Effect of biomass addition on the devolatilization kinetics, mechanisms and thermodynamics of a northeast Indian low rank sub-bituminous coal

Abstract

The effect of addition of biomass on the pyrolysis behaviours of a low rank sub-bituminous coal was investigated using thermogravimetric methods (TG and DTG). Results reveal the presence of interaction between coal and biomass residues. Such synergistic effect is observed to be dependent on heating rate, coal to biomass ratio and chemical constituents present in coal-biomass blends. Thermal decompositions of coal and coal-biomass blends follow order based models involving one or two nuclei initially and three nuclei at the latter stages of conversion. Evaluations of synergistic, kinetics and thermodynamic properties show that 25% replacement of coal by biomass gives best results and therefore can be considered as ideal composition for coal devolatilizing process. Results also reveal that biomass addition lowers the mean values of activation energies (Eo) and Arrhenius constants (Ao) of coal devolatilization process. The Eo and Ao values for coal determined by KAS/DAE methods are 282 kJ.mol−1 and 1 × 1021 min−1 respectively. Similarly, Eo and Ao values for 25% biomass containing blend are 218 kJ.mol−1 and 4 × 1015 min−1 respectively and minimum among the blended compositions. Results also reveal that the kinetic parameters predicted by isoconversional methods are similar to the values predicted by Kissinger method. Considering the simplicity, it can therefore be concluded that Kissinger method is one of the best methods to determine kinetic parameters of coal devolatilization process with and without the presence of biomass. Our results also reveal that the approach used for analysing TG data by Friedman method helps significantly to find the meaningful activation energies.