Investigation of Spontaneous Combustion Inhibition of Coal Fires Utilizing Differential Scanning Calorimetry and Thermogravimetric Analysis

Self-oxidation of coals can result in spontaneous combustion events at any time during mining, transporting, or processing, causing environmental, economical, and safety concerns. The total global primary coal production as of 2012 was 8.7 billion tons. Of that, 1.1 billion tons of coal was mined in the US, which accounts for 41% of the domestic electricity production. Spontaneous coal combustion, although dependent on coal rank, is a naturally occurring phenomenon that often causes damage to industrial and commercial facilities and freight, reduces the caloric value of coal, can release noxious gases and particulate matter, and increases CO2 pollution levels locally and globally. Through the self-oxidation process, as heat accumulates, the internal temperature of the coal continues to rise over time and if left unaltered will lead to spontaneous coal fires. Thus there is a definite need for means to suppress this process. In this study, we investigated methods of spontaneous coal combustion inhibition. During experimentation, coal was ground into a fine dust (500 microns in diameter) and treated with inorganic phosphate and sulfonate salts combined with anionic and non-ionic surfactant blends. Each ingredient was applied to the surface of unreacted coal in combination, systematically varying the concentrations of each component, to reach a cost-effective and efficient formulation. Multiple approaches including thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to analyze these effects. Results showed these novel formulations can reduce spontaneous combustion potential, making coal more thermally stable. Mechanisms by which these formulations inhibit coal spontaneous combustion are proposed.