Change of the Petrographic Characteristics of Semi-Coke in the Iron Ore Sintering Process

This study focuses on the petrographic analysis method to evaluate semi-coke and its combustion behavior in the sintering process, which has been seldom conducted before. Semi-cokes are different in morphological features, porosity, pore structure, and wall thickness, because of differences in the vitrinite and inertinite of the raw coal. Semi-coke displayed isotropy, and even after the drop tube furnace (DTF) and sintering process, it still retained its optical properties. Eight kinds of sintered ash were observed using reflected light microscopy. Petrographic analyzes for the combustion properties of semi-coke were based on its optical structure, morphological development, and unburned char. The results indicated that microscopic morphology was an important characteristic when trying to understand the behavior and burnout of semi-coke. These characteristics can be used to trace the origin of the unburned char in fly ash. The unburned semi-coke mostly existed in the form of inertoid, mixed dense and mixed porous. Meanwhile, it was found that most of the unburned chars were melted into sinter, resulting in inefficient fuel combustion.