Microstructural evolution of metallurgical coke: Evidence from Raman spectroscopy

Highlights

• “Interactive Fitting of Raman Spectra” on carbonaceous matter provides spectral parameters to trace the structural evolution of coke within the entire blast furnace.

• Coke reactivity is dependent on the graphitization state of the feed coke.

• Within the tuyere zone of a blast furnace, the textural coke composition is correlated to its microstructural state, controlled by a temperature gradient towards the tuyere openings.

Abstract

Raman spectroscopy traces the microstructural evolution of carbonaceous matter (CM) during artificial heating. Thermo-chemical reactivity and strength of blast furnace coke at 1100 °C is dependent on the graphitization state of the feed coke. A standard coke reactivity index (CRI) sample is composed of lumps, showing a high microstructural variability. The frequency distribution of the D-STA parameter estimated by the “Interactive Fitting of Raman Spectra” (IFORS) software suggests a positive correlation between degree of CM organization and CRI. Samples from the tuyere region of an operating blast furnace evidence graphitization of CM at temperatures higher than 1900 °C. IFORS parameters, calibrated by x-ray diffraction-based lattice dimensions and transmission electron microscopy data constrain a temperature gradient decreasing from the raceway to the deadman zone. The gradient controls a continuous variation of the petrographic coke texture. As an application, the IFORS method is able to map the graphitization zones in the hearth of a working blast furnace.