Air and oxy-fuel combustion kinetics of low rank lignites

The air and oxy-fuel combustion processes of two low-grade lignite coals were investigated by thermogravimetric analysis (TGA) method. Coals were provided from two different coal mines in the Aegean region of Turkey. Oxy-fuel combustion experiments were carried out with three different gas mixtures of 21%02-79% CO2; 40% O-2-60% CO2 and 50% 02-50% CO2 at 950 degrees C and heating rates of 10 degrees C/min, 20 degrees C/min and 40 degrees C/min. The kinetics of the oxy-fuel combustion of coals were studied by using four different methods namely, Coats-Redfern (model-fitting method), Friedman (FR), Flynn-Wall-Ozawa's (FWO) and Kissinger-Akahira-Sunose's (KAS) methods. The apparent activation energies of combustion process calculated by FWO method are slightly but systematically higher than that calculated by the KAS and FR methods for the oxy-fuel atmospheres. Combustion behavior of both coals in the oxy-fuel combustion environment could vary significantly, likely due to their characteristics such ash and volatile matter contents. (C) 2016 Energy Institute. Published by Elsevier Ltd. All rights reserved.