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It is imperative to have an in-depth understanding of the effect of extraneous moisture on the spontaneous combustion of coal not only for the control and prevention of coal spontaneous combustion in the coal mining industry, but also for the optimization design and application of the technological process. In this study, the type of moisture in a coal body has been redefined for the first time from the perspective of disaster prevention and control, i.e., original occurrence of moisture in the coal matrix and the extraneous moisture from the technological process. A suit of coal bodies with different extraneous moisture was prepared by soaking long-flame coal with a low water content. Using a temperature-programmed oxidation test, the effects of extraneous moisture on the temperature increase rate of coal bodies and the emission characteristics of gaseous products during coal spontaneous combustion were studied. Moreover, combined with the characterization of thermal analysis and of pore structure test, the action the mechanism of extraneous moisture on the coal spontaneous combustion process was also explored. The experimental results indicated that the effect of the extraneous moisture content varied with the development of coal spontaneous combustion. In the slow oxidation stage, extraneous moisture played a physical inhibition role in the coal oxidation. In the accelerated oxidation stage, extraneous moisture exhibited a catalytic effect on the coal–oxygen reaction or directly participated in the reaction. After entering the rapid oxidation stage, a delayed effect appeared. When the coal temperature exceeded 180 °C, the spontaneous combustion characteristics of coals with different initial moisture contents gradually tended to achieved balance.

Polyurethane elastomer (PUE) was firstly applied to mining coal roadway as air-leak sealant. It is very important for air-leak sealants to possess the super mechanical properties and good flame retardant performance when applied to the coal-rock mass with cracks. The reinforced and toughened PUE nanocomposites were obtained by adding surface modified TiO 2 and SiO 2 nanoparticles. The modified PUE was characterized in terms of morphology, structure, and thermal stability by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), infrared spectroscopy (IR), and thermogravimetric analysis (TGA). Its flame-retardant performance and mechanical properties were also tested. The results showed that the surface modified nanoparticles were uniformly dispersed in the PUE matrix and enhanced its thermal stability and flame retardant performance. The dual effects of uniform dispersion of nanoparticles and hydrogen bonding between nanoparticles and PUE improved the mechanical properties of the composites. The PUE modified by nanoparticles was successfully applied to coal mines and showed great air-leak sealing effect.

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It is imperative to have an in-depth understanding of the chemical inhibition mechanism for spontaneous combustion of coal, not only for controlling and preventing spontaneous combustion of coal in the coal mining industry but also for reducing emissions of hazardous gases. N,N-dibenzylhydroxylamine (DBHA) as a hydroxylamine free radical scavenger can be chosen as a feasible stabilizer for the spontaneous combustion of coal. In this study, the inhibitory performance of DBHA was examined by investigating coal mass changes and heat release obtained from thermogravimetric and differential scanning calorimetry. The effect of DBHA on change of the active groups during coal oxidation at different temperatures was determined by in situ Fourier-transform infrared spectroscopy. Density functional theory was also introduced to optimize the active radical model and calculate thermodynamic parameters. Experimental results showed that DBHA exerted a strong inhibitory effect on the spontaneous combustion of coal, especially for lignite and sub-bituminous coal. DBHA can combine with a hydroperoxide intermediate to form a stable compound, causing the effect of reducing the free hydroxyl content in coal and interrupting the formation of aldehydes and carboxylic acids. Additionally, it can combine with alkyl radicals to form stable compounds. DBHA exhibits an inhibitory effect by increasing the activation energy at each stage, especially during the accelerated oxidation and quick oxidation stages. Furthermore, the possible reaction paths between free radicals and DBHA were also proposed on the basis of the experimental findings.

The CO formation rules of coal were analyzed by a self-developed testing device under ambient temperature. The changes of functional groups caused by oxidation were obtained using Fourier-transform infrared spectroscopy (FTIR). The experimental results showed that CO was generated during the ambient temperature oxidation. The highest concentration level of CO could be 389 ppm. The methylene and aldehyde groups on the side chains were involved in the reaction. For the quantum mechanical approach, we employed the density functional theory with the 6–31 G (d, p) basis set. Density functional theory–based computations interpreted the possible reaction sites on a coal molecule by electronic static potential analysis. The rationality of the predicted reactions was also evaluated by transition state analysis and energy analysis. This research theoretically proved that coal could be oxidized to carbon monoxide under ambient temperatures and gave the possible reaction paths.

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