Using a fluidised bed to measure and investigate the thermal diffusivities and pyrolysis of some woods at temperatures of 200–600 °C

Abstract

Small cubes (sides ≤ 7 mm) of four different woods, with thermocouples inside them to constantly measure the temperature at their centre, have been pyrolysed in electrically heated beds of sand, fluidised by nitrogen. These determinations of a particle’s central temperature have provided values of the effective thermal diffusivity of each wood, as well as of the resulting solid, at 5 different stages, whilst it changed from dried wood at room temperature to the char left after being pyrolysed at progressively higher temperatures up to 600 °C. In addition, these woods underwent endothermic decomposition, particularly whilst being heated from ∼250 to 340 °C and from 380 to 460 °C. However, at ∼480 to 540 °C, all four woods thermally decomposed exothermally and actually raised the temperature at the cube’s centre above that of the fluidised bed. In addition, the times for complete pyrolysis were measured and their dependence on particle size was investigated.