A unified mechanism of the combustion reactions of lignocellulosic fuels

Thermogravimetric curves in air, measured for beech and fir wood and three agro-industrial residues (hazelnut shells, olive husks and wheat straw) at different heating rates (5-40 K/min), are subjected to kinetic evaluation. It is shown that a five step mechanism (three reaction for the devolatilization stage and two reactions for the combustion stage) provides good predictions in all cases. Moreover, for the combustion stage (amounts of volatile released between 25 and 40%) the activation energies are the same (113 and 183 kJ/mol). On one side, the devolatilization stage is also very similar for the residues which require activation energies of 125, 170 and 164 kJ/mol for the pseudo-components hemicellulose, cellulose and lignin. On the other, the behavior of the last two pseudo-components is also similar for the beech and fir wood (activation energies of 200 and 176 kJ/mol) whereas the different nature of hemicellulose requires significant changes (activation energies of 147 and 110 kJ/mol, respectively).