Low temperature heating and oxidation to prevent spontaneous combustion using Powder River Basin coal

Powder River Basin coal, a subbituminous coal, was studied for its low temperature oxidation tendency after a simple surface oxidation treatment. The influence of the heating temperature on the coal properties was studied. The tendency of this dried coal to oxidize at low temperatures was successfully eliminated by lightly oxidizing the coal in the air at 100 to 200 ºC. The surface reactions during the process were also studied. We found that the passivation treatment appears to consume the functional groups that are prone to low temperature oxidation, such as aliphatics. The passivation effect was weakened when the oxidation temperature went above 200 °C, as decomposition happens. The oxidation reactions are monitored through two different methods: analyzing the CO2 and water produced using quadrupole mass spectrometry (QMS) and analyzing the heat release at oxidation using the differential scanning calorimetry (DSC). Gas chromatography–mass spectrometry (GC-MS) was used to analyze the coal tar material produced from low temperature heating. Scanning electron microscopy (SEM), Surface area measurements, and Fourier Transform Infrared Spectroscopy (FTIR) are used for surface characterization of the solids. •Low temperature oxidation on the coal surface successfully passivated the coal, reducing the likelihood of spontaneous combustion.•Further oxidation occurred when the oxidation temperature went above 200 °C, demonstrating a limit to the passivation effect.•Differential scanning calorimeter, SEM, surface area measurements, and FTIR were used for the study of the surface properties.