Configuration predictions of large liquefied petroleum gas (LPG) pool fires using CFD method

Liquefied petroleum gas (LPG) has potential pool fire risks due to its flammability. The configuration of pool fires plays a significant role when applying the solid flame model or point source model to assess the risks from heat radiation. However, no existing correlations can precisely predict the configuration of large LPG (100% propane) pool fires. To enhance the fundamental understanding on how pool diameter and wind velocity can influence the configuration of large LPG pool fires, an experimentally validated Computational Fluid Dynamics (CFD) model is employed to simulate fires using different burning rate models. Fire temperature profiles, flame heights, and flame tilts predicted by the CFD model were compared with empirical models and experimental data. Accordingly, new correlations for flame height and flame tilt as functions of pool diameter D and wind velocity u_w have been developed. The comparisons demonstrate that the new correlations have the best overall accuracy in the prediction of flame height and tilt for large LPG pool fires under different conditions (10 m ≤ D ≤ 20 m, 0 ≤ u_w ≤ 3 m·s⁻¹).     

LNG池火热辐射模型及安全距离影响因素研究

重点对LNG池火热辐射模型,模型应用方式,以及热辐射安全距离的影响因素做了详细研究,给出池火热辐射模型采用及安全距离计算的方法。对常用的热辐射计算模型(点源模型、LNGFire3和PoFM ISE模型)加以介绍,并对3种模型做了对比研究。PoFM ISE模型充分考虑大池火直径时不完全燃烧的因素以及风速对火焰高度的影响,建议当风速大于1.5 m/s,池火直径大于20 m时采用。同时,进一步研究影响LNG池火热辐射安全距离的各种因素,包括池火直径、风速、环境温度和湿度,从而得出不同条件下池火热辐射安全距离的要求。     

Evaluation of CFD simulations of transient pool fire burning rates

Fire is the most commonly occurring major accident hazard in the chemical and process industries, with industry accident statistics highlighting the liquid pool fire as the most frequent fire event. Modelling of such phenomena feeds heavily into industry risk assessment and consequence analyses. Traditional simple empirical equations cannot account for the full range of factors influencing pool fire behaviour or increasingly complex plant design. The use of Computational Fluid Dynamics (CFD) modelling enables a greater understanding of pool fire behaviour to be gained numerically and provides the capability to deal with complex scenarios.This paper presents an evaluation of the Fire Dynamics Simulator (FDS) for predictive modelling of liquid pool fire burning rates. Specifically, the work examines the ability of the model to predict temporal variations in the burning rate of open atmosphere pool fires. Fires ranging from 0.4 to 4 m in diameter, involving ethanol and a range of liquid hydrocarbons as fuels, are considered and comparisons of predicted fuel mass loss rates are compared to experimental measurements.The results show that the liquid pyrolysis sub-model in FDS gives consistent model performance for fully predictive modelling of liquid pool fire burning rates, particularly during quasi-steady burning. However, the model falls short of predicting the subtleties associated with each phase of the transient burning process, failing to reliably predict fuel mass loss rates during fire growth and extinction. The results suggest a range of model modifications which could lead to improved prediction of the transient fire growth and extinction phases of burning for liquid pool fires, specifically, investigation of: ignition modelling techniques for high boiling temperature liquid fuels; a combustion regime combining both infinite and finite-rate chemistry; a solution method which accounts for two- or three-dimensional heat conduction effects in the liquid-phase; alternative surrogate fuel compositions for multi-component hydrocarbon fuels; and modification of the solution procedure used at the liquid-gas interface during fire extinction.     

坡地建筑外立面火灾温度演化研究

针对坡地建筑外立面开口火溢流行为,为了预测不同坡地角度时圆形开口建筑火溢流的外立面热羽流温度分布规律,采用1∶8缩尺寸建筑火灾模型,开展圆形开口建筑火溢流实验研究。结果表明:在建筑火灾燃烧状态稳定下,对于确定开口尺寸、火源功率以及坡地坡度(倾斜挡墙)下,带有圆形开口的燃烧室内温度基本均匀且保持一致;针对圆形开口建筑,倾斜挡墙坡度越大,外立面的温度越高;基于热羽流温度实验数据,建立考虑不同开口尺寸、火源功率和倾斜挡墙角度影响下圆形开口建筑火灾溢出热羽流的竖向温度预测模型。     

An experimental study on the burning rate of a continuously released n-heptane spill fire on an open water surface

Spill fires are common during oil product storage and transportation after a loss of containment. Since the burning fuel is moving and the fuel depth is quite shallow, the burning rate in a spill fire is different from that of a pool fire with a static burning zone. Unlike pool fires, which have been studied for decades and have well-established correlations for burning rate, research on spill fires is inadequate. In this paper, continuously released n-heptane spill fire experiments were conducted on open water surfaces with varying fuel discharge rates. The pool diameters were measured, and the spill fire burning rates were estimated based on a dynamic balance between fuel supply and combustion. The burning rates in n-heptane pool fires from the literature were reviewed and compared with the estimated burning rates in spill fires of the same dimension. The spill fire burning rate was found to be close to that in a pool fire during the initial burning phase but lower than that in a bulk burning pool fire and that in a “fuel-level-controlled” pool fire. The distinction between the burning rates of spill fires and pool fires is explained by the heat balance analysis of the fuel layer. A model for the spill fire burning rate was proposed accordingly. The results calculated with the presented model are closer to the measured data than those calculated with pool fire models.     

Scale effect of flame instability mechanisms on propagation velocity

Blast pressure is a major source of the damage caused by an accidental gas explosion. Its magnitude depends on the thermal expansion rate and hence on the flame propagation velocity. This paper discusses the influence of two flame instability mechanisms, i.e., diffusive-thermal and hydrodynamic instabilities, on flame propagation velocity with an emphasis on their scale effects as the flame continuously increases its size during an explosion. The Sivashinsky equation is numerically solved to simulate flame propagation behaviors. It is found that flame propagation velocity, V_f, is independent of flame size under the influence of diffusive-thermal instability, whereas V_f increases with flame size under the influence of hydrodynamic instability. The latter result is understood as a result of flame’s fractal structure. Fractal dimension is determined from the dependency of V_f on flame size, and the obtained fractal dimension is close to the known experimental value.     

Assessment of four turbulence models in simulation of large-scale pool fires in the presence of wind using computational fluid dynamics (CFD)

Pool fires are the most common of all process industry accidents. Pool fires often trigger explosions which may result in more fires, causing huge losses of life and property. Since both the risk and the frequency of occurrence of pool fires are high, it is necessary to model the risks associated with pool fires so as to correctly predict the behavior of such fires.Among the parameters which determine the overall structure of a pool fire, the most important is turbulence. It determines the extent of interaction of various parameters, including combustion, wind velocity, and entrainment of the ambient air. Of the various approaches capable of modeling the turbulence associated with pool fires, computational fluid dynamics (CFD) has emerged as the most preferred due to its ability to enable closer approximation of the underlying physical phenomena.A review of the state of the art reveals that although various turbulence models exist for the simulation of pool fire no single study has compared the performance of various turbulence models in modeling pool fires. To cover this knowledge-gap an attempt has been made to employ CFD in the assessment of pool fires and find the turbulence model which is able to simulate pool fires most faithfully. The performance of the standard k–? model, renormalization group (RNG) k–? model, realizable k–? model and standard k–ω model were studied for simulating the experiments conducted earlier by Chatris et al. (2001) and Casal (2013). The results reveal that the standard k–? model enabled the closest CFD simulation of the experimental results.     

Improved models of failure time for atmospheric tanks under the coupling effect of multiple pool fires

Fire accidents of chemical installations may cause domino effects in atmospheric tank farms, where a large amount of hazardous substances are stored or processed. Pool fire is a major form of fire accidents, and the thermal radiation from pool fire is the primary hazard of domino accidents. The coupling of multiple pool fires is a realistic and important accident phenomenon that enhances the propagation of domino accidents. However, previous research has mostly focused on the escalation of domino accidents induced by a single pool fire. To overcome the drawback, in this study, the failure of a storage tank under the coupling effect of multiple pool fires was studied in view of spatial and temporal synergistic process. The historical accident statistics indicated that the accident scenario of two-pool fires accounted for 30.6% in pool fires. The domino accident scenario involving three tanks is analyzed, and the typical layout of tanks is isosceles right triangle based on Chinese standard “GB50341-2014”. The thermal response and damage of a target tank heated by pool fires were numerically investigated. The volume of 500 m³, 3000 m³, 5000 m³ and 10000 m³ were selected. Flame temperature was obtained by FDS, and then was input onto the finite element model. The temperature field and stress field of target tanks were simulated by ABAQUS. The results showed that the temperature rise rate of the target tanks under multiple pool fires was higher than that under a single pool fire. The failure time of the tank under the coupling effect of multiple fires was lower than that under the superposition of multiple fires without the first stage. The stress and yield strength were compared to judge the failure of the target tank. The model of failure time for the tank under the coupling effect of pool fires was established. Through the verification, the deviation of this model is 4.02%, which is better than the deviation of 15.76% with Cozzani's model.     

烃类池火灾热辐射量化分析模型探讨

为澄清有关烃类池火灾热辐射量化分析模型选择中存在的问题,针对"池火计算方法"模型进行量纲分析和物理意义方面的讨论,提出该模型在概念使用、量纲关系、热释放速率的计算以及池火焰模化等方面存在的问题。系统阐述点源模型、Shokri-Beyler模型、Mudan模型等常用烃类池火灾热辐射通量分析模型的适用条件和应用范围。点源模型适用于被辐射目标物从池火焰接受的热辐射通量小于5 kW.m-2情况下池火灾热辐射的量化分析;Shokri-Beyler模型主要应用于估算被辐射目标物从池火焰接受的热辐射通量大于5 kW.m-2的情况;Mudan模型可用于估算无风或有风条件下被辐射目标物从池火焰接受的热辐射通量。     

An experimental and modeling study of continuous liquid fuel spill fires on water

The spread of burning fuel spilled from oil product containers during offshore storage and transportation may cause large damage and trigger further accidents. Some analytical models already exist to predict the spread and burning behavior of liquid fuel spill fires, however, few experimental studies have been conducted to verify the model results. In this paper, continuous n-heptane spill fire experiments were conducted in a rectangular trench covered with water. The burning area, fuel spread rate, and thermal flux with different discharge flow rates and ignition delay times were investigated by both experimental and modeling means. The spill fire burning area, with 5 typical phases during burning, has a quasi-steady value which is directly proportional to the discharge rate but irrelevant to the ignition delay times. The steady burning rate, as the ratio of discharge rate over burning area, was estimated. A spread model was modified to simulate the spread of continuous liquid fuel spill fires in a one-dimensional channel, based on the balance between gravity and viscous forces. A cuboid solid flame model was used to compute the thermal flux from spill fires. The burning fuel spread and the heat flux calculated by the models agree with the experimental results.     

Improvement in the prediction of gasoline pool fire behaviour: CFD modelling and validation

The development and implementation of mathematical models through Computational Fluid Dynamics (CFD) techniques has been acknowledged as a promising tool for the prediction of hydrocarbon pool fires behaviours. In this sense, different approaches, with different assumptions and simplifications, and accounting for different phenomena, have been developed in the literature. However, the deviations in the predictions of the experimentally determined parameters, such as temperatures profiles, flame heights and radiative heat flux, by the implemented models are still high. Therefore, the implementation of these models to predict combustion phenomena and flame behaviours for various scenarios is limited. In this work, the software C3D is used to model gasoline pool fires of different diameters, and under different wind conditions, in order to improve the quality of the predictions of the flame behaviour. The modelled cases correspond to the experimental studies reported in literature. The results from the implemented model show an improved predictive quality when compared with other modelling works reported on literature for the same experimental cases. The deviations in the time averaged temperature, flame height, surface emissive power and radiative heat flux, has been calculated to be 5.0%, 0.05%, 6.32% and 3.82%, respectively.     

庚烷池火多火源燃烧特性的实验研究

多火源燃烧是森林火灾和城市群发性火灾中重要而又特殊的火灾现象,相关研究很少。通过恒定控制液面高度的实验系统,对直径0.1m、0.2m和0.4m的庚烷池火在单个火源、两火源燃烧和三火源线性排列时的火焰高度、火焰体积和燃烧速率等特性进行了实验研究。研究发现,三火源燃烧时中间火源的火焰高度、火焰体积和燃烧速率明显高于两火源燃烧和单火源燃烧,三火源燃烧时边上火源与两火源的燃烧状况难以区分。这些燃烧特性随着火源间距的减小,呈现增大趋势。热量反馈增强和空气卷吸受限这两种火源相互作用机制相互耦合,且随着火源间距的减小而增强,在S/D（S为火源间距,D为油池直径）为2～4时,两种机制强烈竞争,在其他参数范围内热量反馈增强效应占主导作用。研究还发现火焰体积与热释放速率有较好的线性相关关系,单位火焰体积的热释放速率约为1614kW/m3。     

不同边沿高度油池火燃烧行为的实验和数值模拟研究

采用实验和FDS数值模拟相结合的方法,探讨了边沿高度对油池火燃烧特性的影响。在实验部分,研究了燃烧速率和表观火焰高度随边沿高度的变化趋势,并分别分析了各个阶段的热反馈机制。在实验获得不同尺度、边沿高度正庚烷油池火燃烧速率的前提下,建立相应尺度的不同边沿高度油池火的Fire Dynamics Simulator(FDS)计算模型以针对火焰高度进行了数值模拟研究,分析了实际火焰高度、火焰下探高度随边沿高度的变化趋势,并提出了相关的无量纲拟合式。     

不同通风条件下柴油池火的实验研究

为了分析不同通风条件对柴油池火燃烧特性及引燃特性的影响,进行205 mm带水垫层柴油池火的引燃实验,通过对池火燃料的质量损失速率、火焰高度、温度及热辐射等的监测,分析通风环境中柴油池火的热传递规律。结果表明:当风速为0.5 m/s时,火灾进入旺盛阶段的时间提前,火焰平均温度最高;当风速为1 m/s时,风速的增加导致油池火的质量损失速率增加,位于主火源下风向的待引燃火源获得的热辐射通量增大,火灾旺盛阶段火焰的平均温度降低,火焰高度降低,下风向相邻油盘引燃的时间提前;1 m/s情况下,205 mm带水垫层柴油池火的安全间距需增加到1D以上;通风环境对池火发展及蔓延的影响是显著的,应适当加大下风向可燃物的安全间距,合理选择通风排烟风速,优化火灾应急救援策略。     

纵向风对隧道火灾拱顶最高温度及其位置的影响

研究了燃烧风洞内不同纵向风速、不同火源功率条件下,隧道近火源区顶部温度沿纵向分布情况。结果表明,纵向风对不同尺寸火源条件下的顶部温度的影响呈不同特征。对较小尺寸火源,隧道顶部温升随风速增加而减小至稳定值;而对较大尺寸火源,顶部温升随风速增加先增加后减小。对于矩形火源,当纵向风较小(0.5~1.5m/s)时,长边平行于纵向风时顶部最高温升大于长边垂直于纵向风的情况;而当纵向风较大(≥2 m/s)时,两种油盘放置方式的顶部最高温升一致。纵向风作用下,顶部最高温升位置向下游呈现"两次移动"特征,即随着纵向风速增加该位置先向下游移动,当风速达到某一值时,隧道拱顶的加热机制由对流和辐射共同主控转变为辐射单独主控,最高温升位置突变回到上游后再次逐渐向下游移动。     

受限空间脉冲细水雾灭火数值模拟

为研究脉冲细水雾灭火效果和灭火机理,采用FDS软件对连续和脉冲细水雾熄灭受限空间油盘火进行了数值模拟。通过模拟和理论分析确定了脉冲细水雾周期为8 s开启、8 s暂停,并设置了冷却和窒息两种灭火条件,对两种细水雾熄灭不同尺寸的柴油池火进行了研究。结果表明:连续细水雾无法熄灭直径15 cm和20 cm的小尺寸油盘火,对直径25 cm中尺寸油盘火的灭火机理为冷却,对直径为30cm和35 cm大尺寸油盘火的灭火机理为窒息;脉冲细水雾能够熄灭不同尺寸的油盘火,且灭火效率高,火焰熄灭均发生在喷头暂停喷水期间,灭火机理为水雾蒸发稀释氧气而窒息。     

烃类流体火灾伤害破坏作用定量分析

对烃类流体火灾的伤害破坏作用进行正确的定量分析是开展重大消防目标火灾风险评估工作的基础。针对烃类流体火灾伤害破坏作用定量分析中存在的问题,系统论述烃类流体火灾伤害破坏作用的定量分析方法,分析并讨论火球、池火、喷射火和蒸气云火灾等不同火灾形式的热辐射通量计算模型及其前提条件,对不同热辐射伤害破坏作用准则及伤害概率模型的适用条件和模型基础进行了论述。     

The study of burning behaviors and quantitative risk assessment for 0# diesel oil pool fires

The liquid fuel safety issues on fuel storage, transportation and processing have gained most attention because of the high fire risk. In this paper, some 0# diesel pool fire experiments with different diameters (0.2–1 m) were conducted with initial fuel thicknesses of 2 cm and 4 cm, respectively, to obtain liquid fuel combustion characteristics. Some key parameters including mass burning rate, flame height and the flame radiative heat flux, associated with fire risk, were investigated and determined. Subsequently, a detail quantitative risk assessment framework for 0# diesel pool fire is proposed based on the 0# diesel burning characteristics. In the framework, the probability of personal dead and the facility failure are calculated by the vulnerability models, respectively. In the end, 10 special tank fire scenarios were selected to show the whole risk calculation process. The tank diameter and the distance to pool fires were paid more attention in the cases. The safety distances in the cases are provided for the persons and nearby facilities, respectively. The paper enriches the basic experimental data and the provided framework is useful to the management of 0# diesel tank areas.     

Numerical simulation of small-scale pool fires of LNG

Liquefied natural gas (LNG) has been largely indicated as a promising alternative solution for the transportation and storage of natural gas. In the case of accidental release on the ground, a pool fire scenario may occur. Despite the relevance of this accident, due to its likelihood and potential to trigger domino effects, accurate analyses addressing the characterization of pool fires of LNG are still missing.In this work, the fire dynamic simulator (FDS) has been adopted for the evaluation of the effects of the released amount of fuel and its composition (methane, ethane, and propane), on the thermal and chemical properties of small-scale LNG pool fire. More specifically, the heat release rate, the burning rate, the flame height, and thermal radiation, at different initial conditions, have been evaluated for pool having diameter smaller than 10 m. Safety distances have been calculated for all the investigated conditions, as well.Results have also been compared with data and correlations retrieved from the current literature. The equation of Thomas seems to work properly for the definition of the height over diameter ratio of the LNG pool fire for all the mixture and the investigated diameters.The addition of ethane and propane significantly affects the obtained results, especially in terms of radiative thermal radiation peaks, thus indicating the inadequacy of the commonly adopted assumption of pure methane as single, surrogate species for the LNG mixture.     

起居室典型材料的火灾温度场实验研究

就建筑火灾发生频率较高的起居室为研究对象,主要对该类住宅中的一些常见和使用广泛的典型家具及装修材料,纸张（报纸）、多层胶合板以及软垫分别进行了火灾燃烧实验,对火场中重要参数温度场进行了测试与分析。对由典型装修材料组成的单室,既起居室火灾进行了全尺寸火灾实验,目的是掌握起居室内火灾的发生发展、燃烧过程和火灾蔓延特点。研究表明,住宅火灾中聚合材料、人工填充泡沫等人造材料的热释放速率最大,最高可达305kW,是火灾前期起居室升温的主要热源;全尺寸火灾实验过程中火焰蔓延较快,扩展幅度较大,蔓延过程中多股火焰交叉处温度可达250％左右,容易造成火势火场传播,同时释放出大量深色烟气,火场能见度极低。全尺寸起居室实验表明,短短3min27s内火场温度达到850℃。