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.     

Forced ventilation effect by Air-Fin-Cooler in modularized onshore LNG plant

Many base load onshore LNG plants use large number of Air-Fin-Coolers normally mounted on the center pipe rack of the LNG process train. Further, the LNG plant modularized approach requires large, complex structures (modules) for supporting the LNG process equipment and for allowing sea and land transportation. This results in additional congestion of the plant and large voids under module-deck, which are confined by large girders. Thus, in case of leaks, the proper ventilation to reduce the accumulation of gas is critical for the safety of the plant.This paper evaluates the Air-Fin-Cooler induced air flow in modularized LNG plants using Computational Fluid Dynamics (CFD) analysis.The results of this evaluation show that the ventilation of the Air-Fin-Cooler induced air flow is influenced by the process train orientation. Further, a moderate increase is observed in specific design conditions or areas, such as shorter separation distances between modules. Based on the results of this evaluation, four design measures are proposed to optimize the use of Air-Fin-Cooler, such as train orientation against prevailing wind direction and use of the grating deck material.     

Quantitative risk analysis of fire and explosion on the top-side LNG-liquefaction process of LNG-FPSO

Since the massive use and production of fuel oil and natural gas, the excavating locations of buried energy-carrying material are moving further away from onshore, eventually requiring floating production systems like floating production, storage and offloading (FPSO). Among those platforms, LNG-FPSO will play a leading role to satisfy the global demands for the natural gas in near future; the LNG-FPSO system is designed to deal with all the LNG processing activities, near the gas field. However, even a single disaster on an offshore plant would put the whole business into danger. In this research, the risk of fire and explosion in the LNG-FPSO is assessed by quantitative risk analysis, including frequency and consequence analyses, focusing on the LNG liquefaction process (DMR cycle). The consequence analysis is modeled by using a popular analysis tool PHAST. To assess the risk of this system, 5 release model scenarios are set for the LNG and refrigerant leakages from valves, selected as the most probable scenarios causing fire and explosion. From the results, it is found that the introduction of additional protection methods to reduce the effect of fire and explosion under ALARP criteria is not required, and two cases of the selection of independent protection layers are recommended to meet the SIL level of failure rate for safer design and operation in the offshore environment.     

Dynamic risk analysis of offloading process in floating liquefied natural gas (FLNG) platform using Bayesian Network

The growing demand for natural gas has pushed oil and gas exploration to more isolated and previously untapped regions around the world where construction of LNG processing plants is not always a viable option. The development of FLNG will allow floating plants to be positioned in remote offshore areas and subsequently produce, liquefy, store and offload LNG in the one position. The offloading process from an FLNG platform to a gas tanker can be a high risk operation. It consists of LNG being transferred, in hostile environments, through loading arms or flexible cryogenic hoses into a carrier which then transports the LNG to onshore facilities. During the carrier's offloading process at onshore terminals, it again involves risk that may result in an accident such as collision, leakage and/or grounding. It is therefore critical to assess and monitor all risks associated with the offloading operation. This study is aimed at developing a novel methodology using Bayesian Network (BN) to conduct the dynamic safety analysis for the offloading process of an LNG carrier. It investigates different risk factors associated with LNG offloading procedures in order to predict the probability of undesirable accidents. Dynamic failure assessment using Bayesian theory can estimate the likelihood of the occurrence of an event. It can also estimate the failure probability of the safety system and thereby develop a dynamic failure assessment tool for the offloading process at a particular FLNG plant. The main objectives of this paper are: to understand the LNG offloading process, to identify hazardous events during offloading operation, and to perform failure analysis (modelling) of critical accidents and/or events. Most importantly, it is to evaluate and compare risks. A sensitivity analysis has been performed to validate the risk models and to study the behaviour of the most influential factors. The results have indicated that collision is the most probable accident to occur during the offloading process of an LNG carrier at berth, which may have catastrophic consequences.     

Backtracking and prospect on LNG supply chain safety

The safety issues of Liquefied Natural Gas (LNG) in production, storage, loading/unloading, transportation/shipping, and re-gasification have became a major concern, since an accident in the LNG industry would be very costly. Understanding the threat of LNG not only contributes to the process safety and reliability in the research and development (R&D) system, but improves the efficiency of loss prevention, fire protection and emergency responses. As of April 2019, in order to obtain the present status and trend of LNG safety research, basing 1122 documents of the Web of Science database about safety research of LNG as a data source, CiteSpace and VOS viewer were used for network knowledge map analysis. A comprehensive knowledge map of LNG safety field was obtained from several research aspects including scientific research power, research hot spots and trends, research knowledge base and frontier. According to the study results, the development of LNG safety research was divided into four stages from 1970s to 2019, China and South Korea made a lot of contributions, and the United States is the most influential. Among them, the research from 2005 to 2019 was the most representative. Current research results indicate that a combination of Formal Safety Assessment (FSA) methodology and Dynamic Procedure for Atypical Scenarios Identification (DyPASI) will fully identify risks; The PHAST and TerEx programs quickly define safety zones. Computational Fluid Dynamics (CFD) software package can provide accurate quantitative data for the study of LNG safety. Research on quantitative risk assessment (QRA) and LNG evaporated gas (BOG) has been a hot topic and trend in this field. The application of expansion foam in LNG accident mitigation covers most of the research content in this field, and the optimization of LNG liquefaction process has a great influence on this industry. As the international demand for LNG energy output increases, floating liquefied natural gas (FLNG) will have considerable development, and increasingly researchers attach vital importance to the safety of LNG offshore production integrated unit.     

Forced ventilation effect by Air-Fin-Cooler on flammable gas cloud dispersion

This paper is the second installment of a paper published on Process Safety and Environment Protection in 2013, which evaluates the Air-Fin-Cooler (AFC) forced ventilation effect over natural ventilation inside congested LNG process train, i.e., modularized LNG, considering the Air Change per Hour (ACH) using Computational Fluid Dynamics (CFD) analysis. This second paper evaluates the effect of forced ventilation on gas cloud dispersion using CFD in order to evaluate possible design measures, such as safety distance in trains and whether to shut down the AFC in case of releases. The results of this evaluation show that gas cloud accumulation is reduced by AFC induced air flow in the case of shorter separation distances between modules. Based on the results, two design measures are proposed, i.e., keep AFC running during emergency and train orientation against prevailing wind direction.     

Evaluating a safety culture campaign: Some lessons from a Norwegian case

The focus of the present study is on the implementation and some of the results of an evaluation of a safety culture campaign that partly was aimed at increasing workmate interventions (care). I focus on three groups either working on or with a Norwegian offshore platform: onshore managers, crane operators and process operators. The research questions are: “Has the safety culture campaign contributed to new safety cultures related to care in the three groups, why/why not and what can we learn from this?”. The study indicates that two of the groups have developed new safety cultures that sensitize them to new hazards, motivate and legitimize new preventive practices. In accordance with the interpretive approach to culture in organizations, these changes are discussed in light of members’ of each group’s negotiation over the meaning and relevance of campaign efforts on workmate interventions. Lessons that can be learned from the study are discussed.     

Risk-based shutdown management of LNG units

Global demand for natural gas may double by 2030, with Liquefied Natural Gas (LNG) growing perhaps fivefold - driven by continued cost reduction. Propane Pre-cooled Mixed Refrigerant (PPMR) of Air Products and Chemicals Inc. (APCI) currently holds 78% of the liquefaction plants on the market. Since the PPMR process has the largest production capacity, its operational reliability needs to be high as any failure may result in catastrophic consequences. Therefore, operational reliability has a key importance in LNG plants. To achieve an acceptable reliability, usually, a constant interval of a preventive maintenance method is used. The limitation of such a method is that the shutdown strategy is not optimum. This study focuses on determining a risk-based shutdown management strategy for APCI plants with capacity of 4.5 million tons per annum. To achieve the minimum risk for the expected life of an LNG plant, a combination of preventive maintenance, active redundancy and standby redundancy is considered. Results of this study reveal that such a combination can significantly reduce the operational risk. This combination improves the plant reliability and maintains it above a minimum operational reliability.     

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.     

Inherent safety in offshore oil and gas activities: a review of the present status and future directions

Inherent safety is a proactive approach for hazard/risk management during process plant design and operation. It has been proven that, considering the lifetime costs of a process and its operation, an inherently safer approach is a cost-optimal option. Inherent safety can be incorporated at any stage of design and operation; however, its application at the earliest possible stages of process design (such as process selection and conceptual design) yields the best results.Although it is an attractive and cost-effective approach to hazard/risk management, inherent safety has not been used as widely as other techniques such as HAZOP and quantitative risk assessment. There are many reasons responsible for this; key among them are a lack of awareness and the non-availability of a systematic methodology and tools.The inherent safety approach is the best option for hazard/risk management in offshore oil and gas activities. In the past, it has been applied to several aspects of offshore process design and operation. However, its use is still limited. This article attempts to present a complete picture of inherent safety application in offshore oil and gas activities. It discuses the use of available technology for implementation of inherent safety principles in various offshore activities, both current and planned for the future.     

Validation of FLACS against experimental data sets from the model evaluation database for LNG vapor dispersion

The siting of facilities handling liquefied natural gas (LNG), whether for liquefaction, storage or regasification purposes, requires the hazards from potential releases to be evaluated. One of the consequences of an LNG release is the creation of a flammable vapor cloud, that may be pushed beyond the facility boundaries by the wind and thus present a hazard to the public. Therefore, numerical models are required to determine the footprint that may be covered by a flammable vapor cloud as a result of an LNG release. Several new models have been used in recent years for this type of simulations. This prompted the development of the “Model evaluation protocol for LNG vapor dispersion models” (MEP): a procedure aimed at evaluating quantitatively the ability of a model to accurately predict the dispersion of an LNG vapor cloud.This paper summarizes the MEP requirements and presents the results obtained from the application of the MEP to a computational fluid dynamics (CFD) model – FLACS. The entire set of 33 experiments included in the model validation database were simulated using FLACS. The simulation results are reported and compared with the experimental data. A set of statistical performance measures are calculated based on the FLACS simulation results and compared with the acceptability criteria established in the MEP. The results of the evaluation demonstrate that FLACS can be considered a suitable model to accurately simulate the dispersion of vapor from an LNG release.     

Inherently safer design in offshore oil and gas projects

Like all hazardous installations, inherently safer design (ISD) is one of the key tools in offshore oil and gas projects to minimize risks in offshore facilities. As the life cycle of offshore facilities is relatively short compared with onshore counterparts and there are many projects running every year, the potential is high for raising inherent safety standards and lowering safety risks throughout the offshore industry as old facilities are phased out. This paper gives an overview of offshore facilities and examples of implementation of ISD. Good examples of ISD are numerous. Industry guidance on ISD implementation abound. Yet, the systematic implementation of it in the industry is patchy. There are many reasons for factors which impede the effective, efficient and consistent implementation of ISD in projects. This paper describes some of them and proposes solution to address them. They include (a) the effective integration of ISD into hazard management systems with appropriate language to engage all disciplines in projects, (b) the phasing of resources to enable the project to capture ISD measures which are only available during early phases, (c) application of appropriate ISD goals and ISD performance metrics at various stages and (d) the appropriate use of quantified risk assessment to support ISD.     

Acoustic analysis of blast waves produced by rapid phase transition of LNG released on water

Massive offshore and onshore storage of fuel have led the international community to raise questions about the hazards on the surrounding installations and people. Among the possible accidental scenarios when cryogenic gas as liquefied natural gas (LNG) is spilled on water at a very fast rate, the phenomenon of rapid phase transition (RPT) may occur: large amounts of energy are released during phase transition which can generate explosions. The related consequences should be added to the possible consequences of fire in terms of flash fire, fireball, pool fire, and vapour cloud explosion for confined and congested geometry surrounding the release point.In this paper, the analysis of RPT of LNG has been studied from the point of view of blast wave production, through ab initio acoustic analysis for monopole source. Maximum overpressures, as calculated at the source point and along the blast pathway are compared with results of large scale experiments. Safety distances are given for the sake of comparison with threshold distances reported in the open literature.     

The digital representation of safety systems at “Seveso” plants and its potential for improving risk management

At Seveso plants, duty holders must have a complex system for assessing and managing risks. The pillars of this system are the safety report and the safety management system, with a number of underlying documents. The strength of the system is the high standardization of these documents. Regulations, standard codes and guidelines define content, structure and formats. The weakness is the high complexity. Managers and workers perceive documents as difficult to understand and far from actual operations. Major threats for the credibility of documents (and therefore for the safety systems) come from the continuous organizational and technical changes, which in a short time can make most documents obsolete; as well as by near misses, which continuously show the holes in safety systems. A big effort is required to follow up the plant changes and the near misses. In order to help safety managers, a new software has been developed. At Seveso plants, it has been possible build an integrated digital representation, because all documents are perfectly structured. This representation may be used both for updating the relevant documents after a change and to improve documents after a near miss or an accident. In this way, safety documents are always up to date and trustworthy and the huge knowledge, which is usually hidden inside safety documents, is clearly revealed and revived. The approach is basically “knowledge based” and the intention is to provide safety managers with an easy and simple tool. IRISonLine is a software that has been developed by ISPESL to provide safety managers of “Seveso” establishments with a tool for improving the management of change and of near misses.     

Application of risk analysis in the liquefied natural gas (LNG) sector: An overview

In recent years, the global demand for liquefied natural gas (LNG) as an energy source is increasing at a very fast rate. In order to meet this demand, a large number of facilities such as platforms, FPSO (floating production, storage and offloading), FSRU (floating storage and regasification unit) and LNG ships and terminals are required for the storage, processing and transportation of LNG. Failure of any of these facilities may expose the market, companies, personnel and the environment to hazards, hence making the application of risk analysis to the LNG sector a very topical issue throughout the world. To assess the risk of accidents associated with LNG facilities and carriers, various risk analysis approaches have been employed to identify the potential hazards, calculate the probability of accidents, as well as assessing the severity of consequences. Nonetheless, literature on classification of the risk analysis models applied to LNG facilities is very limited. Therefore, to reveal the holistic issues and future perspectives on risk analysis of LNG facilities, a systematic review of the current state-of-the-art research on LNG risk analysis is necessary. The aim of this paper is to review and categorize the published literature about the problems associated with risk analysis of LNG facilities, so as to improve the understanding of stakeholders (researchers, regulators, and practitioners). To achieve this aim, scholarly articles on LNG risk analysis are identified, reviewed, and then categorized according to risk assessment methods (qualitative, semi-qualitative or quantitative; deterministic or probabilistic; conventional or dynamic), tools (ETA, FTA, FMEA/FMECA, Bayesian network), output/strategy (RBI, RBM, RBIM, facility siting, etc.), data sources (OREDA handbook, published literature, UK HSE databases, regulatory agencies' reports, industry datasets, and experts’ consultations), applications (LNG carriers and LNG fuelled ships, LNG terminals and stations, LNG offshore floating units, LNG plants), etc. Our study will not only be useful to researchers engaged in these areas but will also assist regulators, policy makers, and operators of LNG facilities to find the risk analysis models that fit their specific requirements.     

Safety design: Towards a new philosophy

Thinking on safety integration right from design stage is of some interest in research terms. How can we increase the overall efficiency of a working system, whilst reducing risks at source and consequently costs? Can future operation of a working system be anticipated? What can be anticipated? Can we help designers to respond to statutory requirements by experience feedback and by structuring our knowledge of working system operational performance?Based on a “user-focused” design approach, this paper is structured in two sections. The first section comprises analysis of the existing position by focusing specifically on the question of safety at design stage, the second part includes generic recommendations for making work equipment design safer and more “secure”.     

Key parametric analysis on designing an effective forced mitigation system for LNG spill emergency

Concerns over public safety and security of a potential liquefied natural gas (LNG) spill have promoted the need for continued improvement of safety measures for LNG facilities. The mitigation techniques have been recognized as one of the areas that require further investigation to determine the public safety impact of an LNG spill. Forced mitigation of LNG vapors using a water curtain system has been proven to be effective in reducing the vapor concentration by enhancing the dispersion. Currently, no engineering criteria for designing an effective water curtain system are available, mainly due to a lack of understanding of the complex droplet–vapor interaction. This work applies computational fluid dynamics (CFD) modeling to evaluate various key design parameters involved in the LNG forced mitigation using an upwards-oriented full-cone water spray. An LNG forced dispersion model based on a Eulerian–Lagrangian approach was applied to solve the physical interactions of the droplet–vapor system by taking into account the various effects of the droplets (discrete phase) on the air–vapor mixture (continuous phase). The effects of different droplet sizes, droplet temperatures, air entrainment rates, and installation configurations of water spray applications on LNG vapor behavior are investigated. Finally, the potential of applying CFD modeling in providing guidance for setting up the design criteria for an effective forced mitigation system as an integrated safety element for LNG facilities is discussed.     

Understanding and eliminating pressure fluctuations in an extended chlor-alkali plant due to the size detail of seal pots: A design correlation

When chlorine lines from a new caustic soda plant were added to chlorine lines from an older plant that used the same chlorine compression and liquefaction systems, we encountered abnormal pressure fluctuations on the chlorine side of the new plant. These fluctuations were being transmitted to the chlorine cycle in the older plant, posing a safety hazard in both facilities. After checking the pressure control systems, a design correlation for positive-pressure seal pot was observed and it was found from the inconsistency in the sizes of those equipments in the two plants. The problem was solved by reducing the diameter of the chlorine pipeline in the positive-pressure seal pot of the new plant. After implementing this solution, pressure fluctuations were fully removed, and satisfactory pressure control was attained in both plants.     

Underwater LNG release: Does a pool form on the water surface? What are the characteristics of the vapor released?

One of the scenarios of concern in assessing the safety issues related to transportation of LNG in a marine environment (ship or underwater pipeline) is the release of LNG underwater. This scenario has not been given the same level of scientific attention in the literature compared to surface releases and assessment of consequences therefrom. This paper addresses questions like, (1) does an LNG spill underwater form a pool on the water surface and subsequently evaporate like an LNG spill “on the surface” producing cold, heavier than air vapors?, and (2) what is the range of expected temperatures of the vapor, generated by LNG release due to heat transfer within the water column, when it emanates from the water surface?Very limited data from two field tests of LNG underwater release are reviewed. Also presented are the results from tests conducted in other related industries (metal casting, nuclear fission and fusion, chemical processing, and alternative fuel vehicles) where a hot (or cold) liquid is injected into a bulk cold (or hot) liquid at different depths.A mathematical model is described which calculates the temperature of vapor emanating at the water surface, and the liquid fraction of released LNG that surfaces, if any, to form a pool on the water surface. The model includes such variables as the LNG release rate, diameter of the jet at release, depth of release and water body temperature. Results obtained from the model for postulated release conditions are presented. Comparison of predicted results with available LNG underwater release test data is also provided.