Approach enhancing inherent safety application in onshore LNG plant design

This study aims to provide the approach for inherent safety design of onshore LNG plants to be applied at the very early stages (concept definition phase) of the project development. Onshore LNG plant development project starts from the “Concept Definition” phase, where financial feasibility is estimated and major conditions, such as site location and plant foot print, are set.The inherent safety design basic criteria and design measures should be identified and selected when setting the basic conditions during the Concept Definition phase of the project development, such as the site location (relative location from populated areas), site condition (prevailing wind direction) and plant production capacity (number of process train, number of product tanks). The safety measures, which are usually not fully developed at the project early stages in the current design execution practices, are the emergency systems, which mitigate an accident escalation, the modularized plant and layout, and the tank selection.The inherent safety design measures discusses in this paper were identified based on the categories of plot plan, emergency system, and module plant application.The proposed approach will contribute to improve inherent safety design of onshore LNG plants and it will also yield schedule and cost benefits.     

Accident prevention approach throughout process design life cycle

The accident rate in the chemical process industry (CPI) has not been decreasing although majority of accident causes have been identified and could have been prevented by using existing knowledge. These recurring accidents show that the existing knowledge has not been used effectively. In this paper, accident knowledge learned from earlier accident analyses are utilized to predict the common design errors during chemical plant design. An accident prevention approach throughout process design life cycle is proposed for a safer design consideration where designers are guided to identify common design errors, accident contributors and critical points to look for. The accident prevention approach has been applied to analyze the BP Texas City Refinery Explosion and Fire tragedy.     

Qualitative Assessment for Inherently Safer Design (QAISD) at preliminary design stage

Conventional hazard evaluation techniques such as what-if checklist and hazard and operability (HAZOP) studies are often used to recognise potential hazards and recommend possible solutions. They are used to reduce any potential incidents in the process plant to as low as reasonably practicable (ALARP) level. Nevertheless, the suggested risk reduction alternatives merely focus on added passive and active safety systems rather than preventing or minimising the inherent hazards at source through application of inherently safer design (ISD) concept. One of the attributed reasons could be the shortage of techniques or tools to support implementation of the concept. Thus, this paper proposes a qualitative methodology that integrates ISD concept with hazard review technique to identify inherent hazards and generate ISD options at early stage of design as proactive measures to produce inherently safer plant. A modified theory of inventive problem solving (TRIZ) hazard review method is used in this work to identify inherent hazards, whereby an extended inherent safety heuristics tool is developed based on established ISD principles to create potential ISD options. The developed method namely Qualitative Assessment for Inherently Safer Design (QAISD) could be applied during preliminary design stage and the information required to apply the method would be based on common process and safety database of the studied process. However, user experiences and understanding of inherent safety concept are crucial for effective utilisation of the QAISD. This qualitative methodology is applied to a typical batch reactor of toluene nitration as a case study. The results show several ISD strategies that could be considered at early stage of design in order to prevent and minimise the potential of thermal runaway in the nitration process.     

Risk reduction concept to provide design criteria for Emergency Systems for onshore LNG plants

The functional safety requirement is widely applied in the process plant industry in accordance with the international standards, such as IEC and ISA. The requirement is defined as safety integrity level (SIL) based on the risk reduction concept for protection layers, from original process risk to tolerable risk level. Although the standards specify both, the Prevention System and the Emergency System, as level of protection layers, the standards specify in detail only the use of the Prevention System (i.e., Safety Instrumented System (SIS)). The safety integrity level is not commonly allocated to the Emergency System (e.g., Fire and Gas System, Emergency Shutdown System and Emergency Depressuring System). This is because the required risk reduction can be normally achieved by only the Prevention System (i.e., SIS and Pressure Safety Valve (PSV)). Further, the risk reduction level for the Emergency System is very difficult to be quantified by the actual SIL application (i.e., evaluated based on the single accident scenario, such as an accident from process control deviation), since the escalation scenarios after Loss of Containment (LOC) greatly vary depending on the plant design and equipment. Consequently, there are no clear criteria for evaluating the Emergency System design. This paper aims to provide the functional safety requirement (i.e., required risk reduction level based on IEC 61508 and 61511) as design criteria for the Emergency System.In order to provide clear criteria for the Emergency System evaluation, a risk reduction concept integrated with public’s perception of acceptable risk criteria is proposed and is applied to identify the required safety integrity level for the Emergency System design. Further, to verify the safety integrity levels for the Emergency Systems, the probabilistic model of the Emergency Systems was established considering each Emergency System (e.g., Fire and Gas System, Emergency Shutdown System and Emergency Depressuring System) relation as the Overall Emergency System. This is because the Overall Emergency System can achieve its goal by the combined action of each individual system, including inherent safe design, such as separation distance.The proposed approach applicability was verified by conducting a case study using actual onshore Liquefied Natural Gas Plant data. Further, the design criteria for Emergency Systems for LNG plants are also evaluated by sensitivity analysis.     

Origin of equipment design and operation errors

The paper discusses the origin of chemical process equipment accidents by analyzing past accident cases available in the Failure Knowledge Database (FKD). The design and operation errors of the process equipment that caused the accidents were analyzed together with their time of occurrence. It was found that design errors contributed to 79% of accidents while the rest were only due to human and organizational errors in the operation stage and external factors. The most common types of errors were related to layout, organizational errors in the operation stage, considerations of reactivity and incompatibility, and wrongly selected process conditions (each approx. 13% of total accident contributors). On average there were about 2 design errors per accident. The timing of the errors was quite evenly distributed between various lifecycle stages. Nearly half (47%) of the errors were made in process design-oriented stages, one fourth (26%) in detailed engineering, and one fifth (20%) in operation. In addition, the most frequent design and operation errors for each equipment type were identified. A points-to-look-for list was created for each equipment type, showing also the typical time of occurrence of the error. The knowledge of type and timing of design errors can be utilized in design to focus the hazard analysis in each stage on the most error-prone features of design.     

Method for identifying errors in chemical process development and design base on accidents knowledge

It has been claimed that the high accident rate in the chemical process industry is due to poor dissemination of accident knowledge that affects directly the level of learning from accidents. In response to this situation, this paper utilized past accident knowledge as a basis to develop a safety oriented design tool whereby the accident information were directly disseminated into plant design. The method was developed based on our previous accident analysis of design error in which the common design errors were ranked in accordance to their frequency and its origins during normal plant design project. Based on the design error ranking and its origin at a specific design phases, a method for design error detection is proposed. The method is expected to be able to identify the possible design error and its causes throughout chemical process development and design. The main objective is to trigger safe design thinking at the specific design phases so that appropriate action for risk reduction could be timely implemented. The Bhopal and BP Texas tragedies are used as case studies to test and verify the method. The proposed method can detect up to 74% of design errors.     

设计初期化工过程本质安全化设计策略

该文提出了一种在设计初期进行化工过程本质安全化设计的策略。首先进行危险物质与危险能量两类共计11种危险类型的危险辨识。针对辨识出的危险类型,通过与相应的临界条件比较进行快速的危险评价,对于不可接受的危险必须采取本质安全化措施,可接受的危险可有选择性地进行本质安全化设计。在设计初期可以使用的本质安全化原则主要是消除、最小化、替代和缓和,针对11种危险类型可以应用不同的本质安全化设计模型,以使实际进行本质安全化设计时更加简单与快捷。该文把提出的本质安全化设计策略应用到一个甲苯硝化制硝基甲苯的工艺,形成了多种本质安全化措施,可以用来在设计初期消除或减少危险。     

The design of BP ETAP platform against gas explosions

Risks of personal injury from gas explosion, together with fire and smoke ingress, were among the key hazards that the Eastern Trough Area Project (ETAP) team intended to design out as far as possible. This paper describes the process ETAP followed to achieve this. The process involved the early application of the appropriate advance technology and personnel at the concept selection stage and right through different stages during design, and an integrated team including explosion specialists.All major design decisions on explosion optimisation were made at the early stage of front-end engineering design (FEED), resulting in a relatively straightforward detailed design phase. These early design decisions had the effect of not only reducing gas explosion consequences, but simplifying layout, e.g. reducing pipe run and structures. The end result is a design which gives inherently low risk to personnel and Temporary Refuge impairment without the uncertainties of high cost of late remedial work to take account of high explosion loads, and consequent project delay.     

性能化设计思想在化工设施布局安全设计中的应用

指令性规范是目前化工设施平面布局安全设计的主要依据,但其在应用中存在着条款僵化、安全理论基础不全面、可拓展性不明确等问题。本文将性能化设计思想引入到化工企业平面布局安全设计中,初步提出了一种包含危险辨识、性能化目标确定、后果评估及安全设施效用评估等主要组成部分的基于性能化设计思想的平面布局安全设计体系。对体系中最重要的部分—性能化目标确定进行了重点分析,将化工设施布局安全设计分为装置内设备之间的位置设计、厂区内装置区之间的位置设计以及厂区与外部单位之间的位置设计三个级别,从工艺关联性等角度对各级别布局设计中事故场景选择及设施可接受受损水平进行分析,并提出了通过匹配事故场景和设施可接受受损水平来确定性能化目标的方法。     

Simulation-based approach to design of inherently safer processes

Safety of chemical processes and plants is a matter of high priority. The design of an inherently safer process is one of very beneficial ways of achieving this goal.The paper describes the method of designing an inherently safer process for a chosen set of equipment and materials involved by applying non-linear optimization. The optimization is aimed at finding an operational mode, which guarantees safety of the process under normal conditions and provides maximal attainable safety in case of one typical accident scenario – cooling failure. Discussion covers problem statement, choice of the optimization criteria, appropriate methods for defining control variables.An important practical challenge is stability analysis of the optimized process mode with respect to permissible deviations of control parameters and variables from the estimated values. The original method for the stability analysis of a non-stationary process is proposed. It comprises simplified preliminary evaluation method followed by the more detailed numerical optimization-based analysis.Several examples illustrate application of the methods proposed.     

Estimation of chemical concentration due to fugitive emissions during chemical process design

Fugitive emissions are not an environmental concern alone, but are also a health concern. From occupational health standpoint, fugitive emissions are the main sources of origin of the continuous exposure to workers. Operating plants regularly measure release and concentration levels through a plant-monitoring program. However, for processes which are still ‘on paper’, predictive estimation methods are required. Therefore, three methods for estimating concentration of the fugitive emissions are presented for the process development and design phases of petrochemical processes. The methods estimate the fugitive emission rates and plant plot dimensions resulting to fugitive emission concentrations. The methods were developed for the type and amount of information available in three process design stages; conceptual design, preliminary process design, and detailed process design. The methods are applied on a real benzene plant; the estimated benzene concentrations are compared to the actual concentration measured at the plant. The results show that as the information mounts up during design, the concentration estimate becomes more accurate. The results indicate that the methods presented provide simple estimates of fugitive emission-based concentrations during the design stages.     

Inherent occupational health assessment during preliminary design stage

Chemical process routes can already be assessed as early as in the development and design phases. Process screening should not look at economic and technical aspects only, but also the safety, health, and environmental performances. In this paper, a method called the Health Quotient Index (HQI) is presented for the preliminary process design phase. The HQI provides a simple approach to quantify workers' health risk from exposure to fugitive emissions e.g. in petrochemical plants. The method utilizes process data from flow sheet diagram, which is already available at the preliminary design stage. Since the mechanical details of the process are still unknown, a database of the precalculated fugitive emissions for typical operations in chemical plants was created to simplify the assessment. The HQI can be used to rank alternative process concepts or to quantify the risk level of processes. As a case study, six process routes for producing methyl methacrylate are discussed. Three health indexes are compared in the case study. The HQI is able to highlight the difference of hazard levels between the routes better as a result of more detailed assessment of the exposures.     

Assessing the hazards from a BLEVE and minimizing its impacts using the inherent safety concept

Many worlds' major process industry accidents are due to BLEVE such as at Feyzin, France, 1966 and San Juan Ixhuatepec, Mexico City, 1984. One of the approaches to eliminate or minimize such accidents is by the implementation of inherently safer design concept. This concept is best implemented where the consequence of BLEVE can be evaluated at the preliminary design stage, and necessary design improvements can be done as early as possible. Thus, the accident could be avoided or minimized to as low as reasonably practicable (ALARP) without resorting to a costly protective system. However, the inherent safety concept is not easy to implement at the preliminary design stage due to lack of systematic technique for practical application. To overcome these hurdles, this paper presents a new approach to assess process plant for the potential BLEVE at the preliminary design stage and to allow modifications using inherent safety principles in order to avoid or minimize major accidents. A model known as Inherent Fire Consequence Estimation Tool (IFCET) is developed in MS Excel spreadsheet to evaluate BLEVE impacts based on overpressure, radiation heat flux and missile effects. In this study, BLEVE impacts are the criteria used as the decision-making for the acceptability of the design. IFCET is integrated with iCON process design simulator for ease of data transfer and quick assessment of potential BLEVE during the design simulation stage. A case study was conducted to assess of potential BLEVE from a propane storage vessel at the design simulation stage using this new approach. The finding shows promising results that this approach has a potential to be developed as a practical tool.     

Inherent risk assessment—A new concept to evaluate risk in preliminary design stage

Quantitative Risk Assessment (QRA) has been a very popular and useful methodology which is widely accepted by the industry over the past few decades. QRA is typically carried out at a stage where complete plant has been designed and sited. At that time, the opportunity to include inherent safety design features is limited and may incur higher cost. This paper proposes a new concept to evaluate risk inherent to a process owing to the chemical it uses and the process conditions. The risk assessment tool is integrated with process design simulator (HYSYS) to provide necessary process data as early as the initial design stages, where modifications based on inherent safety principles can still be incorporated to enhance the process safety of the plant. The risk assessment tool consists of two components which calculate the probability and the consequences relating to possible risk due to major accidents. A case study on the potential explosion due to the release of flammable material demonstrates that the tool is capable to identify potential high risk of process streams. Further improvement of the process design is possible by applying inherent safety principles to make the process under consideration inherently safer. Since this tool is fully integrated with HYSYS, re-evaluation of the inherent risk takes very little time and effort. The new tool addresses the lack of systematic methodology and technology, which is one of the barriers to designing inherently safer plants.     

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.     

Intervention strategies for accident-involved drivers: An experimental evaluation of current California policy and alternatives

This project was designed to evaluate current and alternative strategies for selecting and treating accident-involved drivers in California. The current accident-based selection criteria were contrasted with an expanded selection strategy that included convictions as well as accidents as criteria for selection. The standard diagnostic reexamination treatment was compared to two alternative behavior modification treatments—an accident avoidance session and a mailed educational pamphlet/self-administered test. Interaction between treatments and selection criteria revealed that accident-involved drivers with minimum conviction histories were amenable to treatment intervention, while accident-involved drivers with more extensive conviction histories were not. Treatment effects were statistically significant (p < .02), with each of the treatment groups having posttreatment accident means in excess of 20% lower than comparable control groups.     

Process design optimization and risk analysis

Hazard identification and risk assessment are key aspects in process plant design. They are often applied in the final stages of the process at whatever the cost, unless financial constraints are imposed. However, a much better solution would be to introduce risk analysis earlier by including it in earlier stages of the design process, such as when the cost of a plant and the cost of any accidents that may occur are estimated. In this paper, an optimization methodology is proposed, in which both cost and risk (with a deterministic approach) are taken into account, to improve on the current situation. If a decision variable is chosen, an objective function will be established that makes it possible to analyze variations in overall costs, including the cost of the investment and the cost of accidents. This leads to an optimum situation in which costs are kept to a minimum. Of course, this optimization is subject to constraints, the greatest of which is the fact that risk must not exceed tolerated threshold levels. The procedure is explained and two examples, one involving a toxic release and the other a BLEVE/fireball, are used to illustrate it.     

Inherent risk assessment methodology in preliminary design stage: A case study for toxic release

At preliminary design stage, process designers normally lack of information on the risk level from process plant. An inherently safer process plant could be designed if the information of risk levels could be known earlier at the preliminary design stage. If the risk level could be determined, there is a possibility to eliminate or reduce the risk by applying the well-known concept: inherent safety principle. This paper presents a technique to determine the risk levels at preliminary process design stage using a 2-region risk matrix concept. A model to calculate the severity and likelihood of a toxic release accident was developed in Microsoft Excel spreadsheet. This model is integrated with process design simulator, iCON to allow for data transfer during preliminary design stage. 2-region risk matrix is proposed and used to evaluate the acceptability of the inherent risk based on the severity and likelihood rating. If the inherent risk level is unacceptable, modification for improvement can be done using the inherent safety principles. A case study has been carried out to illustrate the benefit of applying this newly developed technique. It was successfully shown that an inherently safer plant could easily be designed by applying this technique.