Heat Release in Thermally Disintegrating Wood
Keywords:
Pyrolysis, thermal decomposition, exothermic point, self-heating, spontaneous ignition, heat of combustionAbstract
Wood contains more energy than do its products of slow pyrolysis. Consequently, slow pyrolysis must be an exothermic process, and cannot consume heat as generally believed. Heat release in experiments with thermally slowly decomposing wood has indeed been reported in the literature. The exothermic nature of pyrolysis explains why wood self-heats when its temperature has been somehow raised above 80 C and when the released heat does not dissipate. This way the temperature may reach the level of oxidation and combustion. Such pyrolytic self-heating occurs in piles of sawdust, wood chips, and bark, in hot-stacked boards and paper rolls, in dryers for veneer and other wood, and in structural lumber near heat sources. In contrast to other kinds of self-heating, pyrolytic self-heating cannot be prevented by exclusion of oxygen: instead the process has to be decelerated by cooling the material.References
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