction activity. The excessive oxidation of RC by air–steam seems to destroy the dynamic balance between structural characteristics, which is also the main reason why the combustion reactivity of the corresponding oxidized RC is inhibited.