Pyrolysis of large mallee wood particles: Temperature gradients within a pyrolysing particle and effects of moisture content

Abstract

Temperature profiles inside a large pyrolysing particle were studied and are reported in this paper. Mallee trunks of similar diameter from the same tree were used to prepare cylindrical samples with 40 mm length. A fluidised-bed reactor was used to pyrolyse the large particles. The temperature profiles inside the particles were recorded during pyrolysis to allow the calculation of corresponding heating rate profiles inside the particle. The effects of moisture were studied by pyrolysing some particles with 15 to 20% moisture content. The temperature profiles obtained from the pyrolysis of dry and wet samples have been compared to identify the possible effects of moisture on the temperature profiles. A possible change in the thermal conductivity of the wood was identified around 100 °C, which caused a peak in the heating rate profile. Some possible exothermic peaks were observed at around 325 °C and 425 °C. A peak in the heating rate profile at around 200 °C in the case of the pyrolysis of wet particles was believed to be related to the changed 3-D macromolecular structure of the biomass in the presence of moisture. Some yields of tar and char along with other analytical results were presented to support our observations on the temperature profiles. Our results indicate that moisture can potentially alter the overall pyrolysis reactions and product distribution, in particular through changes in the 3-D macromolecular structure of biomass.