Search

On the basis of the four factors of spontaneous combustion of coal, the causes of such combustion in the tunnel fall of ground were comprehensively analyzed. The causes include the generation of float coal, influence of hot wind pressure on the laneway, and airflow dynamic pressure caused by sloping roadways. According to the characteristics of a fire that occurred in the intake airflow roadway of working face 12190 in the Geng Cun Coal Mine, a three-phase foam composed of mud, nitrogen, and water was used to extinguish the fire. The foam was injected into the fire zone through boreholes on the tunnel roof. Given the precise scheme and reliability of the technology, the fire was successfully extinguished. The specific technological process and parameters of the technology are discussed in detail. It is concluded that the three-phase foam is useful in preventing spontaneous combustion of coal in the tunnel fall of ground. It serves as a new method for preventing such phenomenon in extra-thick coal seam.

The gas explosions often occur under mine gas and spontaneous combustion coupling in coal mines. The coupling of mine gas and spontaneous combustion is a complex disaster, and the character of the disaster is not clear now. The paper primarily discussed the character of gas explosion under mine gas and spontaneous combustion coupling. The explosion concentration range of mixed gases including CH 4 and CO is studied. And the potential area and the course of explosion detonated by spontaneous combustion of coal is analyzed. When the spontaneous combustion of coal occurs, it can produce plenty of CO and fire-heating air pressure in the goaf. Experiments show that the upper limit of explosion concentration rises rapidly and the lower limit rises slowly with the increase of CO in the mixed gas of CH 4 and CO. The fire-heating air pressure results in continuous mix of the gases and heat convection under vortex action between the combustion zone and non-firing zone. Thus, gas explosion occurs. In order to prevent high-concentration gas in the goaf and spontaneous combustion which detonates gas explosion in the coal mine, three-phase foam with nitrogen is adopted to restrain gas explosion and reduce coal temperature.

In order to investigate the inhibition characteristics of green and environmentally friendly sand suspending thickener, we applied the self-designed Temperature Program Experiment System to test three different inhibiting substances, the calcium chloride, the soluble glass, and the sand suspending thicker, for comparison. Comparing the oxidation temperature curves of the primordial coal with the ones processed by inhibiting substances, we found that the temperatures of processed coals were all quite low and the temperature of the coal processed by sand suspending thickener the lowest. Therefore, the sand suspending thickener is the best material among the tested materials for fire-fighting in coal mine.

In this paper, the concept of the crack opening deformation rate at a small distance r m behind a growing crack-tip under plane-strain condition has been generalized, so as to derive a simplified theoretical formula of CTOA at an advancing tip under the conditions of plane-stress and large-scale yielding for power-hardening materials. The results obtained by this formula are in agreement with calculation results by finite-element method as well as experimental data. The characterizing energy dissipation rate within the fracture process zone at the growing crack tip G FPZ has been defined and calculated, and found to vary in the same trend as that of CTOA, thus suggesting that G FPZ is a physical parameter pertinent to crack propagation and independent of specimen geometry. A general theoretical relationship between G FPZ and the crack-tip opening parameters ( δ t and CTOA) has been obtained.