Effect of initial temperature on the explosion pressure of various liquid fuels and their blends

In this work, the effect of initial temperature on the explosion pressure, P_ex, of various liquid fuels (isooctane, toluene and methanol) and their blends (isooctane-toluene and methanol-toluene, with three different fuel-fuel ratios) was investigated by performing experiments in a 20-l sphere at different concentrations of vaporized fuel in air. The initial temperature was varied from 333 K to 413 K.Results show that, as the fuel-air equivalence ratio, Φ, is increased, a transition occurs from a “thermodynamics-driven” explosion regime to a “radiant heat losses-driven” explosion regime. The maximum pressure, P_max, is found in the former regime (Φ < 3), which is characterized by a trend of decreasing P_ex with increasing initial temperature. This trend has been explained by thermodynamics. In the latter regime (Φ > 3), P_ex increases with increasing initial temperature. This trend has been addressed to the decrease in emissivity (and, thus, radiant heat losses) with the increase in temperature.     

Minimum Ignition Temperature of layer and cloud dust mixtures

The prevention of dust explosions is still a challenge for the process industry. Ignition, in particular, is a phenomenon that is still not completely understood. As a consequence, safety conditions pertaining to ignition suppression are rarely identified to an adequate level. It is well known that, in general, the ignition attitude of a dust depends on several factors, such as the nature of the chemical, the particle size, moisture content, etc., but there is still a lack of knowledge on the effect of the single variables.This paper has the aim of providing data on the Minimum Ignition Temperatures of dust mixtures obtained from a mixing of a combustible dust (flour, lactose, sucrose, sulphur) and an inert dust (limestone, extinguishing powders) as well as from the mixing of two different combustible dusts. Various mixtures with different weight ratios have been tested in a Godbert Greenwald (GG) furnace and on a hot plate in order to measure the effect of mixture composition on the Minimum Ignition Temperature (MIT_L) of the layer and on the Minimum Ignition Temperature (MIT_C) of the cloud. In order to further verify the effects of inert dust particle size, inerts sieved to different size ranges have been tested separately. Generally, both MIT_L and MIT_C increase as the inert content is increased. MIT_C is poorly affected by inert particle size when limestone is used. The MIT_L of pure flour is higher than the MIT_L of mixtures containing up to 40% of 32–75 μm of limestone. This was probably due to the behaviour of pure flour during the test, which demonstrated strong tendency to produce char, cracks in the layer and detachment from the hot plate.     

Dynamic response and effect of apertures on explosion parameters of flameproof apparatus

Explosion parameters for closed flameproof apparatus are changed when apertures like gap (e.g. push button) and porous structures (breathing element) are introduced on the cover or wall of the flameproof enclosures. Similarly, an interconnecting tube between two enclosures, results in significant change in explosion parameters. It is observed that the maximum explosion pressure, maximum rate of pressure rise and severity index are higher for enclosures with apertures on cover or body than that of enclosures without apertures. In case of two interconnected identical enclosures, the explosion parameters are increased in the secondary enclosure and higher than that of primary enclosure and also of isolated enclosure.     

Theoretical estimation of the lower flammability limit of fuel-air mixtures at elevated temperatures and pressures

We present an approach for predicting the lower flammability limits of combustible gas in air. The influence of initial pressure and temperature on lower flammability limit has been examined in this study. The lower flammability limits of methane, ethylene and propane in air are estimated numerically at the pressure from one to 100 bar and the temperature from ambient to 1200 K. It was found that the predicted LFLs of methane, ethylene and propane decrease slightly with the elevated pressure at the high temperature. The LFLs variation for methane-air mixture is 0.17, 0.18, 0.18 volume% with the initial pressure from one to 100  bar at the initial temperature of 800 K, 1000 K and 1200 K respectively, which is significantly higher than that at lower temperature. And the LFL of methane-air mixture at 1200 K and 100 bar reaches 1.03 volume% which is much lower than that at 1 bar and ambient temperature. On the other hand, the LFLs variation is 0.11–0.12 volume% for ethylene-air mixture and 0.06–0.07 volume% for propane-air mixture with the initial temperature from 800 K to 1200 K at the same range of pressure. The LFL values at high temperatures and pressures represent higher risk of explosion.     

Propagation of ethylene–air flames in closed cylindrical vessels with asymmetrical ignition

A study of explosions in several elongated cylindrical vessels with length to diameter L/D = 2.4–20.7 and ignition at vessel's bottom is reported. Ethylene–air mixtures with variable concentration between 3.0 and 10.0 vol% and pressures between 0.30 and 1.80 bara were experimentally investigated at ambient initial temperature. For the whole range of ethylene concentration, several characteristic stages of flame propagation were observed. The height and rate of pressure rise in these stages were found to depend on ethylene concentration, on volume and asymmetry ratio L/D of each vessel. High rates of pressure rise were found in the early stage; in later stages lower rates of pressure rise were observed due to the increase of heat losses. The peak explosion pressures and the maximum rates of pressure rise differ strongly from those measured in centrally ignited explosions, in all examined vessels. In elongated vessels, smooth p(t) records have been obtained for the explosions of lean C₂H₄–air mixtures. In stoichiometric and rich mixtures, pressure oscillations appear even at initial pressures below ambient, resulting in significant overpressures as compared to compact vessels. In the stoichiometric mixture, the frequency of the oscillations was close to the fundamental characteristic frequency of the tube.     

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.     

液化石油气罐区危险性的定量评价

液化石油气罐区的主要危险是贮罐区发生火灾、爆炸事故。运用数学模型对液化石油气贮罐的危险性进行定量化评价，估算其爆炸事故的严重程度、波及范围、影响程度等     

工业粉尘“二次爆炸”过程研究

开展了工业粉尘“二次爆炸”过程实验室研究工作。对玉米淀粉、小麦粉等粮食粉尘进行了研究，得到了“二次爆炸”发展过程以及最后形成的爆轰波特性，还进一步研究了粉尘层冲击波卷扬过程和分析讨论了粉尘“二次爆炸”过程的影响因素。     

硝铵炸药生产中的事故防范

通过分析硝铵炸药生产中发生的火灾和爆炸事故，认为硝铵混合物在高温条件下的热分解是引发这类事故的主要原因；还给出硝酸铵热分解的要点，并提出预防恶性事故的措施。【关键词】     

城镇燃气爆炸极限影响因素与计算误差的分析

可燃气体的爆炸极限是消防报警和安全使用燃气的重要参数之一 ,笔者对影响城市燃气爆炸极限的因素进行了讨论 ;同时指出有关文献上公布的燃气爆炸极限是一定条件下测定的 ,当空气中含有略低于文献公布爆炸下限或略高于文献公布爆炸上限的可燃气体 ,在一定的条件下也可能产生爆炸。对燃气爆炸极限的计算方法及其计算误差进行了分析 ,指出在使用测试或计算爆炸极限时应考虑安全系数