不同含水率煤尘在瓦斯爆炸诱导下爆炸传播规律研究

为了探究不同含水率煤尘在瓦斯爆炸诱导下的爆炸传播规律,利用自行搭建的直管瓦斯爆炸诱导煤尘二次爆炸实验系统,从冲击波压力和火焰传播速度2个方面,研究了不同含水率沉积煤尘在瓦斯爆炸诱导下的爆炸传播规律和原因。研究结果表明:当煤尘含水率小于40%时,管道内沉积煤尘会在瓦斯爆炸诱导下产生二次爆炸,同时沉积煤尘总量一定时,沉积煤尘二次爆炸产生的冲击波超压峰值和火焰传播速度随着煤尘含水率的增加先增大后减小;当沉积煤尘含水率为20% 时,煤尘二次爆炸产生的冲击波超压峰值、火焰传播速度峰值达到最大值,分别为1.657 MPa和468.060 m/s;当沉积煤尘含水率大于40%时,沉积煤尘无法产生二次爆炸,此时爆炸产生的威力小于单一瓦斯爆炸,火焰传播速度衰减较无煤尘的瓦斯爆炸更快,沉积煤尘起到抑制瓦斯爆炸传播的作用。研究结果可以为防治煤尘二次爆炸提供理论依据。     

运用本质安全原理预防煤粉爆炸

旨在将本质安全原理与粉尘爆炸(以煤粉爆炸为例)的风险控制联系起来。利用20 L球形爆炸装置的标准测试方法测试煤粉及煤粉-CaCO3混合物的爆炸下限、最大爆炸压力、压力上升速度等爆炸特性。基于本质安全基本原理和试验结果,讨论预防煤粉爆炸的各种基本方法,并重点阐述本质安全原理与粉尘爆炸影响因素、不同的预防方法、过程设备的选择等之间的关系,对已制定的爆炸风险控制措施进行完善和补充。     

激波诱导下煤粉的爆炸压力测试

因气体爆炸导致沉积粉尘的二次爆炸的威力远大于单纯的气体或者粉尘爆炸产生的威力,利用自制的装置,诱导煤粉爆炸的激波由甲烷气体爆炸产生,对激波诱导下煤粉的爆炸压力Pmax、爆炸压力上升速率(dp/dt)max进行了实验研究。该实验分别研究煤粉浓度及煤粉粒度对爆炸指数的影响,其结果表明:对于不同的煤粉浓度,存在一个理想煤粉浓度值,在这个浓度下的煤粉爆炸压力值最大;随着煤粉粒度的减小,其爆炸压力不断升高。     

Effect of shock strength on dust entrainment behind a moving shock wave

Secondary dust explosion is a serious industrial issue because it occurs under conditions corresponding to an increased quantity and concentration of dispersed, combustible dust when compared with the primary explosion. The problems of lifting and dispersion of a dust layer behind a propagating shock wave must therefore be understood to ensure safety regarding secondary dust explosion hazards. Using a new shock-tube facility for studying shock propagation over dust layers, limestone dust was subjected to Mach numbers ranging from 1.10 to 1.60. A shadowgraph technique was applied by using a high-speed camera (15,000 fps) for visualization of the dust-layer height change behind the moving shock wave. Also, the effect of dust-layer thickness on the entrainment process was observed by performing tests with two different layer depths, namely 3.2- and 12.7-mm thicknesses. New correlations were developed between the shock strength and the dust entrainment height as a function of time for each layer depth. In general, the results herein are in agreement with trends found in previous work, where there is a linear relationship between dust growth rate and shock Mach number at early times after shock passage. Also, new data were collected for image analyses over longer periods, where the longer observation time and higher camera framing rates led to the discovery of trends not previously observed by earlier studies, namely a clear transition time between the early, linear growth regime and a much-slower average growth regime. This second regime is however accompanied by surface instabilities that can lead to a much larger variation in the edge of the dust layer than seen in the early growth regime. In addition, for the linear growth regime, there was no significant difference in the dust-layer height growth between the two layer thicknesses; however, the larger thickness led to higher growth rates and much larger surface instabilities at later times.     

高炉喷吹用潞安贫瘦煤爆炸下限与返回火焰长度的试验研究

该试验通过测定爆炸下限与返回火焰长度这两个参数来确定4种煤粉的爆炸性。爆炸下限指能使喷入一定装置中的粉尘云点燃并维持火焰传播的最小粉尘浓度,是确定粉尘爆炸性重要参数,试验室通常使用20L的爆炸装置进行测定。喷吹现场广泛采用长管式煤粉爆炸性测试仪检测煤尘引燃后产生的返回火焰长度,该长度随煤粉爆炸性的强弱而显著变化:返回火焰长度大于600 mm可认定该煤粉具有强爆炸性;在400~600 mm之间则煤粉具有中强度爆炸性;小于400 mm则煤粉具有弱爆炸性。结果表明:20 L球测得4种煤粉的爆炸下限在60~85 g/m3之间;长管式煤粉爆炸性测定仪测得4种煤粉的返回火焰长度在20~50 mm之间。由测定的返回火焰长度可知,试验所用的4种煤样均属于弱爆炸性煤种。     

Recent trends in rock dust modifications for improved dispersion and coal dust explosion mitigation

Underground coal mine explosions is perhaps the most hazardous danger in the coal mining industries. Efforts have been made to abate the coal dust explosion by applying rock dust either dry or wet. Dry dust has the best lift characteristic which efficiently quenches the flame propagation of a potential explosion. As a trade-off, undesired respirable dust particles are thereby generated imposing a severe health hazard on coal miners. Wet dusting is an alternative to dry dusting which significantly reduces the exposure to respirable dust particles. However, wet dust is subject to adverse caking issues which lead to a drastic reduction in the dispersibility of the particles. The present work summarizes the studies conducted to date regarding the surface modification of rock dust particles for the purpose of eliminating or alleviating the problems accompanying coal mine dusting applications, meanwhile improving the dispersive properties of dust particles and the ability to suppress the coal dust explosion.     

矿井瓦斯煤尘爆炸传播数值模拟研究

基于连续相、燃烧、颗粒相数理方程建立瓦斯煤尘爆炸传播数理模型,并应用连续相、颗粒相计算方法,依据大型巷道瓦斯爆炸、瓦斯煤尘爆炸传播实验数据,借助普遍应用的流场模拟平台,成功开发瓦斯、煤尘爆炸数值模拟系统。该系统可有效地模拟煤矿瓦斯、煤尘的爆炸事故过程,对瓦斯爆炸的爆燃转爆轰、煤尘是否参与爆炸、爆炸冲击传播速度、衰减规律以及爆炸灾害的波及范围都能进行较准确的模拟。     

Methane/coal dust/air explosions and their suppression by solid particle suppressing agents in a large-scale experimental tube

Methane/coal dust/air explosions under strong ignition conditions have been studied in a 199 mm inner diameter and 30.8 m long horizontal tube. A fuel gas/air manifold assembly was used to introduce methane and air into the experimental tube, and an array of 44 equally spaced dust dispersion units was used to disperse coal dust particles into the tube. The methane/coal dust/air mixture was ignited by a 7 m long epoxypropane mist cloud explosion. A deflagration-to-detonation transition (DDT) was observed, and a self-sustained detonation wave characterized by the existence of a transverse wave was propagated in the methane/coal dust/air mixtures.The suppressing effects on methane/coal dust/air mixture explosions of three solid particle suppressing agents have been studied. Coal dust and the suppressing agent were injected into the experimental tube by the dust dispersion units. The length of the suppression was 14 m. The suppression agents examined in this study comprised ABC powder, SiO₂ powder, and rock dust powder (CaCO₃). Methane/coal dust/air explosions can be efficiently suppressed by the suppression agents characterized by the rapid decrease in overpressure and propagating velocity of the explosion waves.     

Numerical modelling of dust-layered detonation structure in a narrow tube

The problems of lifting and dispersing of a dust layer behind the propagating shock wave as well as ignition, combustion of coal particles and dust-layered detonation formation in a tube are numerically investigated. The layered detonation is formed at large distance from the place of the primary shock wave initiation (～100 diameters of the tube). The strong oblique transverse shocks caused by combustion zone were discovered. The acceleration of leading shock wave and dust-layered detonation formation are connected with increasing and intensification of combustion zone which strongly depends on arising system of the oblique waves due to the development of the dust layer instabilities and vice versa. In the applied model, the moving medium is treated as a two-phase, two-velocity and two-temperature continuum with mechanical and thermal interphase interaction. The numerical procedure is based on the finite-volume approach and is implemented for parallel computing. The results obtained are of interest for applications in predictive modelling of accidents in industrial systems with reactive dust.     

大尺度管道中煤粉爆炸的试验研究

煤粉爆炸传播特性的试验研究对于深入了解和预防矿井煤尘爆炸事故有重要意义。利用自制的长29.6 m,内径199 mm的试验管道,对煤粉-空气混合物爆炸压力波传播过程进行试验研究。采用压电传感器测量压力信号,得到爆炸压力波沿管道传播过程中不同测点处的压力时间历程曲线,探讨煤粉粒度和浓度对其爆炸超压的影响规律。结果表明:煤粉-空气混和物在弱点火条件下能够实现粉尘火焰的形成和传播。煤粉爆炸压力波传播过程中速度为400~430 m/s,峰值超压为68~72 kPa。煤粉爆炸峰值超压随着煤粉粒度的减小而增大,但煤粉粒度对其爆炸峰值超压的影响程度随着浓度的增加将逐渐减弱。     

Experimental study on the minimum explosion concentration of anthracite dust: The roles of O2 mole fraction,inert gas and CH4 addition

The explosion characteristics of anthracite coal dust with/without small amount of CH₄ (1.14 vol %) were investigated by using a 20 L spherical explosion apparatus with an emphasis on the roles of oxygen mole fraction and inert gas. Two methods based on overpressure and combustion duration time were used to determine the minimum explosion concentration (MEC) or the lower explosion limit (LEL) of the pure anthracite coal dust and the hybrid coal-methane mixtures, respectively. The experiment results showed that increasing oxygen mole fraction increases the explosion risk of coal dust: with increasing oxygen mole fraction, the explosion pressure (P_ex) and the rate of explosion pressure rise ((dp/dt)_ex)) increase, while MEC decreases. The explosion risk of anthracite dust was found to be lower after replacing N₂ with CO₂, suggesting that CO₂ has a better inhibition effect on explosion mainly due to its higher specific heat. However, the addition of 1.14% CH₄ moderates the inhibition effect of CO₂ and the promotion effect of O₂ on anthracite dust explosion for some extent, increasing explosion severity and reducing the MEC of anthracite dust. For hybrid anthracite/CH₄ mixture explosions, Barknecht's curve was found to be more accurate and conservative than Chatelier's line, but neither are sufficient from the safety considerations. The experimental results provide a certain help for the explosion prevention and suppression in carbonaceous dust industries.     

Numerical study of dust lifting in a channel with vertical obstacles

In the paper, several results of numerical computation of multiphase flows in a channel with complex geometry are considered. The objective of the research was to study the dust lifting process from a layer behind a shock wave in a rectangular channel with vertical obstacles in the upper part of the tube. It is to be shown that that kind and also any sort of geometry may crucially change the whole phenomena of dust enhancement and of combustion. This is very important for safety in, for example, coal mines where channels are usually of more sophisticated structure than is usually assumed by most researchers.     

Study on the preparation of novel NiB/Hβ-Al2O3 micro-mesoporous suppressant and its inhibition mechanism of coal dust explosion flame

Coal dust explosion is one of the serious accidents in the coal industry. It is of great significance to study the flame suppression of coal dust explosions. In this paper, a novel active component NiB with amorphous structure for explosion suppression was synthesized by the chemical reduction method. Furthermore, the novel explosion suppressant NiB/Hβ-Al₂O₃ was prepared through the kneading method by loading novel amorphous NiB nanoparticles on Hβ-Al₂O₃ with the micro-mesoporous structure as the carrier. The morphology and structure of NiB/Hβ-Al₂O₃ were characterized by XRD, BET, SEM, and FTIR, which showed that the NiB/Hβ-Al₂O₃ has proper pore structure and NiB nanoparticles are uniformly distributed as active components for explosion suppression in suppressant. Hartmann tube was used to evaluate the inhibition of coal dust deflagration. The results showed that the flame propagation distance and velocity decreased with the increase of the explosion suppressant. When the addition of explosion suppressant was 30 wt%, the explosion of coal dust was suppressed effectively. Furthermore, combing with the analysis results of the products after coal dust deflagration, the physical and chemical inhibition mechanism of the novel NiB/Hβ-Al₂O₃ explosion suppressant on coal dust deflagration was put forward.     

Review of the DESC project

Dust Explosion Simulation Code (DESC) was a project supported by the European Commission under the Fifth Framework Programme. The main purpose of the project was to develop a simulation tool based on computational fluid dynamics (CFD) that could predict the potential consequences of industrial dust explosions in complex geometries. Partners in the DESC consortium performed experimental work on a wide range of topics related to dust explosions, including dust lifting by flow or shock waves, flame propagation in vertical pipes, dispersion-induced turbulence and flame propagation in closed vessels, dust explosions in closed and vented interconnected vessel systems, and measurements in real process plants. The new CFD code DESC is based on the existing CFD code FLame ACceleration Simulator (FLACS) for gas explosions. The modelling approach adopted in the first version entails the extraction of combustion parameters from pressure–time histories measured in standardized 20-l explosion vessels. The present paper summarizes the main experimental results obtained during the DESC project, with a view to their relevance regarding dust explosion modelling, and describes the modelling of flow and combustion in the first version of the DESC code. Capabilities and limitations of the code are discussed, both in light of its ability to reproduce experimental results, and as a practical tool in the field of dust explosion safety.     

Dynamics of dust dispersion from the layer behind the propagating shock wave

The aim of the research was to investigate experimentally the process of dust lifting from a layer. The delay in lifting the dust from the layer behind the propagating shock wave and the vertical velocity of the dust cloud were calculated from the dust concentration measurements. Quantitative relations between those measurements and the parameters of the gas flow are presented. The results were compared with those obtained from the analysis of the frame pictures of the process. The pictures were made by using a high-speed camera working together with a Schlieren system. The measurements of the dust concentration behind the propagating shock wave are presented and analysed.The research was carried out for two selected dusts: black coal dust and silicon dust, and for different initial conditions: three shock wave velocities: 450, 490 and 518 m/s and three dust layer thickness equal to 0.1, 0.4 and 0.8 mm. Measurement results of the mean vertical component of dust cloud velocity between the layer and the first laser beam will be used in a new model, where the dust dispersing process is modelled as an injection of the dust from the layer. The dust concentration measurements will be very useful for validation of the model.     

Influences of coal dust components on the explosibility of hybrid mixtures of methane and coal dust

In order to study the influences of coal dust components on the explosibility of hybrid mixture of methane and coal dust, four kinds of coal dust with different components were selected in this study. Using the standard 20 L sphere, the maximum explosion pressure, explosion index and lower explosion limits of methane/coal dust mixtures were measured. The results show that the addition of methane to different kinds of coal dust can all clearly increase their maximum explosion pressure and explosion index and decrease their minimum explosion concentration. However, the increase in the maximum explosion pressure and explosion index is more significant for coal dust with lower volatile content, while the decrease in the minimum explosion concentration is more significant for coal dust with higher volatile content. It is concluded that the influence of methane on the explosion severity is more pronounced for coal dust with lower volatile content, but on ignition sensitivity it is more pronounced for coal dust with higher volatile content. Bartknecht model for predicting the lower explosion limits of methane/coal dust mixture has better applicability than Le Chatelier model and Jiang model. Especially, it is more suitable for hybrid mixtures of methane and high volatile coal dust.     

A correlation of the lower flammability limit for hybrid mixtures

Hybrid mixtures are widely encountered in industries such as coal mines, paint factories, pharmaceutical industries, or grain elevators. Hybrid mixtures explosions involving dust and gas can cause great loss of lives and properties. The lower flammability limit (LFL) is a critical parameter when conducting a hazard assessment or developing mitigation methods for processes involving hybrid mixtures. Unlike unitary dust or gas explosions, which have been widely studied in past decades, only minimal research focuses on hybrid mixtures, and data concerning hybrid mixtures can rarely be found. Although methods to predict the LFL have been developed by using either Le Chatelier's Law, which was initially proposed for homogeneous gas mixtures, or the Bartknecht curve, which was adopted for only certain hybrid mixtures, significant deviations still remain. A more accurate correlation to predict an LFL for a hybrid mixtures explosion is necessary for risk assessment. This work focuses on the study of hybrid mixtures explosions in a 36 L dust explosion apparatus including mixtures of methane/niacin, methane/cornstarch, ethane/niacin and ethylene/niacin in air. By utilizing basic characteristics of unitary dust or gas explosions, a new formula is proposed to improve the prediction of the LFL of the mixture. The new formula is consistent with Le Chatelier's Law.     

Preparation and performance of novel APP/NaY–Fe suppressant for coal dust explosion

Coal dust explosion occurs easily in the coal chemical industry. To ensure safety in industrial production, NaY zeolite was used as carrier modified with Fe ions and combined with ammonium polyphosphate (APP) to prepare a novel composite suppressant for coal dust explosion. The explosion suppression performance of novel APP/NaY–Fe suppressant was investigated by flame propagation inhibition experiments. The results show that Fe ion modification can effectively improve the explosion suppression performance. By increasing content, the explosion suppression performance of the explosion suppressant increases. The maximum explosion pressure P_max of coal dust drops to 0.13 MPa when 50 wt% explosion suppressants were added, and the coal dust explosion cannot continue to expand. Complete suppression of explosion could be achieved by adding 66 wt% explosion suppressants. Combined with XRD, SEM and TG results, the explosion suppression mechanism was proposed. The novel explosion suppressant has high thermal stability, good dispersity and its explosion suppression components distribute uniformly. It shows good explosion suppression performance by the synergistic effect among explosion-suppression components.     

燃烧管中烟煤粉粉尘云传播参数的试验研究

利用自行设计的长29.6 m,内径199 mm,配有特殊扬尘装置的大犁卧式燃烧爆炸管道试验系统,对弱点火条件下烟煤粉与空气两相悬浮流中的爆炸过程进行了试验研究,用压电传感器测量了管内各测点的压力信号,观测到快速爆燃的状态稳定,分析了爆燃波稳定传播机理.结果表明:在煤粉浓度为300g/m~3及弱点火条件下,悬浮烟煤粉粉尘云中爆燃波能够稳定传播,且稳态传播距离持续20 m以上,峰值超压和波速平均值分别约为70 kPa和430m/s.     

固体惰性介质对煤粉爆炸压力的影响研究

通过对固体惰性介质在减轻煤粉爆炸作用的实验研究,给出影响固体惰化剂作用效果的主要影响因素。实验分别选用来自加拿大和中国的3种煤粉和石灰石,对每种实验样品的成分、粒度都进行分析。用20L球形容器进行实验,测定煤粉中加入不同含量的石灰石后煤粉爆炸的Pmax和(dp/dt)max值。结果表明,石灰石能够起到减轻煤粉爆炸影响的作用,并且随着煤粉粒度的减小,要达到相同的抑爆效果需要的石灰石的用量将加大。