Devolatilisation of beech wood char: Kinetics from thermogravimetric analyses and drop-tube reactor experiments

Reliable devolatilisation kinetics of primary wood chars are essential to describe the secondary release of volatiles in entrained flow gasification processes but have not been derived yet. Therefore, this study developed devolatilisation kinetics of a commercially available beech wood char using thermogravimetric analyses and drop-tube reactor experiments for design of entrained flow gasification processes. The thermogravimetric analyses were performed at low heating rates (2/5/10/30/50K/min) up to 1273 K, whereas the drop-tube reactor experiments were conducted at high heating rates (∼104K/s), high temperatures (1273/1373/1473/1573/1673/1873 K) and short residence times (200/400 ms). Thermogravimetric kinetics were subsequently obtained based on multi first-order reaction logistic distributed activation energy models, while kinetics based on single first-order reaction Arrhenius law and modified Yamamoto models were derived from the drop-tube reactor experiments and corresponding CFD predictions. Finally, single-particle simulations were carried out to compare the kinetics from both kind of experiments at high-heating-rate conditions. The comparisons demonstrate that the thermogravimetric kinetics are in reasonable agreement with the drop-tube reactor kinetics but provide lower devolatilisation rates. Furthermore, gas species concentrations measurements from the drop-tube reactor experiments were used to estimate an average volatiles composition. The results indicate that the volatiles composition at high-temperature conditions can likely be described using the gas species concentrations at high-temperature equilibrium conditions.