Kinetic Modeling of the Devolatilization of Pulverized Coal, Poplar Wood, and Their Blends in a Thermogravimetric Analyzer and a Flat Flame Reactor

Devolatilization kinetics of coal, poplar wood, and blendscontaining10 and 20 wt % of biomass were characterized. Measurements were carriedout under inert atmosphere with heating rates between 10 K min(-1) and & SIM;10(6) K s(-1) using a thermogravimetric analyzer (TGA) and a flat flame reactor(FFR). Measured data were simulated using the chemical percolationdevolatilization (CPD) model and a global kinetic scheme based ontwo competitive reactions integrating a refined differential reactionmodel. The CPD model failed to simulate TGA results but reproducedFFR data relatively well. As for the global model, selecting kineticparameters from the literature turned out to lead to unsuitable predictions.Fitted values of the activation energies E (a,i ), pre-exponential factors A ( i ), mass stoichiometric coefficients Y ( i ), and the reaction model factor n were therefore inferred using a genetic algorithm-basedoptimization procedure, leading to obtain an excellent agreement betweensimulated and measured data. The assessed E (a,i) values were found to be lower for wood than for coal, which is consistentwith the higher energy required to break the strong C-C bondsholding the highly cross-linked aromatic structures of coal. Besides,blending coal with 20 wt % of wood induced a decrease of E (a,i ) values, which went from 99.79 to86.1 kJ mol(-1) and from 186.72 to 171.57 kJ mol(-1) for the first and second reactions prevailing atlow and high temperatures, respectively. Finally, the fact that theactivation energy of the first devolatilization reaction was foundto be lower with the blend containing 20% of wood than for wood illustratedthe probable existence of synergies, as also exemplified by the characteristicdevolatilization times for blended samples, which were found to berelatively similar to and even lower than that of wood.