Focusing on the patterns and characteristics of extraordinarily severe gas explosion accidents in Chinese coal mines

中国煤矿重特大瓦斯爆炸事故形式与特征研究

Process Safety and Environmental Protection, In press, accepted manuscript, Available online 12 May 2018

Jinjia Zhang, David Cliff, Kaili Xu, Greg You

摘要：Extraordinarily severe gas explosion accidents (ESGEAs) (thirty fatalities or more in one accident) have a high occurrence frequency in Chinese coal mines. There are 126 ESGEAs that occurred in China from 1950 to 2015, and they were investigated through statistical methods in this study to review the overall circumstances and to provide quantitative information on ESGEAs. Statistical characteristics about accident-related factors, such as gas accumulation, ignition sources, operating locations, accident time, coal mine regions and coal mine ownership, were assessed in this paper. The statistical analysis shows that disorganized ventilation fan management was the most frequent cause of gas accumulation in ESGEAs, while illegal blasting was the most prominent cause of the ignition source in ESGEAs. Furthermore, ESGEAs were found to occur frequently in certain provinces (e.g., Shanxi, Henan and Heilongjiang) and during November and December of the year. Moreover, most accidents and the largest death tolls generally occur in state-owned coal mines. Based on the results of statistical studies, some countermeasures were proposed in this study.

Flame propagation behaviors and temperature characteristics in polyethylene dust explosions

聚乙烯粉尘爆炸过程中的火焰传播特性及温度特征

Powder Technology, Volume 328, 1 April 2018, Pages 345-357

Bo Gan, Wei Gao, Haipeng Jiang, Yanchao Li, Mingshu Bi

摘要：To reveal the flame propagation mechanism in polyethylene (PE) dust explosions, the flame propagation behaviors and temperature characteristics of polyethylene dust clouds were experimentally studied in an open duct. Flame propagations in polyethylene dust clouds with different concentrations and particle size distributions were recorded using high-speed photography. The flame temperatures were measured using two fine thermocouples comprising Pt–Pt/Rh13% wires of diameter 25 μm. Because of severe agglomeration, the minimum explosible concentration of polyethylene particles with diameter < 75 μm was higher than that of the particles with diameter 75–100 μm. It was observed that the flame front gradually became continuous as the particle size increased with the same polyethylene dust concentration of 300 g/m3. With higher polyethylene dust concentration, the flame front of the polyethylene particles of size <75 μm could quickly become discrete, and the floating flame appeared early, while the flame front of the 100–212 μm polyethylene particles transformed from a continuous flame into several independent diffusion flames. It was demonstrated that the flame propagation velocities were not constant, and that they fluctuated owing to the turbulence and expansion of the combustion products. The average flame propagation velocity increased initially, and then decreased with increasing dust concentration. The peak velocity of the polyethylene particles of size <75 μm was 4.79 m/s at a mass density of 300 g/m3, while the peak velocity of the 75–100 μm particles was 4.55 m/s at a mass density of 400 g/m3, and that of the 100–212 μm particles was 2.67 m/s at a mass density of 500 g/m3. In addition, it was found that the maximum flame temperatures of the different polyethylene particles were approximately the same; the temperatures were 1585.4 °C, 1511.8 °C, and 1508.4 °C for the polyethylene particles of sizes of 100–200 μm, <75 μm, and 75–100 μm, respectively. This phenomenon may be caused by the combustion behavior of the molten polyethylene particles. When the dust concentration is increased within the optimum concentration, flame temperature increased with the increase in flame propagation velocity. The flame temperature of the polyethylene particles of size <75 μm decreased as the flame propagation velocity decreased, while the flame temperature of the 75–100 μm polyethylene particles did not change significantly.

The quantitative studies on gas explosion suppression by an inert rock dust deposit

基于惰性岩石粉尘沉积的气体爆炸抑制量化研究

Journal of Hazardous Materials, Volume 353, 5 July 2018, Pages 62-69

Yifan Song, Qi Zhang

摘要：The traditional defence against propagating gas explosions is the application of dry rock dust, but not much quantitative study on explosion suppression of rock dust has been made. Based on the theories of fluid dynamics and combustion, a simulated study on the propagation of premixed gas explosion suppressed by deposited inert rock dust layer is carried out. The characteristics of the explosion field (overpressure, temperature, flame speed and combustion rate) at different deposited rock dust amounts are investigated. The flame in the pipeline cannot be extinguished when the deposited rock dust amount is less than 12 kg/m3. The effects of suppressing gas explosion become weak when the deposited rock dust amount is greater than 45 kg/m3. The overpressure decreases with the increase of the deposited rock dust amounts in the range of 18–36 kg/m3 and the flame speed and the flame length show the same trends. When the deposited rock dust amount is 36 kg/m3, the overpressure can be reduced by 40%, the peak flame speed by 50%, and the flame length by 42% respectively, compared with those of the gas explosion of stoichiometric mixture. In this model, the effective raised dust concentrations to suppress explosion are 2.5–3.5 kg/m3.

Experimental analysis on post-explosion residues for evaluating coal dust explosion severity and flame propagation behaviors

评价煤尘爆炸猛烈度与火焰传播特性的后爆炸残渣实验分析

Fuel, Volume 215, 1 March 2018, Pages 417-428

Qingzhao Li, Chuangchuang Yuan, Qinglin Tao, Yuannan Zheng, Yang Zhao

摘要：Coal dust explosion is a major threat to coal mine and other coal processing or utilizing industries. A deep investigation and accurate knowledge of coal dust explosion mechanism are still essential for the development of safety techniques for coal dust explosion prevention. In present work, the explosion severity of coal dust/air mixture, flame propagating properties, the characteristics of gas and solid residues had been studied. And, the correlations between the residues characteristics and explosion severity had been analyzed systematically. Results show that there is a linear relationship between explosion flame propagation speed (VF) and dust concentration (Cdust). With the increasing of vitrinite reflectance (Ro,max), explosion pressure (Pm), explosion pressure rise rate (dP/dt)m, explosion index (Kst) and flame propagation speed (VF) are all presenting a first increasing and then decreasing trends. During coal dust explosion, much more solid fragments are produced by the thermal stress and blast shock impacts. Compared with raw coal dust, particle size dispersities of all residues are increased obviously. Chemical functional groups in the coal dust particles, such as aromatic CH, aromatic C  C, aliphatic CH bonds, and oxygen-containing functional groups, etc. are all involved in coal dust explosion process. Furthermore, aliphatic CH and oxygen-containing matters may be the key factors influencing on the reactivity of dust explosion. For coal dust explosion under poor dust concentration conditions, the main gas components in the mixtures are CO2 product, residual oxygen and nitrogen gas in balance. The other combustible component (CO, CH4, C2H2, C2H4, C2H6 and C3H8) is almost undetectable. However, under dust-rich conditions, the combustible components would be increased sharply. The firstly detected combustible gases (CO, CH4, C2H2, C2H4, C2H6 and C3H8) can be used as the characteristic gases to determine the maximum explosion intensity of coal dust explosion.

Investigation on the structure evolution of pre and post explosion of coal dust using X-ray diffraction

基于X射线衍射的煤尘爆炸前后结构演化研究

International Journal of Heat and Mass Transfer, Volume 120, May 2018, Pages 1162-1172

Qingzhao Li, Qinglin Tao, Chuangchuang Yuan, Yuannan Zheng, Junfeng Liu

摘要：To reveal the effects of coal dust explosion on its crystal structures evolution, the micro structure of six different rank of coal dust and its explosion solid products had been studied using 20 L explosion sphere vessel and X-ray diffraction (XRD) analyzer. The correlations between structural parameters and explosion severity had been analyzed detailed. Results show that coal dusts with higher volatile matter contents (Vdaf), lower vitrinite reflectance (Ro,max) and less ash contents (Aad) show stronger explosion severity. The effects of vitrinite reflectance (Ro,max) on the explosion severity parameters present the same role as the influence of volatile matter contents (Vdaf). Coal dusts with developed porous structure (SBET and VBJH) also present higher explosion reactivity. Interestingly, six selected coal samples present the strongest explosion severity at the same optimum explosion concentration (250 g/m3). For the different rank raw coal, the difference of the shape and intensity of 0 0 2 peak varies greatly. With the decreasing of coal ranks, the 0 0 2 band tends to be blunt and the peak intensity is relatively short. Quantitative analysis show that the lattice parameters (La, Lc, and Navg) of six coal samples are found to relatively increase with increasing vitrinite reflectance (Ro,max), whereas the d002 slightly decreases. The explosion treatments have significant effects on the ordering of coal aggregate structure. Compared with raw coal sample, the relative intensity of 0 0 2 bands at about 26° is reduced by the explosion treatments, which would increase the degree of graphitization of the explosion solid products. With the increasing of explosion pressure, the relative intensity of 0 0 2 peak would be gradually decreased. However, the shape of 0 0 2 peak for the explosion solid products tend to be more asymmetric and blunter than that at lower explosion conditions. Compared with the parent coals, the inter-layer spacing d002, Lc and Navg of all explosion products would be slightly reduced correspondingly. However, there is no clear rule for the evolution of La parameter. Moreover, calculated aromaticity (fa) of the coals ranges from 0.2208 to 0.6883, which is linear positively increased with the coal maturity by vitrinite reflectance.