Kinetic study of biomass char combustion in a low temperature fluidized bed reactor

Abstract

The purpose of this work is the kinetic study of biomass char combustion in a low temperature fluidized bed reactor. This char was obtained from fast pyrolysis of beech stick in an annex batch fluidized bed reactor at 923K and atmospheric pressure. Operating conditions of the combustion were thoroughly characterized so that the reaction takes place in isothermal conditions and a constant oxygen partial pressure. The kinetic study was performed for temperatures up to 643K, oxygen partial pressures ranging from 5065 to 21273Pa and cylindrical char particles (D=4mm and L=9mm). The Volumetric Model was found to be in very good agreement with experimental data. Values of activation energy and reaction order with respect to oxygen are respectively equal to 144kJ/mol and 0.59. The reaction scheme during char combustion showed that char first reacts with oxygen to form CO which is further oxidized either at the particle surface or in the gas phase to produce CO2. Besides, it was found that the char reactivity in combustion is higher in a fluidized bed reactor compared to TGA. This was explained by diffusional effects of oxygen and CO oxidation within the crucible in the TGA.