Effect of atmosphere reaction and heating rate on the devolatilization of a Colombian sub-bituminous coal

Abstract This work studies the combined effect of heating rate and reaction atmosphere on the devolatilization of sub-bituminous type A coal (SubbA coal). Non-isothermal thermogravimetric analysis (TGA) was performed on SubbA coal undergoing pyrolysis. Mass loss dataset was fit to a lumped kinetic model using two different model-free fitting methods (FWO and Vyazovkin). Meaningful differences were obtained in devolatilization kinetics under N 2 (traditional combustion) and CO 2 (oxy-combustion process with gas recirculation). Through TGA it was found that at low heating rates, the pyrolysis mass loss rate is higher in N 2 than in CO 2 . Based on the activation energy distribution, CHN analysis on residual char, and tracking the evolution of products in gaseous phase during devolatilization in CO 2 , it was demonstrated that at temperatures higher than 660 °C, CO 2 reacts with the formed char. This gasification reaction becomes a controlling stage of the thermochemical transformation in CO 2 . Additional pyrolysis experiments were conducted in a fast-heating hot plate reactor (HPR) with 2 mm particles in N 2 and CO 2 using heating rates between 50 °C/s and 1200 °C/s. These higher heating rates are similar to those of fluidized beds. In the HPR experiments, devolatilization is more intense for CO 2 than N 2 . Differences arising from the two environments are likely caused by the different thermal and diffusive properties of both gases.