A comprehensive investigation on the structural transformation and dissolution loss reaction of coke during gasification in CO2 atmosphere

Abstract

The in-situ investigation of the structural transformation of coke during gasification can provide useful insights into its dissolution loss reaction in blast furnaces. In this study, the structural properties of coke are evaluated by analyzing its carbon matrix, pore distribution, and ash composition using scanning electron microscopy (SEM), wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), Raman spectroscopy, mercury intrusion porosimetry (MIP), and X-ray fluorescence (XRF) spectrometry. The pore evolution and carbon structural transformation during gasification in CO2 atmosphere are analyzed in-situ using synchrotron radiation SAXS-WAXS techniques for three coke samples prepared from coals with varying ranks. The strength and reactivity of coke are assessed based on its structure and dissolution-loss reaction mechanism during gasification. The results indicate that the high breakage resistance index (M13) of coke is attributed to the interlocking of bent aromatic carbon layers with AD/AG less than 1.837. The amorphous structures characterized by A(VL+VR+SL+S)/AD higher than 0.935 in coke serve as the initiation site of reaction with CO2, leading to a decrease in the fractal dimension (DS) and interlayer spacing (d002) as well as an increase in the stacking width (La). Subsequently, the etching of the carbon microcrystals and the dissolution loss of defective carbon structures alternately occur during gasification. The rough pore surface with DS more than 2.91 hinders the CO2 diffusion, while the carbon matrix with AD/AG more than 2.269 effectively decreases the coke reactivity index (CRI) of coke. Overall, the findings of this study can offer a theoretical foundation for coke quality evaluation and effective optimization of iron-making processes.