Material Pyrolysis Properties, Part II: Methodology for the Derivation of Pyrolysis Properties for Charring Materials

A methodology for deriving material pyrolysis properties is proposed and validated by using three charring materials (pure cellulose, and two different particle boards designated as N and F). The methodology uses experimental data obtained in a pyrolysis apparatus together with an accurate integral thermal pyrolysis model for the charring pyrolysis process (see CST, 88, 309–328, 1993). The effects of various parameters on pyrolysis rates and surface temperatures are investigated by applying the integral pyrolysis model. This analysis shows that, in addition to the unpyrolyzed (virgin) material thermal properties, char conductivity (k_c) and heat of pyrolysis (L) are adequate to describe the transient pyrolysis process for a charring material. The thermal capacity of char is shown to have negligible effects on the pyrolysis process because surface radiation loss from the hot char surface is the dominant mechanism causing the reduction of pyrolysis rates in charring materials. This result, which is for the first time documented definitely, is a significant achievement in characterizing the pyrolysis properties for charring materials. The thermal properties of the virgin material (Jtpc)_rand the pyrolysis temperature. T_p, are determined from surface temperature and mass loss histories during the heat-up period until pyrolysis starts. The char conductivity (k_c) is derived from the surface temperature histories during pyrolysis while the heat of pyrolysis is derived from the mass pyrolysis rate histories by comparison of the experimental data and the results from the integral model.