Evaluation of Reaction Order and Activation Energy of Char Combustion by Shift Technique

Abstract

Combustion of chars obtained from the pyrolysis of lignocellulosic materials at 1200 K has been studied using a TGA at different temperatures (583-670 K) and oxygen partial pressures (10-101 kPa). The kinetic parameters vary significantly depending on burn-off when calculated on the basis of multiple and independent combustion runs. The apparent reaction order increases from 0.64 to 0.95 and apparent activation energy increases from 116 to 125 kJmol⁻¹, Experiments carried out with gas and temperature shifts suggest that the dependency of the kinetic parameters on bum-off are spurious consequences of changes in the internal area. The shift technique yields an oxygen reaction order of 0.5, which decreases slightly with bum-off, and an activation energy of 120 KJmol⁻¹, which increases slightly with burn-off. These values are found for the combustion of nine chars irrespective of their panicle sizes, ash content or parent material. The data obtained are attributed to a strong pore diffusion control on a common intrinsic kinetics characterised by zero reaction order and the activation energy of 240 Umol⁻¹.

Keywords:

• Lignocellulosic
• Char
• Combustion
• Reaction order
• Activation energy

Additional information

Notes on contributors

FRANCESCO ZIMBARDI

e-mail [email protected]