This study evaluated the effects of air humidity on the spontaneous combustion characteristics of coal. Four levels of air relative humidity (dry air, 30%, 60%, and 100%) were used as the experimental air flow. The crossing point temperature (CPT) and oxidation products were measured using a self-designed spontaneous combustion system. We found CPT values of 153°C, 151°C, 150°C, and 148°C for the four levels of air humidity, respectively. The concentration of oxidation production increased with an increase in air humidity. Then, the thermal characteristics of coal were studied using the thermogravimetric and differential scanning calorimetric methods. It was found that a peak temperature II appeared at 417.28°C, 411.25°C, 402.64°C, and 385.68°C for the four air humidities, respectively. As a consequence, the adsorbed water had pushed the coal oxidation into the next stage.

This study evaluated the potential application of hydroxypropyl guar gum (HPG) and xanthan gum (XG) (HPG/XG weight ratio 1:1) to stabilize highly concentrated fly ash suspensions (FAS) (300 g/L) used for retarding spontaneous combustion of coal. The rheological behaviors of FAS were measured with different HPG/XG mixture concentrations including 1.2, 1.4, 1.6, 1.8, and 2 g/L, respectively. The effects of concentrations on the static stability of FAS were investigated to determine the optimal concentration. It was found that increasing HPG/XG concentration was beneficial to the viscoelasticity of FAS as evidenced by higher elastic modulus (G′), and FAS can be stabilized over 72 h when HPG/XG concentration increased to 1.6 g/L. Retarding spontaneous combustion experiments indicated that FAS significantly elevated the crossing point temperature of coal and reduced the carbon monoxide during low-temperature oxidation, efficiently retarding spontaneous combustion of coal.

Foamed gel, a new technology for preventing and controlling coal mine fires, was put forward and developed in order to overcome the deficiency of fire-fighting technologies and materials in coal mines. The properties of adhesiveness, permeability, cementation, and plugging of foamed gel have been experimentally studied. It can be shown from the results that the apparent viscosity of foamed gel reaches 7274 mPa·s, 18 times that of the stock solution. The permeability of foamed gel is 33.84%, 2.35 and 1.65 times of that of water and common foam, respectively. Furthermore, the time of permeability reaching the maximum is only 40 min, half of that of water and common foam. One day later, the weight of slack coal coagulated by foamed gel is 57–93.8% of that of the coal sample, and it is still 13.4–52.6% of that after 10 days. The foamed gel cannot only fill the fractures among coal and block air leakage, but also endure the wind pressure of over 2500 Pa. Thus, it can effectively prevent and control coal spontaneous combustion. Furthermore, by using spontaneous combustion testing apparatus, the researches have been conducted to investigate the release rate of CO of coal mixed with the foamed gel. It can be seen from the results that the inhibiting effect of foamed gel is significant, which can efficiently slow down the oxidation rate of coal and control the release amount of CO.