Reflectance parameters of cokes in relation to their reactivity index (CRI) and the strength after reaction (CSR), from coals of the Upper Silesian Coal Basin, Poland

Coke samples made from coals and blends of the Upper Silesian Coal Basin, Poland were studied to determine relationships between their reflectance parameters (Rmax, Rmin, Rbi) and technological indices CRI and CSR. It was found that coke reactivity with CO2 decreased, and coke strength after reaction increased, with increasing mean maximum reflectance (Rmax) and bireflectance (Rbi) and with decreasing mean minimum reflectance (Rmin) of cokes. It was also observed that for cokes with bireflectance below 4.0%, CRI indices are higher than the CSR, but when coke bireflectances rises above 4.0% then their CSRs surpassed the CRI values. Thus, Rbi ≅ 4.0% seems to correspond with structural transformation of cokes resulting in the increase of their mechanical strength and adequate decrease of reactivity with CO2 and, as a consequence, improving coke quality. Relationships of the CRI and CSR indices with cokes reflectance parameters turned out to be similar but distinctly stronger than those with cokes microtextures.The results obtained showed additionally, that higher inertinite content in parent coals (≥ 30 vol.%) could make poorer resultant cokes, i.e. increase of the CRI and decrease of the CSR factors. This influence varies depending on the rank of initial coals and is greater for middle rank coals than those from lower ranks.The results show that reflectance parameters of coke, especially bireflectance, make possible the prediction of CRI and CSR indices, and thus can be used for estimation of coke quality.

► Reflectance parameters of cokes well correlate to their CRI and CSR indices. ► Rbi defines CRI to CSR ratio: for Rbi < 4.0%, CRI > CSR; for Rbi > 4.0%, CSR > CRI. ► Inertinite ≥ 30% disturbs correlation between reflectance and technological indices of cokes. ► Reflectance parameters of cokes enable prediction of their technological properties.