Critical mass flow rate in accordance with the omega-method of DIERS and the Homogeneous Equilibrium Model

A correlation frequently used in practice for the design of the relief cross-section next to the Homogeneous Equilibrium Model is the so-called ω-method. For the determination of the ω-parameter a definition was originally reported by J.C. Leung in 1986. A new expression was proposed by the same author in 1995. Predictions of the critical mass flow rate using both the new and the old ω-parameter formulations as well as the Homogeneous Equilibrium Model are compared for some typical substances. Results demonstrate that the deviations as a rule are acceptable for practical use, if the proposed range of application and recommended property data calculation are respected.     

Safety relief analysis for methanol-acetic anhydride system by stationary methods and dynamic simulation

The Leung method proposed by the Design Institute of Emergency Relief Systems (DIERS) is widely used in the design of relief systems involving two-phase flow. However, this method is not always suitable for all the situations. The calculating results may be unacceptably large, especially under high overpressure. To aid selection of appropriate vent sizing methods, a typical vapor system experiment (esterification of methanol-acetic and anhydride) was conducted by the vent sizing unit (VSU) of accelerating rate calorimeter (ARC). Seven different stationary methods were used to calculate the venting size under overpressure of 10%, 20%, 50%, 100% and 200%. Through the systematic comparison of different methods, a conservatism order of stationary methods was summarized as well as the selecting principles for these methods were discussed. Process simulation was also applied to investigate the relationship between reactor temperature/pressure and its relief size, which could be used in the prediction of vent size in vapor system conveniently without complex calculating procedure.     

Importance of accounting for the piping system and boundary conditions in determining the maximum surge pressure following heat-exchanger tube-rupture

Shell-tube type heat exchangers are often used to exchange heat between a high-pressure fluid and a low-pressure fluid, and the pressure difference between the two fluids could be significantly high. If the difference in the design pressure between the low-pressure (LP) and high-pressure sides is greater than that covered by American Petroleum Institute (API 520 and 521) 10/13^th rule, dynamic analysis is required to ascertain that the maximum surge pressure that could be reached does not compromise the integrity of the LP side of the exchanger. API guidelines also notes that attention should also be given not only to the shell-side of the heat exchanger under evaluation, but also to the “upstream and downstream systems” This paper offers further insight into the importance of including the surrounding piping systems around the subject heat-exchanger where a tube-rupture scenario is considered, and also directs attention to the importance of correctly specifying the appropriate boundary conditions (B.C.) at the far ends of both the upstream and downstream piping systems. It demonstrates the effects of specifying different B.C. on the maximum pressure surge via a case study of a hot separator vapour condenser in a bitumen hydrotreating unit, where the process fluid on the tube-side is a vapour–liquid mixture at 9660 kPa(g). The vapour mass fraction of the process fluid is approximately 0.5, and is mostly hydrogen. The fluid on the LP side is cooling water connected to the plant supply and return cooling systems as well as another adjacent low pressure condenser. The design pressure for the cooling water piping system and the adjacent condenser is 1380 kPa(g).     

Pressure relief sizing of reactive system using DIERS simplified methods and dynamic simulation method

Incidents involving uncontrolled chemical reactions continue to result in fatality, injury and economic loss. These incidents are often the result of inadequate pressure relief system designs due to a limited knowledge of the chemical reactivity hazard. A safe process design requires knowledge of the chemical reactivity of desired as well as undesired chemical reactions due to upset conditions. Simplified, cost effective methods to relief system sizing are presented by The Design Institute of Emergency Relief Systems (DIERS). They require multiple experiments, and sizing is only valid for the system composition and thermal inertia represented by the small scale experiments. Results are often conservative, especially for gassy systems. Detailed, dynamic computer simulation is highly accurate and can be used for iterative design and multiple scenario evaluation.In this study, an accelerating rate calorimeter (ARC^®) and a low thermal inertia calorimeter (automatic pressure tracking adiabatic calorimeter – APTAC™) were used to collect chemical reactivity data for the dicumyl peroxide and toluene system. Results of the pressure relief system sizing using the dynamic simulation method are presented and compared with DIERS simplified methods.     

Dynamic safety analysis of process systems with an application to a cryogenic ammonia storage tank

A method for calculating the dynamic reliability of safety systems and its application to a refrigerated liquid cryogenic ammonia storage tank is presented. The method is based on the theory of Markov chains and can model dynamic phenomena of the process and its safety systems. It offers the capability of modelling realistically the competing process of repairing failed safety systems and the exceeding of safe limits by some critical physical parameters of the process. The results of the Markovian analysis are compared to those of the classical Fault Tree/Event Tree methods and it is shown that the proposed method offers a substantial improvement over the classical approach. The probability of failure from overpressure of a cryogenic ammonia storage tank depends in general on the level of the ammonia in the tank at the time of accident initiation. Assuming a uniform distribution for the ammonia level in the tank, the average upper and lower limits for the failure probability over a year provided by the FT/ET methods span three orders of magnitude [1.4×10⁻¹–1.0×10⁻⁴] depending on whether repair is considered or not. The proposed approach realistically determines this failure probability at 3.3×10⁻³. Additional results from specific levels of ammonia are also provided.     

基于J2EE的塔里木石油公路交通安全信息系统架构与实现

在WebService结构的基础上,提出一种B/S结构的交通安全管理信息系统;介绍了塔里木石油公路交通安全信息系统的设计模式;阐述了在传统的Web平台的缺点与局限性下选择基于J2EE的系统架构平台的选择的理由;并对基于J2EE平台的多层体系构架设计与实现方法进行详细分析;给出了系统的主要功能模块及其关键技术,如系统的集成、查询、发布和工作流的实现等;最终实现了塔里木石油公路交通安全信息管理的信息化、网络化。     

Modeling of explosion dynamics in vessel-pipe systems to evaluate the performance of explosion isolation systems

Explosion isolation systems provide critical protection for interconnected vessels and work areas, preventing the spread of explosions through interconnecting pipes and ducts. These systems not only prevent propagating events, but also mitigate the elevated explosion hazards of interconnected vessels, related to pressure piling and enhanced turbulence. Explosion isolation systems can, however, fail catastrophically when they are not properly designed for a use case.Evaluating the performance of explosion isolation systems includes assessing their pressure resistance, flame-barrier efficacy, and determining appropriate installation distances, which typically requires extensive testing. To predict the performance of a system for use cases outside the tested conditions, models are needed to reliably predict both the explosion dynamics and the isolation system response.In this study, a physics-based model for explosion dynamics in vented vessel-pipe systems is developed and validated. An extensive series of large-scale validation experiments were conducted, including tests using an 8 m³ vessel with attached pipes, varying the pipe dimensions, ignition location, and mixture reactivity. The model accurately captures the effects of experimental parameters and predicts the time available for isolation systems to form a flame barrier. This model can help to predict installation distances and reduce the number of tests needed to comprehensively evaluate explosion isolation systems and their use cases.     

基于VSP2的引发剂质量分数对醋酸乙烯聚合反应失控特性及安全泄放设计影响研究

为了解决醋酸乙烯聚合反应失控所引起的超压问题,通过VSP2绝热量热仪研究了醋酸乙烯聚合反应的失控特性,并通过Leung's法对某醋酸乙烯聚合反应器的安全泄放面积进行了计算;然后,在其他条件不变的情况下,研究引发剂质量分数对失控特性和泄放面积的影响,结果表明,引发剂质量分数对反应总放热量的影响不大,体系绝热温升为105~115℃;但引发剂质量分数越大,失控反应的最大温升速率和最大压升速率越大。这是因为引发剂质量分数越大,在相同泄放压力和最大累积压力下,单位质量反应物的放热速率就越大,也就需要更大的泄放面积;最后,引入无量纲数W~*、G~*和A~*,拟合出它们与引发剂质量分数X*的关系式,结果表明,在研究范围内所需安全泄放面积随引发剂质量分数线性增大。     

Individual risk analysis of high-pressure natural gas pipelines

Transmission pipelines carrying natural gas are not typically within secure industrial sites, but are routed across land out of the ownership of the pipeline company. If the natural gas is accidentally released and ignited, the hazard distance associated with these pipelines to people and property is known to range from under 20 m for a smaller pipeline at lower pressure to up to over 300 m for a larger pipeline at higher pressure. Therefore, pipeline operators and regulators must address the associated public safety issues.This paper focuses on a method to explicitly calculate the individual risk of a transmission pipeline carrying natural gas. The method is based on reasonable accident scenarios for route planning related to the pipeline's proximity to the surrounding buildings. The minimum proximity distances between the pipeline and buildings are based on the rupture of the pipeline, with the distances chosen to correspond to a radiation level of approximately 32 kW/m². In the design criteria for steel pipelines for high-pressure gas transmission (IGE/TD/1), the minimum building proximity distances for rural areas are located between individual risk values of 10⁻⁵ and 10⁻⁶. Therefore, the risk from a natural gas transmission pipeline is low compared with risk at the building separated minimum distance from chemical industries.     

Rigorous Calculation of Critical Flow Conditions for Pressure Safety Devices

Sizing and verification of pressure relieving systems is an important topic in the design of process plants in order to assure equipments and people protection against malfunctions and hazards. The calculation of the critical flow (choke) condition is analysed with respect to existing standard calculations procedures (API and Omega methods) that implement approximate procedures and may not be extended to temperature/pressure regions near the thermodynamic critical point. These procedures may be replaced by a more rigorous calculation based on the evaluation of the local sonic velocity with equations of state. The method applies to systems composed of pure chemical components as well as to multi-component mixtures existing in the single phase and multi-phase regions. As a consequence of an exact calculation of the critical flow conditions, more accurate values of the discharged flowrate may be obtained. Comparisons with calculations performed using the standard API RP 520 procedure and Omega method are presented.     

Challenges in performing technical safety reviews of modifications – A case study

The aim of the present study, is to identify strengths and weaknesses of the technical safety review process at a Swedish Nuclear Power Plant (NPP). In this context, the function of safety reviews are understood as expert judgements on proposals for design modifications¹ and redesign of technical systems (i.e. commercial nuclear reactors), supported by formalised safety review processes. The chosen methodology is using two complementary methods: interviews of personnel performing safety reviews, and analysis of safety review reports from 2005 to 2009.The study shows that personal integrity is a trademark of the review staff and there are sufficient support systems to ensure high quality. The partition between primary and independent review is positive, having different focus and staff with different skills and perspectives making the reviews, which implies supplementary roles. The process contributes to “getting the right things done the right way”. The study also shows that though efficient communication, feedback, processes for continuous improvement, and “learning organizations” are well known success factors in academia, it is not that simple to implement and accomplish in real life.It is argued that future applications of safety review processes should focus more on communicating and clarifying the process and its adherent requirements, and improve the feedback system within the process.     

Brake reactions of distracted drivers to pedestrian Forward Collision Warning systems

Introduction: Forward Collision Warning (FCW) can be effective in directing driver attention towards a conflict and thereby aid in preventing or mitigating collisions. FCW systems aiming at pedestrian protection have been introduced onto the market, yet an assessment of their safety benefits depends on the accurate modeling of driver reactions when the system is activated. This study contributes by quantifying brake reaction time and brake behavior (deceleration levels and jerk) to compare the effectiveness of an audio-visual warning only, an added haptic brake pulse warning, and an added Head-Up Display in reducing the frequency of collisions with pedestrians. Further, this study provides a detailed data set suited for the design of assessment methods for car-to-pedestrian FCW systems. Method: Brake response characteristics were measured for heavily distracted drivers who were subjected to a single FCW event in a high-fidelity driving simulator. The drivers maintained a self-regulated speed of 30 km/h in an urban area, with gaze direction diverted from the forward roadway by a secondary task. Results: Collision rates and brake reaction times differed significantly across FCW settings. Brake pulse warnings resulted in the lowest number of collisions and the shortest brake reaction times (mean 0.8 s, SD 0.29 s). Brake jerk and deceleration were independent of warning type. Ninety percent of drivers exceeded a maximum deceleration of 3.6 m/s² and a jerk of 5.3 m/s³. Conclusions: Brake pulse warning was the most effective FCW interface for preventing collisions. In addition, this study presents the data required for driver modeling for car-to-pedestrian FCW similar to Euro NCAP's 2015 car-to-car FCW assessment. Practical applications: Vehicle manufacturers should consider the introduction of brake pulse warnings to their FCW systems. Euro NCAP could introduce an assessment that quantifies the safety benefits of pedestrian FCW systems and thereby aid the proliferation of effective systems.     

多组节理边坡稳定性FLAC3D数值分析

边坡稳定性对工程安全构成直接的威胁,对多组节理且较发育的岩体边坡稳定性安全评价,利用赤平投影方法能比较好地反映不稳定结面与边坡的几何空间关系、不稳定结构体的可能变形位移方向,为FLAC3D数值计算模型的建立提供依据。以某公路段岩体节理边坡稳定性安全评价为研究对象,通过赤平投影和FLAC3D数值计算模型稳定性分析表明,A1,J1节理组对边坡稳定性影响极大;A3,J1,A3,J2与A1,J1组节理构成贯通结构面,边坡不稳定体为两组结构面切割形成的滑体,边坡安全系数为0.67,需要支护加固。该方法对复杂节理边坡稳定性安全评价比较好地避免了采用工程经验建立数值计算模型的盲目性。     

Safety assessment of natural gas storage tank using similarity aggregation method based fuzzy fault tree analysis (SAM-FFTA) approach

Fault tree analysis (FTA) is an important method to analyze the failure causes of engineering systems and evaluate their safety and reliability. In practical application, the probabilities of bottom events in FTA are usually estimated according to the opinions of experts or engineers because it is difficult to obtain sufficient probability data of bottom events in fault tree. However, in many cases, there are many experts with different opinions or different forms of opinions. How to reasonably aggregate expert opinions is a challenge for the engineering application of fault tree method. In this study, a fuzzy fault tree analysis approach based on similarity aggregation method (SAM-FFTA) has been proposed. This method combines SAM with fuzzy set theory and can handled comprehensively diverse forms of opinions of different experts to obtain the probabilities of bottom events in fault tree. Finally, for verifying the applicability and flexibility of the proposed method, a natural gas spherical storage tank with a volume of 10,000 m³ was analyzed, and the importance of each bottom event was determined. The results show that flame, lightning spark, electrostatic spark, impact spark, mechanical breakdown and deformation/breakage have the most significant influence on the explosion of the natural gas spherical storage tank.     

城市地下交通联系隧道烟气控制探讨

为了给城市地下交通联系隧道(UTLT)防排烟系统设计和人员应急救援提供参考依据,以重庆某UTLT二期工程一段主隧道为例,开展全尺寸火灾试验,探讨了横向排烟方案的烟控效果,并验证了Alpert顶棚最高温升衰减模型。结果表明,UTLT主隧道段采用横向排烟方案,当防烟分区长度为120 m时,采用的排烟量设计方法是合理的。当隧道为上坡时,最有利的烟气控制模式为同时开启着火分区及下游相邻分区的排烟系统和与排烟分区紧邻的上、下游两个分区的补风系统。隧道顶部烟气最高温升衰减规律为:下游距火源无量纲距离r/H0.57及上游部分,呈指数衰减;下游距火源无量纲距离r/H0.57部分,呈幂函数衰减,且衰减程度与排烟方案有关。     

The integration of HAZOP expert system and piping and instrumentation diagrams

The main purpose of hazard and operability (HAZOP) analysis is to identify the potential hazards in the process design which nowadays is generally developed through a computer aided design (CAD) package. Due to the time and effort consuming nature of HAZOP, it is not done in every engineering firm for every design project. To make HAZOP an integral part of process design, an integration framework is proposed in this paper to seamlessly integrate the commercial process design package Smart Plant P&ID (SPPID, Intergraph) with one of the HAZOP expert systems (named as LDGHAZOP) developed by authors. This integration makes it possible to perform HAZOP analysis easily at anytime of the whole lifecycle of a chemical plant as long as the process design is available, which might help the improvement of design quality. One industrial case study is used to illustrate the ability of the integrated system.     

矿山企业安全生产管理缺陷预警系统

矿山企业安全管理预警是针对可能发生的事故进行事先预测和防范.介绍了企业安全管理预 警系统的模型、预警系统各模块的功能及基于J2EE模式体系的设计与实现.     

A Comparison of Skin Temperatures and Clothing Microclimate During Moderate Intermittent Exercise in the Cold Between One and Two Layers of Cotton and Polypropylene Underwear

The purpose of this study was to compare the effects of 2 kinds of underwear made from hydrophobic and hydrophilic fabrics on the mean skin temperatures and clothing microclimate (temperature, humidity) in participants performing intermittent exercise in cold environmental conditions.

One or 2 layers of cotton underwear (C1, C2) with a 2-piece long-sleeved shirt and long-legged trousers, and 1 or 2 layers of polypropylene underwear (P1, P2) with a 2-piece long-sleeved shirt and long-legged trousers were used as experimental underwear. In addition, the participants wore a 2-piece ski suit as 100% polyester clothing including 100% polyester padding. Ten young adult females volunteered as participants. The experiments were performed in a climatic chamber at an ambient temperature (T_a) of 0°C and an air velocity of 0.26 m s^?1.

The major findings are summarized as follows: (a) Although the clothing microclimate humidity was not different within the ski suit of outer clothing between C1 and P1, it was significantly higher in P2 than in C2; (b) Clothing microclimate temperature inside the ski suit did not differ between C1 and P1, whereas it was significantly higher in P2 than in C2; (c) The thermal gradient between innermost and outermost of clothing microclimate at back level did not show any difference between C1 and P1, but it was significantly higher in C2 than in P2. These results are discussed in terms of thermal physiology and clothing sciences.     

A generalized differential method to calculate lumped kinetic triplet of the nth order model for the global one-step heterogeneous reaction using TG data

Computing kinetic triplet is of importance for the process safety of combustion/gasification industries to establish the chemical reaction scheme and to assess the hazardous risk. Few approaches have been capable of calculating lumped kinetic triplet at one time efficiently, which might be attributed to the fact that the analytical solution for the nonlinear ordinary differential equation (NNODE) for the n^th order reaction model has not been found yet. This paper presents an analytical solution of NNODE to compute kinetic triplet. Results showed that the proposed method (mass fraction curve-fitting error ϕ = 1.49%–2.07%) is more efficient to compute kinetic triplet of the n^th order reaction model, comparing to genetic algorithm (GA) optimization (ϕ = 1.43%–1.81%), Coats-Redfern (ϕ = 2.36%–3.16%), peak-shape, and isoconversional methods. A compensation effect between lnA and E_a is observed due to heating rates. Effects of exported data quality and smooth processing on computation of kinetic triplet are discussed. It is the first time that an analytical solution of NNODE (n^th order model) for global one-step heterogeneous reaction is derived for computing kinetic triplet. This work may help to search for analytical solutions of power-law and Avrami-Erofeev models in the future to efficiently calculate kinetic triplet for accelerating and sigmoidal reaction systems.     

A reliability evaluation method based on the weakest failure modes for side-by-side offloading mooring system of FPSO

Offshore structures are complex systems, and numerous failure modes must be taken into consideration when reliability analysis in different loads and environment conditions are conducted on them. It is difficult to obtain structural system reliability with respect to complicated systems with numerous failure modes and dependency consideration among them. This paper applies the combination of the weakest failure modes theory with structural reliability theory to conduct reliability analysis on of side-by-side offloading mooring system of FPSO. Firstly, the numerical simulation of the system in different conditions is addressed to acquire the statistical data of time-history stress of components including hawsers, fenders and yoke, based on which, the reliability indexes of all the failure modes and correlation coefficient matrix are derived. Then the weakest failure modes, i.e. the representative failure modes that have significant impact on the system, are located through Probability Network Evaluation Technique. The probability of structural system is estimated through the weakest failure modes by considering the system as series. The analysis results indicate that two environment conditions (0°&0°&0° and 0°&30°&45° in combinations of wave, wind and current) are relative dangerous, which is in good correspondence with the practical expertise. The method is verified to be an effective and convenient evaluation approach for structural reliability analysis in terms of complex systems. It is beneficial for the identification of structure indicators from the weakest failure mode group and conduct optimum of structural system configurations in the design stage.