粉尘爆炸泄压面积计算及影响因素分析

随着涉粉行业各类企业数量的增长,以及粉尘爆炸产生的巨大危害,企业对粉尘泄爆、防爆越来越重视。在粉尘泄爆方面,泄爆装置的泄放面积影响最大泄爆压力,国内外不同标准的计算方法也有区别,因此针对不同标准的计算方法做出了比较并举例计算说明,为泄爆装置尺寸的选择提供理论依据。     

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780,260,50 ms,封闭时间最大节省70.91%;随着泄爆面积比的增大,封闭火区内的压力的峰值、峰值数量和达到封闭状态时间减小,泄爆能力增强;火焰速度峰值和衰减速率增大;温度的初始峰值、峰值数量和达到稳定状态时间减小,最大峰值反而增大,说明泄爆门对瓦斯爆炸火焰无抑制作用。     

铝粉爆炸无火焰泄压技术及装备研究

为有效防止粉尘爆炸泄爆引起的二次爆炸及火灾问题，基于泄压理论、消火机理，设计开发无火焰泄压装置，装置主要由消火结构、底座、爆破片及夹持机构组成，消火结构由不锈钢金属丝网组成。选择铝粉尘为测试粉尘，通过自建除尘系统试验平台进行试验研究。结果表明:无火焰泄压装置可成功阻止火焰传播，装置释放的冲击波在5 m外均小于5 kPa，除尘系统内部最大泄爆压力为0.1 MPa，装置前端火焰传播速度均大于100 m/s。     

泄爆面积对柱形容器泄爆过程压力影响

为了研究泄爆面积对柱形压力容器泄爆过程中压力变化的影响,采用经典流体力学软件FLU ENT在泄爆口直径分别为50、80、100mm情况下对容器内甲烷和空气混合气体泄爆过程进行了数值模拟,研究了不同情况下容器内压力发展变化规律以及爆炸流场参数分布。结果表明当泄爆压力为0.04MPa,泄爆口直径50mm时,泄爆口开启后压力容器内压力呈现继续上升趋势;泄爆口直径为80、100mm时,泄爆口开启后压力均立即下降,采用直径100mm泄爆口时压力下降速率更快,容器内压力降至环境压力所需时间更短。     

化工装置气体爆炸泄压的研究进展

从实验研究和理论分析两方面,总结了单容器和连通容器气体爆炸泄压的研究现状和成果。单容器的实验研究介绍了直接泄爆和泄爆导管泄爆两方面,理论研究介绍了直接泄爆的经验模型。连通容器主要介绍了实验研究。此外,分析了现有研究工作的不足,提出了该领域未来的研究方向。     

泄爆导管长度对除尘器泄爆影响的模拟分析

使用FLACS软件DESC模块,对连接不同长度泄爆导管的除尘器泄爆模型进行了模拟,研究泄爆过程中除尘器内部以及泄爆方向上的超压与高温变化规律。研究结果表明,泄爆导管内部要比除尘器内部先达到最大爆炸压力,但压力值却要小于除尘器内的超压;在泄爆方向上,距泄爆口越远,导管内的爆炸压力也越小,且在泄爆导管末端压力下降的趋势明显加快;随着导管长度从1 m增加到6 m,除尘器与泄爆导管内部的最大爆炸压力也逐渐增大,在泄爆导管长6 m时,除尘器内部达到了81.8 kPa的最大爆炸压力;而对于不同长度的导管泄爆模型,泄爆导管内部都达到了2 000 K左右的高温,且导管越长,最大爆炸温度所能持续的时间也越长。     

洗煤厂干燥系统泄爆设计研究

在洗煤厂的干燥系统中极易发生煤粉燃烧爆炸事故,为了减轻爆炸危害,对干燥系统进行泄爆设计尤其重要。应用20 L粉尘爆炸特性测试系统,对某洗煤厂煤样煤尘云爆炸性参数进行测试,得出最大爆炸压力0.74 MPa,最大爆炸压力上升速率为58.5 MPa/s,计算出最大爆炸指数为15.88 MPa/(m·s)。根据测试结果计算出洗煤厂干燥系统干燥器、除尘器及冷却器泄爆面积分别为5.15,0.68,0.62 m~2。并结合现场实际环境对泄爆装置及泄爆口位置进行分析设计。     

煤矿火区快速封闭泄爆门研究

目前煤矿发生火灾事故后,火区封闭时间过长极易引发瓦斯爆炸等次生灾害,且煤矿现有的阻隔爆技术存在许多 不足,针对这些问题,研发一种用于煤矿火区的快速封闭泄爆门。通过对泄爆门的结构设计、封闭与泄爆机制及有益效 果等方面进行阐述,并采用流体力学FLUENT软件计算得出不同数量泄爆窗的泄爆门与监控泄爆门前截面的压力、速度之 间的变化情况。结果表明:6个泄爆窗比2个泄爆窗的封闭时间快1 200 ms,快速封闭时间节省了68.57%。随着泄爆窗的 增多,瓦斯爆炸冲击波压力和传播速度都大幅度降低。当煤矿发生火灾事故封闭火区时,快速封闭泄爆门不仅具有快速 密闭功能,也同时具有泄爆功能,为煤矿安全提供新的隔爆技术。     

基于人工神经网络的气体泄爆最大超压预测研究

为解决传统经验公式在预测气体泄爆中最大超压出现时的较大偏差或过于保守的问题，提出使用人工神经网络预测气体泄爆最大超压。基于124组实验数据，采用BP与RBF神经网络，通过优化算法计算与迭代循环对泄爆样本中的影响因素进行降维与选择，并确定2类神经网络本身在学习与计算气体泄爆样本时的相关参数。结果表明:PCA（主成分分析法）在当前样本条件下的降维效果较差，而通过迭代对比确认气体泄爆样本中的5类特征全部保留时神经网络的训练模拟效果最好；通过对124组实验数据进行随机挑选训练集与测试集的训练模拟结果发现，神经网络对气体泄爆中最大超压的预测效果较好；通过对比Molkov提出的和经Fakandu等改进的NFPA 68经验公式以及2类神经网络的预测结果表明，神经网络相比于传统气体泄爆经验公式具有明显优势。     

球形容器内可燃气体泄爆过程的数值模拟

利用流体力学软件Fluent对球形容器泄爆过程中流场进行数值模拟,分析泄爆导管长度和泄放压力对爆炸压力和爆炸强度的影响,以及泄爆过程中火焰阵面和速度场的变化。研究表明,泄爆过程增大了燃烧火焰的面积,燃烧火焰在泄爆过程中发生湍流,燃烧速度得到极大地加速,泄爆导管对于容器内的高压气体的泄放起到了约束作用,泄爆导管的长度是影响泄爆过程中容器内部压力变化的重要因素。     

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.     

中庭建筑回廊排烟方法的模拟实验研究

根据中庭建筑的特点，提出中庭建筑“回廊＋中庭顶部”的排烟方案。基于此方案，运用区域模拟思想，分析了回廊排烟条件下中庭建筑内烟气运动过程，建立了回廊溢出烟气质量卷吸流量的简化模型，推导了有／无回廊排烟条件下中庭排烟量的相互关系公式，从理论上说明了方案是可行的，并进一步通过模拟实验进行了验证。     

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。     

Coupling effects of venting and inerting on explosions in interconnected vessels

The coupling effects of venting and CO₂ inerting on stoichiometric methane-air mixture explosions were investigated in an isolated vessel and interconnected vessels. The results indicate that venting mitigates the explosion intensity, especially for small vessels. For vessels connected by pipes, a venting design following EN 14994 (2007) and NFPA 68 (2013) could not meet the venting requirements. For an isolated big vessel and interconnected vessels, increasing the CO₂ volume fraction (Φ) from 0 to 15.0 vol% decreased the maximum explosion overpressure (P_max) and maximum rate of overpressure rise ((dP/dt)_max) and delayed t_max. For closed interconnected vessels, P_max varied approximately linearly with Φ. For both isolated vessel and interconnected vessels, the coupling effects of venting and CO₂ inerting on methane-air explosion were more efficient than those of individual mitigative method (that is, venting alone or CO₂ inerting alone).     

Numerical analysis of hydrogen deflagration mitigation by venting through a duct

This paper presents a model and simulation results for the mitigation of a hydrogen–air deflagration by venting through a duct. A large eddy simulation (LES) model, applied previously to study both closed-vessel, and open atmosphere hydrogen–air deflagrations, was developed further to model a hydrogen–air explosion vented through a duct. Sub-grid scale (SGS) flame wrinkling factors were introduced to model major phenomena which contribute to the increase of flame surface area in vented deflagrations. Simulations were conducted to validate the model against 20% hydrogen–air mixture deflagrations (vent diameters 25 and 45 cm) and 10% hydrogen–air mixture deflagration (vent diameter 25 cm). There was reasonable correlation between the simulations and the experimental data. The comparative importance of different physical phenomena contributing to the flame wrinkling is discussed.     

Dynamics of explosion venting in a compartment with methane-air mixtures

A series of experiments on explosion venting of methane-air mixtures are performed to scrutinize the pressure evolution as well as the flame dynamics and morphology at various vent conditions. Specifically, a premixed flame is ignited at the center of a polycarbonate cylindrical compartment, with three various vent areas considered (with negligible vent relief pressure). As expected, the highest maximum pressure is observed in the case of the smallest vent area. For all three cases, the pressure evolution experiences two major peaks, associated with the instants (i) when the maximum flame front surface area in the chamber is reached and (ii) when an external explosion occurs due to venting of unburned gases, respectively. For the fuel-rich mixtures, a flashback is observed subsequent to the external explosion, constituting the key outcome of the present work. The flame tip velocities show two general trends, namely, exponential acceleration towards the vent, while a flame propagates towards the blocked side of the compartment with no acceleration, which is important to know in the fire/explosion safety applications.     

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.     

Flameless venting of dust explosion: Testing and modeling

Flameless venting is a sort of dual mitigation technique allowing, in principle, to vent a process vessel inside a building where people are working without transmitting a flame outside the protected vessel. Existing devices are an assembly of a vent panel and a metal filter so that the exploding cloud and the flame front is forced to go through the filter. Within the frame of ATEX Directive, those systems need to be certified. To do so a standard (NF EN 16009) has been issued describing which criteria need to be verified/measured. Among them, the “efficiency” factor as defined earlier for standard vents. This implies that flameless venting systems are basically considered as vents. But is it really so? This question is discussed on the basis of experimental results and some implications on the practical use and certification process are drawn. The practical experience of INERIS in testing such systems is presented in this paper. Schematically, with a flameless vent the pressure is discharged but not the flame so that combustion is proceeding to a much longer extent inside the vessel than with a classical vent so that the physics of the explosion is different. In particular it is shown that besides the problem of the unloading of the confined explosion, there is a highly complicated fluid mechanics problem of a fluid-particle flow passing through a porous media (the flameless device grids arrangement in the filter), which passing surface is progressively reduced. To characterize Flameless venting the problem can be addressed sequentially, considering separately the vent panel and the flameless mesh. A model is proposed to estimate the overall venting efficiency of the flameless vent. However, it does not address the flame quenching issue, which is a different problem of heat exchange between the devices and the evacuated burnt products.