Liquefied Natural Gas Release Research Articles

Structural impact under accidental LNG release on the LNG bunkering ship: Implementation of advanced cryogenic risk analysis

The potential risk associated with the accidental release of Liquefied Natural Gas (LNG) is a notable concern during the design phase of gas-handling facilities. One of the risk is an excessive cryogenic exposure to structures or equipment, leading to hazardous situations. This study aims to introduce a novel method that implements Advanced Cryogenic Risk Analysis (ACRA) to enhance the safety of LNG bunkering ship structure in case of cryogenic flow leakage. The method involves evaluating thermal loads based on the preceding simulated LNG release scenarios using Computational Fluid Dynamics (CFD). These thermal parameters are then employed in structural analysis through the Finite Element (FE) approach.The integration of thermal data from CFD simulations into the FE model was achieved using the Random Forest algorithm. The LNG bunkering structure is represented using DH36-grade steel material. Furthermore, to accurately capture the mechanical properties of DH36 steel, cryogenic tensile tests were conducted across a temperature range from 298.15 K to 113.15 K. The resulting stress-strain data from these tests were utilized to establish a reliable material model for conducting FE analysis.This paper comprehensively presents a novel ACRA procedure by utilizing physical parameter of the gas release cosnequence such as the steel temperature profile to identify the brittle failure under the accidental gas release on the LNG bunkering ship. In addition, quantitative risk analysis (QRA) was also presented regarding the cryogenic spill hazard, to link the probability and consequence aspects of the LNG bunkering risk, particularly the results of steel temperature, stress, and strain experienced by the ship’s structure. Furthermore, the individual risk was also estimated. The implications of the findings are discussed in detail regarding the cryogenic risk, cryogenic tensile test and numerical analyses.

Determination of cryogenic temperature loads for finite-element model of LNG bunkering ship under LNG release accident

Abstract The rising demand for liquefied natural gas (LNG)-fueled ships requires the LNG bunkering facility that partially uses a ship-to-ship operation. The bunkering process of LNG fuel may have a greater risk due to LNG volatility. The cryogenic temperature of LNG poses a threat to the personnel and structural embrittlement to ships. Therefore, cryogenic spill protection optimization was introduced concerning the structural strength analysis using finite element (FE) by utilizing cryogenic temperature loads provided by the computational fluid dynamics (CFD) model of an LNG release. This study aims to build a platform for transferring the temperature load profile from CFD to FE software accurately. The CFD model usually uses a structured Cartesian grid, and the FE method adopts an unstructured tetrahedral or hexahedral mesh. As a result, both configurations store results at different positions, and it is not preferred for the load profile to be transferred directly. The error will be greater due to the variance of positions. Random Forest, a machine learning method, has been employed that uses a regression technique to deal with a continuous variable. An accurate load profile for the FE model can be obtained by adopting decision tree learning in Random Forest. The procedure for determining the temperature load profile is presented in this article.

Characterization of Medium-Scale Accidental Releases of LNG

The need for sustainable energy sources has recently promoted the use of liquefied natural gas (LNG) as a low-carbon fuel. Although economic evaluations indicate the transportation of LNG as a convenient solution for long distances between markets and reservoirs, several concerns are still present regarding its safe use and transportation. The preliminary evaluations performed in this work indicate that credible releases deriving from real bunkering operations result in pools having a diameter smaller than 1 m, which has been poorly investigated so far. Hence, an experimental campaign devoted to the characterization of a medium-scale release of LNG was carried out either in the presence or absence of an ignition source. An evaporation rate of 0.005 kg s−1 m−2 was collected for the non-reactive scenario, whereas the measured burning rate was 0.100 kg s−1 m−2. The reduction factor of 20 demonstrates the inaccuracy in the commonly adopted assumption of equality between these values for the LNG pool. Flame morphology was characterized quantitatively and qualitatively, showing a maximum ratio between flame height and flame diameter equal to 2.5 and temperatures up to 1100 K in the proximity of the flame.

Пожарная опасность взрывных режимов испарения сжиженного природного газа

Introduction. The fire hazard of explosive regimes of liquefied natural gas (LNG) evaporation was analyzed on the basis of the published research findings. These regimes include the rollover and the rapid phase transition (RPT). Characteristics of explosive regimes of LNG evaporation. Rollover occurs in LNG storage tanks in case of spontaneous mixing of LNG layers having different temperatures and densities. These layers emerge when the “fresh” product is loaded into a vessel containing the residual amount of product stored there before. A rapid increase in the LNG evaporation rate accompanies a pressure rise inside the tank, which can exceed an allowable pressure of the tank. RPT occurs at a contact of LND and water in the case of a release of liquefied natural gas onto a water surface. An explosive evaporation of LNG can cause in this case a formation of a shock wave and a large-scale vapor cloud. Investigations of rollovers. It was mentioned that a stratification of LNG in a storage tank is a necessary condition of a rollover. Two layers with different temperatures and densities are formed during this stratification. A superheating of a lower layer occurs at a heat exchange between the LNG and tank walls with a decrease of a density of this layer. A preferential evaporation of light components of LNG (methane, nitrogen) takes place in the upper layer, and the density of this layer increases. When the densities of these layers are equalized a spontaneous mixing of these layers occurs with an explosive evaporation of the product in the lower superheated layer. A time delay of rollover can reach 60–70 hours after the supply of the “fresh” product into the tank with “old” product. Investigations of a rapid phase transition. An energy released at the explosive evaporation and a pressure in a shock wave depend on many factors such as a LNG release rate, a position of a source of the LNG release — over or under a water level, a product composition, water temperature etc. It was found that a pressure hazardous for buildings and structures can take place at distances 250–500 m from the point of the release. The empirical correlation was proposed connecting a water temperature at the RPT occurrence and the superheating tempe­rature of LNG at which a boiling takes place in the regime of a homogeneous nucleation. Conclusions. It was shown that a realization of the explosive regimes of the LNG evaporation increases a fire hazard of objects for a storage and a transportation of liquefied natural gas. Recommendations for a prevention of such regimes are formulated.

Неопределённости расчёта параметров взрыва газовоздушного облака при аварийном выбросе сжиженного природного газа в открытом пространстве

Purpose. Increasing production of liquefied natural gas (LNG) in the Russian Federation raise the risk of the accidental LNG releases. To prevent the negative consequences of a possible gas-air cloud explosion during LNG release, it is necessary to predict probable emergency scenarios. Regulatory documents for determining fire risk make it possible to define the likely consequences of an explosion of liquefied hydrocarbon gases (LPG) vapor clouds, however the application of calculation methods for LNG requires additional analysis. Methods. The analysis of methods for calculating the parameters of a gas-air cloud explosion in an open space is carried out, the consequences of real gas-air clouds explosions during the emergency LNG release are analyzed. Findings. The analysis of the methods has showed the main uncertainties in predicting the parameters of LNG vapor cloud explosion. Propagation features of LNG vapor cloud, the influence of various gases that are part of LNG are not taken into account. Research application field. The results obtained will allow improving the method for calculating the pressure of the gas-air clouds explosion during the emergency LNG release. Conclusions. The analysis of the real accident with LNG release has showed that the calculated pressures obtained on the basis of the methods are incomparable with the explosion consequences. The further direction for improving the methodology of calculating the explosion pressure of gas-air clouds during the emergency LNG release is determined. To improve the methodology it is necessary to determine the effect of combustible gases, which are part of LNG, on the parameters of the explosion, and also take into account the effect of low temperatures of LNG vapor cloud.

Consequence Analysis of Accidental LNG Release on the Collided Structure of 500 cbm LNG Bunkering Ship

The growing demand for liquefied natural gas (LNG)-fueled ships necessitates the establishment of an LNG bunkering facility. Ship-to-ship (STS) is one of the most practical forms of LNG bunkering systems. Although there are benefits to the LNG bunkering of ships, risk and safety issues are a concern due to the volatile cargo. Ship collision could result in accidental LNG release. The purpose of this study was to build LNG leakage scenarios, establish critical zones based on gas concentrations, and estimate the temperature reduction in a bunkering ship’s structure resulting from the use of cryogenic fluid. The condition of a target ship’s structure, both intact and when damaged due to collision, was considered. Leak size, leak direction, leak position, release rate, and reservoir pressure were included as leak parameters, and environmental parameters, such as the wind direction, wind speed, and ambient temperature, were also included. The release duration was set based on the shutdown duration of the emergency shutdown valve (ESD). A total of 72 leakage scenarios were generated for the main CFD analysis. Convergence tests were conducted to determine the appropriate grid and iteration numbers for a computational fluid dynamics (CFD) simulation. The gas dispersion characteristics and the cryogenic flow impact on the LNG bunkering ship’s structure are discussed through a parametric study.

CFD implementation to mitigate the LNG leakage consequences: A review of explosion accident calculation on LNG-fueled ships

Liquefied Natural Gas (LNG) has a significant benefit in reducing air pollutants such as sulfur oxide, nitrogen oxide, and particulate matter emitted by Diesel Oil or Heavy Fuel Oil. The International Maritime Organization (IMO) regulates these pollutants in MARPOL Protocol Annex VI. It was implemented by establishing an Emission Control Area (ECA) in 2010 that restricts exhaust gas of ships. This regulation has resulted in new shipbuilding orders or conversions to adopt the LNG-fueled systems. Besides the benefits of LNG fuel, storing, transporting, and distributing this fuel has a different problem with conventional fuels. LNG is volatile, and it has a low flashpoint that could lead to spontaneous ignition. To assess the safety and mitigation for LNG-powered ships, Computational Fluid Dynamics (CFD), such as Kameleon Fire Ex (KFX) and Flame Acceleration Simulator (FLACS), is considered to simulate the LNG release. This technical measure is taken to observe the possible damage or loss due to the cryogenic effect, the extreme temperature of the jet fire, or Vapor Cloud Explosion (VCE). These consequences could happen sequentially that known as the “Domino Effect”. The effect of the leak and environment-related parameters could influence the severity of the damage. The applications of CFD for the LNG release cases are discussed and highlighted in this review.

Layout optimization for safety evaluation on LNG-fueled ship under an accidental fuel release using mixed-integer nonlinear programming

The Liquefied Natural Gas (LNG)-fueled ship is an alternative solution to deal with the Emission Control Area (ECA) issued by the International Maritime Organization (IMO). LNG fuel has eco-green characteristics since sulfur oxide and particulate matter are eliminated. The equipment sitting on the Fuel Gas Supply System (FGSS) layout needs a good arrangement to prevent the domino effect. This study’s scopes are to establish the feasible FGSS layout based on the equipment position and conduct an accidental LNG release that adopts the Computational Fluid Dynamics (CFD). Mixed-Integer Nonlinear Programming (MINLP) is provided as an optimization tool. The MINLP framework is written in the Python programming language. The minimum separation distance, deck size, and non-overlapping functions of equipment are included as the MINLP constraint. The separation distances are provided based on the Center of Chemical Process Safety (CCPS) recommendation. Also, several options of the separation distance are added that consist of 5.0, 6.0, and 7.0 m to observe the congestion effect. The total pipe length is considered as the MINLP objective that can be used to estimate the pipe cost. The proposed MINLP framework is designated to generate a feasible layout that has an adequate separation distance and minimum cost of the pipe. CFD results show that the increase of separation distance can reduce the gas accumulation effectively which eventually reduces the severity of other consequences. Finally, the feasible layout is proposed based on a series of several consequences under an accidental LNG release, such as gas dispersion, fire, and vapor cloud explosion.

Model for Cryogenic Flashing LNG Leak

The growth of liquefied natural gas (LNG)’s importance for curbing greenhouse gas emissions has increased the interest in understanding LNG’s risks, particularly regarding small-diameter leaks (<25 mm). Recently, INERIS performed a series of pressurized LNG release experiments for orifice sizes of up to 9 mm. Based on INERIS findings and the Isenthalpic Homogeneous Equilibrium Model (HEM), this paper created a leak model for flashing LNG leak. The leak model consists of nine equations and quantifies leak parameters for risk assessment. One potential use of this leak model is providing an equivalent leak boundary condition for computational fluid dynamic (CFD) simulation to predict gas dispersion. Using the leak model as input, FLACS gas dispersion simulation was carried out for one INERIS experiment leak case. Compared to TR56, the Singapore safety guideline for LNG bunkering, the dispersion result does not contradict the expected plume reach. Further validation with risk analysis tools and actual experiments is needed to confirm that the leak model is fit for use.

Experimental investigation of LNG release underwater and combustion behavior under crosswinds

Liquefied natural gas (LNG) trade has increased globally; therefore, assessments of the hazards of its accidental release and associated consequences must be conducted to ensure LNG security during marine transportation. This study aims to understand the dynamic behavior occurring when an LNG jet is released underwater and the combustion behavior of a flammable vapor cloud on the water’s surface with airflows from 0 to 4m/s. A series of controlled LNG vertical jet release experiments were conducted using a cryogenic storage tank with three orifices. Various instruments were employed to measure the flow rate and pressure in pipelines during different leakage scenarios, and the emanating LNG vapor clouds were immediately ignited with the mass loss rate of 0.016, 0.037, and 0.049kg/s in three orifices, respectively. The flame behavior was recorded by a video camera. With respect to flame length rapidly decreased with crosswinds of 0−2m/s and then gradually decreased to a constant value with the velocities increase to 4m/s. A dimensionless number of Ri was employed to analyze the relative magnitude between the buoyancy force and transverse flow. The flame tilt angle was found in accordance trend with flame length for first increased and further reach to become constant at Ri−1 increase to 2. As existing correlations provide an overestimation, a new correlation was established to describe the flame length as a function of crosswind speed, and a good prediction was found for measured tilt angles with the correlated values.

Safety-zone layout design for a floating LNG-Fueled power plant in bunkering process

The use of natural gas (NG) as an energy source is increasing. This paper studies the safety-zone layout design of a floating power plant fueled by NG. Hazards from the unwanted release of liquefied NG (LNG) in bunkering or NG in operation always exist, and it is thus important to reduce the associated risk to an acceptable level. One engineering technique used to reduce this risk involves the design of a safety zone to prevent and minimize exposure to unwated release of LNG or NG that may occur during the bunkering process. Industry practices are available for the design of the layout of such safety-zones, but their applicability to floating power plants is uncertain, and a more intuitive approach is required. The objective of this study is to discuss the challenges of establishing safety zones on floating power plants by reviewing and comparing existing industrial practices and to propose a hybrid approach for the design of a safety-zone layout. The applicability of the proposed hybrid approach is discussed with an applied example.

Computational equation discovery of relationships between container ship fuel consumption and hull and propeller fouling phenomena

Abstract Nowadays, when we try to automatize all activities, there is a growing demand for energy in all forms. Increasingly we reach for new energy sources that can be problematic to store or to transport, owing to their toxicity or explosive propensity. The article examines the issues of determining danger zones occurring as a result of liquefied natural gas (LNG) release. The range of danger zones caused through LNG release depends on a multitude of factors. The basic parameter that needs to be considered is a type of the released substance as well as the manner of its release. The range of a danger zone is determined by, inter alia, the concentration of a released substance and the atmospheric conditions existing at the time when depressurization occurs. The article analyses the problem of the range of danger zones in a function of wind speed and surface roughness with a defined value of Pasquill stability for various LNG types, starting with pure methane, and ending with the so-called LNG-heavy. The difficulty of the task becomes more complicated when the analysed surface over which a depressurization incident takes place involves water. The problem deepens even further when the analysed substance possesses explosive properties. Then, apart from regular substance concentration, upper and lower flammability limit ought to be considered. Calculations were conducted with DNV-Phast software, version 7.11.

Consequence Analysis of LNG Leaks During Offloading Operations: Effects of Substrate Types, Atmospheric Conditions, and Basic Process Control System Intervention

With the increasing demands for liquefied natural gas (LNG), more and more LNG terminals are being constructed, and the risk of leakage during LNG off-loading processes has been given increasing amounts of attention. In the case of leakage accident during unloading, the control system is still running when the emergency stop condition is not reached. The adjustment of the control system to unloading parameters will affect the size of the leakage amount. However, the consequences of hazardous material leakage accidents predicted by correlation models depend on the amount of leakage. For precisely calculating the leakage amount and analyzing the leakage consequence, an HYSYS model and a flame acceleration simulator (FLACS) model were presented. This paper consists of two main parts: 1) an HYSYS model to calculate the spill flow rate according to various operating conditions that are with and without basic process control system (BPCS) intervention and 2) a FLACS model that estimates the consequences of vapor explosions and pool fires. This paper presents the conventional estimation method and compares it with a new method that estimates the risk according to spill flow rate, meteorological conditions, and substrate type (solid or grated) on pool spreading and vapor cloud dispersion. Using six scenarios, simulations are used to demonstrate that the HYSYS-FLACS model calculates the equivalent stoichiometric clouds (Q9) and pooling areas as being much larger than those calculated by the conventional model. During an emergency, the HYSYS-FLACS model can be used to estimate the consequences of an unplanned LNG release.

CFD methodology for simulation of LNG spills and rapid phase transition (RPT)

Abstract Hazards related to transportation and storage of Liquefied Natural Gas (LNG) are widely studied due to an increasing importance of LNG in the overall energy supply. Large scale LNG spills on water are of particular interest as much of LNG transport is conducted by sea. The present work focuses on modelling approaches and their capabilities to predict different phenomena related to LNG spills. It describes in detail a developed CFD based methodology that is able to simulate the behaviour of LNG spills from their initial release, spreading on the water surface, Rapid Phase Transition (RPT) to subsequent dispersion. The methodology is based on a homogeneous multiphase formulation of the liquid layer and therefore suitable for implementation in most of commercial CFD packages. An LNG release from a process train on a FLNG vessel was used to demonstrate capabilities of the developed approach. A CFD simulation was conducted to calculate the volume and distribution of the flammable cloud, and the overpressure generated by an RPT event.

Assessment of the Range of Danger Zones Determined in a Function of LNG Chemical Composition

Abstract Nowadays, when we try to automatize all activities, there is a growing demand for energy in all forms. Increasingly we reach for new energy sources that can be problematic to store or to transport, owing to their toxicity or explosive propensity. The article examines the issues of determining danger zones occurring as a result of liquefied natural gas (LNG) release. The range of danger zones caused through LNG release depends on a multitude of factors. The basic parameter that needs to be considered is a type of the released substance as well as the manner of its release. The range of a danger zone is determined by, inter alia, the concentration of a released substance and the atmospheric conditions existing at the time when depressurization occurs. The article analyses the problem of the range of danger zones in a function of wind speed and surface roughness with a defined value of Pasquill stability for various LNG types, starting with pure methane, and ending with the so-called LNG-heavy. The difficulty of the task becomes more complicated when the analysed surface over which a depressurization incident takes place involves water. The problem deepens even further when the analysed substance possesses explosive properties. Then, apart from regular substance concentration, upper and lower flammability limit ought to be considered. Calculations were conducted with DNV-Phast software, version 7.11.

Numerical simulation of LNG release and dispersion using a multiphase CFD model

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.

Experimental and numerical study of liquefied natural gas (LNG) pool spreading and vaporization on water

The investigation of pool spreading and vaporization phenomenon is an essential part of consequence analysis to determine the severity of LNG spills on water. In this study, release of LNG on water during marine operations is studied through experimental and numerical methods The study involves emulation of an LNG leak from transfer arms during side by side loading operations. The experimental part involves flow of LNG in a narrow trench filled with water and subsequent measurement of pool spreading and vaporization parameters. The numerical part involves CFD simulation using a three dimensional hybrid homogenous Eulerian multiphase solver to model the pool spreading and vaporization phenomenon. In this method, LNG is modeled as dispersed phase droplets which can interact with continuous phases − water and air through interphase models. The numerical study also employs a novel user-defined routine for capturing the LNG vaporization process. The CFD solver was capable of capturing the salient features of LNG pool spreading and vaporization phenomena. It was observed from experiment and CFD simulation that wind influenced both pool spreading and vaporization phenomenon through entrainment and convection.

Thermodynamic aspects of an LNG tank in fire and experimental validation

Mechanical behaviour of a Liquefied Natural Gas (LNG) tank and the thermodynamic behaviour of its containment under extreme heat load – for instance when subjected to external fire source as might occur during an accident - are extremely important when addressing safety concerns. In a scenario where external fire is present and consequent release of LNG from pressure relief valves (PRV) has occurred, escalation of the fire might occur causing difficulty for the fire response teams to approach the tank or to secure the perimeter. If the duration of the tank exposure to fire is known, the PRV opening time can be estimated based on the thermodynamic calculations. In this paper, such an accidental scenario is considered, relevant thermodynamic equations are derived and presented. Moreover, an experiment is performed with liquid nitrogen and the results are compared to the analytical ones. The analytical results match very well with the experimental observations. The resulting analytical models are suitable to be applied to other cryogenic liquids.

CFD Modeling of LNG Spill: Humidity Effect on Vapor Dispersion

The risks entailed by an accidental spill of Liquefied Natural Gas (LNG) should be indentified and evaluated, in order to design measures for prevention and mitigation in LNG terminals. For this purpose, simulations are considered a useful tool to study LNG spills and to understand the mechanisms that influence the vapor dispersion. In the present study, the ADREA-HF CFD code is employed to simulate the TEEX1 experiment. The experiment was carried out at the Brayton Fire Training Field, which is affiliated with the Texas A&M University system and involves LNG release and dispersion over water surface in open- obstructed environment. In the simulation the source was modeled as a two-phase jet enabling the prediction of both the vapor dispersion and the liquid pool spreading. The conservation equations for the mixture are solved along with the mass fraction for natural gas. Due to the low prevailing temperatures during the spill ambient humidity condenses and this might affect the vapor dispersion. This effect was examined in this work by solving an additional conservation equation for the water mass fraction. Two different models were tested: the hydrodynamic equilibrium model which assumes kinetic equilibrium between the phases and the non hydrodynamic equilibrium model, in order to assess the effect of slip velocity on the prediction. The slip velocity is defined as the difference between the liquid phase and the vapor phase and is calculated using the algebraic slip model. Constant droplet diameter of three different sizes and a lognormal distribution of the droplet diameter were applied and the results are discussed and compared with the measurements.

Analysis of the boiling liquid expanding vapor explosion (BLEVE) of a liquefied natural gas road tanker: The Zarzalico accident

The road accident of a tanker transporting liquefied natural gas (LNG) originated a fire and, finally, the BLEVE of the tank. This accident has been analyzed, both from the point of view of the emergency management and the explosion and fireball effects. The accidental sequence is described: fire, LNG release, further safety valves release, flames impingement on vessel unprotected wall, vessel failure mode, explosion and fireball. According to the effects and consequences observed, the thermal radiation and overpressure are estimated; a mathematical model is applied to calculate the probable mass contained in the vessel at the moment of the explosion. The peak overpressure predicted from two models is compared with the values inferred from the accident observed data. The emergency management is commented.