Dynamic model for a heat exchanger tube rupture discharging a high-pressure flashing liquid into a low-pressure liquid-filled shell

Shell-tube type heat exchangers are often used to exchange heat between a high-pressure fluid and a low-pressure fluid. The pressure difference between these two fluids could be significantly high. In the event of a partial or full rupture of a tube, a problem may arise in that a transient pressure rise phenomenon could occur due to the flashing of the high-pressure sub-cooled fluid in the tube into the low-pressure shell, which may cause the shell to rupture with subsequent damage to equipment. This paper presents a dynamic model to describe the transient phenomenon occurring on the shell side following various scenarios of tube rupture. The spatial and temporal aspects of the flow transients along the pressure safety valve riser are accounted for by solving the one-dimensional continuity and momentum hyperbolic partial differential equations as applied to the liquid-filled riser. The dynamics of the attached piping system are also accounted for via two mechanistic models; the first is based on an inertial-resistive assumption of the fluids in this system, while the other is based on the assumption of anechoic perturbations passing through a long section of the attached piping. The latter is justified in cases where the attached piping is long enough such that reflections from the downstream end do not interfere with transients occurring in the shell during the initial phase of fluid flashing into the shell side following rupture. The various phases of this phenomenon are described, however the paper focuses on the initial phase of the phenomenon during which shell overpressure may be encountered. The model is applied to two ethylene heaters in tandem; the first uses propylene on the shell side to heat the ethylene on the tube side, while the second uses methanol, also on the shell side. The ratio between the shell design pressure to the tube design pressure in these two heaters are 0.169 and 0.154, respectively, hence the motivation to accurately model the transients involved in this phenomenon. The practical aspects and discussion around techniques to alleviate potential overpressure scenarios due to tube rupture are emphasized throughout the paper.     

Revised emergency vacuum relief device sizing for atmospheric distillation systems

Conventional vacuum relief methodologies are usually protective responses; that is, they accomplish their purpose by substitution of an inert gas (usually nitrogen) for the process gases removed by an external vacuum source, or for condensable vapour collapsed by an internal process mechanism (e.g. condensation). While this approach is theoretically possible for all potential vacuum scenarios, it becomes practically impossible to implement for installations where a rapid phase change can impart near-instantaneous system pressure reductions. The procedure outlined in this paper takes a preventive approach: eliminate the source of vacuum generation before the safe lower system pressure limit is reached. For distillation and other refluxing systems, this vacuum source is usually the main overhead condenser, which is designed to collapse large volumes of condensable vapour. To eliminate the vacuum source requires elimination of the system's ability to rapidly condense vapour. This goal is accomplished by introduction of inert gas directly into the condensing system to ‘blanket’ the heat transfer surface and stop condensation. The procedure determines the rate, amount and location for introduction of inert gas. The required design data include: (i) system starting pressure, (ii) maximum allowable system vacuum, (iii) volume of the condensing system, and (iv) normal system condensing rate. By determining the rate at which the condenser removes vapour volume from the system, and designing an inert gas delivery system to meet or exceed this rate, the vacuum generation potential of the system is effectively eliminated using a much smaller quantity of inert gas than with the more traditional volume substitution methods.     

低压环境下不同三元圆柱锂电池热失控危险特性对比研究

为研究21700和18650新旧2型多用途锂离子电池在航空运输低压环境下的热失控特性差异，采用动压变温实验舱搭建实验平台开展实验。将实验环境压力设定为飞机巡航时的环境压力30 kPa，对比常压101 kPa，使用外部热源加热的方式触发锂电池热失控，利用热传播引发相邻电池热失控，分别从热失控温度变化特性、热释放速率和热解气体组分浓度变化进行分析。研究结果表明:能量密度更高的21700电池热失控峰值温度更高，高温危险性要高于18650电池，但触发热失控所需的热量更多，电池间热传播时间会延长；低压环境有利于降低锂电池热失控燃爆峰值温度，减小燃爆热释放速率，但会产生更多CxHy和CO等具有燃爆性的热解气体，可能会在有限空间内与氧气混合引起二次燃爆。     

API Standard 521 new alternative method to evaluate fire relief for pressure relief device sizing and depressuring system design

Since the 1950's, API Standards have provided guidance on determining relief loads for equipment exposed to pool fires. The API method is empirical based on tests performed in the 1940's. There is increasingly widespread interest in analytical methods based on heat transfer principles to model fire heat input. The API committee agreed to include an analytical method in the 6th edition of API Standard 521 to establish relief loads for pressure relief devices and to design depressuring systems for the fire scenario. The analytical method provides more flexibility than the empirical method but has limitations (e.g., too many permutations are possible leading to potential under-sizing of the pressure relief device).This paper discusses the basis for the empirical method in API Standard 521 and provides comparisons of the empirical and analytical method with two more recent large-scale pool fire tests. This pool fire test data indicates that the empirical method will provide a conservative estimate of pool fire heat input for most applications and is still the method of choice when designing pressure relief systems. However, these recent tests indicate the empirical method needs to be modified when a vessel or equipment is partially confined by adjacent embankments or walls equal or greater than the vessel height. In such cases, the wetted area exponent should be 1.0 instead of 0.82.The analytical method is useful in determining time-versus-temperature profiles for heating unwetted vessels of varying wall thicknesses and materials of construction. These profiles, which depend upon the type of fire (e.g., unconfined pool fire, jet fire, etc.), can be combined with tensile strength and stress-rupture data to specify a depressuring system's pressure-versus-time profile. This will minimize failure and/or mitigate the effects of failure due to overheating from fire exposure.     

工作压力对细水雾雾场特性参数影响的实验研究

为了研究工作压力对细水雾雾场特性参数的影响,针对高、中低压细水雾喷头,测量、计算了不同工作压力下细水雾的雾化锥角、雾通量分布、粒径分布及雾动量,得到了高压细水雾与中低压细水雾雾场特性参数的区别及不同工作压力下细水雾雾场特性参数的变化规律,为细水雾喷头的开发及设计应用提供了相应的实验依据。     

Influence of water storage on deflagration characteristics of methane in confined space

Comparative experiments were conducted under different water level heights and methane concentration conditions using a self-designed explosion experiment pipeline. The results showed that, in comparison with the scenario without water storage, when the water level was 2 cm and methane concentration was 6.5–12.5%, there was a dual effect including a pressure decrease caused by the endothermic cooling of liquid water and a pressure increase caused by the expansion of water vapour. These effects caused the pressure time history curve to exhibit a double-peak or multi-peak structure, and the average decrease in the peak deflagration pressure was 23.76%. The heat of vaporisation absorbed by the stored water and barrier effect of water vapour on the transfer of the heat slowed down the increase in the deflagration temperature. The average decrease in the peak deflagration temperature of methane was 13.82%, and the time to reach the peak deflagration temperature was extended as a whole, with an average delay of 0.22 s. Water storage also changed the shape of the deflagration flame front, which exhibited ‘knife’, ‘V’, and ‘crescent’ structures. Moreover, the flame propagation speed was significantly reduced, with the peak and average flame propagation speeds decreased by 83.3% and 83.6%, respectively. The research results can provide a certain reference for preventing gas explosions in typical confined spaces, and also help to explore new anti-explosion methods, which can be applied to marine equipment such as ships.     

深水钻井热交换作用下的井壁稳定性分析

为了研究深水钻井过程中热交换作用对井壁稳定性的影响规律,建立了钻井液、钻柱、海水和地层各介质热交换作用下温度控制方程,根据热弹性理论计算温度变化对井周应力的影响,结合地层强度准则与拉伸破坏准则确定深水井壁坍塌压力与破裂压力。结果表明,钻井液循环对地层产生的冷却作用能够降低井壁坍塌压力与破裂压力,但破裂压力降低幅度比坍塌压力的降低幅度稍大。因此,尽管钻井液的冷却效果能够抑制井壁坍塌,但应注意低温度的井壁更易形成诱导缝,甚至引发地层漏失。计算结果对深水钻井作业具有指导意义。     

200 MW燃气流风洞高压氧气系统安全操作分析

为保证200 MW燃气流风洞高压氧气系统安全运行,从初始能量出发,对高压氧气系统充气、供气、排气时管道内的激波管流动、绝热压缩等过程进行安全分析,并提出针对性安全措施。结果表明:对于充气管道内存在的激波管流动,当驱动气体压力为20 MPa、被驱动气体压力为0.1 MPa时,激波反射后末端气体温度远远高于200 ℃,通过减小阀门开启速度,对阀前管道进行充气以减小上下游压差,可避免因绝热压缩产生的高温;供气管道充填时,管道内最高温度为73 ℃,通过控制充填速度,可进一步降低管道内氧气温度;通过高压排气、低压排气2种模式,可满足国标中对氧气流速的要求。研究结果可为氧气管道远程安全操作提供参考。     

Simulation study on near-field structure and flow characteristics of high-pressure CO2 released from the pipeline

The accidental release of high-pressure carbon dioxide (CO₂) can cause serious damages to both humans and pipeline equipment. Therefore, it is of great significance to have a deeper understanding about the release characteristics of high-pressure CO₂ for improving the safety level of Carbon Capture and Storage (CCS) technologies. Both industrial-scale and laboratory-scale studies have been carried out to predict the release behaviors. In recent years, computational fluid dynamics (CFD) simulation has become a crucial method to study the instantaneous changes and microscopic details of the fluid behaviors. In this paper, the simulation method was employed to study the near-field structure and flow characteristics of high-pressure CO₂ released from pipelines. The Peng-Robinson Equation of State (EOS) was used to compute the thermodynamic properties of high-pressure CO₂, and SST k-ω model was applied to simulate the structure and physical parameters of the under-expanded jet. In addition, the multi-phase mixture model was introduced to study the phase transition. The non-equilibrium liquid/vapor transition is modeled by introducing ‘source terms’ for mass transfer and latent heat. Compared to the experimental results, the simulation results showed good agreement. Furthermore, the influences of operating conditions, including different stagnation pressure, stagnation temperature, and nozzle size, were analyzed.     

苯胺冷凝器换热管的泄露失效原因分析及对策

针对苯化工装置冷凝器换热管早期失效的问题展开讨论,提出造成腐蚀穿孔的几种原因,阐述造成腐蚀的原理。结合实际,提出改变结构形状,进行防腐处理,改善循环水质等措施,避免泄漏的发生。     

数值分析方法在一起高危工艺分析中的应用

以二级放热反应为研究对象,在反应体系温度、浓度均匀分布的假设基础上,根据反应速率方程和热平衡方程,建立高危工艺反应的温度和转化率随时间变化的数学模型。采用数值计算技术,以一阶差分代替微分,并结合工艺中的恒温过程、绝热过程和飞温过程,编写计算程序求得其转化率、温度在不同时间点的数值解,揭示爆炸事故的发展过程,定量分析操作参数的影响和转化率、温度随时间分布的规律。同时通过对绝热反应时间、冷凝器的冷却能力的分析,结合冷凝器的移热能力和反应放热对反应体系热积累的影响,讨论防止反应失控发生的可能性。最后探讨冷凝器热负荷余量、反应物投料浓度比等因素对控制反应失控的影响。     

基于监测数据的土壤源热泵系统设计优化分析

针对建筑中地源热泵系统实际地下换热过程复杂、设计困难等问题,以苏州地区某浅埋式地源热泵系统为研究对象,运用TRNSYS软件搭建地源热泵仿真模型,对一定条件下埋管内冷却水流速与地源热泵系统性能的耦合关系进行了模拟分析。仿真结果表明相同蓄热体积下埋管深度对系统性能影响较小。增大冷却水流速有利于土壤温度恢复,但系统耗电量增加。该浅埋式地源热泵系统冷却水流速1~2 m/s均在合理范围内,且埋管深度越大,最佳设计流速越小。     

常压及低压下锂电池热失控随数量变化特性

为明确在地面常压环境和商用飞机巡航高度低气压环境下锂电池热失控火灾危险特性随电池数量的变化关系,分别于95 kPa地面常压环境和20 kPa低压环境下,开展不同电池数量梯度的热失控试验,测量热释放速率,总热释放量,烟气温度,CO、CO2和碳氢等气体的实时体积分数.结果表明:最高热释放速率和总热释放量与电池数量均呈幂函数...     

换热器不锈钢换热管束开裂原因分析

一台换热器换热管束发生了开裂泄漏.采取全面检验的方式,通过宏观检查、化学成分分析、断口微观形貌和能谱分析、金相分析等方法,对换热管开裂原因进行了分析.结果表明:该换热管开裂为氯化物应力腐蚀开裂.壳程介质循环冷却水中CI元素含量是应力腐蚀开裂的主要因素,结构缺陷、敏感的工作温度区间、水中溶解氧和含S杂质导致了应力腐蚀的快速发展.     

某炼油厂冷却循环水系统故障与危害性分析

根据采集的某炼油厂一年的冷却循环水系统的故障数据,采用故障模式影响及危害性分析方法对该系统的可靠性进行了分析.由该系统结构特点,划分了水冷塔、换热器、水冷塔风机、水泵、水管、阀门等7个子系统及19种故障模式,统计了各子系统的故障率,分析了系统的故障模式及其故障原因,计算了各子系统的危害度.结果表明水泵及水冷塔风机的危害度最高,换热器的危害度排第三,但其故障率排第四,说明在做故障分析时不能只统计故障率而不进行危害度分析.最后提出了相应的改进措施,经过一年的实际运行,效果明显.     

Integrated leakage detection and localization model for gas pipelines based on the acoustic wave method

With the development of natural gas transportation systems, major accidents can result from internal gas leaks in pipelines that transport high-pressure gases. Leaks in pipelines that carry natural gas result in enormous financial loss to the industry and affect public health. Hence, leak detection and localization is a major concern for researchers studying pipeline systems. To ensure the safety and improve the efficiency of pipeline emergency repair, a high-pressure and long-distance circular pipe leakage simulation platform is designed and established by similarity analysis with a field transmission pipeline, and an integrated leakage detection and localization model for gas pipelines is proposed. Given that the spread velocity of acoustic waves in pipelines is related to the properties of the medium, such as pressure, density, specific heat, and so on, this paper proposes a modified acoustic velocity and location formula. An improved wavelet double-threshold de-noising optimization method is also proposed to address the original acoustic wave signal collected by the test platform. Finally, the least squares support vector machine (LS-SVM) method is applied to determine the leakage degree and operation condition. Experimental results show that the integrated model can enhance the accuracy and precision of pipeline leakage detection and localization.     

湿法脱硫系统优化分析

分析了运用烟塔合一等技术对现有湿法脱硫系统简化的可行性.在湿法脱硫系统中,利用冷却塔排烟气代替烟囱排烟,取消烟囱和GGH换热器,将增压风机和引风机合二为一,可提高能源的利用效率,减少设备的投资,降低系统运行及维护费用.     

飞机货舱低气压环境对火灾探测参量影响研究

旨在为飞机货舱火灾探测系统设计和研制提供理论支撑,在飞机货舱环境模拟实验舱内开展了70kPa、80kPa、90kPa和100kPa下正庚烷火灾实验,分析了低气压环境对顶棚温度、烟气密度和气体浓度火灾探测参量的影响规律。低压下空气密度较小,卷吸系数减小,导致顶棚最高温升增加,顶棚温度衰减变快。同时,低压下烟气密度降低,并与压力呈指数关系,指数系数约为0.946,扩展了前人研究结果的应用范围。CO浓度最大值随压力降低而增加,且CO增长速率与压力呈负指数关系。CO2增长速率随着压力降低而略有减小。     

Experimental Study of the Interation Between the Water Mists and PVC Fire

Effect of water mist on the small-scale solid fuel polyvinyl chloride (PVC) fire in the confined space has been studied experimentally with the heat release rate measured by a cone calorimeter in this paper.The water mist is generated by a single pressure nozzle and the diffusion flame is produced from PVC samples respectively. The LDV/APV system is employed to determine the water mist characteristics. The Cone Calorimeter is used to measure the heat release rate, oxygen and carbon monoxide concentrations and other important parameters of the interaction under various conditions.The results of the test showed that heat extraction cooling (flame cooling and fuel surface cooling) plays a dominating role to suppress the PVC fire, when the water mist with enough volume flux are applied to the diffusion flame in the confined space. The higher the operation pressure, the easier the suppression. The faster the PVC fire suppressed by water mist with large enough water flux, the less the total amount of toxic gases (CO, CO₂) produced.     

基于风险的检验技术在苯加氢装置管道的应用

简述基于风险的压力管道检验技术基本理念,讨论压力管道的危害风险和失效模式,介绍了风险评估方法及其适用场合、风险评估程序。对某苯加氢装置的管道系统进行风险检验评价,对该管道的各种危险因素进行分析,并对其基础数据和检验检测结果进行了研究和探讨,近而采用5×5风险矩阵法和定性分析,对苯加氢装置管道系统进行风险评估,根据该评估结论,提出了科学制定检修计划的建议和控制风险措施。研究结果表明:基于风险的检验技术,既能节约大量的停机和检验维修费用,又能有效地提高重点设备的安全性和管理水平。