Thermogravimetric behaviour of Different Biomass Feedstocks and their Pyrolysis Kinetics

Abstract

In this study, biomass feedstocks; softwood pellet, straw pellet, torrefied wood chips and pyrolysis char were investigated in terms of their thermal behaviorto obtain their kinetic parameters (Ea;A). Thermogravimetric analysis (TGA) of the samples under N2 atmosphere were carried out at four different heating rates (2-15 °C/min) at 25-850 °C. Coats&Redfern and Isoconversional Methods were chosen as the model-fitting and model free methods to calculate pyrolysis kinetic parameters. Straw pellet has the highest ash content (5.85 wt%) and agglomeration index of 1.27. It seemed to be more prone to agglomeration during thermochemical conversion. Its lowest ash fusion temperature (FT=1256 °C) supported its agglomeration tendency as well. In the scope of kinetic analysis, the choice on the starting and end points of decomposition stages was determinative in Coats&Redfern method, whereas Isoconversional method was evaluated to be independent from the choice of the stages. Calculated activation energies and characterization studies indicated that both torrefied wood chips and softwood pellet were the samples which might be more reactive to thermochemical conversions and less prone to agglomeration. Although pyrolysis char gave the lowest agglomeration index (0.37),its high decomposition temperature (>850 °C) is the potential drawback in front of its utilization via pyrolysis.