Physical and chemical properties of selected Turkish lignites and their pyrolysis and gasification rates determined by thermogravimetric analysis

Pyrolysis and CO2-gasification behavior of lignites representing four different deposits in Turkey were investigated by Thermogravimetric Analysis (TGA) in the temperature range from 750 °C to 1000 °C. The rates of pyrolysis and CO2-gasification were evaluated from the corresponding TGA profiles. As expected, maximum pyrolysis rates for each coal were shown to be constant with respect to the final carbonization temperature. Lignites used in this study are from the tertiary period, chosen from major coal deposits in Turkey and their carbon contents are in the range of 60–70% (daf) based on ultimate analysis. They have shown different gasification reactivities under similar conditions and the reactivity sequence was found to be temperature dependent.In an attempt to correlate the maximum reactivities with textural properties of coals; BET (N2) and Dubinin–Radushkevich (CO2) areas of original coals, chars and gasification products were determined. To assess the catalytic effect of mineral constituents on gasification, chemical composition of ashes were also analyzed. Enhanced reactivity of one particular lignite at a relatively high temperature (1000 °C) was attributed to favorable distribution of micropores and feeder pores evolved during gasification and its relatively high iron content which has been known to be one of the species which can catalyze gasification reaction at the prevailing temperature. Apparent activation energies were evaluated using the Arrhenius plots of the maximum reactivities and the values were found to be in the range of 29.0–124.8 kJ/mol.