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Contribution of Gas-Phase Oxidation to Overall Heat Generation for Reverse Smoldering of Piled Dry-Leaves

Yasunobu Inoue and Masataro Suzuki

Department of Mechanical Engineering, Nagaoka University of Technology, Nagaoka 940-2188, Japan


Abstract: The heat generation from gas-phase reactions in vacant spaces inside a reverse smoldering packed-bed is evaluated experimentally. The bed is a pile of cut leaves of dried plants. Its top is ignited so that the smoldering progresses vertically downward. The temperature in the bed is measured to confirm that the smoldering process reaches a quasi-steady state. The smoldering is assumed to consist of three reactions: the pyrolysis generating char and pyrolysis gas, the combustion generating exhaust gas and residue, and the gas-phase combustion of the pyrolysis gas also generating exhaust gas. The amount of heat generated from each of these reactions is evaluated from the balance of enthalpies between reactants and products. Enthalpies of unburned leaves, the char, and the residue are measured after those are collected from the corresponding regions. The exhaust gas is collected, and the volume fractions of oxygen, carbon monoxide, and methane are measured. The pyrolysis gas is simulated by a gas that is generated from unburned leaves while those are heated from the room temperature to 400 °C in the air. The heat generated in the gas phase is estimated at 733 J/g, which is about 18% of the total heat generation of 4043 J/g in the reverse smolder.

Key words: Smoldering, heat generation, gas-phase oxidation.
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