WOOD THERMAL PROFILE DURING THE PYROLYSIS PROCESS

Resumo

The objective of this project was to obtain the temperature profile formed in the wood during the slow pyrolysis process. For this, small holes were opened into the wood using a drill, three thermocouples were inserted in the radial portion along the length of the wood and on the surface - center direction. Three Eucalyptus wood logs, 35 cm long, 30% moisture and 8, 9 and 12 cm diameters, were used. The final pyrolysis temperature was 400 °C. The gravimetric yield of the products was calculated after the pyrolysis process.  The formation of thermal gradients was observed in the wood throughout the process. The temperature difference between the surface and the center can reach up 200 °C, in the pyrolysis of the largest diameter wood.  Thermal heights formed in the wood at 100 °C were detected, being more evident in the central portion. The thermal variation perceived in the wood can be explained by the presence of water, which demands energy for its evaporation and changes the temperature gradients, and the heat conductivity is poor due to the wood being a porous material, mainly in the carbonized zone.

These phenomena influence the heat transfer during the pyrolysis process. On the surface - to - center direction, the formation of temperature gradients generates transient thermal threshold due to the drying process. Thus, a temperature gradient was formed between the surface and the center of the wood during the pyrolysis and the total time of the process will be higher in the largest diameter wood.