埋地管道在不同含水率的土壤中泄漏数值模拟

针对管道在土壤中发生泄漏问题,借助CFD软件及采用有限容积法建立土壤多孔介质中油气水三相流的流固耦合数学模型,分别模拟了管道在土壤含水率为0、0.1及0.2的三种情况下泄漏前后周围土壤温度场变化及油品在土壤中扩散分布情况。模拟结果表明:泄漏前,管道周围温度场分布相同,均呈椭圆形分布,热影响区温度由内向外逐渐降低。泄漏后,三种情况下,油品在土壤中运移趋势基本相同,但由于土壤含水率不同,管道周围温度场变化情况及相同时间内油品的泄漏量不同。     

LNG储罐泄漏过程外罐壁传热特性研究

以某全容式LNG储罐为研究对象,建立了二维非稳态LNG储罐泄漏传热模型,采用有限元法研究了储罐泄漏过程外罐壁的传热特性,分析了泄漏过程温度沿外罐壁厚度和高度方向的变化情况。结果表明:外罐壁温度场分布受其厚度和高度影响,其传热特性有所不同。沿厚度方向其温度场呈线性分布,且最大温度梯度为10.2 K/m(泄漏100 h);沿高度方向其温度场呈分区分布,2.65～14.65 m区域温升较快,最大增幅为6.514K/m,而14.65～26.65 m区域温升呈线性变化,最大增幅为4.376 K/m;泄漏时间为420 h LNG储罐传热达到稳态。     

乳液装置反应器换热器封头泄漏原因分析及解决措施

针对中国石化集团四川维尼纶厂乳液装置反应器换热器封头密封处频繁发生泄漏的问题,结合实际生产工艺、工况以及连接螺栓、密封垫片的选型和安装情况,找到了导致其泄漏的原因:温度交替变化的影响;压力升降变化;安装方法不当;垫片质量差选型不当;螺栓强度差;密封面损坏变形。采取了3项主要技术措施进行实施:密封垫片重新选型;提高螺栓强度;修复换热器法兰密封面。该换热器实施改造后,在大修周期内未发生过泄漏,密封效果明显。     

基于可见蒸汽云对LNG喷射泄漏爆炸下限区域的预测

喷射泄漏在LNG泄漏事故中比较常见,由于其蒸汽本身无色无味,难从感观上判断其泄漏扩散范围。但由于其温度低,喷射泄漏会使周边环境空气中水蒸气液化成可见蒸汽云。通过建立LNG喷射泄漏计算流体力学模型,对不同环境条件和喷射速度下的扩散情形进行数值模拟,得到了LNG泄漏扩散区域的温度场和浓度场。根据环境条件和温度场分布,得到了可见蒸汽云区域范围,并总结出可见蒸汽云区域范围与爆炸下限区域范围的关系。喷射泄漏发生时,可以为预测爆炸下限区域范围,划定安全隔离范围和消防救援提供帮助。     

大型储罐液化天然气(LNG)危险性分析及安全控制措施

以新疆某2万吨/年二甲基亚砜生产装置为对象,分析其生产工艺过程中的火灾爆炸危险有害因素,及采取的工艺安全措施,可为类似同类装置安全管理提供借鉴。以新疆某LNG工厂10000 m3液化天然气低温储罐为例,分析了储罐泄漏、火灾爆炸、翻滚的危险性,介绍本工程储罐的压力、液位、温度等储罐安全控制措施的成功经验,可为类似LNG大型低温储罐安全控制设计和建造提供借鉴。     

海上模块化LNG接收终端泄漏扩散安全特性分析

研究表明:启动流量、绝热层的导热系数和厚度可以明显改变管内流体的温度分布,且启动流量越大、绝热层导热系数越小、厚度越大、管内流体温度越高,生成水合物的风险越小。为了分析上模块化LNG接收终端平台生产运行的安全性,基于相关泄漏扩散理论,利用Fluent软件分别针对平台上多个关键工艺处理模块进行了泄漏扩散规律数值模拟,并进行了LNG泄漏扩散风险分析。研究结果表明,风速会有效降低平台上LNG泄漏扩散的危险性。CGB平台上各工艺模块应分别考虑燃烧爆炸风险与人员健康风险。当LNG发生中度泄漏(20%管径)时,各种气象条件时最大落地浓度均达不到爆炸下限;当重度泄漏(100%管径)时,各种气象条件时最大落地浓度均可达到爆炸下限,达到爆炸下限浓度半径为13.3~91.7 m。     

LNG储罐泄漏扩散火灾后果分析

对液化天然气在储存和运输过程中发生泄漏并引发火灾、爆炸等重大事故过程进行了分析,针对发生泄漏的具体情况,以高斯模型和ILO模型为基础,开发了可视化LNG泄漏后果分析软件,可以获得火灾危害的定量数据、泄漏后浓度扩散范围和热辐射通量图。软件数据库中含有石油化工常用物质的各种物性参数;界面友好,过程简单易操作;评价结果客观、真实、可靠。     

热油在不同孔隙度土壤中泄漏的温度场模拟

针对热油在孔隙度不同的土壤中发生泄漏问题,利用CFD仿真模拟软件,建立土壤多孔介质的流固耦合的相变数学模型。模拟结果表明:泄漏前,管道周向温度场等温线呈现出扁圆形分布,热影响区温度由内到外依次降低,且不随土壤孔隙度的大小变化而影响管道周边的温度场分布;泄漏后,由于土壤孔隙度不同,热油在土壤中的扩散趋势和范围明显不同,以致土壤中热影响区域变化迥异。小孔隙度情况下,毛细作用占主导,渗透力较小区域会随着时间推移由周边区域弥补,最终发散现象不太明显;相比在大孔隙度下,毛细作用不明显,热油更易寻找阻力较小通道,加之后续热油推挤,随着时间延续发散现象愈加明显,等温线图愈加不规则。     

埋地天然气管道泄漏温度场模拟

为了解埋地管道泄漏后附近温度场的分布情况,以便对管道发生小孔泄漏进行泄漏检测,本文对埋地输气管道泄漏前后建立了二维物理模型和数学模型并给出了相应的边界条件。利用计算流体软件Fluent对环境温度、输送压力、泄漏口孔径与泄漏方向四种泄漏工况分别进行了管道泄漏后的数值模拟。结果表明:环境温度、输送压力是决定管道泄漏后土壤温度场分布的决定性因素;泄漏口孔径也会对土壤温度分布造成影响,但影响效果小于环境温度和输送压力的影响;泄漏方向更大程度影响冷影响区的相对位置,而对冷影响区域的大小影响不大。本文最终得到了不同工况下管道泄漏后周围土壤温度场的分布情况,对当前广泛应用的光纤传感器的现场应用有一定的指导意义。     

液化天然气水平连续泄漏重气的扩散过程

结合SLAB稳态烟羽模型,针对液化天然气(LNG)连续泄漏、水平喷射源的重气扩散过程进行了模拟研究,分析了液化天然气泄漏后混合云团扩散形成的浓度场、温度场和其它特征参数。利用MATLAB语言编制液化天然气连续泄漏扩散模拟程序,对两种试验环境条件(不同风速、大气温度、大气稳定度、相对湿度和地表粗糙度等环境参数)下扩散云团的特性参数进行模拟计算,得到各云团参数随下风向距离的变化规律。     

LNG槽车瞬态泄漏特性及事故后果研究

我国每年危化品道路运输量占总货运量的30%以上,运输安全事故发生率居高不下。通过构建槽车泄漏事故,针对液相泄漏经典模型对于瞬态研究的局限性,结合罐内气体状态方程和复合积分法改进泄漏模型,研究了卧罐泄漏速率与时间耦合关系。结果表明,泄漏速率随时间推移呈二阶指数衰减关系,利用泄漏速率函数与时间叠加修正高斯模型,将修正后的关系运用到火灾爆炸事故后果计算中,得出泄漏最远距离为37.5 m,喷射火和沸腾液体扩展蒸汽爆炸(Boiling Liquid Expand Vapor Explosion, BLEVE)分别造成15和298 m内人员致死率达37%,蒸气云爆炸15 m内人员致死率为1%。利用Fluent和Aloha模型验证了模型精度,可为危险液体储罐泄漏定量风险评价和突发事件事前预判提供理论依据。     

Influence of multisource fire on temperature distribution and natural smoke exhaust effect in urban tunnels with a shaft

The combustion characteristics of multisource fire and single-source fire are quite different, and there is little research on the influence of multisource fire on the natural smoke extraction effect of shaft in urban tunnels. Therefore, in this article, the method of numerical simulation was used to study the influence of fire power and distance between two fire sources on the natural smoke extraction effect of shaft and the temperature distribution in tunnel in the case of multisource fire. Typical characteristics of smoke are analyzed, such as mass flow rate, temperature distribution, velocity vector, and CO concentration. The simulation results show that when there is a certain distance between the fire sources, the two flames are inclined and close to each other. The smoke temperature under the ceiling is higher under multiple fire sources than that under single fire source. In addition, when one of the fire sources is located at the downstream of the shaft, the smoke emission in the shaft is relatively high. As the distance between fire sources continues to increase, the smoke exhaust rate basically remains stable, and an empirical relationship between smoke exhaust rate and fire source location is established.     

A numerical study on the effects of naturally ventilated shaft and fire locations in urban tunnels

In more and more tunnels, natural ventilation mode with vertical shafts has been gradually employed. However, there are few studies investigating the influences of fire and shaft positions on natural ventilation performance currently. Therefore, this study investigated the effects of the transverse distance from fire source to tunnel sidewall, the longitudinal distance from fire source to shaft, and the transverse distance from shaft to sidewall on natural ventilation effectiveness in a tunnel fire by using Fire Dynamics Simulator. The typical characteristic parameters of smoke, such as mass flow rate, temperature distribution, and velocity vector were analyzed; besides, the phenomenon of plug‐holing was discussed. The results have shown that the mass flow rate of gas exhausted by the shaft decreases slightly with the increase of longitudinal distance from fire source to shaft. When the longitudinal distance from fire source to shaft is constant, changing the transverse distance from shaft to sidewall will have a more obvious effect on the effectiveness of exhausting smoke than changing the transverse distance from fire source to sidewall; in addition, the phenomenon of plug‐holing is more serious when the shaft is close to the sidewall.     

Numerical analysis of smoke flow under the effect of longitudinal airflow in a tunnel fire

This study investigated the influence of the longitudinal airflow on the smoke propagation in a tunnel by large-eddy simulation, which is now widely applied to study the turbulent flow. The smoke movement characteristics were studied in detail, with varying the longitudinal airflow in the tunnel. Six fire scenarios have been simulated with Fire Dynamics Simulator (FDS) and the results of the longitudinal distribution of CO concentration, temperature distribution, interface height, stratification, and the efficiency of smoke extraction in the tunnel have been analyzed to evaluate the different fire cases. FDS predicted a CO concentration distribution compared to calculated values using the Hu model. Furthermore, the predicted maximum smoke temperatures are compared to those given by the Kurioka model. A reasonably good agreement has been obtained for both models. The obtained results showed that the increase of the forced airflow velocity has for results a loss of stratification and significant decrease in the efficiency of extraction.     

Influence of longitudinal fire location on smoke characteristics under the tunnel ceiling

The critical ventilation velocity is almost the most well‐investigated fire phenomenon in the tunnel fire research field whereas previous studies have always investigated it when the fire source is distant from the downstream tunnel exit. Fortunately, a recent study provided a set of data on the critical ventilation velocity for tunnel fires occurring near tunnel exits by small‐scaled experiments, nevertheless, with a lack of further analysis. To demonstrate the relationship of the critical ventilation velocity and the distance between the fire and tunnel exit more explicitly and detailedly, a quantitative and graphical study was carried out and a correlation was presented in this paper. Inspired by this, a set of small‐scaled experiments were carried out to investigate the influence of different longitudinal fire locations on maximum smoke temperature under the tunnel ceiling. Results show that unlike the critical ventilation velocity, the maximum smoke temperature was not obviously affected by longitudinal fire location. Copyright © 2014 John Wiley & Sons, Ltd.     

LNG泄漏扩散影响因素模拟研究

为了研究液化天然气(LNG)泄漏扩散规律,用PHAST软件对某150 m~3 LNG储罐的泄漏扩散过程进行了模拟,分析了LNG储罐泄漏口径、环境风速及环境温度对LNG泄漏扩散过程产生的影响。模拟结果表明,50 mm泄漏口径、100 mm泄漏口径和灾难性破裂时天然气的扩散距离分别为160、296、365 m,泄漏口径越大,气云扩散范围越广;环境风速在1.5、5和8 m/s情况下,天然气扩散距离达到245、162、146 m,环境风速越大,气云扩散距离越小;环境温度在283和298 K的情况下,天然气云扩散距离为222和245 m,环境温度越高,气云扩散距离越大。     

C型独立货舱LNG船温度压力变化分析

对于没有配置再液化系统的半冷半压型液化天然气运输船,液货舱内的温度、压力在航程中会逐渐上升,同时液货的密度和体积也会相应改变。以14000 m³液化天然气运输船为研究对象,提出温度和压力日变化量的简化计算方法,经过实船计算验证,在装载率较高的情况下,采用简化方法计算的温度和压力日变化量的偏差较小,可满足基本的工程计算要求。讨论并分析了装载率和储罐压力释放阀最大许用设定值之间的关系以及装载率对液货温度压力变化规律的影响。     

大型液化天然气储罐内液体内分层和翻滚影响因素分析

液化天然气（LNG）的储存温度和组分的变化都会引发诸多问题,如分层、翻滚、蒸发等。基于双扩散理论和黏性流体方程,建立了紊流态LNG分层和翻滚演变的数学模型。模型的模拟计算结果可以直观地看到LNG分层和翻滚演变过程。模拟结果表明,LNG的分层是产生翻滚现象的根本原因,储罐内LNG受热后的热边界层的流动是产生翻滚的直接原因,利用紊流态LNG分层与翻滚演变模型对影响LNG分层、产生翻滚的各种因素进行了分析,得出当漏热强度超过30 W·m^-2后,改变漏热强度,对翻滚现象的产生时间影响不大;当储罐的充满率均为70%时,储罐的容积越大,储罐内的LNG分层发生翻滚的时间越长。为预防LNG储罐发生翻滚的各种措施提供了理论依据。     

CFD analysis of smoke backlayering dispersion in tunnel fires with longitudinal ventilation

In a longitudinally ventilated tunnel fire, the backlayering flow propagated in the opposite direction to the air current is the most fatal contaminations to users which are blocked upstream of the fire. In the present paper, numerical simulations were conducted using Fire Dynamic Simulator, which is based on large eddy simulations to estimate the backlayering arrival time in a longitudinally ventilated tunnel fire. The effect of a vehicle obstruction on the backlayering arrival time will be also investigated. For this, a vehicle model occupying about 31% of the tunnel cross section is simulated upstream of the fire source with its location relative to the tunnel floor is varied. The numerical investigation shows that the inertia and the buoyancy forces produced by ventilation and fire, respectively, affect the backlayering spread. The backlayering arrival time increases with the longitudinal ventilation velocity while it decreases with the fire heat release rate. When a vehicle obstruction existed within the tunnel, the numerical results show an increase of backlayering arrival time. This increase is significantly more important with the fire distance when the vehicle obstruction approaches the tunnel floor. Two correlations are developed, with and without obstruction in the tunnel, to predict the backlayering arrival time against the distance to fire. Copyright © 2016 John Wiley & Sons, Ltd.     

水泥和混凝土在超低温环境下的 性能变化及其应用要求

超低温混凝土目前主要应用于液化天然气(LNG)储罐的外部保护层,当内罐出现泄漏时,水泥混凝土保护层可以缓存液化天然气,防止液化天然气泄漏到外界造成各类危害。通过研究总结国内外超低温环境下水泥和混凝土各种性能变化,分析超低温混凝土的使用条件,为其推广应用提供参考和借鉴。