Calorimetric and heat transfer studies of the spontaneous combustion of two low carbon fuels

The self-heating and heat transfer characteristics of creosote-treated wooden railway tie dust and roofing asphalt shingle particles, which are considered as low carbon fuels, are investigated. Self-heating was measured with isothermal calorimetry and thermal conductivity was measured using a guarded hot plate. The self-heating of petroleum coke and poplar wood pellets were also measured as reference materials. Self-heating models and heat transfer parameters were then defined assuming constant moisture content. The self-heating of petroleum coke was found to be similar to coal, while both poplar pellets and railway tie dust were found to be more reactive compared to oven test results of similar materials. As both poplar pellets and railway ties both had significant water content, the higher reactivity was attributed to the effect of moisture. Furthermore, critical conditions for spontaneous combustion were evaluated with the Frank-Kamenetskii parameter, assuming an ambient temperature of 40 °C. It was found that cubic volumes of railway tie dust and asphalt particles, 1.6 m and 58 m to a side, respectively, would spontaneously combust; however, compaction effects associated with asphalt softening may invalidate the assumptions of the Frank-Kamenetskii spontaneous combustion theory.