Experimental study of torrefied wood fixed bed: Thermal analysis and source term identification

In this paper, self-heating scenarii were experimented on torrefied wood chips under atmospheres containing oxygen. These tests were carried out in a packed bed reactor. The experimental device was equipped with numerous thermocouples at different levels in the wood bed reactor ensuring temperature monitoring. The impact of oxygen supply was investigated at low-temperature (150 °C) both regarding oxygen content and atmosphere gas flow rate. The related results pointed out the propensity of the wood bed to self-heating particularly under a growing oxygen content or a low flow rate of oxidizing gas causing thus a spontaneous combustion. Furthermore, during self-heating, the source term was assessed relying on the local energy balance equation based on the experimental temperature fields. To summarize all results, source term values were fitted to a basic heat generation term of an oxidation reaction expressed as follows: Π=ΔH×∊×Aexp-EaRT×ρO2n. The optimized parameter values are: Ea = 99.8 kJ/mol, A = 2.50 × 109 s−1kgm3(1-n), n = 0.734, ΔH=14.062MJ/kgO2.