Safety-centered process control design based on dynamic safe set

The objective of this research is to develop an approach for the process control design problem with safety as the primary target. The work proposes the concept of dynamic safe set (DSS) to characterize and evaluate the safeness of a closed-loop system.The DSS is defined as a set of initial states of the process that guarantees safe operation, which is represented by a set of safety-critical constraints that is to be satisfied at all times. The DSS calculation accounts for potential safety threatening disturbances that may significantly affect the dynamics of the system. An addon control scheme based on the DSS concept is proposed to guide the system when it is under sudden and large set point changes that may be needed during abnormal situations. Existing system theoretic concepts of maximal output admissible sets is used to mathematically formulate and determine the DSS. The concept of dynamic safety margin (DSM) is proposed as a quantitative measure of the size of DSS. An approach based on the DSS and DSM concepts for process control design with the objective to maximize safety, subject to other performance constraints, is proposed.The approach is tested on an exothermic CSTR case study. The results showed the strong effect of steady state operating conditions, control parameters and actuator design parameters on DSM. A grid of design parameters that includes the reactor set point, the controller parameters, and the heat exchanger design parameter was analyzed. The analysis led to identifying a maximally safe control system design. The proposed approach allowed to formulate the process control design problem by bringing safety upfront, without compromising performance metrics.     

Algorithmic fault tree synthesis for control loops

Efficient process control is an integral part of the design and operation of a safe and productive chemical plant. It is crucial for fault tree analysis since control systems are designed to prevent process deviations. How to handle control loops is a major concern in the research of computer-aided fault tree synthesis for the chemical process industry (CPI). This paper presents a systematic methodology to produce fault tree models for control loops and protective safe guards. Two examples are provided to illustrate the basic idea.     

Cyclist casualty severity at roundabouts – To what extent do the geometric characteristics of roundabouts play a part?

Introduction: In general, priority junctions are converted into roundabouts to increase capacity and reduce vehicle accidents. However, previous research has indicated that roundabouts are dangerous for vulnerable users, especially cyclists. Method: This paper investigates which design factors influence cyclist casualty severity at give way (non-signalized) roundabouts with mixed traffic, using the UK STATS19 National dataset of cyclist casualties. First, the correlation matrix was generated to observe the relationship between variables. Second, dimension reduction was applied to geometric design variables in order to reduce the number of variables and generate the factors. Finally, the binary logistic regression method, with serious and slight casualties as dependent variables, was applied in three steps. The first Binary Logistic Regression Model (BLRM) included speed limit, sociodemographic, and meteorological conditions. The variables in the second BLRM consisted of geometric design variables. The third BLRM included the factors that were generated by dimension reduction. Results: The correlation matrix revealed that the number of lanes on approach and half width on approach were statistically significantly correlated, while the variables, such as geometric design (entry path radius, number of arms, number of flare lanes on approach, type of roundabout and number of circulating lanes), sociodemographic (casualty gender and age), speed limit and meteorologically related factors (daylight, weather and road surface condition), did not show any statistical significance. From the dimension reduction process, two main factors were identified, including Approach Capacity (Factor 1) and Size of Roundabout (Factor 2), and they were subsequently used as independent variables in the logistic regression analysis. The subsequent BLRMs showed that a higher speed limit reduces the safety for cyclists at roundabouts. The probability of a serious casualty increases by approximately five times (odds ratio 4.97) for each additional number of lanes on approach and by 4% (odds ratio 1.04) with a higher entry path radius. It was also found that Factor 2 (Approach Capacity) increases the casualty severity (odds ratio 1.86) for cyclists at roundabouts. Practical applications: While this research studied roundabouts in the UK, the methodological approach and statistical analysis techniques are applicable to other countries and the findings are likely to be of value to decision makers worldwide.     

Risk analysis and risk management approaches applied to the petroleum industry and their applicability to IO concepts

Due to changes introduced by Integrated Operations (IO) it is possible that traditional risk analysis and risk management approaches in the oil and gas industry are also challenged. In this paper we study the impact on these approaches by asking two questions: (1) what methods for risk analysis are used in the Norwegian oil and gas industry? (2) What are the risk analysis and risk management challenges in an IO context from the perspective of actors in the Norwegian oil and gas industry? An explorative approach was chosen and the empirical findings are based on three separate studies: (1) a survey of risk analysis and risk management in different business sectors in the oil and gas industry; (2) qualitative interviews about the generation of knowledge for decisions that involve risk in an operating company; and (3) qualitative interviews of people working with risk analyses in different companies exploring their use of risk analysis methods. The four main results are: due to IO it is necessary to look for other inputs to risk analyses; establish suitable assessment approaches to human and organizational issues; develop resilience-based approaches for operational risk assessment; and, utilize IO to improve the risk management process.     

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.     

Model selection and fault detection approach based on Bayes decision theory: Application to changes detection problem in a distillation column

The fault detection of industrial processes is very important for increasing the safety, reliability and availability of the different components involved in the production scheme. In this paper, a fault detection (FD) method is developed for nonlinear systems. The main contribution consists in the design of this FD scheme through a combination of the Bayes theorem and a neural adaptive black-box identification for such systems. The performance of the proposed fault detection system has been tested on a real plant as a distillation column. The simplicity of the developed neural model of normal condition operation, under all regimes (i.e. steady-state and unsteady state), used in this case is realised by means of a NARX (Nonlinear Auto-Regressive with eXogenous input) model and by an experimental design. To show the effectiveness of proposed fault detection method, it was tested on a realistic fault of a distillation plant of laboratory scale.     

The effect of a participative product design process on user performance

The use of hand tools can lead to accidents, overexertion injuries and discomfort. So, there is certainly room for better-designed hand tools, especially hand tools that contribute to better performance. In the literature, the benefits of a participative product design approach are clearly shown. However, the effect of this approach is hardly ever measured at the hand tool performance level.The goal of this project was to study the effect of a participative product design process on indicators of health, performance and comfort.Two sets of screwdrivers were tested. One set was developed by a participative product design approach and the control by a traditional approach.The study indicates positive effects of the participative approach. Some indicators for health and safety (discomfort in the hand and blisters) were significantly better for the test set compared with the control set. The effect on productivity is clearly shown (16% higher productivity) and the positive effects on comfort are also shown.It is discussed that it is plausible that in the long run some of the effects found in this study would still be seen under real working conditions, but long-term effects on health and safety still need to be studied.     

Quantitative risk assessment integrated with dynamic process simulation for reactor section in heavy oil desulfurization process

A new methodology for quantitative risk assessment (QRA) integrated with dynamic simulation and accident simulation is proposed. The objective of this study is to discover inherent risks that are undetectable by conventional risk analysis methods based on steady-state conditions. The target process is the reactor section in the heavy oil desulfurization (HOD) process, which is likely to pose vast potential risks due to the high operating conditions of pressure and temperature. First, a dynamic simulation of a shut-down procedure was performed to observe the behavior of process variables using Aspen HYSYS V10, which is a commercially available process software. Based on the results of the dynamic simulation, several blind spots indicating a higher operating pressure than that in the steady-state simulation were identified. To assess the risks of the detected blind spots, a QRA was performed using the commercial software of SAFETI V8.22, which performs risk calculation based on consequence and frequency data. As a result of applying the proposed method to the HOD process, the risk assessment outcome was identified as intolerably risky unlike that of steady-state conditions, thereby indicating that dynamic simulations can serve as a method to spot inherent risks that are undetectable in steady-state conditions. In addition, mitigation procedures that reduce the risk of the process to a tolerable level are performed, thereby enabling a safer and more reliable process.     

储罐两环段喷淋圈管对供给强度的影响

国内储罐火灾爆炸事故时有发生,储罐消防冷却系统实施有效的冷却是控制火势和扑救初期火灾的主要因素之一。为了研究油罐消防喷淋系统在灭后冷却中的影响,本文选取4座5×10~3内浮顶罐组,开展消防冷却水系统喷洒实验,通过测试分析发现:实际的冷却水供给强度不满足规范的要求,并探讨了储罐固定冷却水系统供给强度不足的原因,结合分析的原因建议对规范中着火罐和临近罐供水强度要求统一均为2.5 L/(min·m^2),其冷却水喷淋圈管设置应为四段以上。     

An index to account for safety and controllability during the design of a chemical process

Inherent safety is well known as the best technique of risk management, but its implementation is a challenge when there is a conflict with other factors, in particular with the process dynamic performance when the application of the minimization principle is considered. In this work, a combined safety-controllability index applicable during the design stage of a process is presented. The index accounts for the process controllability and the risk of the chemical inventory inside the process. The condition number is used to assess controllability, and the quantitative risk analysis technique is carried out to obtain a distance of affectation as a metric for individual risk. The index, based on a combination of normalized values of metrics for controllability and risk, was applied to three case studies dealing with distillation processes that separate flammable and toxic chemicals. The effect of relevant design variables such as column diameter and residence time was analyzed. It is shown how conflicts between safety and controllability exist for different values of those design variables and how a proper controllability-risk compromise can be identified with the use of the proposed index.     

Optimization of dilution ventilation layout design in confined environments using Computational Fluid Dynamics (CFD)

Dilution ventilation systems have been widely used to control the airborne toxic and explosive material in confined spaces. Layout design of dilution ventilation is critical to industrial hygiene control and ventilation efficiency. A properly designed dilution ventilation system can significantly improve the safety of confined workshops and maintain a comfortable work condition. In this work, Computational Fluid Dynamics (CFD) has been used to analyze the performance of dilution ventilation system in the confined workshop environment. Seven different ventilation layouts are proposed to evaluate ventilation performance of different installation layouts. Carbon monoxide (CO), which has the similar density as air, is selected as the sample contaminant to conduct steady-state CFD simulations. The simulation results of different layouts are examined and compared to get the optimal layout design for the best contaminant control. Results have shown that the layout with two opposite inlets has the highest ventilation efficiency among seven proposed layouts. This work can serve as a reference to increase dilution ventilation efficiency and minimize the energy cost in general confined areas.     

Kullback-Leibler distance-based enhanced detection of incipient anomalies

Accurate and effective anomaly detection and diagnosis of modern engineering systems by monitoring processes ensure reliability and safety of a product while maintaining desired quality. In this paper, an innovative method based on Kullback-Leibler divergence for detecting incipient anomalies in highly correlated multivariate data is presented. We use a partial least square (PLS) method as a modeling framework and a symmetrized Kullback-Leibler distance (KLD) as an anomaly indicator, where it is used to quantify the dissimilarity between current PLS-based residual and reference probability distributions obtained using fault-free data. Furthermore, this paper reports the development of two monitoring charts based on the KLD. The first approach is a KLD-Shewhart chart, where the Shewhart monitoring chart with a three sigma rule is used to monitor the KLD of the response variables residuals from the PLS model. The second approach integrates the KLD statistic into the exponentially weighted moving average monitoring chart. The performance of the PLS-based KLD anomaly-detection methods is illustrated and compared to that of conventional PLS-based anomaly detection methods. Using synthetic data and simulated distillation column data, we demonstrate the greater sensitivity and effectiveness of the developed method over the conventional PLS-based methods, especially when data are highly correlated and small anomalies are of interest. Results indicate that the proposed chart is a very promising KLD-based method because KLD-based charts are, in practice, designed to detect small shifts in process parameters.     

Two-tier Haddon matrix approach to fault analysis of accidents and cybernetic search for relationship to effect operational control: a case study at a large construction site.

The Haddon matrix is a potential tool for recognizing hazards in any operating engineering system. This paper presents a case study of operational hazards at a large construction site. The fish bone structure helps to visualize and relate the chain of events, which led to the failure of the system. The two-tier Haddon matrix approach helps to analyze the problem and subsequently prescribes preventive steps. The cybernetic approach has been undertaken to establish the relationship among event variables and to identify the ones with most potential. Those event variables in this case study, based on the cybernetic concepts like control responsiveness and controllability salience, are (a) uncontrolled swing of sheet contributing to energy, (b) slippage of sheet from anchor, (c) restricted longitudinal and transverse swing or rotation about the suspension, (d) guilt or uncertainty of the crane driver, (e) safe working practices and environment.     

Fault detection approach for systems involving soft sensors

This paper develops a new approach for fault detection which involves soft sensors for process monitoring. Unlike existing approaches, which compare current measurements, or linear combinations thereof, to values of these measurements representing normal operations, the methodology presented here deals directly with the state estimates that need to be monitored. The advantage of such an approach is that the effect of abnormal process conditions on the state variables can be directly observed and that it is possible to include nonlinear relationships between measurements and states. At the same time, this type of approach has the drawback that the variances of the unmeasured states are not equal to the variances of the actual process variables due to the use of a soft sensor. However, for many popular soft sensor techniques, such as Kalman filters and related approaches, it is possible to compute variances of the predicted states that correspond to normal operating conditions. This paper presents a general framework for using soft sensors for process monitoring, i.e., soft sensor design and computation of the statistics that represent normal operating conditions, and illustrates this framework in three specific applications. It should be pointed out that the contribution of this work does not lie with the soft sensor design or the computation of the statistics itself as either part has individually already been addressed in the existing literature. However, the authors are not aware of any studies where both tasks are combined for process monitoring, which forms the contribution of this work.     

航空承运人审定监察系统研究

阐述了建设民用航空承运人审定监察系统的必要性,探讨了航空承运人审定监察系统的概念和特征,指出航空承运人审定监察系统是国家民用航空监管部门使用的,利用系统构型模型和数据收集工具完成对航空承运人系统设计评估和系统运行绩效的评估,进而对航空承运人依据规章提出改进系统设计和运行的要求,对航空承运人开展风险管理的流程、工具、信息系统的集合。此系统具有管理性、系统性、自动化三个特征。文中研究并提出了该系统的框架结构、主要功能模块设置,分析了该系统与不同组织机构间的协调关系。其中系统以＂两个闭环流程＂,＂六个的功能模块＂实现了审定监察工作的闭环管理,实现了正式的风险管理与安全保证功能在局方审定监察工作中的强化与落实。     

Model-based hazard identification in multiphase chemical reactors

Chemical productions operated in extreme conditions (high pressure, high temperature) require a detailed analysis of all potentially dangerous situations that can lead to a major industrial accident and thus cause a loss of life and property. Many accidents in the near or distant history underline the need of a detailed safety analysis in process industries, not only in the phase of plant design but also during the operation of the plant. It would be shown that simulation of a chemical unit using an appropriate mathematical model and the nonlinear analysis theory can be a suitable tool for safety analysis. This approach is based on mathematical modeling of a process unit where both the steady-state analysis, including the analysis of the steady states multiplicity and stability, and the dynamic simulation are used. Principal objective of this paper is to summarize problems regarding the model-based hazard identification in processes. A case study, focused on phenomena of multiple steady states in ammonia synthesis reactor will be presented. The influence of the model complexity and model parameters uncertainly on the quality of safety analysis would be underline.     

Strength reliability analysis of aluminium–carbon fiber/epoxy composite laminates

Strength reliability of composite laminated structures relates to a series of parameters such as the design sizes, material parameters and load level. By introducing the Monte Carlo simulation and response surface method respectively, a static strength-based reliability model is proposed to predict the reliability of aluminium–carbon fiber/epoxy composite laminates for composite vessels. The burst pressure of composite vessels for different layer structures is predicted using finite element analysis. In the reliability analysis, two design parameters for composite vessels: the radius of polar axis and the winding thickness of each composite layer at the cylinder are assumed to obey the uniform distribution and Gaussian distribution respectively, and the burst pressure of composite vessels is taken as the random output response. Effects of the number of sampling and the limit strength on the strength reliability of composite vessels are explored. Besides, the numerical results obtained using two methods and two distributions for two random input parameters are compared in terms of the calculation efficiency and accuracy. Numerical results also indicate the proposed probability method exhibits preferable advantage over the conventional design method merely using empirical safety coefficient.     

基于因子交互作用矩阵的采空区危险度评价研究

基于因子交互作用影响矩阵及采空区危险度影响因子分析,选取12个采空区危险度主要影响因子,建立采空区危 险度多因子交互作用矩阵模型。通过专家打分法,确定各影响因子相互作用权值,得到影响矩阵对单一因子的影响值及 单一因子对矩阵系统的影响值,从而得出采空区危险度因子影响权重表。分析影响权重表,得到对采空区影响最大的因 子为矿柱尺寸及分布和岩体断裂及破损带。采用差值法,对采空区危险度进行等级划分,最后得到采空区危险度分级图 。经过实例验证,影响矩阵法分析评价结果与实际吻合,表明采用影响矩阵法评价采空区危险度是可行的,具有实际应用 意义,可在实际矿山工程中应用推广。     

Development of worksystem safety capability index (WSCI)

This study proposes a new way of analyzing and evaluating worksystem safety based on probability models, control charts, loss functions and safety capability index. The step-by-step procedures for development of worksystem safety capability index (WSCI) are presented. The development starts with the adoption of process approach to model safety. The key feature of this development is the effective assimilation of quality engineering concepts into safety study. A case study was done in an underground coal mining situation to operationalize the development. Time between occurrences (TBO) of injuries and number of injuries (NOI) per month are considered as safety performance variables. The application shows encouraging results for safety improvement through adoption of control charts, expected loss and WSCI. The development opportunity, application potential and future scope of research are discussed.