Lower flammability limits of hybrid mixtures containing 10 micron coal dust particles and methane gas

10微米煤尘分子与甲烷气体混合物的可燃下限

Process Safety and Environmental Protection, Volume 120, November 2018, Pages 215-226

Chris T. Cloney, Robert C. Ripley, Michael J. Pegg, Faisal Khan, Paul R. Amyotte

摘要：Mixtures of combustible dust and flammable gas pose an increased explosion risk in processing equipment due to reduced flammability limits over the dust and gas alone. Although correlations have been proposed based on experimental testing for predicting the flammability limits of hybrid mixtures from those of the dust and gas, none appear to be applicable across a range of fuel mixtures. The objective of this work is to use computational fluid dynamics to explore the lower flammability limits of 10 μm coal dust particles and methane gas under laminar, free-flame conditions, and to compare the limits to the experimentally determined mixing rules. This comparison gives an understanding of the baseline behaviour upon which different fuel mixtures, equipment geometry, and various operational conditions can be added in the future. The results from the computational model suggest that Le Chatelier's Law, which proposes linear mixing between the dust and gas limits, is applicable for the small particles studied. Bartknecht's curve, which proposes wider flammability limits than linear, appeared to be overly conservative, while new relations that predict narrowing of the limits did not appear to delineate flammable mixtures under the conditions investigated.

Factors influencing and a statistical method for describing dust explosion parameters: A review  

粉尘爆炸参数影响因素及统计方法综述

Journal of Loss Prevention in the Process Industries, Volume 56, November 2018, Pages 386-401

Jiangshi Zhang, Peihui Xu, Longhao Sun, Wenyue Zhang, Jianghong Jin

摘要：The maximum and minimum values of dust explosion parameters are indeterminate because the possibility of explosion has not been quantified under conditions that approach the explosion limit. In this review, the influencing factors, laws, and mechanisms of dust explosion characteristics are described by comparing the differences in the methods for measuring the parameters in the ASTM, EN, GB, and ISO standards. The variation law of explosion parameters changes when crossing the limit values of the characteristic diameters and dust concentration. The similarities of certain influence mechanisms are also introduced. In addition, a new method is introduced to quantify explosion probability. The statistical nature of ignition is revealed by discussing the variability of the data overlap region of the “explosion” and the “no explosion” near the MEC and MIE measurements. The influence of sample size and positive factors on the statistical phenomena of ignitions were analyzed. The variability of the results increases when the conditions are not conducive to explosions. The values with 50% probability of explosion are independent of the number of trials and are less affected by the regression models. Reliable statistics can be obtained by sequential analysis methods in a small number of tests. The present work is a more accurate guide for the risk assessment of dust explosions, and introduces a potential statistical method to more accurately analyze the actual explosion characteristics.

Study on the inhibition influence on gas explosions by metal foam based on its density and coal dust  

煤尘环境下不同密度金属泡沫对气体爆炸的抑制影响

Journal of Loss Prevention in the Process Industries, Volume 56, November 2018, Pages 451-457

Yajun Wang, Shuguang Jiang, Zhengyan Wu, Hao Shao, Lei Wang

摘要：Metal foam is another type of material that can inhibit gas explosion flames and pressure waves. However, there are continuous explosions and coal dust explosions in the coal mine; thus, research on metal foam's inhibition performance under the environment of coal dust and its destructive characteristics after the explosion are necessary. We studied the suppression influence and destruction of metal foam used as a gas explosion transfer device designed for this research. First, a barrier performance experiment was conducted using metal foam whose density ranged from 0.33 to 0.54 g/cm3. Then, we examined the deformation and damage characteristics of different-density metal foams after the explosion. The experimental results demonstrate that the ability to suppress the explosion is better when the volume density of the metal foam is high. There is no obvious damage or deformation when the density is heavier than 0.5 g/cm3; thus, it could be resistant to the impact of the secondary explosion. Second, 5–100 g of coal dust was added in the pipe, and the inhibition performance of the metal foam was reduced. Especially, 50 g of coal dust can raise the explosion overpressure and flame speed. The quality of coal powder can reduce the barrier performance in a specified range.

The influence of dust originating from carbon black nanopowders on the explosion characteristics of lean methane/air mixtures within a turbulent environment  

湍流环境下碳黑纳米粉末粉尘对低浓度甲烷/空气混合物爆炸特性的影响

Journal of Loss Prevention in the Process Industries, Volume 55, September 2018, Pages 61-70

Georgios F. Kylafis, Alison S. Tomlin, P. Andrew Sleigh, Malcolm Lawes, Alexis Vignes

摘要：Industrial requirements present some unique challenges that can be met only by the application of engineered nanomaterials (ENMs). The completion of risk assessments based on the knowledge of the change in the explosion severity of turbulent gas/air mixtures caused by the accidental dispersion of nanopowders is vital before integrating such materials into existing systems. In this work, known amounts of selected carbon black nanopowders were mixed with methane near the lower-flammability-limit (LFL) to form hybrid mixtures of variable dust concentration. Mixtures were ignited in a 23 L cylindrical combustion vessel that allowed the control of isotropic turbulence through specially designed fans. The particle size distribution, the explosion pressure history and the flame speed derived from high speed Schlieren cine photographs, were measured. The influence of dispersed amounts of nanopowders on explosion severity was investigated by comparing the results with those obtained for pure methane-air explosions. Results indicated that the release of a relatively low mass of nanopowder into methane-air mixtures resulted in a more severe explosion than that of a higher amount. Also, despite the very low content of volatiles in the selected nanopowders, a hybrid mixture can be ignitable at an equivalence ratio well below the LFL of the gas. However this ignitability was shown to be related to the agglomeration state of powder in the dispersion phase, indicating that as the mean particle size decreases, a hybrid mixture with an extremely low content of flammable gas could be ignitable. From a risk assessment point of view, these results may have great significance for specific industrial processes aiming to utilise ENMs.