Char structure characterised by Raman spectroscopy and its correlations with combustion reactivity

Raman spectroscopy was applied to characterise the microstructure of coal chars generated under various heat treatment conditions, which was correlated with the combustion reactivity measured by thermogravimetric analysis. The Raman spectra were fitted with the combination of 4 Lorentzian bands and 1 Gaussian band. It was found that the increase of char microstructural order under heat treatment can be characterised by Raman parameters, in particular the band area ratios, indicated by the increase in IG/IAll and the decrease in ID1/IG, ID2/IG, ID3/IG and ID4/IG with increasing treatment temperature and/or time. The combustion reactivity of the chars from demineralised coals was found to have good correlations with the band area ratios, independent of coal type and heat treatment condition. It was found that the presence of inorganic matter in coal chars marginally affected the evolution of the average char microstructure. However, it did affect the char reactivity evolution. It was confirmed that the thermal deactivation of coal char during heat treatment was dependent not only on the ordering of char crystalline structure but also on the loss of catalytic activity of the inorganic matter.