Study on the Effect of Heat Treatment and Gasification on the Carbon Structure of Coal Chars and Metallurgical Cokes using Fourier Transform Raman Spectroscopy

Abstract

Differences in the development of carbon structures between coal chars and metallurgical cokes during high-temperature reactions have been investigated using Raman spectroscopy. These differences are important for differentiation between different types of carbons present in the dust recovered from the top gas of the blast furnace. Coal chars have been prepared from a typical injectant coal under different heat-treatment conditions. These chars reflected the effect of peak temperature (from 900 to 2400 °C), residence time at peak temperature (from 2 s to 1 h), heating rate (from 1 to 6000 K/s), and pressure (from 3 to 40 bara) on the evolution of their carbon structures. The independent effect of gasification on the development of the carbon structure of a representative coal char has also been studied. A similar investigation has also been carried out to study the effect of heat-treatment temperature (from 1300 to 2000 °C) and gasification on the carbon structure of a typical metallurgical coke. Two Raman spectral parameters, the intensity ratio of the D band (1284−1600 cm−1) to the G band (ca. 1600 cm−1) (ID/IG) and the intensity ratio of the valley between D and G bands to the G band (IV/IG), have been found useful in assessing changes in carbon structure. An increase in ID/IG indicates the growth of basic graphene structural units (BSUs), across the temperature range studied. A decrease in IV/IG appears to suggest the elimination of amorphous carbonaceous materials and ordering of the overall carbon structure. The Raman spectral differences observed between coal chars and metallurgical cokes are considered to result from the difference in the time−temperature history between the raw injectant coal and the metallurgical coke. These observed differences may lay the basis for differentiation between metallurgical coke fines and coal char residues present in the dust carried over the top of the blast furnace.