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Hydraulic slotting is a technique to enhance coal bed methane (CBM) recovery and prevent gas disasters. The drilling fields are usually arranged in floor roadway rather than roof roadway, but submerged jet effects caused by hydraulic slotting in roof roadway have not been carried out extensively. Concerning this issue, this paper conducted a series of numerical simulation and physical experiments on hydraulic slotting in roof roadway. It is shown that when the impact load of middle- and high-pressure water jet is applied to the sample, downlink borehole slotting can cause much stronger disturbance than uplink slotting due to the submerged jet. The fracture characteristics of samples also reflect that cavitation erosion caused by submerged jet promotes the fracture formation under middle and high impact load conditions. [ABSTRACT FROM AUTHOR]

Competitive adsorption of CO2/N2/CH4 on coals is important to evaluate potential application of CO2- or N2 – ECBM, which is not fully addressed in previous studies. In this paper, CH4, CO2, and N2 adsorption behaviors are experimentally compared at different reservoir temperatures (307 K, 318 K, and 333 K) and pressure up to 9 MPa. It is found that adsorption capacities all decrease with increasing temperature for CH4, CO2, and N2, while the differences in maximum adsorption capacity at different temperatures is not significant. Maximum adsorption capacity of anthracite coal is much larger than those of bituminous coals, while the maximum adsorption capacities of two selected bituminous coal are close to each other. The maximum adsorption capacity of CO2 is 1.93 mmol/g，which is significantly higher than that of CH4 and N2 with exactly 1.80 mmol/g and 1.11 mmol/g respectively. However, for a given coal sample, gas type does not affect the thermal-stimulated desorption capacities significantly. [ABSTRACT FROM AUTHOR]

High‐voltage electrical pulse (HVEP) technology, a potential method for degassing coal seam in the future, has made great progress in field application. However, the previous studies mainly concentrated on the coal‐crushing effect of the action of single pulse, ignoring the influence of cyclic single pulse on the fracture structure of coal. In this paper, Huaibei anthracite coal and Inner Mongolia bituminous coal were taken as the experimental objects to study the effect of cyclic single pulse on the fracture structure of coal. The results show that the uneven distribution of electric field in the coal causes the crack to break along the interface between the mineral and the coal. Besides, the characteristics of cracks and functional groups of coal before and after electrical breakdown were investigated through scanning electron microscope and Fourier transform infrared spectroscopy. The results suggest that the relative contents of oxygen‐containing functional groups are reduced after electrical breakdown, which promotes the gas desorption from the surfaces of coal samples. Moreover, changes in CH4 adsorption capacity of HVEP‐treated coal were studied through a high‐pressure adsorption instrument, with the adsorption temperature set from 40 to 120°C. The results show that the adsorption amount of electrically broken coal is smaller than that of raw coal, which proves that temperature and current exert similar influences on the adsorption capacity of coal sample. Additionally, current waveforms indicate that the peak current increases with the number of cycle, whereas the breakdown time decreases with it. However, the peak current and breakdown time will eventually become stable as the number of cycles grows, demonstrating that electrical properties of coal are changed in the process of breakdown, which thus affects the next discharge. [ABSTRACT FROM AUTHOR]

Abstract: Through a roadway model with cross-section area of 80×80mm2 and length of 100 m, the changing laws of overpressure, temperature, density, combustion rate and gas velocity after the explosion of methane-air mixtures with concentration of 9.5% and filling lengths of 2 m, 6 m, 10 m and 14 m were simulated by using AutoReaGas software. The results show that in the explosion propagation process, the peak overpressure firstly decreases, then increases, and then attenuates until to zero. However, flame propagation speed firstly increases, then begins to reduce and decreases until to zero. With the increase of methane filling length, the safety distance firstly increases and then decreases slightly, and the maximum distance of flame propagation increases linearly. With the increase of methane filling length, the initial peak overpressure and the maximum peak overpressure obviously increase, the peak overpressure and the maximum temperature in other points almost continually increase, and the distance where peak overpressure begins to rise and obtains its maximum value also increases. The time of flame arrival in the same point at various filling lengths is almost the same before flame speed begins to decrease, indicating that flame speed is almost the same before it decreases. Research results can be used to provide guidance for the safety of underground persons, the disaster relief and treatment of gas explosion in underground coal mines. [Copyright &y& Elsevier]

Abstract: In order to study the propagation characteristics of strong shock wave, a theoretical analysis is performed in this paper. Based on some assumptions, the relationships of the peak overpressure and the gas velocity during a gas explosion with the propagation distance were derived by using the explosion and aerodynamics theory. The results show that the peak overpressure of a strong shock wave is inversely proportional to the propagation distance and the cross-section area of the roadway, but directly proportional to the total energy of the gas explosion. However, the gas velocity is inversely proportional to the square root of the propagation distance and the cross-section area, but directly proportional to the square root of the total energy of the gas explosion. According to these results, some preventive measures can be taken to reduce the loss caused by the gas explosions in underground coal mines. [Copyright &y& Elsevier]