Abstract
Understanding the ignition mechanism of spontaneous combustion is critical for preventing it. In this work, the effects of different test conditions including oxygen concentration, heating rate, oxidation carrier gas flow rate, and sample amount on the ignition temperature were studied with a thermal gravimetric analyzer. Further, the effects of coal properties on the ignition temperature were also investigated using 15 different low-rank coals. A heterogenous ignition model was proposed that small amount of active species is the key material leading to ignition. The heterogenous ignition mechanism well explained the complex effects of test conditions and coal properties on the ignition temperature of low-rank coal. Finally, an empirical formula for predicting the ignition temperature was derived for the rapid assessment of the spontaneous combustion potential.
Highlights
1 Introduction gas flow rate, heating rate and sample amount were changed to observe the ignition temperature variation
3.1 Effect of experimental conditions on ignition temperature DLT-52 was used as a typical sample
When oxygen concentration is 20%, the ignition temperature reaches to 260 °C, when pure oxygen is used, the ignition temperature drops to 212 °C
Summary
1 Introduction gas flow rate, heating rate and sample amount were changed to observe the ignition temperature variation. The highly active chemical structure and spontaneous combustion tendency of low-rank coal cause several challenges in its mining, storage, and utilization [1]. Several researches have focused on the development of an index for assessing its spontaneous combustion potential, such as absorption of flowing oxygen [2], activation energy of the oxidation reaction [3], adiabatic heating rate [4], characteristic temperatures [5] and indicative gases [6]. Scholars focused on the changes in the active functional groups present in the coal prior to the ignition and 2 Experimental section suggested that the oxidation of these groups at low temperatures was the main contributor to spontaneous combustion [10]. 2.1 Sample preparation different test conditions exhibits significant differences, and the known mechanistic knowledge does not adequately illustrate the causes for such variations
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