Influence of parameter uncertainty on modeling of industrial ammonia reactor for safety and operability analysis

Chemical reactors represent probably the most hazardous units of chemical industry. Safety analysis of a chemical reactor requires basic knowledge of all particular processes which can be described by mathematical models. Most of the model parameters involved in the prediction of reactor behavior are uncertain. These uncertainties can cause discrepancies mainly in the prediction by models with nonlinear behavior and they can be the source of confusion in the design of chemical reactors and consequently also in the safety and operability analysis.The main aim of this work was to analyze the influence of uncertainties in the model parameters on the prediction of operating quantities by mathematical models with nonlinear behavior. Such analysis can be used for safety and operability analysis of an industrial catalytic ammonia reactor. The industrial fixed-bed reactor was used by a mathematical model with nine parameters. Analyses of the influence of uncertainty in a single model parameter and their combination were carried out by the Monte Carlo approach. It is shown that even a small uncertainty in one of the key parameters or in a combination of these key parameters can result in several steady states results of the operating quantities and can be the source of confusion in the design and consequently also in the safety and operability analysis.     

Model-based HAZOP study of a real MTBE plant

Integration of a mathematical model approach with hazard and operability (HAZOP) analysis is presented in this contribution. The presented analysis is based on the mathematical modelling of a process unit, where both the steady-state analysis (including continuation and bifurcation analyses), and the dynamic simulation are used. The main benefit of this integration is the ability to perform a detail safety analysis for a relatively complicated process. Such an approach may dramatically decrease the possibility that several sources of hazard will be overlooked. Of course, the presented methodology may also seriously reduce the time necessary for the hazard identification process. In this paper, a methyl tertiary-butyl ether (MTBE) production unit was chosen to identify potential hazard and operational problems of a real process. This simplified case-study unit consists of two investigated types of equipment: a tubular fixed bed reactor and a reactive distillation column.     

Process analysis of an industrial waste-to-energy plant: Theory and experiments

Thermal conversion is fundamental in an integrated waste management system due to the capability of reducing mass and volume of waste and recovering energy content from unrecyclable materials. Indeed, power generation from industrial solid wastes (ISW) is a topic of great interest for its appeal in the field of renewable energy production as well as for an increasing public concern related to its emissions. This paper is based on the process engineering and optimization analysis, commissioned to the University Campus-Biomedico of Rome by the MIDA Tecnologie Ambientali S.r.l. enterprise, ended up in the construction of an ISW thermo-conversion plant in Crotone (Southern Italy), where it is nowadays operating. The scientific approach to the process analysis is founded on a novel cascade numerical simulation of each plant section and it has been used initially in the process design step and after to simulate the performances of the industrial plant. In this paper, the plant process scheme is described together with the values of main operating parameters monitored during the experimental test runs. The thermodynamic and kinetic basics of the mathematical model for the simulation of the energy recovery and flue gas treatment sections are presented. Moreover, the simulation results, together with the implemented parameters, are given and compared to the experimental data for 10 specific plant test runs. It was found that the model is capable to predict the process performances in the energy production as well as in the gas treatment sections with high accuracy by knowing a set of measurable input variables. In the paper fundamental plant variables have been considered such as steam temperature, steam flow rate, power generated as well as temperature, flow rate and composition of the resulting flue gas; therefore, the mathematical model can be simply implemented as a reliable and efficient tool for management optimization of this kind of plants.     

基于HAZOP分析的加氢装置工程设计方法

加氢装置属甲类火灾、爆炸危险生产装置。为了在设计阶段尽可能消除或控制潜在风险,本文总结了多套加氢装置HAZOP分析报告中的设备类别及其分析内容,提出了基于危险与可操作性(HAZOP)分析的加氢装置工程设计方法。在传统工程设计方法的基础上增加了参数敏感性工程设计方法,依据分析报告中的设计建议,利用ASPEN软件计算过程参数变化对目标参数的影响程度,确定参数稳定操作区域;建立了数据库管理界面实现了加氢装置工程安全设计经验知识的有序管理。应用基于HAZOP分析的加氢装置工程设计方法,有助于将安全隐患问题在设计阶段消除或加以控制,可为降低石化装置改造成本和提高装置的安全水平提供方法依据。     

混凝土结构施工中人因差错的模拟

以施工现场人因差错真实准确的调查实测数据为依据,笔者采用人的可靠性分析方法建立了混凝土结构施工中人因差错发生及其对混凝土强度影响规律的数学模型,并编制了相应的模拟计算程序。将该模拟计算程序所得的考虑人因差错的混凝土强度模拟计算结果与实测的混凝土强度调查结果进行比较,二者具有很好的一致性,说明该数学模型和模拟计算程序是比较符合实际的,也是比较合理的。上述模拟计算结果为考虑人因差错的结构安全性分析以及人因差错的有效控制措施研究提供了参考依据。     

Analysis of gas dispersion and ventilation within a comprehensive CAD model of an offshore platform via computational fluid dynamics

Maintaining an adequate air flow with a desired air quality that is free from hazardous gases is among the most important actions taken toward the improvement of safety in any process plant. Due to the increased focus on the consequences of existing hazardous material on safety, health, and the environment, air quality and sufficient ventilation within a plant has been increasingly considered in the design stage. This paper investigates and analyzes methane and hydrogen sulfite dispersion and the effect of air ventilation within a CAD model of an offshore platform using computation fluids dynamics (CFD). In addition, this method and its principals could be utilized in any other hazardous environment. Simulations of possible hazardous events along with solutions for preventing or reducing their probability are presented to better assess the data. These investigations are performed by considering hypothetical hazardous scenarios which consist of gas leakages from pipes and process equipment under different conditions. After drafting a precise and highly detailed CAD model of the plant and performing CFD simulations on this model, the results of gas behaviors, dispersion, distribution, accumulation, and its possible hazards are investigated and analyzed. The larger amount of details of the actual plant model in CFD simulation are obtained by using a combination of different methods and software. These include PDMS for 3-D drawing of the plan, Rinoceros for geometrical integration of the process equipment and facilities, and Sharc Harpoon which meshes the model. Moreover, the probability of inducing ignitable or toxic concentration of gases within the atmosphere and air ventilation of the unit is considered by these investigations.     

Process safety aspects in water-gas-shift (WGS) membrane reactors used for pure hydrogen production

The syngas produced by coal gasification processes can be utilized in Pd-based water-gas-shift membrane reactors for the production of pure H₂. Pd/alloy composite membrane reactors exhibit comparative advantages over traditional packed bed reactors such as simultaneous reaction/separation in one compact unit and increased reaction yields. Furthermore, the development of comprehensive process intensification strategies could further enhance membrane reactor performance resulting in a substantially smaller and functional, inherently safer, environmentally friendlier and more energy efficient process.A systematic non-isothermal modeling framework under both steady state and dynamic/transient conditions for a catalytic high temperature water-gas shift reaction in a Pd-based membrane reactor has been developed to characterize the dynamic behavior of the process system at various operating conditions from a process safety standpoint. In particular, various reaction conditions as well as key process variables such as feed temperature and flow rate, catalyst loading, driving force for H₂ permeation are considered as they are critically related to various safety aspects in the operation of a Pd-based membrane reactor. Within the proposed framework, process parameters and operating conditions which may induce hazards and compromise process safety are identified, analyzed and characterized. Finally, the proposed approach is evaluated through detailed simulation studies in an illustrative case study involving a real Pd-based membrane reactor used for pure hydrogen production and separation that exhibits complex behavior over a wide operating regime.     

Economic assessment of inherently safe membrane reactor technology options integrated into IGCC power plants

Pd/alloy-based (Pd/Cu, Pd/Au) membrane reactors embedded into Integrated Gasification Combined Cycle (IGCC) plants (IGCC-MR) enable the storage and/or use of the energy value of H₂ to produce electricity while the CO₂ enriched retentate exit stream becomes particularly suitable for high pressure CO₂ capture-sequestration. There is undoubtedly a lack of operating experience associated with IGCC-MR plants, and therefore, sound process intensification principles/practices should be followed not only to enhance process system performance but also to ensure process safety and economic feasibility of an IGCC-MR plant. Motivated by the above considerations, a comprehensive process economic assessment framework for an inherently safe membrane Pd/alloy-based reactor integrated into an IGCC plant is proposed. In particular, a detailed Net Present Value (NPV) model has been developed to evaluate the economic viability of an IGCC-MR plant where the membrane reactor module design conforms to basic inherent safety principles. Sources of irreducible uncertainty (market, regulatory and technological) are explicitly recognized such as the power plant capacity factor, Pd price, membrane life time and CO₂-taxes due to future regulatory action/policies. The effect of the above uncertainty drivers on the project's/plant's value is studied through Monte Carlo methods resulting in detailed NPV-distribution and process economic outcome profiles. The simulation results derived suggest that in the presence of (operational, economic and regulatory) uncertainties, inherently safe membrane reactor technology options integrated into IGCC plants could become economically viable. In particular, comparatively more attractive NPV distribution profiles are obtained when concrete safety risk-reducing measures are taken into account through pre-investment in process safety (equipment).     

Use of bifurcation analysis for identification of a safe CSTR operability

Exothermic reactions are the most interesting systems for safety analysis because of their potential safety problems and the possibility of exotic behavior like multiple steady states. An operability and safety analysis of an exothermic reaction (hydrolysis of propylene oxide to tri-propylene glycol with consecutive reactions in a CSTR) with cooling is reported in this work. The information obtained from the bifurcation diagram is used to identify a set of unsafe operation points, which have been chosen on the base of requirement of maximal production of the process. An important information of safe reactor operation is the time in which the operator must handle a critical situation. For this reason, dynamics simulation of a failure in the cooling medium flow rate has been done and discussed for each of the selected operation points.     

Safety analysis of CSTR towards changes in operating conditions

Exothermic reactions are the most interesting systems for safety analysis because of their potential safety problems and the possibility of exotic behavior such as multiple steady states. A sensitivity analysis of an exothermic reaction involving the hydrolysis of propylene oxide to propylene glycol in a CSTR with jacket cooling is presented here. The objective of this article is to determine how multiple steady states might arise. A comparison of the static and continuation method of the identification of multiple steady states and their stability is presented. Finally, the implications of safety analysis for operation and control of reactors with multiple steady states are discussed.     

Cost-based fire risk assessment in natural gas industry by means of fuzzy FTA and ETA

Fire is the most prevalent accident in natural gas facilities. In order to assess the risk of fire in a gas processing plant, a fault tree analysis (FTA) and event tree analysis (ETA) has been developed in this paper. By utilizing FTA and ETA, the paths leading to an outcome event would be visually demonstrated. The framework was applied to a case study of processing plant in South Pars gas complex. All major underlying causes of fire accident in a gas processing facility determined through a process hazard analysis (PHA). Fuzzy logic has been employed to derive likelihood of basic events in FTA from uncertain opinion of experts. The outcome events in event tree has been simulated by computer model to evaluate their severity. In the proposed methodology the calculated risk has the unit of cost per year which allows the decision makers to discern the benefit of their investment in safety measures and risk mitigation.     

基于ADAMS仿真平台的自行火炮故障仿真预测方法

针对故障仿真预测技术的现状和发展,分析了ADAMS仿真平台和专家系统的优缺点.根据自行火炮系统结构的特殊性,提出基于ADAMS(Automatic Dynamic Analysis Mechanical System)仿真平台和专家系统的故障仿真系统的建模方法和设计思想.仿真过程根据用户输入的初始状态真实体现出系统在服役状态的量变,产生动态模糊关系矩阵,并由动态模糊综合评判得到系统可能出现的故障,由预测结果调用知识库中的诊断知识产生实际发生的故障部件.这样建立的仿真模型不仅能表达领域对象的动态属性、行为特性,又能表达专家的经验、判断决策等知识,还具备较强的数值计算及过程控制能力.     

环氧乙烷生产装置的安全分析与评价

综合运用道化学公司火灾、爆炸危险指数评价法,事故树分析以及事件树分析对环氧乙烷生产装置进行安全评价,定量地得出装置的危险程度,定性地分析了各危险因素的大小以及系统中各元件的故障率对事故发生概率的影响程度,并提出了改进措施.结果表明,该装置的危险程度很大,必须加强安全生产管理,采取有效措施控制氧气的浓度,从而降低危险性等级,保证生产安全.     

JHA在橇式脱水装置检修过程中的应用

工作危害分析法（Job Hazard Analysis，简称JHA），是一种比较细致的分析作业过程中存在危害的方法，它将一项工作活动分解为相关联的若干个步骤，识别出每个步骤中的危害，并设法控制事故的发生。集气站橇式脱水装置检修工期紧、工作量大，文章在简要的介绍了橇式脱水装置工艺流程的同时，对橇式脱水装置检修过程进行描述，运用JHA分析了橇式脱水装置检修中的风险，制定了相应的安全对策，不仅保证了施工过程的安全，同时避免了检修过程中造成的环境污染。     

基于基准系统比较法的雷达间隔评估

为缓解我国目前飞行流量日渐增加、空域紧张等情况,提出了一种系统评估航空器雷达间隔的新方法。首先,介绍了雷达间隔研究所使用的基准系统比较法,给出了分析方法和评估流程;其次,在综合考虑影响飞行安全各种因素的基础上,利用近距离危险接近概率(CAP)模型和基准系统比较法,建立了航空器间的雷达间隔评估模型,可对航空器飞行安全进行量化分析评估;最后,利用统计学知识和实测数据对该方法进行对比验证。结果表明:1)不同精度的雷达与雷达安全间隔密切相关,直接影响空中交通流量和航空器的运行效率;2)对于普通二次雷达,N-N模型更能反映雷达角度误差的分布情况;3)当雷达间隔为5 n mile时,危险进近概率为1.382 1×10-11,用精度更低(雷达角度误差为0.138 13)的雷达替换时,为保证航空器飞行安全,雷达间隔应增大到5.3 n mile;4)使用高精度雷达进行管制指挥和监控,可提高飞行流量,缓解航班延误,提升管制效率。     

A formulation to optimize the risk reduction process based on LOPA

This paper presents a mixed integer nonlinear programming (MINLP) model to improve the computational use of the layer of protection analysis (LOPA). For a given set of independent protection layers to be implemented in a process, the proposed optimization model is solved to: a) Include costs associated with the different prevention, protection and mitigation devices, and b) Satisfy the risk level typically specified in the LOPA analysis through the occurrence probability. The underline purpose focuses on improving the analysis process and decision making to obtain the optimal solution in the safeguards selection that satisfies the requirements to be considered as IPL’s. The optimization is based on economic and risk tolerance criteria. As a first stage of this proposal, the safety instrumented system (SIS) design is optimized so that the selection of SIS components minimizes the risk and satisfies the safety integrity level (SIL) requirements. A case study is presented to validate the whole proposed approach.     

Consequence risk analysis using operating procedure event trees and dynamic simulation

Faults due to human errors cost the petrochemical industry billions of dollars every year and can have adverse environmental consequences. Unquantified human error probabilities exist during process state transitions performed each day by process operators using standard operating procedures. Managing the risks associated with operating procedures is an essential part of managing the overall safety risk. Additional operator training and safety education cannot eliminate all such faults due to human errors; therefore, we propose an operating procedure event tree (OPET) like analysis with branches and events specifically designed to perform risk analysis on operating procedures. The OPET method adapts event trees to analyze the risk due to human error while performing operating procedures. We consider human error scenarios during the procedure and determine the likely consequences by applying dynamic simulation. The modified event tree provides an estimate of the error frequencies.Operating procedure steps were developed, and potential operator faults were determined for two typical equipment switching procedures found in chemical plant operations. Then, dynamic simulation using Aspen HYSYS software was applied to determine the overpressure related consequences of each fault. Finally, the error frequencies resulting from those scenarios were analyzed using operating procedure event trees. We found that a typical ethylene plant gas header would overpressure with 0.6% frequency per manual dryer switch. Since dryer switches occur from every few days up to once per shift, these results suggest that dryer switching should be automated to ensure safe and environmentally friendly operation. Process dryer switching performed manually by operators opening and closing gate valves can be automated with control valves and a distributed control system. A sample distillation column was found to overpressure with 0.85% frequency per manual reflux pump switch.     

Research on multilevel information loss of the sharing process for safety information

To reveal the mechanism of information loss in the flow of safety information, and to derive an evaluation method for describing this information loss, this paper analyzes the flow of safety information based on research in safety informatics and cognitive psychology. Theoretical analysis shows that the flow of safety information can be divided into four stages: transformation, transmission, perception, and cognition. This paper describes a simplified model of the flow of safety information based on these four stages. Then, the concept of adaptive subjects is introduced, and the sources and losses of safety information are explored. In addition, a model of safety information flow loss is constructed. This model is used to analyze the connection between the information loss at each stage of the sharing process, and then a “ladder hierarchical” model for the loss of safety information is developed. Comprehensive analysis of this ladder hierarchical model of safety information leads to a formal mathematical model of safety information loss. Finally, according to the various development stages of the safety information sharing process, four key factors that affect the multilevel information loss of the safety information sharing process are extracted by the hierarchical method.     

民航安全状况与社会经济指标关联分析

为了分析中国民航的安全趋势,基于中国民航1995-2014年安全生产历史数据和民航安全运行关系密切的26项社会经济指标,利用因子分析、相关系数等数学方法,建立了多元线性回归模型分析民航安全状况与社会经济指标的管理关联性。该模型表明对民航安全具有显著影响的社会经济指标包括国民经济、产业结构和人员素质。通过对比安全生产指标的拟合值和实际值,分析民航安全趋势的变化规律,并利用自回归移动平均模型预测2015-2018年民航安全生产指标值。计算结果显示该时间段内民航安全生产指标将处于历史高位,且呈现缓慢上升趋势。最后给出了针对行业安全监管、安全运行等方面的改进建议。     

Modeling the effects of production pressure on safety performance in construction projects using system dynamics

Introduction: Construction incidents occur due to system failures, not due to a single factor such as unsafe behavior or condition. Therefore, construction safety should be investigated using a systematic view capable of illustrating the complex nature of incidents. Construction projects are also often behind their planned schedule and suffer from various pressures caused by contractual deadlines or clients. Previous studies demonstrated that such pressures negatively affect safety performance; however, the process of how production pressure influences safety performance is not fully investigated. Method: The present research aimed to understand the feedback mechanism of how production pressure interactively affects safety performance and safety-related managerial components in a construction project. Ground theory method (GTM) is used to create a conceptual causal loop diagram that shows the relationship between incident rate and other variables such as labor hour, actual and planned progress, safety climate, rework, and safety training. Moreover, a power plant construction project was used as a case study to practically investigate the conceptual model; a case study is employed to build a System Dynamics (SD) model. The simulation model was then validated using behavior reproduction and sensitivity analysis. Results: The results of the inequality statistics show that the simulation model can be used to forecast trends in the incident rate.