Influence of Gases on the Thermal Destruction of Coal

Abstract

The reaction of coal with gases complicates its extraction and processing. In particular, nitrogen and carbon dioxide are used to localize and extinguish underground fires and warehouse fires. On heating coal aggregations, different gases may have very different effects on coal’s organic mass. Thermogravimetric analysis reveals individual stages in the decomposition of coal and permits prediction of its behavior in the presence of gases. In the present work, the reactivity of coal’s organic mass on pyrolysis in inert gas (nitrogen), oxidizing gas (oxygen), and redox gas (CO₂) is assessed. The coal samples employed are of limited and moderate metamorphic development; they are susceptible to oxidation and self-ignition in coal beds, in storage, and in transportation. Thermogravimetric analysis indicates that, if oxygen is present, it will be adsorbed, with increase in the sample mass in the range 150–350°C. On that basis, the risk of coal oxidation and self-ignition may be assessed. In the presence of nitrogen and carbon dioxide but not oxygen, reducing reactions predominate, with the formation of solid carbon residue. In contrast to pyrolysis in inert gas (nitrogen), pyrolysis in carbon dioxide is accompanied by gasification, with increase in the coal’s mass loss at low and moderate temperatures.