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In a complex processing facility, there is likelihood of occurrence of cascading scenarios, i.e. hydrocarbon release, fire, explosion and dispersion of combustion products. The consequence of such scenarios, when combined, can be more severe than their individual impact. Hence, actual impact can be only represented by integration of above mentioned events. A novel methodology is proposed to model an evolving accident scenario during an incidental release of LNG in a complex processing facility. The methodology is applied to a case study considering transitional scenarios namely spill, pool formation and evaporation of LNG, dispersion of natural gas, and the consequent fire, explosion and dispersion of combustion products using Computational Fluid Dynamics (CFD). Probit functions are employed to analyze individual impacts and a ranking method is used to combine various impacts to identify risk during the transitional events. The results confirmed that in a large and complex facility, an LNG fire can transit to a vapor cloud explosion if the necessary conditions are met, i.e. the flammable range, ignition source with enough energy and congestion/confinement level. Therefore, the integrated consequences are more severe than those associated with the individual ones, and need to be properly assessed. This study would provide an insight for an effective analysis of potential consequences of an LNG spill in any LNG processing facility and it can be useful for the safety measured design of process facilities.

Rapid development of Liquefied Natural Gas (LNG) industry and LNG vapor's flammable nature have brought up many safety issues. Computational fluid dynamics (CFD) modeling provides a powerful tool for studying the LNG spill, vapor dispersion, as well as other related safety assessments; however, traditional single phase model is unable to describe the LNG pool formation and phase change, which are essential to risk management. In this paper, we propose an integrated multiphase CFD model to simulate the complete spill process (including LNG release, LNG-water interaction, LNG evaporation and vapor dispersion) based on Falcon-1 and Burro-8 test. The computed results are compared with the experimental data and other simulation results. It is demonstrated that the multiphase CFD model provides better results than other approaches in accuracy and fully describing the LNG spill process. In addition, the effect of an impoundment on LNG spill and dispersion mitigation is also investigated. The results show that impoundment can significantly control the vapor's dispersion and shorten the hazard area, especially on lateral direction.

Liquefied natural gas (LNG) is widely used to cost-effectively store and transport natural gas. However, a spill of LNG can create a vapor cloud, which can potentially cause fire and explosion. High expansion (HEX) foam is recommended by the NFPA 11 to mitigate the vapor hazard and control LNG pool fire. In this study, the parameters that affect HEX foam performance were examined using lab-scale testing of foam temperature profile and computational fluid dynamics (CFD) modeling of heat transfer in vapor channels. A heat transfer model using ANSYS Fluent® was developed to estimate the minimum HEX foam height that allows the vapors from LNG spillage to disperse rapidly. We also performed a sensitivity analysis on the effect of the vaporization rate, the diameter of the vapor channel, and the heat transfer coefficient on the required minimum height of the HEX foam. It can be observed that at least 1.2 m of HEX foam in height are needed to achieve risk mitigation in a typical situation. The simulation results can be used not only for understanding the heat transfer mechanisms when applying HEX foam but also for suggesting to the LNG facility operator how much HEX foam they need for effective risk mitigation under different conditions.

Liquefied Natural Gas (LNG) is a clean, efficient and economic energy, which is mainly transported by LNG carriers in the marine industry. Possible spilling of cryogenic LNG puts safety of crew in danger due to fire and explosion hazards. Taking into account various uncertainties, a modified fault tree model for LNG spill accident during LNG carriers’ handling operations is constructed in this study. Human factor analysis is introduced with a goal to predict human errors in LNG carriers’ handling operation. Finally, the results of the Fault Tree Analysis (FTA) and Human Reliability Analysis (HRA) are combined, so that risks can be assessed using Monte Carlo Simulation (MCS). Comparing the results of risk assessment with the traditional FTA and corresponding criterion set, an important reference for LNG carrier management is provided for administration.

The significant hazards associated with LNG ship-to-ship bunkering could involve LNG vapour dispersion and LNG pool fires. The boil-off LNG vapour initially behaves as a denser-than-air vapour due to its cryogenic temperature and then is dissipated, as the vapour cloud heated up by surrounding environment. LNG pool fires occur due to either the source ignites immediately or a flash fire burns back to the source. It could cause thermal radiation damage to the surrounding properties or people. Due to different LNG discharge locations, i.e. below waterline, at waterline and above waterline, three possibilities of lumped LNG vapour source planes were compared to investigate the vapour dispersion behaviours and fire radiation hazards in different cases. The present study is aimed at capturing the features of different hazards, analysing the potential hazardous area and investigating a possible mitigation method by applying computational fluid dynamics. Thermal radiant heat flux and temperature were utilised to analyse the material effectiveness on both the LNG bunker and the cargo vessel. The water curtain, which is commonly used to prevent material stress cracking in case of LNG leakage, were considered appropriately to mitigate the radiation hazard.

We review liquid hydrogen (LH 2 ) as a maritime vessel fuel, from descriptions of its fundamental properties to its practical application and safety aspects, in the context of the San Francisco Bay Renewable Energy Electric Vessel with Zero Emissions (SF-BREEZE) high-speed fuel-cell ferry. Since marine regulations have been formulated to cover liquid natural gas (LNG) as a primary propulsion fuel, we frame our examination of LH 2 as a comparison to LNG, for both maritime use in general, and the SF-BREEZE in particular. Due to weaker attractions between molecules, LH 2 is colder than LNG, and evaporates more easily. We describe the consequences of these physical differences for the size and duration of spills of the two cryogenic fuels. The classical flammability ranges are reviewed, with a focus on how fuel buoyancy modifies these combustion limits. We examine the conditions for direct fuel explosion (detonation) and contrast them with initiation of normal (laminar) combustion. Direct fuel detonation is not a credible accident scenario for the SF-BREEZE. For both fuels, we review experiments and theory elucidating the deflagration to detonation transition (DDT). LH 2 fires have a shorter duration than energy-equivalent LNG fires, and produce significantly less thermal radiation. The thermal (infrared) radiation from hydrogen fires is also strongly absorbed by humidity in the air. Hydrogen permeability is not a leak issue for practical hydrogen plumbing. We describe the chemistry of hydrogen and methane at iron surfaces, clarifying their impact on steel-based hydrogen storage and transport materials. These physical, chemical and combustion properties are pulled together in a comparison of how a LH 2 or LNG pool fire on the Top Deck of the SF-BREEZE might influence the structural integrity of the aluminum deck. Neither pool fire scenario leads to net heating of the aluminum decking. Overall, LH 2 and LNG are very similar in their physical and combustion properties, thereby posing similar safety risks. For ships utilizing LH 2 or LNG, precautions are needed to avoid fuel leaks, minimize ignition sources, minimize confined spaces, provide ample ventilation for required confined spaces, and to monitor the enclosed spaces to ensure any fuel accumulation is detected far below the fuel/air mix threshold for any type of combustion.

The deflagration characteristics of premixed LNG vapour-air mixtures with different mixing ratios were quantitatively and qualitatively investigated by using CFD (computational fluid dynamics) method. The CFD model was initially established based on theoretical analysis and then validated by a lab-scale deflagration experiment. The flame propagation behaviour, pressure-time history, and flame speed were compared with the experimental data, upon which a good agreement was achieved. A large-scale deflagration fire during LNG bunkering process was conducted using the model to investigate the flame development and overpressure effects. Mesh independence and time scale were tested in order to obtain the suitable grid resolution and time step. Deflagration cases with two different LNG vapour volume fractions, i.e., 10.4% and 15.0%, were simulated and compared. The one with a volume fraction of 10.4% which was around stoichiometric mixing ratio had the highest flame propagating speed. High flame velocity observed in the simulation was coupled with the thin flame front where overpressure occurred. The CFD model could capture the main features of deflagration combustion and account for LNG fire hazard which could provide an in-depth insight when dealing with complicated cases.

A computational fluid dynamics code was used for modeling the complete spill and dispersion process of liquefied natural gas (LNG) in the Falcon 1 test, which has stable conditions, low wind speeds, and large spill volume and flow rate, in addition to the presence of an obstacle in the flow domain. The simulation results have good agreement with experimental data and can accurately capture the vapor cloud dispersion process. The model was then used to investigate the effect of air and sea surface temperatures on LNG spill and vapor cloud dispersion. The results show that an increase in the temperature has little effect on the initial growth rate of the LNG pool (0–50 s). However, as the LNG discharge rate starts to decrease (∼50–400 s), the effect of the increasing temperature becomes more apparent, with the pool size decreasing. Overall, this leads to a significant increase in downwind dispersion (by up to 26%) accompanied by a slight decrease in lateral dispersion (by up to 6%) and a slight increase in ...

The flammable vapor cloud is the primary hazard caused by a liquefied natural gas (LNG) spill on land. If it is not properly mitigated, an ignition of the vapor cloud will result in a fire or explosion hazard. High expansion foam is recommended by NFPA 11 and NFPA 471 for LNG spill hazards mitigation. This work studied the physical interaction of the LNG and expansion foam system using a foam generator and a foam test apparatus that are built in-house. The performance of the foam generator was characterized in terms of the foam expansion ratio and generation rate. The temperature profile in the foam zone quantitatively confirmed the warming effect of foam on LNG vapor. The foam breaking rate was determined at the initial stage and steady state. The boil-off effect was studied quantitatively with more details using this novel foam generator. The vapor channel formation and vapor concentration were also investigated for the mitigation effect.

Computational fluid dynamics (CFD) modeling is a useful tool for studying the spillage, dispersion, and related safety issues of liquefied natural gas (LNG). This paper presents a CFD code that directly models the complete spill and pool formation process (direct CFD simulation method), taking into consideration heat and mass transfer governing equations and the Monin−Obukhov similarity theory for atmospheric stability. The model was validated against experimental data from the Burro test series under atmospheric conditions which allowed the LNG dispersion to be predominately gravity-driven. The direct CFD simulation method clearly provides better predictions than the conventional approach, which simply estimates the pool size from natural gas inlet conditions and uses a fixed vaporization rate. The direct CFD simulation method was further applied to investigate the effect of an impoundment on LNG spill and dispersion mitigation. It was clearly shown that an impoundment can confine the LNG spill and contr...

Numerical modeling of the dynamic dispersion behaviors of heavier-than-air gas in the atmosphere often does not consider the phase change physics of the involved small quantity of water. The present paper develops a computational fluid dynamic (CFD) model in consideration of the phase change to model atmospheric cloud flow resulting from the liquefied natural gas (LNG) spills. The two-phase flow is modeled based on the single-fluid mixture model, and the species dispersion of natural gas, water vapor, oxygen and nitrogen in the atmosphere are calculated based on the respective convective–diffusion conservation equations. The original Hertz–Knudsen relation is modified to determine the mass transfer between the water vapor and the droplet, in which, the sensitivity of condensation and evaporation coefficients on simulating results are examined. The results of the calculations are compared with the counterparts without accounting for the phase change, the experimental data from Burro and Coyote trials and the simulated results of commonly used software SLAB and FEM3. The comparisons validate the improvements of the present two-phase modeling approach.

LNG vapour dispersion known as dense gas dispersion is one of the main hazards from accidental LNG spill and is of critical importance in risk assessment. Most of the previous studies on this topic were conducted in the single-phase framework which is incapable of considering the effect of fog formation. LNG importing and exporting terminals are typically located at coastal areas where there is a high chance of fog formation. In this study, a multiphase CFD model has been developed to investigate the dynamic mixing of cryogenic LNG vapour cloud and ambient air. The effect of fog formation on LNG vapour dispersion was studied. The model was validated by historical experiments conducted by LLNL, upon which good agreements were achieved. Case studies of different relative humidity were performed in order to investigate the LNG vapour dispersion behaviour affected by different fog concentrations. It was found that the affected area of the vapour dispersion is enlarged if the air relative humidity is increased. The findings in this study could improve the understanding of the mechanism of LNG vapour dispersion in humid environments, and help to provide more reliable risk assessments for LNG plants.

The pressure in liquefied natural gas (LNG) storage tank continues to increase due to the heat transfer from ambient air to low temperature LNG, which raises safety concerns. Accordingly, there is increasing interest to explore the technical approaches capable of recovering Boil-Off Gas (BOG) and even eliminating the ventilation of LNG storage tank. This research numerically analyzed the greenhouse gas emissions of the re-liquefaction of BOG using the following four approaches: 1) a Claude cycle driven by electrical motor with the electricity produced by burning coal; 2) a Claude cycle driven by a gas turbine fuelled by BOG released; 3) a Claude cycle driven by a SI engine fuelled by gasoline; 4) burning nature gas directly released by BOG. The impact of heat transfer coefficient, LNG tank configuration, size, and percentage of LNG stored in tank on the rate of BOG and energy needed for the re-liquefaction of methane vapor were investigated. The greenhouse gas emissions (GGE) was examined and compared. The data presented in this paper provide guideline for the management of pressure development in LNG storage tank.

LNG progressively become favorable energy to replace oil-based fuel due to lower cost and more environment-friendly. In order to support an emerging LNG demands in Kalimantan, PT Badak NGL, one of the leading LNG Company in the world, develops the land-transported LNG loading facility. This facility performs loading the LNG into a small-scale tank (ISO Tank) with 20 m3 capacities. Safety reviews over this facility were conducted. Based on these reviews, the LNG filling station requires supplemental safeguards, such as LNG spill containment and firefighting foam system besides firewater system and dry chemical system. The spill containment provides holding LNG spill within the limits of plant property, while the high expansion foam system deals to minimize the vaporization rate to prevent a fire incident. This paper mainly discusses designing of such supplemental safeguards. The requirement of the spill containment is 20 m3 (6.3 × 3.3 × 2.0) m and the foam system should be capable generating foam at least ...

With increasing consumption of natural gas, the safety of liquefied natural gas (LNG) utilization has become an issue that requires a comprehensive study on the risk of LNG spillage in facilities with mitigation measures. The immediate hazard associated with an LNG spill is the vapor hazard, i.e., a flammable vapor cloud at the ground level, due to rapid vaporization and dense gas behavior. It was believed that high expansion foam mitigated LNG vapor hazard through warming effect (raising vapor buoyancy), but the boil-off effect increased vaporization rate due to the heat from water drainage of foam. This work reveals the existence of blocking effect (blocking convection and radiation to the pool) to reduce vaporization rate. The blanketing effect on source term (vaporization rate) is a combination of boil-off and blocking effect, which was quantitatively studied through seven tests conducted in a wind tunnel with liquid nitrogen. Since the blocking effect reduces more heat to the pool than the boil-off effect adds, the blanketing effect contributes to the net reduction of heat convection and radiation to the pool by 70%. Water drainage rate of high expansion foam is essential to determine the effectiveness of blanketing effect, since water provides the boil-off effect.

Research into the environmental effect of greenhouse emissions is now intense. One of the sources contributing to the effect is boil-off gas (BOG) flaring into the atmosphere. BOG formation is caused by heat leakage from the liquefied natural gas (LNG) storage tank. Heat leakages are determined by the effectiveness of heat thermal transmittance of the structural tank and ambient condition. The objective of this present study is therefore to determine the relationship between heat thermal transmittance and ambient condition, and the boil-off rate for a specific 40,447m 3 LNG tank size corresponding to a 160,000m 3 LNG ship size. General estimations of the amounts of BOG generated are useful in determining the amount of BOG that will need to flare in order to control the greenhouse effect and the amount of pollution entering the environment. This study analyzes both the steady and unsteady behavior of heat transfer mechanisms using ANSYS Fluent software. Results show that dynamic transient simulation only takes effect on the first five days of a voyage. There is then a linear relationship between the investigated parameters of the boil-off rate of LNG. These linear relations are of the utmost use for LNG tank manufacturer and researchers requiring a preliminary view in order to determine LNG tank specification. The result obtained is also validated by studies by previous researcher.

Mitigation techniques for liquefied natural gas (LNG) facilities require further investigation to minimize the uncertainty in determining the impact and consequence of an LNG spill on public safety and security. Water curtain systems have been proven to reduce the hazard zone by diluting the vapor concentration below the flammability limits when directly applied to LNG vapors. Currently, no definitive engineering criteria for designing effective water curtains applicable to LNG facilities are available, mainly due to a lack of understanding of the complex interaction between the droplets and LNG vapor. This work applies LNG forced dispersion modeling to study the physical mechanisms involved in enhancing vapor dispersion. Computational fluid dynamics (CFD) codes have been utilized to examine the effects of momentum imparting from the droplets to the air–vapor mixture, the thermal transfer between the two phases (droplet/vapor), and various air entrainment rates on the behavior of the LNG vapor. This work ...

The global demand of liquefied natural gas (LNG) has risen rapidly in recent years for the reasons of energy security and sustainable development. This has led to considerable recent research interests and efforts in the LNG production chain and associated risks in handling, storage, and transport of LNG, largely driven by the intrinsic process safety issues of LNG, potential terrorist threats, and public confidence in LNG safety. This review presents an overview on some recent advances in the LNG value chain, covering upstream gas production and gathering, liquefaction, shipping, and regasification processes. Recent developments in the experimentation and modeling of LNG spills associated with the LNG value chain are then summarized, covering the events following a LNG spill, including LNG pool formation, vapor dispersion, and combustion. The consequent hazards and safety issues are also discussed, with a focus on the methods for improving the safety of personnel, facilities, and ships. The key technical...

Liquified gas fuels are widely used around the world, and the growth of LNG and LPG consumption continues to increase. However, using these fuels can lead to accidents if they are released to the environment. Consequently, the challenge to control and predict such hazards has become an objective in emergency planning and risk analysis. In a previous article the “Dispersion Safety Factor” (DSF) was proposed, defined as the ratio between the distance at which the lower flammability limit concentration occurs and that corresponding to the visible contour of a vapor cloud. Its interest was demonstrated by applying it to the specific case of an LNG spill. With the appropriate modifications, this factor may be applied to the dispersion of other substances; in this communication it is applied to the atmospheric dispersion of propane, and two expressions are proposed to estimate it. Due to the similarity between the properties of both gases, these expressions could probably be applied as well to the dispersion of propylene.

Liquefied natural gas (LNG) is an energy source with worldwide steady growth: natural gas supply, as gas demand, is expected to grow in the near future. LNG is stored in tanks at pressure slightly higher than the atmospheric value and at its boiling point. Despite the high degree of insulation in the tank walls, it is impossible to avoid a net input heat transfer from the surroundings, so that vaporization is always present. It causes an increase in the pressure of the tank and a consequent boiloff in order to avoid overpressure. The change in composition and density of the liquid phase is called LNG aging or weathering. This phenomenon has been studied in order to obtain a model that can predict the variations that occur in the tank over time. Unlike other previously developed models, the proposed model does not require knowledge of the boiloff rate; instead, it calculates the rate directly from the heat flow to the tank. As a consequence, from a comparison with experimental data, it is proved that a mor...

Natural gas is a convenient, clean and cheap energy source. It has many applications including as fuel for power generation, industrial and home heating and as a chemical feedstock. It is usually transported in the liquid form because of the tremendous reduction in volume, when liquefied 600m 3 of natural gas reduce into 1m 3 .LNG (Liquefied Natural Gas) is carried at -163°C and slightly above atmospheric pressure. All the special features of LNG carriers arise from the need to carry cargo at such a low temperature of -163°C. When the tanks are not full, the motion of the ship caused by the wind and waves result in the movement of LNG within the tanks. These movements (sloshing) can severely damage the containment system of the LNG tanker. The present research aims to check the structural stability of a spherical LNG tanker (Kvaerner Moss spherical tank) considering the sloshing effect with different LNG filling levels.

The cryogenic temperature of LNG induces unexpected thermal stress on a metallic structure when LNG comes in contact with it. The induced thermal stress may combine with other operational stress causing the system to face abnormally high stress rates. Furthermore, small cracks, imperfections or design flaws can propagate at high rate under the new increased stress condition. This may lead to catastrophic failure of the structure. In this study, a methodology is proposed for the assessment of the impact of a fugitive LNG spill on a typical steel structure. The study outlines an insight into the structural integrity assessment of the structure during an LNG spill. The focus of the study is to model an LNG pool formation in a complex offshore structure using Flame Acceleration Simulator (FLACS), and to analyse the temperature profile of the pool using thermal analysis. The thermal stress obtained from the transient analysis is considered as a load for LNG spill impact assessment. Ten different semi-elliptical crack sizes are considered to analyse the impact of thermal stress on crack propagation. The outcome of this study reveals that the fugitive release of LNG does not cause immediate crack propagation, however, it has a significant impact on the operational life of the structure. This study confirms that the fugitive release of LNG is a serious hazard for structural integrity and demands effective preventive and/or control measures.

The risks of hazards of liquefied natural gas (LNG) carrier operations and their fundamental causes are investigated in this study. A new framework is developed through the combination of a risk matrix approach and a fuzzy evidential reasoning (FER) method. The risk matrix approach is employed to identify the major hazards associated with the LNG carrier operations. In the risk matrix methodology, linguistic terms are used to estimate how likely hazards may occur in LNG carrier operations at sea, and the consequences of the hazards. The failures of an LNG spill from a transfer arm and an LNG containment system are identified as the hazards of “very high risk”. The fault tree analysis (FTA) diagrams of “very high risk” hazards (top events) are used to identify their causes (basic events) and failure logics. Due to the unavailability of historical failure data, the safety/risk level of each cause is investigated using the FER approach. In the FER approach, the safety levels of the basic events of the top event are assessed using three safety parameters (i.e. occurrence likelihood, consequence severity and failure consequence probability) and combined using evidential reasoning (ER) in fuzzy environment in order to reveal the top events’ safety/risk levels.

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.

This paper examines the problem of evaporation of Liquefied Natural Gas (LNG) occurring at different places in the LNG supply chain. Evaporation losses in the LNG supply chain are one of the key factors for LNG safety, technical and economic assessment. LNG is stored and transported in tanks as a cryogenic liquid, i.e. as a liquid at a temperature below its boiling point at near atmospheric pressure. Due to heat entering the cryogenic tank during storage and transportation, a part of the LNG in the tank continuously evaporates creating a gas called Boil-Off Gas (BOG), which changes the quality of LNG over time. The general methods of handling and utilization of the Boil-Off Gas at different points in the LNG supply chain are presented. Attention is given to the issue of LNG energy content transferred during loading and unloading of LNG tankers, as well as to the Boil-Off Gas generated by evaporation of the cargo during maritime transport. The results presented in the paper have been derived from the scientifi research project 250 - 2502209 - 2366 „Management of Ship Power Systems under Fault Conditions and Failure“ supported by the Ministry of Science, Education and Sports of the Republic of Croatia.

The international transport, storage and utilisation of LNG is growing rapidly. Whilst the LNG industry has an excellent safety record, the possibility of an accidental release cannot be discounted. Internationally-accepted standards, such as the 59A Standard of the US National Fire Protection Association (NFPA), provide direction on the assessment of LNG spill hazards and hazard range criteria which must be met. Modelling of the atmospheric dispersion of LNG vapour from accidental spills is one of the critical steps in such hazard analyses. This paper describes a comprehensive evaluation protocol devised for the 59A Standard, specifically for the assessment of LNG vapour dispersion models. The evaluation protocol is based on methodologies developed in previous European Union studies, which have been extended, significantly adapted and tailored to the specific requirements of the evaluation of models for the dispersion of LNG vapour. The protocol comprises scientific evaluation of the numerical and physical basis of models for the dispersion of LNG vapour, model verification, and validation; resulting in a comprehensive model evaluation report which includes qualitative and quantitative criteria for model acceptance. A supporting suite of validation data, and guidance on the use of this data, has also been produced. The NFPA 59A (2009) standard states that LNG vapour dispersion models are acceptable for use if they have been evaluated in accordance with this protocol.

The use of LNG (liquefied natural gas) as fuel brings up issues regarding safety and acceptable risk. The potential hazards associated with an accidental LNG spill should be evaluated, and a useful tool in LNG safety assessment is computational fluid dynamics (CFD) simulation. In this paper, the ADREA-HF code has been applied to simulate LNG dispersion in open-obstructed environment based on Falcon Series Experiments. During these experiments LNG was released and dispersed over water surface. The spill area is confined with a billboard upwind of the water pond. FA1 trial was chosen to be simulated, because its release and weather conditions (high total spill volume and release rate, low wind speed) allow the gravitational force to influence the cold, dense vapor cloud and can be considered as a benchmark for LNG dispersion in fenced area. The source was modeled with two different approaches: as vapor pool and as two phase jet and the predicted methane concentration at sensors' location was compared with the experimental one. It is verified that the source model affect to a great extent the LNG dispersion and the best case was the one modeling the source as two phase jet. However, the numerical results in the case of two phase jet source underestimate the methane concentration for most of the sensors. Finally, the paper discusses the effect of neglecting the −9.3° experimental wind direction, which leads to the symmetry assumption with respect to wind and therefore less computational costs. It was found that this effect is small in case of a jet source but large in the case of a pool source.

Liquefied Natural Gas (LNG) fleets are coasting with various condition and behavior. These variable leads to different type of LNG fleets build every year with unavoidable generated Boil-off Gas (BOG). Estimation of BOG generated inside LNG tank play significant role in determines the ship specification and management method of BOG including venting, propulsion or requalification. Hence, in the present study, the right choices of boundary condition and parameter have been implementing in order to have good estimation amount of BOG evaporates for specific LNG tank. Three dimensional model of cargo with capacity 160000 m3 LNG carrier are simulate using ANSYS Fluent with specific ambient air temperature of 5oC and ambient seawater temperature of 0oC have been chosen as a calculation case, gain the total heat transfer rate and Boil-off Rate (BOR). The result shows that the calculation model and simulation are feasible with typical LNG fleet specification and International Marine Organization (IMO) standard.

Liquefied natural gas (LNG) as a fuel shows a large energy to volume ratio. In addition, its combustion is characterized by low levels of production of CO2, SOX, NOX and particulate matter in comparison to conventional fuels. To reduce the emission of SOX into the atmosphere the sulphur content of heavy fuel oils used for marine propulsion will be restricted in the near future. However, LNG is a combustible cryogenic liquid and as such presents specific safety hazards. The large scale use of LNG in the marine sector requires appropriate transport, storage and transfer facilities. The risks connected with the operation of these facilities are analyzed. Specific safety characteristics of the equipment involved are incorporated in the analysis. Safety distances are determined based upon a study of the effects of accidents during which LNG is released. It is found that the pressure at which LNG is released during an accident greatly influences the effect distances. At pressures near atmospheric, the hazards of LNG are comparable to those of conventional liquid fuels such as gasoline. At higher pressures, it behaves more like a combustible gas liquefied by compression.

Ignition of natural gas (composed primarily of methane) is generally not considered to pose explosion hazards when in unconfined and low- or medium-congested areas, as most of the areas within LNG regasification facilities can typically be classified. However, as the degrees of confinement and/or congestion increase, the potential exists for the ignition of a methane cloud to result in damaging overpressures (as demonstrated by the recurring residential explosions due to natural gas leaks). Therefore, it is prudent to examine a proposed facility’s design to identify areas where vapor cloud explosions (VCEs) may cause damage, particularly if the damage may extend off site. An area of potential interest for VCEs is the dock, while an LNG carrier is being offloaded: the vessel hull provides one degree of confinement and the shoreline may provide another; some degree of congestion is provided by the dock and associated equipment. In this paper, the computational fluid dynamics (CFD) software FLACS is used to evaluate the consequences of the ignition of a flammable vapor cloud from an LNG spill during the LNG carrier offloading process. The simulations will demonstrate different approaches that can be taken to evaluate a vapor cloud explosion scenario in a partially confined and partially congested geometry.

The present study provides new measurements of the rate of evaporation of cryogenic liquids, liquefied natural gas (LNG) and liquid nitrogen (LN2), floating on a water surface with different levels of turbulence intensity. The turbulent water surface is generated with an upward-pointing submerged jet with controlled jet velocity, an approach which has often been used in studies of free-surface turbulence. Direct measurements of the rate of evaporation were carried out for different pool thicknesses and turbulence intensities of the water surface. These tests reveal a strong dependence of the evaporation rate on the turbulence intensity, as well as a dependence on the thickness of the cryogenic liquid layer above the water surface. Models of LNG spills on water currently use a single rate of evaporation; these findings show that this approach is inadequate. Future models should incorporate the water turbulence intensity, and possibly the LNG spill thickness for improved accuracy.

Liquefied Natural Gas (LNG) storage facilities generally include channels to convey potential spills of the liquid to an impoundment. There is increasing concern that dispersion of vapors generated by flow of LNG in a channel may lead to higher than limit vapor concentrations for safety at site boundary from channels that may be close to the dike walls. This issue is of recent concern to regulatory agencies, because the calculation of vapor hazard distance(s) from LNG flow in a channel is not required under existing LNG facility siting standards or regulations. An important parameter that directly affects the calculated LNG vapor dispersion distance is the source strength (i.e., the rate of vaporization of LNG flow from the wetted channel surfaces, as a function of spatial position and time). In this paper a model is presented which considers the variation of the depth of the flowing LNG with spatial location and time, and calculates the spatial and temporal dependence of the mass rate of vapor generation. Self similar profiles for the spatial variation of the thermal boundary layer in the liquid wetted wall and liquid depth variation are assumed. The variation with time of the location of the liquid spread front and the evaporation rate are calculated for the case of a constant LNG spill rate into a rectangular channel. The effects of two different channel slopes are evaluated. Details of the results and their impact on dispersion distances are discussed.

Federal safety regulations require the use of validated consequence models to determine the vapor cloud dispersion exclusion zones for accidental liquefied natural gas (LNG) releases. One tool that is being developed in industry for exclusion zone determination and LNG vapor dispersion modeling is computational fluid dynamics (CFD). This paper uses the ANSYS CFX CFD code to model LNG vapor dispersion in the atmosphere. Discussed are important parameters that are essential inputs to the ANSYS CFX simulations, including the atmospheric conditions, LNG evaporation rate and pool area, turbulence in the source term, ground surface temperature and roughness height, and effects of obstacles. A sensitivity analysis was conducted to illustrate uncertainties in the simulation results arising from the mesh size and source term turbulence intensity. In addition, a set of medium-scale LNG spill tests were performed at the Brayton Fire Training Field to collect data for validating the ANSYS CFX prediction results. A comparison of test data with simulation results demonstrated that CFX was able to describe the dense gas behavior of LNG vapor cloud, and its prediction results of downwind gas concentrations close to ground level were in approximate agreement with the test data.

New performance metrics are necessary to quantify the inherent margins of safety 1 in vapor dispersion models for liquefied natural gas (LNG) spills. Currently, vapor dispersion model calculations in the 49 Code of Federal Regulations, Part 193 as well as Standard 59A of the National Fire Protection Association (2001 edition) reduce the lower flammability limit (LFL) of methane in air by a safety factor of two (to 50% LFL) to ensure that flammable vapors do not extend beyond an LNG facility’s property line during an LNG spill. Yet, neither document explicitly states the additional distance or the additional confidence level this existing safety standard creates to separate the public from LNG vapors at 100 percent LFL within the facility vs. 50 percent LFL at the facility property line. Although researchers have successfully validated how vapor dispersion models calculate conservative buffer (exclusion) zones, their collective work did not readily explain to the general public the inherent margins of safety in these models. Havens and Spicer developed correlations to demonstrate how well DEGADIS 2 predictions compared with field testing measurements in the late 80s ( Havens & Spicer, 1985 ). Their research also confirmed that peak gas concentrations exceeded time averaged measurements during some field trials as well as DEGADIS predictions. Then Hanna, Chang, and Strimaitis (1993) explained how several vapor dispersion models could be compared by calculating geometric mean bias and geometric variance and shared these validation results with the public. The works of the Havens and Hanna teams were also influential in explaining why the maximum concentration of methane in air at the property limits of an LNG facility should be 50 percent of its lower flammability limit during an LNG spill. Eleven years later, Chang and Hanna discussed how the relationships between fractional bias, geometric mean bias, geometric variance, and normalized mean square error could explain vapor dispersion model over and under prediction ( Chang & Hanna, 2004 ). Despite these successful efforts, there has been reluctance to embrace vapor dispersion model results, because exclusion zones are not described as creating margins of safety (i.e. additional separation distance) or higher confidence levels (i.e. a likelihood of being correct) that protect the public. This paper proposes an improved performance metric to evaluate the validity of vapor dispersion models and a statistical methodology to determine the confidence level and the inherent margin of safety in calculating vapor dispersion exclusion zones. Descriptions of the new metric and methodology are presented in this document for the DEGADIS vapor dispersion model, together with example calculations.

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.

A new method for the analysis of LNG spills into trenches has been developed to quantify vapor dispersion hazard distances. The model uses three steps to capture the behavior of an LNG spill into a trench. The first is to analytically calculate the evolving LNG flow, the second to calculate the vaporization rate along the trench, and the third is to calculate the dispersion of the vapors using a CFD model that has been validated for this application in the presence of complex geometries. This paper presents case studies that show the effect of wind perpendicular and parallel to the large aspect ratio trenches on vapor dispersion. The case studies also demonstrate the effect of complex terrain and obstacles such as vapor fences on vapor dispersion. The simulations show that wind direction relative to the trench has a significant effect on cloud shape, height, and maximum downwind distance. The addition of vapor fences to mitigate vapor dispersion hazards from an LNG spill into the LNG containment trench is shown to be effective.

Effective safety measures to prevent and mitigate the consequences of an accidental release of flammable LNG are critical. Water spray curtain is currently recognized as an effective technique to control and mitigate various hazards in the industries. It has been used to absorb, dilute and disperse both toxic and flammable vapor cloud. It is also used as protection against heat radiation, in case of fighting vapor cloud fire. Water curtain has also been considered as one of the most economic and promising LNG vapor cloud control techniques. Water curtains are expected to enhance LNG vapor cloud dispersion mainly through mechanical effects, dilution, and thermal effects. The actual phenomena involved in LNG vapor and water curtain interaction were not clearly established from previous research. LNG spill experiments have been performed at the Brayton Fire Training Field at Texas A&M University (TAMU) to understand the effect of water curtain in controlling and dispersing LNG vapor cloud. This paper summarizes experimental methodology and presents data from two water curtain tests. The analysis of the test results are also presented to identify the effectiveness of these two types of water spray curtains in enhancing the LNG vapor cloud dispersion.

The use of computational fluid dynamics (CFD) models to simulate LNG vapor dispersion scenarios has been growing steadily over the last few years, with applications to LNG spills on land as well as on water. Before a CFD model may be used to predict the vapor dispersion hazard distances for a hypothetical LNG spill scenario, it is necessary for the model to be validated with respect to relevant experimental data. As part of a joint-industry project aimed at validating the CFD methodology, the LNG vapor source term, including the turbulence level associated with the evaporation process vapors was quantified for one of the Falcon tests. This paper presents the method that was used to quantify the turbulent intensity of evaporating LNG, by analyzing the video images of one of the Falcon tests, which involved LNG spills onto a water pond. The measured rate of LNG pool growth and spreading and the quantified turbulence intensity that were obtained from the image analysis were used as the LNG vapor source term in the CFD model to simulate the Falcon-1 LNG spill test. Several CFD simulations were performed, using a vaporization flux of 0.127 kg/m2 s, radial and outward spreading velocities of 1.53 and 0.55 m/s respectively, and a range of turbulence kinetic energy values between 2.9 and 28.8 m2/s2. The resulting growth and spread of the vapor cloud within the impounded area and outside of it were found to match the observed behavior and the experimental measured data. The results of the analysis presented in this paper demonstrate that a detailed and accurate definition of the LNG vapor source term is critical in order for any vapor cloud dispersion simulation to provide useful and reliable results.

Previous research suggests that high expansion foam with an expansion ratio of 500 to 1 is one of the best options for controlling liquefied natural gas (LNG) pool fire on land. However, its effectiveness heavily depends on the foam application rate, foam generator location, and the design of LNG spill containment dike. Examination of these factors is necessary to achieve the maximum benefit for applying HEX on LNG pool fires. While theoretical study of the effects of foam on LNG fires is important, the complicated phenomena involved in LNG pool fire and foam application increase the need for LNG field experimentation. Therefore, five LNG experiments were conducted at Texas A&M University's Brayton Fire Training Field. ANGUS FIRE provided Expandol solution to form 500 to 1 high expansion foam (HEX) and its latest LNG Turbex Fixed High Expansion Foam Generators. In this paper, data collected during five experiments are presented and analyzed. The effectiveness of high expansion foam for controlling LNG pool fires with various application rates at two different types of containment pits is discussed. LNG fire behaviors and the effects of dike wall height are also presented and discussed.

The installation of new liquefied natural gas (LNG) storage facilities in the United States to meet the demand of natural gas has brought increasing attention to LNG safety issues. Because of its highly flammable nature, one of the major hazards LNG poses is the formation of a flammable vapor cloud from any accidental release, which may result in a massive fire. The safety measures to prevent and mitigate an accidental LNG release are critical to protect employees and the public from injury or harm. The water spray curtain is currently a recognized technique to control and mitigate many toxic and flammable vapors. Much theoretical and experimental work has been carried out to determine the effectiveness of the water spray curtain in dispersing heavier vapor. However, LNG vapor dispersion behaves differently from other dense gases due to its low molecular weight and extremely low temperature. Previous studies show that water spray curtains can enhance LNG vapor dispersion from small spills. However, to develop comprehensive and structured engineering guidelines for the design of an effective water spray curtain for controlling LNG vapor many key questions still remain unanswered. In this context, it is essential to carry out research to understand the effects of water curtain on LNG vapor clouds. An experimental methodology to study the LNG vapor dispersion behaviors with the application of water spray curtain is presented in this article. This field experiment involved the fundamental study of forced dispersion, dilution due to air entrainment, and heat exchange to determine the effectiveness of water spray in reducing the LNG vapor “exclusion zone.” This article discusses and outlines the experimental method and some results based on gas concentration data analysis to emphasize the observed effectiveness of water spray curtain on LNG vapor dispersion. © 2008 American Institute of Chemical Engineers Process Saf Prog 2008

Recent discussions on the fate of LNG spills into impoundments have suggested that the commonly used combination of SOURCE5 and DEGADIS to predict the flammable vapor dispersion distances is not accurate, as it does not account for vapor entrainment by wind. SOURCE5 assumes the vapor layer to grow upward uniformly in the form of a quiescent saturated gas cloud that ultimately spills over impoundment walls. The rate of spillage is then used as the source term for DEGADIS. A more rigorous approach to predict the flammable vapor dispersion distance is to use a computational fluid dynamics (CFD) model. CFD codes can take into account the physical phenomena that govern the fate of LNG spills into impoundments, such as the mixing between air and the evaporated gas. Before a CFD code can be proposed as an alternate method for the prediction of flammable vapor cloud distances, it has to be validated with proper experimental data. This paper describes the use of Fluent, a widely-used commercial CFD code, to simulate one of the tests in the “Falcon” series of LNG spill tests. The “Falcon” test series was the only series that specifically addressed the effects of impoundment walls and construction obstructions on the behavior and dispersion of the vapor cloud. Most other tests, such as the Coyote and the Burro series, involved spills onto water and relatively flat ground. The paper discusses the critical parameters necessary for a CFD model to accurately predict the behavior of a cryogenic spill in a geometrically complex domain, and presents comparisons between the gas concentrations measured during the Falcon-1 test and those predicted using Fluent. Finally, the paper discusses the effect vapor barriers have in containing part of the spill thereby shortening the ignitable vapor cloud and therefore the required hazard area. This issue was addressed by comparing the Falcon-1 simulation (spill into the impoundment) with the simulation of an identical spill without any impoundment walls, or obstacles within the impoundment area.

Traditionally, natural gas is transported by pipelines or by ships as liquefied natural gas (LNG). Because of large costs of liquefaction plants and carriers for natural gas, LNG transportation system has been applied only to very large gas fields. For meeting the increasing demand and stable supply of natural gas, small and medium size gas fields need to be utilized. To enable the utilization of small and medium size gas fields, it is necessary to develop another transportation system for natural gas, with lower initial costs.Gas hydrate is a crystalline solid which consists of gas molecules each surrounded by a cage of water molecules. Use of gas-hydrates for transportation of natural gas was first proposed by Gudmundsson et al. (Norway) in 1996. The temperature of natural gas hydrate (NGH) through transportation remains higher than that of liquefied natural gas (LNG), and accordingly, transportation of NGH is expectably more flexible in terms of its facilities and equipments. NGH can be a medium for natural gas transportation for comparatively small gas fields to which LNG transportation system is not economically applicable.The development of the NGH transportation system started in year 2001. This paper outlines the system and results of current study.

Although no LNG ship has experienced a loss of containment in over 40 years of shipping, it is important for risk management planning to understand the predicted consequences of a spill. A key parameter in assessing the impact of an LNG spill is the pool size. LNG spills onto water generally result in larger pools than land spills because they are unconfined. Modeling of LNG spills onto water is much more difficult than for land spills because the phenomena are more complex and the experimental basis is more limited. The most prevalent practice in predicting pool sizes is to treat the release as instantaneous or constant-rate, and to calculate the pool size using an empirical evaporation or burn rate. The evaporation or burn rate is particularly difficult to estimate for LNG spills on water, because the available data are so limited, scattered, and difficult to extrapolate to the large releases of interest. A more effective modeling of possible spills of LNG onto water calculates, rather than estimating, the evaporation or burn rate. The keys to this approach are to: * Use rigorous multicomponent physical properties. * Use a time-varying analysis of spill and evaporation. * Use a material and energy balance approach. * Estimate the heat transfer from water to LNG in a way that reflects the turbulence. These keys are explained and demonstrated by predictions of a model that incorporates these features. The major challenges are describing the effects of the LNG-water turbulence and the heat transfer from the pool fire to the underlying LNG pool. The model includes a fundamentally based framework for these terms, and the current formulation is based on some of the largest tests to-date. The heat transfer coefficient between the water and LNG is obtained by applying a "turbulence factor" to the value from correlations for quiescent film and transition boiling. The turbulence factor is based on two of the largest unignited tests on water to-date. The heat transfer from the fire to the pool is based on the burning rate for the largest pool fire test on land to-date. Language: en

With the impending natural gas boom in the United States, many companies are pursuing Department of Energy (DOE) approval for exporting liquefied natural gas (LNG), which is a cryogenic liquid. The next decade also promises to demonstrate growth in LNG-fueled fleets of vehicles and marine vessels, as well as growth in other natural gas uses. The future expansion in the LNG infrastructure will lead to an increased focus on managing the risks associated with spills of LNG. Risk analysis involving LNG spill scenarios and their consequences requires determining the size of resulting ignitable flammable vapor clouds. This in turn depends strongly on the rate of evaporation of the spilled LNG. The evaporation of a cryogenic LNG spill (and thus the flammable vapor cloud hazard) can be quite a complex process, and it is primarily controlled by the rate of spreading of the pool and by the transient conductive heat transfer from the ground to the spilled liquid. Radiative and convective heat transfer are also present, but the conductive heat transfer rate dominates in the evaporation of a cryogenic liquid spilled into a trench or sump initially at ambient temperature. The time-dependent evaporation rate can be calculated using a variety of models, such as the built-in model in PHAST Det Norske Veritas (DNV) or other proprietary models that account for pool spreading, heat conduction within the substrate, and phase change. Trenches and sumps used to contain LNG spills are normally lined with various types of concrete, including insulated or aerated concrete. The authors have found that for a cryogenic liquid, the choice of thermal properties for concrete can greatly affect the source term. This paper presents a sensitivity study of the effects of substrate properties on the evaporation rate of LNG. The study will look at the dependence for a range of sump diameters. The PHAST model results will be compared to results obtained using an in-house shallow water equation (SWE) liquid propagation and heat transfer model. The results of the paper will provide guidance for the selection of substrate properties during modeling as well as a comparison of the relative evaporation rates expected for different surfaces, such as regular concrete and insulated concrete.

Multifarious proposals for siting, design, construction, and operation of onshore and offshore liquefied natural gas (LNG) import terminals in California have recently undergone a rigorous federal and state regulatory appraisal. The regulations call for compliance with various environmental, public safety, and security mandates encoded in legal statutes. Public safety from the hazards of a large-scale LNG spill over water, during LNG tanker transit or marine terminal operation, emerged as the dominant concern for the affected local communities. To address their apprehension, extensive modeling of potentially perilous beyond design basis spill scenarios, ensuing from natural, accidental, and malevolent intentional events was conducted. It entailed finite element modeling for vessel collision with diverse LNG tanker types and applying computational fluid dynamics to predict the extent of LNG spread over water, atmospheric dispersion of vapor cloud, and the consequences of ignition. The objective was...

Onboard the Norwegian Coast Guard vessel KV Bergen, as well as other LNG fuelled vessels, there has been reports of a sudden fall in the fuel tank system pressure, resulting in de-loading of the NG engines. This study examines the factors which caused the LNG tank pressure on KV Bergen to fall, leading to the de-loading of the Natural Gas (NG) engines. One reason for the drop in tank pressure is that external disturbances from rough seas destroy the liquid surface layer, causing an increase in the rate of condensation occurring inside the tank. The rate of heat and mass transferred to the vapor section by the Pressure Build Up (PBU) unit is less than the heat and mass absorbed during the mixing inside the LNG tank. A process is developed to calculate the possible fall in LNG tank pressure caused by complete mixing of the liquid and vapor. © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under CC BY-NC-ND license.