LPG球罐全面检验中辅助工程应注意的问题

根据（TSG／R7001-2004）《压力容器定期检验规则》要求，液化石油气（LPG）球罐一般每3～6年应停机一次进行全面检验。球罐是容积最大的压力容器，特别是介质为液化石油气的球罐，具有高度的危险性。据了解，一般在空气中含有2％～10％的液化石油气时，遇到火源就会爆炸，其爆炸速度为2000—3000m／s，火焰温度达2000℃，而且泄漏出来的气体会随风飘移，能在很短的时间内就能造成数千甚至数万m2的爆炸气体危险区。     

探讨液化石油气储罐区安全阀开启压力的整定

液化石油气具有易燃、易爆的特性,液化石油气储罐区的设备必须设置安全阀,但储罐区涉及到的安全阀比较多,如何确定这些安全阀的开启压力,本文就对对影响确定储罐区设备上的安全阀开启压力进行了分析计算。     

热冲击下LPG储罐力学响应研究

液化石油气(LPG)储罐在遭受火焰侵袭时通常会面临较为恶劣的环境.在高温和内压作用下,金属材料强度下降,罐体将会出现局部屈服变形,严重时可能会发生破裂甚至爆炸.对储罐在喷射火焰下其壁面的力学响应规律进行了研究,在分析壁面应力产生机理的同时,利用有限元分析ANSYS软件对该物理过程进行了数值模拟,得出了壁面不同位置的应力分布.结果表明:在喷射火焰情形下,LPG储罐的力学响应与火焰的喷射方向有关,面向火焰一侧的壁面由于温度上升更快,材料强度下降的速度也较快,故较之背向火焰一侧的壁面发生破坏的可能性增大;另外,储罐壁面顶部附近由于温度最高,材料的强度下降最明显,因此发生破坏的可能性最大.     

液化石油气储罐空气置换计算

计算3种液化石油气储罐空气置换方式所需氮气数量。在没有真空设备情况下,可采用“边充边排”的方法对新制造（或检修后）的液化石油气储罐进行充氮置换处理，使罐内气体氧含量不大于13％。     

液化石油气爆炸抑制研究

以氮气为例,通过实验和理论分析综合研究了惰性气体对液化石油气的爆炸特性的抑制机理。结论表明：惰性气体对最大允许氧含量和爆炸极限具有相似的影响,能大大缩小液化石油气爆炸极限范围和最大允许氧含量范围;根据相关理论,得出了最大允许氧含量和爆炸极限两者的互推公式;在液化石油气/空气混合气体中,液化石油气的最大允许氧含量随体积分数增大而增大,而混合气体中实际氧含量随体积分数增大而减小,两者在最大允许氧含量上限处汇合;根据最大允许氧含量和爆炸极限之间的关系,得出了爆炸抑制中惰性气体需求量估算方法和公式。     

液化气体储罐爆沸过程的影响因素

液化气储罐在生产使用过程中可能发生泄漏,造成危害性事故,严重时会发生沸腾液体膨胀、蒸气爆炸(BLEVE).为了研究过热液体突然泄压时的爆沸过程,建立了小型实验装置,以水为实验介质,进行BLEVE的模拟实验研究.实验中发现,储罐内的介质突然泄放会出现压力突降和剧烈反弹,可能导致BLEVE.实验结果表明,液体充装率、初始压力及开口面积都会引起一定程度的爆沸,对压力突降及再反弹有较大影响.充装率在60%～90%的范围内压力反弹最大;泄放压力增大时,压力反弹速率增大;开口面积增大会提高泄放时液体的过热度,导致爆沸过程更剧烈;液相存在热分层时,泄放引起爆沸的剧烈程度及升压速度远低于同压力下液体温度均匀时的程度.     

大型液化石油气球罐检验前后的置换

随着工业的不断发展，液化石油气球罐越来越多，也越来越趋向大型化。为确保其安全经济的运行，对球罐的检验技术也相应的提出了更高的要求，尤其对球罐的置换的技术细节上，达到既安全又经济的实现球罐置换，是一个值得研究的课题。置换是液化石油气球罐全面检验前后必做的一项工作，也是保证检验安全进行的重要环节。球罐置换通常采用直接置换和间接置换两种方法。前者比较简便也较经济，但在置换过程中罐内必定存在可能爆炸的液化石油气一空气浓度范围，即形成爆炸性的混合气体，时刻存在爆炸的危险：后者是以水或惰性气体作为置换的中间介质进行置换的一种相对安全的方法。笔者通过对某燃气公司1000m^3液化石油气球罐的检验，总结了一些实用方法，以供检验人员参考探讨。     

液化石油气燃烧系统改造

液化石油气燃烧系统改造北京重型电机厂甘龙元，蔡增泰北京重型电机厂铸铁分厂有五台５０ｍ３燃气的砂型烘干窑，燃烧系统经改造，单耗从５０～６０ｋｇ标准煤／ｔ降至３０～３５ｋｇ标准煤／ｔ。改造前砂型烘干所用液化石油气是通过地下管道由液化站储罐送到工作地点，每...     

在用卧式液化石油气储罐缺陷检验与成因分析

液化石油气在石化、燃气等工业及民用生活中得到广泛的应用。LPG主要从炼油厂回收液化石油气，通过原油蒸馏、二次加工、脱硫等工艺。其含硫量、水分难于保证符合要求。H2S与LPG储罐的腐蚀息息相关，将H2S指标控制在合理的范围内。可有效地减缓金属的腐蚀开裂等缺陷．是LPG储罐安全运行的必要保证．     

液化气储配站贮罐的排空方法

近几年来,我国石油工业迅速发展,液化石油气产量也日益增长,为改变我国城市燃料结构和发展以液化石油气为原料的化学工业创造了良好的条件。我国许多中小城市和厂矿也建成许多液化石油气储配站,但站建成竣工或贮罐大、中修以及定期安全开罐检查后,都应将空气从系统中排除干净。液化石油气是一种易燃易爆的气体,贮罐中空气排除不净容易引起爆炸事故。贮罐排空气的方法有下列几种:     

锅炉沸腾液体膨胀蒸汽爆炸_BLEVE_的小尺寸模拟试验

1前言在锅炉设计中,依照传统的设计思想,人们所专注的是在最经济的条件下使用什么材料、设计多厚,使结构在实际运行中能够保证安全,锅炉的安全与结构强度有绝对性的关联。很多人认为只要设备的强度设计足够即可安全的运行直至报废。但事实上,在长期使用下,由于设备老化和操作失     

Simulation on thermal stratification and de-stratification in liquefied gas tanks

The phenomena of thermal stratification and de-stratification in liquefied gas tanks with heat leak through the side wall were researched numerically. The calculating model developed on ANSYS FLUENT 12.0 was verified through the experimental results from literature. The flow behaviors of the liquid and the temperature distributions at stratification and de-stratification stages were illustrated and the interaction between them was analyzed. When the liquid is stratified, the flow field presents a semi-circulation near the liquid surface with a plume-like flow under it and there exists a cold core under the surface which resisting the warmer circulating flow. The de-stratification of the stratified liquid begins when the circulating loops close with the resistance reduced because of the disappearance of the cold core, and once the circulation forms, it extends down to make the thermal stratifications disappear layer by layer from up to down.     

Numerical study on thermodynamic growth of single hydrogen bubble in an infinite space

In the liquid hydrogen storage and delivery, cavitation and boiling bubbles are prone to occur, which reduces the safety and economy of the liquid hydrogen delivery. For the bubble in liquid hydrogen, its growth process is different from that of room temperature media owing to the thermodynamic properties. In this paper, a single bubble growth model in liquid hydrogen is developed considering temperature distribution inside the bubble. The growth of single bubble in liquid hydrogen is described and predicted by solving Rayleigh-Plesset equation, thermal diffusion equation, thermal equilibrium equation, and heat conduction equation in semi-infinite space simultaneously. The growth trend of bubble radius, radius growth rate, vapor pressure, thermal boundary layer thickness and temperature difference between boundary and center are investigated by the model. The influence of superheat and ambient pressure on the growth of single bubble in liquid hydrogen is investigated by analysis of variance (ANOVA) and range analysis method. The mechanism of the single bubble transform from dynamic growth to thermal growth is clarified by comparing the critical time of the above physical indicators.     

Direct numerical simulations of the ignition of lean primary reference fuel/air mixtures with temperature inhomogeneities

The effects of fuel composition, thermal stratification, and turbulence on the ignition of lean homogeneous primary reference fuel (PRF)/air mixtures under the conditions of constant volume and elevated pressure are investigated by direct numerical simulations (DNSs) with a new 116-species reduced kinetic mechanism. Two-dimensional DNSs were performed in a fixed volume with a two-dimensional isotropic velocity spectrum and temperature fluctuations superimposed on the initial scalar fields with different fuel compositions to elucidate the influence of variations in the initial temperature fluctuation and turbulence intensity on the ignition of three different lean PRF/air mixtures. In general, it was found that the mean heat release rate increases slowly and the overall combustion occurs fast with increasing thermal stratification regardless of the fuel composition under elevated pressure and temperature conditions. In addition, the effect of the fuel composition on the ignition characteristics of PRF/air mixtures was found to vanish with increasing thermal stratification. Chemical explosive mode (CEM), displacement speed, and Damköhler number analyses revealed that the high degree of thermal stratification induces deflagration rather than spontaneous ignition at the reaction fronts, rendering the mean heat release rate more distributed over time subsequent to thermal runaway occurring at the highest temperature regions in the domain. These analyses also revealed that the vanishing of the fuel effect under the high degree of thermal stratification is caused by the nearly identical propagation characteristics of deflagrations of different PRF/air mixtures. It was also found that high intensity and short-timescale turbulence can effectively homogenize mixtures such that the overall ignition is apt to occur by spontaneous ignition. These results suggest that large thermal stratification leads to smooth operation of homogeneous charge compression-ignition (HCCI) engines regardless of the PRF composition.     

Numerical investigation of a large bore,direct injection,spark ignition,hydrogen-fuelled engine

This paper presents Unsteady Reynolds Averaged Navier Stokes (URANS) simulations of a large bore, hydrogen-fuelled direct injection spark ignition (DISI) engine at different spark and start of injection (SOI) timings. Six cases are simulated, including three with various spark timings at a low boost level and three with advanced to late injection timings at a higher boost level. The numerical simulations are validated with experimental data for four out of six cases, while the other two are considered blind computational fluid dynamics (CFD) simulations. It is shown that the autoignition occurs with advanced spark timing due to high in-cylinder pressure and unburnt temperature. For different SOIs, it is demonstrated that flame propagation involves a spark-initiated flame combined with an autoignition generated flame. The case with the late injection timing features poor mixing and slower combustion due to the presence of lean mixtures near the spark plug. As a result, this case features the lowest thermal efficiency when SOI is varied. In all cases, both mixture and temperature stratification are present. Simulations of zero-dimensional chemical reactors demonstrate that this stratification must be correctly captured for accurate prediction of autoignition timing.     

Fluid thermal stratification in a non-isothermal liquid hydrogen tank under sloshing excitation

To the safe space operation of cryogenic storage tank, it is significant to study fluid thermal stratification under external heat leaks. In the present paper, a numerical model is established to investigate the thermal performance in a cryogenic liquid hydrogen tank under sloshing excitation. The interface phase change and the external convection heat transfer are considered. To realize fluid sloshing, the dynamic mesh coupled the volume of fluid (VOF) method is used to predict the interface fluctuations. A sinusoidal excitation is implemented via customized user-defined function (UDF) and applied on tank wall. The grid sensitivity study and the experimental validation of the numerical mode are made. It turns out that the present numerical model can be used to simulate the unsteady process in a non-isothermal sloshing tank. Variations of tank pressure, liquid and vapor mass, fluid temperature and thermal stratification are numerically investigated respectively. The results show that the sinusoidal excitation has caused large influence on thermal performance in liquid hydrogen tank. Some valuable conclusions are arrived, which is important to the depth understanding of the non-isothermal performance in a sloshing liquid hydrogen tank and may supply some technique reference for the methods of sloshing suppression.     

1D plane numerical model for boiling liquid expanding vapor explosion (BLEVE)

The depressurization of a vessel containing saturated or subcooled liquid may occur in a variety of industrial processes and often poses a potentially hazardous situation. A 1D plane numerical model was developed for estimating the thermodynamic and the dynamic state of the boiling liquid during a boiling liquid expanding vapor explosion (BLEVE) event. Based on the choice of the initial nucleation sites density, the model predicts, simultaneously, the bubble growth processes in the liquid at the superheat-limit state, the front velocity of the expanding liquid, and the shock wave pressure formed by the liquid expansion through the air.Conditions of shock formation were found to be normally associated with high initial temperatures that can bring the liquid to its superheat-limit state during the initial depressurization. Furthermore, the high initial temperature also induces a generation of higher vapor pressures that forces a rapid mixture expansion.Model predictions of the shock wave strengths, in terms of TNT equivalence, were compared against those obtained by simple energy models. As expected, the simple energy models over predicts the shock wave strength. However, the simple model which accounts for the expansion irreversibility, produces results which are closer to current model predictions.     

The peculiarities of hot liquid droplets heating and evaporation

The change of the thermal state of a sprayed liquid droplet is calculated using the method of combined analytical and numerical research, which requires the balance of energy flows, incoming to the droplet and outgoing from it. The method evaluates unsteadiness of heat and mass transfer processes and interaction, which occurs under the influence of the Stefan’s hydrodynamic flow, radiant flow absorbed in semitransparent liquid and the Knudsen layer, which surrounds the droplets. The expedience of the thermal state’s evaluation of dispersed liquid is verified using the parameter, expressed by the ratio of liquid’s initial temperature on equilibrium evaporation temperature of droplets. As the above-mentioned parameter is less than 1, liquid is offered to be called “cold”; “warm”, as the parameter equals 1 and “hot”, as it exceeds 1. In each case the peculiarities of the thermal state change of sprayed liquid droplets are individual during an unsteady phase transformation mode. The characteristic curves, representing the change of transfer parameters, are determined for conductively heated droplets and when the Knudsen layer’s influence is neglected. These curves join together variation of the parameters of the thermal state change and phase transformation for droplets of infinitesimal set of diameters, but with the same initial liquid temperature, as the droplets evaporate in gas with constant parameters. Deviations from the characteristic curves allow evaluating the influence of more complicated boundary conditions on the interaction of transfer processes.     

Slip and micro flow characteristics near a wall of evaporating thin films in a micro channel

The microscopic liquid flow and heat transfer characteristics near the solid–liquid interface in the evaporating thin film region of a mini channel were investigated based on the augmented Young–Laplace equation and kinetic theory. A physical model using the boundary layer approximation and a constant slip length was developed to obtain the solid–liquid interfacial thermal resistances and interfacial temperatures. The results show that the ordered micro layer and micro flow near the wall reduce the effective liquid superheat and the liquid pressure difference mainly due to the reduced capillary pressure gradient. The solid–liquid interfacial thermal resistances and U‐shaped temperature drops tend to reduce the thin film spreading and heat transfer. The effects of the solid–liquid interfacial thermal resistances on the thin film evaporation outweigh the effects of the thermal conductivity enhancement due to the liquid ordering. The concepts of the micro flow and ordered adsorbed flowing micro layer are clarified to express the Kapitza resistance analytically in terms of the slip length and micro layer thickness. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; 39(7): 460–474, 2010; Published online 3 June 2010 in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20310     

Enhanced thermal stratification in a liquid storage tank with a porous manifold

Experiments were conducted to investigate the effectiveness of a porous manifold in the formation and maintenance of thermal stratification in a liquid storage tank. A thermal storage tank with a capacity of 315 L and a height-to-radius ratio of 4 was used for the experiment. The porous manifold used was made from rolling up a nylon screen into the shape of a tube. Stratification was observed at a Richardson number as low as 0.615. Flow visualization was also performed to confirm the effectiveness of the porous manifold in the promotion and maintenance of stable thermal stratification. From the results of flow visualization, one can conclude that a porous manifold is able to reduce the shear-induced mixing between fluids of different temperature, and thus is able to promote and maintain a stable stratification.