Reactivity Analysis of Pakistani Thar Lignite Reserves in Oxidizing Thermogravimetric Analysis Atmospheres

Abstract

In this study, three lignite coal samples from the largest lignite-based coalfield in Sindh, Pakistan, were sourced together with four bituminous coal samples from the Khushab District in Punjab, Pakistan. A non-isothermal thermogravimetric analysis of these coal samples was performed at two heating rates of 10 and 40 °C/min in a Shimadzu TGA-50 thermogravimetric analyzer under reaction environments comprising 21–30% O2/70–79% N2 and 21–30% O2/70–79% CO2 to investigate their specific reaction kinetics under these four different combustion atmospheres. The inherent activation energies and orders of reaction under the aforementioned reaction atmospheres were calculated using the Friedman method (a differential isoconversional approach) and the Ghetti method. In this work, the primary dominating factor on the rate of mass loss from devolatilization was the higher heating rate (40 °C/min), and the second factor was the higher oxygen concentration of 30%. Overlapping of devolatilization and char oxidation zones was also observed at higher oxygen concentrations of 30%. Increased reactivity of the Pakistani lignite was observed at a heating rate of 40 °C/min and high oxygen concentrations of 30%.