The investigation of correlated factors of external explosion during the venting process

Experimental investigations were done in the paper for the process of venting explosion in a ϕ200 mm×400 mm cylindrical vessel. Compared with the normal venting process, the phenomenon of external explosion was observed and discussed first. Moreover, when CH₄–air mixture gases were used and the vent diameter was 55 mm, three kinds of condition were selected: ϕ=0.8, ϕ=1.0 and ϕ=1.3. And two ignition positions were selected: at the vessel center and at the bottom. Then the venting processes influenced by these factors were experimented and discussed, too.     

水平管道泄爆面开启压力对甲烷爆燃压力的影响*

为了研究泄爆面不同开启压力对甲烷爆燃压力的影响,针对受限空间内甲烷/空气混合物爆燃传播过程,建立由水平管道构成的数值模型。研究结果表明:水平管道内存在爆燃压力积聚和泄放的双重效应,随着泄爆面开启压力的增加,测点爆燃压力峰值增大而且测点间爆燃压力峰值差异逐渐减小;在泄爆面不同开启压力条件下,泄压效应造成泄爆面及外部空气域爆燃压力衰减,随着泄爆面开启压力的增加,泄爆面开启时间近似呈线性增大;与水平管道内和泄爆面附近测点相比,水平管道外侧测点的爆燃压力峰值和振荡幅值均显著衰减,而且随着泄爆面开启压力的增加,测点爆燃压力峰值及测点间爆燃压力峰值差异均逐渐增大。     

连通容器气体密闭爆炸与泄爆过程的实验研究

利用球型容器与管道组合,开展连通容器气体爆炸与泄爆实验,分析连通条件下,火焰在管道中的传播过程及其对起爆容器和传爆容器的压力影响。实验结果表明:连通容器气体爆炸中,火焰从起爆容器到传爆容器传播经历了一段不断加速,但加速度不断减小的过程;泄爆过程中,火焰传播过程与密闭爆炸时基本一致。管道中火焰加速传播,使得传爆容器的爆炸压力和强度相较于作为起爆容器时均明显增加,危险更大,采用与起爆容器相同的泄爆面积,无法满足对连通容器中传爆容器的泄爆。同时,泄爆是一个快速的能量泄放过程应选择合理的泄爆方式,防止二次危害。     

Application and effect of negative pressure chambers on pipeline explosion venting

Explosion venting is a frequently-used way to lower explosion pressure and accident loss. Recently, studies of vessel explosion venting have received much attention, while little attention has been paid to pipe explosion venting. This study researched the characteristics of explosion venting for Coal Bed Methane (CBM) transfer pipe, and proposed the way of explosion venting to chamber in order to avoid the influence of explosion venting on external environment, and investigated the effects of explosion venting to atmosphere and chamber. When explosion venting to atmosphere, the average explosion impulse 4.89 kPa s; when explosion venting to 0 MPa (atmospheric pressure) chamber, average explosion impulse is 7.52 kPa s; when explosion venting to −0.01 MPa chamber, explosion flame and pressure obviously drop, and average explosion impulse decreases to 4.08 kPa s; when explosion venting to −0.09 MPa chamber, explosion flame goes out and average explosion impulse is 1.45 kPa s. Thus, the effect of explosion venting to negative chamber is far better than that to atmospheric chamber. Negative chamber can absorb more explosion gas and energy, increase stretch of explosion flame, and eliminate free radical of gas explosion. All these can promote the effect of explosion venting to negative chamber.     

Characteristics of dust explosion venting pressure and flame under high activation pressure

A 20 L spherical explosive device with a venting diameter of 110 mm was used to study the vented pressure and flame propagation characteristics of corn dust explosion with an activation pressure of 0.78–2.1 bar and a dust concentration of 400∼900 g/m³. And the formation and prevention of secondary vented flame are analyzed and discussed. The results show that the maximum reduced explosion overpressure increases with the activation pressure, and the vented flame length and propagation speed increase first and then decrease with time. The pressure and flame venting process models are established, and the region where the secondary flame occurs is predicted. Whether there is pressure accompanying or not in the venting process, the flame venting process is divided into two stages: overpressure venting and normal pressure venting. In the overpressure venting stage, the flame shape gradually changes from under-expanded jet flame to turbulent jet flame. In the normal pressure venting stage, the flame form is a turbulent combustion flame, and a secondary flame occurs under certain conditions. The bleed flames within the test range are divided into three regions and four types according to the shape of the flame and whether there is a secondary flame. The analysis found that when the activation pressure is 0.78 bar and the dust concentration is less than 500 g/m³, there will be no secondary flame. Therefore, to prevent secondary flames, it is necessary to reduce the activation pressure and dust concentration. When the dust concentration is greater than 600 g/m³, the critical dust concentration of the secondary flame gradually increases with the increase of the activation pressure. Therefore, when the dust concentration is not controllable, a higher activation pressure can be selected based on comprehensive consideration of the activation pressure and destruction pressure of the device to prevent the occurrence of the secondary flame.     

Experimental study on gas explosion and venting process in interconnected vessels

A pilot scale interconnected vessels experiment system was established, and the closed and vented gas explosion characteristics in the system were studied, using 10% methane–air mixture. Regularity of pressure variation in vessels and flame propagation in linked pipes was analyzed. Furthermore, the effects of transmission style, ignition position, pipe length, and initial pressure on explosion severity were discussed. For the closed explosion: explosion in interconnected vessels presents strongly destructive power to secondary vessel, especially transmission from the big vessel to the small one; the worst ignition position is shifting from ignition in the interconnected pipe to the walls of the two vessels; as far as ignition in big vessel is concerned, the peak pressure in secondary vessel increases with the pipe length much faster than that for ignition in small vessel; the peak pressures in two vessels are approximate linear functions of initial pressure. For the vented explosion: the transmission style and interconnected pipe length have significant impacts on the effect of venting on the protection; in order to obtain the better venting effect, the use of a divergent interconnected pipe from the big vessel to the small one in industry is advised and it is necessary to reduce the interconnected pipe length as far as possible or install flame arrester in the interconnected pipe.     

竖直分支管道泄爆开启压力对甲烷爆燃压力的影响研究

针对市政排污管网等典型受限空间内可燃气体爆燃风险,建立由水平管道和竖直分支管道构成的数值模型,研究竖直分支管道不同泄爆开启压力对甲烷爆燃压力的影响.研究结果表明:不同泄爆开启压力条件下,管道内存在爆燃压力积聚和泄放的双重效应;水平管道内各测点压力时程曲线均表现为先增大后减小而后出现亥姆霍兹振荡,随着与爆源距离的增加,初...     

关于抗爆与泄爆设计方法的研究

文章就抗爆与泄爆设计的各个方面做了介绍。     

泄爆面积比对泄爆门封闭泄爆特性的影响研究

为研究泄爆面积比对泄爆门泄爆特性的影响,运用FLUENT软件建立煤矿井下1:1巷道模型,在不同泄爆面积比的工况下对瓦斯爆炸传播规律及泄爆过程进行模拟,分析其变化特征和封闭泄爆效果.结果表明:S0工况条件下,压力和温度衰减后保持在0.29 MPa和565 K;S1～S4工况条件下,S4比S1,S2和S3达到封闭状态时间快...     

Effect of the vent burst pressure on explosion venting of rich methane-air mixtures in a cylindrical vessel

The effect of the vent burst pressure on explosion venting of a rich methane-air mixture was experimentally investigated in a small cylindrical vessel. The experimental results show that Helmholtz oscillation of the internal flame bubble of the methane-air mixture can occur in a vessel with a vent area much smaller than that reported by previous researchers, and the period of Helmholtz oscillation decreases slightly when the vent burst pressure increases. The maximum overpressure in the vessel increases approximately linearly with the increase in the vent burst pressure; however, the pressure peaks induced by Helmholtz oscillation always remain approximately several kilopascals. The external flame reaches its maximum length in a few milliseconds after vent failure and then oscillates in accordance with the pressure oscillation in the vessel. The maximum length of the external flame increases, but its duration time decreases with the increase in the vent burst pressure.     

Experimental study of the venting characteristics of dust explosion through a vent duct

To further understand the dynamic mechanism of dust explosion through a vent duct, we designed a small-scale cylindrical vessel connected with a vent duct and performed a dust explosion venting experiment under different opening pressures using corn starch as the explosive medium in this study. The results show that weakening effect of duct on venting is positively correlated with the opening pressure. The explosion pressure in the duct presents a three-peak-structure with time, successively caused by the membrane breaking shock wave, the secondary explosion in the tube, and the continuous combustion, and decreases gradually with the propagation distance. Meanwhile, the three pressure peaks are positively correlated with the opening pressure, while the time interval between them goes to contrary. The increase of opening pressure leads to the increase of secondary explosion intensity and reverse flow in the vessel, further accelerates the reaction rate in the vessel, and then shortens the duration of combustion in the vessel until the phenomenon of flame reignition in the vessel disappears.     

Experimental study of flame acceleration and the deflagration-to-detonation transition under conditions of transverse venting

Results of experiments on critical conditions for flame acceleration and the deflagration-to-detonation transition in tubes with transverse venting are presented. Tests were made with hydrogen mixtures in two tubes (inner diameter of 46 and 92 mm) with obstacles. Ratios of vent area to total tube area were 0.2 and 0.4. Venting was shown to influence flame acceleration significantly. The greater the vent ratio, the more reactive the mixture necessary for development of fast flames. Critical conditions for flame acceleration in tubes with venting, expressed through a critical mixture expansion ratio σ_cr, were found to be σ_cr/σ₀1+2, where σ₀ is the critical value for a closed tube. Critical conditions for detonation onset in a vented tube were found to be very close to those in a closed tube with similar configuration of obstacles.     

泄爆导管对球形容器内气体爆炸泄放过程影响的试验

设计了球形容器内气体爆炸通过导管泄爆的试验系统,选用体积分数为10%(特殊说明除外)的甲烷和空气预混气体开展试验,研究了泄爆导管长度、容器容积、点火位置、气体体积分数、破膜压力等因素的影响。结果表明:泄爆导管越长,容器内的正压力峰值和负压力峰值越大;密闭爆炸时,球形容器的容积对爆炸压力峰值几乎无影响;不同容积球形容器内气体爆炸通过相同导管泄爆时(导管长度均为6 m,直径均为0.06 m),容积大的容器内的压力锋值为小容器压力值的3.3倍,且大容器内的压力上升速率也明显高于密闭爆炸的情况;有泄爆导管存在时,尾部点火容器内的压力峰值高于中心点火;泄爆导管的存在使得容器内的压力峰值高于直接泄爆时的压力峰值;无论有、无泄爆导管,容器内的压力峰值均随破膜压力增加而增加,但差值越来越小,说明导管的存在对容器爆炸泄爆过程的影响趋向缓和,但导管的存在总是阻碍了泄爆过程,增加了爆炸的严重程度,因此,在泄爆设计时要充分考虑导管的影响,适当提高容器自身的耐压强度。     

基于1 m3泄爆装置的墨粉爆炸泄压机制研究*

为了研究墨粉在爆炸泄压过程中燃烧与流动的变化机制,通过改变泄爆片尺寸、墨粉浓度以及泄爆片的惯性力等参数对爆炸泄放过程中反应釜中压力以及外场火焰形态变化进行试验研究,同时与完全封闭空间内不同墨粉浓度的压力曲线对比。研究结果表明:相同泄爆开口尺寸下,粉尘浓度与受控爆炸压力（采用爆炸泄压保护措施后工业腔体内产生的压力）负相关;开口尺寸增加可以提升泄压效率;结合外场火焰形态的变化情况揭示声动火焰不稳定性对反应釜中压力发展的影响;通过无惯性泄爆试验的对比证明泄爆片惯性对受控爆炸压力的影响不可忽视。     

构造煤承压过程瓦斯渗透特性实验研究

构造煤具有瓦斯含量高、渗透率低等特征,是瓦斯抽采和灾害预防的难点。在采用“二次成型”法制取原煤样试件的基础上使用自行设计的“三轴应力瓦斯渗透性模拟实验装置”通过“应力-渗透性”实验,针对构造煤原煤试件不同瓦斯压力条件下的应力加、卸载过程的瓦斯渗透规律进行了研究。实验结果表明:加载阶段,随着加载应力的增大渗透率降低,初期阶段降幅最为急剧,围压升到3 MPa时,渗透率均下降近65%;卸载阶段渗透率随着应力的减小而增大,围压完全卸载后渗透率只恢复到初始值的25%;同样的应力条件下,煤基质收缩对构造煤的影响作用大于有效应力的增加,渗透率随着其内部瓦斯压力的降低而增大。实验结果可为构造煤“卸压增透”效果最佳化提供参考,进一步完善低渗透率煤层的瓦斯抽采理论及方法体系。     

A simple design method of dust explosion venting size at elevated static activation pressure

To develop the application of explosion venting technology in high-pressure vessels, a new model for the design of dust explosion venting size was presented, which took the physicochemical phenomenon deriving from the elevation of the static activation pressure into account. Firstly, for confined pressure rise, the wall quenching effect originating from the dust flame thickness was considered by adopting the three-zone model. Secondly, for the venting pressure rise, the energy loss due to the discharge of high-energy burnt mixture (quantified as the specific surface area loss of the flame) was taken into account and the induced turbulence factor was introduced. Thirdly, for the venting pressure drop, a dynamic pressure relief capability evaluation model which takes into account the flame morphology evolution (tear-shaped flame) and the proportion of discharged mixture (relative volume ratio) at elevated activation pressure was proposed. The predicted maximum reduced pressure and venting size were checked against the PMMA explosion experiments and a more great performance was obtained compared with standards.     

Experimental study on water sealing of fire barriers and explosion venting of large-scale pipeline with low-concentration gas

Low-concentration gas transported in pipelines may lead to explosion accidents because gas with a concentration of less than 30% is prone to explode. To reduce the incidence of gas explosions, water sealing of fire barriers is implemented, and explosion venting devices are installed along the pipeline. To investigate their suppression effect on low-concentration gas explosion, experiments using methane–air premixed gas under different conditions were implemented on a DN500 pipeline test system. The effects of three types of explosion venting forms (rupture disc, asbestos board, and plastic film) on explosion overpressure and flame were compared and analysed. Results show that the rupture disc, asbestos board, and plastic film can achieve adequate explosion venting, causing the peak decay rates of explosion overpressure to reach 82.37%, 81.72%, and 90.79%, respectively. The foregoing indicates that the greater the static activation pressure of the explosion venting form, the higher the peak explosion overpressure at each measurement point. Moreover, the shorter the explosion flame duration, the greater the flame propagation velocity. The research results provide an essential theoretical foundation for the effective suppression of gas explosion accidents in the process of low-concentration gas transportation.     

文丘里洗涤器压力损失试验研究

使用空气-水系统,试验研究文丘里洗涤器操作参数(液气比、喉管气速)及喉管长度对其压力损失的影响.结果表明,喉管气速对压力损失的影响比液气比的大,压力损失随液气比增加呈线性增加,而随喉管气速的变化基本为平方关系.在此基础上,探讨了在文丘里洗涤器设计时如何根据捕集效率优化设计文丘里喉管长度.     

外墙保温材料在火灾中的燃烧现象小尺寸实验研究

利用外墙保温材料的小尺寸燃烧实验来研究外墙保温材料在火灾过程中的燃烧特性,分析总结外墙保温材料在火灾过程中的燃烧现象.建立外墙保温材料火灾实验模型,对外墙保温材料火灾实验的实验方法以及数据测定方式进行了介绍.采用不同阻燃性质的保温材料,研究阻燃成分阻止竖向燃烧的效果.观察不同的保温材料在燃烧过程中的点燃性能.根据材料的阻燃性能、点火位置、固定方式的不同,总结燃烧痕迹的变化规律.分析非阻燃材料在燃烧的过程中的熔滴生成,发现产生的熔滴对未燃保温材料的点燃现象.观察不同的保温材料在燃烧过程中的烟气生成及烟气层的形成.通过小尺寸火灾试验的方法来研究建筑外墙保温材料火灾的特性,提出使用阻燃型外墙保温材料的必要性.     

障碍物对采用泄爆管泄放气体爆炸影响的数值模拟

采用k-ε湍流模型和漩涡耗散概念模型(EDC)建立了泄爆管泄放气体爆炸的模型,并模拟容器内置障碍物时泄爆管泄放气体爆炸火焰的传播过程,分析了障碍物形状、阻塞率、位置、个数对超压(pred)和压力上升速率的影响.结果表明:障碍物的出现导致燃烧速度和pred上升,正方形障碍物导致的爆炸后果最严重;增加障碍物个数或增大障碍物阻塞率均可增加超压和燃烧速度;障碍物置于容器中心,爆炸后果较强,而靠近点火源或泄爆口,后果有所减弱.