Investigation of mixed-wood char gasification kinetics under a simulated gasifier atmosphere using the KIVAN drop tube reactor

This study investigates the high–pressure gasification kinetics of a mixed–wood char (MWC) under simulated gasifier atmospheres in the pressurized drop tube reactor KIVAN, in order to generate transferable single–particle kinetics for biomass gasification. Gasification with CO 2 , H 2 O, their binary mixture, and a simulated gasifier atmosphere (CO 2 + H 2 O + CO + H 2 ) was examined at 15 bar and 850–950 ℃, covering conditions representative of internal circulation (INCI) gasifiers. Based on axial gas-composition measurements in the pressurized drop tube reactor KIVAN under entrained-flow conditions, conversion curves as a function of particle residence time were derived and evaluated using the random pore model (RPM) combined with Arrhenius and power-law expressions to determine kinetic parameters. For gasification in pure CO 2 , MWC exhibits an activation energy E A = 173 kJ/mol, while under H 2 O E A = 144 kJ/mol is obtained, confirming a higher reactivity in steam than in CO 2 at identical partial pressures. In the mixed CO 2 –H 2 O atmosphere, an intermediate activation energy of E A = 127 kJ/mol is obtained, whereas for the simulated gasifier atmosphere containing CO 2 , H 2 O, CO, and H 2 , a lower value of E A = 95 kJ/mol is observed. For all kinetic descriptions, the structural parameter of the RPM is Ψ = 2.0, and the RPM reproduces the experimental data with correlation coefficients R 2 > 95%, while the overall mean model deviations are generally below 5%. Cross–comparison shows that the CO 2 and H 2 O contributions in the mixed atmosphere are strictly additive: the measured kinetics coincide with predictions from the sum of the single–gas rate constants, indicating separate active sites. Although the activation energies for the mixed CO 2 –H 2 O atmosphere and the simulated gasifier atmosphere differ, the resulting conversion behavior under the investigated entrained–flow conditions is very similar, and no pronounced inhibition by CO and H 2 is observed. Thus, for MWC under the present conditions, carbon conversion is effectively governed by the partial pressures of CO 2 and H 2 O, which simplifies kinetic modelling for design and scale–up of pressurized biomass gasifiers.