Thermal Behavior of Some Indian Coals: Inferences from Simultaneous Thermogravimetry–Calorimetry and Rock–Eval

Abstract

In this work, thermal behaviors of ten coal samples (across different thermal maturity levels) collected from five different open cast mines in the Jharia and Raniganj basins, India, were examined using differential scanning calorimeter (DSC), thermogravimetry (TG–DTG), Rock–Eval, and organo-petrographic techniques. Rank played a critical factor in controlling their thermal behavior, and with increasing coal rank the combustion parameters shifted towards higher temperatures. The oil-window mature non-coking coals were marked by least ignition and burnout temperatures, least DSC Tpeak, DTG Tpeak, and maximum reactivity. In contrast, the coking-coal samples of peak-oil window and condensate wet–gas window stages of maturity, because of their higher thermal maturity level and lower reactivity, required higher temperatures for combustion. Among the peak-oil window mature coking coals, one sample (C4) showed distinct lower combustion parameters relative to others, although vitrinite reflectance (Ro; %) and Rock–Eval pyrolysis Tmax showed similar results as the other coals. This sample was marked by higher reactive maceral content. Highest combustion parameters and least reactivity were shown by the Jhama sample (baked coal), followed by the condensate wet–gas window mature coking coals. The Rock–Eval S4 Tpeak clearly resolved the coal samples with distinct maturities and complemented the results from TG–DTG–DSC thermograms. Our results indicate that Rock–Eval S4Tpeak can be used to decipher convincingly the thermal maturity level of coals.