室内氢气泄漏扩散的数值模拟

氢能是有发展前景的新型能源之一,氢气的安全储存是氢能应用必须解决的问题。本文建立了基于大容量金属储氢装置的室内氢气泄漏扩散模型,利用计算流体力学软件FLUENT,对室内储氢罐的泄漏扩散过程进行数值模拟,得到了氢气泄漏扩散的速度分布、浓度分布。分析数值模拟结果,得出在该模拟条件下,氢气泄漏时的流动状态为射流湍流;泄漏后上浮扩散,空间密闭时积累于室顶;通风条件下大部分区域的氢气浓度仍然高于安全限值。通过数值模拟,总结出氢气在室内环境下的泄漏扩散规律,可为氢气泄漏事故的处理消防安全设置提供依据。     

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.     

硫化氢捕消剂清除硫化氢效果研究

硫化氢气体是高毒性气体,当其发生泄漏事故时将产生严重危害。目前,应对硫化氢泄漏事故的方法较少,主要为消防水喷淋和人员疏散,不能完全消除硫化氢的危害。针对硫化氢气体的特点,研制了在泄漏事故中用于清除硫化氢气体的捕消剂。硫化氢捕消剂为干粉状的,由吸附载体、反应组分和疏水组分组成。当发生硫化氢泄漏时,将捕消剂喷洒在泄漏源周围的空气中,使捕消剂与硫化氢充分接触反应以降低危害程度和范围。清除硫化氢实验结果表明,硫化氢捕消剂能够有效地清除泄漏在空气中的硫化氢气体。     

大尺度障碍物与泄爆面对天然气内爆炸的协同作用规律研究

为阐释民用建筑内部大尺度物品与门窗等泄爆面对天然气爆炸灾害的协同作用机制，基于典型厨房空间布局及内部物品特征，借助计算流体动力学技术研究了不同泄爆面开启压力和不同大尺度障碍物体积阻塞率条件下天然气内爆炸火焰速度、爆炸超压的分布规律。研究结果表明:大尺度障碍物与泄爆面对室内天然气爆炸过程具有显著的协同作用，共同促进火焰速度与爆炸超压的显著增长，并缩短峰值超压到达时间；大尺度障碍物的存在虽然显著降低了室内天然气的体积，但从增加房间内湍流源和相对长径比的角度进一步促进了泄爆效应；大尺度障碍物与泄爆面协同作用下，室内火焰速度呈现明显的阶段性特征，并在泄爆面附近发生波动。研究结论可为民用建筑物内气体爆炸事故调查分析和灾害评估提供科学依据。     

Accident modeling of toxic gas-containing flammable gas release and explosion on an offshore platform

Toxic gas-containing flammable gas leak can lead to poisoning accidents as well as explosion accidents once the ignition source appears. Many attempts have been made to evaluate and mitigate the adverse effects of these accidents. All these efforts are instructive and valuable for risk assessment and risk management towards the poisoning effect and explosion effect. However, these analyses assessed the poisoning effect and explosion effect separately, ignoring that these two kinds of hazard effects may happen simultaneously. Accordingly, an integrated methodology is proposed to evaluate the consequences of toxic gas-containing flammable gas leakage and explosion accident, in which a risk-based concept and the grid-based concept are adopted to combine the effects. The approach is applied to a hypothetical accident scenario concerning an H₂S-containing natural gas leakage and explosion accident on an offshore platform. The dispersion behavior and accumulation characteristics of released gas as well as the subsequent vapor cloud explosion (VCE) are modeled by Computational Fluid Dynamics (CFD) code Flame Acceleration Simulator (FLACS). This approach is concise and efficient for practical engineering applications. And it helps to develop safety measures and improve the emergency response plan.     

Flammability of gas mixtures containing volatile organic compounds and hydrogen

An experimental program was conducted to evaluate the accuracy of some current methods for predicting the flammability of gas mixtures containing hydrogen and flammable or nonflammable volatile organic compounds (VOCs) in air. The specific VOCs tested were toluene, 1,2-dichloroethane, 2-butanone, and carbon tetrachloride. The lower flammability limits (LFLs) of gas mixtures containing equal molar quantities of the components were determined in a 19.4-l laboratory flammability chamber using a strong spark ignition source and a pressure criterion for flammability. All but one of the LFL values for the individual components were in agreement with earlier literature values. However, the LFL of 1,2-dichloroethane was found to be significantly lower than the range of values reported for previous determinations in smaller chambers. Two methods for calculating the LFL of mixtures were considered. The Group Factor (atomic) Contribution Method was determined to be generally more accurate than the LeChatelier Method for estimating the LFL of the gas mixtures reported here, although the LeChatelier Method was usually more conservative. The Group Factor Method predicted higher values (nonconservative) for the LFLs of several mixtures than were experimentally measured. For the case of a mixture of hydrogen and carbon tetrachloride, the Group Method estimation of the LFL was seriously in error.     

The hazards and risks of hydrogen

An analysis was completed of the hazards and risks of hydrogen, compared to the traditional fuel sources of gasoline and natural gas (methane). The study was based entirely on the physical properties of these fuels, and not on any process used to store and extract the energy. The study was motivated by the increased interest in hydrogen as a fuel source for automobiles.The results show that, for flammability hazards, hydrogen has an increased flammability range, a lower ignition energy and a higher deflagration index. For both gasoline and natural gas (methane) the heat of combustion is higher (on a mole basis). Thus, hydrogen has a somewhat higher flammability hazard.The risk is based on probability and consequence. The probability of a fire or explosion is based on the flammability range, the auto-ignition temperature and the minimum ignition energy. In this case, hydrogen has a larger flammability zone and a lower minimum ignition energy—thus the probability of a fire or explosion is higher. The consequence of a fire or explosion is based on the heat of combustion, the maximum pressure during combustion, and the deflagration index. Hydrogen has an increased consequence due to the large value of the deflagration index while gasoline and natural gas (methane) have a higher heat of combustion. Thus, based on physical properties alone, hydrogen poses an increase risk, primarily due to the increased probability of ignition.This study was unable to assess the effects of the increased buoyancy of hydrogen—which might change the probability depending on the actual physical situation.A complete hazard and risk analysis must be completed once the actual equipment for hydrogen storage and energy extraction is specified. This paper discusses the required procedure.     

石化行业控制室承爆风险评估方法研究

针对传统的气体爆炸风险评估方法的不足之处,提出采用一种基于CFD技术的气体爆炸风险评估方法,对某煤气化厂区氢气爆炸对控制室造成的风险进行模拟计算与预测分析。并把研究结果与传统的TNT当量法、Multi-Energy方法预测结果进行比较。结果表明,该方法能考虑到密集管道与复杂装置布局、气云大小等因素对爆炸超压的影响,且能用于超压波的近场预测,以及确定空间不同位置处的爆炸超压,更适用于石化行业控制室的承爆风险评估。     

居室天然气泄漏扩散过程仿真研究

随着我国城市环境保护的提高,城市燃料结构也在逐步改变。天然气作为一种清洁、高效的能源已经成为居民应用最广泛的燃料。随着天然气用户的不断增加,其事故次数也在不断上升。为了系统的研究居室内天然气泄漏扩散的过程和发展,预防居民家庭天然气火灾和爆炸事故以及发生事故后的应急提供依据。本文以普通的居民居室为研究对象,建立居室天然气泄漏扩散几何模型。并对室内天然气泄漏后的扩散状态进行仿真模拟,得到天然气泄漏后的室内扩散过程,以及在不同时间内存在爆炸极限的区域和达到爆炸极限的范围,并对爆炸后果进行了评估。结果显示：在设定条件下,泄漏发生后640 s,冰箱电源处达到爆炸下限,790 s时达到爆炸上限;其爆炸能量已达到使大型钢架结构破坏,大部分人员死亡的程度。泄漏1800 s后,可燃区域就扩散到厨房之外,存在于客厅之中了。     

Influence of concentration distribution of hydrogen in air on measured flammability limits

There is a clear difference between exiting data on the measured flammability limits of hydrogen-air mixture. The non-uniformity of concentration distribution of hydrogen in air is a contributor to deviations of the upper flammability limit (UFL) and the lower flammability limit (LFL) measured in different experiments. This paper presents a numerical model to simulate the gas mixing process from start to stability, to predict the concentration distribution, and to research the influence of concentration distribution of hydrogen in air on measured UFLs and LFLs. The commercial software package Fluent was used to carry out the numerical simulation for the concentration distribution of hydrogen in air in the vessels with length-to-diameter ratios (L: D) of 1:1, 3:1, 5:1 and 7:1 respectively. Based on the numerical simulation and analysis, the influence of concentration distribution on measured flammability limits was demonstrated for hydrogen in air in the vessel. It is found that the deviations of measured flammability limits of hydrogen in air are the minimum in the vessel with length-to-diameter ratio of 1:1, and augment with the augmentation of vessel length-to-diameter ratio. Moreover, it is presented that the deviations of measured flammability limits of hydrogen in the center of the vessel are lower than that in the top and the bottom.     

Inerted vessels: Avoiding hazards caused by gas buoyancy

Performing hot work on a process vessel that previously contained a flammable hydrocarbon liquid poses a significant explosion and fire hazard. To reduce the combustion hazard potential, the facility operator may choose to purge and blanket the vessel with an inert gas such as nitrogen or carbon dioxide. Numerous accidents have occurred during hot work due to inadequate inerting operations. Oftentimes the source of the problem was inadequate gas composition control caused by gas buoyancy.A useful paradigm for analyzing the inerting process is the well-stirred control volume with a spatially uniform chemical composition (i.e., perfect mixing). Certain features of the vessel construction, in concert with the physical properties of the inert gas, can interfere with the complete mixing of the inert gas with the vessel atmosphere. This paper discusses how to evaluate the potential for buoyant flows to disrupt and interfere with the design goal of perfect mixing. Three case studies of accident investigations are used to illustrate the potentially detrimental effects of buoyancy on inerting operations. Finally, recommendations are presented on how to use buoyancy to improve the effectiveness of inerting operations.     

厂房内H_2连续泄漏扩散的模拟分析

利用计算流体动力学软件Fluent对厂房内易燃易爆气体H2泄漏扩散过程进行了数值模拟,研究H2连续泄漏扩散规律。计算结果表明,厂房内H2泄漏一定时间后扩散将达到稳定,室内H2浓度将不再变化;根据室内H2浓度分布规律,得出H2泄漏报警装置应设在泄漏口正对墙壁上,且厂房的排风口应开设在H2钢瓶喷射方向上的屋顶处;结合H2的毒性级别和爆炸极限,划分该厂房为紧急防爆疏散区,必须在泄漏初期进行紧急人员疏散并做好防火防爆措施。研究结果为厂房内H2泄漏事故应急救援、泄漏报警装置及排风口的位置设置提供重要技术支持和理论依据。     

Study on the effect of explosion suppression equipment on hydrogen explosions

Hydrogen safety is a critical component of modern industrial safety production. In this study, a set of hydrogen explosion suppression equipment is designed independently. The suppression effects of the equipment on hydrogen explosions are studied at normal room temperature and pressure. The experimental results show that the actuation time of the equipment and the spraying mode of the suppressant are the main factors leading to the failure of the hydrogen explosion suppression equipment. The flame, with a hydrogen equivalence ratio of 0.7 and 1.0, spreads out of control when the suppressant touches the flame front. At this time, the addition of the suppressant enhances flame propagation and increases pressure. In addition, because the suppressant does not fully cover the developing flame, the hydrogen flame with the equivalence ratio of 0.5 eventually breaks through the suppressant cloud, and the explosion happens. However, when the initial flame is completely covered by the suppressant, the hydrogen explosion is suppressed by hydrogen explosion suppression equipment. This research provides a solid and reliable foundation for hydrogen explosion suppression equipment in industrial safety and production protection.     

Lower flammability limits of flammable ternary organic mixtures: Synergistic behavior

Organic flammable liquids and their mixtures, which possess high risk of combustion and explosion, are widely used as raw materials and solvents in chemical and pharmaceutical industries. Lower flammability limits (LFL) is one of the most important parameters to characterize the combustion and explosion hazards of combustible gases and liquid vapors. The LFL of various ternary organic mixtures consist of ketone (acetone and butanone), ester (ethyl acetate) and alcohol (ethanol and isopropanol) were tested at 25 °C and atmospheric pressure. The results showed that resulted LFL values of the experiment were always lower than those calculated by volume fraction weighting method when the volume fraction of alcohol was less than 20 vol% but more than 10 vol%. The co-existence of alcohol and ethyl acetate had synergistic effect on reducing the LFL values of ternary organic mixtures and thus increased their explosive risk. The mechanism of synergistic effect was analyzed, and the results showed that the OH· and H· radicals produced by the oxidation decomposition of alcohols and esters accelerated the oxidation process of ternary organic mixtures, which led to the decrease of experimental LFL values and thus corresponding increased of their explosive risk. This study would be expected to provide some guidance for designing or choosing safer and more suitable ternary organic mixtures prior to their applications for engineering.     

Using computational fluid dynamics (CFD) for blast wave predictions

Explosions will, in most cases, generate blast waves. While simple models (e.g., Multi Energy Method) are useful for simple explosion geometries, most practical explosions are far from trivial and require detailed analyses. For a reliable estimate of the blast from a gas explosion it is necessary to know the explosion strength. The source explosion may not be symmetric; the pressure waves will be reflected or deflected when hitting objects, or even worse, the blast waves may propagate inside buildings or tunnels with a very low rate of decay. The use of computational fluid dynamics (CFD) explosion models for near and far field blast wave predictions has many advantages. These include more precise estimates of the energy and resulting pressure of the blast wave, as well as the ability to evaluate non-symmetrical effects caused by realistic geometries, gas cloud variations and ignition locations. This is essential when evaluating the likelihood of a given leak source as cause of an explosion or equally when evaluating the potential risk associated with a given leak source for a consequence analysis.In addition, unlike simple methods, CFD explosion models can also evaluate detailed dynamic effects in the near and far field, which include time dependent pressure loads as well as reflection and focusing of the blast waves. This is particularly valuable when assessing actual near-field blast damage during an explosion investigation or potential near-field damage during a risk analysis for a facility. One main challenge in applying CFD, however, is that these models require more information about the actual facility, including geometry details and process information. Collecting the necessary geometry and process data may be quite time consuming. This paper will show some blast prediction validation examples for the CFD model FLACS. It will also provide examples of how directional effects or interaction with objects can significantly influence the dynamics of the blast wave. Finally, the challenge of obtaining useful predictions with insufficient details regarding the geometry will also be addressed.     

输气管道高后果区蒸气云爆炸超压预测方法探究*

为准确预测输气管道高后果区在发生蒸气云爆炸事故时的超压分布情况,对国内外运用较为广泛的蒸气云爆炸超压预测经验模型和数值模拟方法进行调研,并分别应用其对某输气管道全尺寸泄漏燃爆实验进行超压预测,结合实验数据和输气管道高后果区管理现状进行方法准确性和工程适用性分析。研究结果表明:基于等效TNT假设的Henrych模型、Mills模型和等效TNT当量数值模拟方法均不适合准确预测蒸气云爆炸超压,TNO多能法和混合气体数值模拟方法所预测的结果较为接近实验结果。TNO多能法使用简便且推广性强,但主观性较大,易高估或低估爆炸后果;混合气体数值模拟方法操作繁琐且推广性差,但分析结果精度较高。在对高后果区进行安全管控时,可结合TNO多能法与混合气体数值模拟方法同时对管道工况进行评估,确定TNO多能法的爆源强度等级,继而推广使用TNO多能法。该研究结果可在较大程度上保证评估的准确性并节约成本。     

Concentration model for gas releases in buildings and the mitigation effect

In case of accidents involving releases of hazardous materials, calculating the gas dispersion is essential for assessing risks. In general, the leaked chemical is assumed to be instantly dispersed to the atmosphere if the leak occurs in the outdoor location. However, a different approach should be made for the incidents when sources are located inside a building. For the indoor release, the gas will be diluted prior to the release to the atmosphere and the gas release from a building to the atmosphere demands the application of another model before the dispersion calculation. The indoor release model calculates average indoor concentration and volumetric flowrate to the exterior. The model is fast and reasonably accurate compared to rigorous but time-consuming computational fluid dynamics (CFD) models. The model results were compared with experimental data, and CFD simulation results both with simple geometry to demonstrate validation and assess the performance of the indoor release model. Lastly, the behavior and effect of mitigation of indoor release were demonstrated by using the model results.     

架空及埋地天然气管道泄漏扩散数值研究

天然气在管道运输过程中,由于含硫等腐蚀性气体对管道内壁的腐蚀作用,在管内其他压力的作用下,会引起穿孔泄漏。泄漏后的天然气扩散后,可能会引发火灾、中毒或爆炸。因此,进行天然气管道泄漏扩散及数值模拟研究,对管道输送安全运营和保障人生财产安全意义重大。该文利用CFD软件对架空及埋地含硫天然气管道穿孔泄漏后的甲烷、硫化氢气体的扩散进行了数值模拟。结果表明,受土壤毛孔阻力的影响,埋地天然气管道泄漏爆炸范围比架空天然气管道泄漏要小,但其在地面的影响时间长,硫化氢的中毒范围比架空要低30m左右。为天然气的安全输送及环境保护提供了理论依据。