Search Results (6)

This study investigated the inhibitory effect and mechanism of modified ultrafine ABC powder on the explosion of a methane (CH₄)/coal dust mixed system. Through experiments, it was found that the addition of ABC powder significantly weakened the deflagration characteristics of the CH₄/coal dust mixture system. During decomposition, heat was absorbed to generate ammonia and phosphoric acid. Inert gases such as CO₂ and water vapor produced during decomposition could dilute the oxygen concentration. Phosphate ions produced during the decomposition of ammonium phosphate would bind with free radicals during combustion, reducing their reactivity. The explosion reaction was suppressed through a dual mechanism of physical cooling and chemical consumption of free radicals. The experimental results showed that the weight loss rate of modified ABC powder was 49% at 800 °C, while the weight loss rate of unmodified ABC powder was 78%. The modified ABC powder had better thermal stability and could absorb more heat at high temperatures, further suppressing explosive reactions. This study provides a new modification scheme for explosion suppressants for coal mine safety, which has important theoretical and practical application value. Full article

Coal mining frequently sees explosions caused by methane/coal dust mixtures, resulting in significant harm to people and property damage. This study utilized the Hartmann pipe experiment to investigate the inhibition mechanisms of ultrafine water mist (UWM) containing phosphorus-based sodium inhibitors (sodium dihydrogen phosphate (NaH₂PO₄) and sodium phytate (C₆H₆Na₁₂O₂₄P₆)) on methane/coal dust hybrid explosions. The results indicate that UWM containing NaH₂PO₄ and C₆H₆Na₁₂O₂₄P₆ significantly reduces flame propagation velocity, flame height, and flame temperature, thereby effectively inhibiting the development of methane/coal dust hybrid explosion flames. UWM containing C₆H₆Na₁₂O₂₄P₆ exhibited superior inhibition performance, reducing the flame temperature to 157.6 °C, the peak flame propagation velocity by 2.26 m/s, and the flame height by 5.66 mm. The inhibition mechanism of UWM containing phosphorus-based sodium inhibitors primarily involves physical heat absorption and chemical inhibition. The evaporation of UWM absorbs heat, thereby reducing the temperature in the reaction zone. Simultaneously, it generates a large amount of water vapor, which dilutes the fuel concentration per unit volume and reduces the collision frequency between fuel molecules and oxygen. The active free radicals (such as sodium oxygen radical (NaO), metaphosphoric acid (HPO₂), HOPO (peroxyphosphate radical), etc.) produced by the decomposition of NaH₂PO₄ and C₆H₆Na₁₂O₂₄P₆ react with free radicals (O, H, and OH), effectively reducing the concentration of free radicals, interrupting the chain reaction, and weakening the explosive severity. The decomposition products of the phosphorus-sodium components increase the heat capacity of the combustion products, dilute and isolate the combustion zone, and further reduce the explosive severity. These findings provide significant scientific and engineering support for the safe management of coal mines. Full article

Ventilation Air Methane (VAM) significantly contributes to global warming. Capturing and mitigating these emissions can help combat climate change. One effective method is the thermal decomposition of methane, but it requires careful control to prevent explosions from the high temperatures involved. This research investigates the influence of methane concentration and coal dust particle properties on the minimum ignition energy (MIE) required for fugitive methane thermal decomposition and flame propagation properties. This knowledge is crucial for the mining industry to effectively prevent and mitigate accidental fires and explosions in VAM abatement plants. Coal dust samples from three different sources were selected for this study. Experiments were conducted using a modified Hartmann glass tube and a Thermal Gravimetric Analyser (TGA). The chemical properties of coal dust were determined through ultimate and proximate analysis. The particle size distribution was determined using a Mastersizer 3000 apparatus (manufactured by Malvern Panalytical, Malvern, UK). The results showed that the MIE is significantly affected by coal dust particle size, with smaller particles (<74 µm) requiring less energy to ignite compared to coarser particles. Additionally, blending methane with coal dust further reduces the MIE. Introducing methane concentrations of 1% and 2.5% into the combustion space reduced the MIE by 25% and 74%, respectively, for the <74 µm coal dust size fraction. It was observed that coal dust concentration can either raise or lower the MIE. Larger coal dust concentrations, acting as a heat sink, reduce the likelihood of ignition and increase the MIE. This effect was noted at a methane concentration of 2.5% and coal dust levels above 3000 g/m³. In contrast, small amounts of coal dust had little impact on MIE variation. Moreover, the presence of methane during combustion increased the upward flame travel distance and propagation velocity. The flame’s vertical travel distance increased from 124 mm to 300 mm for a coal dust concentration of 300 g·m⁻³ blended with 1% and 2.5% methane, respectively. Full article

This research aimed to the characteristics and influence factor of methane and coal dust gas/solid two-phase mixture explosions by experiment. Through comparative analysis of flame propagation characteristics, pressure, flame temperature and products, the characteristics of gas/solid explosions and its influence factor were analyzed. And the influence mechanism was also revealed. Results indicate that the coal dust parameter and methane concentration were the important influence factor on mixture explosions. Explosion intensity could be indirectly affected by influencing the flame propagation. Under the determined coal dust parameter, the explosion parameter showed a change trend of increase firstly and then decrease as the methane concentration increased. And it was the greatest at 6% methane concentration. However, the concentration of coal dust corresponding to the maximum pressure was variable and was decreased successively as the methane concentration increased. The corresponding dust concentrations were 500 g/m³ and 200 g/m³ under 2% and 10% methane concentrations, respectively. Meanwhile, the pressure all presented an increasing trend with the reduction of coal dust diameter under five coal dust concentrations, and the explosion intensity was the greatest at 300 g/m³ coal dust concentration. For 2% methane concentration, the explosion would not occur as the dust concentration was less than 400 g/m³. And the same phenomena also appeared as the methane concentration exceeded 10%. The explosion parameter presented the same change trend with the changes of methane concentration and coal dust parameters. Besides, the thermal stability and decomposition oxidation characteristics of burned coal dust were evidently changed compared with unburned coal dust. The weight loss rate and oxidation reaction rate were decreased, and the corresponding temperature was increased. It indicates that coal dust participated in gas/dust two-phase explosion reactions, and the pyrolysis reaction of volatile matter led to an obvious reduction in the weight loss and oxidation reaction rate. And the precipitation of volatile matter also resulted in an obvious pore structure on its surface. The physical parameters and internal components of coal dust were important factors affecting the reaction rates of gas/dust mixture explosions. Full article

A review of the existing optoelectron monitoring devices revealed that the design of optoelectron detectors of the mine atmosphere does not sufficiently take into account the factor of external optical interference. This includes any extraneous source of thermal emission: a source of artificial lighting or enterprises. As a consequence, the optoelectron detectors -based safety systems currently installed at mining sites are not able to ensure properly the detection of the ignition source in the presence of optical interference. Thus, it is necessary to determine the working spectral wavelength ranges from methane and coal dust explosions. The article presents the results of experimental research devoted to the methane-air mixture and coal dust explosion spectral analysis by means of the photoelectric method. The ignition of a methane-air mixture of stoichiometric concentration (9.5%) and coal dust of size characterized by the dispersion of 63–94 microns and concentration of 200 g/m³ was carried out in a 20 L spherical chamber with an initial temperature in the setup of 18–22 °C at atmospheric pressure. Then, photometry of the explosion light flux was conducted on a photoelectric unit. Operating spectral wavelength ranges from methane and coal dust explosions were determined. For the methane-air mixture, it is advisable to use the spectral regions at the maximum emission of 390 and 900 nm. The spectrum section at the maximum emission of 620 nm was sufficient for dust-air mixture. It enabled us to select the wavelength ranges for automatic explosion suppression systems’ launching references. This will exclude false triggering of the explosion suppression system from other radiation sources. The research results will help to improve the decision-making credibility of the device in its direct design. The results will be used in further research to design noise-resistant optical flame detection sensors with a high response rate. Full article

A gas and coal dust explosion is potential hazard in majority coal mines. A coal mine mobile refuge chamber is a new class of device for miners those who are unable to escape after an accident which can provide basic survival conditions. In this paper, in order to study the propagation law of an underground methane/air mixture explosive wave, and check the failure mode of a coal mine mobile refuge chamber, a full-sized underground tunnel model and a refuge chamber model have been established in ANSYS/LS-DYNA (LSTC, R7.0.0, Livermore, CA, USA, 2014). The simulation results show that the reflected wave pressure on the front surface of the refuge chamber was about twice as high than the incident wave. The pressure on various locations of the chamber was also analyzed. When the peak pressure of the explosive shockwave reached 0.64 MPa, the maximum displacement and stress occur at the center of the front door and the joint of stiffeners and the front plate, respectively. Most parts of the coal mine mobile refuge chamber were in a plastic failure state and the refuge chamber could be defined as damaged. The front door, the front plate, the connecting flange, and the stiffeners on each side were the primary key components. In the end, suggestions were proposed for the refuge chamber. Full article